Biomedical subjects

D Norman

Publications and source records attributed to D Norman.

At least 289 records · Page 16Linked to original sources

PubMedDate not supplied

Age-related metabolite changes and volume loss in the hippocampus by magnetic resonance spectroscopy and imaging.

Magnetic resonance imaging (MRI) studies have produced controversial results concerning the correlation of hippocampal volume loss with increasing age. The goals in this study were: 1) to test whether levels of N-acetyl aspartate (NAA, a neuron marker) change in the hippocampus during normal aging and 2) to determine the relationship between hippocampal NAA and volume changes. Proton magnetic resonance spectroscopic imaging (1H MRSI) and MRI were used to measure hippocampal metabolites and volumes in 24 healthy adults from 36 to 85 years of age. NAA/Cho decreased by 24% (r = 0.53, p = 0.01) and NAA/Cr by 26% (r = 0.61, p < 0.005) over the age range studied, whereas Cho/Cr remained stable, implying diminished NAA levels. Hippocampal volume shrank by 20% (r = 0.64, p < 0.05). In summary, aging effects must be considered in 1H MRSI brain studies. Furthermore, because NAA is considered a marker of neurons, these results provide stronger support for neuron loss in the aging hippocampus than volume measurements by MRI alone.

Adult↗

PubMedDate not supplied

Leptin in pituitary adenomas--a novel paracrine regulatory system.

A growing number of physiological and pathophysiological processes have been shown to be influenced by leptin apart from its first recognised role as a modulator of hypothalamic appetite and weight control centers. We investigated the presence and pattern of distribution of leptin mRNA and the mRNA of the long isoform of the leptin receptor in the normal pituitary and in different types of pituitary adenomas. We also studied leptin secretion from human pituitary tumors in culture, and the in vitro pituitary hormone release following stimulation with human leptin. Leptin mRNA expression was detected at a low level of expression in 50% of tumors but in none of the normal pituitaries. By immunohistochemistry, leptin was present in occasional scattered cells in the normal pituitary and in pituitary tumors. The leptin receptor long isoform was detected in the majority (65%) of pituitary tumors and in all normal pituitaries. It did not segregate with any particular tumor type, and varying levels of expression were detected between the tissues studied. 34% of pituitary adenomas showed leptin release into the incubation media during in vitro culture. Leptin mRNA, the mRNA of the long isoform of the receptor, or in vitro leptin release, did not correlate with tumor type or with any of the other pituitary hormones released. In vitro leptin stimulation of pituitary tumors caused stimulation of FSH and a-subunit secretion from a non-functioning adenoma and TSH secretion from a somatotroph adenoma. As the co-localisation of ACTH and leptin in corticotroph cells was previously suggested, we investigated whether in vivo ACTH release is accompanied by a simultaneous plasma leptin level rise (i) in peripheral plasma samples after food intake-induced ACTH rise in healthy obese and nonobese individuals and (ii) in petrosal sinus samples after CRH injection in Cushing's disease patients. Our data suggest that a rise in ACTH levels is not accompanied by detectable rise in leptin levels in peripheral and in petrosal sinus blood samples. In summary, leptin is synthesized and stored within the pituitary and may modulate other pituitary hormone secretion, although probably it does not contribute to plasma leptin level changes. Pituitary leptin may therefore be a novel paracrine regulator of pituitary function.

Adenoma↗

PubMedDate not supplied

Tolerability and efficacy of Hexabrix in cerebral angiography.

In a double-blind study of 62 patients, Hexabrix was compared with Conray 60% in cerebral angiography. Both agents were injected into the same patient, the patient serving as his own control, and volumes injected into a single vessel were identical. Considerably less pain was experienced with Hexabrix. Changes in pulse, respiration and blood pressure were not significantly different. The two contrast media provided images of comparable quality.

Adult↗

PubMedDate not supplied

Relative uptake of low- and high-osmolality contrast media in CT of brain tumors.

The magnitude and time course of contrast enhancement in spontaneous canine brain tumors was determined for two contrast agents: meglumine iothalamate and sodium meglumine ioxaglate. Tumor enhancement during contrast infusion and at 5, 10, 15, 30 and 45 minutes was measured using quantitative computed tomography. Blood iodine was measured using x-ray fluorescence. Peak contrast enhancement occurred during the infusion, and the magnitude was the same for both agents. Per gram of iodine infused, blood iodine was 12.4% higher with ioxaglate than iothalamate. The monoionic dimer ioxaglate is as effective as iothalamate for enhancement of canine brain tumors.

Animals↗

PubMedDate not supplied

Optimal iodine concentration in digital subtraction arteriography.

