NMR in biomedicine
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Comparative Study
Comparison between prospective and retrospective triggering for mouse cardiac MRI.
High-resolution magnetic resonance imaging (MRI) has evolved into one of the major non-invasive tools to study the healthy and diseased mouse heart. This study presents a Cartesian CINE MRI protocol based on a fast low-angle shot sequence with a navigator echo to generate cardiac triggering and respiratory gating signals retrospectively, making the use of ECG leads and respiratory motion sensors obsolete. MRI of the in vivo mouse heart using this sequence resulted in CINE images with no detectable cardiac and respiratory motion artefacts. ⋯ The retrospective method resulted in almost constant left-ventricle wall signal intensity throughout the cardiac cycle, at the expense of a decrease in the signal-to-noise ratio and the contrast-to-noise ratio between blood and myocardial wall as compared with the prospective method. Prospective and retrospective sequences yielded comparable global cardiac functional indices. The largest mean relative difference found was 8% for the end-systolic volume.
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The advantages of array coil imaging in human whole-body MR systems are well known and have gained relevance in many applications and MR techniques. In the field of small-animal studies, this concept has become increasingly important. ⋯ One two-channel and a four-channel transmit/receive setup operating at 750 MHz show the feasibility of array coil imaging at 17.6 T. All of these coils show excellent performance and deliver high-quality MR images of mice.
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Results of the evaluation of transrectal ultrasound (TRUS) guided needle biopsy of voxels identified as suspicious of malignancy on magnetic resonance spectroscopic imaging (MRSI) in a large cohort of men (n = 83) with abnormal digital rectal examination (DRE) [prostate specific antigen (PSA) 0-4 ng/ml] or PSA less than 10 ng/ml, are reported. Three-dimensional (1)H MRSI was carried out at 1.5 T using a pelvic-phased array coil in combination with an endorectal surface coil. Voxels were classified as suspicious of malignancy based on Cit/(Cho + Cr) metabolite ratio. ⋯ The overall success rate of MRI-directed TRUS-guided biopsy of 25% was higher compared with a 9% success rate achieved without MR guidance in another group of 120 patients. Our results indicate that TRUS-guided biopsy of suspicious area identified as malignant from MRSI can be performed using the coordinates of the voxel derived from MR images. This increases the detection rate of prostate cancer in men with PSA level <10 ng/ml or abnormal DRE and also demonstrates the potential of MR in routine clinical practice.
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A novel short echo-time (1)H chemical shift imaging (CSI) pulse sequence is presented that incorporates localization by adiabatic selective refocusing (LASER) for FOV-reduction, k-space weighted averaging and macromolecule subtraction, to obtain quantitative concentration measurements of N-acetyl-aspartate, glutamate, glucose, myo-inositol, creatine and choline using a nominal voxel size of 0.56 cm(3). A comparison of spectral quality and metabolite concentration measurements was made between LASER-CSI and LASER-single voxel spectroscopy (SVS) in a region of homogeneous parietal white matter (N = 8). No significant differences were found in linewidths, signal-to-noise ratios or the effectiveness of the macromolecule subtraction between SVS and CSI. ⋯ A linear regression of all paired metabolite measurements resulted in a slope = 1.01 +/- 0.03 (r(2) = 0.73). LASER-CSI concentration measurements of N-acetyl-aspartate, glutamate, glucose, myo-inositol, creatine and choline were in agreement (within standard deviations) with LASER-SVS measurements. LASER-CSI is, therefore, a viable and attractive option for future (1)H CSI investigations.
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Tissue perfusion and oxygenation in many organs can be evaluated by various NMR techniques. This review focuses on the specificities, limitations and adaptations of the NMR tools available to investigate perfusion and oxygenation in the skeletal muscle of humans and animal models. A description of how they may be used simultaneously is provided as well. 1H NMR spectroscopy of myoglobin (Mb) monitors intramyocytic oxygenation. ⋯ Limitations of ASL are poor contrast-to-noise ratio and sensitivity to movement; however, with the introduction of specific adaptations, it has been proven possible to measure skeletal muscle perfusion at both rest and during exercise. The possibility of combining these NMR measurements with others into a single dynamic protocol is most interesting. The 'multiparametric functional (mpf) NMR' concept can be extended to include the evaluation of muscle energy metabolism simultaneously with 31P NMR or with lactate double quantum filtered 1H NMR spectroscopy, an approach which would make NMR an exceptional tool for non-invasive investigations of integrative physiology and biochemistry in skeletal muscle in vivo.