Search PubMed⌕ Search

Biomedical subjects

A Alavi

Publications and source records attributed to A Alavi.

At least 199 records · Page 11Linked to original sources
PubMed1993

The role of nuclear medicine in the evaluation of the male genital tract.

Scintigraphic techniques for evaluation of impotence are still evolving. Blood pool studies are most useful in assessing the integrity of arterial inflow, but may also be used to generate indices of venous leak. A non-imaging version of this test may represent a simple and cost-effective alternative. Washout of intracavernosal xenon during erection seems the most useful method of testing venous integrity. Washout using Tc-RBC may emerge as a convenient alternative to the more technically difficult xenon examinations. Development of more effective pharmacologic stimuli may further improve the utility of this quantitative and physiologic examination.

Erectile Dysfunction↗
PubMed1993

Cholescintigraphy in the diagnosis of the complications of laparoscopic cholecystectomy.

Cholescintigraphy has been used to diagnose postoperative bile leaks and obstructions after open cholecystectomy. This imaging technique has been found to be sensitive for detecting bile leaks that arise from cholecystectomy and defects in the filling and emptying of bile ducts. These observations can be applied to patients who are suspected of having bile duct injury after laparoscopic cholecystectomy. Cholescintigraphy can detect a variety of bile leaks including those arising from the gallbladder fossa, cystic duct, and the common bile duct. In addition, cholescintigraphy can be used for management of patients after stenting or bypass surgery, to assess bile flow and operative sites for any residual bile leaks. Postoperative bile duct obstructions can also be seen with cholescintigraphy. In this article we discuss a comprehensive postoperative strategy for the management and diagnosis of biliary defects after laparoscopic cholecystectomy with cholescintigraphy.

Bile Duct Diseases↗
PubMed1993

Lymphoscintigraphy. A reliable test for the diagnosis of lymphedema.

The efficacy of lymphoscintigraphy in the diagnosis of lymphedema was evaluated in 17 patients (total of 20 extremities). Final diagnoses were: three extremities with primary lymphedema, eight with secondary lymphedema, and nine with edema due to other causes. Qualitative interpretation of image patterns was reliable in differentiating lymphedema from edema of other origins (sensitivity 73%, specificity 100%). There were eight true-positive, nine true-negative, no false-positive, and three false-negative extremities. The three false-negative results occurred in extremities that were not imaged within the first hour. Lymphoscintigraphy is a reliable, objective, and noninvasive means of supporting the diagnosis of lymphedema, and lends itself more readily to repeated studies for follow-up than other available tests.

Adult↗
PubMed1993

Chest radiographic findings in patients with acute pulmonary embolism: observations from the PIOPED Study.

PURPOSE: To determine the sensitivity, specificity, and positive and negative predictive values of chest radiographic findings in patients suspected of having acute pulmonary embolism (PE). MATERIALS AND METHODS: Chest radiographs of 1,063 patients with suspected PE were reviewed. PE was confirmed angiographically in 383 patients and excluded in 680 patients. RESULTS: The chest radiograph was interpreted as normal in only 12% of patients with PE. The most common chest radiographic finding in patients with PE was atelectasis and/or parenchymal areas of increased opacity; however, the prevalence was not significantly different from that in patients without PE. Oligemia (the Westermark sign), prominent central pulmonary artery (the Fleischner sign), pleural-based area of increased opacity (the Hampton hump), vascular redistribution, pleural effusion, elevated diaphragm, and enlarged hilum were also poor predictors of PE. CONCLUSION: Although chest radiographs are essential in the investigation of suspected PE, their main value is to exclude diagnoses that clinically mimic PE and to aid in the interpretation of the ventilation-perfusion scan.

Acute Disease↗
PubMed1993

Detailed analysis of patients with matched ventilation-perfusion defects and chest radiographic opacities.