The effects of two different concentrations of the contrast agent Hexabrix were evaluated in a total of 26 patients undergoing cerebral angiography and randomly assigned to two groups. Injection volume, rate, and iodine concentration were constant. Carotid digital exams using 8% and 12% Hexabrix in the same patient showed the higher concentration was preferred for vessels of all sizes. In comparing 12% and 16% concentrations of Hexabrix, there was again a preference for the higher concentration, although results were not statistically significant. Both 12% and 16% Hexabrix in carotid studies resulted in excellent quality exams. Vessel see-through ability was somewhat better with 12% Hexabrix. Subjective symptoms of all patients during the injection were minimal or absent. Hexabrix is theoretically more attractive than conventional agents in that optimal concentration for digital imaging is in a range which is iso-osmotic with serum.

Analog-Digital Conversion↗

PubMedDate not supplied

Iohexol cerebral angiography. Multicenter clinical trial.

Ionic contrast media currently used in cerebral angiography frequently cause discomfort due to hyperosmolality. This double-blind, multicenter trial compared two ionic media, meglumine iothalamate and meglumine-Na diatrizoate, with the new nonionic agent, iohexol, in 277 patients undergoing cerebral angiography. Vital signs, cardiovascular changes, and neurologic status were evaluated before, during, and after injection. Patients were observed for adverse reactions for up to 24 hours following studies. Patient discomfort and image quality were evaluated. Visualization was good or excellent with all media studied. No significant physiological differences were observed between the ionic and iohexol groups, but fewer iohexol patients experienced large increases (greater than 20 mmHg) in systolic blood pressure. Iohexol patients experienced significantly less discomfort; ionic patients reported severe discomfort 21/2 times more often. This finding was attributed to iohexol's low osmolality. Iohexol may be indicated particularly for use in selective angiograms where discomfort is a factor and for patients suspected of having blood-brain barrier disruption.

Adult↗

PubMedDate not supplied

MR imaging of orbital cavernous hemangioma.

Four cases of biopsy proven orbital cavernous hemangioma were studied with magnetic resonance imaging. The hemangiomas were isointense with brain on T1-weighted spin echo (SE) images and well differentiated from adjacent structures due to intense signal from surrounding fat. The T2-weighted SE images of the hemangioma were of high signal intensity in comparison to the orbital fat. The use of surface receiving coils produced striking detail of all soft tissue structures especially on T1-weighted images.

Aged↗

PubMedDate not supplied

MR imaging of pineal cysts.

Identification of pineal cysts with imaging modalities other than magnetic resonance (MR) has been infrequent, despite a reported autopsy incidence of as high a 40%. We recently identified 15 patients in whom pineal cysts were seen on MR. These cysts ranged from 5 to 15 mm in maximum diameter. The cyst walls were thin, usually measuring less than 2 mm. The signal characteristics of the fluid within the cysts paralleled that of CSF, although it differed somewhat in signal intensity from CSF collections in which there was pulsatile motion. All lesions were midline in location. There was no significant mass effect, although mild flattening of the superior colliculi could be seen. Two cases were operated on; at operation, typical pineal cysts were found, with one containing hemosiderin-laden proteinaceous material, which accounted for its markedly higher signal intensity. It is important that this entity be recognized so that these lesions are not confused with pineal tumors.

Cysts↗

PubMedDate not supplied

MR imaging of acute transverse myelitis and AIDS myelopathy.

Acute transverse myelitis (ATM) is a well recognized clinical entity, though its etiology remains obscure. Only a few reports of magnetic resonance imaging of ATM appear in the literature. These reports describe conflicting findings with respect to the signal intensity of the spinal cord on long repetition time (TR) sequences. The purpose of this study is to present our experience with five cases of ATM in which long TR sequences demonstrated abnormal increase in signal intensity of the cord. Magnetic resonance imaging also demonstrated extension of abnormal cord signal intensity over at least six spinal segments and above the clinically determined sensory level in four of five cases. Cord expansion was noted in two of five cases with normal myelograms. A case of acquired immunodeficiency syndrome (AIDS) myelopathy that demonstrated a similar high signal intensity of the cord is also presented. Our findings suggest that both ATM and AIDS myelopathy should be considered in the list of conditions that may result in a diffuse increase in the signal intensity of the cord on long TR sequences.

Acquired Immunodeficiency Syndrome↗

PubMedDate not supplied

Preoperative embolization of juvenile angiofibromas of the nasopharynx.

