QUANTIFICATION OF MULTIPLE-SCLEROSIS LESION VOLUMES IN 1.5 AND 0.5 T ANISOTROPICALLY FILTERED AND UNFILTERED MR EXAMS

Recently, guidelines for the use of MRI in the monitoring of MS have r ecommended the use of imaging systems with mid-field (0.5-1.0 T) or hi gh-held (greater than 1.0 T) strengths. Higher field strengths provide many advantages, including increased signal-to-noise ratios (SNR). SN R also may be increased by post-processing algorithms that reduce nois e. In this paper we evaluate the impact on operator variability of (a) lesion quantification in high-field (1.5 T) versus mid-field (0.5 T) exams; and (b) an anisotropic diffusion filter algorithm that reduces image noise without blurring or moving object boundaries. Inter- and i ntra-operator reliability and variability were studied using repeated quantification of lesions in 1.5 and 0.5 T filtered and unfiltered MR exams of a MS patient. Results indicate that inter-operator variabilit y in 1.5 T unfiltered exams was 0.34 cm(3) and was significantly large r than that in 1.5 T filtered (0.27 cm(3)), 0.5 T unfiltered (0.26 cm( 3)), and 0.5 T filtered (0.24 cm(3)) exams. Similarly, intra-operator variability in 1.5 T unfiltered exams was 0.23 cm(3) and was significa ntly larger than that in 1.5 T filtered (0.19 cm(3)), 0.5 T unfiltered (0.19; cm(3)), and 0.5 T filtered (0.18 cm(3)) exams. In addition, th e minimum significant change between two successive measurements of le sion volume by the same operator, was 0.64 cm(3) in 1.5 T unfiltered e xams, but 0.53 cm(3) or less in other exams. For two different operato rs making successive measurements, the minimum significant change was 0.94 cm(3) in 1.5 T unfiltered exams, but only 0.75 cm(3) or less in o ther exams. Finally, the number of lesions to be monitored for an aver age change in cm volume at a given power and significance level was gr eater by 30%-60% for quantification in 1.5 T unfiltered exams. These r esults suggest that inter- and intra-operator variability are reduced by anisotropic filtering, and by quantification in 0.5 T exams. Reduce d operator variabilities may result from higher detail signal-to-noise ratios (dSNRs) in 0.5 T and filtered exams. (C) 1996 American Associa tion of Physicists in Medicine.