Repeatability and reproducibility of variable flip angle T₁ quantification in the prostate at 3 T

Background: Variable flip angle (VFA) imaging is widely used for the estimation of T₁ relaxation in the prostate, but may have limited repeatability and reproducibility due to its sensitivity to B₁ ⁺ inhomogeneity.

Purpose: To assess the repeatability and reproducibility of prostate T₁ estimation with and without compensating for B₁ ⁺ variation.

Study type: Prospective.

Population: Twenty-one volunteers were prospectively recruited and scanned twice on two 3 T MRI scanners, resulting in 84 VFA T₁ exams.

Field strength/sequence: 3 T/2D saturated turbo fast low angle shot (FLASH) and 3D dual-echo FLASH.

Assessment: Two B₁ ⁺ mapping techniques, including reference region VFA (RR-VFA) and saturated turbo FLASH (satTFL), were used for B₁ ⁺ correction, and T₁ maps with and without B₁ ⁺ correction were tested for intrascanner repeatability and interscanner reproducibility. Volumetric regions of interest (ROIs) were drawn on the transition zone, peripheral zone of the prostate, and the obturator internus left and right muscles in the corresponding slices.

Statistical tests: The average T₁ within each ROI for each scan was compared for both intra- and interscanner variability using concordance correlation coefficient and a Bland-Altman plot.

Results: Both RR-VFA-corrected T₁ and satTFL-corrected T₁ showed higher intra- and interscanner correlation (0.89/0.87 and 0.87/0.84, respectively) than VFA T₁ (0.84 and 0.74). Bland-Altman plots showed that VFA T₁ had wider 95% limits of agreement and a larger range of T₁ for each tissue compared with T₁ with B₁ ⁺ correction.

Data conclusion: The application of B₁ ⁺ correction (both RR-VFA and satTFL) to VFA T₁ results in more repeatable and reproducible T₁ estimation than VFA T₁ . This can potentially provide improved quantification of the prostate dynamic contrast-enhanced MRI parameters. Level of Evidence 1. Technical Efficacy Stage 1. J. Magn. Reson. Imaging 2018.