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Novel Assistive Device for Tomographic Ultrasound Neck Imaging vs. Freehand

Novel Assistive Device for Tomographic Ultrasound Neck Imaging vs. Freehand DE GRUYTER Current Directions in Biomedical Engineering 2020;6(3): 20203008 Marcel Köhler, Elmer Jeto Gomes Ataide, Jens Ziegle, Axel Boese and Michael Friebe Novel Assistive Device for Tomographic Ultrasound Neck Imaging vs. Freehand Abstract: For assessing clinically relevant structures in the available literature [5] [7] [8]. According to [7] there are four neck area, especially the thyroid, it has been shown that 3D or methods for acquiring the required image and position data: tomographic ultrasound (3D US or tUS) is able to outperform 2D array transducers, mechanical 3D probes, mechanical standard 2D ultrasound [1] and computed tomography [2] for localizers and freehand scanners. The freehand scanning certain diagnostic procedures. However, when using a method works by using a conventional 2D ultrasound freehand and unassisted scanning method to acquire a 3D US transducer and equipping it with a tracking device. This volume data set in this area overlapping image slices, a approach enables the user to manually guide the US probe over variation of the probe angulation or differences in training the region of interest (ROI) in desired directions and positions. might lead to unusable scanning results. Based on previous In this scenario, freehand scans mean unassisted scan works [3] [4] we propose the design - with subsequent testing acquisitions. There are many different tracking devices - of an assistive device that is able to aid physicians during the available that utilize a variety of physical principles and come tUS scanning process on the neck. To validate the feasibility with certain advantages and disadvantages [9]. and efficacy we compared the image quality of both freehand and assisted scanning. Electromagnetic (EM) tracking systems for example work based on the generation and measurement of electromagnetic Keywords: Tomographic Ultrasound, Assisted Freehand fields and consist of a transmitter (also called ‘field Scanning, Thyroid Assessment. generator’), a six axis sensor and a processing unit [9] (see Figure 1) The transmitter, consisting of at least three orthogonally placed coils, serves as the origin of coordinates 1 Introduction and generates a three-dimensional electromagnetic field. The processing unit controls the electric current flowing through Conventional 2D Ultrasound (US) B-mode imaging can the coils and each field is simultaneously measured by sensor be used for initial diagnostic procedures concerning soft tissue coils. The position and orientation of the sensor, and with that structures like the salivary glands or the lymph nodes [5] or to of the probe, is then calculated by continuously measuring the detect and analyze thyroid nodules. These US images could be relative changes of the electromagnetic field during the probe the base for creating a three-dimensional volume model by movement. This type of tracking system is not negatively accurately tracking the transducer/probe position during the affected from line of sight issues, but can only be used within scanning process and combining both the position and the relatively short distance from the origin of coordinates. Other image data to perform volume reconstruction and visualization tracking mechanisms include optical, inertial and mechanical [6]. tracking [9]. Using the freehand acquisition method in general and Imaging systems that utilize this method are called 3D or specifically on a vaguely cylindrical object like the neck is tomographic ultrasound systems (tUS). Tomographic strongly dependent on the individual ability of the user. ultrasound systems are classified inconsistently in the Acquisition speed, applied pressure, and probe angulation can negatively impact scan quality and reproducibility. Additionally, effects like motion artefacts and overlapping ______ *Marcel Köhler: Otto-von-Guericke-University, Magdeburg, Germany, marcel.koehler@st.ovgu.de Elmer Jeto Gomes Ataide, Jens Ziegle: Otto-von-Guericke- University, Magdeburg, Germany Axel Boese: Otto-von-Guericke-University, Magdeburg, Germany Michael Friebe: Otto-von-Guericke-University, Magdeburg, Germany Open Access. © 2020 Marcel Kö hler et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. image slices are likely to occur reducing the quality of the 3D To prevent any head / neck movement during the scanning volume even further [3]. procedure the prototype proposed in this paper was designed to be used on a lying patient on an examination table. Ideally a 180° rotation should be realized with the center of rotation Figure 1: Working principle of a freehand tUS system utilizing the roughly in the center of the neck (Figure 2). Based on this electromagnetic tracking method (based on [7]) concept and requirements a prototype was realized using standard parts, 3D printing and a milled acrylic arc (Figure 3). A possible solution to these problems was proposed in [3] and [4]. Designing assistive devices that guide an US probe Figure 2: Basic concept of guided neck scans and tracking sensor around the neck on a fixed circular path during the scanning process improved the image quality compared to a non-guided freehand scan. However, these prototypes were not able to generate usable results for diagnosis and needed to be improved. Based on those initial results this paper deals with the use of a systematic designing approach to conceptualize and build an improved prototype for assisted 3D US acquisitions. 