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Biomedical subjects

R N Bryan

Publications and source records attributed to R N Bryan.

At least 73 records · Page 4Linked to original sources
PubMed1993

A high-field superferric NMR magnet.

Strong, extensive magnetic fringe fields are a significant problem with magnetic resonance imaging magnets. This is particularly acute with 4-T, whole-body research magnets. To date this problem has been addressed by restricting an extensive zone around the unshielded magnet or by placing external unsaturated iron shielding around the magnet. This paper describes a solution to this problem which uses superconducting coils closely integrated with fully saturated iron elements. A 4-T, 30-cm-bore prototype, based on this design principle, was built and tested. The 5 G fringe field is contained within 1 meter of the magnet bore along the z axis. Homogeneity of the raw magnetic field is 10 ppm over 30% of the magnet's diameter after passive shimming. Compared with an unshielded magnet, 20% less superconductor is required to generate the magnetic field. Images and spectra are presented to demonstrate the magnet's viability for magnetic resonance imaging and spectroscopy.

Magnetic Resonance Spectroscopy↗
PubMed1993

Receiver operating characteristic analysis of fracture and pneumonia detection: comparison of laser-digitized workstation images and conventional analog radiographs.

Forty pneumonia and 40 fracture cases were matched by patient age and gender with normal cases. Pediatric cases constituted 25% of this sample. All 160 examinations were laser-digitized at a spot size of 210 microns, a contrast resolution of 12 bits, and a spatial resolution of 2.35 line pairs per millimeter. The digitized images were transmitted 5 miles over a dedicated telephone line at a T1 rate from Francis Scott Key Hospital to Johns Hopkins Hospital (both in Baltimore, Md). At Johns Hopkins Hospital, eight radiologists interpreted the original analog radiograph and corresponding soft-copy display (1,280 x 1,024 pixels). Findings, confidence ratings, and image quality were reported for each reading. A receiver operating characteristic (ROC) analysis was conducted to compare observer performance under the analog and digital reading conditions. The overall sensitivity of the analog method was 89% versus 78% for the digital method (P < .001), while the specificity values were 96% and 92%, respectively (P > .20). ROC analysis similarly indicated a statistically significant difference in favor of analog radiographs (P = .028).

Child↗
PubMed1993

Frameless stereotaxic integration of CT imaging data: accuracy and initial applications.

To evaluate the spatial accuracy of a rapid interactive method of transferring computed tomographic (CT) information between its display on a computer screen to its source (test object, operating field), a multidimensional computer combined with a six-jointed position-sensing mechanical arm was tested with a Plexiglas model consisting of 50 rods of varied height and known location, a plastic replica of the skull, and, subsequently, three patients. The median error value between image and real location was 1-2 mm (P > .95), regardless of the registration target sites. The accuracy, however, increased with the selection of widespread registration points, and 95% of all errors were below 3.70 mm (P > .95). The results compare favorably with the four most commonly used stereotaxic framed units. A misregistration error of 0.3-2.2 mm was found during intraoperative correlation between anatomy on the CT display and actual anatomic location in the operative field.

Child↗
PubMed1993

Volumetric MRI changes in basal ganglia of children with Tourette's syndrome.

To define the site of pathology in Tourette's syndrome (TS), we performed a volumetric MRI study of basal ganglia structures and lateral ventricles on 37 children with this disorder and 18 controls. There were no statistically significant differences in the size of the right or left caudate, putamen, globus pallidus, or ventricles in these populations. In contrast, there were significant differences for measures of symmetry in the putamen and the lenticular region. Virtually all controls (17 right- and one left-handed) had a left-sided predominance of the putamen, whereas in 13 of 37 TS subjects, a right predominance exceeded that of any control. Statistical comparisons among TS patients, with (n = 18) or without (n = 19) attention-deficit hyperactivity disorder (ADHD), and controls showed significant differences for the volume of the left globus pallidus and for lenticular asymmetry. Post hoc evaluations showed that in the TS + ADHD group, the volume of the left globus pallidus was significantly smaller than the volume of the right and that lenticular asymmetry was due to a greater right-sided predominance in the TS+ADHD group. This study lends further support to proposals that claim the basal ganglia is involved in the pathogenesis of TS and also suggests that the comorbid problem of ADHD is related to regional changes that differ from those primarily associated with tics.

