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At least 1,513 records · Page 84Linked to original sources
PubMed2005

Functional anatomy of the prostate: implications for treatment planning.

PURPOSE: To summarize the functional anatomy relevant to prostate cancer treatment planning. METHODS AND MATERIALS: Coronal, axial, and sagittal T2 magnetic resonance imaging (MRI) and MRI angiography were fused by mutual information and registered with computed tomography (CT) scan data sets to improve definition of zonal anatomy of the prostate and critical adjacent structures. RESULTS: The three major prostate zones (inner, outer, and anterior fibromuscular) are visible by T2 MRI imaging. The bladder, bladder neck, and internal (preprostatic) sphincter are a continuous muscular structure and clear definition of the preprostatic sphincter is difficult by MRI. Transition zone hypertrophy may efface the bladder neck and internal sphincter. The external "lower" sphincter is clearly visible by T2 MRI with wide variations in length. The critical erectile structures are the internal pudendal artery (defined by MRI angiogram or T2 MRI), corpus cavernosum, and neurovascular bundle. The neurovascular bundle is visible along the posterior lateral surface of the prostate on CT and MRI, but its terminal branches (cavernosal nerves) are not visible and must be defined by their relationship to the urethra within the genitourinary diaphragm. Visualization of the ejaculatory ducts within the prostate is possible on sagittal MRI. The anatomy of the prostate-rectum interface is clarified by MRI, as is the potentially important distinction of rectal muscle and rectal mucosa. CONCLUSION: Improved understanding of functional anatomy and imaging of the prostate and critical adjacent structures will improve prostate radiation therapy by improvement of dose and toxicity correlation, limitation of dose to critical structures, and potential improvement in post therapy quality of life.

Ejaculation↗
PubMed1986

Magnetic resonance imaging in intractable partial epilepsy: correlative studies.

A study was performed evaluating magnetic resonance imaging (MRI) in 35 patients with intractable complex partial seizures in whom computed tomographic (CT) scans showed no focal abnormalities. These results were correlated with positron emission tomography evaluation (PET), the electroencephalographic ictal onset, and findings during pathological examination. Seven patients had structural lesions that were epileptogenic, detected by MRI; the lesions were tuberous sclerosis, astrocytomas, or hamartomas. Three of these 7 patients underwent PET scanning, which was normal in all. Of 18 patients with mesial temporal sclerosis, 10 were shown by PET to have temporal lobe hypometabolism, though all 18 had normal MRI findings. The results indicate that MRI contributes information to that provided by CT and PET, by detecting nonsclerotic epileptogenic lesions of the temporal lobe.

Astrocytoma↗
PubMed2026

Mapping Focal and Generalized Effects of Common Genetic Variants on Human Brain Structure.

Genome-wide association studies (GWAS) have advanced the quest to understand how specific genetic variants influence human brain structure and function. Recent work has identified hundreds of common variants associated with subcortical brain volumes, sparking interest in how these genetic markers overlap across brain networks. While this can be estimated by hierarchical clustering of the genetic correlation matrix to identify modular patterns of shared architecture, no brain-wide maps of these effects are available. To address this, we computed polygenic scores (PGS) from loci associated with ten brain volume regions of interest (ROIs): nine major subcortical structures and intracranial volume, with each locus weighted by its association with regional volume. In an independent sample from the discovery GWAS, we performed large-scale segmentation of 3D volumetric T1-weighted MRI scans using voxel-based morphometry (VBM) to map 3D profile of regions where gray matter volume (GMV) was associated with each PGS. We found statistically significant, localized effects for PGS defined for the amygdala, thalamus, and basal ganglia, but PGS for brainstem volume was associated with widespread differences throughout the brain. These brain-wide maps reveal patterns consistent with both localized and distributed genetic influences, offering a novel approach to interpret the genomic architecture of brain structure.

GWAS↗
PubMed2003

Analyzing the neocortical fine-structure.

Cytoarchitectonic fields of the human neocortex are defined by characteristic variations in the composition of a general six-layer structure. It is commonly accepted that these fields correspond to functionally homogeneous entities. Diligent techniques were developed to characterize cytoarchitectonic fields by staining sections of post-mortem brains and subsequent statistical evaluation. Fields were found to show a considerable interindividual variability in extent and relation to macroscopic anatomical landmarks. With upcoming new high-resolution magnetic resonance imaging (MRI) protocols, it appears worthwhile to examine the feasibility of characterizing the neocortical fine-structure from anatomical MRI scans, thus, defining neocortical fields by in vivo techniques. A fixated brain hemisphere was scanned at a resolution of approximately 0.3 mm. After correcting for intensity inhomogeneities in the dataset, the cortex boundaries (the white/grey matter and grey matter/background interfaces) were determined as a triangular mesh. Radial intensity profiles following the shortest path through the cortex were computed and characterized by a sparse set of features. A statistical similarity measure between features of different regions was defined, and served to define the extent of Brodmann's Areas 4, 17, 44 and 45 in this dataset.