2 Materials and Methods The designing guideline VDI 2221 by the Association of German Engineers [11] was used as a structured and methodical approach for creating a usable prototype. This designing approach starts with a systematic task analysis to generate a comprehensive list of requirements and boundary conditions for the design. Based on this list (sub-) functions are determined that need to be fulfilled by the design. Different modular concepts to fulfil those functions were created and evaluated. The most important requirements were set as follows: - patient’s head / neck must be stable during the scanning process - circulation radius of the US probe needs to be adaptable Figure 3: Designed prototype (1) item profile foundation and neck to fit different neck sizes pillow; 2) acrylic glass arc; 3) 3D printed arc slide 4) linear slide; 5) - design must not include any magnetic parts materials 3D printed probe attachment; 6) PUIR tUS tracking sensor; 7) GE because of their interference with the electromagnetic 9L US transducer; 8) gel pad filled with US transmission gel tracking system - device needs to be put on / taken off in 5 steps or less and The basis of this prototype is a foundation (1) made from without use of additional tools non-magnetic item profiles and a plate. The patient’s head is placed onto during the scanning process. A detachable acrylic The second evaluation was a quantitative analyses. glass arc (2), working as a circular guide, is placed in the rails Therefore, a structure in 2D slices within the reconstructed of the profiles allowing linear adjustment. Combined with a neck volumes was selected and measured in both cases 3D printed arc slide (3) the required circular motion around the (freehand and assisted). The carotid artery was selected in this neck is realized. This slide also functions as a slot for the radial instance. slide (4) that is needed to adapt the probe circulation radius to The common carotid artery was measured in individual different neck sizes. To hold the US transducer (7) and the US slices of sagittal plane. This can be seen in Figure 5. motion tracking sensor (6), a probe attachment (5) was designed, 3D printed and attached to the linear slide. To compensate unevenness’s of the neck a gel pad filled with US transmission gel (8) was included in the design. Before the scanning process starts the pad is placed around the patient’s neck. The circulation radius is adjusted and fixed by using a locking mechanism on the radial slide. To validate the prototype test scans were obtained and the image quality compared to unassisted freehand scans with regards to motion artefacts and slice overlap. Furthermore, the carotid artery diameter was measured in both scans and Figure 4: Exemplary visual comparison of freehand (1a), 1b)) and compared to findings in [12]. assisted 3D US scans (2a), 2b)), top and tilted view of 2 volume The prototype was tested on 5 male subjects. The test reconstructions from one subject setup included two scan acquisition approaches: freehand tUS scans and assisted scans with the prototype. The freehand scans were performed using an US system (9L probe and Logiq e GE Wisconsin, USA) coupled with an EM tracking and reconstruction system (PIUR Imaging, Vienna, Austria). The same systems along with the prototype were used to conduct the assisted scans. Parameters such as gain, depth and probe frequency were adjusted based on the subject being scanned. Figure 5: Average measured diameter of one subject’s common carotid artery in a) freehand and b) assisted scans 3 Results and Discussion The average diameter of this artery in males is 6.52+/-0.98 mm according to [10]. Both measurements, freehand 5.63+/- The results from tests conducted on one of the subjects has 1.13 mm and assisted 7.25+/-0.58 mm, lie within this range. been included. The results were analyzed qualitatively based But there is a significant deviation of -1.61+/-1.24 mm from on the image quality of the volume reconstructed first (Figure one another. This might be due to applied pressure in 4). combination with unfavorable quick changes in probe Here it can be seen that the freehand volume follows an angulation during the freehand scan that left out the