PubMed Health⌕ Search

Biomedical subjects

C Schiepers

Publications and source records attributed to C Schiepers.

34 records · Page 2Linked to original sources
PubMed1996

Visualisation of loss of 5-HT2A receptors with age in healthy volunteers using [18F]altanserin and positron emission tomographic imaging.

We used [18F]altanserin and positron emission tomography (PET) to image serotonin 5-HT2A receptors in humans. The highest [18F]altanserin uptake is found in the cerebral cortex, with specific-to-nonspecific binding ratios varying from 0.53 to 1.91 in humans between 24 and 48 years of age. In all neocortical regions studied, [18F]altanserin uptake correlates negatively with age. No correlations were found between age and uptake in the cerebellum, the regional cerebral blood flow, or the time course of metabolization of [18F]altanserin. The reduction in cerebral 5-HT2A receptor binding thus directly reflects the loss of specific 5-HT2A receptors with age.

Adult↗
PubMed1996

Three-dimensional correction for spillover and recovery of myocardial PET images.

UNLABELLED: PET permits the quantification of myocardial blood flow, but is hampered by the limited spatial resolution of PET images. METHODS: We evaluated two methods for the correction of resolution effects in PET perfusion 13NH3-ammonia images. In one model, the spillover and recovery coefficients are estimated in the kinetic modeling analysis. The new, second model uses an explicit delineation of the left ventricular wall and a convolution model for the system point spread function to compute the regional values of the spillover and recovery coefficients. RESULTS: The new method is validated with phantom measurements. The two methods are evaluated on animal experiments using 13NH3-ammonia. Both two- and three- compartment models were used to compute absolute flow values. Excellent linear correlations with microsphere data were obtained. The slope of the regression line was lower for corrections based on kinetic modeling as compared to convolution-based correction. In animal experiments, recovery coefficients of 59% for the myocardial wall and 86% for the blood pool were obtained. Spillover from the blood pool into the myocardial was was 14%. CONCLUSION: The new correction method strongly suppresses spillover and recovery effects due to limited resolution.

Algorithms↗
PubMed1995

Metabolism of nitrogen-13 labelled ammonia in different conditions in dogs, human volunteers and transplant patients.

To investigate the rate of metabolism of nitrogen-13 labelled ammonia (13NH3) in different conditions, we have determined the relative amount of unchanged 13NH3 in the blood of dogs, volunteers and transplant patients at different times following injection. In dogs, the determinations were made under basal conditions, during adenosine administration and after coronary occlusion. The results show that adenosine administration increases the metabolic rate whereas coronary occlusion does not affect 13NH3 metabolism. For both human volunteers and transplant patients the metabolic rate of 13NH3 was assessed under basal conditions and during adenosine administration. 13NH3 metabolism proceeds faster in transplant patients than in volunteers under both conditions. Adenosine administration causes a faster 13NH3 turnover in volunteers but not in transplant patients. Application of individual metabolite correction resulted in a 16% decrease in the calculated blood flow compared to uncorrected values. A smaller difference (5%) was observed between correction with mean metabolite values and individually acquired metabolite values.

Adenosine↗
PubMed1995

Contribution of PET in the diagnosis of recurrent colorectal cancer: comparison with conventional imaging.

The clinical value of total body PET with FDG was evaluated in 76 patients presenting with or suspected of recurrent local or distant colorectal cancer. PET results were compared to those of routine imaging (CT pelvis, CT/US liver and CXR). The accuracy of PET for local disease was 95% which was superior to CT-pelvis (accuracy 65%). PET accuracy for liver metastases (98%) compared favourably to CT/US-liver accuracy (93%). Unexpected extra-hepatic mestastases were detected by PET in 14 locations in 10 patients. Also, a primary breast cancer was found in one patient. The main value of PET appeared an improved staging of apparently resectable, local or distant recurrent disease. Thereby, a more adequate indication of major secondary surgery could be attained.

Colorectal Neoplasms↗
PubMed1994

Clinical value of whole-body positron emission tomography with [18F]fluorodeoxyglucose in recurrent colorectal cancer.

To assess the clinical value of whole-body positron emission tomography (PET) with [18F]fluorodeoxyglucose (FDG) in recurrent colorectal cancer, 35 patients were studied: 15 had resectable liver metastases, one a resectable lung metastasis, eight resectable pelvic recurrence, eight a presacral mass with equivocal findings on imaging, and three increasing serum levels of carcinoembryonic antigen (CEA) without clinical or radiological signs of recurrent disease. PET affected management decisions in seven of 16 patients with metastatic disease. In one of eight patients with pelvic recurrence demonstrated by computed tomography (CT), PET detected unknown pulmonary metastases. In five of eight presacral masses with equivocal CT findings, PET was correct and unexpected distant metastases were detected in one of these patients. In two of three patients with increasing CEA levels and normal pelvic CT findings, pelvic recurrence was identified. Overall, whole-body PET affected management in 14 patients. PET is a valuable tool for staging local recurrence and metastatic disease.

