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Biomedical subjects

R N Bryan

Publications and source records attributed to R N Bryan.

At least 163 records · Page 9Linked to original sources
PubMedDate not supplied

Hyperintense thrombus on GRASS MR images: potential pitfall in flow evaluation.

Gradient-recalled acquisition in the steady state (GRASS) MR images, obtained in four patients with angiographic evidence of successful occlusion of cerebral arteriovenous malformations, demonstrated hyperintense signal intraluminally. Although this was initially mistaken as evidence of persistent blood flow in the arteriovenous malformation, the short TR/TE spin-echo images showed hyperintense signal rather than flow void, thereby indicating the presence of subacute thrombus. GRASS images alone should not be used to determine the success of embolotherapy of cerebral arteriovenous malformations or to determine aneurysm patency, since the hyperintense signal is a potential pitfall that may mislead the radiologist in the absence of corroborative images, particularly the short TR/TE spin-echo sequences.

Adolescent↗
PubMedDate not supplied

MR of intracranial epidermoid tumors: correlation of in vivo imaging with in vitro 13C spectroscopy.

We analyzed the MR findings of five patients with benign intracranial epithelial tumors, commonly called epidermoids. The neoplasms were categorized into two groups on the basis of T1-weighted MR signal intensity (relative to brain): high-signal-intensity masses (short T1) and low-signal-intensity masses (long T1). Surgical specimens were obtained and analyzed by means of 13C MR spectroscopy. Epidermoids with short T1 values (white epidermoids) had a high lipid content comprising mixed triglycerides containing unsaturated fatty acid residues. Epidermoids with long T1 values (black epidermoids) exhibited a much reduced lipid content with no triglycerides or fatty acids. There was evidence of trace amounts of cholesterol in the black epidermoids. Our data indicate that epidermoids are a heterogeneous group of neoplasms that behave differently with T1-weighted MR imaging and 13C MR spectroscopy. The combination of MR imaging and spectroscopy holds the potential of further elucidating the nature of epidermoids as well as of other forms of neoplasms.

Brain↗
PubMedDate not supplied

MR imaging of hyperacute intracranial hemorrhage in the cat.

Hyperacute intracerebral hematomas were successfully created in five cats by injecting a prepared blood sample in which the oxygen (O2) saturation ranged from 0-80%. T1- and T2-weighted spin-echo sequences and T2-weighted gradient refocused scans were obtained 2.5-10 hr after injection on a 1.5-T imaging system. Detailed histology or electron microscopy was performed on each brain to confirm the presence of intact red blood cells in a retracted clot matrix. Areas of the hematoma were hypointense relative to brain in all five cats on the gradient refocused scans. The hematoma was isointense relative to brain on the T1- and T2-weighted spin-echo scans in all cats except one, which suffered a seizure/respiratory arrest and died during the scanning procedure. Portions of the hematoma in this animal had a hypointense T2-weighted signal and a hyperintense T1-weighted signal, which corresponded to the predicted MR properties of intracellular methemoglobin. We hypothesize that acute (less than 10 hr old) hematomas that contain virtually 100% intracellular deoxyhemoglobin may not appear hypointense relative to brain on T2-weighted scan sequences at 1.5 T unless surrounding tissue hypoxia and/or anoxia promote additional changes, one of which may be the formation of intracellular methemoglobin.

Acute Disease↗
PubMedDate not supplied

Effect of clot formation and retraction on spin-echo MR images of blood: an in vitro study.

Phantoms were constructed that contained red blood cell (RBC)-free clots in varying stages of clot retraction. MR images of these samples were compared with those of retracted whole venous blood clots and a fresh rat brain standard. Images were obtained at 0.3 T, 0.5 T, 1.0 T, 1.5 T, and 2.4 T with T1-, spin-density- and T2-weighted spin-echo pulse sequences. The presence or absence of venous blood cells in the clot caused only minor differences in T2- and spin-density-weighted images of the clots at or below 1.5 T. On T2-weighted scans, the retraction of the RBC-free clot resulted in a progressive decrease in signal intensity at 2.4 T. Fully retracted RBC-free clots were markedly hypointense relative to serum and ranged from slightly hyperintense to isointense with brain and venous clots at 0.5-1.5 T. There were no striking concomitant signal intensity changes on the spin-density- or T1-weighted scans, which could have caused the changes seen on the T2-weighted images of the clots. Our results indicate that the physical basis of these MR effects in the RBC-free clots is the concentration of plasma protein. The combined concentration of plasma protein and the tightly packed RBC proteins in the venous clots causes the strikingly similar MR appearance of venous and RBC-free clots on clinical images. These results do not demonstrate the presence of the previously postulated selective T2 relaxation of intracellular paramagnetic deoxyhemoglobin in these in vitro venous clots.

