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Results for “Structural MRI”

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At least 1,495 records · Page 83Linked to original sources
PubMed1998

Increased cerebral blood volume in HIV-positive patients detected by functional MRI.

OBJECTIVE: To study changes in cerebral hemodynamics related to HIV infection. BACKGROUND: Cerebral injury is a well-known manifestation of HIV infection. Physiologic changes in the HIV brain may precede structural changes and may be detected by functional MRI (fMRI). METHODS: Dynamic contrast fMRI was used to measure the cerebral blood volume (CBV) in 13 patients infected with HIV and in 7 healthy control subjects. RESULTS: Significant increases in dynamic CBV were found in the deep (p < 0.001) and cortical gray matter (p < 0.05) of HIV-positive (HIV+) patients. Patients with definite cognitive impairment showed significantly greater increases in CBV in the deep gray matter (DGM) compared with those without impairment. In one patient with rapidly progressive cognitive impairment, these abnormalities reversed and paralleled clinical improvement after initiation of zidovudine monotherapy. CONCLUSIONS: This study supports the hypothesis that HIV infection is associated with significant cerebral hemodynamic changes, particularly in the DGM, that may contribute to cognitive dysfunction in AIDS. Functional MRI may be useful for early detection of cerebral injury and for the assessment of novel therapies.

Adult↗
PubMedDate not supplied

[Magnetic resonance arthrography in chronic wrist pain].

PURPOSE: To investigate the clinical role of Magnetic Resonance Arthrography (MRA) of the wrist in subjects with chronic pain. MATERIAL AND METHODS: Thirty-five patients complaining of wrist pain for more 6 months were submitted to MRI and MRA. All patients received an intra-articular (monocompartment radiocarpal joint) injection of 2-10 mL of a 10 mmol saline solution of Gd-DPTA. Two radiologists independently evaluated the conspicuity of the intrinsic intercarpal ligaments and of the triangular fibrocartilage complex and expressed it on a 3-grade semiquantitative scale. On MRI images, complete visualization of the two structures was graded as 0, partial visualization as 1 and no visualization as 2. On MRA images, no contrast agent passage through the ligament or the complex was graded as 0, minimal passage as 1 and complete passage as 2. Sixteen patients had surgical confirmation (arthroscopy in 10 and open surgery in 6 patients). RESULTS: On MRI images the scapholunate ligament was completely visualized in 7 patients (21%) and partially or not visualized in 28 patients (89%). MRA images showed an intact ligament in 15 cases (44%) and a partial or total tear in 20 cases (48% and 8% respectively, 56% in all). On MRI images the luno-pyramidal ligament was completely visualized in 6 patients (18%) and partially or not visualized in 29 cases (82%). On MRA images the luno-pyramidal ligament was intact in 21 cases (58%) and had a partial or total tear in 14 cases (27% and 15% respectively, 42% in all). On MRI images the triangular fibrocartilage complex was normal in 27 cases (76%) and it was only partially visualized in 8 cases (24%). On MRA images the triangular fibrocartilage complex was normal in 13 cases (37%) and had a partial injury in 22 cases (63%). There were no severe side-effects to contrast agent injection, nor severe complications. The overall diagnostic accuracy rates of MRI and MRA were 40% and 81% respectively, with sensitivity and specificity of 63% and 39% (MRI) and of 82% and 79% (MRA). CONCLUSIONS: Compared with MRI, MRA can be considered a useful tool for the visualization of interosseous carpal ligaments and of the triangular fibrocartilage complex. MRA also helps detect injuries in these structures.

Adult↗
PubMedDate not supplied

Blind megaureter with ipsilateral renal agenesis and mullerian anomaly: MR findings in a case.

The magnetic resonance imaging (MRI) of a patient with congenital blind megaureter and mullerian anomaly are presented. A retroperitoneal pelvic mass appeared as elongated tubular cystic structure spreading from parametrium to the adnexa and reaching the recto-sigma. On MRI, the mass was hyperintense on T1 and T2-weighted images and disappeared in STIR sequences. The mass with pseudo-intestinal structure, the retroperitoneal site, and the MRI sequences make the differential diagnosis.

Female↗
PubMed1995

[Imaging superficial skin tumors of the ENT area. High frequency ultrasound in comparison with computerized tomography and magnetic resonance tomography].

