(A) study on high speed angiography using nuclear magnetic resonance imaging

Abstract

New fast 2-D projection and 3-D MR angiography methods have been proposed and experimental results are presented. For the projection MR angiography, a new method of suppressing the static sample signal using a composite [90$^\circ$-$\tau$ -180$^\circ$-2$\tau$ -180$^\circ$-$\tau$] sequence is proposed. The suppression characteristic of the proposed sequence is found to be relatively independent from the T1, T2 values and RF field inhomogeneity. The resulting static signal suppression factor was in the order of $10^{-4}$ to $10^{-6}$ . While the signal of fresh in-flow spins using the composite [90$^\circ$-$\tau$ -180$^\circ$-2$\tau$ -180$^\circ$-$\tau$] sequence was not attenuated and found to be comparable to that of the signal obtainable from the conventional spin echo sequence. Using this technique, we have proposed a new projection MR angiography technique and experimental study was carried out. A block line scan method, a variant of the line scan method, is incorporated with the composite sequence to perform the projection angiography. The resulting images demonstrated high contrast of vessel over the other large static backgrounds without the artefacts or misregistration. For the 3-D MR angiography, a fast 2-D scanning method using 90$^\circ$ SSFP sequence is proposed. This method simply uses the 90$^\circ$ RF flip angle SSFP sequences with a thin (1.2mm) slice selection for the suppression of the static signal. The suppression factor of this 3-D scanning scheme is not as good as the former block line scanning method, but it is sufficient for angiographic application when the maximum ray tracing algorithm is incorporated. Advantages of the proposed methods are, among others, the arbitrary viewing capability of the 3-D image and arbitrary size volume selection capability that will save the total imaging time. In addition, both methods proposed for the angiography do not use the subtraction method. Therefore, they are free from the eddy current effect. The s...