MRI of hyperpolarised gases is usually performed with fast data acquisition to achieve high spatial resolutions despite rapid diffusion-induced signal attenuation.We describe a double-cross k-space sampling scheme suitable for Slow Low Angle SHot (SLASH) acquisition and yielding an increased SNR. It consists of a series of anisotropic partial acquisitions with a reduced resolution in the read direction, which alleviates signal attenuation and still provides a high isotropic resolution. The advantages of SLASH imaging over conventional FLASH imaging are evaluated analytically, using numerical lattice calculations, and experimentally in phantom cells filled with hyperpolarised 3He–N2 gas mixtures. Low-field MRI is performed (here 2.7 mT), a necessary condition to obtain long T2* values in lungs for slow acquisition. Two additional benefits of the SLASH scheme over FLASH imaging have been demonstrated: it is less sensitive to the artefacts due to concomitant gradients and it allows measuring apparent diffusion coefficients for an extended range of times.

In low field nuclear magnetic resonance (NMR) it is desirable to combine proper characteristics of the detection scheme with a good signal to noise ratio. For example, a reduced coupling between the sample and the detection coil is needed for NMR with highly magnetized samples and a large bandwidth is required in magnetic resonance imaging (MRI). We discuss a solution based on a simple active feedback circuit that preserves the signal to noise ratio as opposed to traditional solutions which do not. We give illustrations of its use in experiments on low temperature hyperpolarized liquid ³He-⁴He mixtures and in hyperpolarized ³He gas MRI.