Slice Profile Effects Research Articles

Spoiled gradient-echo as an arterial spin tagging technique for quick evaluation of local perfusion.

To introduce a simple gradient-echo arterial spin tagging (GREAST) technique available for most commercial magnetic resonance (MR) systems, for a quick evaluation of tissue perfusion. The GREAST technique uses a combination of a short TR spoiled gradient-echo (SPGR) sequence with a selective presaturation radio frequency (RF) pulse that allows acquiring each tagged and control image within 10-20 seconds. The phantom and human studies were performed for evaluating the feasibility in measurement of local perfusion and the efficacy in alleviation of the asymmetric magnetization transfer (MT) and slice profile effects. Results show a good linear relationship between the signal attenuation caused by the presaturation pulse and flow rates in the phantom experiment and effective alleviation of the asymmetric MT and slice profile effects for various orientations of imaging slices. Human studies showed good perfusion results in brain imaging. Perfusion imaging on the liver and kidney were also conducted. The results could be significantly improved by effectively lessening motion-related artifacts. The GREAST technique is simple, easy to use, and applicable to examine local perfusion of the brain and other organs in the trunk.

Slice profile effects in adiabatic inversion: application to multislice perfusion imaging.

Imperfections in the slice profile of the adiabatic inversion induced by relaxation effects are shown to cause signal variations in pulsed arterial tagging schemes on the order of magnitude of perfusion changes, and result in gross errors in perfusion quantitation. Significant improvement can be made with minor modifications to the inversion pulse which facilitate the acquisition of quantitative, multislice perfusion images, as demonstrated in both a phantom and a normal human volunteer.

Rapid measurement of T1 with spatially selective pre‐inversion pulses

A method is described for rapidly obtaining a multipoint estimate of T1 from a sample that is homogeneous over a few millimeters. An image of the longitudinal recovery curve is produced through the application of successive "pre-inversion" slices that are perpendicular to the imaging slice. These pre-inversion pulses are analogous to pre-saturation pulses, but they are much thinner and the tip angle is 180 degrees. The baseline for the recovery is measured from sections of the sample that have not been perturbed by the slice selective pre-inversion pulses. The existence of the baseline value and the lack of slice profile effects allows a quick T1 estimate (QT1) to be made with a simple linear regression algorithm. The QT1 values are found to correlate very well with T1 values measured with the scanner in "spectrometer' mode, for volumes as small as 5 x 5 x 5 mm. Possible applications are T1 estimates in homogeneous samples and tissues, and scouting the T1 range of a tissue to be measured with higher resolution volume localization techniques.

Slice profile effects and their calibration and correction in quantitative NMR imaging

The signal values extracted from an NMR image matrix depend upon the NMR properties of the sample material, i.e. the proton density and relaxation times T1 and T2, and also upon various instrument parameters, one such being the slice shape. It is a common approximation to assume an ideal slice profile: one that is perfectly rectangular and invariant in shape for all applications, but in practice real slice profiles are neither. In this study the effect of the slice is included in signal intensity calculations by means of a computer simulation. Comparison is made between these slice-corrected values and values calculated on the basis of an ideal slice. Four pulse sequences are examined: saturation recovery, inversion recovery, spin echo and inversion recovery followed by spin echo.