NMR in biomedicine
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MRS of 13 C4 -labelled glutamate (13 C4 -Glu) during an infusion of a carbon-13 (13 C)-labelled substrate, such as uniformly labelled glucose ([U-13 C6 ]-Glc), provides a measure of Glc metabolism. The presented work provides a single-shot indirect 13 C detection technique to quantify the approximately 2.51 ppm 13 C4 -Glu satellite proton (1 H) peak at 9.4 T. The methodology is an optimized point-resolved spectroscopy (PRESS) sequence that minimizes signal contamination from the strongly coupled protons of N-acetylaspartate (NAA), which resonate at approximately 2.49 ppm. ⋯ The efficacy of the technique was verified on phantom solutions and on two rat brains in vivo during an infusion of [U-13 C6 ]-Glc. LCModel was employed for analysis of the in vivo spectra to quantify the 2.51 ppm 1 H 13 C4 -Glu signal to obtain Glu C4 fractional enrichment time courses during the infusions. Cramér-Rao lower bounds of about 8% were obtained for the 2.51 ppm 13 C4 -Glu 1 H satellite peak with the optimal TE combination.
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Quantitative susceptibility mapping (QSM) of human spinal vertebrae from a multi-echo gradient-echo (GRE) sequence is challenging, because comparable amounts of fat and water in the vertebrae make it difficult to solve the nonconvex optimization problem of fat-water separation (R2*-IDEAL) for estimating the magnetic field induced by tissue susceptibility. We present an in-phase (IP) echo initialization of R2*-IDEAL for QSM in the spinal vertebrae. Ten healthy human subjects were recruited for spine MRI. ⋯ There was no substantial difference on QSM between the single peak and multi-peak fat models, but there were marked differences among different initialization methods. The simulations demonstrated that IP provided the lowest error in the field map. Compared to Zero, VARPRO-GC and SPURS, the proposed IP method provided substantially improved spine QSM in all 10 subjects.
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The purpose of this study is to develop a 3D adiabatic inversion recovery prepared ultrashort echo time Cones (3D IR-UTE-Cones) sequence for high resolution and contrast imaging of the region of osteochondral junction (OCJ) of human knee joint using a clinical 3 T scanner. A feasibility study on direct imaging of the OCJ region was performed on a human patellar cartilage sample and on eight cadaveric knee joints using T1 -weighted, proton density (PD)-weighted and short-T2 -weighted 3D IR-UTE-Cones sequences. Contrast to noise ratio was measured to evaluate the effectiveness of the 3D IR-UTE-Cones sequences for selective imaging of the OCJ region. ⋯ Abnormal OCJ regions, manifested as ill-defined, focal loss or non-visualization of the high intensity band adjacent to the subchondral bone plate, were observed in the knee joints of both ex vivo and in vivo OA patients. The 3D IR-UTE-Cones sequence can image OCJ regions ex vivo and in vivo, with abnormalities depicted with high resolution and contrast. The technique may be useful for demonstrating involvement of OCJ regions in early OA.
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The aim of this study was to develop and evaluate a clinically feasible approach to diffusion-weighted (DW) MRI of the prostate without susceptibility-induced artifacts. The proposed method relies on an undersampled multi-shot DW turbo-STEAM sequence with rotated radial trajectories and a multi-step inverse reconstruction with denoised multi-shot phase maps. The total acquisition time was below 6 min for a resolution of 1.4 × 1.4 × 3.5 mm3 and six directions at b = 600 s mm-2. ⋯ Preliminary results for patients with prostate cancer revealed a correct anatomical localization of lesions with respect to T2 -weighted MRI in both mean DW STEAM images and ADC maps. In summary, DW STEAM MRI of the prostate offers clinically relevant advantages for the diagnosis of prostate cancer compared with state-of-the-art EPI-based approaches. The method warrants extended clinical trials.
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In vivo magnetic resonance spectroscopy (MRS) is the only technique capable of non-invasively assessing metabolite concentrations in the brain. The lack of alternative methods makes validation of MRS measures challenging. The aim of this study is to assess the validity of MRS measures of human brain metabolite concentrations by comparing multiple MRS measures acquired using different MRS acquisition sequences. ⋯ Given that the ground truth for in vivo MRS measures is never known, the method proposed here provides a promising means to assess the validity of in vivo MRS measures, which has not yet been explored widely.