Aged↗
PubMedDate not supplied

Ultra low field brain MRI in HIV transfusion infected patients.

In order to assess possible structural changes and possible alterations in T1 relaxation times in the brains in a group of female patients (67-74 years) infected with HIV following transfusion ultra low field (ULF) magnetic resonance imaging (MRI) was performed. The width of the ventricles, the width of the subarachnoid spaces, the degree of white matter lesions and T1 relaxation times in the frontal white matter, the basal ganglia and thalamus were studied. No temporal structural changes nor alterations in T1 relaxation times were found in the brains in this group of transfusion infected patients, who were followed regularly over a period of 12 months compared both to themselves and to age matched controls.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Proton and sodium 23 magnetic resonance imaging of human ocular tissues. A model study.

Clinical evaluation of uveal melanomas by magnetic resonance imaging (MRI) techniques depends on developing an understanding of the appearance of these tumors in magnetic resonance (MR) images. We have determined MR characteristics of uveal melanomas by proton (1H) and sodium 23 MRI of freshly enucleated human eyes at 1.5 tesla. The MR images were obtained using two-turn proton and 23Na surface coils, designed to both transmit and receive the radiofrequency signal. Proton MRI techniques included saturation recovery and spin echo; the gradient-recalled echo technique was used for 23Na MRI. Proton and 23Na MR images provide complementary information; contrast between intraocular tumors and vitreous, lens, or subretinal hemorrhage may be varied by using MR pulse sequences that emphasize tissues based on T1, T2, proton, or sodium density values. A combination of proton and 23Na MRI provides differentiation between normal ocular structures and intraocular tumors, as well as associated complications, such as retinal detachments and subretinal hemorrhages.

Eye↗
PubMed2006

Cortisol responses of healthy volunteers undergoing magnetic resonance imaging.

Self-reported anxiety is associated with various medical procedures, including structural and functional magnetic resonance imaging (MRI). The present study tested the hypothesis that MRI scanning would be associated with elevated cortisol levels in participants with no prior scanning experience. Baseline and post-scan cortisol levels, as well as measures of state and trait anxiety, were obtained from scanner-naive (n = 6) and scanner-experienced (n = 8) research participants. The anxiety scores and cortisol responses of the scanner-naive and scanner-experienced participants were compared. Subjects novel to MRI were no more anxious before the scan than were subjects familiar with the MRI examination, but the scanner-naive subjects manifested heightened post-scan cortisol secretion when compared to their pre-scan level and when compared to the scanner-experienced participants. The results are consistent with the hypothesis that the scanning environment can induce cortisol elevations and are congruent with the well-established effects of acute stressors on activity of the hypothalamic-pituitary-adrenal (HPA) axis. The implications for neuroimaging studies are discussed.

Adolescent↗
PubMed2002

Encoding activity in the medial temporal lobe examined with anatomically constrained fMRI analysis.

Functional neuroimaging studies have produced a sizable number of observations of increased activity in the human medial temporal lobe (MTL) during encoding of novel memories. The studies have suggested possible functional specialization within the anatomical components of the MTL (hippocampus and the entorhinal, perirhinal, and parahippocampal cortical areas). Neuroimaging studies have just begun to link anatomical regions to specific functions. To address functional specialization hypothesis, a method is described for using high-resolution structural information from magnetic resonance imaging MRI to constrain the analysis of functional magnetic resonance imaging (fMRI) data, for independent assessment of functional activity change in each component of the MTL. With this method, increased activity was detected throughout the MTL in a group of participants (n = 5) who encoded novel pictures. A separate group (n = 5) who encoded words exhibited lower-levels of evoked activity. Laterality effects were found reflecting increased right hemisphere activity during picture encoding (parahippocampal cortex) and increased left hemisphere activity during word encoding (posterior hippocampus and parahippocampal cortex). Neither condition provided evidence for greater activity in the posterior hippocampus than in the anterior hippocampus during encoding, although the greatest increases in activity were observed in the parahippocampal cortex. The anatomically driven methodology is shown to provide detailed comparison of levels of activity change across specific brain areas and to provide increased sensitivity to functional change in each region of the MTL.

Adult↗
PubMedDate not supplied

A simulation study to assess SVD encoding for interventional MRI: effect of object rotation and needle insertion.

Singular value decomposition (SVD) encoding offers great promise to provide high spatial and temporal resolution required for interventional MRI (I-MRI) (1). This study investigates its efficacy when (a) objects are rotated and (b) a small device (ie, a needle) is moved within anatomic structures. It was found that SVD-encoded MRI is biased toward the reference from which encoding vectors are derived, thus providing a potential limitation under conditions in which the object has undergone significant global change. Reference images with partial device insertion may be needed to accurately resolve the device or track the object motion. Theoretically, the differences between the reference and the object being imaged suggest that SVD encoding is suboptimal (in a minimum mean squared error sense). Other encoding/reconstruction algorithms may come closer to achieving the desired advantages in spatial and temporal fidelity.

