Caudal Image Contrast Inversion in MPRAGE at 7 Tesla: Problem and Solution

Abstract

The magnetization-prepared rapid-acquisition gradient-echo (MPRAGE) sequence regularly shows caudal image contrast inversion at 7 T and therefore reduced clinical applicability. The investigators report the technical source of this problem and present a practical solution. A total of 71 subjects were scanned using a 7-T whole-body magnetic resonance imaging system using a 32-channel transmit/receive head coil. In 39 subjects, 45 high-resolution T1 contrast image data sets were acquired with the standard MPRAGE sequence. A modified sequence with an adiabatic wideband uniform rate smooth truncation pulse for magnetization preparation was used for 45 further scans in 39 subjects. In total, seven subjects underwent scans with both sequences. The homogeneity of T1 contrast and the occurrence of caudal image contrast inversion were evaluated in consensus reading by two neuroradiologists. Caudal image contrast inversion was depicted in 19 acquisitions (42.2%) using the standard MPRAGE sequence. Using the adiabatic wideband uniform rate smooth truncation pulse for magnetization preparation, caudal image contrast inversion was depicted in only three acquisitions (6.7%). A χ(2) test showed a significant difference between the two preparation pulses (P < .001). Magnetization preparation with an adiabatic wideband uniform rate smooth truncation pulse in the MPRAGE sequence at 7 T can significantly reduce the occurrence of caudal image contrast inversion and improves signal homogeneity.