Determining the longitudinal accuracy and reproducibility of T<sub>1</sub> and T<sub>2</sub> in a 3T MRI scanner
Madeline Carr, Kathryn E. Keenan, Robba Rai, Peter Metcalfe, Amy Walker, Lois Holloway
Abstract
Abstract Purpose To determine baseline accuracy and reproducibility of T 1 and T 2 relaxation times over 12 months on a dedicated radiotherapy MRI scanner. Methods An International Society of Magnetic Resonance in Medicine/National Institute of Standards and Technology (ISMRM/NIST) System Phantom was scanned monthly on a 3T MRI scanner for 1 year. T 1 was measured using inversion recovery (T 1 ‐IR) and variable flip angle (T 1 ‐VFA) sequences and T 2 was measured using a multi‐echo spin echo (T 2 ‐SE) sequence. For each vial in the phantom, accuracy errors (%bias) were determined by the relative differences in measured T 1 and T 2 times compared to reference values. Reproducibility was measured by the coefficient of variation (CV) of T 1 and T 2 measurements across monthly scans. Accuracy and reproducibility were mainly assessed on vials with relaxation times expected to be in physiological ranges at 3T. Results A strong linear correlation between measured and reference relaxation times was found for all sequences tested ( R 2 > 0.997). Baseline bias (and CV[%]) for T 1 ‐IR, T 1 ‐VFA and T 2 ‐SE sequences were +2.0% (2.1), +6.5% (4.2), and +8.5% (1.9), respectively. Conclusions The accuracy and reproducibility of T 1 and T 2 on the scanner were considered sufficient for the sequences tested. No longitudinal trends of variation were deduced, suggesting less frequent measurements are required following the establishment of baselines.