Benefit of T1 reduction for magnetic resonance coronary angiography: A numerical simulation and phantom study

Contrast agents have dramatically improved magnetic resonance angiography ( MRA) of the abdominal and peripheral arteries. The imaging technique for th ese applications is usually a steady-state acquisition, for which the relat ionship between T1 in blood and the MR signal is well known. However, in el ectrocardiography-triggered angiography with limited acquisition windows, t his relationship is more complex. Therefore the purpose of this work is to define the relationship between the T1 in blood and the MR signal amplitude in three-dimensional magnetic resonance coronary angiography (3D-MRCA), Si mulations were performed using equations describing the MR signal in both s teady-state and triggered acquisition schemes. Triggered acquisition scheme s use flip-angle sweeps to maintain a constant signal during the acquisitio n. In this study, the effect of the flip angle sweep was calculated as a fu nction of T1, The results show that the effect of T1 shortening in contrast -enhanced 3D-MRCA differs substantially from that in conventional contrast- enhanced MRA. The triggered acquisition allows unsaturated blood to enter t he volume between the acquisitions and thereby gives a much higher signal a t long T1s than does steady-state acquisition. Therefore, to gain a benefit in signal amplitude with contrast agents for 3D-MRCA using gradient-echo s equences, the T1 in blood may have to be as low as 50 msec, In addition, wh en using a prepulse to null myocardium, the results indicate the need for a large difference in T1 between blood and myocardium to avoid signal loss i n blood. J. Magn, Reson, Imaging 1999;9:552-556, (C) 1999 Wiley-Liss, Inc.