actual uneven reconstruction pattern and in a large way does not centerline of the artery. Further tests are necessary to see if and depict a true representation of the neck and the structures how the measurement differences change across multiple within it. scans. Apart from this the reconstructed volume using the To conclude, experiments from both scanning methods freehand method depicts deformation of structures and larger generate measurable results. The difference lies in the image overlaps. In comparison to this, the assisted method reconstruction and subsequent visualization of the 3D depicts a much more realistic representation of the neck and volumes. Volume reconstruction and visualization from structures within it. freehand scans appear more to have more irregularities and It also significantly reduces image overlaps and deformations. Assisted volumes depict a more uniform deformation of structures. This is attributed to the rigid reconstruction and visualization. This is due to the fact that the structure of the prototype that disallows the application of probe always follows a ‘standard’ guided path. That makes it larger force on the epidermis that causes deformation. Reviews and Computational Applications, Singapore, a more suitable method to compare structural changes in the Springer Science+Business Media, 2015, pp. 57-89. neck over an extended time period. Improving the prototype in [10] R. Slapa, W. Jakubowski, J. Slowinska-Srzednicka und K. terms of user friendliness (e.g. by including a cable guidance) Szopinski, „Advantages and disadvantages of 3D ultrasound and optimizing the use of the gel pad will be the next steps in of thyroid nodules including thin slice volume rendering,“ Thyroid research vol. 4,1 1, Bd. 4(1):1, pp. 1-12, 7 January creating a standardized method for reliably acquisition of 3D US scans. The reproducibility across varied demographics still [11] A. o. G. E. (VDI), VDI 2221 - Systematic approach to the need to be further investigated. The measurements of the development and design of technical systems and products, carotid arteries in this study were done on individual 2D slices Duesseldorf, Germany: VDI-Gesellschaft Produkt- und Prozessgestaltung (VDI Product and Process Development within the reconstructed volumes. This resulted in a small incorporated), 1993. difference between the measurements. Furthers measurements [12] J. Krejza, M. Arkuszewski und S. Kasner, „Carotid Artery and analyses in the 3D volumes itself (not individual 2D slices) Diameter in Men and Women and the Relation to Body and need to be conducted, compared and extended to other Neck Size,“ Stroke, Nr. 37, pp. 1103-1105, 2006. structures within the neck such as thyroid, salivary glands, lymph nodes, etc. If this acquisition method and prototype can be further developed it could be also used for assessing other body parts like internal structures in the abdominal region. References [1] L. W.-B., Z. B., Q.-L. Zhu und e. al., „Comparison between thin-slice 3-D volumetric ultrasound and conventional ultrasound in the differentiation of benign and malignant thyroid lesions,“ Ultrasound in Medicine and Biology, pp. 3096-3101, December 2015. [2] J.-w. Li, C. Chang, M. Chen, W. Zeng, Y. Gao, S.-c. Zhou, F. Wang, N. Hu und Y.-l. Chen, „Is Ultrasonography More Sensitive Than Computed Tomography for Identifying Calcifications in Thyroid Nodules?,“ Journal of Ultrasound in Medicine, p. 2183–2190, 01 October 2016. [3] E. J. G. Ataide, J. Ziegle, M. Kalmar, A. Boese und M. Friebe, „Assistive Scanning Brace for Improved 3D Tomographic Ultrasound Neck Scans,“ in 40th International Engineering in Medicine and Biology Conference, Honolulu, USA, Juli 2018. [4] E. Ataide, J. Ziegle, M. Kalmar, S. Rathi, A. Boese und M. Friebe, „Feasibility and Initial Results of Standardized US Scan Acquisition for Improved Tomographic Visualization,“ in IEEE INDICON, Gujarat, India, 2019. [5] J. E. Langer, S. Mandel und M. Milas, Advanced Thyroid and Parathyroid Ultrasound, Springer International Publishing, [6] D. Barry, C. P. Allott, N. W. John, P. M., Mellor, P. A. Arundel, D. S. Thomson und J. C. Wateron, „Three- Dimensional Freehand Ultrasound: Image Reconstruction and Volume Analysis,“ Ultrasound in Medicine & Biology, Bd. Vol. 28, Nr. 8, pp. 1209-1224, 1997. [7] Z. Z. Q. Huang, „A Review on Real-Time 3D Ultrasound Imaging Technology,“ BioMed Research International, Bd. March 2017, pp. 1-20, 26. March 2017. [8] L. C. R. L. E. Bozzi, „US Image Acquisition,“ in Image Processing in Radiology - Current Applications, Heidelberg, Germany, Springer Science+Business Media, 2007, pp. 3- [9] D. E. O. Dewi, M. M. Fadzil, A. A. M. Faudzi, E. Supriyanto und K. Lai, „Position Tracking Systems for Ultrasound Imaging: A Survey,“ in Medical Imaging Technology - http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Current Directions in Biomedical Engineering de Gruyter

