J Magn Reson Imaging. 2025 Nov 28. doi: 10.1002/jmri.70176. Online ahead of print.
ABSTRACT
BACKGROUND: MRI contrast agents enhance lesion characterization by altering tissue relaxation properties. However, quantitative assessment of contrast enhancement is limited by variability in contrast administration parameters, and lack of efficient and precise contrast concentration independent relaxivity (r1, r2) measurement techniques. MR Fingerprinting (MRF) rapidly, simultaneously and accurately measures T1 and T2, enabling for the first time efficient clinical estimation of relaxivity ratios (r1/r2).
PURPOSE: To introduce an MRF-derived delta-relaxometry method for mapping contrast-specific relaxivity ratios (r1/r2) by accurately measuring ΔR1/ΔR2. We hypothesize that delta-relaxometry ratios offer dose-independent, reproducible measures of tissue enhancement, with potential advantages over conventional contrast-enhanced MRI.
STUDY TYPE: Prospective, observational.
POPULATION: Phantom studies and 29 patients (15 glioblastoma, 14 brain metastases).
FIELD STRENGTH/SEQUENCE: 3 T; pre- and post-contrast 3D whole-brain MR Fingerprinting.
ASSESSMENT: Mathematical derivations established a relationship between ΔR1/ΔR2 and r1/r2. Phantom studies assessed the concentration-dependency of ΔR1/ΔR2 compared to ΔT1 and ΔT2. Reproducibility was assessed by the inter-subject coefficient of variation (CoV). In vivo tumor type differentiation was assessed with whole-lesion histograms.
STATISTICAL TEST: Coefficient of variation; coefficient of determination; Mann-Whitney U tests with Benjamini-Hochberg correction.
RESULTS: ΔR1/ΔR2 is theoretically equivalent to r1/r2, showing contrast-dose independence in phantom studies. ΔR1/ΔR2 showed no dependence on injected dose or timing (p > 0.05), unlike ΔT1 and ΔT2. Delta-relaxometry ratios were highly reproducible, selectively elevated in tumors versus normal tissue, and showed a difference between tumor core and edema (p < 0.05). ΔR1/ΔR2 showed higher intra-subject reproducibility (median CoV: GBM = 27.3%, MET = 22.0%) as compared to ΔT1 (GBM = 57.1%, MET = 106.2%; p < 0.001). Whole-lesion histogram analysis of delta-relaxometry ratios demonstrated GBM versus metastasis differentiation (p < 0.05). “DATA” CONCLUSIONS: In this proof-of-concept study, MRF-derived ΔR1/ΔR2 ratios show potential for reproducible, clinically feasible, dose-independent relaxivity quantification. Delta-relaxometry ratios may offer a novel approach to tissue characterization with minimal background enhancement, distinct from perfusion imaging. Our results suggest delta-relaxometry as a tumor imaging marker worthy of further investigation.
EVIDENCE LEVEL: 3 (retrospective cohort study with imperfectly applied reference standard).
TECHNOLOGY EFFICACY: 1 (feasibility study with quantitative assessment, requires a comparison with standard of care).
PMID:41313583 | DOI:10.1002/jmri.70176
