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From the Weill Medical College of Cornell University, Chief, Division of Ultrasound and Body Imaging, Hospital for Special Surgery, New York City, New York.
Address correspondence and reprint requests to Ronald S. Adler, PhD, MD, Professor of Radiology, Weill Medical College of Cornell University, Chief, Division of Ultrasound and Body Imaging, Hospital for Special Surgery, 535 East 70th St., New York City, NY 10021. Address e-mail to adlerr{at}hss.edu.
The development of compact ultrasound systems has resulted in increased availability of affordable, relatively good quality, and easily transportable ultrasound imaging. Concomitantly, there is new interest in using ultrasound in a large variety of nonradiologic medical subspecialty areas. In one survey, compact ultrasound systems constituted approximately 25%–30% of the ultrasound market, with substantial sales to as many as eight different medical subspecialty areas (1). These numbers are expected to continue to increase, in part driven by ultrasound vendors who see this as a new market and, secondly, by continued improvements in the quality of these systems. It has been predicted, at a recent preconference symposium of the Society of Radiologists in Ultrasound on the future of ultrasound imaging, that the image quality of compact systems will approach those of current high-end machines (manuscript in preparation). Vendors attending a 2004 consensus conference of the American Institute of Ultrasound in Medicine (AIUM) predicted that compact systems may constitute half of the ultrasound market by 2010 (2).
The question then arises as to how such systems fit into the bigger picture of medical imaging? What types of imaging applications are these systems applicable to, and what level of training is necessary to perform them? What are the potential liabilities associated with imaging performed by non-radiologists and are there appropriate targeted applications that are within the realm of a given subspecialty area? Does the introduction of compact ultrasound systems add significantly to clinical performance, or does it incur additional unnecessary expenses, add to patient anxiety, result in additional unnecessary tests, or produce conflicting results? Are there appropriate credentialing bodies to assess adequate training to perform ultrasound, so that an arbitrary set of standards can be avoided? An issue not often addressed is patient (and perhaps referring physician) perception. Can the introduction of less skilled practitioners negatively impact the patient’s perception of the value of performing ultrasound scans? Although many of these questions remain to be answered, and will likely generate disagreements among "competing" medical subspecialties areas, a rational approach to addressing these issues will be necessary as the number of compact systems and potential users proliferate.
One of the rapidly growing applications of compact ultrasound systems is to provide guidance in performing regional anesthesia. There is no doubt that ultrasound can be useful in providing localization for deposition of local anesthetic. There is an increasing literature, which demonstrates the utility of using ultrasound guidance for the delivery of local therapy, although good prospective studies are still lacking (3). If such an application can be shown to be effective within the anesthesia community, then this may indeed be an appropriate use of focused ultrasound, keeping in mind the limitations of the equipment being used and the level of ultrasound training and expertise of the anesthesiologist. It should be recognized that even in the best of circumstances, using high-end equipment and with high levels of expertise, such procedures can be difficult to perform. For example, the presence of microbubbles in the injected material can obscure the needle. Phase aberration artifact, due to changes in speed of sound in fibrofatty tissue, may likewise obscure the needle or make it appear discontinuous. Poor tissue contrast can make it difficult to recognize the appropriate anatomy. Positioning the needle outside the elevational focus of the transducer can also pose challenges in accurate positioning. One must be cognizant of these potential pitfalls when performing an examination (4).
