Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Automatic exposure compensation in intraoral digital radiography: effect on the gray values of dental tissues

Automatic exposure compensation in intraoral digital radiography: effect on the gray values of... Background: This study aimed to investigate the effect of automatic exposure compensation (AEC) of intraoral radiographic systems on the gray values of dental tissues in images acquired with or without high‑ density material in the exposed region using different exposure times and kilovoltages. The influence of the distance of the high‑ density material was also investigated. Methods: Radiographs from the molar region of two mandibles were obtained using the RVG 6100 and the Express systems, operating at 60 and 70 kV and 0.06, 0.10, and 0.16 s. Subsequently, a titanium implant was inserted in the pre‑ molar’s socket and other images were acquired. Using the ImageJ software, two regions of interest were determined on the enamel, coronary dentine, root dentine, and pulp of the first and second molars to obtain their gray values. Results: In the RVG 6100, the implant did not affect the gray values (p > 0.05); the increase in kV decreased it in all tissues (p < 0.05), and the exposure time affected only the root dentine and pulp. In the Express, only enamel and coronary dentine values changed (p < 0.05), decreasing with the implant presence and/or with the increase in expo‑ sure factors. The distance of the implant did not affect the results (p > 0.05). Conclusions: AEC’s performance varies between the radiographic systems. Its effect on the gray values depends not only on the presence or absence of high‑ density material but also on the kV and exposure time used. Keywords: Dental radiography, Dental materials, Digital radiography, Digital system, Periapical radiography Background In some systems, image enhancement is also per- Digital image acquisition systems are increasingly present formed automatically by the software, after image acqui- in dentistry due to their advantages compared to con- sition, but before it is displayed on the monitor, through ventional films, such as requiring less exposure time and an image pre-processing tool called Automatic Exposure presenting the possibility of image enhancement, which Compensation (AEC) [4–6]. This tool increases image avoid repetition and consequently reduce the radiation contrast, modifying pixel values non-linearly, producing dose to the patient [1–3]. high-contrast radiographs [7, 8]. Also, AEC can modify the signal-to-noise ratio, presenting a lower value (i.e. darker image) compared to systems without AEC [7, 9]. Previous studies have shown that AEC can improve the *Correspondence: eduarda.hln@gmail.com accuracy of diagnosis of proximal caries in under- and Present Address: Division of Oral Radiology, Department of Dentistry, Odontomed Imagem ‑ Medical and Dental Services, Av. Dois Rios, 632, overexposed images [4]. It was also stated previously that Ibura, Recife, Pernambuco 51.230‑000, Brazil Full list of author information is available at the end of the article © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecom‑ mons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Maciel et al. BMC Medical Imaging (2022) 22:4 Page 2 of 7 the effect of AEC is influenced by the presence of high- The study sample consisted of periapical radiographs density objects [6, 10]. obtained from two partially edentulous human mandi- Galvão et  al. [6], in an in  vitro study, investigated the bles belonging to the Oral Radiology Department used influence of the presence of high-density material, as well for teaching purposes, selected considering the follow- as its size and exposure time, on the gray values of radi- ing inclusion criteria: mandibles containing adjacent first odensity liquids equivalent to dental tissues. The authors and second molars on at least one side, and absence of concluded that a high-density material present in the the second premolar. Molars with dental restoration or image can influence the AEC adjustment, regardless of endodontic treatment and mandibles with moderate to exposure time and radiographic system. However, the advanced bone loss in the molar region were excluded. gray values of dental tissues were tested employing radi- Finally, two molar regions (one in each mandible) were odensity equivalent liquids separately (one dental tissue available for the acquisition of the study images. at a time on each radiograph), which does not reflect the clinical condition. In addition, apart from radiographic Image acquisition systems and exposure time, other parameters may be All images were acquired using the Heliodent Plus X-ray applied for image acquisition, such as tube current and machine (Sirona Dental Systems, Bensheim, Germany) kilovoltage (kV), which are mainly responsible for the and two digital intraoral systems: final image density and contrast, respectively. By applying different kV (i.e. different beam energy), AEC could act • A Complementary metal-oxide-semiconductor, differently in adjusting the shades of gray, as X-rays beam direct radiography (DR) system, 12-bit depth—RVG with different energy reaches the image receptor. 6100 (Kodak Dental Systems, New York, USA); AEC is an autonomous tool, and thus the pre-process- • A photostimulable phosphor (PSP) plate, computed ing of the image cannot be controlled by the operator. radiography (CR) system, 14-bit depth—Express Also, little is known about the real clinical effect of AEC (Instrumentarium, Tuusula, Finland). on the gray values of dental tissues when high-density objects are present in the radiographed area, and the For both systems, the X-ray machine was set to operate effect of the exposure parameters. Therefore, it is essen - at 7  mA (tube current not adjustable), two kilovoltages tial to understand its functioning and how it can be (60 and 70 kV), and three exposure times (0.06, 0.10, and influenced by factors present in the radiographed area in 0.16  s). In each mandible, periapical radiographs of the clinical situations (i.e., presence of high-density materi- right mandibular molars were acquired with and without als) and technical parameters (i.e. kV and exposure time). the insertion of an 11 × 4 mm titanium dental implant The aim of the present study was to evaluate, in an ex (Titamax, Neodent, Brazil) in the alveolus of the second vivo model, the effect of AEC on dental tissues (enamel, premolar, composing two experimental groups: control crown dentine, root dentine, and pulp), using two dif- group (without high-density material in the radiographed ferent radiographic systems, under different acquisition region) and high-density group (with the dental implant parameters (exposure time and kV). In addition, the in the radiographed region, placed within the edentulous potential influence of the distance from the high-density socket of the right second premolar). Table 1 summarizes material on the gray values was tested. The null hypothe - the study’s protocols and variables. sis was that the effect of AEC does not influence the gray Images were acquired using the parallelism technique. values of dental tissues, regardless of the variables con- An acrylic device was used to standardize the geomet- sidered in the study. ric relationships between the X-ray source/object/image receiver. Between the acquisitions of the control group and the high-density group, the mandible was not moved, Methods so that the exact spatial relationship between it and the This study was approved by the Research Ethics Com - mittee of the Federal University of Pernambuco (proto- col #3.594.302). All procedures performed were under the ethical standards of the Institutional and National Table 1 Exposure protocols and study variables Research Committee and with the 1964 Helsinki Decla- ration and its later amendments or comparable ethical Radiographic system Group kV Time (s) standards. The informed