Signal-to-noise ratio, T₂ , and T2* for hyperpolarized helium-3 MRI of the human lung at three magnetic field strengths

Purpose: To evaluate T₂ , T2*, and signal-to-noise ratio (SNR) for hyperpolarized helium-3 (³ He) MRI of the human lung at three magnetic field strengths ranging from 0.43T to 1.5T.

Methods: Sixteen healthy volunteers were imaged using a commercial whole body scanner at 0.43T, 0.79T, and 1.5T. Whole-lung T₂ values were calculated from a Carr-Purcell-Meiboom-Gill spin-echo-train acquisition. T2* 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 ³ He dose.

Results: As expected, T₂ and T2* values demonstrated a significant inverse relationship to field strength. Hyperpolarized ³ He 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.

Conclusions: Hyperpolarized ³ He 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 T₂ and T2* values may be advantageous for optimizing pulse sequences inherently sensitive to such effects. The three-fold increase in T2* 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. © 2016 International Society for Magnetic Resonance in Medicine.