Adolescent↗
PubMed1993

In vivo magnetic resonance spectroscopy of human brain tumors.

In vivo nuclear magnetic resonance (NMR) spectroscopy is a rapidly developing, noninvasive analytical technique that allows sequential studies of brain tumor metabolism. It can be implemented on most conventional high-field magnetic resonance imaging scanners. In animal tumor models, NMR spectroscopy has been used extensively to characterize the metabolic changes associated with tumor growth and response to therapy. Preliminary data in humans indicate the feasibility of recording phosphorus and proton spectra from focal lesions within the brain. It is hoped that the technique will provide useful prognostic information in terms of tumor growth behavior and prediction and detection of response to therapy. However, the technique suffers from relatively coarse spatial resolution, and the methodology is still under development. More studies with larger patient groups are required before the clinical utility of the technique can be fully evaluated.

Brain Neoplasms↗
PubMed1992

MR imaging of cerebral perfusion by phase-angle reconstruction of bolus paramagnetic-induced frequency shifts.

Phase-angle images are acquired dynamically during bolus paramagnetic contrast injection and demonstrate a phase-enhancement effect in perfused cerebral tissues. Signal-to-noise is comparable to that of susceptibility-based signal loss (delta R*) images. Assuming that phase shift is proportional to the tissue paramagnetic agent concentration, as supported by experimental data, the integrated area of the phase time response curves estimated the relative gray to white matter blood volume as 1.8:1 and was sensitive to acute ischemia. The relation between tissue phase shift and concentration is considered.

Animals↗
PubMed1992

Measurement of radiotracer concentration in brain gray matter using positron emission tomography: MRI-based correction for partial volume effects.

Accuracy in in vivo quantitation of brain function with positron emission tomography (PET) has often been limited by partial volume effects. This limitation becomes prominent in studies of aging and degenerative brain diseases where partial volume effects vary with different degrees of atrophy. The present study describes how the actual gray matter (GM) tracer concentration can be estimated using an algorithm that relates the regional fraction of GM to partial volume effects. The regional fraction of GM was determined by magnetic resonance imaging (MRI). The procedure is designated as GM PET. In computer simulations and phantom studies, the GM PET algorithm permitted a 100% recovery of the actual tracer concentration in neocortical GM and hippocampus, irrespective of the GM volume. GM PET was applied in a test case of temporal lobe epilepsy revealing an increase in radiotracer activity in GM that was undetected in the PET image before correction for partial volume effects. In computer simulations, errors in the segmentation of GM and errors in registration of PET and MRI images resulted in less than 15% inaccuracy in the GM PET image. In conclusion, GM PET permits accurate determination of the actual radiotracer concentration in human brain GM in vivo. The method differentiates whether a change in the apparent radiotracer concentration reflects solely an alteration in GM volume or rather a change in radiotracer concentration per unit volume of GM.

Algorithms↗
PubMed1992

Proton NMR spectroscopy of Canavan's disease.

Proton Nuclear Magnetic Resonance (NMR) spectroscopy was used to quantitatively determine cerebral N-Acetyl Aspartate (NAA) concentrations in four patients with Canavan's disease and in four age-matched control subjects. Macroscopic NAA concentrations (mumol/gm wet weight) were not found to be significantly different from controls. Reduced levels of choline and creatine were observed in all patients, and increased levels of lactate and inositol in the eldest three patients.

Adolescent↗
PubMed1992

Magnetic resonance evaluation of stroke.

Stroke is not a specific disease but is, instead, a symptom complex reflecting destruction of brain tissue by cerebrovascular disease. Several different specific diseases are included in the "stroke" category, including intra- and extracerebral hemorrhage as well as ischemic infarction. These different types of stroke have major differences regarding etiology, management, and prognosis. The goal of stroke imaging is to diagnose the type of stroke at clinical presentation, allowing prompt and appropriate management. Magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), and magnetic resonance spectroscopy (MRS) provide powerful noninvasive means to evaluate the pathologic and metabolic changes that occur in acute stroke. These techniques allow the early detection of stroke and greatly increase the ability to determine the etiology of the stroke. One or more of these methods will surely become a standard means of evaluating acute stroke. The information provided, combined with new stroke therapies, should result in improved patient outcome.