Animals↗
PubMedDate not supplied

Acute subarachnoid hemorrhage: in vitro comparison of magnetic resonance and computed tomography.

The computed tomographic (CT) attenuation values and magnetic resonance (MR) signal intensities of simulated acute subarachnoid hemorrhage were compared systematically. In vitro MR and CT measurements (T1, T2, and Hounsfield units) were made of mixtures of normal human cerebrospinal fluid (CSF) and normal heparinized blood, ranging from 0% to 100% by volume. The mixtures were measured in a plexiglass phantom with a Siemens DR3 CT scanner for attenuation measurements (Hounsfield units) and in the Baylor Bruker Instruments Proton Scanner (6-MHz) using inversion-recovery and spin-echo pulse sequence techniques for T1- and T2-calculated relaxation times. A PRAXIS II (10.7 MHz permanent magnet) nonimaging unit was used to measure the relaxation times of the CSF/blood mixtures independently for comparison. The Hounsfield measurements of the densest parts of the layered mixtures showed increasing values with increasing amounts of hemorrhage (0% blood, 0 H; 100% blood, 66 H) in a nonlinear pattern. The T1 times of the mixtures decreased with increasing amounts of blood, ranging from 2200 msec to 500 msec for 100% CSF and 100% blood, respectively. The inverse of the T1 relaxation times was proportional to the percentage of blood. The T2 data for the mixtures were similar in character to the T1 relaxation times, except for shorter T2 times at high concentrations of blood. It was concluded the MRI distinguishes varying blood/CSF mixtures on the basis of relaxation times better than does CT on the basis of Hounsfield units. CT still has an imaging advantage, since high-concentration hemorrhage is clearly different from normal brain, while concentrated acute subarachnoid blood has relaxation times similar to normal brain and is nearly isointense on MRI.

Acute Disease↗
PubMedDate not supplied

MR imaging of optic pathways in patients with neurofibromatosis.

Twenty-one patients with documented neurofibromatosis had MR examinations to evaluate possible intracranial disease. In five cases the indication was a known or suspected optic glioma. Two patients were examined because of a history of seizures; the rest were examined as part of a baseline evaluation. Eighteen patients showed evidence of signal hyperintensity on T2-weighted images. Lesions involved the optic nerves, optic chiasm, optic tracts, lateral geniculate body, optic radiations, basal ganglia, periventricular white matter, cerebellar white matter, and dentate nucleus of the cerebellum. Comparison between MR and concurrent CT scans showed MR to be superior in demonstrating the posterior extent of optic-pathway gliomas. In addition, MR showed focal areas of hyperintensity in the basal ganglia, internal capsule, cerebellum, and/or white matter that were not detected on CT. Although we found MR to be superior to CT in detecting intracranial tumors in patients with neurofibromatosis, and in evaluating the extensive involvement of known lesions, the full clinical implications of our findings remain to be determined.

Adolescent↗
PubMedDate not supplied

Magnetic resonance imaging in multiple sclerosis: results in 32 cases.

A prospective clinical study was performed in 32 patients with multiple sclerosis (MS) to evaluate the sensitivity of lesion detection and accuracy of lesion localization by neurologic examination, delayed enhanced computed tomography (CT) with a double dose of contrast material, and proton magnetic resonance (MR) imaging. After neurologic examination patients were classified by probability of MS (possible, four patients; probable, three patients; and definite, 25 patients) and by disease activity (acute, chronic with acute exacerbation, or chronic progressive). Subsequently they underwent delayed enhanced CT scanning and MR imaging with more than one spin-echo technique. In five of seven patients with possible or probable MS, both MR imaging and delayed enhanced CT were negative. In 25 cases of definite MS, MR imaging detected pathology in 19 (76%) cases, while CT detected lesions in 15 (60%) of 25 cases. In acute lesions (acute or chronic with acute exacerbation), the two techniques were of similar sensitivity (delayed CT was positive in 65% and MR imaging in 60%), while in chronic progressive MS, MR imaging was superior in lesion detection (MR imaging positive in 75%; delayed CT in 25%). While most lesions (55%) were seen in corresponding locations in both studies, neither MR nor delayed CT correlated well with lesion localization by neurologic examination because a large number of asymptomatic lesions were imaged and many symptomatic lesions were undetected.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Radiographic management of juvenile angiofibromas.

