Intern Emerg Med DOI 10.1007/s11739-013-1014-y
EM - ORIGINAL
High-frequency transducers for point-of-care ultrasound applications: what is the optimal frequency range? Srikar Adhikari
Received: 6 October 2013 / Accepted: 21 October 2013 Ó SIMI 2013
Abstract To compare images obtained using two linear transducers with a different range of frequencies, and to determine if there is a significant difference in the quality of images between the two transducers for medical decision-making. This was a single-blinded, cross-sectional study at an academic medical center. Twenty-five emergency medicine clinical scenarios with ultrasound images (using both 10–5 and 14–5 MHz transducers) covering a variety of point-of-care ultrasound applications were presented to four emergency physician sonographers. They were blinded to the study hypothesis and type of the transducer used to obtain the images. On a scale of 1–10, the mean image quality rating for 10–5 MHz transducer was 7.09 (95 % CI 6.73–7.45) and 6.49 (95 % CI 5.99–6.99) for 14–5 MHz transducer. In the majority of cases (84 %, 95 % CI 75.7–92.3 %), sonographers indicated that images obtained with a 10–5 MHz transducer were satisfactory for medical decision-making. They preferred images obtained with a 10–5 MHz transducer over 14–5 MHz transducer in 39 % (95 % CI 30–50 %) of cases. The images obtained with a 14–5 MHz transducer were preferred over 10–5 MHz transducer in only 16 % (95 % CI 7.7–24.3 %) of the cases. The 14–5 MHz transducer has a slight advantage over 10–5 MHz transducer for ocular, upper airway, and musculoskeletal (tendon) ultrasound applications. A 10–5 MHz linear transducer is adequate to obtain images that can be used for medical
Prior Presentations: Abstract presented at American College of Emergency physicians research forum, Denver, Colorado, 10/2012. S. Adhikari (&) Department of Emergency Medicine, University of Arizona Medical Center, PO Box 245057, Tucson, AZ 85724, USA e-mail: [email protected]
decision-making for a variety of point-of-care ultrasound applications. Keywords Portable ultrasound Emergency physician Point-of-care ultrasound Linear transducer
Introduction In the last two decades, ultrasound systems have become more compact and portable [1]. The evolution of portable ultrasound has greatly expanded the use of point-of-care ultrasound by emergency physicians for various applications [2]. The accuracy and noninvasive characteristics of portable ultrasound make it an excellent tool for bedside use in the emergency department (ED). High-frequency linear transducers are commonly used in the ED setting for a variety of point-of-care ultrasound applications [3]. Multiple linear transducers are currently available in a wide range of frequencies for different ultrasound systems [4–6]. The resolution of images may vary with the frequency of the transducer chosen, which can potentially affect medical decision-making. The range of clinical applications that point-of-care ultrasound is being used for is rapidly expanding in the recent years [2]. However, resources are not available for most of the EDs to purchase a variety of high-frequency linear transducers. Additionally, the optimal frequency range of linear transducers for point-of-care ultrasound applications is uncertain. The objective of this study was to compare images obtained using two linear transducers with different range of frequencies and determine if there was a significant difference in the quality of images between the two transducers for medical decisionmaking.
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Methods Study design and setting This was a single-blinded, cross-sectional study at an academic medical center with an active emergency ultrasound program. Hospital credentialing in point-of-care ultrasound was available for emergency physicians and credentialing pathways were based on most recent American College of Emergency Physicians ultrasound guidelines [2]. The study was approved by the Institutional Review Board. Selection of participants Emergency medicine faculties who have expertise in pointof-care ultrasound were invited to participate in this study. Participation was voluntary. The emergency physicians who contributed to this study had hospital privileges to use point-of-care ultrasound in ED. They were either fellowship trained in emergency ultrasound or had significant experience in performing and teaching a wide variety of ED point-of-care ultrasound applications. Specific information regarding prior scanning experience with superficial ultrasound applications was collected. Study protocol Ultrasound images obtained with 10–5 and 14–5 MHz linear transducers were used in this study (Figs. 1, 2, 3). The images were obtained using both transducers in each patient. Appropriate adjustments (gain, depth, etc.) were made to optimize the image quality while scanning with both transducers. The ultrasound images were cropped to remove the scanning parameters. Twenty-five different emergency medicine clinical scenarios covering a variety of point-of-care ultrasound applications were presented to a group of emergency physician sonographers. The images obtained with both transducers were included in each case. All images were numbered to keep track of the transducer used to obtain the images. The images included in this study covered a wide variety of point-of-care ultrasound applications such as ocular, head and neck, upper airway, musculoskeletal, nerve, vascular, and thoracic. The sonographers were blinded to the study hypothesis and the type of the transducer used to obtain the images. They reviewed images obtained with both transducers individually. The sonographers were asked to rate the image quality, compare images obtained with two different transducers and indicate their preference to use the images for medical decision-making.