Biopsy, Needle↗
PubMed2004

MRI of atherosclerosis.

The emergence of high-resolution, rapid imaging methods has enabled MRI to noninvasively image the fine internal structure of atherosclerotic artery walls. This capability has, in turn, captured the interest of clinicians, who see it as an opportunity to assess disease severity based on the characteristics of atherosclerotic lesions themselves, rather than only their effects on the vessel lumen. MRI of atherosclerosis thus has the potential to be used in medical treatment decisions or to assess the effects of experimental treatment options. Given this potential, a number of research groups have been investigating MRI of atherosclerosis in an effort to establish the ability of MRI to determine atherosclerotic plaque burden, detect plaque composition, and ultimately identify vulnerable plaque before it leads to a clinical event. In this review, the current state of the art is summarized for the three primary vessel targets: the carotid artery, the aorta, and the coronary arteries.

Aortic Diseases↗
PubMed2004

NMR measurement of brain oxidative metabolism in monkeys using 13C-labeled glucose without a 13C radiofrequency channel.

We detected glutamate C4 and C3 labeling in the monkey brain during an infusion of [U-13C6]glucose, using a simple 1H PRESS sequence without 13C editing or decoupling. Point-resolved spectroscopy (PRESS) spectra revealed decreases in 12C-bonded protons, and increases in 13C-bonded protons of glutamate. To take full advantage of the simultaneous detection of 12C- and 13C-bonded protons, we implemented a quantitation procedure to properly measure both glutamate C4 and C3 enrichments. This procedure relies on LCModel analysis with a basis set to account for simultaneous signal changes of protons bound to 12C and 13C. Signal changes were mainly attributed to 12C- and 13C-bonded protons of glutamate. As a result, we were able to measure the tricarboxylic acid (TCA) cycle flux in a 3.9 cm3 voxel centered in the monkey brain on a whole-body 3 Tesla system (VTCA = 0.55 +/- 0.04 micromol x g(-1) x min(-1), N = 4). This work demonstrates that oxidative metabolism can be quantified in deep structures of the brain on clinical MRI systems, without the need for a 13C radiofrequency (RF) channel.

Animals↗
PubMed2002

The influence of mercury contact angle, surface tension, and retraction mechanism on the interpretation of mercury porosimetry data.

The use of a semi-empirical alternative to the standard Washburn equation for the interpretation of raw mercury porosimetry data has been advocated. The alternative expression takes account of variations in both mercury contact angle and surface tension with pore size, for both advancing and retreating mercury meniscii. The semi-empirical equation presented was ultimately derived from electron microscopy data, obtained for controlled pore glasses by previous workers. It has been found that this equation is also suitable for the interpretation of raw data for sol-gel silica spheres. Interpretation of mercury porosimetry data using the alternative to the standard Washburn equation was found to give rise to pore sizes similar to those obtained from corresponding SAXS data. The interpretation of porosimetry data, for both whole and finely powdered silica spheres, using the alternative expression has demonstrated that the hysteresis and mercury entrapment observed for whole samples does not occur for fragmented samples. Therefore, for these materials, the structural hysteresis and overall level of mercury entrapment is caused by the macroscopic (> approximately 30 microm), and not the microscopic (< approximately 30 microm), properties of the porous medium. This finding suggested that mercury porosimetry may be used to obtain a statistical characterization of sample macroscopic structure similar to that obtained using MRI. In addition, from a comparison of the pore size distribution from porosimetry with that obtained using complementary nitrogen sorption data, it was found that, even in the absence of hysteresis and mercury entrapment, pore shielding effects were still present. This observation suggested that the mercury extrusion process does not occur by a piston-type retraction mechanism and, therefore, the usual method for the application of percolation concepts to mercury retraction is flawed.

Journal Article↗
PubMed1997

Connective tissue reactions in subdural haematomas: imaging with contrast-enhancement MRI.

The sensitivity of contrast enhanced magnetic resonance imaging (MRI) in the detection of connective tissue reactions accompanying the maturation of subdural haematomas (SDH) was studied. An outer enhancing layer between the SDH and the tabula interna of the vault was shown in 16 out of 17 cases. In early SDH this outer enhancing layer presumably is due to vascular congestion and/or increased vascular permeability. A thickening of the outer enhancing layer and/or an inner enhancing layer between the haematoma and the subarachnoid space was visible in 9 patients and represented a haematoma capsule formed by proliferating granulation tissue. In 5 SDH septations were found, 3 SDH consisted almost completely of enhancing granulation tissue. Thus, contrast enhanced MRI delivers additional information about the structure of SDH, which are useful for determining the extent of surgical treatment especially in chronic SDH.

