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Objective: To investigate the sensitivity of modified Look-Locker inversion recovery (MOLLI) to measure changes in dissolved oxygen (DO) concentrations in water samples and to calculate sequence-specific relaxivity (r 1m ) and limit of detection (LOD)., Materials and Methods: Ten water samples with a range of DO concentrations were scanned at 3 T using two variations of MOLLI schemes. Using linear regression the r 1 of DO was estimated from the measured DO concentrations and T 1 relaxation rates (R 1 ). The results were combined with previously reported values on in vivo stability measures of the MOLLI sequences and used to estimate a LOD., Results: DO concentrations ranged from 0.5 to 21.6 mg L -1 . A linear correlation between DO and R 1 was obtained with both MOLLI sequences, with an average correlation coefficient (R 2 ) 0.9 and an average estimated r 1 ([Formula: see text]) of 4.45 × 10 -3  s -1  mg -1  L. Estimated LOD was ≈ 10 mg L -1 ., Conclusion: MOLLI T 1 -mapping sequences may be used for detecting dissolved oxygen in vivo at 3 T with an [Formula: see text] in the range 4.18-4.8 × 10 -3  s -1  mg -1  L and a corresponding LOD for dissolved oxygen of approximately 10 mg L -1 . MOLLI-based T 1 mapping may be a useful non-invasive tool for quantification of in vivo changes of DO concentration during oxygen challenges.

Objective: To investigate the effects of a range of parameter settings on T 1 measurement stability in the portal vein using the T1-mapping sequences Look-Locker (LL) and Modified Look-Locker inversion recovery (MOLLI)., Materials and Methods: Ten different versions of LL and MOLLI sequences were tested and compared to a reference sequence provided by the MR manufacturer. Ten healthy volunteers were imaged multiple times on two separate scan days at 3T. The mean T 1 values and coefficient of variation (CoV) were calculated for each of the ten sequences and compared to the reference sequence., Results: Six of the tested sequences had T 1 values close to the reference sequence; among those, three sequences achieved lower CoV than the reference sequence. Lowest CoV was achieved using a non-triggered LL sequence with 5 beat readout and a 45 o flip angle (mean T 1 1733 ms ± 89 ms, CoV 1.3% ± 0.58%)., Conclusion: T 1 -measurements in the hepatic portal vein can be performed with high precision using either MOLLI or LL sequences provided that LL sampling duration is sufficiently long and flip angle sufficiently high. The advantage of constant timing outweighed the advantage of ECG-triggering.