Acute Disease↗
PubMed1992

Imaging of neurodegenerative diseases.

Neuroimaging of degenerative brain disorders has continued to advance, primarily with MR imaging, single-photon emission CT, and positron emission tomography. Information gained from these morphologic and functional imaging studies provides insight into the pathologic and pathophysiologic changes associated with these diseases. Recent papers relating to various neurodegenerative disorders such as Alzheimer's disease, vascular dementias, acquired immunodeficiency syndrome-related dementia, Pick's disease, Huntington's disease, progressive supranuclear palsy, and others are reviewed and discussed.

AIDS Dementia Complex↗
PubMed1991

Autistic features in Joubert syndrome: a genetic disorder with agenesis of the cerebellar vermis.

Recent reports in the literature have suggested a link between abnormalities of the cerebellar vermis and the behavioral syndrome of autism. Joubert syndrome is an autosomal recessive disorder characterized by partial or complete agenesis of the cerebellar vermis. However, there is little behavioral or psychiatric description of patients with this genetic condition. In this report, the neuropsychiatric characteristics of two children with Joubert syndrome are described in detail. One child met DSM-III-R diagnostic criteria for autistic disorder, while the other displayed autistic features. The female child displayed stereotypic behavior and impairments in social interaction and communication, had a markedly restricted repertoire of interests, and showed distress over changes in the environment. The male child demonstrated perseveration and preoccupation with sounds and textures, but had no abnormalities in social interaction. Although both children showed developmental disabilities, the degree of cognitive delay was significantly less than that described in previous reports of children with Joubert syndrome. This report adds to the growing body of evidence implicating cerebellar involvement in developmental disabilities and autistic behavior.

Autistic Disorder↗
PubMed1991

Dominant-side intracarotid amobarbital spares comprehension of word meaning.

Abolition of speech production after intracarotid amobarbital injection is generally considered evidence for language laterality. However, complex auditory comprehension may be preserved after injection of the dominant (left) side. The possibility that this sparing may be due to the intracarotid amobarbital injection not adequately deactivating some of the areas responsible for speech comprehension in the posterior part of the hemisphere was tested with a task known to be critically dependent on the left posterotemporal-inferoparietal region, one assessing visuo-verbal semantic relatedness. Even when the intracarotid injection of the left side produced marked deficits of speech production, comprehension of semantic relations was still intact in eight of 15 patients. Ten of these 15 patients also received right carotid injections, none of which affected comprehension of semantic relatedness. These data indicate that the intracarotid amobarbital injection cannot always specify the laterality of all language functions, an important concern when considering surgical procedures in the dominant posterotemporal-inferoparietal region.

Adolescent↗
PubMed1991

Neuroanatomy of fragile X syndrome: the posterior fossa.

The occurrence and specificity of posterior fossa abnormalities as measured from magnetic resonance images of the brain were investigated in a group of 14 males with fragile X syndrome and comparison groups consisting of 17 males with other causes of developmental disability and 18 males with normal IQs. The size of the posterior cerebellar vermis was significantly decreased and the fourth ventricle significantly increased in the group of males with fragile X syndrome compared with males in both comparison groups. These neuroanatomical abnormalities appeared to be secondary to hypoplasia rather than atrophy.

Adolescent↗
PubMed1991

Magnetic resonance imaging of the efficacy of specific inhibition of 5 alpha-reductase in canine spontaneous benign prostatic hyperplasia.

A leading role for prostatic levels of dihydrotestosterone (DHT) in the pathogenesis of benign prostatic hyperplasia is well established, if incompletely understood. The present study provides initial confirmation that 5 alpha-reductase inhibition alone is sufficient to prevent prostatic accumulation of DHT and to produce epithelial regression in the canine prostate. In dogs treated with the specific 5 alpha-reductase inhibitor finasteride, prostatic volume decreased to one-third of the baseline volume, while the prostatic concentration of DHT fell fivefold: both were constant in placebo control dogs. Demonstration that MR imaging can serve as accurate modality to assess prostatic volume was provided by serial measurements of the canine prostate and by correlation of the last imaging measurement with the weight of the excised prostate. Significant intensity changes were observed in T2-weighted images measured post-treatment; these changes correlated with the histopathology of the prostate. These results suggest that beyond quantifying regression, multiecho T2 measurements can be useful in probing accompanying changes occurring on the cellular level.