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Fig. 1 a B-mode image of epiglottis obtained with a 10–5 MHz transducer. b Same image obtained using a 14–5 MHz transducer (e epiglottis, sm strap muscle, pes preepiglottic space, a-m interfaceair mucosal interface)
Statistical analysis All data analyses were performed in SAS version 9.3. (Copyright, SAS Institute Inc., Cary, NC, USA). Data were analyzed using descriptive statistics. Continuous data are presented as means and dichotomous data are presented as percent frequency with 95 % confidence intervals.
Results A total of 50 images were independently reviewed by four emergency physician sonographers. All the participants had performed [250 superficial point-of-care ultrasound examinations. All had used different ultrasound imaging modes (B-mode, M-mode and Doppler) in the past while performing point-of-care ultrasound. No difficulty in interpreting ultrasound images was reported.
Intern Emerg Med Fig. 2 a B-mode image of lower extremity vessels obtained with a 10–5 MHz transducer. b Same image obtained using a 14–5 MHz transducer (fa femoral artery, fv femoral vein)
On a scale of 1–10, the mean image quality rating for 10–5 MHz transducer was 7.09 (95 % CI 6.73–7.45). The mean image quality rating for 14–5 MHz transducer was 6.49 (95 % CI 5.99–6.99). In the majority of cases (84 %, 95 % CI 75.7–92.3 %), the sonographers indicated that images obtained with a 10–5 MHz transducer were satisfactory for medical decision-making. They preferred images obtained with a 10–5 MHz transducer over 14–5 MHz transducer in 39 % (95 % CI 30–50 %) of cases for medical decision-making. The images obtained with a 14–5 MHz transducer were preferred over 10–5 MHz transducer in only 16 % (95 % CI 7.7–24.3 %) of the cases for medical decision-making. The 14–5 MHz transducer has a slight advantage over 10–5 MHz transducer for ocular, upper airway, and musculoskeletal (tendon) ultrasound applications.
Discussion Point-of-care ultrasound is being increasingly used in the ED, intensive care unit, and other clinical settings [7, 8]. The scope of point-of-care ultrasound in the ED is rapidly expanding [2]. Emergency physicians utilize high-frequency transducers for more diverse point-of-care ultrasound applications compared to other specialties. Most recent studies suggest that there is growing interest among emergency physicians in advanced point-of-care ultrasound applications [9–11]. The ability of transducers to generate high-quality images can potentially affect the accuracy with which the abnormalities can be interpreted. This can in turn have a significant impact on medical decisionmaking and patient care in the ED. Currently portable ultrasound systems offer a variety of broadband linear
transducers in a wide range of frequencies (15–6, 14–5, 14–6, 13–6, 10–5 MHz) for bedside use [4–6]. Ultrasound images obtained using linear transducers in the higher frequency range (15–6, 14–5, 14–6 MHz) compared to 10–5 MHz linear transducer may be slightly better in quality while imaging very superficial structures such as tendons and ocular structures. However, the image quality may be suboptimal if the same transducers are used for other applications such as vascular (DVT) and thoracic since the high-frequency beams attenuate as they penetrate deeper into tissues. Having more than one broadband linear array transducer with different range of frequencies might be ideal for different superficial point-of-care ultrasound applications in ED. However, budget constraints often do not allow the purchase of more than one high-frequency linear transducer. In our study, experienced physician sonographers concluded that ultrasound images obtained with a 10–5 MHz linear transducer are satisfactory for medical decision-making. Our participants preferred 10–5 MHz linear transducer over 14–5 MHz for applications such as head and neck, nerve, vascular, and thoracic. They felt images obtained with 10–5 MHz linear transducer were satisfactory for medical decision-making for other applications including ocular, upper airway, and musculoskeletal (tendon). Our study results suggest emergency physicians can obtain optimal images required for medical decision-making with a 10–5 MHz linear transducer for all superficial point-of-care ultrasound applications. This study has a number of limitations, including a small sample size. A convenience sample of emergency physician sonographers participated in this study, which might have introduced a selection bias. The participants in this study may have had more superficial ultrasound experience
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Conclusions A 10–5 MHz linear transducer is adequate to obtain images that can be used for medical decision-making for a variety of point-of-care ultrasound applications. A transducer with a frequency higher than 10 MHz offers marginal benefit in the ED setting for superficial point-of-care ultrasound applications. Acknowledgments
None.
