Time-Resolved CE-MRA at 1.5T and 3.0T

Time-resolved CE-MRA studies using the CAPR sequence were performed in human subject volunteers at 1.5T and 3.0T (GE Signa, Version 12.0 Excite) according to a protocol approved by our institutional review board. The typical scan parameters were: 3D spoiled gradient echo (GRE) sequence using TR/TE of 3.8/1.2 msec; flip angle 30°; BW ±62.5 kHz; sampling matrix 256 (S/I, frequency), 48–96 (A/P, phase), 32–64 (R/L slice); FOV of 25 cm (S/I and A/P) and 12–24 cm (R/L); and typical 2 min. in duration. It was useful to restrict the FOV along both the readout and the slice select directions precisely to the anatomy of interest, as facilitated by the 3DFT nature of the sequence. At both field strengths a similar eight-element head coil (MRI Devices, Waukesha, WI) was used. For all studies, 20 ml of gadobenate dimeglumine agent (MultiHance; Bracco Diagnostics, Princeton, NJ) was administered using an electronic injector into the right antecubital vein at 3 ml/sec followed by 20 ml of saline at 2 ml/sec. The last contrast-free frame was taken as the mask for subtraction of any background signal. 2D SENSE accelerations were typically performed using R_Y = 2 – 2.67 and R_Z = 2, yielding net acceleration factors R = 4 – 5.33. SENSE unfolding coefficients were obtained using a full resolution calibration scan consisting of a sagittal GRE pulse sequence with TR/TE 10/3 ms, flip angle = 10°, NEX = 1, and a bandwidth of ±31.25 kHz acquired prior to contrast injection and scaled by the sum of squares composite image of all coils. Acquisition parameters of in vivo studies are also given in Table 1.