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

Objectives: To assess the accuracy, repeatability, and reproducibility of T and T 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 linearity to the reference values (R > 0.99), repeatability (CV < 3%), and reproducibility (CV < 3%) with lower linearity (R > 0.98), repeatability (CV < 6%), and reproducibility (CV ≤ 4%) for T measurement. The volunteer study demonstrated high T 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 measurement (wCV < 8%). In CSF measurement, dictionaries with a smaller range showed a seemingly better reproducibility (T, wCV 3%; T, wCV 8%) than the much wider range dictionary (T, wCV 5%; T, 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 and moderate for T 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.