Magnetic resonance imaging system stability: Temporal variability in signal intensity, signal-to-noise, T 1 , and T 2 measurements on a 0.15-T resistive system

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Abstract
Signal intensity (SI) variability was evaluated on a 0.15-T resistive instrument using a phantom and was found to increase with time, repetition time (TR), and echo time (TE), ranging from 0.24% standard deviation (SD) over 34 min for 500/30 (TR/TE) images, to 2.1% SD over 5 days for 2000/30 images. Signal-to-noise (S/N) variability increased with time and TE but not TR and ranged from 4.2% SD over 34 min to 7.1% SD over 5 days in 500/30 images. Variability in T1 and T2 measurements on phantoms ranged from 1.8% to 4.8% SD for T1 and 3.6% to 6.5% SD for T2 in the biological range over 5 h. High reproducibility of SI, T1, and T2 measurements was demonstrated over a 6-week period in normal muscle measurements.