Quantification of gadolinium-DTPA concentrations for different inversion times using an IR-turbo flash pulse sequence: a study on optimizing multislice perfusion imaging.

The purpose of this study was to optimize an inversion-recovery (IR) turbo fast low-angle shot (FLASH) for multislice imaging by evaluating the accuracy of calculated the relaxation-rate (R1) for different inversion times (TI). This is important for tracer kinetic modeling because it requires a system responding linearly to input. R1 are linearly related to changes in the concentration of gadolinium (Gd)-diethylenetriaminepentaacetic acid (DTPA), and R1 is a parameter that can be derived from the magnetic resonance (MR) signal. The accuracy of calculated R1 using an IR turbo fast low-angle shot was evaluated in phantoms and for increasing TIs using spectroscopically measured R1 values as reference. Signal curves, obtained in vivo after a bolus injection of Gd-DTPA, were used in an analytical computer program to study the effect of different TI-values on accurate calculation of R1. Results show that TIeff should be <200 ms to measure the bolus-passage of Gd-DTPA in blood accurately, whereas the myocardial response can be measured correctly for TIeff < 870 ms at 1.5 T. The initial slope of the myocardial signal enhancement curve becomes steeper for larger TI values, whereas the calculated R1 curves were similar, indicating that these curves, rather than signal curves, are more suitable even for qualitative perfusion evaluation. It is concluded that the results can be incorporated in a multislice IR turbo fast low-angle shot using the first slice (with a short TI) for assessment of both the arterial input function and the tissue response and the second slice in another position for assessment of the tissue response alone.