Conflict of interest
None.
References
Fig. 3 a Thoracic ultrasound image obtained with a 10–5 MHz transducer. b Same image obtained using a 14–5 MHz transducer
compared to the average emergency physician. This may limit generalizability to other clinical settings. We used images obtained with the linear transducers as opposed to real-time scanning with these transducers.
123
1. Ault MJ, Rosen BT (2010) Portable ultrasound: the next generation arrives. Crit Ultrasound J 2(1):39–42 2. American College of Emergency Physicians (2009) Emergency ultrasound guidelines. Ann Emerg Med 53(4):550–570 3. Scruggs W, Fox JC (2014) Equipment. In: Ma OJ, Mateer J, Reardon R, Joing S (eds) Emergency ultrasound, 3rd edn. McGraw-Hill, New York, pp 15–32 4. Ultrasound transducers (2013). http://www.sonosite.com/ transducers. Accessed 6 Oct 2013 5. Transducers (2013). http://www.zonare.com/solutions/ transducers. Accessed 6 Oct 2013 6. Our universal transducers work with all Ultrasonix systems (2013). http://www.ultrasonix.com/products/transducers. Accessed 6 Oct 2013 7. Frederiksen CA, Juhl-Olsen P, Sloth E (2012) Advances in imaging: ultrasound in every physician’s pocket. Expert Opin Med Diagn 6(3):167–170 8. Griffin J, Nicholls B (2010) Ultrasound in regional anaesthesia. Anaesthesia 65(Suppl 1):1–12 9. Adhikari S, Zeger W, Schmier C, Crum T, Craven A, Frrokaj I, Pang H, Shostrom V (2011) Pilot study to determine the utility of point-of-care ultrasound in the assessment of difficult laryngoscopy. Acad Emerg Med 18(7):754–758 10. Gaspari R, Blehar D, Mendoza M, Montoya A, Moon C, Polan D (2009) Use of ultrasound elastography for skin and subcutaneous abscesses. J Ultrasound Med 28(7):855–860 11. Teismann N, Lenaghan P, Nolan R, Stein J, Green A (2013) Point-of-care ocular ultrasound to detect optic disc swelling. Acad Emerg Med 20(9):920–925
EM - ORIGINAL
High-frequency transducers for point-of-care ultrasound applications: what is the optimal frequency range? Srikar Adhikari
Received: 6 October 2013 / Accepted: 21 October 2013 Ó SIMI 2013
Abstract To compare images obtained using two linear transducers with a different range of frequencies, and to determine if there is a significant difference in the quality of images between the two transducers for medical decision-making. This was a single-blinded, cross-sectional study at an academic medical center. Twenty-five emergency medicine clinical scenarios with ultrasound images (using both 10–5 and 14–5 MHz transducers) covering a variety of point-of-care ultrasound applications were presented to four emergency physician sonographers. They were blinded to the study hypothesis and type of the transducer used to obtain the images. On a scale of 1–10, the mean image quality rating for 10–5 MHz transducer was 7.09 (95 % CI 6.73–7.45) and 6.49 (95 % CI 5.99–6.99) for 14–5 MHz transducer. In the majority of cases (84 %, 95 % CI 75.7–92.3 %), sonographers indicated that images obtained with a 10–5 MHz transducer were satisfactory for medical decision-making. They preferred images obtained with a 10–5 MHz transducer over 14–5 MHz transducer in 39 % (95 % CI 30–50 %) of cases. The images obtained with a 14–5 MHz transducer were preferred over 10–5 MHz transducer in only 16 % (95 % CI 7.7–24.3 %) of the cases. The 14–5 MHz transducer has a slight advantage over 10–5 MHz transducer for ocular, upper airway, and musculoskeletal (tendon) ultrasound applications. A 10–5 MHz linear transducer is adequate to obtain images that can be used for medical
Prior Presentations: Abstract presented at American College of Emergency physicians research forum, Denver, Colorado, 10/2012. S. Adhikari (&) Department of Emergency Medicine, University of Arizona Medical Center, PO Box 245057, Tucson, AZ 85724, USA e-mail: [email protected]
decision-making for a variety of point-of-care ultrasound applications. Keywords Portable ultrasound Emergency physician Point-of-care ultrasound Linear transducer
Introduction In the last two decades, ultrasound systems have become more compact and portable [1]. The evolution of portable ultrasound has greatly expanded the use of point-of-care ultrasound by emergency physicians for various applications [2]. The accuracy and noninvasive characteristics of portable ultrasound make it an excellent tool for bedside use in the emergency department (ED). High-frequency linear transducers are commonly used in the ED setting for a variety of point-of-care ultrasound applications [3]. Multiple linear transducers are currently available in a wide range of frequencies for different ultrasound systems [4–6]. The resolution of images may vary with the frequency of the transducer chosen, which can potentially affect medical decision-making. The range of clinical applications that point-of-care ultrasound is being used for is rapidly expanding in the recent years [2]. However, resources are not available for most of the EDs to purchase a variety of high-frequency linear transducers. Additionally, the optimal frequency range of linear transducers for point-of-care ultrasound applications is uncertain. The objective of this study was to compare images obtained using two linear transducers with different range of frequencies and determine if there was a significant difference in the quality of images between the two transducers for medical decisionmaking.