In order to improve the preoperative diagnosis of superficial skin tumors in the head and neck, 32 patients with 42 basal cell carcinomas, squamous cell carcinomas and malignant melanomas were investigated using different imaging techniques. All patients were examined preoperatively with high-frequency ultrasound (HFU), computed tomography (CT) and magnetic resonance imaging (MRI). New high-frequency ultrasonic scanners (15- and 20-MHz) having an axial resolution of 50-90 microns permit visualization of dermal and cartilaginous structures with an anatomical accuracy to a range of 15 mm in tissue. Exact measurement of the skin tumors and their relation to adjacent structures was feasible. Histologically different tumors could be discriminated by their echo-structure in 80% of the cases. CT and MRI provided additional information when the tumor extension perpendicular to the skin exceeded 15 mm. If tumor extension was less than 15 mm, CT and MRI were inferior to high-frequency ultrasound in the diagnosis of superficial skin tumors and did not provide any additional information. The experience reported has shown that high-frequency ultrasound is a valuable tool for preoperative evaluation of superficial skin tumors in terms of tumor extension and possible invasion of functionally and esthetically important adjacent structures. This knowledge can support preoperative planning of possible resections as well as reconstruction and may help to obtain an appropriate informed consent.

Adult↗
PubMed2001

Cross-sectional imaging techniques in veterinary ophthalmology.

Ultrasonography (US), computed tomography (CT), and magnetic resonance imaging (MRI) are useful, complementary cross-sectional imaging modalities of the eye and orbit. High-resolution US provides excellent morphological information of ocular structures but offers limited information on the periocular tissues. CT and MRI provide valuable morphologic and topographic images of both ocular and periocular structures, thereby giving a more complete picture of the pathological process. US can be performed on awake patients, whereas CT and MRI require general anesthesia. In addition, US equipment is readily available and less costly than CT or MRI units. Fine-needle aspirations and biopsies under US or CT guidance can also be performed. This article reviews the technique and normal findings of ocular and orbital structures as displayed in each of these imaging modalities. Representative clinical cases are presented to illustrate the interpretation principles as well as to provide an illustrative reference for common ocular and orbital changes.

Animals↗
PubMed1997

High resolution magnetic resonance imaging of the calcaneus: age-related changes in trabecular structure and comparison with dual X-ray absorptiometry measurements.

A high-resolution magnetic resonance imaging (MRI) protocol, together with specialized image processing techniques, was applied to the quantitative measurement of age-related changes in calcaneal trabecular structure. The reproducibility of the technique was assessed and the annual rates of change for several trabecular structure parameters were measured. The MR-derived trabecular parameters were compared with calcaneal bone mineral density (BMD), measured by dual X-ray absorptiometry (DXA) in the same subjects. Sagittal MR images were acquired at 1.5 T in 23 healthy women (mean age: 49.3 +/- 16.6 [SD]), using a three-dimensional gradient echo sequence. Image analysis procedures included internal gray-scale calibration, bone and marrow segmentation, and run-length methods. Three trabecular structure parameters, apparent bone volume (ABV/TV), intercept thickness (I.Th), and intercept separation (I.Sp) were calculated from the MR images. The short- and long-term precision errors (mean %CV) of these measured parameters were in the ranges 1-2% and 3-6%, respectively. Linear regression of the trabecular structure parameters vs. age showed significant correlation: ABV/TV (r2 = 33.7%, P < 0.0037), I.Th (r2 = 26.6%, P < 0.0118), I.Sp (r2 = 28.9%, P < 0.0081). These trends with age were also expressed as annual rates of change: ABV/TV (-0.52%/year), I.Th (-0.33%/year), and I.Sp (0.59%/year). Linear regression analysis also showed significant correlation between the MR-derived trabecular structure parameters and calcaneal BMD values. Although a larger group of subjects is needed to better define the age-related changes in trabecular structure parameters and their relation to BMD, these preliminary results demonstrate that high-resolution MRI may potentially be useful for the quantitative assessment of trabecular structure.

Absorptiometry, Photon↗
PubMed2001

Fetal magnetic resonance imaging of the brain: technical considerations and normal brain development.