Adolescent↗
PubMed1997

Three-dimensional contrast-enhanced magnetic resonance angiography of the thoracic vasculature.

Magnetic resonance angiography (MRA) has become a useful non-invasive imaging technique for the assessment of vascular disease. Due to limitations such as respiratory motion artefacts, saturations problems, and long acquisition times, applications of MRA in the thorax have largely been restricted to imaging of the aorta. The recent introduction of breath-hold three-dimensional (3D) contrast-enhanced MRA promises not only to enhance conventional MR protocols for aortic imaging, but to extend the clinical indications of MRI to diseases affecting other vascular structures of the thorax, most notably the pulmonary arteries. This article describes the technical aspects of contrast-enhanced 3D MRA and reviews existing and potential future clinical applications.

Aorta, Thoracic↗
PubMed2006

Tension-type headache.

Tension-type headache, the most common type of primary headache disorder, is reclassified in the second International Headache Society classification with clear diagnostic criteria. Chronic tension-type headache (CTTH) differs from episodic form in frequency, lack of response to most treatment strategies, more medication overuse, and more loss of quality of life. New concepts in the pathophysiology of CTTH emphasize the possible role of central nociceptive pathway sensitization in addition to peripheral myogenic factors. Mechanisms of central sensitization, even though poorly understood, may involve nitric oxide system and N-methyl-D-aspartate receptors. Future treatment modalities are likely to be based on such mechanisms. Using MRI and voxel-based morphometry, structural abnormalities have been found in patients with CTTH for the first time. Pain processing areas such as dorsal rostral and ventral pons, anterior cingulate cortex, anterior and posterior insular cortex, right posterior temporal lobe, orbitofrontal cortex, para hippocampus bilaterally, and the right cerebellum were found to have decreased gray matter in patients with CTTH compared with control subjects and patients with medication overuse headache. Amitriptyline remains the most effective preventive treatment so far. The role of botulinum toxin is not fully defined.

Central Nervous System↗
PubMed1996

Magnetic resonance imaging anatomy of the female urethra: a direct histologic comparison.

OBJECTIVE: To define the urethral structures visible on magnetic resonance imaging (MRI) relevant to stress urinary incontinence. METHODS: The urethra and surrounding tissues were harvested from 13 female cadavers (ages 21-81) and fixed in 10% buffered formalin. High-resolution T1- and T2-weighted images were obtained at 1.5 tesla. Mallory trichrome-stained histologic sections were prepared in corresponding planes from the cadaveric specimens. Immunohistologic stains for smooth muscle (actin) and vascular endothelium (CD-34 and factor VIII) were obtained on two specimens. Histology and MRI were compared using side-by-side correlation of projected images and by superimposing projected images. Comparison was also made to a non-cadaveric urethral MRI of a 29-year-old woman and to the MRI of another specimen imaged pre- and post-fixation. RESULTS: Distinct layers of the cadaveric urethra were seen best on proton density and T2-weighted images. From the center to the periphery, a series of concentric rings were visible: an inner bright ring, the mucosa; a dark ring, the submucosa; an outer bright ring, the smooth muscle of the urethra in a loose connective tissue matrix; and a peripheral dark ring, the striated urogenital sphincter muscle of the urethra in dense connective tissue. No significant alterations were caused by fixation. These cadaveric images matched the non-cadaveric MRI of the 29-year-old woman. CONCLUSION: The internal urethral anatomy visible on high-resolution MRI can be identified and confirmed histologically, and these findings may form the basis for future anatomic investigation of stress urinary incontinence and other urethral abnormalities.

Adult↗
PubMed1994

MRI findings of concurrent acute DVT and dissecting popliteal cyst.

A case of concurrent popliteal vein thrombosis and a dissecting popliteal cyst noted on the same MRI exam is described. Pseudothrombophlebitis is a well known entity in which a ruptured or dissecting popliteal cyst clinically mimics thrombophlebitis; the current case can be considered "pseudo-pseudo thrombophlebitis." This case demonstrates the importance of routine review of the venous structures of the posterior fossa for all MRI exams of the knee.

Acute Disease↗
PubMedDate not supplied

Gradient echo imaging of the lumbar spine.

Journal articles have presented pro and con views of gradient recalled echo (GRE) imaging of the lumbar spine, while it has been illustrated in textbooks that have advanced its diagnostic applicability. This paper reappraises GRE in light of evolving MRI technology. The conspicuity of anatomic structures on axial T1-weighted (T1W) spin-echo (SE) images were matched with T2 GRE images in 55 patients referred for evaluation of low back pain. Disc herniations were hyperintense on GRE images and readily separable from hypointense spondylophytes.

Adipose Tissue↗