THE EFFECT OF SECTION THICKNESS ON MR LESION DETECTION AND QUANTIFICATION IN MULTIPLE-SCLEROSIS

BACKGROUND AND PURPOSE: The purpose of our study was to investigate th e effect of section thickness on MR detection of brain lesion volume a nd measurement precision in patients with multiple sclerosis (MS). MET HODS: Eight subjects with known MS were studied on a 1.5-T MR system. We used a 3D fast fluid-attenuated inversion-recovery sequence to obta in contiguous axial brain images at section thicknesses of 5 mm, 3 mm, and 1 mm, Two sets of images were acquired at each section thickness during two sessions, between which the patient was removed from the sc anner. Lesion volumes were measured at each section thickness using a semiautomated local thresholding technique. RESULTS: We found that pro gressive reduction in section thickness led to detection of smaller le sions, resulting in a significant (8%) increase in lesion volume on MR images as section thickness was reduced from 5 mm to 3 mm, However, d espite a further increase in lesion detection at a section thickness o f 1 mm, this did not result in an increase in total lesion volume. Thi s finding indicates that the relationship between section thickness an d lesion volume on MR images is not linear. Scan-rescan reproducibilit y was improved by reducing section thickness, at the cost of increased analysis time. CONCLUSION: This study shows that acquisition of very thin sections increases the sensitivity and precision of MS lesion mea surement. Serial studies assessing lesion changes over time are needed to define the impact of this increase on sample size requirements for MS treatment trials.