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Features to Consider When Selecting New Ultrasound Imaging Systems
MAHADEVAPPA MAHESH, MS, PhD JAMES M. HEVEZI, PhD
TECHNOLOGY TALK
Features to Consider When Selecting New Ultrasound Imaging Systems Nicholas J. Hangiandreou, PhD, Scott F. Stekel, BS, Donald J. Tradup, RDMS INTRODUCTION
The selection of ultrasound imaging equipment is not a straightforward task. Many factors come into play, including image quality, workflow efficiency, ergonomics and system usability, and system serviceability. In this article, we focus on the selection of general imaging ultrasound scanners for use in radiology and describe our process for equipment selection. The involvement of radiologists, sonographers, medical physicists and technical services personnel, the inhouse equipment service group, and administrators in the equipment selection process is critical to achieving the best possible outcome. The first step in the process is assessment of the clinical practice in terms of commonly performed types of examinations, prevalence of portable imaging, mix of diagnostic work and procedures, resident or sonography student teaching, and the IT environment. This will help focus the practice’s needs for specific transducer models, imaging features, connectivity, and other capabilities. In the remainder of this article, we expand on the last two components of the selection process: evaluation of system features and in-house system evaluation. KEY FEATURES TO CONSIDER IN THE SELECTION PROCESS Available Transducers
Vendors of general imaging ultrasound systems are providing similar transducer catalogues, in terms of medium-frequency and high-frequency linear arrays for vascular and small parts imaging, low-fre-
quency curved and sector/vector arrays for abdominal imaging, medium-frequency sector/vector arrays for neonatal brain imaging, and tightly curved arrays for endovaginal or prostate imaging. New technologies are being implemented to improve the sensitivity of imaging arrays, for example, the use of single crystal lead zirconate titanate elements. Multidimensional transducer arrays that allow elevational electronic focusing are also commercially available and should yield significant improvements in image slice profile and elevational resolution. Handheld motor-driven transducers designed for 3-D and 4-D ultrasound image acquisition have been available for some time, while 2-D transducer arrays for electronic acquisition of 3-D data volumes are emerging. Imaging Features
General reviews of the principles of ultrasound scanner operation and common imaging modes are available in the literature [1-3]. Spatial compound imaging, (noncontrast) tissue harmonic imaging, and extended field-of-view imaging have been modes available on ultrasound systems for some time. More recently, advanced image reconstruction and processing techniques are being offered (eg, speckle reduction processing to improve the detectability of small or low-contrast structures; speed-of-sound [or aberration] correction, which can improve overall image quality when tissues with sound speeds significantly different from 1,540 m/s are present). Several vendors offer integrated electromagnetic transducer tracking systems, which have great potential to im-
© 2011 American College of Radiology 0091-2182/11/$36.00 ● DOI 10.1016/j.jacr.2011.03.015
prove diagnostic examinations and ultrasound-guided procedures [4]. Tracking technologies enable a number of capabilities, including geometrically calibrated freehand 3-D, lesion tagging (eg, thyroid nodules), fusion of real-time ultrasound with prior CT or MR examination data, and fusion of new and old ultrasound examinations, which should improve the repeatability of ultrasound measurements. Many vendors offer ultrasound elastography, which distinguishes tissues on the basis of stiffness differences. Several implementations are available, ranging from methods, which create images of tissue strain (relative stiffness) using external tissue compression or physiologic motion to shear wave methods, which create images of shear modulus (absolute stiffness) similar to MR elastography. Elastography introduces a fundamentally new source of image contrast to ultrasound [5]. Workflow Efficiency and Ergonomic Enhancements
A wide variety of features are being offered to improve operator efficiency and scanner ergonomics and lower the risk for repetitive stress injury. The ability to define and implement standard examination protocols on the scanner works toward both of these goals, while also improving examination consistency. Digital Imaging and Communications in Medicine (DICOM) structured reporting promises to improve examination quality and radiologist reporting efficiency by eliminating the need for manual transcription of ultrasound measurements, but a compatible PACS or radiology information system is also needed. Other ergo521