Novel Assistive Device for Tomographic Ultrasound Neck Imaging vs. Freehand

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Abstract

DE GRUYTER Current Directions in Biomedical Engineering 2020;6(3): 20203008 Marcel Köhler, Elmer Jeto Gomes Ataide, Jens Ziegle, Axel Boese and Michael Friebe Novel Assistive Device for Tomographic Ultrasound Neck Imaging vs. Freehand Abstract: For assessing clinically relevant structures in the available literature [5] [7] [8]. According to [7] there are four neck area, especially the thyroid, it has been shown that 3D or methods for acquiring the required image and position data: tomographic ultrasound (3D US or tUS) is able to outperform 2D array transducers, mechanical 3D probes, mechanical standard 2D ultrasound [1] and computed tomography [2] for localizers and freehand scanners. The freehand scanning certain diagnostic procedures. However, when using a method works by using a conventional 2D ultrasound freehand and unassisted scanning method to acquire a 3D US transducer and equipping it with a tracking device. This volume data set in this area overlapping image slices, a approach enables the user to manually guide the US probe over variation of the probe angulation or differences in training the region of interest (ROI) in desired directions and positions. might lead to unusable scanning results. Based on previous In this scenario, freehand scans mean unassisted scan works [3] [4] we propose the design - with subsequent testing acquisitions. There are many different tracking devices - of an assistive device that is able to aid physicians during the available that utilize a variety of physical principles and come tUS scanning process on the neck. To validate the feasibility with certain advantages and disadvantages [9]. and efficacy we compared the image quality of both freehand and assisted scanning. Electromagnetic (EM) tracking systems for example work based on the generation and measurement of electromagnetic Keywords: Tomographic Ultrasound, Assisted Freehand fields and consist of a transmitter (also called ‘field Scanning, Thyroid Assessment. generator’), a six axis sensor and a processing unit [9] (see Figure 1) The transmitter, consisting of at least three orthogonally placed coils, serves as the origin of coordinates 1 Introduction and generates a three-dimensional electromagnetic field. The processing unit controls the electric current flowing through Conventional 2D Ultrasound (US) B-mode imaging can the coils and each field is simultaneously measured by sensor be used for initial diagnostic procedures concerning soft tissue coils. The position and orientation of the sensor, and with that structures like the salivary glands or the lymph nodes [5] or to of the probe, is then calculated by continuously measuring the detect and analyze thyroid nodules. These US images could be relative changes of the electromagnetic field during the probe the base for creating a three-dimensional volume model by movement. This type of tracking system is not negatively accurately tracking the transducer/probe position during the affected from line of sight issues, but can only be used within scanning process and combining both the position and the relatively short distance from the origin of coordinates. Other image data to perform volume reconstruction and visualization tracking mechanisms include optical, inertial and mechanical [6]. tracking [9]. Using the freehand acquisition method in general and Imaging systems that utilize this method are called 3D or specifically on a vaguely cylindrical object like the neck is tomographic ultrasound systems (tUS). Tomographic strongly dependent on the individual ability of the user. ultrasound systems are classified inconsistently in the Acquisition speed, applied pressure, and probe angulation can negatively impact scan quality and reproducibility. Additionally, effects like motion artefacts and overlapping ______ *Marcel Köhler: Otto-von-Guericke-University, Magdeburg, Germany, marcel.koehler@st.ovgu.de Elmer Jeto Gomes Ataide, Jens Ziegle: Otto-von-Guericke- University, Magdeburg, Germany Axel Boese: Otto-von-Guericke-University, Magdeburg, Germany Michael Friebe: Otto-von-Guericke-University, Magdeburg, Germany Open Access. © 2020 Marcel Kö hler et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License. image slices are likely to occur reducing the quality of the 3D To prevent any head / neck movement during the scanning volume even further [3]. procedure the prototype proposed in this paper was designed to be used on a lying patient on an examination table. Ideally a 180° rotation should be realized with the center of rotation Figure 1: Working principle of a freehand tUS system utilizing the roughly in the center of the neck (Figure 2). Based on this electromagnetic tracking method (based on [7]) concept and requirements a prototype was realized using standard parts, 3D printing and a milled acrylic arc (Figure 3). A possible solution to these problems was proposed in [3] and [4]. Designing assistive devices that guide an US probe Figure 2: Basic concept of guided neck scans and tracking sensor around the neck on a fixed circular path during the scanning process improved the image quality compared to a non-guided freehand scan. However, these prototypes were not able to generate usable results for diagnosis and needed to be improved. Based on those initial results this paper deals with the use of a systematic designing approach to conceptualize and build an improved prototype for assisted 3D US acquisitions. 