Fetal MRI examines non-invasively the unborn fetus. Ultrafast MRI sequences effectively suppress fetal motion. Multiple case reports and studies have shown that fetal MRI is particularly helpful in the evaluation of the central nervous system. The high contrast-to-noise ratio, the high spatial resolution, the multiplanar capabilities, the large field of view and the simultaneous visualisation of fetal and maternal structures have proven to be advantageous. Fetal MRI is particularly helpful in the evaluation of the normal and pathological development of the brain. Despite the fact that no side effects have been reported or are to be expected, the use of MRI during pregnancy is still limited to the second and third trimester of pregnancy. Magnetic resonance imaging contrast media are not to be used as it passes the placenta. Ultrasound remains the primary screening modality for fetal pathology; fetal MRI can serve as an adjunct or second-line imaging modality.

Brain↗
PubMed2001

Neuropathological abnormalities in schizophrenia: evidence from magnetization transfer imaging.

Post-mortem and structural brain imaging studies in schizophrenia have reported macroscopic changes such as global and regional cortical volume reductions, but it has been more difficult to characterize the histopathological changes that underlie these abnormalities. Magnetization transfer imaging (MTI), a novel MRI technique, more sensitive to subtle or early neuropathological changes than conventional MRI, provides a quantitative measure of macromolecular structural integrity represented by the magnetization transfer ratio (MTR). In this study, we used MTI to examine 25 patients with schizophrenia compared with 30 age-matched controls. A voxel-based analysis of the MTR maps revealed widespread MTR reductions in the cortex unrelated to volume reduction, predominantly in the frontal and temporal regions, in the schizophrenic patients when compared with controls. MTR reductions in bilateral parieto-occipital cortex and the genu of the corpus callosum were associated with the severity of negative symptoms in the schizophrenic patients. However, MTR changes were not related to other clinical variables of age, duration of illness and current dose of antipsychotic medication. This study demonstrates that MTR abnormalities in the cortex can be detected in chronic schizophrenia that may reflect subtle neuropathological changes involving neurones or neuronal processes. Longitudinal studies are needed to determine whether these abnormalities are related to disease progression or other disease manifestations such as cognitive changes.

Adult↗
PubMed2003

Determining and visualizing uncertainty in estimates of fiber orientation from diffusion tensor MRI.

Diffusion tensor MRI (DT-MRI) permits determination of the dominant orientation of structured tissue within an image voxel. This has led to the development of 2D graphical methods for representing fiber orientation and DT-MRI "tractography," which aims to reconstruct the 3D trajectories of white matter fasciculi. Most contemporary fiber orientation mapping schemes and tractography algorithms employ the directional information contained in the eigenvectors of the diffusion tensor to approximate white matter fiber orientation. However, while the uncertainty associated with every estimate of an eigenvector has long been recognized, no attempts to quantify this uncertainty in vivo have been reported. Here, a method is proposed for determining confidence intervals in fiber orientation from real DT-MRI data using the bootstrap method. This is used to construct maps of the "cone of uncertainty," allowing simultaneous viewing of fiber orientation and its uncertainty, and to examine the relationship between orientation uncertainty and tissue anisotropy.

Anisotropy↗
PubMed1999

Brain correlates of memory dysfunction in alcoholic Korsakoff's syndrome.

OBJECTIVES: To investigate the relation between anterograde amnesia and atrophy of brain structures involved in memory processing in alcoholic Korsakoff's syndrome. METHODS: The volume of brain structures involved in memory processing was measured with MRI from 13 subjects with Korsakoff's syndrome, 13 subjects with chronic alcoholism without Korsakoff's syndrome, and 13 control subjects. The brain structures analysed were the hippocampus, the parahippocampal gyrus, the mamillary bodies, the third ventricle, and the thalamus. Brain volumes were correlated with the delayed recall of a verbal learning test. RESULTS: Compared with subjects with chronic alcoholism and control subjects, subjects with Korsakoff's syndrome had a reduced volume of the hippocampus, the mamillary bodies, and the thalamus, and enlargement of the third ventricle. The impairment of delayed recall correlated with the volume of the third ventricle (r=-0.55, p=0.05) in the Korsakoff group. CONCLUSIONS: Anterograde amnesia in alcoholic Korsakoff's syndrome is associated with atrophy of the nuclei in the midline of the thalamus, but not with atrophy of the mamillary bodies, the hippocampus, or the parahippocampal gyrus.

Alcoholism↗
PubMed1992

Magnetic resonance imaging of tendon and ligament abnormalities: Part II. Pelvis and lower extremities.

