Scan-Rescan Variation of Measures Derived from Brain Magnetization Transfer Ratio Histograms Obtained in Healthy Volunteers by Use of a Semi-interleaved Magnetization Transfer Sequence

Summary: A novel semiinterleaved gradient-echo (GE) se-quence for quantitative measurement of magnetization transfer ratio (MTR) is described. With this sequence, sev-eral lines of k-space are collected for the non-MT image then several lines are collected for the MT image, thus building up the entire k-space in distinct acquisition blocks, with a good trade-off between motion-induced misregistra-tion and degree of MT effect. The scan-rescan coefficients of variation for several MTR histogram-derived measures from 10 healthy volunteers scanned serially with this se-miinterleaved sequence proved to be lower than those achieved using a conventional GE sequence. This sequence may be useful in a clinical environment to measure MTR changes over time more reliably than when acquiring the non-MT and MT images sequentially, which inevitably are affected by patient motion. Magnetization transfer ratio (MTR) histogram analysis is increasingly being used to assess brain disorders in numerous neurologic conditions, in-cluding multiple sclerosis (MS) (1). Animal (2) and postmortem human (3) studies have shown that brain areas with decreased MTR correspond to ar-eas in which severe demyelination and axonal loss have occurred. The advantage of histogram analy-sis over more conventional region-of-interest anal-ysis is that it provides quantitative indexes that re-flect the overall extent of brain disease (4). This is particularly important in diseases, such as MS, with widespread, multifocal lesions of different sizes and heterogeneous intrinsic abnormalities, which may go undetected on conventional MR imaging sequences (5). Quantities derived from MTR histograms are promising as objective and accurate measures for Address reprint requests to Dr. Massimo Filippi, Neuroim