Juvenile angiofibromas are benign, vascular, locally aggressive neoplasms that are preferably treated by surgical resection, or irradiation if surgery is not possible. Adequate surgery in the past has been limited by incomplete knowledge of the anatomy of the tumor and technical difficulties related to the vascularity. To better define the tumor, 12 patients with juvenile angiofibroma have been studied by axial and coronal high resolution computed tomography (CT). The extent of the neoplasm was better demonstrated by CT than by other techniques. Based on the CT findings, we propose an anatomic classification that is helpful in determining treatment methods. Nine patients were considered operable, and eight of these underwent preoperative embolization with Silastic spheres and Gelfoam. The preoperative embolization significantly reduced operative difficulty and the necessity for blood transfusions. Based on these cases, we believe the current radiographic management of juvenile angiofibromas should consist of plain films, CT, angiography and, in surgical cases, preoperative embolization.

Adolescent↗
PubMedDate not supplied

NMR evaluation of stroke in the rat.

Cortical stroke was produced in rats by cautery occlusion of the middle cerebral artery distal to the lenticulostriate origins. Brains were removed, and nuclear magnetic resonance (NMR) scans of whole fixed brains and in vitro measurements of small samples were obtained. Brain tissue was then processed for histology. Routine scans used a modified spin-echo technique. Spin-density and T2-dependent scans were also obtained. Infarcts were detectable in 6 hr due to diminution of the spin-echo intensity from T2 prolongation. NMR changes increased gradually over 48 hr and coincided anatomically with evidence from the neuropathologic sections. NMR imaging is a very sensitive method of evaluating acute cerebral infarction in this animal model.

Animals↗
PubMedDate not supplied

Neuroangiography with iohexol.

Iohexol is a new, nonionic water-soluble contrast agent undergoing early clinical trials in the United States. Using a double-blind, parallel format, iohexol was compared with meglumine iothalamate (60 patients) for selective cerebral angiography, and with sodium meglumine diatrizoate (40 patients) for arch aortography. Iohexol produced significantly less pain than meglumine iothalamate or sodium meglumine diatrizoate. There were no significant differences in terms of heart rate, blood pressure, or electrocardiogram (ECG) changes. Both produced a transient tachycardia and hypotension after arch aortography, but significantly less so with iohexol. No significant complications occurred. Film quality was comparable between contrast agents except for diminished motion artifacts with iohexol. Iohexol appears to be a superior neuroangiographic contrast agent to current ionic drugs.

Adult↗
PubMedDate not supplied

Effect of bromocriptine and pergolide on pituitary tumor size and serum prolactin.

Forty-two patients with elevated serum prolactin were treated in a randomized, open-label trial with the conventional ergot bromocriptine, or a new ergot pergolide. Before treatment, the patients underwent thorough endocrine evaluation and computed tomographic scan. All patients had prolactin levels greater than 25 ng/ml, and 27 patients had a pituitary mass. Follow-up studies performed after 6 months of treatment showed both drugs effectively reduced prolactin levels to normal, though pergolide effects were more rapid. There was no change in the contents of the pituitary fossa in the 10 patients with hyperprolactinemia but without pituitary mass. Sixty percent of patients with pituitary mass had diminution of tumor size. Pergolide appears to be an effective medical treatment for hyperprolactinemia and pituitary tumor and offers a possible alternative to bromocriptine and surgical treatment.

Bromocriptine↗
PubMedDate not supplied

Choroidal osteoma.

Choroidal osteomas are benign, juxtapapillary, choroidal tumors that mandate no treatment. They occur predominantly in young (median age, 20 years) females (90%). While ophthalmoscopy and fluorescein angiography reveal suggestive ophthalmic findings, echography, plain radiography, and especially computed tomography (CT) are important in establishing the correct diagnosis. These lesions may be clinically confused with various dystrophic lesions, atypical or amelanotic malignant choroidal melanoma, metastatic carcinoma, leukemic or lymphomatous infiltrates, choroidal hemangioma, choroidal scars of the macula, and organized subretinal hemorrhage. The exclusion of the differential consideration of malignant melanoma is most important since radiation and enucleation are therapeutic possibilities. Review of the literature shows that all nine reported cases with CT scans had clearly demonstrable calcific densities in the posterior pole of the affected eye. Four other cases are reported here with a summary of the typical clinical, radiologic, and pathologic findings. The role of CT in the evaluation of choroidal osteoma and the distinctiveness of the CT findings are stressed.

Adolescent↗
PubMedDate not supplied

Neurotoxic effects of water-soluble contrast agents on rat hippocampus.