Magnetic resonance imaging (MRI) has provided an ideal means, unmatched by other preexisting modalities, of examining musculoskeletal abnormalities, particularly those involving tendons and ligaments in the lower extremities. Lack of motion artifact, convenience of application of surface coil, and absence of overlying structures have made the lower extremities ideally suited to MRI. In addition, the abundance of adjacent adipose tissue provides a superb contrast background. Although evaluation of trauma remains the most common reason for MRI examination, many other conditions may also affect tendons and ligaments. As in other soft-tissue, chondral, and osteochondral lesions, MRI provides exquisite details of abnormalities in these structures. Part II of this review systematically reviews the abnormalities of tendons and ligaments in the pelvis and lower extremities.

Adolescent↗
PubMed2005

Morphology of the suburethral pubocervical fascia in women with stress urinary incontinence: a comparison of histologic and MRI findings.

To correlate MRI with histologic findings of the suburethral pubocervical fascia in women with urodynamic stress incontinence. Thirty-one women with urodynamically proven stress urinary incontinence without relevant prolapse underwent preoperative MRI. Tissue specimens obtained from the pubocervical fascia were examined immunohistochemically (types I and III collagen, smooth muscle actin) and the results compared with the MRI findings. MRI demonstrated an intact pubocervical fascia in 61.3% of the cases and a fascial defect in 38.7%. A fascial defect demonstrated by MRI was associated with a decrease in actin (P<0.09) and an increase in collagen III (P<0.01) compared to an intact fascia. In women with stress urinary incontinence, smooth muscle actin in the pubocervical fascia is decreased, changed in structure, and replaced by type III collagen. MRI allows evaluation of the pubocervical fascia and its morphologic changes.

Actins↗
PubMedDate not supplied

Azygos continuation syndrome with aneurysm of the azygos vein: CT and MR appearances.

We present a case of azygos vein continuation with aneurysm of the azygos vein simulating a tumor in the right upper mediastinum. The dynamic CT examination initially showed a structure of malignant appearance during the early arterial phase. Further dynamic CT revealed marked enhancement of the mass during the late venous phase, suggesting a vascular structure. Confirmation of diagnosis was made by MRI using a fast gradient echo imaging technique in cine mode, showing turbulent flow in the azygos aneurysm, and contrast-enhanced MR angiography, demonstrating a dilated azygos vein. Dynamic CT has a potential pitfall in the diagnosis of vascular structures.

Aneurysm↗
PubMed1999

[Early diagnosis of Alzheimer's disease by neuroimaging methods].

Visual examinations of the brain, MRI in particular, are very important but always only auxiliary methods in the diagnosis of Alzheimer's disease. Since several years the results obtained in them could have been confirmed objectively by introduction of various methods for measurement of cerebral structures undergoing atrophy. The development of functional MRI programmes, particularly those of regional blood flow in capillaries, has helped in detection of early Alzheimer lesions. The main difficulty in these diagnostic methods is the continuum of lesions resulting from physiological senescence and those being pathological atrophy of Alzheimer type.

Age Factors↗
PubMed1999

Cardiac rhabdomyosarcoma: diagnosis by MR imaging.

We report a case of cardiac rhabdomyosarcoma the initial clinical features of which were pericardial effusion, clinical symptoms of congestive heart failure and probable pulmonary thromboembolism, in which echocardiography constituted the first approach to the diagnosis of cardiac tumor and MRI confirmed it, precisely delimiting the tumoral extension and possible infiltration of pericardiac structures. A brief literature review of this entity is given, the MRI findings obtained in our case are described, and we discuss the advantages and limitations of this technique as compared with other alternatives of image diagnosis.

Adult↗
PubMed2002

Analysis of right ventricular function in healthy mice and a murine model of heart failure by in vivo MRI.

Because of its complex geometry, assessment of right ventricular (RV) function is more difficult than it is for the left ventricle (LV). Because gene-targeted mouse models of cardiomyopathy may involve remodeling of the right heart, the purpose of this study was to develop high-resolution functional magnetic resonance imaging (MRI) for in vivo quantification of RV volumes and global function in mice. Thirty-three mice of various age were studied under isoflurane anesthesia by electrocardiogram-triggered cine-MRI at 7 T. MRI revealed close correlations between RV and LV stroke volume and cardiac output (r = 0.97, P < 0.0001 each). Consistent with human physiology, murine RV end-diastolic and end-systolic volumes were significantly higher compared with LV volumes (P < 0.05 each). MRI in mice with LV heart failure due to myocardial infarction revealed significant structural and functional changes of the RV, indicating RV dysfunction. Hence, MRI allows for the quantification of RV volumes and global systolic function with high accuracy and bears the potential to evaluate mechanisms of RV remodeling in mouse models of heart failure.