consent requirement for this RVG 6100 Control 60 and 70 0.06–0.10–0.16 ex  vivo study was waived by the Research Ethics Com- High‑ density 60 and 70 0.06–0.10–0.16 mittee of the Federal University of Pernambuco, and Express Control 60 and 70 0.06–0.10–0.16 permission to use the ex vivo sample was granted by this High‑ density 60 and 70 0.06–0.10–0.16 committee. M aciel et al. BMC Medical Imaging (2022) 22:4 Page 3 of 7 Fig. 1 Acquisition of the radiographic image with the Express system (high‑ density group) Fig. 2 Representation of the square regions of interest located in the enamel, dentin (crown), dentin (root), and pulp of the first and second molars in an image obtained with the Express system image receiver was kept the same throughout the study (Fig. 1). Considering the objective nature of the analyses pro- posed in the present study, each acquisition was repeated distance to the high-density material on the mean gray 5 times [6]. The repetitions of acquisitions also aimed to values. For that, the difference between the gray values (Δ verify the reproducibility of the method and record the gray values) in the high-density group and control group possible variability of gray values between acquisitions. were calculated for the ROIs placed on enamel and den- u Th s, 240 radiographs were acquired (2 molar regions tine (both crown and root) of the first molar and the sec - × 2 radiographic systems × 2 groups × 2 kV × 3 expo- ond molar, and compared by t-test. Those comparisons sure times × 5 repetitions). were performed only for those protocols that showed a statistically significant difference in the first part of the study. The significance level was set at 5% (α = 0.05). Objective assessment of gray values of dental tissues To have a standardization between the two systems used, all images were saved in TIFF format and exported with Results 8-bit depth to ImageJ software (U.S. National Institutes of The results related to the RVG 6100 system are shown Health, Bethesda, Maryland, USA). In the radiographs of in Table  2. For this system, the presence of the implant each mandible, two regions of interest (ROIs) of size 0.65 did not significantly affect the gray values of any of the mm ×  0.65 mm were determined on the enamel, crown dental tissues, regardless of the exposure time and the dentine, root dentine, and pulp of the evaluated teeth kV (p = 0.895). However, there were differences between (Fig.  2). The ROIs were recorded in the ImageJ software the images acquired with 60 and 70  kV (p  <  0.001): for using the ROI manager tool, which standardizes the ROI all dental tissues, images obtained with higher kV showed position on all images. In each ROI, the mean and stand- lower gray values (i.e., darker image). By comparing the ard deviation (SD) of the gray values of each tissue were images obtained in the same kV with different exposure recorded. times, it was observed that the time affected only the gray values of the tissues of lower physical density (root Statistical analysis dentine and pulp) (p  <  0.001). In the control group, the The mean and SD values of each tissue were tabulated in increase from 0.06 to 0.16 s decreased the gray values of an Excel spreadsheet (Microsoft Corporation, Redmond, the root dentine at 70  kV and of the pulp at both kilo- WA, USA) and analyzed using the SPSS software (v. 22.0, voltage (p  =  0.026); in the high-density group, images IMB Corp., Armonk, New York, USA). Two-way analysis acquired with 0.16  s showed lower gray values than the of variance (ANOVA) was used to compare the gray val- others, when 70 kV was used (p < 0.001). ues between the groups tested (control and high-density) Table  3 details the results for the Express system, with the varying protocol (kV and exposure time) within which shows that only the gray values of enamel and each tissue and radiographic system, followed by Tukey’s crown dentine underwent significant changes accord - post-hoc test for multiple comparisons. An additional ing to the study variables (p  <  0.001). The presence analysis was performed to evaluate the influence of the of the implant caused a decrease in the gray values of Maciel et al. BMC Medical Imaging (2022) 22:4 Page 4 of 7 Table 2 Mean and standard deviation (SD) of the gray values of dental tissues in the RVG 6100 radiographic system distributed according to the group, exposure time, and kilovoltage Dental tissues Group t = 0.06 s t = 0.10 s t = 0.16 s 60 kV 70 kV 60 kV 70 kV 60 kV 70 kV Enamel Control 135.0 (12.7) Aa 118.1 (13.8) Ab 139.2 (11.9) Aa 118.2 (12.9) Ab 141.7 (13.2) Aa 115.4 (13.3) Ab High‑ density 134.8 (12.7) Aa 118.4 (13.1) Ab 139.6 (12.1) Aa 119.2 (13.2) Ab 142.2 (13.3) Aa 116.1 (13.7) Ab Crown dentine Control 112.2 (11.8) Aa 93.1 (11.4) Ab 114.3 (10.5) Aa 91.9 (10.3) Ab 115.4 (11.3) Aa 88.5 (10.5) Ab High‑ density 111.7 (11.5) Aa 93.1 (10.7) Ab 114.6 (10.5) Aa 93.0 (10.8) Ab 116.0 (11.4) Aa 89.1 (10.9) Ab Root dentine Control 97.3 (6.5) Aa 78.9 (6.3) Ab 98.5 (8.4) Aa 77.4 (7.8) Abc 99.2 (9.1) Aa 73.8 (7.9) Ac High‑ density 97.5 (6.1) Aa 79.3 Ab 99.6 (7.7) Aa 78.9 (7.1) Ab 100.5 (8.0) Aa 74.9 (6.8) Ab Pulp Control 49.7 (6.1) Aa 35.2 (5.1) Ac 47.2 (5.8) Aab 32.6 (4.3) Acd 46.2 (5.6) Ab 29.8 (4.1) Ad High‑ density 48.9(6.2) Aa 35.0 (5.0) Ab 47.7 (5.8) Aa 33.7 (4.7) Ab 47.0 (5.7) Aa 30.3 (4.1) Ac Different uppercase letters indicate a statistical difference between the control and high-density groups, within each dental tissue (vertical comparisons) Different lowercase letters indicate a statistical difference between kV at the same exposure time and between exposure times at the same kV, within each group (horizontal comparisons) Table.3 Mean and standard deviation (SD) of the gray values of dental tissues in the Express radiographic system distributed according to the group, exposure time, and kilovoltage Dental tissue Group t = 0.06 s t = 0.10 s t = 0.16 s 60 kV 70 kV 60 kV 70 kV 60 kV 70 kV Enamel Control 227.5 (8.4) Aa 225.1 (10.3) Aab 226.0 (9.1) Aab 215.5 (10.1) Ac 220.5 (10.8) Ab 213.1 (10.8) Ac High‑ density 224.2 (10.4) Aa 217.2 (9.6) Bc 224.0 (10) Aab 208.5 (10.7) Bd 217.7 (11.5) Ab 205.4 (8.3) Bd Crown dentine Control 192.4 (13.4) Aa 190.5 (10.4) Aab 193.2 (11.6) Aa 181.0 (11.1) Ac 185.0 (8.8) Abc 185.2 (16) Abc High‑ density 187.7 (12.3) Aa 182.4 (9.7) Bab 189.5 (11) Aa 173.4 (8.4) Bc 180.2 (9) Abc 177.1 (11) Bbc Root dentine Control 172.4 (28.8) Aa 169.6 (22.4) Aa 171.9 (26.6) Aa 166.5 (21.4) Aa 167.7 (22.7) Aa 171.6 (26.4) Aa High‑ density 168.5 (25.3) Aa 162.7 (22.9) Aa 167.7 (25.2) Aa 158.4 (19.4) Aa 162.3 (21.5) Aa 164.1 (22.1) Aa Pulp Control 83.5 (24.3) Aa 95.6 (20.1) Aa 90.5 (24.5) Aa 98.1 (17.6) Aa 93.4 (20.8) Aa 92.4 21.5) Aa High‑ density 77.4 (22.4) Aa 89.4 (20.8) Aa 82.5 (23.2) Aa 93.6 (17.6) Aa 88.9 (19.8) Aa 88.3 (19.8) Aa Different uppercase letters indicate a statistical difference between the control and high-density groups, within each dental tissue (vertical comparisons) Different lowercase letters indicate a statistical difference between kV at the same exposure time and between exposure times at the same kV, within each group (horizontal comparisons) both dental tissues at 70 kV, regardless of the exposure Discussion time (p < 0.001). The increase in kV decreased the val - It has been demonstrated here that the performance of ues of crown dentine at 0.10  s and enamel at 0.10 and the AEC depends not only on the presence or absence of 0.16  s in the control and high-density groups, and of high-density material in the radiographed area but also enamel at 0.06  s in the high-density group (p  <  0.001). on the kV and exposure time used and the physical den- The increase in the exposure time from 0.06 to 0.16  s sity of the radiographed anatomical structures. All these decreased the gray values of the enamel at both possible variables might influence on one system but not kV (p  =  0.047) and of the crown dentine at 60  kV on the other, as the AEC can act differently for