Sensitivity of contrast enhanced MRI in multiple sclerosis. Effects of gadolinium dose, magnetization transfer contrast and delayed imaging.

Although clinical end points remain the definitive measure of therapeutic efficacy in multiple sclerosis, more sensitive markers of disease activity are required to screen potential disease-modifying agents. The use of gadolinium contrast-media in MRI studies increases both the reliability and sensitivity of detecting active lesions in multiple sclerosis. We studied three potential methods for further improving sensitivity; the use of 0.3 mmol/kg (triple dose) gadolinium-diethylenetriaminepenta-acetic acid (Gd-DTPA), magnetization transfer (MT) contrast imaging and the introduction of a delay between contrast-medium injection and imaging. Fifty patients were studied (seven with benign, 14 with relapsing-remitting, 10 with secondary progressive, 16 with primary progressive and three with transitional multiple sclerosis). Imaging was performed on two occasions, 24-72 h apart, with triple- and single-dose Gd-DTPA. Pairs of contrast-enhanced T 1-weighted studies, with and without MT, were obtained at three different times, i.e. within early (0-20 min), short-delay (20-40 min) and long-delay (40-60 min) time-windows. Nineteen patients did not have the full complement of studies. Seven patients suffered minor self-limiting adverse events possibly related to triple-dose Gd-DTPA. Overall, triple-dose Gd-DTPA resulted in a 75% increase in the number of enhancing lesions detected compared with the single dose (P < 0.002). The use of MT or delay alone did not significantly increase the sensitivity of either single- or triple-dose studies. The combination of MT and short delay increased the number of enhancing lesions detected with single-dose Gd-DTPA by 47% (P < 0.05) and with triple-dose Gd-DTPA by 27% (P < 0.01). Detection was not significantly further improved by a long delay. The most sensitive modality was MT imaging with a long delay following triple-dose Gd-DTPA, resulting in the detection of 126% more enhancing lesions than in standard single-dose imaging (P < 0.05). This applies to all subgroups except for primary progressive multiple sclerosis, in which none of these methods alone or in combination improved the sensitivity. We conclude that for relapsing-remitting and secondary progressive multiple sclerosis, the combination of triple-dose Gd-DTPA and delayed MT imaging more than doubles the sensitivity to contrast-enhancing lesions.