NMR in Biomedicine
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Accuracy of MRI/MRSI‐based transrectal ultrasound biopsy in peripheral and transition zones of the prostate gland in patients with prior negative biopsy Abstract The purpose of the study was to evaluate the accuracy of transrectal ultrasound biopsy (TRUS‐biopsy) performed on regions with abnormal MRI and/or MRSI for both the transition (TZ) and the peripheral (PZ) zones in patients with suspected prostate cancer with prior negative biopsy, and to analyze the relationship between MRSI and histopathological findings. MRI and MRSI were performed in 54 patients (mean age: 63.9 years, mean PSA value: 11.4 ng/mL) and the ability of MRI/MRSI‐directed TRUS biopsy was evaluated. A three‐point score system was used for both techniques to distinguish healthy from malignant regions. Descriptive statistics and ROC analyses were performed to evaluate the accuracy and the best cut‐off in the three‐point score system. Twenty‐two out of 54 patients presented cancer at MRI/MRSI‐directed TRUS biopsy, nine presented cancer only in PZ, eight both in PZ and TZ, and five exclusively in TZ. On a patient basis the highest accuracy was obtained by assigning malignancy on a positive finding with MRSI and MRI even though it was not significantly greater than that obtained using MRI alone (area under the ROC curve, AUC: 0.723 vs 0.676). On a regional (n = 648) basis the best accuracy was also obtained by considering positive both MRSI and MRI for PZ (0.768) and TZ (0.822). MRSI was false positive in 11.9% of the regions. Twenty‐eight percent of cores with prostatitis were false positive findings on MRSI, whereas only 2.7% of benign prostatic hyperplasia was false positive. In conclusion, the accuracy of MRI/MRSI‐directed biopsies in localization of prostate cancer is good in patient (0.723) and region analyses (0.768). The combination of both MRI and MRSI results makes TRUS‐biopsy more accurate, particularly in the TZ (0.822) for patients with prior negative biopsies. Histopathological analysis showed that the main limitation of MRSI is the percentage of false positive findings due to prostatitis. Copyright © 2010 John Wiley & Sons, Ltd.
NMR in Biomedicine - Tập 23 Số 9 - Trang 1017-1026 - 2010
Transrectal ultrasound‐guided biopsy of prostate voxels identified as suspicious of malignancy on three‐dimensional <sup>1</sup>H MR spectroscopic imaging in patients with abnormal digital rectal examination or raised prostate specific antigen level of 4–10 ng/ml Abstract 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. TRUS‐guided biopsy of suspicious voxels was performed using the z ‐ and x ‐coordinates obtained from MR images and two to three cores were taken from the suspected site. A systematic sextant biopsy was also carried out. MRSI showed voxels suspicious of malignancy in 44 patients while biopsy revealed cancer in 11 patients (25%). Patients who were negative for malignancy on MRSI were also negative on biopsy. An overall sensitivity of 100%, specificity of 54%, negative predictive value of 100% and accuracy of 60% were obtained. The site of biopsy was confirmed (n = 20) as a hypo‐intense area on repeat MRI while repeat MRSI revealed high choline and low citrate. 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. Copyright © 2006 John Wiley & Sons, Ltd.
NMR in Biomedicine - Tập 20 Số 1 - Trang 11-20 - 2007
Molecular diffusion, tissue microdynamics and microstructure Abstract Diffusion NMR is the only method available today that noninvasively provides information on molecular displacements over distances comparable to cell dimensions. This information can be used to infer tissue microstructure and microdynamics. However, data may be fairly difficult to interpret in biological tissues which differ markedly from the theoretical “infinite isotrope medium”, as many factors may affect the NMR signal. The object of this paper is to analyze the expected effects of temperature, restriction, hindrance, membrane permeability, anisotropy and tissue inhomogeneity on the diffusion measurements. Powerful methods, such as q‐space imaging, diffusion tensor imaging and diffusion spectroscopy of metabolites further enhance the specificity of the information obtained from diffusion NMR experiments.
