Background and purpose: Although MR spectroscopy and functional MR imaging of the brain have been successful at 4 T, conventional fast spin-echo imaging of the brain at 4 T has not been adequately evaluated. The purpose of this study was to compare the detection of white matter abnormalities in multiple sclerosis (MS) at 1.5 T and 4 T.
Methods: Fifteen patients with clinically definite MS were imaged at both 1.5 T and 4 T within a 1-week period. Comparison was made between fast spin-echo long-TR images at both field strengths. Pulse sequences were tailored to maximize resolution and signal-to-noise ratio in clinically relevant imaging times (< 7 min). Four interpreters independently reviewed the images obtained at both field strengths in separate sessions and evaluated them for lesion identification, size, characterization, and subjective resolution. Differences in interpretations at 1.5 T and 4 T were subsequently recorded.
Results: Images obtained at 4 T showed a mean of 88 more lesions as compared with images obtained at 1.5 T. All the lesions measured less than 5 mm and were typically aligned along perivascular spaces. Twenty-five consensually identified lesions on 4-T images were not seen at all on 1.5-T images. Moreover, 4-T images showed 56 additional consensually identified lesions, which were indistinct and seen only in retrospect on 1.5-T images. These lesions were frequently (n = 48) identified in large confluent areas of white matter signal intensity abnormality at 1.5 T. All observers also agreed that 4-T images subjectively enhanced the perception of normal perivascular spaces and small perivascular lesions.
Conclusion: MR imaging at 4 T can depict white matter abnormalities in MS patients not detectable at 1.5 T through higher resolution with comparable signal-to-noise ratio and imaging times.