each digi - (p = 0.036). tal system, as previously reported [6, 10]. The influence of the distance to the high-density mate - In the RVG 6100 system, the presence of the implant rial was tested only for those variables (Express system did not significantly affect the gray values of the dental and kV) and dental tissues (enamel and crown dentine) tissues in the exposure times and kV used. According to that presented significant differences in the first evalua - our knowledge, this was the first time that a system that tion. No difference was observed for the variation of the present AEC did not show significant changes in any of average gray values (Δ Gray Values) (control images— the gray values of the structures present in the radio- high-density images) between the first molar and second graphed area when a high-density material was intro- molar, in any of the kV and dental tissues tested (Fig.  3; duced into it, differently from what was found in other p > 0.08). studies that also carried out similar evaluations [6, 10]. M aciel et al. BMC Medical Imaging (2022) 22:4 Page 5 of 7 Previous studies that evaluated the effect of AEC in the presence of high-density material obtained varying results for each digital system. Galvão et  al. [6] evalu- ated this effect in three different systems at 70  kV and demonstrated that, in two of them, Digora Toto (CMOS) and VistaScan (PSP), the presence of high-density mate- rial decreased the gray values of all e quivalent den- tal tissue materials, regardless of the exposure time; while in the third system, Digora Optime (PSP), there was a decrease only in the pulp equivalent tissue and there was an increase in dentine equivalent tissue for 0.1 and 0.16  s and an increase in enamel equivalent tis- sue in 0.16  s. Dashpuntsag et  al. [10] also evaluated the Digora Optime system, at 60  kV, which demonstrated a similar operation to the Megadixel system (CCD) in the radiographs of a thin aluminum phantom: the addition of a high-density plate reduced the gray values and the contrast of the image. In the thick aluminum phantom, however, they presented opposite reactions: the gray values decreased in the Megadixel and increased in the Digora Optime system [10]. Therefore, it is noticed that the AEC is intensified by the presence of high-density material in the radiographed area can present different effects according to the digital system used. In addition, some of these systems, as in the case of Digora Optime, can have a bidirectional function, causing both increas- ing and decreasing gray values according to the exposed structure. It is worth emphasizing that these previous Fig. 3 Graphs showing the mean Δ gray values and standard studies used phantoms with tissue-equivalent liquids rep- deviation between high‑ density and control groups for enamel and dentine of the first (1 M) and second molars (2 M) using 60 kV and resenting each dental tissue individually [6] or aluminum 70 kV with an exposure time of 0.06 s for the Express system scales [10] in their study designs, unlike ours that used real teeth and mandibles. This was also the first study that evaluated the effect of the distance of the high-density material on the gray Such fact may be attributed to the fact that previous values of the adjacent dental tissues. This was achieved studies did not simulate a clinical scenario for this evalu- through a statistical evaluation of the difference of vari - ation. The clinical disposition of the dental tissues and ations in gray values that occurred between the tissues the attenuation of X-rays by bone and soft tissues cover- of the first and second molars, with the introduction of ing (this latter represented here by an acrylic plate) may the dental implant in the image. u Th s, we observed that be factors that reduce the final effect of AEC activation there was no significant influence of distance on any tis - by a high-density object. sue. Differently, Galvão et al. [6] evaluated the size of the In the Express system, only the gray values of ename l equivalent high-density material in the radiographed and crown dentine change significantly, decreasing with region, representing what would be a different amount the presence of the implant (at 70  kV) and/or with the of high-density material in the image, but also found a increase in exposure factors. This result differs from the similar result: this factor did not affect the gray values study by Galvão et  al. [6] in which all materials equiva- significantly. Even so, as these authors did not use dental lent to dental tissues (pulp, enamel, and dentine) were tissues for radiographic acquisition, the variable “amount influenced by the presence of a high-density material of high-density material” in the radiographed area still (e.g., implant). In the present study, we classified dentin needs to be further studied. as “crown” and “root” because, although dentin has the Regarding kilovoltage, in the RVG 6100 system, the same physical density throughout the entire tooth, its increase in kV from 60 to 70 decreased the gray values radiographic density could change as a result of overlap- in all dental tissues and exposure times, thus being the ping enamel or alveolar bone depending on the region parameter that most caused changes in the image. In the evaluated. Maciel et al. BMC Medical Imaging (2022) 22:4 Page 6 of 7 Express system, the increase in kV decreased the gray val- ROI Manager tool. Such an exact standardization would ues only f or crown dentine and enamel (tissues of greater hardly be achieved in the software of each device. physical density). In theory, the increase in kV qualita- The results obtained here are not sufficient to fully tively modifies the X-ray photons, increasing their capa - explain the action of the AEC in the gray values of the bility to pass through the tissues. In systems without the tissues, given that the AEC is an automatic tool whose AEC, this also results, although indirectly, in the dark- performance is not disclosed by the manufacturers. ening of the radiograph (reduction of gray values), since According to Hayawaka et al. [8], the AEC function algo- more X-ray photons will reach the image receiver [5]. As rithm produces a high-contrast image irrespective of this is expected when the AEC function is not present exposure, in a non-linear manner. Thus, the AEC algo - but also occurred in systems with AEC, it seems that the rithm could provide compensation for different degrees AEC does not interfere so strongly in the changes caused of exposure by stretching the range of pixel values to by kV in the image. Hence, it is shown the importance increase the image contrast, probably detecting the mini- of taking kV into account when comparing studies and mum and maximum pixel values of the image, redistrib- when translating these findings to clinical application. No uting and shifting these values to change the displayed previous study has demonstrated the influence of kV on image [8]. As AEC activity cannot be turned off by the AEC function, and this makes it difficult to compare our operator, it is not possible to compare with the results of results. the same system without AEC. Our findings, however, The behavior of the radiographic systems studied was clarify that the effect of AEC in a clinical situation differs the opposite when we analyzed the results regarding the from that in assessments of the radiographic density of exposure time. In the RVG 6100 system, the increase in liquids or aluminum scales [6, 10]. time decreased the gray values of pulp and root dentine, In addition, few studies have evaluated AEC from a while in the Express system, the increase in exposure clinical perspective, such as the effect of AEC on the time decreased the values of enamel and crown dentine accuracy of diagnosing proximal caries [4] and the reper- in some protocols. As is known, increased exposure usu- cussion of the presence of high-density material on this