NMR in Biomedicine - Tập 8 Số 7 - Trang 375-386 - 1995
Manganese‐enhanced magnetic resonance imaging (MEMRI): methodological and practical considerations Abstract Manganese‐enhanced MRI (MEMRI) is being increasingly used for MRI in animals due to the unique T 1 contrast that is sensitive to a number of biological processes. Three specific uses of MEMRI have been demonstrated: to visualize activity in the brain and the heart; to trace neuronal specific connections in the brain; and to enhance the brain cytoarchitecture after a systemic dose. Based on an ever‐growing number of applications, MEMRI is proving useful as a new molecular imaging method to visualize functional neural circuits and anatomy as well as function in the brain in vivo . Paramount to the successful application of MEMRI is the ability to deliver Mn2+ to the site of interest at an appropriate dose and in a time‐efficient manner. A major drawback to the use of Mn2+ as a contrast agent is its cellular toxicity. Therefore, it is critical to use as low a dose as possible. In the present work the different approaches to MEMRI are reviewed from a practical standpoint. Emphasis is given to the experimental methodology of how to achieve significant, yet safe, amounts of Mn2+ to the target areas of interest. Copyright © 2004 John Wiley & Sons, Ltd.
NMR in Biomedicine - Tập 17 Số 8 - Trang 532-543 - 2004
<sup>13</sup>C MRS studies of neuroenergetics and neurotransmitter cycling in humans In the last 25 years, 13 C MRS has been established as the only noninvasive method for the measurement of glutamate neurotransmission and cell‐specific neuroenergetics. Although technically and experimentally challenging, 13 C MRS has already provided important new information on the relationship between neuroenergetics and neuronal function, the energy cost of brain function, the high neuronal activity in the resting brain state and how neuroenergetics and neurotransmitter cycling are altered in neurological and psychiatric disease. In this article, the current state of 13 C MRS as it is applied to the study of neuroenergetics and neurotransmitter cycling in humans is reviewed. The focus is predominantly on recent findings in humans regarding metabolic pathways, applications to clinical research and the technical status of the method. Results from in vivo 13 C MRS studies in animals are discussed from the standpoint of the validation of MRS measurements of neuroenergetics and neurotransmitter cycling, and where they have helped to identify key questions to address in human research. Controversies concerning the relationship between neuroenergetics and neurotransmitter cycling and factors having an impact on the accurate determination of fluxes through mathematical modeling are addressed. We further touch upon different 13 C‐labeled substrates used to study brain metabolism, before reviewing a number of human brain diseases investigated using 13 C MRS. Future technological developments are discussed that will help to overcome the limitations of 13 C MRS, with special attention given to recent developments in hyperpolarized 13 C MRS. Copyright © 2011 John Wiley & Sons, Ltd.
NMR in Biomedicine - Tập 24 Số 8 - Trang 943-957 - 2011
Neurochemical changes in the rat prefrontal cortex following acute phencyclidine treatment: an <i>in vivo</i> localized <sup>1</sup>H MRS study Abstract Acute phencyclidine (PCP) administration mimics some aspects of schizophrenia in rats, such as behavioral alterations, increased dopaminergic activity and prefrontal cortex dysfunction. In this study, we used single‐voxel 1 H‐MRS to investigate neurochemical changes in rat prefrontal cortex in vivo before and after an acute injection of PCP. A short‐echo time sequence (STEAM) was used to acquire spectra in a 32‐µL voxel positioned in the prefrontal cortex area of 12 rats anesthetized with isoflurane. Data were acquired for 30 min before and for 140 min after a bolus of PCP (10 mg/kg, n = 6) or saline (n = 6). Metabolites were quantified with the LCModel. Time courses for 14 metabolites were obtained with a temporal resolution of 10 min. The glutamine/glutamate ratio was significantly increased after PCP injection (p < 0.0001, pre‐ vs . post‐injection), while the total concentration of these two metabolites remained constant. Glucose was transiently increased (+70%) while lactate decreased after the injection (both p < 0.0001). Lactate, but not glucose and glutamine, returned to baseline levels after 140 min. These results show that an acute injection of PCP leads to changes in glutamate and glutamine concentrations, similar to what has been observed in schizophrenic patients, and after ketamine administration in humans. MRS studies of this pharmacological rat model may be useful for assessing the effects of potential anti‐psychotic drugs in vivo . Copyright © 2009 John Wiley & Sons, Ltd.