Aged↗
PubMed1994

Diagnostic value of 99Tcm-d,l-HMPAO-labelled leukocyte scintigraphy in the detection of vascular graft infections.

Prosthetic vascular graft infection is a relatively uncommon complication of peripheral vascular surgery. We retrospectively analysed technetium-99m-d,l-hexamethylpropylene amine oxime (99Tcm-d,l-HMPAO) labelled leukocyte scans of 21 patients with a suspected vascular graft infection. Operative findings, bacteriological cultures, radiological findings or clinical follow-up were used to confirm the diagnosis. We found eight true-positive and six true-negative cases. There were no false-positive scintigraphic diagnoses. The false-negative rate was 33% (n = 7). Our results show a sensitivity of 53%, a specificity of 100% and an accuracy of 66%. The conclusion is that a negative 99Tcm-d,l-HMPAO-labelled leukocyte scan is of limited value in ruling out a vascular graft infection. A combination of computed tomography (CT-scan) and a 99Tcm-d,l-HMPAO-labelled leukocyte scan is probably the most efficient way of diagnosing a vascular graft infection.

Adult↗
PubMed1994

Histological alterations in chronically hypoperfused myocardium. Correlation with PET findings.

BACKGROUND: In patients with chronic coronary artery disease (CAD) and left ventricular dysfunction, flow/metabolic studies of the myocardium with positron emission tomography (PET) are able to distinguish viable but dysfunctional myocardium from irreversible ischemic injury and scar tissue. In this study, PET findings of blood flow and metabolism in chronically hypoperfused myocardium were correlated with histology. METHODS AND RESULTS: We studied 33 patients suffering from CAD. In each patient, myocardial blood flow and metabolism were measured with PET 1 or 2 days before revascularization. During surgery, transmural biopsies were taken from the left ventricular anterior wall and planimetrically scored for the degree of myolysis (sarcomere loss). The amount of connective tissue was calculated using morphometric techniques. Contrast ventriculography demonstrated abnormal wall motion in 23 patients. Fourteen patients with a mismatch pattern (decreased flow with preserved metabolism) in the biopsy region after quantitative analysis of the PET data showed 11 +/- 6 vol% fibrosis and 25 +/- 13% cells with sarcomere loss. The space formerly occupied by sarcomeres was mainly replaced by glycogen and mitochondria. A significant wall motion improvement was noted 3 months after surgery. Nine patients showed a match pattern (concordant flow/metabolism defects). The biopsies revealed 35 +/- 25% fibrosis and 24 +/- 15% glycogen-storing cells. The biopsies of the 10 patients with normal anterior wall motion showed 8 +/- 4% fibrosis and 12 +/- 8% glycogen-accumulating cells. CONCLUSIONS: It can be concluded that areas with impaired wall motion and a PET match pattern show extensive fibrosis. Regions with reduced flow and preserved FDG metabolism, however, contain predominantly viable cells. In these regions, significant recovery of wall motion is found after revascularization. Regions with normal wall motion contain predominantly viable cells. Cells with reduced contractile material and increased glycogen content are mainly found in areas with wall motion impairment but are also present in areas with normal wall motion and a severe stenosis of the coronary vessel.

Biopsy↗
PubMed1993

Different perceptual tasks performed with the same visual stimulus attribute activate different regions of the human brain: a positron emission tomography study.

To investigate the processing of visual form in human cerebral cortex, we used the PET (positron emission tomography) activation technique to compare the human brain regions that are involved in a visual detection task and two orientation discrimination tasks: the temporal same-different (TSD) task, which includes a short-term memory component, and the identification (ID) task, which is without this component. As a control task we used passive viewing. Stimuli were identical in all four tasks. Subtraction of passive viewing from detection showed that the detection task activates early visual cortical regions (areas 17/18) as well as several motor brain regions, while decreasing activity in several higher order frontal, temporal, and parietal regions. Comparing the ID task to the detection task revealed no further visual cortical activation, while comparison of the TSD task to the detection task revealed an activation of several right visual cortical regions, one of which remained significant after the subtraction of ID from TSD (right area 19). These experiments demonstrate the task dependence of visual processing, even for very closely related tasks, and the localization of the temporal comparison component involved in orientation discrimination in human area 19.

Adult↗
PubMed1993

A rare case of sebaceous carcinoma with very malignant characteristics.

A case of a sebaceous carcinoma is presented. This carcinoma of the skin appendages requires diagnosis by histopathology because the clinical appearance is often atypical. Because of the frequency of metastases to local lymph nodes and bone, a careful physical examination and appropriate radiologic/scintigraphic examinations of these organs should be performed routinely. The case presented illustrates the very malignant character of this tumor.

Adenocarcinoma↗
PubMed1992

Evaluation of the skeletal kinetics of fluorine-18-fluoride ion with PET.