522 Technology Talk
nomic features include adjustable positioning of the console and monitor and innovative probe designs. Technical Features
Grayscale display calibration will greatly facilitate matching of the scanner display with PACS displays, ensuring that the ultrasound images will look the same in the scan room and reading room. Connectivity features include basic DICOM work list query and retrieve and storage to the PACS, options for compressing exported single-frame and multiframe images, and options for live video export of real-time scanning data. Rapid system boot and shutdown, special “sleep” modes, and wireless networking compatibility are all important for portable imaging. It is critical to evaluate service contract options, field service response time, and available capabilities for remote diagnostics and support. For practices with several like scanners, customer-accessible methods for cloning a standard scanner configuration to multiple scanners (eg, via thumb drive or the local area network) can ensure uniformity. In general, even if many features that are offered on a particular system are currently of limited value to your clinical practice, assessment of the availability of cutting-edge features is a useful measure of the creativity and innovation of the equipment vendor and the future potential for the scanner. PREPURCHASE SCANNER EVALUATION
The portability and safety of ultrasound imaging allows each system under consideration to be evaluated in your practice for 1 or 2 days, and the value of hands-on experience using a system before purchase cannot be overemphasized. This evaluation could include phantom testing, volunteer imaging, and patient scanning. Some technical scanner
capabilities may also be demonstrated in the course of these evaluations, (eg, pulling examination orders from the existing work list server and sending image data to the existing PACS, in both wired and wireless modes, as well as evaluating image appearance on the PACS. A nondisclosure agreement should be obtained before the evaluation. The candidate scanner should undergo the same in-house safety testing that any purchased scanner is subjected to before clinical use. In general, planning the evaluation ahead of time will allow the practice to gain the greatest value from the limited on-site evaluation time. Performance Testing
Numerous phantom-based ultrasound performance tests have been reported in the literature. Some rely mainly on manual and subjective methods, and others use computerized image analysis [6-9]. Generally, computerized testing methods are preferable because these are objective and offer greater sensitivity and repeatability, and thus greater potential for revealing meaningful, possibly subtle, performance differences between candidate scanners. Computerized testing tools may be provided by the medical physicist. Care should be taken when testing different candidate scanners to ensure an “apples-to-apples” comparison because scan controls are not necessarily calibrated similarly across scanner models. Volunteer Imaging
Our evaluations involve two volunteers, one “thinner” and easier to scan and one “thicker” and more difficult to scan. Ideally, the same volunteers participate in evaluations of all candidate scanners. Each volunteer is scanned at the same time using the current scanner in the practice (the “gold standard”) and the candidate scanner. We have documented a list of 20 to
25 clinical image views spanning the range of examinations done in our practice, including B-mode, spectral Doppler, and color Doppler images. Each view is obtained with the current and candidate scanners. A staff sonographer manipulates the transducer for both scanners and optimizes the scan parameters for the current scanner. The applications specialist optimizes scan parameters for the candidate scanner under the direction of the staff sonographer. The sonographer attempts to match the imaging plane with both scanners. Images are moved to the PACS, and corresponding images are compared side by side by ultrasound staff members. It is rarely possible to effectively anonymize the images, so each reviewer rates candidate image quality compared with the gold standard according to the following scale: 1 ⫽ better image quality than the gold standard; 2 ⫽ equivalent image quality to the gold standard; 3 ⫽ poorer image quality, but clinically acceptable; and 4 ⫽ not clinically acceptable. The numeric grading approach allows impressions to be summarized and compared in various ways (eg, for radiologists and sonographers, or for B-mode and Doppler). Patient Imaging