Electrical activity in cells directly exposed to water-soluble radiographic contrast agents was investigated by intracellular and extracellular recordings from neurons in in vitro rat hippocampus slices. Measurements included extracellular field potentials, intracellular resting membrane potential and membrane conductance, postsynaptic events, action potential configurations and spontaneous electrical activity. The neurons were exposed to test solutions of an ionic contrast agent, sodium diatrizoate, and a nonionic contrast agent, metrizamide, as well as control solutions. The ionic contrast agent produces bursts of action potentials having epileptogenic characteristics which is temporally followed by a depression of all electrical activity. The nonionic contrast agent produces minimal convulsive-like electrical bursts, but does produce a consistent depression of transmembrane electrical potentials, though in a lesser degree than the ionic contrast agents. The excitatory electrical events appear to be related to large depolarizing post-synaptic events while the later electrical depression is at least partially due to hyperpolarization. The depressing effects may be related to the hyperosmolality of the test solutions; however, no excitatory changes are related to hyperosmolality. These results provide the initial data on the neurotoxicity of water-soluble contrast agents at the intraneuronal level.

Action Potentials↗
PubMedDate not supplied

Epileptogenic effects of radiographic contrast agents: experimental study.

Electrical activity in cells directly exposed to water-soluble radiographic contrast agents was investigated by intracellular recordings from neurons of the abdominal ganglia of Aplysia. Measurements of membrane resting potential, membrane conductance, synaptic and action potential configuration, and spontaneous electrical activity were performed. Test solutions included sodium diatrizoate, meglumine iothalamate, metrizamide, and control solutions. Solutions (100 and 200 mOsm) of these agents did not significantly alter resting membrane potential, membrane conductance, action potential frequency or configuration, or excitatory postsynaptic potentials. Inhibitory postsynaptic potentials were suppressed by contrast agents. These results suggest that contrast agents affect at least some neurons by disinhibition.

Action Potentials↗
PubMedDate not supplied

Neurotoxic effects of water-soluble contrast agents on rat hippocampus: extracellular recordings.

Synaptically evoked extracellular field potentials were obtained from the pyramidal cell layer of the Cal field of rat hippocampus slices. Synaptic activity was evoked by Schaffer's collateral stimulation. The effects of the water-soluble contrast agents Na-diatrizoate and metrizamide, as well as control solutions of NaCl and sucrose, were studied. Test solutions were 300-345 mOsm and had iodine concentrations of 3-30 mg I/ml. The effects of test solutions are apparent within 10 minutes and reversible within 30-45 minutes. Control recordings have a small positive potential, followed by a large negative spike and a final slow positive wave. Contrast agents have two effects. The first is an epileptogenic property characterized by repetitive negative spikes arising from an extended slow positive field. The second effect is a depression characterized by a reduction in the amplitude of the synaptically evoked fields, particularly the negative spikes. Na-diatrizoate predominately produces the first effect, while metrizamide principally produces the second. Hyperosmolar solutions only produce depression. These results correlate well with the clinical setting where Na-diatrizoate is a potent convulsant, while metrizamide produces symptoms compatible with neuronal depression. These results indicate that contrast agent seizure activity is not due to hyperosmolarity but to a more direct chemical effect. The depression, however, may be related to a hyperosmolar effect.

Animals↗
PubMedDate not supplied

Irreversible regional cerebral ischemia: serial MR imaging and proton MR spectroscopy in a nonhuman primate model.

PURPOSE: To delineate the changes in proton MR spectroscopy and imaging that occur with acute, irreversible ischemia of the basal ganglia of a baboon. MATERIALS AND METHODS: The M1 segments of the middle cerebral arteries of six adult male baboons were occluded by endovascular means with microcatheters and N-butyl cyanoacrylate adhesive. Cerebral blood flow measurements were taken with positron emission tomography or radioactive microsphere techniques. Serial spatially localized proton MR spectroscopy of the basal ganglia and MR imaging of the brain were performed. The distribution of ischemic and infarcted tissue was demonstrated by histopathologic techniques or triphenyltetrazolium chloride staining. RESULTS: Radioactive microsphere or positron emission tomography measurements demonstrated no significant cerebral blood flow within the basal ganglia after occlusion of the middle cerebral artery. Proton MR spectroscopy of the basal ganglia demonstrated increasing cerebral lactate and decreasing N-acetyl aspartate within 30 minutes of middle cerebral artery occlusion. Changes in the MR imaging signal intensity of the basal ganglia were observed as early as 3.1 hours on T2-weighted, 3.3 hours on T1-weighted, and 6.1 hours on spin density-weighted images. The distribution of these changes correlated well with the histopathologic features of ischemia and infarction that were seen throughout the basal ganglia. CONCLUSION: Changes in MR imaging signal intensity corresponded to ischemia and infarction in our baboon model of acute irreversible ischemia of the basal ganglia. Increasing cerebral lactate and decreasing N-acetyl aspartate preceded changes in MR imaging signal intensity.

Animals↗