Arterial spin labeling in combination with a look-locker sampling strategy: inflow turbo-sampling EPI-FAIR (ITS-FAIR).
Arterial spin labeling (ASL) permits quantification of tissue perfusion without the use of MR contrast agents. With standard ASL techniques such as flow-sensitive alternating inversion recovery (FAIR) the signal from arterial blood is measured at a fixed inversion delay after magnetic labeling. As no image information is sampled during this delay, FAIR measurements are inefficient and time-consuming. In this work the FAIR preparation was combined with a Look-Locker acquisition to sample not one but a series of images after each labeling pulse. This new method allows monitoring of the temporal dynamics of blood inflow. To quantify perfusion, a theoretical model for the signal dynamics during the Look-Locker readout was developed and applied. Also, the imaging parameters of the new ITS-FAIR technique were optimized using an expression for the variance of the calculated perfusion. For the given scanner hardware the parameters were: temporal resolution 100 ms, 23 images, flip-angle 25.4 degrees. In a normal volunteer experiment with these parameters an average perfusion value of 48.2 +/- 12.1 ml/100 g/min was measured in the brain. With the ability to obtain ITS-FAIR time series with high temporal resolution arterial transit times in the range of -138 - 1054 ms were measured, where nonphysical negative values were found in voxels containing large vessels.
Günther
M
M
Deutsches Krebsforschungszentrum (DKFZ), Forschungsschwerpunkt Radiologische Diagnostik und Therapie (E0201), Heidelberg, Germany. m_s_guenther@yahoo.com
Bock
M
M
Schad
L R
LR
D000328:Adult; D002560:Cerebrovascular Circulation; D017352:Echo-Planar Imaging / Q000379:methods*; D006801:Humans; D010477:Perfusion; D012815:Signal Processing, Computer-Assisted; D013113:Spin Labels; D013997:Time Factors
D013113:Spin Labels