ally causes the darkening of the entire radiograph. u Th s, diagnostic task [11], which presented controversial we could attribute to the AEC the fact that the tissues results. Dashpuntsag et  al. [10] also demonstrated that with higher and lower physical density were not affected the alteration of contrast in the image caused by AEC in the RVG 6100 and Express, respectively. Dashpuntsag can impair the accuracy of other diagnostic tasks, such et  al. [10] also evaluated the effect of the exposure time as the detection of minimal bone regeneration in peri- variation on radiographs from thin and thick aluminum odontal treatments, root cracks, and fractures. Likewise, scales. On the thin scale, the increase in time hardly the change of gray values by AEC can seriously affect the caused changes in gray values in the Digora Optime sys- results of radiographic density surveys, especially those tem, while causing an important variation in Megadixel in which a clinical scenario is not simulated, such as system. On the thick scale, increasing the time decreased in vitro studies of the density of types of cement and res- the gray values in Digora and increased in Megadixel. ins and other dental materials. Thus, the presence of AEC This indicates that the effect of the variation in exposure in radiographic systems can represent disadvantages time in AEC systems depends on the thickness of the in its use. Moreover, the X-ray unit used in the present exposed structures and the radiographic system used. study had a fixed tube current at 7 mA. The tube current, In the present study, the images were evaluated on an as the exposure time, is directly related to the number of 8-bit scale instead of the original scale of each system to photons produced and reaching the receptor. Therefore, obtain a standardization between them and to compare one may expect that tube current and exposure time our findings with previous studies, which have also used could impact the AEC intensity similarly. Future stud- that methodology. This scale presents a more homogene - ies evaluating the effect of AEC on gray values of dental ous distribution of gray values over the 254 possibilities tissues in clinical conditions varying exposure param- between black and white, while larger scales may group eters in other digital systems are encouraged. In addition, the values in a more heterogeneous way (which makes it investigating AEC influence on other diagnostic tasks is more difficult to identify statistical differences in the vari - also recommended. ation of gray values). As for the use of the ImageJ soft- ware, it is a software that is widely used in radiological studies with methodologies similar to ours [6]. This soft - Conclusions ware, in addition to precisely measuring the gray values In conclusion, AEC’s performance varies between digital in the chosen scale, also enabled us to standardize the radiographic systems. Its effect on the gray values of den - size and location of the ROIs in the images, through its tal tissues depends not only on the presence or absence M aciel et al. BMC Medical Imaging (2022) 22:4 Page 7 of 7 6. Galvão NS, Nascimento EHL, Lima CAS, Freitas DQ, Haiter‑Neto F, Oliveira of a high-density material in the radiographed area but ML. Can a high‑ density dental material affect the automatic exposure also on the kV and exposure time used. compensation of digital radiographic images? Dentomaxillofac Radiol. 2019;48:2–7. 7. Hayakawa Y, Farman AG, Scarfe WC, Kuroyanagi K. Technical report. Abbreviations Processing to achieve high‑ contrast images with computed dental AEC: Automatic exposure compensation; kV: Kilovoltage; ROI: Region of inter‑ radiography. Dentomaxillofac Radiol. 1996;25:211–4. est; SD: Standard deviation. 8. Hayakawa Y, Farman AG, Scarfe WC, Kuroyanagi K. Pixel value modifica‑ tion using RVG‑4 automatic exposure compensation for instant high‑ Acknowledgements contrast images. Oral Radiol. 1996;12:11–8. Not applicable. 9. Yoshiura K, Welander U, McDavid W, Li G, Shi X‑ Q, Kawazu T, et al. Perceptibility curves for the Digora system. Dentomaxillofac Radiol. Authors’ contributions 2003;32:191–7. ERCM, EHLN, MLAP, and AAP acquired the images, EHLN, HGA and FMMRP 10. Dashpuntsag O, Yoshida M, Kasai R, Maeda N, Hosoki H, Honda E. Numeri‑ analyzed and interpreted the images data regarding the gray values of dental cal evaluation of image contrast for thicker and thinner objects among tissues. All authors contributed to the writing of the manuscript. All authors current intraoral digital imaging systems. Biomed Res Int. 2017;2017:1–10. read and approved the final manuscript. 11. Galvão NS, Leandro Nascimento EH, Gaêta‑Araujo H, Freitas DQ, Haiter ‑ Neto F, Oliveira ML. Automatic exposure compensation and subjective Funding image enhancement in the radiographic diagnosis of caries. Braz Oral This study was financed in part by the National Research Council—Brazil Res. 2020;34:1–8. (CNPq). Publisher’s Note Availability of data and materials Springer Nature remains neutral with regard to jurisdictional claims in pub‑ The datasets generated and analyzed during the current study are available lished maps and institutional affiliations. from the corresponding author on reasonable request. Declarations Ethics approval and consent to participate This study was approved by the Research Ethics Committee of the Federal University of Pernambuco (protocol #3.594.302). All procedures performed were in accordance with the ethical standards of the Institutional and National Research Committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The informed consent require‑ ment for this ex vivo study was waived by the Research Ethics Committee of the Federal University of Pernambuco. Consent for publication Not applicable. Competing interests The authors declare that they have no competing interests. Author details Department of Clinical and Preventive Dentistry, Federal University of Pernambuco (UFPE), Av. Prof. Artur de Sá, 329‑481, Recife, Pernambuco 52171‑011, Brazil. Present Address: Division of Oral Radiology, Department of Dentistry, Odontomed Imagem ‑ Medical and Dental Services, Av. Dois Rios, 632, Ibura, Recife, Pernambuco 51.230‑000, Brazil. Oral Radiology Area, School of Dentistry, Federal University of Alfenas (UNIFAL‑MG), R. Gabriel Monteiro da Silva, 700, Alfenas, Minas Gerais 37130‑001, Brazil. Received: 12 September 2021 Accepted: 28 December 2021 Re Read ady y to to submit y submit your our re researc search h ? Choose BMC and benefit fr ? Choose BMC and benefit from om: : References fast, convenient online submission 1. Rovaris K, Vasconcelos K, dedo Nascimento EHL, Oliveira ML, Freitas DQ, Haiter‑Neto F. Brazilian young dental practitioners’ use and acceptance of thorough peer review by experienced researchers in your field digital radiographic examinations. Imaging Sci Dent. 2016;46:239–44. rapid publication on acceptance 2. Vandenberghe B, Jacobs R, Bosmans H. Modern dental imaging: a review support for research data, including large and complex data types of the current technology and clinical applications in dental practice. Eur Radiol. 2010;20:2637–55. • gold Open Access which fosters wider collaboration and increased citations 3. van der Stelt PF. Better imaging. J Am Dent Assoc. 2008;139(SUPPL.):S7‑13. maximum visibility for your research: over 100M website views per year 4. Yoshiura K, Nakayama E, Shimizu M, Goto TK, Chikui T, Kawazu T, et al. Eec ff ts of the automatic exposure compensation on the proximal caries At BMC, research is always in progress. diagnosis. Dentomaxillofac Radiol. 2005;34:140–4. 5. Stuart C, White MJP. Oral radiology. Principles and interpretation. 7th ed. Learn more biomedcentral.com/submissions Mosby/Elsevier; 2013. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png BMC Medical Imaging Springer Journals

Automatic exposure compensation in intraoral digital radiography: effect on the gray values of dental tissues

Loading next page...
