Determining the longitudinal accuracy and reproducibility of T₁ and T₂ in a 3T MRI scanner

Abstract

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.

Conformance of a 3T radiotherapy MRI scanner to the QIBA Diffusion Profile

“…Saturation was mainly investigated due to past studies completed on the same MRI scanner having identified similar effects when undertaking phantom imaging. 26 Further investigations, out of the scope of this study, would be required to find the cause and factors affecting the signal saturation.…”

“…This effect is not easy to detect: in the offline computed ADC maps, saturation was found to primarily affect the SDs derived from the DWI‐ADC fit, while minimally impacting the actual ADC value. Saturation was mainly investigated due to past studies completed on the same MRI scanner having identified similar effects when undertaking phantom imaging 26 . Further investigations, out of the scope of this study, would be required to find the cause and factors affecting the signal saturation.…”

Quantitative Relaxometry Metrics for Brain Metastases Compared to Normal Tissues: A Pilot MR Fingerprinting Study

“…T1 and T2 mapping, for example, are indexes that determine free water content [ 18 ] and tissue morphology [ 19 ], respectively. Though they have shown potential for the determination of early tumor progression in the brain [ 20 ], long MRI acquisition times and limits of one acquisition per quantitative map [ 21 , 22 , 23 ] have prevented the day-to-day adoption of conventional quantitative relaxometry in clinical practice.…”

T1 relaxation time of ISMRM/NIST T1 phantom spheres at 7 T

“…The International Society for Magnetic Resonance in Medicine (ISMRM) and the National Institute of Standards and Technology (NIST) developed a calibration phantom, 1,2 consisting of 14 spheres filled with nickel chloride (NiCl 2 ) solutions of various concentrations, that has been used to validate T1 mapping techniques, as well as for reproducibility comparisons across platforms and sites. The T1 relaxation times of the 14 T1 spheres carefully measured by NMR are available from the NIST to serve as reference or ground truth T1 values at a range of temperatures for 1.5 and 3 T. 2 The ISMRM/NIST system phantom has thus demonstrated its utility in a large body of research at 1.5 and 3 T for the validation of quantitative methods and assessment of multivendor and multisite repeatability (see 1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16] and the references therein). However, the reference T1 values at 7 T are not available from the NIST.…”

“…The T1 relaxation times of the 14 T1 spheres carefully measured by NMR are available from the NIST to serve as reference or ground truth T1 values at a range of temperatures for 1.5 and 3 T 2 . The ISMRM/NIST system phantom has thus demonstrated its utility in a large body of research at 1.5 and 3 T for the validation of quantitative methods and assessment of multivendor and multisite repeatability (see 1,3–16 and the references therein). However, the reference T1 values at 7 T are not available from the NIST.…”