Determining the longitudinal accuracy and reproducibility of T and T in a 3T MRI scanner.

PURPOSE

To determine baseline accuracy and reproducibility of T and T 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 was measured using inversion recovery (T -IR) and variable flip angle (T -VFA) sequences and T was measured using a multi-echo spin echo (T -SE) sequence. For each vial in the phantom, accuracy errors (%bias) were determined by the relative differences in measured T and T times compared to reference values. Reproducibility was measured by the coefficient of variation (CV) of T and T 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 > 0.997). Baseline bias (and CV[%]) for T -IR, T -VFA and T -SE sequences were +2.0% (2.1), +6.5% (4.2), and +8.5% (1.9), respectively.

CONCLUSIONS

The accuracy and reproducibility of T and T 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.