Reproducibility of quantitative dynamic MRI of normal human tissues

Abstract

The aim of the study was to establish the normal range and to evaluate the reproducibility of dynamic contrast enhanced MRI (DCE-MRI) parameter estimates in normal human pelvic tissues. Nineteen patients with prostate cancer, undergoing androgen deprivation treatment, had paired DCE-MRI examinations of the pelvis using spoiled gradient-echo sequences. Quantitative enhancement parameters were calculated for each examination: transfer constant (K(trans)), leakage space (v(e)) and maximum contrast medium accumulation (MCMA) of pelvic muscles, bone marrow and fat. Descriptive and reproducibility statistics were calculated: within-patient standard deviation (wSD), repeatability and within-patient coefficient of variation (wCV). The femoral head and ischiorectal fat showed large numbers of non-enhancing pixels (81 and 88%, respectively). The ischial bone marrow had the highest values of kinetic parameter estimates (K(trans) 0.554 min(-1), v(e) 18.5% and MCMA 0.164 mmol/kg). Muscle parameters values were lower (K(trans) 0.126-0.137 min(-1), v(e) 10.6-11.5% and MCMA 0.077-0.086 mmol/kg). The mean difference between paired examinations was not significantly different from zero for any parameter. v(e) and MCMA had the lowest wCV (between 19 and 29%). For individuals, a log(10) K(trans) change of approximately 0.90 in muscles and 0.52 in the ischium would be statistically significant. The corresponding absolute changes for v(e) are 6.7% in muscle and 13.6% in the ischium. For a group of 19 patients, small changes are statistically significant (muscle log(10) K(trans) 0.208 and v(e) 1.5% and ischium log(10) K(trans) 0.123 and v(e) 3.1%). Fat and the femoral head are unreliable tissues from which to obtain kinetic parameter estimates due to poor enhancement. v(e) and MCMA have smaller coefficient of variation than K(trans) in muscles and ischium. Reproducibility studies of normal and pathological tissues should be incorporated into clinical research protocols that measure treatment effects by DCE-MRI techniques.