QUANTITATIVE TECHNIQUES FOR LESION LOAD MEASUREMENT IN MULTIPLE-SCLEROSIS - AN ASSESSMENT OF THE GLOBAL THRESHOLD TECHNIQUE AFTER NON UNIFORMITY AND HISTOGRAM MATCHING CORRECTIONS

The quantitative assessment of abnormalities on brain MRI (magnetic re sonance imaging) in multiple sclerosis (MS) provides a widely used end point in monitoring treatment efficacy. Semi-automated intensity thres holding (global thresholding) is an established method of lesion segme ntation, but it is limited by the heavy dependence of derived volumes on the chosen intensity threshold. Inconsistency in threshold choice s ubstantially contributes to its suboptimal reproducibility. A potentia l improvement to global thresholding is to utilize the histogram match ing algorithm to correct for variations in scanner sensitivity. This s tudy evaluated whether or not a single intensity threshold could then be applied across multiple histogram matched images. Eight MS patients were scanned at baseline and after nine months. After nonuniformity c orrection, the histogram matching correction was applied, reducing the mean absolute percentage variation in normal appearing white matter s ignal intensity from 15.2 to 3.8% for baseline scans and from 11.9 to 2.1% across serial studies. Lesion volumes were measured with the glob al threshold technique using a single threshold selected from one scan . A local thresholding technique (contouring) was also performed as a gold standard measure. Agreement between techniques for baseline lesio n volumes was only moderate with an intra-class correlation coefficien t (ICC) of 0.46 and there was little agreement for change in lesion vo lume (ICC = 0.17), reflecting inconsistencies in the volume of non-les ion regions included by the threshold. Agreement was improved by delet ing non-lesion regions, but this was time consuming and less reproduci ble than contouring method. At present, the contour technique remains a more appropriate method for lesion load quantification.