title: Compressed sensing to accelerate magnetic resonance spectroscopic imaging: evaluation and application to 23Na-imaging of mouse hearts.
abstract: BACKGROUND
  Magnetic Resonance Spectroscopic Imaging (MRSI) has wide applicability for non-invasive biochemical assessment in clinical and pre-clinical applications but suffers from long scan times. Compressed sensing (CS) has been successfully applied to clinical 1H MRSI, however a detailed evaluation of CS for conventional chemical shift imaging is lacking. Here we evaluate the performance of CS accelerated MRSI, and specifically apply it to accelerate 23Na-MRSI on mouse hearts in vivo at 9.4 T.
  
  
  METHODS
  Synthetic phantom data representing a simplified section across a mouse thorax were used to evaluate the fidelity of the CS reconstruction for varying levels of under-sampling, resolution and signal-to-noise ratios (SNR). The amplitude of signals arising from within a compartment, and signal contamination arising from outside the compartment relative to noise-free Fourier-transformed (FT) data were determined. Simulation results were subsequently verified experimentally in phantoms and in three mouse hearts in vivo.
  
  
  RESULTS
  CS reconstructed MRSI data are scaled linearly relative to absolute signal intensities from the fully-sampled FT reconstructed case (R(2) > 0.8, p-value < 0.001). Higher acceleration factors resulted in a denoising of the reconstructed spectra, but also in an increased blurring of compartment boundaries, particularly at lower spatial resolutions. Increasing resolution and SNR decreased cross-compartment contamination and yielded signal amplitudes closer to the FT data. Proof-of-concept high-resolution, 3-fold accelerated 23Na-amplitude maps of murine myocardium could be obtained within ~23 mins.
  
  
  CONCLUSIONS
  Relative signal amplitudes (i.e. metabolite ratios) and absolute quantification of metabolite concentrations can be accurately determined with up to 5-fold under-sampled, CS-reconstructed MRSI. Although this work focused on murine cardiac 23Na-MRSI, the results are equally applicable to other nuclei and tissues (e.g., 1H MRSI in brain). Significant reduction in MRSI scan time will reduce the burden on the subject, increase scanner throughput, and may open new avenues for (pre-) clinical metabolic studies.
authors.affiliation: British Heart Foundation Experimental Magnetic Resonance Unit, Radcliffe Department of Medicine - Division of Cardiovascular Medicine, University of Oxford, Roosevelt Drive, Oxford, OX3 7BN, UK.
authors.forename: Mahon L
authors.initials: ML
authors.lastname: Maguire
authors.affiliation: Medical Imaging Research Centre, Dayananda Sagar College of Engineering, Bangalore, 560078, India.
authors.forename: Sairam
authors.initials: S
authors.lastname: Geethanath
authors.affiliation: British Heart Foundation Experimental Magnetic Resonance Unit, Radcliffe Department of Medicine - Division of Cardiovascular Medicine, University of Oxford, Roosevelt Drive, Oxford, OX3 7BN, UK.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Lygate
authors.affiliation: School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ, 85287-9709, USA.
authors.forename: Vikram D
authors.initials: VD
authors.lastname: Kodibagkar
authors.affiliation: British Heart Foundation Experimental Magnetic Resonance Unit, Radcliffe Department of Medicine - Division of Cardiovascular Medicine, University of Oxford, Roosevelt Drive, Oxford, OX3 7BN, UK. jurgen.schneider@cardiov.ox.ac.uk.
authors.forename: Jürgen E
authors.initials: JE
authors.lastname: Schneider
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D003198:Computer Simulation; D044962:Data Compression / Q000379:methods*; D005583:Fourier Analysis; D016014:Linear Models; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation; D051379:Mice; D009206:Myocardium / Q000378:metabolism*; D019047:Phantoms, Imaging; D059629:Signal-To-Noise Ratio; D012975:Sodium Isotopes; D013997:Time Factors
chemical_list: D015415:Biomarkers; D012975:Sodium Isotopes