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The first 3 T MRI systems were introduced to clinical practice over a decade ago, and access to these systems has become increasingly available worldwide. Although they were first used for neurological imaging, several studies have demonstrated the abilities and potential advantages of 3 T systems over conventional 1.5 T systems for musculoskeletal disorders, including for their use in sports medicine.1 ,2 The introduction of 3 T MRI generated great expectations in the field, with hope for marked improvement in the diagnosis of musculoskeletal disorders.3
What does ‘3T’ mean for a clinician? Why should I care?
Tesla units are used to quantify the strength of a magnet field. In comparison to 1.5 T systems, 3 T MRI is characterised by increased MR signal with relatively less increase in background noise—thus having a higher signal-to-noise ratio (SNR).3 This advantage can be used to either decrease scanning time or improve spatial resolution. The increase in scan speed means increased patient comfort and throughput; increased resolution, especially in combination with surface coils, may prove advantageous for the visualisation of small structures such as the ligaments of the wrist or ankle.4
While several studies have shown similar or slightly increased diagnostic performance when using 3 T systems over 1.5 T in joint imaging using arthroscopy as a gold standard,1 ,5 ,6 there are no studies using the clinical gold standard of “How often has 3 T changed my treatment decision compared to 1.5 T MRI?” (figure 1).
As radiologists, we love beautiful images! Of course, we also aim to provide our referrers with the most appealing examinations possible and, certainly, these will often be based on 3 T imaging. Having the choice of an examination at 1.5 or 3 T for the same price—of course I would opt for the 3 T—given the radiologist invests the same amount of time he/she would for a 1.5 T examination. A 3 T MRI performed in 10 min will look similar or worse than that of a 1.5 T MRI at 20 min. If I were claustrophobic, I would greatly appreciate the shorter examination without compromising diagnostic accuracy.
Comparative data—how does the 1.5 T compare to the 3 T
Be aware that apples should be compared with apples and oranges with oranges. A recent meta-analysis suggests that previous comparisons between 1.5 and 3 T MRI were performed when an older, usually 1.5 T MR system was being replaced with a novel 3 T device, which may have confounded comparison.7 There are few comparisons of equal generation of 1.5 and 3 T MR systems with advanced coil technology in institutions with access to both. The available data are often from older, 1.5 T systems, which are likely to perform poorly against newer equipment, whether the 1.5 or 3 T.
As with scanning time—resolution matters in specific circumstances—for example, small ligaments of the wrist are probably superiorly visualised at 3 T and some of these pathologies may require surgery once detected. In rare cases, it may be important to distinguish an advanced partial rupture from a complete ACL tear—a scenario where 3 T seems slightly superior2—however, in the end the clinical assessment, and the patient's symptoms and functional limitations will guide the treatment. We, as radiologists, need to remember that we provide service to the treating clinician and are an adjunct to the battery of diagnostic tests available, with some pathologies likely to remain undetected by either 1.5 or 3 T MRI. Software focusing on pattern recognition will help in our daily duties in the future, but the end of the profession of radiology is not in sight as long as we are perceived as true partners in the clinical diagnostic process.
Future of 3 T MRI
Emerging applications, such as compositional MRI, which enables the visualisation of early (‘biochemical’) pathologies that are not visualised by morphological (‘structural’) MRI, are more easily or exclusively applicable in high field systems such as 3 T. We hope that these will also play a role in clinical sports medicine in the near future. Applications may include outcome evaluation of cartilage repair surgery, postsurgical assessment of ligament reconstruction or defining patients at higher risk for re-injury or premature osteoarthritis in a postinjury situation. The role of contrast application including dynamic contrast-enhanced MRI, which enables evaluation of treatment effect in inflammatory conditions, remains to be shown. The role of even higher field strengths in the clinical routine—for example, 7 T MRI, which is today only available in a research environment8—remains to be seen.
Yes, 3 T MRI often produces more beautiful images and whenever there is a chance we would love report on these. How often did it change treatment decisions?—Likely not too often. Modern coil technology is highly advanced and our workhorse in musculoskeletal radiology will remain the 1.5 T system for quite a while. So in our opinion, we would suggest that you do not feel treated inferiorly to your neighbour who told you that he just had a 3 T MRI, the ‘latest technology’, while you only had one at the 1.5 T standard of care. The treatment decision by the referring orthopaedic surgeon or sports medicine physician will likely not differ.
Competing interests AG received consultancies, speaking fees and/or honoraria from Tissue Gene, Ortho Trophix and Genzyme, and is President of Boston Imaging Core Lab (BICL), a company providing image assessment services. FWR is Chief Medical Officer and shareholder of BICL.
Provenance and peer review Not commissioned; externally peer reviewed.
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