2 Materials and Methods The designing guideline VDI 2221 by the Association of German Engineers [11] was used as a structured and methodical approach for creating a usable prototype. This designing approach starts with a systematic task analysis to generate a comprehensive list of requirements and boundary conditions for the design. Based on this list (sub-) functions are determined that need to be fulfilled by the design. Different modular concepts to fulfil those functions were created and evaluated. The most important requirements were set as follows: - patient’s head / neck must be stable during the scanning process - circulation radius of the US probe needs to be adaptable Figure 3: Designed prototype (1) item profile foundation and neck to fit different neck sizes pillow; 2) acrylic glass arc; 3) 3D printed arc slide 4) linear slide; 5) - design must not include any magnetic parts materials 3D printed probe attachment; 6) PUIR tUS tracking sensor; 7) GE because of their interference with the electromagnetic 9L US transducer; 8) gel pad filled with US transmission gel tracking system - device needs to be put on / taken off in 5 steps or less and The basis of this prototype is a foundation (1) made from without use of additional tools non-magnetic item profiles and a plate. The patient’s head is placed onto during the scanning process. A detachable acrylic The second evaluation was a quantitative analyses. glass arc (2), working as a circular guide, is placed in the rails Therefore, a structure in 2D slices within the reconstructed of the profiles allowing linear adjustment. Combined with a neck volumes was selected and measured in both cases 3D printed arc slide (3) the required circular motion around the (freehand and assisted). The carotid artery was selected in this neck is realized. This slide also functions as a slot for the radial instance. slide (4) that is needed to adapt the probe circulation radius to The common carotid artery was measured in individual different neck sizes. To hold the US transducer (7) and the US slices of sagittal plane. This can be seen in Figure 5. motion tracking sensor (6), a probe attachment (5) was designed, 3D printed and attached to the linear slide. To compensate unevenness’s of the neck a gel pad filled with US transmission gel (8) was included in the design. Before the scanning process starts the pad is placed around the patient’s neck. The circulation radius is adjusted and fixed by using a locking mechanism on the radial slide. To validate the prototype test scans were obtained and the image quality compared to unassisted freehand scans with regards to motion artefacts and slice overlap. Furthermore, the carotid artery diameter was measured in both scans and Figure 4: Exemplary visual comparison of freehand (1a), 1b)) and compared to findings in [12]. assisted 3D US scans (2a), 2b)), top and tilted view of 2 volume The prototype was tested on 5 male subjects. The test reconstructions from one subject setup included two scan acquisition approaches: freehand tUS scans and assisted scans with the prototype. The freehand scans were performed using an US system (9L probe and Logiq e GE Wisconsin, USA) coupled with an EM tracking and reconstruction system (PIUR Imaging, Vienna, Austria). The same systems along with the prototype were used to conduct the assisted scans. Parameters such as gain, depth and probe frequency were adjusted based on the subject being scanned. Figure 5: Average measured diameter of one subject’s common carotid artery in a) freehand and b) assisted scans 3 Results and Discussion The average diameter of this artery in males is 6.52+/-0.98 mm according to [10]. Both measurements, freehand 5.63+/- The results from tests conducted on one of the subjects has 1.13 mm and assisted 7.25+/-0.58 mm, lie within this range. been included. The results were analyzed qualitatively based But there is a significant deviation of -1.61+/-1.24 mm from on the image quality of the volume reconstructed first (Figure one another. This might be due to applied pressure in 4). combination with unfavorable quick changes in probe Here it can be seen that the freehand volume follows an angulation during the freehand scan that left out the actual uneven reconstruction pattern and in a large way does not centerline of the