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Biomedical subjects

P E Valk

Publications and source records attributed to P E Valk.

At least 19 recordsLinked to original sources
PubMed2002

Brain function and cognition in a community sample of elderly Latinos.

BACKGROUND: Previous studies using PET to measure cerebral glucose metabolism in AD have found metabolic reductions in the temporoparietal and posterior cingulate cortices in individuals with dementia and those at risk of developing it. This study was designed to extend this finding to individuals selected from a population-based cohort of Mexican Americans with a wide spectrum of cognitive ability. METHODS: A group of 93 individuals was selected from the Sacramento Area Latino Study on Aging, and subjects were categorized into four groups of increasing levels of cognitive impairment: normal, memory impaired, cognitively impaired but not demented (CIND), and demented. PET was performed with the tracer [(18)F]-fluorodeoxyglucose, and data were analyzed with both statistical parametric mapping and an atrophy-corrected volume of interest approach. RESULTS: Individuals with dementia had metabolic reductions that were most robust in the posterior cingulate cortex, whereas CIND subjects had less statistically robust reductions in the posterior cingulate cortex. Cingulate hypometabolism increased the risk of dementia and was a significant risk factor for dementia in logistic regression models that also incorporated MR measures of hippocampal volume and white matter hyperintensities. CONCLUSION: Posterior cingulate cortical hypometabolism is clearly detected in individuals with dementia who are selected from a population with lower education and a high prevalence of cerebrovascular risk factors, supporting the generalizability of this finding. These metabolic reductions occur prior to the onset of dementia but only in those persons with relatively advanced symptoms.

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PubMed2001

Effect of whole-body (18)F-FDG PET imaging on clinical staging and management of patients with malignant lymphoma.

UNLABELLED: Correct staging is important in selecting the appropriate treatment for lymphoma patients. PET imaging with (18)F-FDG is useful for staging of lymphoma as well as for monitoring of therapy. However, to our knowledge, the clinical impact of PET on staging and management of lymphoma patients has not been reported. METHODS: Standardized questionnaires were mailed to referring physicians asking them whether and how the results of PET imaging had influenced clinical staging and management of the disease in their patients. Management changes, when present, were classified as intermodality (e.g., medical to surgical, surgical to radiation, medical to no treatment) or intramodality (e.g., altered medical, surgical, or radiotherapy approach). RESULTS: The referring physicians returned 52 of 108 questionnaires (48.1%). Physicians indicated that PET led to a change in the clinical stage in 44% of patients: 21% were upstaged and 23% were downstaged. Findings of the PET examination resulted in intermodality changes in management in 42% of patients, in intramodality changes in 10%, and in a combination of the management changes in 10%. Other, not further specified, treatment changes were reported in 6% of patients. PET did not result in any management changes in only 32% of patients. CONCLUSION: This survey-based study of referring physicians indicates that FDG PET has a major impact on the management of lymphoma patients, contributing to changes in clinical stage in 44% and changes in treatment in >60% of cases.

Adolescent↗
PubMed2001

Impact of whole-body 18F-FDG PET on staging and managing patients with breast cancer: the referring physician's perspective.

UNLABELLED: FDG PET has emerged as an important clinical imaging modality for diagnosing and staging cancer. However, the impact of FDG PET on staging and managing patients with breast cancer from the referring physician's point of view is unknown. METHODS: The referring physicians of 160 breast cancer patients received standardized questionnaires inquiring if and how PET findings altered their patient's stage and their clinical management decisions. Management changes were classified as intermodality if the change was from one modality to another (e.g., medical to surgical, surgical to radiation, medical to no treatment, and vice versa) or as intramodality if the change was within the same modality (e.g., altered medical or radiotherapy approach). RESULTS: Fifty of the 160 surveys were completed (31% response rate). PET changed the clinical stage in 36% of patients (28% upstaged, 8% downstaged) and resulted in intermodality changes in 28% of patients and intramodality changes in 30% of patients. CONCLUSION: The results of this prospective survey show that FDG PET has a major impact on the management of breast cancer patients, influencing both clinical stage and management in more than 30% of patients.

Adult↗
PubMed2000

Factors associated with false-positive staging of lung cancer by positron emission tomography.

BACKGROUND: Positron emission tomography imaging is gaining popularity as a noninvasive staging tool in non-small cell lung cancer. Nonmalignant processes can also affect radio-tracer uptake. This study seeks to identify factors associated with false-positive staging of mediastinal metastases. METHODS: A retrospective review was performed of 100 patients with early stage non-small cell lung cancer referred for positron emission tomography scan evaluation. All had pathologic confirmation of their disease. Positron emission tomography scans, radiology records, operative reports, and pathology results were reviewed. Patients with positron emission tomography scans interpreted as positive for mediastinal involvement and negative pathology at operation were selected. RESULTS: Seven patients were found to have a false-positive positron emission tomography evaluation for mediastinal metastases. All but 1 patient had a concurrent inflammatory process or an anatomic factor associated with the false positive. The sensitivity and specificity in detecting involved mediastinal nodes was 87.5% and 90.7%, respectively. The negative predictive value was 95.8%. CONCLUSIONS: Although positron emission tomography has been established as an accurate modality to stage non-small cell lung cancer, false-positive evaluation of mediastinal metastases can occur in the setting of concurrent inflammatory lung diseases or for centrally located tumors. Pathologic evaluation of mediastinal disease should be pursued whenever suggested by a positive positron emission tomography scan especially in the face of those factors described.

