Magnetic Resonance Imaging (MRI), Low-Field

More documents

Recommendations

Info

Magee et al. (2003) used a 0.2 T open-design MR scanner for detection of supraspinatus tendon tearsand labral tears in 40 patients, compared with 1.5 T and arthroscopy. The authors stated that high-fieldstrengthimages altered reviewers' interpretations of low-field-strength scans for nine of 40 patients. Infour patients, full-thickness supraspinatus tendon tears could be diagnosed definitively on the high-fieldstrengthunit but not on the open unit. Three labral tears and two superior labral anteroposterior lesionscould be depicted definitively on the high-field-strength unit but not on the open unit. All tears wereconfirmed at arthroscopy. The authors concluded that high-field-strength MRI units provide better spatialand contrast resolution and allow more accurate interpretations than low-field-strength units; thesefindings may affect clinical treatment.Shellock et al. (2001) used a 0.2 T extremity-dedicated MR scanner to detect lesions of the rotator cuffand glenoid labrum in 47 patients, compared to the surgical findings. For the rotator cuff tears, thesensitivity, specificity, positive predictive value, and negative predictive value were 89%, 100%, 100%,and 90% (three false negatives), respectively. For the labral lesions, the sensitivity, specificity, positivepredictive value, and negative predictive value were 89%, 95%, 80%, and 97% ( two false positives, onefalse negative), respectively. The findings indicated that there was good agreement comparing the lowfieldMR results to the surgical findings for determination of lesions of the rotator cuff and glenoid labrum.This study did not evaluate conventional MRI compared to low-field or surgical findings.Loew et al. (2000) used a 0.2 T open-design MR scanner to compare the image quality, sensitivity,specificity, and diagnostic accuracy of low-field MR with 1.5 T MR after arthrography of the shoulder.Thirty-eight patients either with suspected chronic instability (n = 12) or rotator cuff abnormalities (n = 26)were examined. Intra-articular injection of diluted Gd-DTPA was followed in randomized order either firstby imaging on an open 0.2 T system or on a 1.5 T system. The image material was evaluatedindependently by two radiologists in a blinded fashion with respect to overall image quality and thedetection of rotator cuff as well as capsular and labral abnormalities. Surgical correlation was available in27 (71%) of 38 patients. For both systems, sensitivity and specificity for rotator cuff tears were 100%each, and for labrum pathologies, these values were 100 and 93%, respectively. The authors concludedthat low-field MR compares favorably to high-field MR in the detection of major abnormalities of theglenohumeral joint, at least when MR arthrography is used. Disadvantages are the duration of theexamination and thus the risk of reduced image quality caused by motion artifacts. It should be noted thatthere was an intentional use of different sequences at each MR unit. Also, the small number of patients(27) evaluated limits the power of the statistical results.Tung et al. (2000) used a 0.2 T open-design MR scanner to diagnose a glenoid superior labralanteroposterior (SLAP) tears compared to 1.5 T MR. Forty-one patients with SLAP tears and 26symptomatic patients with normal superior labra were retrospectively evaluated. Both groups of patientshad either high-field (n = 46) or low-field (n = 21) MRI and arthroscopy. For the diagnosis of SLAP tear,the sensitivity of high-field MRI was 90%, specificity was 63%, and accuracy was 80%. The sensitivity oflow-field MRI was 64%, specificity was 70%, and accuracy was 67%. Authors stated that the performancecharacteristics of high-field MRI are superior to those of low-field MRI for the diagnosis of a superior labraltear. Again, the small number of patients evaluated limits the power of the statistical results.Merl et al. (1999) prospectively evaluated the diagnostic quality of an open design 0.2 T MR scannercompared with high-field MR scanners measured by the applicable gold standard. Over a period of 3months, 401 patients with suspected renal tumors (n=78), diseases of the capsulolabral complex and therotator cuff of the shoulder joint (n=122), diseases of the spinal canal (n=105) and of the brain with focalneurological deficit (n=96) were prospectively evaluated in four participating centers. They all underwentclinical evaluation, low-field and high-field MRI and surgical or follow-up confirmation of diagnosis.Clinical, histopathologic, high-field and low-field MRI diagnoses were recorded in standardizedquestionnaires that were centrally evaluated. Statistical evaluation comprised two parts: receiveroperating characteristic (ROC) analysis assessed accuracy of MRI and clinical diagnoses; furthermore,rates of concordance of high- and low-field MRI diagnosis were calculated. Researchers did not compareimages and record differences between the different systems, but both class of units were measuredagainst the clinical gold standard and their diagnostic accuracy determined. Researchers found nostatistically relevant difference in high-field MRI diagnosis compared to low-field MRI diagnostic accuracymeasured by clinical or surgical gold standard in three of the four regions examined; in cerebralexaminations there was a small yet significant advantage for the high-field systems. The authorsPage 6 of 17Coverage Position Number: 0444