We performed a retrospective evaluation of the data obtained from the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study to determine the prevalence and distribution of pulmonary embolism (PE) in patients with matching ventilation-perfusion (V/Q) defects and chest radiographic opacities (triple matches). From the 1,487 patients in whom diagnostic V/Q scans were obtained, 247 (17%) patients were recorded as having matching V/Q defects and chest radiograph opacities in at least one lung zone. Diagnostic angiograms were available for 275 lung zones (233 patients) which demonstrated matching V/Q defects and chest radiograph opacities. The overall prevalence of PE in all lung zones with triple matches was 26%. The prevalences of PE in the upper, middle and lower lung zones were 11%, 12% and 33%, respectively. Pulmonary embolism was significantly more common in lower lung zone triple matches compared with the upper and middle lung zone triple matches (p < 0.005). There was no correlation between the size of the V/Q and chest radiographic abnormalities and the prevalence of PE. We conclude that in patients with matching V/Q defects and chest radiographic opacities isolated to the upper and middle zones the V/Q scan can be interpreted as representing a low probability of PE. Similar findings in the lower lung zones represent an intermediate probability of PE. The application of this modification to V/Q scan interpretation criteria will aid in reducing the number of intermediate V/Q lung scan interpretations.

Humans↗
PubMed1993

Cholescintigraphy in the diagnosis of acute cholecystitis: morphine augmentation is superior to delayed imaging.

Morphine-augmented radionuclide hepatobiliary imaging has been used as an alternative to delayed imaging for the diagnosis of acute cholecystitis. Previous studies have indicated that the morphine-augmentation is as useful as, or more useful than, delayed imaging. A careful comparison of the efficacy of the two techniques appears warranted because: (1) most early studies did not compare the efficacy of the two techniques in a single report using comparable patient populations; (2) the reported efficacy of morphine-augmentation is based primarily on study designs which excluded cases of early gallbladder visualization without morphine, while most delayed imaging protocols included these cases; and (3) there were concerns about the potential consequences of a false-negative morphine examination. This study compared the efficacy of morphine-augmentation with delayed imaging in those cases in which the gallbladder was not visualized during the first hour of study. Of 306 consecutive patients who were scanned to rule out acute cholecystitis, the gallbladder was visualized within 1 hr in 215 cases. In the remaining 91 cases, 46 patients had delayed imaging (17 true-positive, 10 true-negative, 19 false-positive and 0 false-negative), and 45 had morphine-augmentation (24 true-positive, 15 true-negative, 4 false-positive and 2 false-negative). The data indicate that delayed imaging has a significantly lower specificity and positive-predictive value for acute cholecystitis than morphine-augmentation and a slightly higher (statistically insignificant) sensitivity and negative-predictive value. These results appear to be supported by a reanalysis of the data that has already been reported in the literature.

Acute Disease↗
PubMed1993

Biodistribution and dosimetry of iodine-123-IBF: a potent radioligand for imaging the D2 dopamine receptor.

Iodine-123-labeled iodo-benzofuran (IBF) is a potent D2 dopamine receptor antagonist that has been developed as a potential SPECT imaging agent. This report documents its biodistribution and radiation dosimetry in seven healthy humans. Approximately 100 MBq of IBF were administered to each volunteer. Urine was collected to measure the fraction of the activity that was voided by the renal system. Conjugate images were serially acquired over 24 hr to determine the fraction of activity in the other organs. Standard image analysis techniques were used to measure the geometric mean count rates in the brain, GI tract, heart, liver, lungs and thyroid at each time point. Corrections for attenuation were made with 123I transmission scans. Multicompartmental modeling was used to stimulate and predict the biokinetic behavior of 123I-IBF in the rest of the body. The absorbed doses for 24 organs were then estimated with the MIRD formalism. Rapid biological washout minimized the absorbed dose to most tissues. The excretory organs were exposed to the most radiation. The lower large intestine received about 0.13 mGy/MBq (0.48 rad/mCi), and the urinary bladder received 0.11 mGy/MBq. This low radiation burden will allow more than 370 MBq (10 mCi) to be administered to healthy research subjects during each study of the D2 receptor. Since high quality images of the brain can be obtained with half this amount, the findings suggest that 123I-labeled IBF has a large margin of radiation safety in humans. Its stability in vivo and its high target-to-background contrast ratio in the human brain may make it a useful SPECT imaging agent.

Adult↗
PubMed1993

Comparison of radionuclide bone scans and magnetic resonance imaging in detecting spinal metastases.