123
Intern Emerg Med
Methods Study design and setting This was a single-blinded, cross-sectional study at an academic medical center with an active emergency ultrasound program. Hospital credentialing in point-of-care ultrasound was available for emergency physicians and credentialing pathways were based on most recent American College of Emergency Physicians ultrasound guidelines [2]. The study was approved by the Institutional Review Board. Selection of participants Emergency medicine faculties who have expertise in pointof-care ultrasound were invited to participate in this study. Participation was voluntary. The emergency physicians who contributed to this study had hospital privileges to use point-of-care ultrasound in ED. They were either fellowship trained in emergency ultrasound or had significant experience in performing and teaching a wide variety of ED point-of-care ultrasound applications. Specific information regarding prior scanning experience with superficial ultrasound applications was collected. Study protocol Ultrasound images obtained with 10–5 and 14–5 MHz linear transducers were used in this study (Figs. 1, 2, 3). The images were obtained using both transducers in each patient. Appropriate adjustments (gain, depth, etc.) were made to optimize the image quality while scanning with both transducers. The ultrasound images were cropped to remove the scanning parameters. Twenty-five different emergency medicine clinical scenarios covering a variety of point-of-care ultrasound applications were presented to a group of emergency physician sonographers. The images obtained with both transducers were included in each case. All images were numbered to keep track of the transducer used to obtain the images. The images included in this study covered a wide variety of point-of-care ultrasound applications such as ocular, head and neck, upper airway, musculoskeletal, nerve, vascular, and thoracic. The sonographers were blinded to the study hypothesis and the type of the transducer used to obtain the images. They reviewed images obtained with both transducers individually. The sonographers were asked to rate the image quality, compare images obtained with two different transducers and indicate their preference to use the images for medical decision-making.
123
Fig. 1 a B-mode image of epiglottis obtained with a 10–5 MHz transducer. b Same image obtained using a 14–5 MHz transducer (e epiglottis, sm strap muscle, pes preepiglottic space, a-m interfaceair mucosal interface)
Statistical analysis All data analyses were performed in SAS version 9.3. (Copyright, SAS Institute Inc., Cary, NC, USA). Data were analyzed using descriptive statistics. Continuous data are presented as means and dichotomous data are presented as percent frequency with 95 % confidence intervals.
Results A total of 50 images were independently reviewed by four emergency physician sonographers. All the participants had performed [250 superficial point-of-care ultrasound examinations. All had used different ultrasound imaging modes (B-mode, M-mode and Doppler) in the past while performing point-of-care ultrasound. No difficulty in interpreting ultrasound images was reported.
Intern Emerg Med Fig. 2 a B-mode image of lower extremity vessels obtained with a 10–5 MHz transducer. b Same image obtained using a 14–5 MHz transducer (fa femoral artery, fv femoral vein)
On a scale of 1–10, the mean image quality rating for 10–5 MHz transducer was 7.09 (95 % CI 6.73–7.45). The mean image quality rating for 14–5 MHz transducer was 6.49 (95 % CI 5.99–6.99). In the majority of cases (84 %, 95 % CI 75.7–92.3 %), the sonographers indicated that images obtained with a 10–5 MHz transducer were satisfactory for medical decision-making. They preferred images obtained with a 10–5 MHz transducer over 14–5 MHz transducer in 39 % (95 % CI 30–50 %) of cases for medical decision-making. The images obtained with a 14–5 MHz transducer were preferred over 10–5 MHz transducer in only 16 % (95 % CI 7.7–24.3 %) of the cases for medical decision-making. The 14–5 MHz transducer has a slight advantage over 10–5 MHz transducer for ocular, upper airway, and musculoskeletal (tendon) ultrasound applications.
