Dual-relaxation, temporally-constrained, dynamic contrast-enhanced MRI using inversion recovery TrueFISP

Introduction: Inversion recovery (IR) TrueFISP imaging sequences have recently been used to acquire dynamic contrast enhanced (DCE) MRI data due to their short acquisition time, sensitivity to changes in tissue longitudinal relaxation times and superior signal-to-noise characteristics [1]. Use of an inversion recovery preparation offers the ability to quantify relaxation time changes at each dynamic time point, thereby improving the accuracy of the subsequent pharmacokinetic analysis, albeit at the expense of temporal resolution. However, the signal intensity of such sequences is also sensitive to transverse relaxation (T2=1/R2). In the novel analysis approach outlined in this study, T2 relaxation changes induced by Gd-DTPA are estimated in addition to T1 changes, using data acquired with an IRTrueFISP sequence. Furthermore, data analysis is undertaken using a maximum likelihood approach that 1) undertakes pharmacokinetic modelling on an entire dynamic, multiple-inversion time dataset (8 inversion times and 75 time points), thereby providing temporal constraint within the T1 and T2 estimation, 2) incorporates a high signal-to-noise, 20 inversion time reference IR-TrueFISP acquisition for accurate native T1 and T2 estimation and 3) takes into account the Rician noise distribution associated with magnitude MR data [2]. A pilot study to evaluate the approach is described here, using orthotopic PC3 prostate tumours. Background Theory: Data Model: The signal intensity, S, given by an IR-TrueFISP sequence is given by ) 1 ( ) , | ( * / 2 1 1 T TI stst INVe S T T TI S − − = [3] where TI is the inversion time. A