 
/lp/springer-journals/automatic-exposure-compensation-in-intraoral-digital-radiography-lqRS0480wR
Publisher
Springer Journals
Copyright
Copyright © The Author(s) 2022
eISSN
1471-2342
DOI
10.1186/s12880-021-00733-x
Publisher site
See Article on Publisher Site

Abstract

Background: This study aimed to investigate the effect of automatic exposure compensation (AEC) of intraoral radiographic systems on the gray values of dental tissues in images acquired with or without high‑ density material in the exposed region using different exposure times and kilovoltages. The influence of the distance of the high‑ density material was also investigated. Methods: Radiographs from the molar region of two mandibles were obtained using the RVG 6100 and the Express systems, operating at 60 and 70 kV and 0.06, 0.10, and 0.16 s. Subsequently, a titanium implant was inserted in the pre‑ molar’s socket and other images were acquired. Using the ImageJ software, two regions of interest were determined on the enamel, coronary dentine, root dentine, and pulp of the first and second molars to obtain their gray values. Results: In the RVG 6100, the implant did not affect the gray values (p > 0.05); the increase in kV decreased it in all tissues (p < 0.05), and the exposure time affected only the root dentine and pulp. In the Express, only enamel and coronary dentine values changed (p < 0.05), decreasing with the implant presence and/or with the increase in expo‑ sure factors. The distance of the implant did not affect the results (p > 0.05). Conclusions: AEC’s performance varies between the radiographic systems. Its effect on the gray values depends not only on the presence or absence of high‑ density material but also on the kV and exposure time used. Keywords: Dental radiography, Dental materials, Digital radiography, Digital system, Periapical radiography Background In some systems, image enhancement is also per- Digital image acquisition systems are increasingly present formed automatically by the software, after image acqui- in dentistry due to their advantages compared to con- sition, but before it is displayed on the monitor, through ventional films, such as requiring less exposure time and an image pre-processing tool called Automatic Exposure presenting the possibility of image enhancement, which Compensation (AEC) [4–6]. This tool increases image avoid repetition and consequently reduce the radiation contrast, modifying pixel values non-linearly, producing dose to the patient [1–3]. high-contrast radiographs [7, 8]. Also, AEC can modify the signal-to-noise ratio, presenting a lower value (i.e. darker image) compared to systems without AEC [7, 9]. Previous studies have shown that AEC can improve the *Correspondence: eduarda.hln@gmail.com accuracy of diagnosis of proximal caries in under- and Present Address: Division of Oral Radiology, Department of Dentistry, Odontomed Imagem ‑ Medical and Dental Services, Av. Dois Rios, 632, overexposed images [4]. It was also stated previously that Ibura, Recife, Pernambuco 51.230‑000, Brazil Full list of author information is available at the end of the article © The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecom‑ mons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Maciel et al. BMC Medical Imaging (2022) 22:4 Page 2 of 7 the effect of AEC is influenced by the presence of high- The study sample consisted of periapical radiographs density objects [6, 10]. obtained from two partially edentulous human mandi- Galvão et  al. [6], in an in  vitro study, investigated the bles belonging to the Oral Radiology Department used influence of the presence of high-density material, as well for teaching purposes, selected considering the follow- as its size and exposure time, on the gray values of radi- ing inclusion criteria: mandibles containing adjacent first odensity liquids equivalent to dental tissues. The authors and second molars on at least one side, and absence of concluded that a high-density material present in the the second premolar. Molars with dental restoration or image can influence the AEC adjustment, regardless of endodontic treatment and mandibles with moderate to exposure time and radiographic system. However, the advanced bone loss in the molar region were excluded. gray values of dental tissues were tested employing radi- Finally, two molar regions (one in each mandible) were odensity equivalent liquids separately (one dental tissue available for the acquisition of the study images. at a time on each radiograph), which does not reflect the clinical condition. In addition, apart from radiographic Image acquisition systems and exposure time, other parameters may be All images were acquired using the Heliodent Plus X-ray applied for image acquisition, such as tube current and machine (Sirona Dental Systems, Bensheim, Germany) kilovoltage (kV), which are mainly responsible for the and two digital intraoral systems: final image density and contrast, respectively. By applying different kV (i.e. different beam energy), AEC could act • A Complementary metal-oxide-semiconductor, differently in adjusting the shades of gray, as X-rays beam direct radiography (DR) system, 12-bit depth—RVG with different energy reaches the image receptor. 6100 (Kodak Dental Systems, New York, USA); AEC is an autonomous tool, and thus the pre-process- • A photostimulable phosphor (PSP) plate, computed ing of the image cannot be controlled by the operator. radiography (CR) system, 14-bit depth—Express Also, little is known about the real clinical effect of AEC (Instrumentarium, Tuusula, Finland). on the gray values of dental tissues when high-density objects are present in the radiographed area, and the For both systems, the X-ray machine was set to operate effect of the exposure parameters. Therefore, it is essen - at 7  mA (tube current not adjustable), two kilovoltages tial to understand its functioning and how it can be (60 and 70 kV), and three exposure times (0.06, 0.10, and influenced by factors present in the radiographed area in 0.16  s). In each mandible, periapical radiographs of the clinical situations (i.e., presence of high-density materi- right mandibular molars were acquired with and without als) and technical parameters (i.e. kV and exposure time). the insertion of an 11 × 4 mm titanium dental implant The aim of the present study was to evaluate, in an ex (Titamax, Neodent, Brazil) in the alveolus of the second vivo model, the effect of AEC on dental tissues (enamel, premolar, composing two experimental groups: control crown dentine, root dentine, and pulp), using two dif- group (without high-density material in the radiographed ferent radiographic systems, under different acquisition region) and high-density group (with the dental implant parameters (exposure time and kV). In addition, the in the radiographed region, placed within the edentulous potential influence of the distance from the high-density socket of the right second premolar). Table 1 summarizes material on the gray values was tested. The null hypothe - the study’s protocols and variables. sis was that the effect of AEC does not influence the gray Images were acquired using the parallelism technique. values of dental tissues, regardless of the variables con- An acrylic device was used to standardize the geomet- sidered in the study. ric relationships between the X-ray source/object/image receiver. Between the acquisitions of the control group and the high-density group, the mandible was not moved, Methods so that the exact spatial relationship between it and the This study was approved by the Research Ethics Com - mittee of the Federal University of Pernambuco (proto- col #3.594.302). All procedures performed were under the ethical standards of the Institutional and National Table 1 Exposure protocols and study variables Research Committee and with the 1964 Helsinki Decla- ration and its later amendments or comparable ethical Radiographic system Group kV Time (s) standards. The informed consent requirement for this RVG 6100 Control 60 and 70 0.06–0.10–0.16 ex  vivo study was waived by the Research Ethics Com- High‑ density 60 and 70 0.06–0.10–0.16 mittee of the Federal University of Pernambuco, and Express Control 60 and 70 0.06–0.10–0.16 permission to use the ex vivo sample was granted by this High‑ density 60 and 70 0.06–0.10–0.16 committee. M aciel et al. BMC Medical Imaging (2022) 22:4 Page 3 of 7 Fig. 1 Acquisition of the radiographic image with the Express system (high‑ density group) Fig. 2 Representation of the square regions of interest located in the enamel, dentin (crown), dentin (root), and pulp of the first and second molars in an image obtained with the Express system image receiver was kept the same throughout the study (Fig. 1). Considering the objective nature of the analyses pro- posed in the present study, each acquisition was repeated distance to the high-density material on the mean gray 5 times [6]. The repetitions of acquisitions also aimed to values. For that, the difference between the gray values (Δ verify the reproducibility of the method and record the gray values) in the high-density group and control group possible variability of gray values between acquisitions. were calculated for the ROIs placed on enamel and den- u Th s, 240 radiographs were acquired (2 molar regions tine (both crown and root) of the first molar and the sec - × 2 radiographic systems × 2 groups × 2 kV × 3 expo- ond molar, and compared by t-test. Those comparisons sure times × 5 repetitions). were performed only for those protocols that showed a statistically significant difference in the first part of the study. The significance level was set at 5% (α = 0.05). Objective assessment of gray values of dental tissues To have a standardization between the two systems used, all images were saved in TIFF format and exported with Results 8-bit depth to ImageJ software (U.S. National Institutes of The results related to the RVG 6100 system are shown Health, Bethesda, Maryland, USA). In the radiographs of in Table  2. For this system, the presence of the implant each mandible, two regions of interest (ROIs) of size 0.65 did not significantly affect the gray values of any of the mm ×  0.65 mm were determined on the enamel, crown dental tissues, regardless of the exposure time and the dentine, root dentine, and pulp of the evaluated teeth kV (p = 0.895). However, there were differences between (Fig.  2). The ROIs were recorded in the ImageJ software the images acquired with 60 and 70  kV (p  <  0.001): for using the ROI manager tool, which standardizes the ROI all dental tissues, images obtained with higher kV showed position on all images. In each ROI, the mean and stand- lower gray values (i.e., darker image). By comparing the ard deviation (SD) of the gray values of each tissue were images obtained in the same kV with different exposure recorded. times, it was observed that the time affected only the gray values of the tissues of lower physical density (root Statistical analysis dentine and pulp) (p  <  0.001). In the control group, the The mean and SD values of each tissue were tabulated in increase from 0.06 to 0.16 s decreased the gray values of an Excel spreadsheet (Microsoft Corporation, Redmond, the root dentine at 70  kV and of the pulp at both kilo- WA, USA) and analyzed using the SPSS software (v. 22.0, voltage (p  =  0.026); in the high-density group, images IMB Corp., Armonk, New York, USA). Two-way analysis acquired with 0.16  s showed lower gray values than the of variance (ANOVA) was used to compare the gray val- others, when 70 kV was used (p < 0.001). ues between the groups tested (control and high-density) Table  3 details the results for the Express system, with the varying protocol (kV and exposure time) within which shows that only the gray values of enamel and each tissue and radiographic system, followed by Tukey’s crown dentine underwent significant changes accord - post-hoc test for multiple comparisons. An additional ing to the study variables (p  <  0.001). The presence analysis was performed to evaluate the influence of the of the implant caused a decrease in the gray values of Maciel et al. BMC Medical Imaging (2022) 22:4 Page 4 of 7 Table 2 Mean and standard deviation (SD) of the gray values of dental tissues in the RVG 6100 radiographic system distributed according to the group, exposure time, and kilovoltage Dental tissues Group t = 0.06 s t = 0.10 s t = 0.16 s 60 kV 70 kV 60 kV 70 kV 60 kV 70 kV Enamel Control 135.0 (12.7) Aa 118.1 (13.8) Ab 139.2 (11.9) Aa 118.2 (12.9) Ab 141.7 (13.2) Aa 115.4 (13.3) Ab High‑ density 134.8 (12.7) Aa 118.4 (13.1) Ab 139.6 (12.1) Aa 119.2 (13.2) Ab 142.2 (13.3) Aa 116.1 (13.7) Ab Crown dentine Control 112.2 (11.8) Aa 93.1 (11.4) Ab 114.3 (10.5) Aa 91.9 (10.3) Ab 115.4 (11.3) Aa 88.5 (10.5) Ab High‑ density 111.7 (11.5) Aa 93.1 (10.7) Ab 114.6 (10.5) Aa 93.0 (10.8) Ab 116.0 (11.4) Aa 89.1 (10.9) Ab Root dentine Control 97.3 (6.5) Aa 78.9 (6.3) Ab 98.5 (8.4) Aa 77.4 (7.8) Abc 99.2 (9.1) Aa 73.8 (7.9) Ac High‑ density 97.5 (6.1) Aa 79.3 Ab 99.6 (7.7) Aa 78.9 (7.1) Ab 100.5 (8.0) Aa 74.9 (6.8) Ab Pulp Control 49.7 (6.1) Aa 35.2 (5.1) Ac 47.2 (5.8) Aab 32.6 (4.3) Acd 46.2 (5.6) Ab 29.8 (4.1) Ad High‑ density 48.9(6.2) Aa 35.0 (5.0) Ab 47.7 (5.8) Aa 33.7 (4.7) Ab 47.0 (5.7) Aa 30.3 (4.1) Ac Different uppercase letters indicate a statistical difference between the control and high-density groups, within each dental tissue (vertical comparisons) Different lowercase letters indicate a statistical difference between kV at the same exposure time and between exposure times at the same kV, within each group (horizontal comparisons) Table.3 Mean and standard deviation (SD) of the gray values of dental tissues in the Express radiographic system distributed according to the group, exposure time, and kilovoltage Dental tissue Group t = 0.06 s t = 0.10 s t = 0.16 s 60 kV 70 kV 60 kV 70 kV 60 kV 70 kV Enamel Control 227.5 (8.4) Aa 225.1 (10.3) Aab 226.0 (9.1) Aab 215.5 (10.1) Ac 220.5 (10.8) Ab 213.1 (10.8) Ac High‑ density 224.2 (10.4) Aa 217.2 (9.6) Bc 224.0 (10) Aab 208.5 (10.7) Bd 217.7 (11.5) Ab 205.4 (8.3) Bd Crown dentine Control 192.4 (13.4) Aa 190.5 (10.4) Aab 193.2 (11.6) Aa 181.0 (11.1) Ac 185.0 (8.8) Abc 185.2 (16) Abc High‑ density 187.7 (12.3) Aa 182.4 (9.7) Bab 189.5 (11) Aa 173.4 (8.4) Bc 180.2 (9) Abc 177.1 (11) Bbc Root dentine Control 172.4 (28.8) Aa 169.6 (22.4) Aa 171.9 (26.6) Aa 166.5 (21.4) Aa 167.7 (22.7) Aa 171.6 (26.4) Aa High‑ density 168.5 (25.3) Aa 162.7 (22.9) Aa 167.7 (25.2) Aa 158.4 (19.4) Aa 162.3 (21.5) Aa 164.1 (22.1) Aa Pulp Control 83.5 (24.3) Aa 95.6 (20.1) Aa 90.5 (24.5) Aa 98.1 (17.6) Aa 93.4 (20.8) Aa 92.4 21.5) Aa High‑ density 77.4 (22.4) Aa 89.4 (20.8) Aa 82.5 (23.2) Aa 93.6 (17.6) Aa 88.9 (19.8) Aa 88.3 (19.8) Aa Different uppercase letters indicate a statistical difference between the control and high-density groups, within each dental tissue (vertical comparisons) Different lowercase letters indicate a statistical difference between kV at the same exposure time and between exposure times at the same kV, within each group (horizontal comparisons) both dental tissues at 70 kV, regardless of the exposure Discussion time (p < 0.001). The increase in kV decreased the val - It has been demonstrated here that the performance of ues of crown dentine at 0.10  s and enamel at 0.10 and the AEC depends not only on the presence or absence of 0.16  s in the control and high-density groups, and of high-density material in the radiographed area but also enamel at 0.06  s in the high-density group (p  <  0.001). on the kV and exposure time used and the physical den- The increase in the exposure time from 0.06 to 0.16  s sity of the radiographed anatomical structures. All these decreased the gray values of the enamel at both possible variables might influence on one system but not kV (p  =  0.047) and of the crown dentine at 60  kV on the other, as the