BACKGROUND SUPPRESSION WITH MULTIPLE INVERSION-RECOVERY NULLING - APPLICATIONS TO PROJECTIVE ANGIOGRAPHY

We have developed a technique to accurately null the longitudinal magn etization (M-z) of background material. This suppression involves firs t saturating the longitudinal magnetization (M-z) of a region, and the n applying several nonselective inversions. The inversions are timed r elative to the saturation such that M-z is nulled across a broad range of T-1 at a predetermined time after the initial saturation, B-1 and B-0 inhomogeneity, which could lead to inaccurate suppression, are dea lt with by the combination of a multiple tip saturation sequence and f our adiabatic inversion pulses. The suppression sequence can be used t o form projective angiograms by selectively tagging the imaging region with the saturation pulse. After the inversions are played out, a pro jection taken through the tag region when M-z is nulled will only cont ain signal from blood that has flown into the region after the saturat ion. Since only two dimensions are acquired, the technique can acquire gated projection angiograms in reasonable scan times. Representative inflow MIR angiograms of the carotid arteries and renal arteries show excellent background suppression.