Accelerated Echo-Planar J-Resolved Spectroscopic Imaging in the Human Brain Using Compressed Sensing: A Pilot Validation in Obstructive Sleep Apnea

Abstract

BACKGROUND AND PURPOSE Echo-planar J-resolved spectroscopic imaging is a fast spectroscopic technique to record the biochemical information in multiple regions of the brain, but for clinical applications, time is still a constraint. Investigations of neural injury in obstructive sleep apnea have revealed structural changes in the brain, but determining the neurochemical changes requires more detailed measurements across multiple brain regions, demonstrating a need for faster echo-planar J-resolved spectroscopic imaging. Hence, we have extended the compressed sensing reconstruction of prospectively undersampled 4D echo-planar J-resolved spectroscopic imaging to investigate metabolic changes in multiple brain locations of patients with obstructive sleep apnea and healthy controls. MATERIALS AND METHODS Nonuniform undersampling was imposed along 1 spatial and 1 spectral dimension of 4D echo-planar J-resolved spectroscopic imaging, and test-retest reliability of the compressed sensing reconstruction of the nonuniform undersampling data was tested by using a brain phantom. In addition, 9 patients with obstructive sleep apnea and 11 healthy controls were investigated by using a 3T MR imaging/MR spectroscopy scanner. RESULTS Significantly reduced metabolite differences were observed between patients with obstructive sleep apnea and healthy controls in multiple brain regions: NAA/Cr in the left hippocampus; total Cho/Cr and Glx/Cr in the right hippocampus; total NAA/Cr, taurine/Cr, scyllo-Inositol/Cr, phosphocholine/Cr, and total Cho/Cr in the occipital gray matter; total NAA/Cr and NAA/Cr in the medial frontal white matter; and taurine/Cr and total Cho/Cr in the left frontal white matter regions. CONCLUSIONS The 4D echo-planar J-resolved spectroscopic imaging technique using the nonuniform undersampling–based acquisition and compressed sensing reconstruction in patients with obstructive sleep apnea and healthy brain is feasible in a clinically suitable time. In addition to brain metabolite changes previously reported by 1D MR spectroscopy, our results show changes of additional metabolites in patients with obstructive sleep apnea compared with healthy controls.

Obstructive sleep apnea is associated with altered midbrain chemical concentrations

“…Previous OSA spectroscopy studies found differences in neurochemical levels, such as decreased N -acetylaspartate (NAA), a neuronal marker, and increased levels of the excitatory neurotransmitter glutamate, in limbic brain regions including the hippocampus, thalamus, and putamen (Sarma et al, 2014, 2016). These findings suggest neural injury and increased excitation.…”

“…Participants were instructed to refrain from caffeine and alcohol for 24 h prior to their visit. Metabolites were measured with a novel 2D-magnetic resonance spectroscopy (MRS) method, accelerated 4D echo-planar J-resolved spectroscopic imaging (4D-EP-JRESI) (Sarma et al., 2014). The procedure uses non-uniform undersampling (NUS) for acceleration with compressed sensing reconstruction.…”

“…Data post-processing involved raw data reconstruction, and a series of steps described elsewhere (Sarma et al, 2016, 2014). Metabolite ratios with respect to creatine were calculated using the prior knowledge fitting (ProFit) algorithm with Cramer Lower Bounds (Schulte and Boesiger, 2006; Fuchs et al, 2014), optimized for processing the Siemens data.…”

Proton MRS and MRSI of the brain without water suppression

“…This problem can be alleviated and this technique may potentially be extended to spectroscopic imaging by the synergy of modern techniques and technology, such as high field scanners (>3 T) [82], parallel imaging (e.g., SENSE [83,84] and GRAPPA [85,86]) with multichannel coils, fast acquisition sequences (e.g., EPSI [86,87], spiral acquisition [88]), and compressed sensing (allowing several-fold acceleration by randomly skipping some t 1 steps [89]). This approach is very similar to that used for echo-planar J-resolved MRSI using compressed sensing [90].…”

Brain Metabolic Mapping with MRS: A Potent Noninvasive Tool for Clinical Diagnosis of Brain Disorders

“…The need for determining the neurochemical changes across multiple brain regions in patients with CNS disorders in a clinically viable timeframe has led to developmental of faster 4D echo-planar J-resolved spectroscopic imaging techniques, which combine the advantages of 2D MR spectroscopic imaging and echo-planar spectroscopic imaging. Sarma et al 15 demonstrated 4D echo-planar J-resolved spectroscopic imaging by using the nonuniform undersamplingbased acquisition and compressed sensing reconstruction and showed it to be a clinically viable imaging technique in patients with obstructive sleep apnea. The study highlights the clinical applicability of their methodology, which could detect additional neurochemical changes in patients with obstructive sleep apnea previously reported by 1D MR spectroscopy.…”