PubMed Health⌕ Search

Biomedical subjects

J C Carr

Publications and source records attributed to J C Carr.

At least 19 recordsLinked to original sources
PubMed2006

Intracranial time-resolved contrast-enhanced MR angiography at 3T.

BACKGROUND AND PURPOSE: A method is presented for high-temporal-resolution MR angiography (MRA) using a combination of undersampling strategies and a high-field (3T) scanner. Currently, the evaluation of cerebrovascular disorders involving arteriovenous shunting or retrograde flow is accomplished with conventional radiographic digital subtraction angiography, because of its high spatial and temporal resolutions. Multiphase MRA could potentially provide the same diagnostic information noninvasively, though this is technically challenging because of the inherent trade-off between signal intensity-to-noise ratio (S/N), spatial resolution, and temporal resolution in MR imaging. METHODS: Numerical simulations addressed the choice of imaging parameters at 3T to maximize S/N and the data acquisition rate while staying within specific absorption rate limits. The increase in S/N at 3T was verified in vivo. An imaging protocol was developed with S/N, spatial resolution, and temporal resolution suitable for intracranial angiography. Partial Fourier imaging, parallel imaging, and the time-resolved echo-shared acquisition technique (TREAT) were all used to achieve sufficient undersampling. RESULTS: In 40 volunteers and 10 patients exhibiting arteriovenous malformations or fistulas, intracranial time-resolved contrast-enhanced MRA with high acceleration at high field produced diagnostic-quality images suitable for assessment of pathologies involving arteriovenous shunting or retrograde flow. The technique provided spatial resolution of 1.1 x 1.1 x 2.5 mm and temporal resolution of 2.5 seconds/frame. The combination of several acceleration methods, each with modest acceleration, can provide a high overall acceleration without the artifacts of any one technique becoming too pronounced. CONCLUSION: By taking advantage of the increased S/N provided by 3T magnets over conventional 1.5T magnets and converting this additional S/N into higher temporal resolution through acceleration strategies, intracranial time-resolved MRA becomes feasible.

Cerebrovascular Disorders↗
PubMed2001

Contrast-enhanced magnetic resonance angiography of the carotid circulation.

Contrast-enhanced MR angiography (CE MR angiography) is rapidly becoming the investigation of first choice for evaluating disease of the vascular system. It is particularly applicable to the carotid circulation and has replaced more traditional time-of-flight imaging because of shorter acquisition times and fewer artifacts. With recent advances in gradient hardware, shorter repetition times allow high spatial resolution imaging of the entire carotid circulation form the aortic arch to the circle of Willis in less than 20 seconds. Additional acquisitions can be utilized as part of the same study to accurately time the arrival of contrast in the arterial system and overcome the problem of early venous enhancement. A number of techniques have been developed recently that allow CE MR angiography to be implemented with high temporal resolution. Both atherosclerotic and nonatherosclerotic carotid artery disease can be comprehensively assessed with CE MR angiography, preventing the need for conventional diagnostic angiography.

Arteriosclerosis↗
PubMed2001

Coronary arteries: magnetization-prepared contrast-enhanced three-dimensional volume-targeted breath-hold MR angiography.

A volume-targeted contrast agent-enhanced breath-hold coronary magnetic resonance angiographic technique was optimized and evaluated in 16 volunteers. Substantial increases in coronary signal-to-noise ratio, contrast-to-noise ratio, lengths of depiction, and vessel sharpness were observed on enhanced images. The imaging approach with two 20-mL injections of contrast agent covers the left and right coronary arteries in two breath holds and is a promising method for coronary imaging.

Adult↗
PubMed2001

Cine MR angiography of the heart with segmented true fast imaging with steady-state precession.

In five healthy subjects and 18 patients, cine magnetic resonance (MR) imaging of the heart was performed with a true fast imaging with steady-state precession (FISP) sequence. Results were compared both quantitatively and qualitatively with those at cine fast low-angle shot (FLASH) MR imaging. The blood-myocardial contrast-to-noise ratio (CNR) was 2.0 times higher and the normalized (for measurement time and pixel size) blood-myocardial CNR was 4.0 times higher for true FISP compared with FLASH MR imaging. Qualitative scores for image quality were significantly higher with true FISP MR imaging. Segmented cine true FISP MR imaging generated high-contrast MR images of the heart in healthy subjects and in patients with heart disease and produced image quality superior to that with cine FLASH MR imaging.

Adult↗
PubMed2001

Usefulness of segmented trueFISP cardiac pulse sequence in evaluation of congenital and acquired adult cardiac abnormalities.

OBJECTIVE: The purpose of this study is to compare ultrashort TR, segmented trueFISP (fast imaging with steady-state precession) cine MR imaging with segmented FLASH (fast low-angle shot) cine MR imaging for the detection and characterization of congenital and acquired adult cardiac abnormalities. SUBJECTS AND METHODS: Twenty-five patients with known or clinically suspected cardiac abnormalities were imaged on a 1.5-T scanner. Valve plane movies were obtained in patients with suspected valve morphology or function abnormalities or whose horizontal long-axis images showed jets. For each patient, three radiologists independently compared corresponding matched cine FLASH and trueFISP movies for image quality in evaluating anatomy and function of the great vessels and heart. Image quality was rated on a five-point scale, and data were analyzed using both a Wilcoxon's signed rank test and a repeated-measures analysis of variance. RESULTS: Image quality ratings of trueFISP and FLASH showed a statistically significant difference (F = 58.67; df = 1, 72; p < 0.0001), with the average rating for the trueFISP images being significantly higher (mean rating, 4.1 +/- 0.92) than that for the FLASH images (mean, 3.0 +/- 1.0). However, valve architecture in the aortic valves appeared to be better visualized and was more easily measured in valve plane images with FLASH. No statistically significant differences among the ratings of the interpreters (F = 0.018; df = 2, 72; p = 0.9821) were evident, and, therefore, no suggestion of bias was indicated (F = 0.775; df = 1, 2; p = 0.4645). TrueFISP yielded the correct diagnosis prospectively in 13 (100%) of 13 patients, whereas FLASH yielded the correct diagnosis in 12 (92%) of 13 patients. CONCLUSION: TrueFISP images depict morphologic and functional abnormalities with greater clarity and provide greater diagnostic confidence than FLASH images-and in a fraction of the time. A specific exception is in the assessment of valve leaflet architecture and cross-sectional area calculation (i.e., bicuspid aortic valves); in these evaluations, FLASH maintains a complementary diagnostic imaging role.