AEC can act differently for each digi - (p = 0.036). tal system, as previously reported [6, 10]. The influence of the distance to the high-density mate - In the RVG 6100 system, the presence of the implant rial was tested only for those variables (Express system did not significantly affect the gray values of the dental and kV) and dental tissues (enamel and crown dentine) tissues in the exposure times and kV used. According to that presented significant differences in the first evalua - our knowledge, this was the first time that a system that tion. No difference was observed for the variation of the present AEC did not show significant changes in any of average gray values (Δ Gray Values) (control images— the gray values of the structures present in the radio- high-density images) between the first molar and second graphed area when a high-density material was intro- molar, in any of the kV and dental tissues tested (Fig.  3; duced into it, differently from what was found in other p > 0.08). studies that also carried out similar evaluations [6, 10]. M aciel et al. BMC Medical Imaging (2022) 22:4 Page 5 of 7 Previous studies that evaluated the effect of AEC in the presence of high-density material obtained varying results for each digital system. Galvão et  al. [6] evalu- ated this effect in three different systems at 70  kV and demonstrated that, in two of them, Digora Toto (CMOS) and VistaScan (PSP), the presence of high-density mate- rial decreased the gray values of all e quivalent den- tal tissue materials, regardless of the exposure time; while in the third system, Digora Optime (PSP), there was a decrease only in the pulp equivalent tissue and there was an increase in dentine equivalent tissue for 0.1 and 0.16  s and an increase in enamel equivalent tis- sue in 0.16  s. Dashpuntsag et  al. [10] also evaluated the Digora Optime system, at 60  kV, which demonstrated a similar operation to the Megadixel system (CCD) in the radiographs of a thin aluminum phantom: the addition of a high-density plate reduced the gray values and the contrast of the image. In the thick aluminum phantom, however, they presented opposite reactions: the gray values decreased in the Megadixel and increased in the Digora Optime system [10]. Therefore, it is noticed that the AEC is intensified by the presence of high-density material in the radiographed area can present different effects according to the digital system used. In addition, some of these systems, as in the case of Digora Optime, can have a bidirectional function, causing both increas- ing and decreasing gray values according to the exposed structure. It is worth emphasizing that these previous Fig. 3 Graphs showing the mean Δ gray values and standard studies used phantoms with tissue-equivalent liquids rep- deviation between high‑ density and control groups for enamel and dentine of the first (1 M) and second molars (2 M) using 60 kV and resenting each dental tissue individually [6] or aluminum 70 kV with an exposure time of 0.06 s for the Express system scales [10] in their study designs, unlike ours that used real teeth and mandibles. This was also the first study that evaluated the effect of the distance of the high-density material on the gray Such fact may be attributed to the fact that previous values of the adjacent dental tissues. This was achieved studies did not simulate a clinical scenario for this evalu- through a statistical evaluation of the difference of vari - ation. The clinical disposition of the dental tissues and ations in gray values that occurred between the tissues the attenuation of X-rays by bone and soft tissues cover- of the first and second molars, with the introduction of ing (this latter represented here by an acrylic plate) may the dental implant in the image. u Th s, we observed that be factors that reduce the final effect of AEC activation there was no significant influence of distance on any tis - by a high-density object. sue. Differently, Galvão et al. [6] evaluated the size of the In the Express system, only the gray values of ename l equivalent high-density material in the radiographed and crown dentine change significantly, decreasing with region, representing what would be a different amount the presence of the implant (at 70  kV) and/or with the of high-density material in the image, but also found a increase in exposure factors. This result differs from the similar result: this factor did not affect the gray values study by Galvão et  al. [6] in which all materials equiva- significantly. Even so, as these authors did not use dental lent to dental tissues (pulp, enamel, and dentine) were tissues for radiographic acquisition, the variable “amount influenced by the presence of a high-density material of high-density material” in the radiographed area still (e.g., implant). In the present study, we classified dentin needs to be further studied. as “crown” and “root” because, although dentin has the Regarding kilovoltage, in the RVG 6100 system, the same physical density throughout the entire tooth, its increase in kV from 60 to 70 decreased the gray values radiographic density could change as a result of overlap- in all dental tissues and exposure times, thus being the ping enamel or alveolar bone depending on the region parameter that most caused changes in the image. In the evaluated. Maciel et al. BMC Medical Imaging (2022) 22:4 Page 6 of 7 Express system, the increase in kV decreased the gray val- ROI Manager tool. Such an exact standardization would ues only f or crown dentine and enamel (tissues of greater hardly be achieved in the software of each device. physical density). In theory, the increase in kV qualita- The results obtained here are not sufficient to fully tively modifies the X-ray photons, increasing their capa - explain the action of the AEC in the gray values of the bility to pass through the tissues. In systems without the tissues, given that the AEC is an automatic tool whose AEC, this also results, although indirectly, in the dark- performance is not disclosed by the manufacturers. ening of the radiograph (reduction of gray values), since According to Hayawaka et al. [8], the AEC function algo- more X-ray photons will reach the image receiver [5]. As rithm produces a high-contrast image irrespective of this is expected when the AEC function is not present exposure, in a non-linear manner. Thus, the AEC algo - but also occurred in systems with AEC, it seems that the rithm could provide compensation for different degrees AEC does not interfere so strongly in the changes caused of exposure by stretching the range of pixel values to by kV in the image. Hence, it is shown the importance increase the image contrast, probably detecting the mini- of taking kV into account when comparing studies and mum and maximum pixel values of the image, redistrib- when translating these findings to clinical application. No uting and shifting these values to change the displayed previous study has demonstrated the influence of kV on image [8]. As AEC activity cannot be turned off by the AEC function, and this makes it difficult to compare our operator, it is not possible to compare with the results of results. the same system without AEC. Our findings, however, The behavior of the radiographic systems studied was clarify that the effect of AEC in a clinical situation differs the opposite when we analyzed the results regarding the from that in assessments of the radiographic density of exposure time. In the RVG 6100 system, the increase in liquids or aluminum scales [6, 10]. time decreased the gray values of pulp and root dentine, In addition, few studies have evaluated AEC from a while in the Express system, the increase in exposure clinical perspective, such as the effect of AEC on the time decreased the values of enamel and crown dentine accuracy of diagnosing proximal caries [4] and the reper- in some protocols. As is known, increased exposure usu- cussion of the presence of