Obtaining images from actual patients is extremely useful in evaluating FDA-approved candidate systems. This scanning is done with the patient’s approval in parallel with the standard clinical examination, so standard patient care is not compromised. Selected image views are obtained with the candidate system with the sonographer positioning the transducer and directing the applications specialist to adjust scan parameters. These matched pairs of images may be evaluated as described above for volunteer imaging. Sites intending to purchase multiple systems may sometimes negotiate a more extensive evaluation agreement, allowing
Technology Talk 523
a longer evaluation time and greater opportunity for patient scanning. When evaluating new technology, it is important to actively keep an open mind and maintain a level of tolerance for alternative implementations of familiar features and also to be aware of the possible tendency to harshly judge any system that is different from the current one that staff members are most comfortable with and, in some cases, may have trained on. Modern scanners can provide almost any aesthetic image “look,” but requesting that candidate scanner images be configured to very closely resemble images on the gold-standard scanner may preclude the use of innovative new features (eg, speckle reduction). AFTER A SCANNER IS PURCHASED AND DELIVERED
Acceptance testing of scanner performance by the medical physicist and technical services staff may be recommended for accreditation. Acceptance testing should include the general areas of connectivity, display performance, mechanical integrity, and image quality. All necessary testing to ensure correct operation of all purchased items should be performed. Acceptance testing performance levels should be compared for consistency with vendor specifications (if available), with the prepurchase test results, or between multiple “copies” of the
same equipment items being purchased (eg, transducers). Acceptance testing results also provide an initial baseline for later quality control tests. Effective user training for the staff sonographers and radiologists is essential for rapidly achieving a high level of efficiency and examination quality. As more experience is gained with the new system, initially configured scan parameter presets and examination protocols will evolve, possibly quickly at first. It may be helpful to arrange comprehensive initial training when the scanner is first delivered and then request a return visit by the applications specialist after several weeks of clinical use, to answer questions and assist with preset and protocol changes. CONCLUSIONS
The best scanner selection process will involve all members of the clinical ultrasound team. Assessing the needs of the clinical practice is a critical first step in the process, followed by a review of imaging, ergonomic, efficiency and technical features, and an in-house evaluation of all candidate systems. The in-house evaluation should include phantom testing, volunteer scanning, and patient scanning. The final purchase decision should also consider options and costs for service support and user training. The effort involved in a comprehensive selection process will not be insignificant,
however, it will return great dividends for improving clinical practice quality by identifying the best new US system for your practise. REFERENCES 1. Hangiandreou NJ. AAPM/RSNA physics tutorial for residents. Topics in US: B-mode US: basic concepts and new technology. Radiographics 2003;23:1019-33. 2. Boote EJ. AAPM/RSNA physics tutorial for residents: topics in US: Doppler US techniques: concepts of blood flow detection and flow dynamics. Radiographics 2003;23: 1315-27. 3. Hangiandreou NJ. State-of-the-art ultrasound imaging technology. J Am Coll Radiol 2004;1:691-3. 4. Krücker J, Xu S, Venkatesan A, et al. Clinical utility of real-time fusion guidance for biopsy and ablation. J Vasc Interv Radiol 2011;22:515-24. 5. Garra BS. Imaging and estimation of tissue elasticity by ultrasound. Ultrasound Q 2007;23:255-68. 6. Goodsitt MM, Carson PL, Witt S, Hykes DL, Kofler JM Jr. Real-time B-mode ultrasound quality control test procedures. Report of AAPM Ultrasound Task Group No. 1. Med Phys 1998;25:1385-406. 7. Gibson NM, Dudley NJ, Griffith K. A computerised quality control testing system for B-mode ultrasound. Ultrasound Med Biol 2001;27:1697-711. 8. Thijssen JM, Weijers G, de Korte CL. Objective performance testing and quality assurance of medical ultrasound equipment. Ultrasound Med Biol 2007;33:460-71. 9. American College of Radiology. ACR technical standard for diagnostic medical physics performance monitoring of real time ultrasound equipment. Available at: http:// www.acr.org/SecondaryMainMenuCategories/ quality_safety/guidelines/med_phys/us_ equipment.aspx.
Scott F. Stekel, BS and Donald J. Tradup, RDMS are from Mayo Clinic Rochester, Minnesota. Nicholas J. Hangiandreou, PhD, Mayo Clinic, Department of Radiology, East-2, 200 First Street SW, Rochester, MN 55905; e-mail: [email protected].
