Signal-To-Noise Ratio, T-2, And T-2* For Hyperpolarized Helium-3 Mri Of The Human Lung At Three Magnetic Field Strengths

PurposeTo evaluate T-2, T-2*, and signal-to-noise ratio (SNR) for hyperpolarized helium-3 (He-3) MRI of the human lung at three magnetic field strengths ranging from 0.43T to 1.5T.MethodsSixteen healthy volunteers were imaged using a commercial whole body scanner at 0.43T, 0.79T, and 1.5T. Whole-lung T-2 values were calculated from a Carr-Purcell-Meiboom-Gill spin-echo-train acquisition. T-2* maps and SNR were determined from dual-echo and single-echo gradient-echo images, respectively. Mean whole-lung SNR values were normalized by ventilated lung volume and administered He-3 dose.ResultsAs expected, T-2 and T-2* values demonstrated a significant inverse relationship to field strength. Hyperpolarized He-3 images acquired at all three field strengths had comparable SNR values and thus appeared visually very similar. Nonetheless, the relatively small SNR differences among field strengths were statistically significant.ConclusionsHyperpolarized He-3 images of the human lung with similar image quality were obtained at three field strengths ranging from 0.43T and 1.5T. The decrease in susceptibility effects at lower fields that are reflected in longer T-2 and T-2* values may be advantageous for optimizing pulse sequences inherently sensitive to such effects. The three-fold increase in T-2* at lower field strength would allow lower receiver bandwidths, providing a concomitant decrease in noise and relative increase in SNR. Magn Reson Med 78:1458-1463, 2017. (c) 2016 International Society for Magnetic Resonance in Medicine.