A retrospective comparison was made between 99mTc-MDP bone scans and corresponding spine MR images in 35 patients who had complementary studies within 2 mo. Bone scans were performed with planar imaging of the entire body and MRI was performed with a 1.5 tesla signal scanner using standard techniques with T1- and T2-weighted images. There were 18 male and 17 female patients diagnosed with cancer prior to these studies. Cancer diagnoses included 14 prostate, 12 breast, 1 bladder, 2 renal, 2 lung, 1 each of esophagus, melanoma, myeloma and adenocarcinoma of unknown primary cancer. Of the regions compared, 69 were positive for bony metastases by MRI and 63 regions by bone scans. Thirty-eight regions were concordantly positive and 56 regions concordantly negative. No patients with entirely positive bone scans were negative by MRI, but one patient was entirely positive by MRI but negative by a bone scan. At least one region was discordantly read in 21 patients. Distribution of positive regions was similar on bone scan and MRI. The greatest number and proportion of discordant readings occurred in the lumbar regions and more frequently in patients with prostate cancer. Considering its widespread availability and the ease of performing a whole-body survey for metastasis, radionuclide bone scanning remains the study of choice for initial evaluation of patients with cancer. However, MRI is an excellent complementary technique when bone scan findings are inadequate for answering clinical questions. MRI appears to be quite sensitive and probably more specific for metastasis in certain locations of the spine.

Female↗
PubMed1993

Ventilation-perfusion scintigraphy in the PIOPED study. Part I. Data collection and tabulation.

The Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study of more than 700 patients is the largest existing study of the accuracy of lung scintigraphy in the diagnosis of acute pulmonary embolism. Perfusion scans were obtained in all patients and ventilation scans in almost all, using standardized techniques. Chest radiographs were obtained in all patients within 12 hr of the lung scan. Most patients underwent pulmonary arteriography. The images were interpreted according to a set of interpretive criteria which remained constant throughout the trial. A standardized, detailed description of each image set was derived by consensus of teams of two readers blinded to clinical and arteriographic findings. This communication reports the methods used to describe and categorize the ventilation-perfusion scintigrams obtained in patients who were enrolled in the PIOPED study. Scintigraphic technique is reviewed briefly, probability assessment is described and the scan description is reviewed in detail. The form used to describe the findings on ventilation-perfusion scans is reproduced. Use of this standardized description permits retrospective evaluation of the PIOPED interpretive criteria. In addition, it represents a rigorous approach to scan analysis which could facilitate application of formal interpretive schemes and enhance the reproducibility of lung scan interpretations in the clinical setting.

Data Collection↗
PubMed1993

Ventilation-perfusion scintigraphy in the PIOPED study. Part II. Evaluation of the scintigraphic criteria and interpretations.

This article presents an evaluation of the criteria used for categorical interpretation of the ventilation-perfusion (V/Q) scans performed in the PIOPED study. In addition, the correlation of percent probability estimates with the actual frequency of pulmonary embolism (PE) is presented. Cases which met the PIOPED criteria for various diagnostic categories were selected by computerized search of the detailed scan descriptions that had been done as part of the study. The process by which the scans were described was detailed in Part I of this report. Most of the criteria appropriately categorized V/Q scans which satisfied them. However, we recommend that three criteria should be reconsidered: 1. A single moderate perfusion defect is appropriately categorized as intermediate, rather than as low probability. 2. Extensive matched V/Q abnormalities are appropriate for low probability, provided that the chest radiograph is clear. On the other hand, single-matched defects may be better categorized as intermediate probability. Although due to the small number of cases with this finding, no definite, statistically founded recommendation can be made. 3. Two segmental mismatches may not be the optimum threshold for high probability, and in some cases should be considered for intermediate probability. However, due to the small number of cases with this finding, no definite, statistically founded recommendation can be made. We suggest that the revised criteria resulting from these adjustments should now be used for the interpretation of V/Q scans.

Evaluation Studies as Topic↗
PubMed1993

Role of radionuclide imaging in patients with suspected pulmonary embolism.

The accurate diagnosis of acute pulmonary embolism often represents a challenge to clinicians. The ventilation/perfusion (V/Q) lung scan provides a safe, noninvasive technique, which has been widely used in the diagnosis of pulmonary embolism. Although some controversy still exists in the management of patients with suspected pulmonary embolism, diagnostic strategies for investigating patients have incorporated V/Q scanning, noninvasive venous studies of the lower extremities and clinical assessment of the likelihood of pulmonary embolism. The combination of these strategies will provide acceptable diagnostic accuracy for evaluating patients with suspected pulmonary embolism in the majority of cases.