NMR in Biomedicine - Tập 22 Số 7 - Trang 737-744 - 2009
Reduction in myocardial high energy phosphate spin lattice relaxation times using manganese Abstract Paramagnetic contrast agents are being widely used in proton magnetic resonance imaging. The present study demonstrates the potential usefulness of paramagnetic contrast agents in 31 P NMR spectroscopy. Using the Langendorff perfused rat heart, manganese chloride (Mn2+ ) at a concentration of 50 μM /L was added to the perfusate for 10 or 30 min. 31 P NMR Ti relaxation times were subsequently measured at 121.5 MHz. After the 10 min exposure to Mn2+ , 31 P NMR T i measurements of phosphocreatine and ATP were reduced by ca 25 and 50%, respectively, with no significant change in linewidths. A small additional decrease in T i relaxation times after infusion of Mn2+ for 30 min was not significantly different from the values at 10 min. Potential uses of Mn2+ in 31 P NMR spectroscopy include improving the S/N ratio of spectra and assessment of calcium ion channel activity.
NMR in Biomedicine - Tập 7 Số 3 - Trang 137-140 - 1994
Diffusion tensor fiber tracking of human brain connectivity: aquisition methods, reliability analysis and biological results Abstract We present a description, biological results and a reliability analysis for the method of diffusion tensor tracking (DTT) of white matter fiber pathways. In DTT, diffusion‐tensor MRI (DT‐MRI) data are collected and processed to visualize the line trajectories of fiber bundles within white matter (WM) pathways of living humans. A detailed description of the data acquisition is given. Technical aspects and experimental results are illustrated for the geniculo‐calcarine tract with broad projections to visual cortex, occipital and parietal U‐fibers, and the temporo‐calcarine ventral pathway. To better understand sources of error and to optimize the method, accuracy and precision were analyzed by computer simulations. In the simulations, noisy DT‐MRI data were computed that would be obtained for a WM pathway having a helical trajectory passing through gray matter. The error vector between the real and ideal track was computed, and random errors accumulated with the square root of track length consistent with a random‐walk process. Random error was most dependent on signal‐to‐noise ratio, followed by number of averages, pathway anisotropy and voxel size, in decreasing order. Systematic error only occurred for a few conditions, and was most dependent on the stepping algorithm, anisotropy of the surrounding tissue, and non‐equal voxel dimensions. Both random and systematic errors were typically below the voxel dimension. Other effects such as track rebound and track recovery also depended on experimental conditions. The methods, biological results and error analysis herein may improve the understanding and optimization of DTT for use in various applications in neuroscience and medicine. Copyright © 2002 John Wiley & Sons, Ltd.
NMR in Biomedicine - Tập 15 Số 7-8 - Trang 494-515 - 2002
Diffusion‐tensor MRI: theory, experimental design and data analysis – a technical review Abstract This article treats the theoretical underpinnings of diffusion‐tensor magnetic resonance imaging (DT‐MRI), as well as experimental design and data analysis issues. We review the mathematical model underlying DT‐MRI, discuss the quantitative parameters that are derived from the measured effective diffusion tensor, and describe artifacts thet arise in typical DT‐MRI acquisitions. We also discuss difficulties in identifying appropriate models to describe water diffusion in heterogeneous tissues, as well as in interpreting experimental data obtained in such issues. Finally, we describe new statistical methods that have been developed to analyse DT‐MRI data, and their potential uses in clinical and multi‐site studies. Copyright © 2002 John Wiley & Sons, Ltd.
NMR in Biomedicine - Tập 15 Số 7-8 - Trang 456-467 - 2002
Fiber tracking: principles and strategies – a technical review Abstract The state of the art of reconstruction of the axonal tracts in the central nervous system (CNS) using diffusion tensor imaging (DTI) is reviewed. This relatively new technique has generated much enthusiasm and high expectations because it presently is the only approach available to non‐invasively study the three‐dimensional architecture of white matter tracts. While there is no doubt that DTI fiber tracking is providing exciting new opportunities to study CNS anatomy, it is very important to understand its limitations. In this review we therefore assess the basic principles and the assumptions that need to be made for each step of the study, including both data acquisition and the elaborate fiber reconstruction algorithms. Special attention is paid to situations where complications may arise, and possible solutions are reviewed. Validation issues and potential future directions and improvements are also discussed. Copyright © 2002 John Wiley & Sons, Ltd.
NMR in Biomedicine - Tập 15 Số 7-8 - Trang 468-480 - 2002
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