The juvenile nasopharyngeal angiofibroma is a vascular tumor. Careful and complete removal is challenging because of the brisk bleeding during surgery. The means applied to reduce this blood loss have included preoperative estrogens, ligation of feeding vessels, silicone embolization of feeding vessels, and cryosurgery. We have used preoperative Gelfoam embolization of the internal maxillary artery in seven patients. Our clinical impression of significant reduction in loss of blood was confirmed by comparison with 16 previous patients. The average amount of blood lost in the embolized group was half that of the control group. A study of this type comprises many variables; however, the results do suggest that preoperative embolization of the internal maxillary artery is of advantage in the surgical treatment of juvenile angiofibromas.

Adolescent↗

PubMedDate not supplied

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Heliotherapy↗

PubMedDate not supplied

Artifacts associated with MR neuroangiography.

Neurovascular MR angiography (MRA) is rapidly gaining greater clinical acceptance. To provide functional information, novel techniques of acquisition, information processing, and display are used, generating a new set of artifacts. The purpose of this paper is to outline the causes, provide examples, and note clinical problems associated with MRA artifacts by grouping them into six common types: 1) poor visualization of small vessels, 2) overestimation of stenosis, 3) view-to-view variations, 4) false positives, 5) false negatives, and 6) vessel overlap. This in turn will lead to four generalized solutions: 1) optimize acquisition parameters, 2) edit volume boundaries before performing maximum intensity projection reconstructions, 3) refer to the individual source images, and 4) use alternative image processing. By organizing and simplifying both clinical problems and solutions into major categories, a greater understanding of the current clinical indications and the overall goals of MRA can be achieved.

Angiography↗

PubMedDate not supplied

Perioptic cyst distal to optic nerve meningioma: MR demonstration.

Dilation of the subarachnoid space between the distal edge of an optic nerve sheath meningioma and the eyeball has previously been observed during surgery and considered a rare finding. We observed such perioptic cysts in seven patients with optic nerve meningioma and describe the MR features of this finding.

Adolescent↗

PubMedDate not supplied

Methotrexate for the treatment of patients with multiple episodes of acute cardiac allograft rejection.

Of 142 cardiac allograft recipients who underwent transplantation from December 1985 to January 1991, four women and seven men (mean age, 41 +/- 14 years) required multiple (10.5 +/- 3.3) courses of antirejection treatment over a total follow-up period of 30 +/- 15 months. The underlying heart disease was cardiomyopathy in six patients and coronary disease in five patients. These patients were treated with methotrexate (10 mg/wk for 6 weeks). Rejection treatment before methotrexate therapy included six courses of OKT3, one course of antithymocyte globulin, 33 courses of high-dose steroids, and 45 courses of low-dose steroids for the entire group. The average number of rejection treatments per patient before methotrexate therapy was 8.7 +/- 3.5 treatments or 0.90 +/- 0.51 treatments per month of follow-up. After methotrexate therapy the average number of rejection treatments fell to 1.7 +/- 1.1 treatments or 0.11 +/- 0.08 treatments per month of follow-up (p = 0.0002). Seven patients responded to a single course of methotrexate therapy; three patients required two courses (second course, 20 mg/wk for 6 weeks), and one patient required three courses of methotrexate therapy. The only complication associated with methotrexate therapy was one patient in whom cytomegalovirus interstitial pneumonitis developed while on therapy. Methotrexate was well tolerated and appeared to be effective in halting repeated episodes of rejection in this subset of patients who have had multiple episodes of acute rejection.

Adult↗

PubMedDate not supplied

Hyperglycemia augments ischemic brain injury: in vivo MR imaging/spectroscopic study with nicardipine in cats with occluded middle cerebral arteries.

Hyperglycemia is often associated with an increased frequency of cerebrovascular disease and exacerbation of neuronal injury in focal ischemic cerebral infarction. We used a combination of high-field proton MR imaging and 1H and 31P MR spectroscopy to investigate whether hyperglycemia would adversely influence cerebral metabolism and eventual infarct size following unilateral occlusion of the middle cerebral artery (MCA) of cats pretreated with the calcium channel blocker nicardipine. Normoglycemic animals injected with 10 micrograms/kg of nicardipine (8 micrograms.kg-1.hr-1 maintenance dose) manifested only mild disturbances in phosphorus metabolism and cerebral pH regulation compared with untreated controls, and showed a significant reduction in infarct size 7 hr after MCA occlusion. By comparison, hyperglycemic cats (plasma glucose, 200-300 mg/dl) had significantly reduced cerebral high-energy phosphates, elevated lactic acid, and larger ischemic lesions in the occluded MCA territory, irrespective of whether they were treated with nicardipine. These results indicate that moderate hyperglycemia can exaggerate ischemic brain damage by enhancing formation of tissue lactic acid and impairing normal phosphorus metabolism. One implication of this study is that dextrose should not be provided to patients with acute ischemic stroke.

