Combined parallel and partial fourier MR reconstruction for accelerated 8‐channel hyperpolarized carbon‐13 in vivo magnetic resonance Spectroscopic imaging (MRSI)

Abstract

Purpose To implement and evaluate combined parallel magnetic resonance imaging (MRI) and partial Fourier acquisition and reconstruction for rapid hyperpolarized carbon-13 (13C) spectroscopic imaging. Short acquisition times mitigate hyperpolarized signal losses that occur due to T1 decay, metabolism, and radiofrequency (RF) saturation. Human applications additionally require rapid imaging to permit breath-holding and to minimize the effects of physiologic motion. Materials and Methods Numerical simulations were employed to validate and characterize the reconstruction. In vivo MR spectroscopic images were obtained from a rat following injection of hyperpolarized 13C pyruvate using an 8-channel array of carbon-tuned receive elements. Results For small spectroscopic matrix sizes, combined parallel imaging and partial Fourier undersampling resulted primarily in decreased spatial resolution, with relatively less visible spatial aliasing. Parallel reconstruction qualitatively restored lost image detail, although some pixel spectra had persistent numerical error. With this technique, a 30 × 10 × 16 matrix of 4800 3D MR spectroscopy imaging voxels from a whole rat with isotropic 8 mm3 resolution was acquired within 11 seconds. Conclusion Parallel MRI and partial Fourier acquisitions can provide the shorter imaging times and wider spatial coverage that will be necessary as hyperpolarized 13C techniques move toward human clinical applications.

Development and testing of hyperpolarized 13C MR calibrationless parallel imaging

“…For 13 C receive, an 8-channel array coil was used with 2 sets of four coil elements in a linear arrangement as shown in Fig. 1(a) [24,25]. Each rectangular element was approximately 5 × 10 cm and adjacent elements were overlapped to minimize mutual inductance.…”

“…Each rectangular element was approximately 5 × 10 cm and adjacent elements were overlapped to minimize mutual inductance. The total length of each panel was around 18 cm [24]. …”

Pulse Sequences for Hyperpolarized MRS

“…Example of parallel imaging MRSI results with HP [1-13 C]-pyruvate in a normal rat 57. (a) The k-space undersampling pattern includes acceleration by skipping every other phase encode in k x , a partial Fourier acquisition where half of k-space was not acquired, and a fully-sampled 6 × 6 center of k-space for an autocalibrated SENSE reconstruction.…”

The Need and Initial Practice of Parallel Imaging and Compressed Sensing in Hyperpolarized 13C MRI in vivo

“…Ohliger et al [30] took the use of SENSE reconstruction by using partial Fourier to compensate for the time needed to acquire extra calibration lines to accurately perform the reconstruction. Furthermore, the experiments were similar in setup to the ones performed in Tropp et al, but with the use of an 8-channel receive array, which allowed for acceleration factors of up to 3.75.…”

“…As a final note, for our own HP studies with the bSSFP sequence on a 3T clinical scanner, the use of either a SAKE reconstruction as in Feng et al [33] or the combination of partial Fourier and SENSE as in Ohliger et al [30] would be good first attempts to demonstrate the feasibility of using parallel imaging with this particular sequence. The results can be compared to the current compressed sensing implementation [40] in terms of SNR, spatial resolution, and dynamic acquisition capabilities.…”