Discussion Point-of-care ultrasound is being increasingly used in the ED, intensive care unit, and other clinical settings [7, 8]. The scope of point-of-care ultrasound in the ED is rapidly expanding [2]. Emergency physicians utilize high-frequency transducers for more diverse point-of-care ultrasound applications compared to other specialties. Most recent studies suggest that there is growing interest among emergency physicians in advanced point-of-care ultrasound applications [9–11]. The ability of transducers to generate high-quality images can potentially affect the accuracy with which the abnormalities can be interpreted. This can in turn have a significant impact on medical decisionmaking and patient care in the ED. Currently portable ultrasound systems offer a variety of broadband linear
transducers in a wide range of frequencies (15–6, 14–5, 14–6, 13–6, 10–5 MHz) for bedside use [4–6]. Ultrasound images obtained using linear transducers in the higher frequency range (15–6, 14–5, 14–6 MHz) compared to 10–5 MHz linear transducer may be slightly better in quality while imaging very superficial structures such as tendons and ocular structures. However, the image quality may be suboptimal if the same transducers are used for other applications such as vascular (DVT) and thoracic since the high-frequency beams attenuate as they penetrate deeper into tissues. Having more than one broadband linear array transducer with different range of frequencies might be ideal for different superficial point-of-care ultrasound applications in ED. However, budget constraints often do not allow the purchase of more than one high-frequency linear transducer. In our study, experienced physician sonographers concluded that ultrasound images obtained with a 10–5 MHz linear transducer are satisfactory for medical decision-making. Our participants preferred 10–5 MHz linear transducer over 14–5 MHz for applications such as head and neck, nerve, vascular, and thoracic. They felt images obtained with 10–5 MHz linear transducer were satisfactory for medical decision-making for other applications including ocular, upper airway, and musculoskeletal (tendon). Our study results suggest emergency physicians can obtain optimal images required for medical decision-making with a 10–5 MHz linear transducer for all superficial point-of-care ultrasound applications. This study has a number of limitations, including a small sample size. A convenience sample of emergency physician sonographers participated in this study, which might have introduced a selection bias. The participants in this study may have had more superficial ultrasound experience
123
Intern Emerg Med
Conclusions A 10–5 MHz linear transducer is adequate to obtain images that can be used for medical decision-making for a variety of point-of-care ultrasound applications. A transducer with a frequency higher than 10 MHz offers marginal benefit in the ED setting for superficial point-of-care ultrasound applications. Acknowledgments
None.
Conflict of interest
None.
References
Fig. 3 a Thoracic ultrasound image obtained with a 10–5 MHz transducer. b Same image obtained using a 14–5 MHz transducer
compared to the average emergency physician. This may limit generalizability to other clinical settings. We used images obtained with the linear transducers as opposed to real-time scanning with these transducers.
123
1. Ault MJ, Rosen BT (2010) Portable ultrasound: the next generation arrives. Crit Ultrasound J 2(1):39–42 2. American College of Emergency Physicians (2009) Emergency ultrasound guidelines. Ann Emerg Med 53(4):550–570 3. Scruggs W, Fox JC (2014) Equipment. In: Ma OJ, Mateer J, Reardon R, Joing S (eds) Emergency ultrasound, 3rd edn. McGraw-Hill, New York, pp 15–32 4. Ultrasound transducers (2013). http://www.sonosite.com/ transducers. Accessed 6 Oct 2013 5. Transducers (2013). http://www.zonare.com/solutions/ transducers. Accessed 6 Oct 2013 6. Our universal transducers work with all Ultrasonix systems (2013). http://www.ultrasonix.com/products/transducers. Accessed 6 Oct 2013 7. Frederiksen CA, Juhl-Olsen P, Sloth E (2012) Advances in imaging: ultrasound in every physician’s pocket. Expert Opin Med Diagn 6(3):167–170 8. Griffin J, Nicholls B (2010) Ultrasound in regional anaesthesia. Anaesthesia 65(Suppl 1):1–12 9. Adhikari S, Zeger W, Schmier C, Crum T, Craven A, Frrokaj I, Pang H, Shostrom V (2011) Pilot study to determine the utility of point-of-care ultrasound in the assessment of difficult laryngoscopy. Acad Emerg Med 18(7):754–758 10. Gaspari R, Blehar D, Mendoza M, Montoya A, Moon C, Polan D (2009) Use of ultrasound elastography for skin and subcutaneous abscesses. J Ultrasound Med 28(7):855–860 11. Teismann N, Lenaghan P, Nolan R, Stein J, Green A (2013) Point-of-care ocular ultrasound to detect optic disc swelling. Acad Emerg Med 20(9):920–925