Animals↗

PubMedDate not supplied

Diffusion-weighted MR imaging of the brain: value of differentiating between extraaxial cysts and epidermoid tumors.

This study demonstrates the use of diffusion-weighted MR imaging in improving the specificity of the diagnosis of extraaxial brain tumors. Three surgically proved lesions (one arachnoid cyst and two epidermoid tumors) and two nonsurgically proved lesions (arachnoid and ependymal cysts) were evaluated with T1- and T2-weighted spin-echo studies followed by intravoxel incoherent motion (IVIM) MR imaging. The IVIM images of the lesions were displayed as an apparent diffusion coefficient (ADC) image obtained at 0.65 G/cm (maximum gradient b value = 100 sec/mm2) and compared with external oil and water phantoms. The ADC of arachnoid cysts was similar to stationary water whereas the ADC of epidermoid tumors was similar to brain parenchyma, indicating the solid nature and the slower diffusion rate of the epidermoid tumors. Cisternal CSF demonstrated uniformly high ADC, primarily because of bulk flow, which enhanced image contrast. Improved delineation of postsurgical changes was also possible. Our preliminary results show that diffusion-weighted MR imaging can be useful in distinguishing between arachnoid cysts and epidermoid tumors.

Adult↗

PubMedDate not supplied

Gd-DTPA-enhanced MR imaging of pituitary adenomas.

Eleven previously nonoperated patients with suspected pituitary microadenomas were scanned on a 1.5-T GE system before and after administration of IV gadolinium-DTPA (0.1 mmol/kg). Six patients had Cushing disease, four had hyperprolactinemia, and one had acromegaly. Surgical confirmation was available in all cases, and these findings were correlated with results of CT and venous sampling, when available. The normal pituitary gland, infundibulum, and cavernous sinuses enhance immediately after the administration of gadolinium-DTPA, allowing contrast between the enhancing normal glandular tissue and low-intensity microadenomas. Contrast-enhanced MR detected a lesion not seen on the unenhanced images in two patients with Cushing disease and in one patient with hyperprolactinemia. Tumor delineation was improved with gadolinium administration in two additional cases. In six patients, administration of gadolinium did not significantly alter the precontrast interpretation. Adenomas were found at surgery in all 11 patients. The tumor was correctly localized on MR in four of the six patients with Cushing disease, resulting in an accuracy of 66.7%. In another patient, although a focal lesion was detected on MR, location of the adenoma at surgery was discrepant with the MR findings and was therefore considered a false-positive study. In the single false-negative examination, both pre- and postcontrast MR failed to detect a surgically confirmed microadenoma suspected on both contrast-enhanced CT and venous sampling. Correct localization of the adenoma was achieved in all of the five non-Cushing patients, yielding an accuracy of 100%. Immediate T1-weighted coronal scans were most useful in detecting intrasellar disease. Delayed scans obtained 30 min after injection did not improve the differentiation of pituitary gland from microadenoma.(ABSTRACT TRUNCATED AT 250 WORDS)

Acromegaly↗

PubMedDate not supplied

Three-dimensional gradient-recalled MR imaging as a screening tool for the diagnosis of cervical radiculopathy.

The purpose of the study was to implement and assess a fast-screening, three-dimensional Fourier transformation (3DFT) MR sequence for the cervical spine. This sequence maintains adequate signal-to-noise and image contrast similar to gradient-recalled echo two-dimensional Fourier transformation (2DFT) imaging. Thirty patients with radiculopathy were examined with 3DFT gradient-recalled echo imaging. The data set consisted of 60 contiguous 1.5- to 2.0-mm-thick axial slices with a total coverage of 9 to 12 cm. In 10 patients, comparison was made with 4-mm-thick axial T1-weighted spin-echo 2DFT or gradient-recalled echo 2DFT studies. With the use of a volume acquisition, adequate signal-to-noise and image contrast similar to T2*-weighted gradient-recalled echo 2DFT acquisitions were obtainable. Coverage was improved despite the use of thinner sections without interslice gap. Thin-section 3DFT provided superior detail of acquired foraminal and spinal canal stenosis and disk morphology. Limitations included increased sensitivity to patient motion and "wraparound" artifact in the slice-select direction. Overall, diagnostic confidence was improved with 3DFT owing to the reduction of partial volume artifact. We have adopted this technique as the primary screening method for diagnosing cervical radiculopathy.

Evaluation Studies as Topic↗