The Effect of Repetition Time on the Maximum Linear Relationship Between Contrast Agent Concentration and Signal Intensity on T1-Weighted Image Using Inversion Recovery (IR) Sequence

Background/objective: the relaxation time t1 depends on the concentration of paramagnetic contrast agent. to calculate perfusion parameters from dynamic contrast-enhanced mri acquisitions, measurement of the concentration is necessary. at low concentrations, the relationship between changes in 1/t1 and concentration can be considered to be linear. to maximize the concentration, and hence the signal to noise ratio (snr) in perfusion images, the range of this linearity should be known. this work studied the effect of two repetition times (tr) on the linearity using inversion recovery turbo fast low angle shot (turboflash) sequences at different effective inversion times (ti).patients and methods: to assess the relationship between signal intensity (si) and concentration, a water-filled phantom containing vials of different concentrations of gd-dtpa (0 to 19.77 mmol/l) was used. the mean si was obtained in the region of interest using t1- weighted images. coil non-uniformity was corrected on si. results: this study shows that an increase in tr is associated with a decrease in the maximum linear relationship between effective ti and concentration where the square correlation (r2) between corrected si and concentration were equal to 0.95 or 0.99. conclusion: in spite of tr = 2 or 3s and r2= 0.95 or 0.99 at a typical effective ti = 800ms, which is normally used for in vivo perfusion, the maximum linearity is about twice that previously reported (i.e. 0.8mmol/l) for measuring the perfusion parameters. the higher dose will improve the snr in perfusion images.