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Most MR angiography (MRA) techniques use macroscopic blood motion to characterize the flowing spins. A different approach is represented by the use of contrast enhancement of blood pooling agents. The intravenous injection of one of these agents, namely Gd-DTPA polylysine, produces a shortening of the blood T1 below the T1 values of fat and soft tissues. In this study on experimental MRA in rabbits, we used an imaging sequence with a 90 degrees saturation pulse and a 180 degrees inversion recovery pulse. Both the saturation and inversion recovery times were adjusted to suppress the signals of soft tissues and fat. The remaining ultrashort T1 blood was imaged with a projective velocity refocused spin echo or gradient echo sequence. Magnetic resonance angiography provided excellent vessel detail with a 30-60 s acquisition time. In addition, there was no need for further processing after image acquisition because the projection was obtained immediately. The disadvantages of the technique are the need for contrast medium injection and the nonselectivity of MRA.
Marchal et al. (Mon,) studied this question.