Recent articles by Sites et al. (5,6) describe the utility of using compact ultrasound as a tool for anesthesiologists not only for guiding the performance of regional anesthesia, but also for providing a "new" diagnostic tool to assist surgeons in diagnosing and localizing abnormalities during surgery. These authors produced examples in which their ultrasound scans, before performance of a regional block, demonstrated findings that altered or aided surgical and medical management in the cases described. The authors further argue that these cases are justification for performing screening diagnostic ultrasounds by the anesthesiologists, and that such examinations should become routine before performing a regional block. Similarly, they point out that they can provide intraoperative localization of specific abnormalities, such as in the case of a nerve sheath tumor. In reading both these articles, one can likewise draw the conclusion that appropriate presurgical screening and planning could easily have prevented unnecessary operating room (OR) delays and tests in all the cases they describe. In our institution, there is extensive presurgical screening with a relatively low threshold for performing diagnostic imaging studies and localization of specific abnormalities, so that OR time is not compromised and potential patient risks can be minimized. There is a close working relationship between Radiology and the surgical and medical staff. Compact ultrasound is indeed used as a method to guide regional anesthesia by our anesthesiologists, without the need to expand its use in the OR. Even this application of ultrasound has, however, raised concerns among some of our own anesthesiologists regarding the potential problems when limited ultrasound experience is combined with limited equipment capabilities.
Sites et al. (5) describe the difficulties posed by the lack of credentialing bodies for anesthesiologists performing ultrasound, and note that these obstacles can be overcome by defining a set of credentialing criteria within the anesthesia community. They refer to the experience of the American College of Emergency Physicians in their own pursuit of limited ultrasound credentialing, in which 40 h of didactic instruction and 150 observed cases are considered adequate training to perform ultrasound. If one compares this to the level of experience of a fellowship-trained radiologist, a significant disparity becomes evident. Typically, radiology training includes approximately 6 mo of ultrasound rotation as a resident along with numerous teaching conferences discussing case material over a 4-yr-period, as well as didactic lectures on ultrasound physics. Ultrasound is one of several areas in which residents are required to be proficient as part of their board examination. Fellowship usually includes an additional 4–6 mo of continuous exposure to ultrasound. Our radiology fellows are directly involved in up to 500 interventional procedures each during the course of their training. In our practice, we perform approximately 12,000 examinations each year, of which approximately 8000 involve an ultrasound-guided intervention. We use high-end equipment and have extensive experience performing ultrasound-guided interventions in the musculoskeletal system, as well as being experienced diagnostic imagers, using ultrasound, computed tomography, and magnetic resonance imaging. This expertise and focused fellowship experience allows direct comparison and use of all available imaging modalities. Performing intraoperative ultrasound by radiology is by no means a new concept, and has been available in many institutions for well over 20 years (7).
Ultrasound will no doubt become an integral part of performing regional blocks, and some of the issues raised by Sites et al. (5) are valid and should be addressed. My own feeling is that it is best to develop a collaborative relationship between radiology and anesthesia, helping to provide ultrasound training, oversight, back-up, and documentation. Radiologists are already in a position to provide the appropriate level of training and didactic material necessary to perform the focused ultrasound examination required to guide a regional block. The AIUM is a multidisciplinary organization, including a large variety of medical subspecialties, as well as ultrasound physicists and technologists, who would be in the best position to produce a set of appropriate credentials to perform focused ultrasound or suggest uniform guidelines that may be applied within each subspecialty area. This was, in fact, one of the conclusions of the 2004 consensus meeting of the AIUM, which included 19 different professional organizations within the medical community.
Ultrasound technologists provide a readily available resource, skilled in ultrasound imaging and in assisting in guided procedures. Wireless image acquisition and retrieval makes it possible to document these procedures, either as single image acquisitions or as cine loop data on a PACS workstation for review by the anesthesiologist and radiologist. These systems are conducive to consultation with an experienced radiologist during the procedure. I believe that a radiologist should be available to come to the OR on an as-needed basis if a remote consultation is not possible or does not adequately address the issue. Such collaboration would be less apt to result in unnecessary delays or tests. There would be less likelihood of producing conflicting results. Most importantly, there would be multiple "eyes" available to assess a potential problem, thereby providing oversight and back-up to the anesthesiologist. As physicians, we all wish to avoid the scenario of one or two horror stories that can be exploited by the media when someone with limited knowledge and experience applies new technology. Ultrasound is an extraordinary modality, and one that should be used appropriately, depending on the expertise of the operator.
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