artery. Further tests are necessary to see if and depict a true representation of the neck and the structures how the measurement differences change across multiple within it. scans. Apart from this the reconstructed volume using the To conclude, experiments from both scanning methods freehand method depicts deformation of structures and larger generate measurable results. The difference lies in the image overlaps. In comparison to this, the assisted method reconstruction and subsequent visualization of the 3D depicts a much more realistic representation of the neck and volumes. Volume reconstruction and visualization from structures within it. freehand scans appear more to have more irregularities and It also significantly reduces image overlaps and deformations. Assisted volumes depict a more uniform deformation of structures. This is attributed to the rigid reconstruction and visualization. This is due to the fact that the structure of the prototype that disallows the application of probe always follows a ‘standard’ guided path. That makes it larger force on the epidermis that causes deformation. Reviews and Computational Applications, Singapore, a more suitable method to compare structural changes in the Springer Science+Business Media, 2015, pp. 57-89. neck over an extended time period. Improving the prototype in [10] R. Slapa, W. Jakubowski, J. Slowinska-Srzednicka und K. terms of user friendliness (e.g. by including a cable guidance) Szopinski, „Advantages and disadvantages of 3D ultrasound and optimizing the use of the gel pad will be the next steps in of thyroid nodules including thin slice volume rendering,“ Thyroid research vol. 4,1 1, Bd. 4(1):1, pp. 1-12, 7 January creating a standardized method for reliably acquisition of 3D US scans. The reproducibility across varied demographics still [11] A. o. G. E. (VDI), VDI 2221 - Systematic approach to the need to be further investigated. The measurements of the development and design of technical systems and products, carotid arteries in this study were done on individual 2D slices Duesseldorf, Germany: VDI-Gesellschaft Produkt- und Prozessgestaltung (VDI Product and Process Development within the reconstructed volumes. This resulted in a small incorporated), 1993. difference between the measurements. Furthers measurements [12] J. Krejza, M. Arkuszewski und S. Kasner, „Carotid Artery and analyses in the 3D volumes itself (not individual 2D slices) Diameter in Men and Women and the Relation to Body and need to be conducted, compared and extended to other Neck Size,“ Stroke, Nr. 37, pp. 1103-1105, 2006. structures within the neck such as thyroid, salivary glands, lymph nodes, etc. If this acquisition method and prototype can be further developed it could be also used for assessing other body parts like internal structures in the abdominal region. References [1] L. W.-B., Z. B., Q.-L. Zhu und e. al., „Comparison between thin-slice 3-D volumetric ultrasound and conventional ultrasound in the differentiation of benign and malignant thyroid lesions,“ Ultrasound in Medicine and Biology, pp. 3096-3101, December 2015. [2] J.-w. Li, C. Chang, M. Chen, W. Zeng, Y. Gao, S.-c. Zhou, F. Wang, N. Hu und Y.-l. Chen, „Is Ultrasonography More Sensitive Than Computed Tomography for Identifying Calcifications in Thyroid Nodules?,“ Journal of Ultrasound in Medicine, p. 2183–2190, 01 October 2016. [3] E. J. G. Ataide, J. Ziegle, M. Kalmar, A. Boese und M. Friebe, „Assistive Scanning Brace for Improved 3D Tomographic Ultrasound Neck Scans,“ in 40th International Engineering in Medicine and Biology Conference, Honolulu, USA, Juli 2018. [4] E. Ataide, J. Ziegle, M. Kalmar, S. Rathi, A. Boese und M. Friebe, „Feasibility and Initial Results of Standardized US Scan Acquisition for Improved Tomographic Visualization,“ in IEEE INDICON, Gujarat, India, 2019. [5] J. E. Langer, S. Mandel und M. Milas, Advanced Thyroid and Parathyroid Ultrasound, Springer International Publishing, [6] D. Barry, C. P. Allott, N. W. John, P. M., Mellor, P. A. Arundel, D. S. Thomson und J. C. Wateron, „Three- Dimensional Freehand Ultrasound: Image Reconstruction and Volume Analysis,“ Ultrasound in Medicine & Biology, Bd. Vol. 28, Nr. 8, pp. 1209-1224, 1997. [7] Z. Z. Q. Huang, „A Review on Real-Time 3D Ultrasound Imaging Technology,“ BioMed Research International, Bd. March 2017, pp. 1-20, 26. March 2017. [8] L. C. R. L. E. Bozzi, „US Image Acquisition,“ in Image Processing in Radiology - Current Applications, Heidelberg, Germany, Springer Science+Business Media, 2007, pp. 3- [9] D. E. O. Dewi, M. M. Fadzil, A. A. M. Faudzi, E. Supriyanto und K. Lai, „Position Tracking Systems for Ultrasound Imaging: A Survey,“ in Medical Imaging Technology -

Journal

Current Directions in Biomedical Engineering – de Gruyter

Published: Sep 1, 2020

Keywords: Tomographic Ultrasound; Assisted Freehand Scanning; Thyroid Assessment

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