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 TI_eff should be <200 ms to measure the bolus-passage of Gd-DTPA in blood accurately, whereas the myocardial response can be measured correctly for TI_eff < 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.