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

Abstract

A novel semiinterleaved gradient-echo (GE) sequence for quantitative measurement of magnetization transfer ratio (MTR) is described. With this sequence, several 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 misregistration 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 semiinterleaved 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.

fig 1.

Data collection scheme for the semiinterleaved MT sequence. For each image, k-space data are collected in three blocks. The first one third of the non-MT image (block labeled 1) is followed by the first one third of the MT image (block labeled 2). This is followed by acquisition of the second and third blocks of the two images (labeled 3 through 6) in this semiinterleaved fashion. For the first few lines of blocks 2 through 6, the macromolecular magnetization saturation is not in a steady state, leading to slightly lower MT values than for sequential acquisition, but the likelihood of misregistration between the non-MT and MT images is considerably reduced