high-density material on this ally causes the darkening of the entire radiograph. u Th s, diagnostic task [11], which presented controversial we could attribute to the AEC the fact that the tissues results. Dashpuntsag et  al. [10] also demonstrated that with higher and lower physical density were not affected the alteration of contrast in the image caused by AEC in the RVG 6100 and Express, respectively. Dashpuntsag can impair the accuracy of other diagnostic tasks, such et  al. [10] also evaluated the effect of the exposure time as the detection of minimal bone regeneration in peri- variation on radiographs from thin and thick aluminum odontal treatments, root cracks, and fractures. Likewise, scales. On the thin scale, the increase in time hardly the change of gray values by AEC can seriously affect the caused changes in gray values in the Digora Optime sys- results of radiographic density surveys, especially those tem, while causing an important variation in Megadixel in which a clinical scenario is not simulated, such as system. On the thick scale, increasing the time decreased in vitro studies of the density of types of cement and res- the gray values in Digora and increased in Megadixel. ins and other dental materials. Thus, the presence of AEC This indicates that the effect of the variation in exposure in radiographic systems can represent disadvantages time in AEC systems depends on the thickness of the in its use. Moreover, the X-ray unit used in the present exposed structures and the radiographic system used. study had a fixed tube current at 7 mA. The tube current, In the present study, the images were evaluated on an as the exposure time, is directly related to the number of 8-bit scale instead of the original scale of each system to photons produced and reaching the receptor. Therefore, obtain a standardization between them and to compare one may expect that tube current and exposure time our findings with previous studies, which have also used could impact the AEC intensity similarly. Future stud- that methodology. This scale presents a more homogene - ies evaluating the effect of AEC on gray values of dental ous distribution of gray values over the 254 possibilities tissues in clinical conditions varying exposure param- between black and white, while larger scales may group eters in other digital systems are encouraged. In addition, the values in a more heterogeneous way (which makes it investigating AEC influence on other diagnostic tasks is more difficult to identify statistical differences in the vari - also recommended. ation of gray values). As for the use of the ImageJ soft- ware, it is a software that is widely used in radiological studies with methodologies similar to ours [6]. This soft - Conclusions ware, in addition to precisely measuring the gray values In conclusion, AEC’s performance varies between digital in the chosen scale, also enabled us to standardize the radiographic systems. Its effect on the gray values of den - size and location of the ROIs in the images, through its tal tissues depends not only on the presence or absence M aciel et al. BMC Medical Imaging (2022) 22:4 Page 7 of 7 6. Galvão NS, Nascimento EHL, Lima CAS, Freitas DQ, Haiter‑Neto F, Oliveira of a high-density material in the radiographed area but ML. Can a high‑ density dental material affect the automatic exposure also on the kV and exposure time used. compensation of digital radiographic images? Dentomaxillofac Radiol. 2019;48:2–7. 7. Hayakawa Y, Farman AG, Scarfe WC, Kuroyanagi K. Technical report. Abbreviations Processing to achieve high‑ contrast images with computed dental AEC: Automatic exposure compensation; kV: Kilovoltage; ROI: Region of inter‑ radiography. Dentomaxillofac Radiol. 1996;25:211–4. est; SD: Standard deviation. 8. Hayakawa Y, Farman AG, Scarfe WC, Kuroyanagi K. Pixel value modifica‑ tion using RVG‑4 automatic exposure compensation for instant high‑ Acknowledgements contrast images. Oral Radiol. 1996;12:11–8. Not applicable. 9. Yoshiura K, Welander U, McDavid W, Li G, Shi X‑ Q, Kawazu T, et al. Perceptibility curves for the Digora system. Dentomaxillofac Radiol. Authors’ contributions 2003;32:191–7. ERCM, EHLN, MLAP, and AAP acquired the images, EHLN, HGA and FMMRP 10. Dashpuntsag O, Yoshida M, Kasai R, Maeda N, Hosoki H, Honda E. Numeri‑ analyzed and interpreted the images data regarding the gray values of dental cal evaluation of image contrast for thicker and thinner objects among tissues. All authors contributed to the writing of the manuscript. All authors current intraoral digital imaging systems. Biomed Res Int. 2017;2017:1–10. read and approved the final manuscript. 11. Galvão NS, Leandro Nascimento EH, Gaêta‑Araujo H, Freitas DQ, Haiter ‑ Neto F, Oliveira ML. Automatic exposure compensation and subjective Funding image enhancement in the radiographic diagnosis of caries. Braz Oral This study was financed in part by the National Research Council—Brazil Res. 2020;34:1–8. (CNPq). Publisher’s Note Availability of data and materials Springer Nature remains neutral with regard to jurisdictional claims in pub‑ The datasets generated and analyzed during the current study are available lished maps and institutional affiliations. from the corresponding author on reasonable request. Declarations Ethics approval and consent to participate This study was approved by the Research Ethics Committee of the Federal University of Pernambuco (protocol #3.594.302). All procedures performed were in accordance with the ethical standards of the Institutional and National Research Committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The informed consent require‑ ment for this ex vivo study was waived by the Research Ethics Committee of the Federal University of Pernambuco. Consent for publication Not applicable. Competing interests The authors declare that they have no competing interests. Author details Department of Clinical and Preventive Dentistry, Federal University of Pernambuco (UFPE), Av. Prof. Artur de Sá, 329‑481, Recife, Pernambuco 52171‑011, Brazil. Present Address: Division of Oral Radiology, Department of Dentistry, Odontomed Imagem ‑ Medical and Dental Services, Av. Dois Rios, 632, Ibura, Recife, Pernambuco 51.230‑000, Brazil. Oral Radiology Area, School of Dentistry, Federal University of Alfenas (UNIFAL‑MG), R. Gabriel Monteiro da Silva, 700, Alfenas, Minas Gerais 37130‑001, Brazil. Received: 12 September 2021 Accepted: 28 December 2021 Re Read ady y to to submit y submit your our re researc search h ? Choose BMC and benefit fr ? Choose BMC and benefit from om: : References fast, convenient online submission 1. Rovaris K, Vasconcelos K, dedo Nascimento EHL, Oliveira ML, Freitas DQ, Haiter‑Neto F. Brazilian young dental practitioners’ use and acceptance of thorough peer review by experienced researchers in your field digital radiographic examinations. Imaging Sci Dent. 2016;46:239–44. rapid publication on acceptance 2. Vandenberghe B, Jacobs R, Bosmans H. Modern dental imaging: a review support for research data, including large and complex data types of the current technology and clinical applications in dental practice. Eur Radiol. 2010;20:2637–55. • gold Open Access which fosters wider collaboration and increased citations 3. van der Stelt PF. Better imaging. J Am Dent Assoc. 2008;139(SUPPL.):S7‑13. maximum visibility for your research: over 100M website views per year 4. Yoshiura K, Nakayama E, Shimizu M, Goto TK, Chikui T, Kawazu T, et al. Eec ff ts of the automatic exposure compensation on the proximal caries At BMC, research is always in progress. diagnosis. Dentomaxillofac Radiol. 2005;34:140–4. 5. Stuart C, White MJP. Oral radiology. Principles and interpretation. 7th ed. Learn more biomedcentral.com/submissions Mosby/Elsevier; 2013.

Journal

BMC Medical ImagingSpringer Journals

Published: Jan 5, 2022

Keywords: Dental radiography; Dental materials; Digital radiography; Digital system; Periapical radiography

References