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The main imaging methods used in rheumatology include conventional radiography, computed tomography (CT), magnetic resonance imaging (MRI), and ultrasonography. In clinical practice, musculoskeletal ultrasound (MSUS) has become an established imaging method for the diagnosis and followup of patients with rheumatic diseases. The main advantages of this technique include absence of radiation exposure, multiplanar imaging capability, and cost efficiency; it is also a dynamic real-time investigation.

Identifying the presence of erosions early in the course of rheumatoid arthritis (RA), before radiographic changes are apparent, may allow the clinician to initiate a more aggressive therapy with improved patient outcome. Several studies on MRI have proved this technique's superior ability to evaluate early RA (1–3). However, high costs limit its wide-spread use, especially in countries where the availability of modern MRI systems is limited. Ultrasound appears to be an alternative method of detecting the erosions that conventional radiography fails to recognize (4). Some researchers have found ultrasound to be as sensitive or even more sensitive than MRI in the detection of synovitis and tenosynovitis (2, 5). In addition, power Doppler sonography has proved to be a valuable tool for the assessment of synovial and entheseal inflammation (5, 6). Recent developments in the application of sonographic contrast media in rheumatology will determine if these methods will play an additional role in the assessment of synovitis (7, 8).

Of all the imaging methods used in rheumatology, MSUS is considered to be the most operator-dependent imaging modality, thus adequate training is of paramount importance. However, in the absence of agreement on an international training curriculum, there are considerable differences in the degree and type of training required for rheumatologists as well as radiologists to perform MSUS. For example, in Germany, a rheumatologist has to perform 200 joint and soft tissue MSUS examinations under the surveillance of an experienced teacher to become eligible for board certification. Training courses are offered by the German Society for Ultrasound in Medicine and consist of 3 theoretical and practical training courses that last 2–3 days each (9). Based on the guidelines of this society, standardized examination procedures for the musculoskeletal system have been published (10). A self-teaching approach has been proposed by Filippucci et al (11) who claim that a novice may be able to obtain acceptable sonographic images within 24 hours of active scanning. However, they also state that adequate interpretation of sonographic findings requires close supervision by an expert tutor. We clearly reject the idea of self teaching, because any imaging modality and especially a dynamic real-time investigation such as sonography can only be taught by close interaction with an experienced teacher.

Some European authors have proposed guidelines for MSUS in rheumatology based on the literature and their personal experiences. Backhaus et al (12) have published such guidelines, including recommendations on technical equipment, teaching and training as well as a list of detectable diseases, patient positioning, and standard technique. In the US, the program requirements for Residency Education in Rheumatology state that the institutions in which the rheumatologist should be trained must include access to computerized tomography and MRI. Teaching and consultation at the primary education site, including faculty in radiology, must be included in the program. Furthermore, the program “must provide sufficient experience for the resident to acquire skill in the performance or interpretation of bone and joint imaging techniques.” Proper teaching of imaging techniques occurs almost exclusively in an environment conducive to learning. First, one must have opportunities to study the physics of the technique. For cross-sectional imaging, proper topographic anatomy must be taught. The understanding of this anatomy improves when different cross-sectional anatomic information can be integrated. In our opinion, learning without the insights into MRI and CT anatomy results in more superficial and one-sided knowledge.

In contrast with a rheumatology program, 4 years of radiology residency training in North America requires 4 months of ultrasound training taught through hands-on practice, case solving, and lectures on ultrasound physics and technology. In most programs, sonographic training will be spread evenly in 1-month blocks over the 4-year curriculum. The bone and joint anatomy depicted by ultrasound is taught along with the anatomy depicted by other imaging modalities such as radiography, CT, and MRI. A minimum of 10 unknown ultrasound cases are presented to the examinees; MSUS cases have been included in board examination for several years.

Another topic that should be discussed in the context of rheumatologists performing MSUS is self referral. Recent studies on the utilization of ultrasound in musculoskeletal practices have already shown a dramatic increase in the number of MSUS studies performed by nonradiologists. As a matter of fact, the most significant percentage of increases in Medicare reimbursements for MSUS utilization have been in podiatry (13). When rheumatologists start self referring ultrasound examinations, they will probably increase the cost of imaging 4.4–7.5 times per episode of care just like other self-referring physicians have done in the past with imaging in their respective specialties (14). In contrast, radiologists work as consultants. Business growth in a radiology practice relates to expertise and service. In our opinion, without the incentive of self referral, radiologists tend to make more sound decisions with respect to recommendations about surgery or other treatment. A consulted specialist does not have the luxury of “hanging on” to patients. From our viewpoint, transfer of care, such as a referral for imaging, preserves objectivity in imaging.