5-alpha Reductase Inhibitors↗
PubMed1991

Rapid diagnosis of Legionella infection by a nonisotopic in situ hybridization method.

The authors report a nonradioactive adaptation of DNA hybridization technology for the direct detection of Legionella organisms in situ in routinely processed histologic specimens. The probe used consisted of synthetic oligodeoxynucleotides, complementary to the ribosomal RNA of all clinically relevant Legionella species, labeled with biotinylated dUTP at their 3' ends. By in situ DNA hybridization and detection with an avidin-alkaline phosphatase complex. Legionella was visualized by light microscopy within the alveoli of lung specimens in 9 of 13 direct fluorescent antibody- or culture-positive cases of Legionnaires' disease. No cross-hybridization was observed in lung specimens infected with Pseudomonas aeruginosa, Klebsiella pneumoniae, Streptococcus pneumoniae, or other pathogens. The authors' results illustrate a novel adaptation of in situ DNA hybridization techniques, usually used for viruses, to the detection of a bacterial organism. The method enables direct visualization of bacterial nucleic acid in infected tissues and may facilitate early diagnosis and treatment of legionellosis.

Adult↗
PubMed1991

Iohexol cervical myelography in adult outpatients.

The incidence of adverse reactions following standard film or screen cervical myelography with iohexol in 32 adult outpatients was reported. Iohexol at a dose of 1,080-3,000 mg of iodine was administered via a lateral C1-C2 approach in 26 patients and via a lumbar route in 6 patients. All 32 patients underwent postmyelographic cervical spine computed tomography and were discharged after the procedure was completed. No adverse reactions occurred in 53.1% of patients. The most common adverse reaction was headache (31.3%); other minor adverse reactions included exacerbation of pre-existing pain (12.5%), neck stiffness (9.4%), and vomiting (6.3%). Good to excellent technical quality was seen on all myelograms and computed tomographic scans. Outpatient cervical myelography with iohexol appears to be a safe and cost-effective alternative to inpatient examination.

Ambulatory Care↗
PubMed1991

Sodium, ATP, and intracellular pH transients during reversible complete ischemia of dog cerebrum.

We tested the hypotheses that with the onset of cerebral ischemia, massive cellular sodium influx does not occur until adenosine triphosphate is fully depleted and that on reperfusion, neuronal sodium efflux does not occur until adenosine triphosphate is fully restored. We examined the temporal relationships among transcellular sodium, energy metabolism, and intracellular pH with sodium and phosphorus magnetic resonance spectroscopy in a new, hemodynamically stable, brain stem-sparing model of reversible, complete cerebral ischemia in eight anesthetized dogs. Inflation of a neck tourniquet after placement of glue at the tip of the basilar artery resulted in decreased blood flow to the cerebrum from 29 +/- 5 to 0.3 +/- 0.5 ml/min/100 g. Medullary blood flow was not significantly affected, and arterial blood pressure was unchanged. Sodium signal intensity decreased and did not lag behind the fall in adenosine triphosphate. After 12 minutes of ischemia, reperfusion resulted in a more rapid recovery of sodium intensity (12.4 +/- 4.8 minutes) than either adenosine triphosphate (16.5 +/- 3.7 minutes) or intracellular pH (38.9 +/- 1.8 minutes). Because intracellular sodium has a weaker signal than extracellular sodium, the decreased sodium intensity is interpreted as sodium influx and indicates that sodium influx does not require full depletion of adenosine triphosphate. Rapid recovery of sodium intensity during early reperfusion may represent sodium efflux, although increased plasma volume and sodium uptake from plasma may also contribute. If our interpretation of the sodium signal is correct, delayed recovery of adenosine triphosphate may be due to the utilization of adenosine triphosphate for the restoration of transcellular sodium gradient.

Adenosine Triphosphate↗