Animals↗
PubMed2004

Failure of trabecular bone with simulated lytic defects can be predicted non-invasively by structural analysis.

Pathologic fracture is a significant risk for patients afflicted with metastatic or benign skeletal tumors. The quandary for physicians who treat these patients is that after making the diagnosis they must try to predict the load bearing capacity of the involved bone and the fracture risk from images seen in radiological examinations. Since bone fails at a relatively constant strain independent of density we demonstrate that using a mechanics of materials approach that the cross-sectional structural properties of the bone most affected by the lytic defect governs the load bearing capacity of the entire bone. Homogeneous cylindrical cores of trabecular bone were harvested from the vertebral bodies of whale spines, and prepared with circular or slotted through-hole defects of varying sizes to simulate lytic skeletal tumors. Each specimen was imaged using quantitative computed tomography (CT), dual energy X-ray absorptiometry (DXA), and magnetic resonance imaging (MRI) to obtain data for calculating cross-sectional structural properties: axial, flexural, and torsional rigidity. The specimens were then divided into groups uniformly distributed with respect to defect sizes and shapes, and subjected to uniaxial tension, four-point bending or torsion until failure. A strong positive relationship was found between measured tensile yield loads, bending, and torsional yield moments vs. axial, flexural and torsional structural rigidities respectively, calculated from QCT, DXA, and MRI data [QCT: tension r2=0.951 , bending r2=0.909, torsion r2=0.914; DXA: tension r2=0.926, bending r2=0.841, torsion r2=0.916 (p<0.001); MRI: tension r2=0.916; bending r2=0.856, torsion r2=0.852]. For cylindrical cores of trabecular bone with simulated lytic defects, the load bearing capacity of the entire core was directly proportional to the axial, bending, or torsional rigidity at the weakest cross-section through the core containing the defect. Therefore structural rigidity analysis of cross-sectional geometric data measured non-invasively by QCT, DXA, and MRI of bones containing lytic defects may be used to predict the load bearing capacity of the involved bone and the relative fracture risk in vivo.

Biomechanical Phenomena↗
PubMed2002

No loss of cartilage volume over three years in patients with knee osteoarthritis as assessed by magnetic resonance imaging.

OBJECTIVE: Magnetic resonance imaging (MRI) has the potential to provide accurate quantification of structural changes in joint disease, with sensitivity to change, as it can provide direct visualization of the cartilage and bone. In this study, we investigated whether knee cartilage volume, as assessed by MRI, is sensitive to change over time in patients with osteoarthritis (OA). DESIGN: Sixteen patient volunteers (10 male, six female) with established OA of the knee were entered into the study and demographic data recorded. At baseline, 12 months and 37+/-2 months, patients underwent simple measures of disease severity, as well as extended weight-bearing AP knee X-rays. In addition the patient's index knee was imaged using MR at 1.0 T using a 3-D spoiled gradient-echo sequence with fat-suppression, repetition time 50 ms, echo time 11 ms, flip-angle 40 degrees, sagittal slice thickness 1.56 mm and in-plane pixel resolution 0.55 mm. Manual image segmentation was performed on all knee cartilage compartments and the respective cartilage volumes determined. RESULTS: Eleven of the original patients recruited completed the 3-year study. Radiographic features indicated that the majority had a spectrum of well-established OA at entry. The average decrease in medial tibiofemoral joint space width was 0.21+/-0.37 mm (mean+/-S.D.). Comparison of MR images at baseline and 37+/-2 months indicated little evidence of cartilage lesion shape or size change in any of the compartments. There was no significant MRI volume change in any of the knee cartilage compartments over the course of 1 year. The change in total knee cartilage volume, as measured by MRI, was a loss of only 1.6%, or 0.36+/-1.3 ml (mean+/-S.D.), over the 3 years. CONCLUSIONS: The failure to identify loss of cartilage volume over 3 years in this cohort of patients with established knee OA using MRI challenges the face validity of this endpoint to assess structural changes in OA.

Aged↗