TECHNOLOGY TALK
Features to Consider When Selecting New Ultrasound Imaging Systems Nicholas J. Hangiandreou, PhD, Scott F. Stekel, BS, Donald J. Tradup, RDMS INTRODUCTION
The selection of ultrasound imaging equipment is not a straightforward task. Many factors come into play, including image quality, workflow efficiency, ergonomics and system usability, and system serviceability. In this article, we focus on the selection of general imaging ultrasound scanners for use in radiology and describe our process for equipment selection. The involvement of radiologists, sonographers, medical physicists and technical services personnel, the inhouse equipment service group, and administrators in the equipment selection process is critical to achieving the best possible outcome. The first step in the process is assessment of the clinical practice in terms of commonly performed types of examinations, prevalence of portable imaging, mix of diagnostic work and procedures, resident or sonography student teaching, and the IT environment. This will help focus the practice’s needs for specific transducer models, imaging features, connectivity, and other capabilities. In the remainder of this article, we expand on the last two components of the selection process: evaluation of system features and in-house system evaluation. KEY FEATURES TO CONSIDER IN THE SELECTION PROCESS Available Transducers
Vendors of general imaging ultrasound systems are providing similar transducer catalogues, in terms of medium-frequency and high-frequency linear arrays for vascular and small parts imaging, low-fre-
quency curved and sector/vector arrays for abdominal imaging, medium-frequency sector/vector arrays for neonatal brain imaging, and tightly curved arrays for endovaginal or prostate imaging. New technologies are being implemented to improve the sensitivity of imaging arrays, for example, the use of single crystal lead zirconate titanate elements. Multidimensional transducer arrays that allow elevational electronic focusing are also commercially available and should yield significant improvements in image slice profile and elevational resolution. Handheld motor-driven transducers designed for 3-D and 4-D ultrasound image acquisition have been available for some time, while 2-D transducer arrays for electronic acquisition of 3-D data volumes are emerging. Imaging Features
General reviews of the principles of ultrasound scanner operation and common imaging modes are available in the literature [1-3]. Spatial compound imaging, (noncontrast) tissue harmonic imaging, and extended field-of-view imaging have been modes available on ultrasound systems for some time. More recently, advanced image reconstruction and processing techniques are being offered (eg, speckle reduction processing to improve the detectability of small or low-contrast structures; speed-of-sound [or aberration] correction, which can improve overall image quality when tissues with sound speeds significantly different from 1,540 m/s are present). Several vendors offer integrated electromagnetic transducer tracking systems, which have great potential to im-
© 2011 American College of Radiology 0091-2182/11/$36.00 ● DOI 10.1016/j.jacr.2011.03.015
prove diagnostic examinations and ultrasound-guided procedures [4]. Tracking technologies enable a number of capabilities, including geometrically calibrated freehand 3-D, lesion tagging (eg, thyroid nodules), fusion of real-time ultrasound with prior CT or MR examination data, and fusion of new and old ultrasound examinations, which should improve the repeatability of ultrasound measurements. Many vendors offer ultrasound elastography, which distinguishes tissues on the basis of stiffness differences. Several implementations are available, ranging from methods, which create images of tissue strain (relative stiffness) using external tissue compression or physiologic motion to shear wave methods, which create images of shear modulus (absolute stiffness) similar to MR elastography. Elastography introduces a fundamentally new source of image contrast to ultrasound [5]. Workflow Efficiency and Ergonomic Enhancements
A wide variety of features are being offered to improve operator efficiency and scanner ergonomics and lower the risk for repetitive stress injury. The ability to define and implement standard examination protocols on the scanner works toward both of these goals, while also improving examination consistency. Digital Imaging and Communications in Medicine (DICOM) structured reporting promises to improve examination quality and radiologist reporting efficiency by eliminating the need for manual transcription of ultrasound measurements, but a compatible PACS or radiology information system is also needed. Other ergo521
522 Technology Talk