Adult↗
PubMed1997

Association of granulocyte transmigration with structural and cellular parameters of injury in experimental radiation enteropathy.

Inflammatory cells are involved in the pathogenesis of tissue injury through release of cytokines and biologically active compounds. This study used a novel, noninvasive method to assess the association between granulocyte transmigration and structural and molecular changes in radiation enteropathy. A 4 cm loop of rat small intestine was exposed to 0, 2.8, 12, or 23 Gy localized irradiation. Feces was collected in metabolic cages before and 3, 7, 14, 28, and 42 days after irradiation. Granulocyte marker protein (GMP) was measured in buffer extracts of feces by enzyme-linked immunosorbent assay (ELISA). Irradiated and shielded intestine were procured at 2 and 26 weeks and assessed for histopathologic injury [radiation injury score (RIS)], ED-2 positive macrophages, and interleukin-1 alpha (IL-1 alpha) positive cells. Irradiated intestine exhibited characteristic histopathologic alterations and increased numbers of macrophages and IL-1 alpha positive cells. There was a highly significant dose-dependent increase in post-radiation GMP (P < 0.0001). Maximal GMP excretion occurred 3-7 days after irradiation. Six weeks after irradiation, GMP excretion had returned to normal in the 2.8 and 12 Gy groups, but was still 3.5 times higher in the 23 Gy group than in controls. The associations between early GMP excretion and RIS and fibrosis at 26 weeks were highly significant (P < 0.001 and P < 0.0001, respectively). Post-radiation granulocyte transmigration is dose-dependent and correlates with structural and molecular changes, as well as with subsequent chronic injury. The GMP assay is a sensitive, non-invasive indicator of acute intestinal radiation injury and a promising biological predictor of chronic toxicity. Our data underscore the importance of consequential mechanisms in radiation enteropathy.

Animals↗
PubMed1997

Surface interpolation with radial basis functions for medical imaging.

Radial basis functions are presented as a practical solution to the problem of interpolating incomplete surfaces derived from three-dimensional (3-D) medical graphics. The specific application considered is the design of cranial implants for the repair of defects, usually holes, in the skull. Radial basis functions impose few restrictions on the geometry of the interpolation centers and are suited to problems where the interpolation centers do not form a regular grid. However, their high computational requirements have previously limited their use to problems where the number of interpolation centers is small (< 300). Recently developed fast evaluation techniques have overcome these limitations and made radial basis interpolation a practical approach for larger data sets. In this paper radial basis functions are fitted to depth-maps of the skull's surface, obtained from X-ray computed tomography (CT) data using ray-tracing techniques. They are used to smoothly interpolate the surface of the skull across defect regions. The resulting mathematical description of the skull's surface can be evaluated at any desired resolution to be rendered on a graphics workstation or to generate instructions for operating a computer numerically controlled (CNC) mill.

Algorithms↗
PubMed1992

Comparison of AIDS in women in rural and urban Georgia.

Through 1990, 308 cases of AIDS had been reported in female residents of Georgia (aged 13 years and older); 77 (25%) were white and 228 (75%) black. The mean age of the white women (43.8 years) was greater than that of the black women (34.5 years). One hundred sixty-six women were from Atlanta (metro Atl), the major metropolitan center in Georgia, and 142 (46%) from other regions of the state (other areas). Blacks represented 74% and 76% of all cases in women in metro Atl and other areas respectively. Of the 308 cases, 178 (58%) were related to intravenous (IV) drug use (99 metro Atl, 79 other areas), including 104 (58%) women who were IV drug users and 74 who were sexual partners of IV drug users. These proportions were similar in the two regions. Among cases related to IV drug use, 85 (86%) women in metro Atl and 69 (87%) women elsewhere in the state were black. The cumulative rate of AIDS in women in metro Atl (14.4/100,000) was twice that of women in the rest of the state (6.7/100,000). The rate for AIDS cases related to IV drug use in black women (27.8/100,000 population) was 19 times that in white women (1.5/100,000). The median survival of all women was significantly greater in metro Atl than in other areas (400 and 296 days respectively), with a difference also in those reported only with Pneumocystis carinii pneumonia (466 and 373 days respectively).

Acquired Immunodeficiency Syndrome↗
PubMed1987

Daily release of copper from dental alloy restorations in a patient with Wilson's disease.

Wilson's disease is a rare genetic disorder in which copper accumulates in tissues. Its victims must adhere to a strict dietary regimen yielding less than 2 mg of copper per day. Three major variables have been identified as being of critical importance in the treatment of these patients: the amount of copper naturally occurring in foods, the amount of copper introduced during the preparation of foods, and the amount of copper in the environment. An environmental variable that rarely has been addressed is the amount of copper in dental restorations. A case report is presented to discuss the possible consequences of copper-containing dental restorations for the patient with Wilson's disease.

Adult↗