To evaluate the feasibility of quantitatively assessing regional skeletal fluoride uptake in humans in focal and generalized bone disease, we investigated the skeletal kinetics of [18F]fluoride ion with dynamic PET imaging. Dynamic image sets were acquired over a 60-min interval in a multiplane PET device, and input functions (plasma 18F time-activity curves) were measured directly from arterialized blood and, in some cases, determined from image-derived left ventricular cavity activity measurements. Our results indicate: 1. A steady-state ratio of [18F]fluoride ion concentration in plasma to whole blood greater than unity (1.23 for plasma to directly assayed whole blood and 1.44 for plasma to left ventricular cavity imaged concentrations. This concentration difference produces a scaling factor that must be considered when using image derived or directly measured input functions. 2. The preferred tracer kinetic model configuration for [18F]fluoride ion skeletal kinetics is a three compartment model that includes a "bound" and "unbound" bone [18F]fluoride ion compartment. 3. The rate constant for forward transport of [18F]fluoride ion from plasma to the extravascular space of bone (K1) and the regional blood volume parameter generate estimates of bone blood flow and vascular volume, respectively, that are in the physiologic range of reported for mammals. Estimates of the uptake constant for fluoride in bone, using nonlinear regression (KNLR = 0.0360 +/- 0.0064 ml/min/ml), are in very good agreement with an estimate of the same parameter obtained with Patlak graphical analysis (KPAT = 0.0355 +/- 0.0061 ml/min/ml). 4. Generating parametric images of KPAT facilitates quantification of regional bone [18F]fluoride ion kinetics. The method is computationally practical, and, with either the parametric imaging approach or with standard region of interest analysis, can be used to generate quantitative estimates of fluoride uptake (a "bone metabolic index") in focal skeletal regions or in more generalized distributions.

Adult↗
PubMed1992

Whole-body positron emission tomography: Part I. Methods and performance characteristics.

Methods for whole-body PET imaging have been developed to provide a clinical tool for the detection and evaluation of primary and metastatic cancers. The axial FOV of the PET system is extended by imaging at multiple bed positions to cover the whole body. In typical rectilinear PET scans, only a small fraction of the data is collected to form two-dimensional projection images. In this work, 100% of the projection data was collected to form the two-dimensional projection images. These projection images were generated for continuous angles over 180 degrees by resorting sinogram data. In addition, tomographic images were formed by using filtered backprojection reconstruction without attenuation correction. Coronal and sagittal cuts were then extracted from the three-dimensional data set. The tomographic images were reconstructed to a resolution of 10.8 mm in all dimensions because of statistical limitations of the data. Both methods of image formation resulted in images of high quality with the tomographic reconstruction providing the highest contrast and resolution. An acquisition time of 1-2 min/bed position after a 10-mCi injection of [18F]fluoride ion or [18F]FDG was found to give a sufficient number of counts for producing images of good resolution and contrast, from a total scanning time of 32-64 min.

Deoxyglucose↗
PubMedDate not supplied

Cancer detection with whole-body PET using 2-[18F]fluoro-2-deoxy-D-glucose.

OBJECTIVE: This study was done to determine the feasibility and potential utility of whole-body PET using the glucose analogue 2-[18F]fluoro-2-deoxy-D-glucose (FDG) for the detection of primary malignancies and metastatic lesions. MATERIALS AND METHODS: This was a prospective, nonrandomized study of whole-body FDG-PET imaging carried out at a large university teaching hospital in Los Angeles, CA, U.S.A. The study group consisted of all patients referred for PET imaging (87) with a suspected diagnosis of primary or recurrent malignancy and who had eventual histological confirmation of their lesions. RESULTS: In the 87 patients, whole-body PET studies were positive (presence of focal FDG uptake relative to surrounding tissues uptake) in 61 of 70 patients (87%) with subsequent biopsy-confirmed primary or recurrent malignant lesions, including carcinomas of breast, lung, ovary, prostate, colon, urinary bladder, and gallbladder origin, as well as malignant melanoma, carcinoid, osteosarcoma, lymphoma, and spinal cord astrocytoma. The PET images revealed no focal hypermetabolism at the known site of tumor in patients with primary prostate carcinoma (two), microscopic ovarian carcinoma (two), breast carcinoma (one), low-grade carcinoid tumors (two), and one patient with recurrent microscopic osteogenic sarcoma. The PET studies detected the primary lesion in 15 of 17 patients with breast carcinoma and in 6 of 6 patients with primary lung carcinoma. Of the 17 patients with benign biopsies, 13 patients had FDG-PET studies without focal areas of uptake. CONCLUSION: Because of the high glycolytic rate of malignant tissue, the whole-body FDG-PET technique has promise in the detection of a wide variety of both primary and metastatic malignancies. The presence of FDG uptake in benign inflammatory conditions may limit the specificity of the technique. The sensitivity for the detection of malignant lesions was 87% and the positive predictive value was 94%. The whole-body FDG-PET method is promising both in determining the nature of a localized lesion and in defining the systemic extent of malignant disease.

Deoxyglucose↗