nomic features include adjustable positioning of the console and monitor and innovative probe designs. Technical Features
Grayscale display calibration will greatly facilitate matching of the scanner display with PACS displays, ensuring that the ultrasound images will look the same in the scan room and reading room. Connectivity features include basic DICOM work list query and retrieve and storage to the PACS, options for compressing exported single-frame and multiframe images, and options for live video export of real-time scanning data. Rapid system boot and shutdown, special “sleep” modes, and wireless networking compatibility are all important for portable imaging. It is critical to evaluate service contract options, field service response time, and available capabilities for remote diagnostics and support. For practices with several like scanners, customer-accessible methods for cloning a standard scanner configuration to multiple scanners (eg, via thumb drive or the local area network) can ensure uniformity. In general, even if many features that are offered on a particular system are currently of limited value to your clinical practice, assessment of the availability of cutting-edge features is a useful measure of the creativity and innovation of the equipment vendor and the future potential for the scanner. PREPURCHASE SCANNER EVALUATION
The portability and safety of ultrasound imaging allows each system under consideration to be evaluated in your practice for 1 or 2 days, and the value of hands-on experience using a system before purchase cannot be overemphasized. This evaluation could include phantom testing, volunteer imaging, and patient scanning. Some technical scanner
capabilities may also be demonstrated in the course of these evaluations, (eg, pulling examination orders from the existing work list server and sending image data to the existing PACS, in both wired and wireless modes, as well as evaluating image appearance on the PACS. A nondisclosure agreement should be obtained before the evaluation. The candidate scanner should undergo the same in-house safety testing that any purchased scanner is subjected to before clinical use. In general, planning the evaluation ahead of time will allow the practice to gain the greatest value from the limited on-site evaluation time. Performance Testing
Numerous phantom-based ultrasound performance tests have been reported in the literature. Some rely mainly on manual and subjective methods, and others use computerized image analysis [6-9]. Generally, computerized testing methods are preferable because these are objective and offer greater sensitivity and repeatability, and thus greater potential for revealing meaningful, possibly subtle, performance differences between candidate scanners. Computerized testing tools may be provided by the medical physicist. Care should be taken when testing different candidate scanners to ensure an “apples-to-apples” comparison because scan controls are not necessarily calibrated similarly across scanner models. Volunteer Imaging
Our evaluations involve two volunteers, one “thinner” and easier to scan and one “thicker” and more difficult to scan. Ideally, the same volunteers participate in evaluations of all candidate scanners. Each volunteer is scanned at the same time using the current scanner in the practice (the “gold standard”) and the candidate scanner. We have documented a list of 20 to
25 clinical image views spanning the range of examinations done in our practice, including B-mode, spectral Doppler, and color Doppler images. Each view is obtained with the current and candidate scanners. A staff sonographer manipulates the transducer for both scanners and optimizes the scan parameters for the current scanner. The applications specialist optimizes scan parameters for the candidate scanner under the direction of the staff sonographer. The sonographer attempts to match the imaging plane with both scanners. Images are moved to the PACS, and corresponding images are compared side by side by ultrasound staff members. It is rarely possible to effectively anonymize the images, so each reviewer rates candidate image quality compared with the gold standard according to the following scale: 1 ⫽ better image quality than the gold standard; 2 ⫽ equivalent image quality to the gold standard; 3 ⫽ poorer image quality, but clinically acceptable; and 4 ⫽ not clinically acceptable. The numeric grading approach allows impressions to be summarized and compared in various ways (eg, for radiologists and sonographers, or for B-mode and Doppler). Patient Imaging
