The conventional arterial spin labeling (ASL) method measures blood perfusion by the subtraction of tag and control. The pseudo-continuous arterial spin labeling (PCASL) method offers higher SNR than pulsed ASL (PASL) by a fitting algorithm or a sinusoidal demodulation. However, PCASL method does not provide robust perfusion values in the physiological unit because the tagging efficiency of PCASL can be significantly modulated by both gradient imperfections and the presence of off-resonance fields at the tagged vessels.
UC San Diego researchers have developed a novel multi-phase (more than two) pseudo-continuous arterial spin labeling (MP-PCASL) method for MRI to remedy the problems encountered by the conventional ASL methods. MP-PCASL provides consistent tagging efficiency resulting in more robust and accurate blood perfusion quantification than the conventional 2-phase (2P) PCASL. The tagging efficiency is enhanced by using algorithms to derive an estimate from the MP-PCASL to correct the errors in the phase tracking. A short scan is performed first using MP-PCASL to obtain error correction estimation, followed by 2P-PCASL with phase errors corrected using the estimate. Secondly, the different phase errors across blood vessels are compensated by adding small XY shim gradient during labeling.
The conventional 2P-PCASL can be optimized for the applications listed above because MP-PCASL provides:
Imaging studies of human subjects demonstrated that MP-PSCAL method provides more robust cerebral blood flow values than the conventional PCASL method and higher SNR than FAIR ASL. For fMRI, a uniform and near-optimal tagging efficiency across all tagged vessels can be achievable and comparison of the visual activation in one female subject across different ASL methods shows that the optimized MP-PCASL provides higher tSNR than PICORE ASL.
Patent application filed.
|United States Of America||Issued Patent||9,084,554||07/21/2015||2009-264|