Compressive sensing could accelerate 1H MR metabolic imaging in the clinic

Abstract

Purpose: To retrospectively evaluate the fidelity of magnetic resonance (MR) spectroscopic imaging data preservation at a range of accelerations by using compressed sensing.

Materials and methods: The protocols were approved by the institutional review board of the university, and written informed consent to acquire and analyze MR spectroscopic imaging data was obtained from the subjects prior to the acquisitions. This study was HIPAA compliant. Retrospective application of compressed sensing was performed on 10 clinical MR spectroscopic imaging data sets, yielding 600 voxels from six normal brain data sets, 163 voxels from two brain tumor data sets, and 36 voxels from two prostate cancer data sets for analysis. The reconstructions were performed at acceleration factors of two, three, four, five, and 10 and were evaluated by using the root mean square error (RMSE) metric, metabolite maps (choline, creatine, N-acetylaspartate [NAA], and/or citrate), and statistical analysis involving a voxelwise paired t test and one-way analysis of variance for metabolite maps and ratios for comparison of the accelerated reconstruction with the original case.

Results: The reconstructions showed high fidelity for accelerations up to 10 as determined by the low RMSE (< 0.05). Similar means of the metabolite intensities and hot-spot localization on metabolite maps were observed up to a factor of five, with lack of statistically significant differences compared with the original data. The metabolite ratios of choline to NAA and choline plus creatine to citrate did not show significant differences from the original data for up to an acceleration factor of five in all cases and up to that of 10 for some cases.

Conclusion: A reduction of acquisition time by up to 80%, with negligible loss of information as evaluated with clinically relevant metrics, has been successfully demonstrated for hydrogen 1 MR spectroscopic imaging.

Figure 1:

Reconstruction of the data grid for a representative brain MR spectroscopic imaging data set for the acceleration factors of one (1X), two (2X), five (5X), and 10 (10X). Center: Anatomic MR image shows MR spectroscopic imaging region of interest (yellow square) that corresponds to grids. Two locations (red and green voxels) are further examined in Figure 2.

Figure 2:

Spectra from two selected voxels (red and green voxels from Fig 1) from a representative brain MR spectroscopic imaging data set for the acceleration factors of one (1X), two (2X), five (5X), and 10 (10X). The y-axis limits for all the plots are 20.25 to 1. Cho = choline, Cr = creatine.

Figure 3:

Comparative metabolite maps of NAA, creatine (Cr), choline (Cho), and choline-to-NAA index (CNI) for a healthy brain data set for the acceleration factors of one (1X), two (2X), five (5X), and 10 (10X). The yellow box on the MR anatomic image (Fig 1) indicates the MR spectroscopic imaging region of interest depicted on the maps. a.u. = arbitrary unit.

Figure 4:

Spectra from two selected voxels from representative (left) brain tumor and (right) prostate cancer MR spectroscopic imaging data sets for the acceleration factors of one (1X), two (2X), five (5X), and 10 (10X). In each case, the left column shows a voxel from healthy tissue, while the right column shows a voxel in the tumor-bearing region. The y-axis limits for all the plots are 20.25 to 1. Cho = choline, Cit = citrate, Cr = methyl signal of total creatine, Cr₂ = methylene signal of total creatine.

Figure 5a:

Comparative metabolite and ratio maps from (a) brain tumor (NAA, creatine [Cr], choline [Cho]) and (b) prostate cancer (citrate [Cit], creatine, choline) MR spectroscopic imaging data sets for the acceleration factors of one (1X), two (2X), five (5X), and 10 (10X). Ratio maps depict choline-to-NAA index (CNI) for the brain tumor data and (choline + creatine)/citrate for the prostate cancer data. Top: Yellow box on anatomic MR images indicate the MR spectroscopic imaging region of interest depicted on the maps. a.u. = arbitrary unit.

Figure 5b:

Comparative metabolite and ratio maps from (a) brain tumor (NAA, creatine [Cr], choline [Cho]) and (b) prostate cancer (citrate [Cit], creatine, choline) MR spectroscopic imaging data sets for the acceleration factors of one (1X), two (2X), five (5X), and 10 (10X). Ratio maps depict choline-to-NAA index (CNI) for the brain tumor data and (choline + creatine)/citrate for the prostate cancer data. Top: Yellow box on anatomic MR images indicate the MR spectroscopic imaging region of interest depicted on the maps. a.u. = arbitrary unit.

Figure 6:

Graph of RMSE values for MR spectroscopic imaging data according to acceleration factors of two (2X), three (3X), four (4X), five (5X), and 10 (10X) in comparison with the original data.