Accuracy, repeatability, and reproducibility of T 1 and T 2 relaxation times measurement by 3D magnetic resonance fingerprinting with different dictionary resolutions

Objectives To assess the accuracy, repeatability, and reproducibility of T 1 and T 2 relaxation time measurements by three-dimensional magnetic resonance fingerprinting (3D MRF) using various dictionary resolutions. Methods The ISMRM/NIST phantom was scanned daily for 10 days in two 3 T MR scanners using a 3D MRF sequence reconstructed using four dictionaries with varying step sizes and one dictionary with wider ranges. Thirty-nine healthy volunteers were enrolled: 20 subjects underwent whole-brain MRF scans in both scanners and the rest in one scanner. ROI/VOI analyses were performed on phantom and brain MRF maps. Accuracy, repeatability, and reproducibility metrics were calculated. Results In the phantom study, all dictionaries showed high T 1 linearity to the reference values ( R 2 > 0.99), repeatability (CV < 3%), and reproducibility (CV < 3%) with lower linearity ( R 2 > 0.98), repeatability (CV < 6%), and reproducibility (CV ≤ 4%) for T 2 measurement. The volunteer study demonstrated high T 1 reproducibility of within-subject CV (wCV) < 4% by all dictionaries with the same ranges, both in the brain parenchyma and CSF. Yet, reproducibility was moderate for T 2 measurement (wCV < 8%). In CSF measurement, dictionaries with a smaller range showed a seemingly better reproducibility (T 1 , wCV 3%; T 2 , wCV 8%) than the much wider range dictionary (T 1 , wCV 5%; T 2 , wCV 13%). Truncated CSF relaxometry values were evident in smaller range dictionaries. Conclusions The accuracy, repeatability, and reproducibility of 3D MRF across various dictionary resolutions were high for T 1 and moderate for T 2 measurements. A lower-resolution dictionary with a well-defined range may be adequate, thus significantly reducing the computational load. Key Points • A lower-resolution dictionary with a well-defined range may be sufficient for 3D MRF reconstruction. • CSF relaxation times might be underestimated due to truncation by the upper dictionary range. • Dictionary with a higher upper range might be advisable, especially for CSF evaluation and elderly subjects whose perivascular spaces are more prominent.