Obtaining images from actual patients is extremely useful in evaluating FDA-approved candidate systems. This scanning is done with the patient’s approval in parallel with the standard clinical examination, so standard patient care is not compromised. Selected image views are obtained with the candidate system with the sonographer positioning the transducer and directing the applications specialist to adjust scan parameters. These matched pairs of images may be evaluated as described above for volunteer imaging. Sites intending to purchase multiple systems may sometimes negotiate a more extensive evaluation agreement, allowing
Technology Talk 523
a longer evaluation time and greater opportunity for patient scanning. When evaluating new technology, it is important to actively keep an open mind and maintain a level of tolerance for alternative implementations of familiar features and also to be aware of the possible tendency to harshly judge any system that is different from the current one that staff members are most comfortable with and, in some cases, may have trained on. Modern scanners can provide almost any aesthetic image “look,” but requesting that candidate scanner images be configured to very closely resemble images on the gold-standard scanner may preclude the use of innovative new features (eg, speckle reduction). AFTER A SCANNER IS PURCHASED AND DELIVERED
Acceptance testing of scanner performance by the medical physicist and technical services staff may be recommended for accreditation. Acceptance testing should include the general areas of connectivity, display performance, mechanical integrity, and image quality. All necessary testing to ensure correct operation of all purchased items should be performed. Acceptance testing performance levels should be compared for consistency with vendor specifications (if available), with the prepurchase test results, or between multiple “copies” of the
same equipment items being purchased (eg, transducers). Acceptance testing results also provide an initial baseline for later quality control tests. Effective user training for the staff sonographers and radiologists is essential for rapidly achieving a high level of efficiency and examination quality. As more experience is gained with the new system, initially configured scan parameter presets and examination protocols will evolve, possibly quickly at first. It may be helpful to arrange comprehensive initial training when the scanner is first delivered and then request a return visit by the applications specialist after several weeks of clinical use, to answer questions and assist with preset and protocol changes. CONCLUSIONS
The best scanner selection process will involve all members of the clinical ultrasound team. Assessing the needs of the clinical practice is a critical first step in the process, followed by a review of imaging, ergonomic, efficiency and technical features, and an in-house evaluation of all candidate systems. The in-house evaluation should include phantom testing, volunteer scanning, and patient scanning. The final purchase decision should also consider options and costs for service support and user training. The effort involved in a comprehensive selection process will not be insignificant,
however, it will return great dividends for improving clinical practice quality by identifying the best new US system for your practise. REFERENCES 1. Hangiandreou NJ. AAPM/RSNA physics tutorial for residents. Topics in US: B-mode US: basic concepts and new technology. Radiographics 2003;23:1019-33. 2. Boote EJ. AAPM/RSNA physics tutorial for residents: topics in US: Doppler US techniques: concepts of blood flow detection and flow dynamics. Radiographics 2003;23: 1315-27. 3. Hangiandreou NJ. State-of-the-art ultrasound imaging technology. J Am Coll Radiol 2004;1:691-3. 4. Krücker J, Xu S, Venkatesan A, et al. Clinical utility of real-time fusion guidance for biopsy and ablation. J Vasc Interv Radiol 2011;22:515-24. 5. Garra BS. Imaging and estimation of tissue elasticity by ultrasound. Ultrasound Q 2007;23:255-68. 6. Goodsitt MM, Carson PL, Witt S, Hykes DL, Kofler JM Jr. Real-time B-mode ultrasound quality control test procedures. Report of AAPM Ultrasound Task Group No. 1. Med Phys 1998;25:1385-406. 7. Gibson NM, Dudley NJ, Griffith K. A computerised quality control testing system for B-mode ultrasound. Ultrasound Med Biol 2001;27:1697-711. 8. Thijssen JM, Weijers G, de Korte CL. Objective performance testing and quality assurance of medical ultrasound equipment. Ultrasound Med Biol 2007;33:460-71. 9. American College of Radiology. ACR technical standard for diagnostic medical physics performance monitoring of real time ultrasound equipment. Available at: http:// www.acr.org/SecondaryMainMenuCategories/ quality_safety/guidelines/med_phys/us_ equipment.aspx.
Scott F. Stekel, BS and Donald J. Tradup, RDMS are from Mayo Clinic Rochester, Minnesota. Nicholas J. Hangiandreou, PhD, Mayo Clinic, Department of Radiology, East-2, 200 First Street SW, Rochester, MN 55905; e-mail: [email protected].