In the February issue of Arthritis Care & Research, Brown et al provided an important contribution to the search for an international consensus definition of standards of training and indications for the application of MSUS in rheumatology (15). They identified 57 experts in MSUS, of which 18 rheumatologists and 18 radiologists completed 2 iterative rounds of answering questionnaires, resulting in a consensus concerning the appropriate indications, anatomic areas, and knowledge and skills needed for a rheumatologist to perform MSUS. The authors used consensus-defining methodology termed the Delphi exercise, which enabled group consensus to be achieved in 30 of the proposed 37 categories. Agreement was assessed on 2 levels: if the expert agreed with the issue under consideration, and if the expert agreed with the opinion of other experts on a certain issue. Concerning the appropriate indications, agreement above a 70% threshold value was achieved for monitoring disease activity, bursitis, effusion, inflammatory arthritis, and guided aspiration and injection. Concerning anatomic areas, group agreement was established for the hand, wrist, elbow, hip, knee, ankle and heel, forefoot, and shoulder. Agreement on appropriate knowledge and skills that a rheumatologist needs to perform MSUS was very high and included aspects of anatomy, pathology, ultrasound physics, and several other areas.

A striking difference in scoring between rheumatologists and radiologists was observed. The agreement scores of radiologists were consistently lower than those of their rheumatologic colleagues, with statistically significant differences for all indications and in all anatomic areas. Interpretation of these findings remains a topic to be discussed. It certainly reflects the enthusiasm of rheumatologists to perform MSUS for all indications and in all anatomic areas. Most of these rheumatologists are trained only in one imaging modality, i.e., MSUS, and the discrepancy might also reflect the more cautious approach of radiologists towards single imaging modality use.

MRI is an excellent tool for the early and followup assessment of rheumatologic diseases without the drawback of operator dependency. It is unparalleled in its ability to allow the visualization of articular tissues, and multiple studies have shown MRI to be more sensitive than radiography (1, 16, 17) and ultrasound (3, 18) in detecting bone erosions. Furthermore, MRI has the unique ability to show bone marrow changes that may precede actual erosion (19). MSUS cannot provide this information. The application of MRI in rheumatology will prove to be cost efficient if it can reduce unnecessary treatment of patients with costly biologic therapies. Recently developed dedicated extremity MRI systems with field strengths of up to 1.0T have been developed as lower-cost alternatives that are capable of showing radiographically-occult bone erosions, synovitis, and possibly osteitis and tendonitis (20, 21).

The use of CT in rheumatologic practice has been fairly limited. Drawbacks for its use when compared with MRI and MSUS include exposure to ionizing radiation and inferiority in visualizing soft tissues. However, due to near-isotropic voxel acquisition, modern multislice CT systems are capable of depicting bony pathology in any chosen imaging plane with a resolution as small as 0.5 mm. These technical improvements may open new areas for application of CT in the imaging of rheumatologic diseases (22).

The imaging methods that are currently available are all complementary. MSUS has proved to be a very sensitive method for soft tissue diagnosis and for assessment of the osseous surface; CT for bone structure abnormalities; and MRI for the evaluation of cartilage, bone marrow, and articular soft tissue. We believe that only a physician trained in all imaging methods can act as a true gatekeeper. In a system with radiologists as imaging consultants, there is a heavier focus on patient care. Referral to imaging consultants guards patients against the practice of greedy self referral. The radiologist will choose the most cost-efficient modality to query a specific rheumatologic disease, knowing that the consultant's behavior is subjected to 360 degrees of scrutiny.

None of the above-mentioned techniques that can be used in rheumatology will replace radiography as the baseline method for the assessment of bone damage. However, several complementary tools have now become available for the evaluation of patients who are at risk of developing inflammatory arthritis and who have equivocal radiographic findings. In addition, the newer imaging methods let us monitor disease activity and progression. It is of great importance that both rheumatologists and radiologists engage in the development of MSUS, a task that will best be served by cooperation and constant communication between the specialties as has been excellently shown by Brown et al (15).

REFERENCES

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