Very-low-field MRI of laser polarized xenon-129.

Abstract We describe a homebuilt MRI system for imaging laser-polarized xenon-129 at a very low holding field of 2.2 mT. A unique feature of this system was the use of Maxwell coils oriented at so-called “magic angles” to generate the transverse magnetic field gradients, which provided a simple alternative to Golay coils. We used this system to image a laser-polarized xenon-129 phantom with both a conventional gradient-echo and a fully phase-encoded pulse sequence. In other contexts, a fully phase-encoded acquisition, also known as single-point or constant-time imaging, has been used to enable distortion-free imaging of short- T 2 ∗ species. Here we used this technique to overcome imperfections associated with our homebuilt MRI system while also taking full advantage of the long T 2 ∗ available at very low field. Our results demonstrate that xenon-129 image quality can be dramatically improved at low field by combining a fully phase-encoded k -space acquisition with auxiliary measurements of system imperfections including B 0 field drift and gradient infidelity.