Nobuyasu Ichinose

Magnitude subtraction vs. complex subtraction in dynamic contrast-enhanced 3D-MR angiography: Basic experiments and clinical evaluation†

Magnitude subtraction and complex subtraction in dynamic contrast‐enhanced three‐dimensional magnetic resonance (3D‐MR) angiography were compared using a phantom and 23 human subjects. In phantom studies, complex subtraction showed far better performance than magnitude subtraction, especially for longer echo times, with thicker slices, and without fat suppression. With complex subtraction, non‐fat‐suppressed studies showed contrast‐to‐noise ratios comparable to those in fat‐suppressed studies. In human subjects, complex subtraction was superior to magnitude subtraction in 9 subjects, but comparable to magnitude subtraction in 14 subjects. There were no cases in which magnitude subtraction was superior to complex subtraction. Although the differences observed in human studies when complex subtraction was applied with thinner slices, shorter echo times, and the fat‐suppression technique were not as pronounced as those seen in phantom studies, complex subtraction should be performed in dynamic contrast‐enhanced 3D‐MR angiography because there are no drawbacks in complex subtraction. Further research is necessary to assess the feasibility of dynamic contrast‐enhanced 3D‐MR angiography without fat suppression in human subjects using complex subtraction, as suggested by the results of phantom studies. If it is found to be feasible, dynamic contrast‐enhanced 3D‐MR angiography without fat suppression using complex subtraction may prove to be a robust technique that eliminates the need for shimming and can reduce the acquisition time. J. Magn. Reson. Imaging 1999;10:813–820.

2111 Recent progress on non-contrast-enhanced MRA techniques

Methods All experiments were performed on 1.5-T clinical imagers. A flow-spoiled fresh blood imaging (FS-FBI) technique, ECG-gated 3D partial Fourier FSE, allows separation of arteries from veins by applying appropriate flow spoiling gradient pulses in the read-out (RO) direction. To find suitable ECG delay time, ECG-prep scan, single-slice multiple phases, is applied to acquire single shot images with different ECG delay times. The application of the ECGprep technique can be used as non-contrast time-resolved MRA like images by acquiring multiple phases across small incremental trigger delay times during the period of steep signal changes from systolic to diastolic phase. The renal artery examinations using non-contrast MRA techniques are a must for patients with renal insufficiency and vascular disease. In order to depict the multiple directional vasculatures of renal arteries, respiratory-gated balanced SSFP with an arterial spin labeling (time-spatial labeling inversion pulse; time-SLIP) technique was applied to gain superior in-flow effect using an axial scan. The marked blood by the time-SLIP traveled from the aorta to renal branches was acquired using balanced SSFP readout. The time-SLIP pulse was optimized to have good contrast between blood and background cortex and medulla. An inferior sat-band pulse was placed to eliminate venous flow.