conclude that the open low-field scanner (using clinical and surgical gold standard as reference) is able toachieve comparable diagnostic accuracy compared to high-field scanners at lower costs and greaterpatient comfort. They stated that limitations due to field strength (signal-to-noise ratio, resolution, scantime) seem to be relevant only in a very small number of cases that warrant high-field examination.Allmann et al. (1998) used a 0.2 T MR scanner to determine the diagnostic accuracy of glenohumeralinstabilities with low-field MRI compared to 1.0 T MRI. A preselected group of 35 symptomatic patientswith recurrent shoulder luxations underwent imaging and therapeutic arthroscopy, which was used asstandard reference. The sensitivity, specificity, and accuracy of MR images acquired at 1.0 T for labrumpathology were 91%, 67%, 91% and 70%, 80%, 71% for the capsular complex, respectively. Comparedwith the above, the sensitivity, specificity, and accuracy for 0.2 T MR revealed 91%, 67%, 91% for thelabrum pathology and 63%, 80%, 66% for the capsular complex respectively. In the evaluation ofcapsular lesions, a comparison between the 0.2 T and the 1.0 T MR indicated a higher sensitivity andaccuracy for the high-field images. Concerning labral lesions, the sensitivity and accuracy of the 0.2 Tand the 1.0 T MR were comparable. A selection bias could not be avoided because arthroscopy wasused as the gold standard. It should be noted that a highly selected patient population - because onlythose subjects with more than eight luxations and arthroscopy, - impacted results (e.g., lower specificityfor labral lesions).Spine: Jinkins et al. (2005) stated that weight-bearing open-design MRI allows for improved sensitivityand specificity; however, no supporting data was provided. Vitaz et al. (2004) used a 0.5 T MRI scannerto prospectively evaluate the first 20 patients referred for MRI for neck pain. There was no comparator; nocomparison to conventional MRI can be drawn.In a review article, Weishaupt et al. (2003) stated that conventional MRI of the lumbar spine (i.e., in thesupine position) remains the imaging method of choice for the assessment of degenerative disk disease.Weight-bearing imaging in upright seated or upright standing positions (usually combined with flexion andextension movements) using vertical open-configuration MR scanners may be helpful in patients withequivocal findings on conventional MRI, clinically suspected position-dependent nerve root compromise,or in cases of suspected spinal canal or neuroforaminal stenosis with equivocal or borderline findings onconventional MRI.Weishaupt et al. (2000) used a 0.5 T open-design MR scanner to evaluate whether positional MRI of thelumbar spine demonstrated nerve root compromise not visible on supine 1.0 T MR. A total of 30 patientswith chronic low back pain unresponsive to nonsurgical treatment and with disk abnormalities but withoutcompression of neural structures were included. Results demonstrated nerve root contact withoutdeviation was present in 34 of 152 instances in the supine position, in 62 instances in the seated flexionposition, and in 45 instances in the seated extension position. As compared with the supine position, inthe seated flexion position nerve root deviation decreased from 10 to eight instances; in the seatedextension position, it increased from 10 to 13 instances. Nerve root compression was seen in one patientin the seated extension position. The authors concluded that positional MRI more frequentlydemonstrates minor neural compromise than does supine MRI. The relevance or value of this finding onlow back pain treatment or patient outcomes is unknown.Vitzthum et al. (2000) used a 0.5 T open-design MR scanner to study healthy volunteers and patientssuffering from degenerative disorders of the lumbar spine to determine the relationship of differentstructures of the lower lumbar spine during interventional movement examination. In 50 patients withdegenerative disorders of the lumbar spine (41 with disc herniation, five with osteogenic spinal stenosis,and four with degenerative spondylolisthesis), the range of rotation was increased in the relevant spinalsegments. Signs of neural compression were increased under motion. The authors concluded thatdynamic examination in which vertical, open 0.5 T MRI was used demonstrated that the extent of neuralcompression and the increasing range of rotation are important signs of segmental instability. Therelevance or value of this finding on low back pain treatment or patient outcomes is unknown.Rheumatology: The Outcome MEasures in Rheumatoid Arthritis Clinical Trials (OMERACT) andEuropean League Against Rheumatism (EULAR) initiative is an informal international network of workinggroups and gatherings interested in outcome measurement across the spectrum of rheumatologyintervention studies. The proposed OMERACT MRI scoring system is based upon conventional strengthPage 7 of 17Coverage Position Number: 0444
Page 1: CIGNA HEALTHCARE COVERAGE POSITIONS
Page 4 and 5: guidance in minimally invasive neur
Page 8 and 9: MRI, and provides a framework for s
Page 10: National Agency for Accreditation a
Page 13 and 14: 24. FONAR. Index of Upright MRI Res
Page 15 and 16: 55. Nour SG, Lewin JS. Percutaneous
Page 17: 86. Zlatkin MB, Hoffman C, Shellock

Magnetic Resonance Imaging (MRI), Low-Field

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?