Comparison of test-retest repeatability of DESPOT and 3D-QALAS for T₁ and T₂ mapping

Relaxometry, specifically T₁ and T₂ mapping, has become an essential technique for assessing the properties of biological tissues related to various physiological and pathological conditions. Many techniques are being used to estimate T₁ and T₂ relaxation times, ranging from the traditional inversion or saturation recovery and spin-echo sequences to more advanced methods. Choosing the appropriate method for a specific application is critical since the precision and accuracy of T₁ and T₂ measurements are influenced by a variety of factors including the pulse sequence and its parameters, the inherent properties of the tissue being examined, the magnetic resonance imaging (MRI) hardware, and the image reconstruction. The aim of this cohort study is to evaluate and compare the test-retest repeatability of two advanced MRI relaxometry techniques: Driven Equilibrium Single Pulse Observation of T₁ and T₂ (DESPOT), and three-dimensional Quantification using an interleaved Look-Locker acquisition Sequence with a T₂ preparation pulse (3D-QALAS), for T₁ and T₂ mapping in a healthy volunteer cohort.

Ten healthy volunteers underwent brain MRI at 1.3 mm³ isotropic resolution, acquiring DESPOT and 3D-QALAS data (~11.8 and ~5 min duration, including field maps, respectively), test-retest with subject repositioning, on a 3.0 Tesla Philips Ingenia Elition scanner. To reconstruct the T₁ and T₂ maps, we used an equation-based algorithm for DESPOT and a dictionary-based algorithm that incorporates inversion efficiency and B1-field inhomogeneity for 3D-QALAS. The test-retest repeatability of this cohort study was assessed using the coefficient of variation (CoV), intraclass correlation coefficient (ICC) and Bland-Altman plots.

Our results indicate that both the DESPOT and 3D-QALAS techniques demonstrate good levels of test-retest repeatability for T₁ and T₂ mapping across the brain. Higher whole-brain voxel-to-voxel ICCs are observed in 3D-QALAS for T₁ (0.84±0.039) and in DESPOT for T₂ (0.897±0.029). The Bland-Altman plots show smaller bias and variability of T₁ estimates for 3D-QALAS (mean of -0.02 s, and upper and lower limits of -0.14 and 0.11 s, 95% confidence interval) than for DESPOT (mean of -0.02 s, and limits of -0.31 and 0.27 s). 3D-QALAS also showed less variability (mean 1.08 ms, limits -1.88 to 4.04 ms) for T₂ compared to DESPOT (mean of 2.56 ms, and limits -17.29 to 22.41 ms). The within-subject CoVs for 3D-QALAS range from 0.6% [T₂ in cerebrospinal fluid (CSF)] to 5.8% [T₂ in gray matter (GM)], while for DESPOT they range from 2.1% (T₂ in CSF) to 6.7% (T₂ in GM). The between-subject CoVs for 3D-QALAS range from 2.5% (T₂ in GM) to 12% (T₂ in CSF), and for DESPOT they range from 3.7% [T₂ in white matter (WM)] to 9.3% (T₂ in CSF).

Overall, 3D-QALAS demonstrated better repeatability for T₁ and T₂ measurements than DESPOT, in addition to reduced acquisition time.