Humans↗
PubMed1993

SPECT in patients with cortical visual loss.

Single-photon emission computed tomography (SPECT) with 99mTc-hexamethylpropyleneamine oxime (HMPAO) was used to investigate changes in cerebral blood flow in seven patients with cortical visual impairment. Traumatic brain injury (TBI) was the cause of cortical damage in two patients, cerebral ischemia in two patients and carbon monoxide (CO) poisoning, status epilepticus and Alzheimer's Disease (AD) each in three separate patients. The SPECT scans of the seven patients were compared to T2-weighted magnetic resonance image (MRI) scans of the brain to determine the correlation between functional and anatomical findings. In six of the seven patients, the qualitative interpretation of the SPECT studies supported the clinical findings (i.e., the visual field defect) by revealing altered regional cerebral blood flow (rCBF) in the appropriate regions of the visual pathway. MR scans in all of the patients, on the other hand, were either normal or disclosed smaller lesions than those detected by SPECT. We conclude that SPECT may reveal altered rCBF in patients with cortical visual impairment of various etiologies, even when MRI studies are normal or nondiagnostic.

Adult↗
PubMed1993

Quantitative analysis of PET and MRI data in normal aging and Alzheimer's disease: atrophy weighted total brain metabolism and absolute whole brain metabolism as reliable discriminators.

Average whole brain metabolic rates, when corrected for brain atrophy, are similar between patients with Alzheimer's disease (AD) and age-matched controls. To elucidate the relationship between reduced cognitive function and cerebral metabolism in patients with AD, we hypothesized that the absolute amount of glucose used by the entire brain may prove to be a more reliable indicator of the disease than metabolic rates calculated for a unit of brain weight. Twenty patients with the probable diagnosis of AD and 17 similarly aged controls underwent 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) studies as well as magnetic resonance imaging (MRI) within a few days of each other. Average metabolic rates, when corrected for atrophy, were 3.91 +/- 1.02 and 4.43 +/- 0.87 (mg of glucose per 100 cc brain tissue per min +/- s.d.) respectively for AD patients and controls. Two other indices were determined, atrophy weighted total brain metabolism (calculated by multiplying the brain volume, determined by MR analysis, by the average metabolic rate) and absolute whole brain metabolism (calculated by multiplying the brain volume by the average metabolic rate corrected for atrophy). The former showed a very significant difference between the two groups (29.96 +/- 7.90 for AD patients compared to 39.1 +/- 7.0 for controls, p < 0.001). Atrophy weighted total brain metabolism also correlated very well with mini mental status exam (MMSE) scores (r = 0.59, p < 0.01). Absolute whole brain metabolism was significantly different between AD and control groups and correlated well with MMSE. These data demonstrate that although the metabolic rate per unit weight of the brain is unchanged in AD compared to controls, atrophy weighted total brain metabolism and absolute whole brain metabolism are significantly affected. Both indices may prove to be a sensitive correlate for cognitive dysfunction in AD.

Aged↗
PubMed1993

The dosimetry of iodine-123-labeled TISCH: a SPECT imaging agent for the D1 dopamine receptor.

TISCH is an iodinated D1 specific dopamine receptor antagonist that may be useful as a SPECT imaging agent. This report documents its pharmacological safety in animals and its radiation dosimetry in humans. The dose of radiation that 123I-TISCH delivered to seven healthy subjects was estimated with the absorbed fraction technique. Conjugate images of the body were serially acquired for up to 24 hr after the administration of a known amount of activity. The count rates in the organs that could be visualized were measured on each image. These count rates were corrected for attenuation with 123I transmission scans. The doses to the other organs that did not take up enough activity to be visualized on the images were estimated with established models. The dosimetry was calculated for each subject individually before the results were averaged. Rapid biological washout minimizes the radiation exposure to most organs. The dose to the large bowel is limiting in healthy volunteers. The proximal colon receives about 0.67 rad/mCi (180 microGy/MBq) or about 5 rads for every 7.5 mCi of TISCH injected. This low radiation burden should make it feasible to study the D1 dopamine receptor in patients who have neuropsychiatric disorders before and after treatment.

Adult↗