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PubMed2000

Clinical trials of cost effectiveness in technology evaluation.

This article discusses models of efficacy, design of clinical trials and the role of mathematical modeling in diagnostic technology evaluation and determination of cost-effectiveness. A multi-tiered model of efficacy, which views diagnostic imaging as part of a global process of patient management and outcome, has been described. The first tier involves imaging efficacy, which must be determined by clinical trial. Direct comparison of new and established modalities in a single study population has major advantages over randomized controlled trials, which are extremely costly and time-consuming and are not appropriate for most evaluations of diagnostic modalities. Selection of patients for inclusion in the trial, interpretation and verification of results, and determination of a reference standard are all possible sources of bias, which need to be identified and controlled. Decision analysis modeling can be used to assess diagnostic, therapeutic, patient-outcome and cost efficacy, once imaging efficacy has been evaluated by clinical trial. Decision analysis is easier and less expensive to perform than clinical trials, and results are easily generalizable to other settings. Disadvantages arise from the nondescriptive nature of modeling and lack of transparency, which make it difficult to evaluate the appropriateness of decision tree structures and input data. Modeling is an unavoidable fact of life in technology evaluation, since the resources that would be required for full evaluation of imaging modalities by clinical trial are not available.

Bias↗
PubMed1999

Whole-body PET imaging with [18F]fluorodeoxyglucose in management of recurrent colorectal cancer.

HYPOTHESIS: Metabolic imaging by positron emission tomography (PET) using [18F]fluorodeoxyglucose will be more accurate than anatomic imaging by computed tomography (CT) for detection of recurrent colorectal cancer. More accurate staging of recurrent tumor by PET will lead to more appropriate management decisions. DESIGN: Prospective blinded study comparing PET with CT, using histologic diagnosis, serial CT imaging, and clinical follow-up as criterion standards, with a fully blinded, retrospective reinterpretation of PET studies. Changes in diagnosis resulting from PET findings were correlated with subsequent treatment and surgical findings. Potential cost savings resulting from use of PET for preoperative staging were calculated. SETTING: Private practice in an outpatient tertiary referral center. PATIENTS: A group of 155 consecutive patients with imaging for diagnosis or staging of recurrent colorectal cancer. Twenty-one patient (14%) were excluded due to lack of a criterion standard. Computed tomographic scans were available for comparison for 115 patients. RESULTS: Positron emission tomographic scan sensitivity and specificity were 93% and 98%, respectively, compared with 69% and 96% for CT. Ninety-five percent confidence intervals for the differences between the modalities were 16% to 32% for sensitivity and 1% to 5% for specificity. The sensitivity of both modalities varied with anatomic site of recurrence. Positron emission tomographic scans were true positive in 12 (67%) of 18 patients with elevated serum carcinoembryonic antigen levels and negative CT findings. In 23 (29%) of 78 preoperative studies in which CT showed a single site of recurrence, PET showed tumor at additional sites. At surgery, nonresectable, PET-negative tumor was found in 7 (17%) of 42 patients who had PET evidence of localized recurrence only. Potential savings resulting from demonstration of nonresectable tumor by PET were calculated at $3003 per preoperative study. CONCLUSIONS: Positron emission tomography was more sensitive and specific than CT for detection of recurrent colorectal cancer. Preoperative detection of nonresectable tumor by PET may avoid unnecessary surgery, and thereby reduce the cost of patient treatment.

Adult↗
PubMed1998

Analytical decision model for the cost-effective management of solitary pulmonary nodules.

PURPOSE AND METHODS: Multiple strategies are currently being used to manage patients who present with indeterminate solitary pulmonary nodules (SPN). We have used decision-analysis models to assess the cost-effectiveness of various strategies for the diagnosis and management of SPN. Four decision strategies were compared: a wait and watch strategy, a surgery strategy, a computed tomography (CT)-based strategy, and a CT-plus-positron emission tomography (PET) strategy. An incremental cost-effectiveness ratio (ICER) was used to compare all strategies to the wait and watch strategy. RESULTS: A CT-plus-PET strategy was the most cost-effective over a large pretest likelihood (probability of having a malignant nodule), with a range of 0.12 to 0.69. Furthermore, within this likelihood range, the potential cost savings of using the CT-plus-PET strategy over the CT strategy ranged from $91 to $2,200 per patient. This translates to a yearly national savings of approximately $62.7 million. CONCLUSION: Decision-analysis modeling indicates the potential cost-effectiveness of [18F]2-fluoro-2-deoxy-D-glucose (FDG)-PET in the management of SPN. Furthermore, the decision trees developed can be used to model various features of the management of SPN, including modeling the cost-effectiveness of other newly emerging technologies.

Adult↗
PubMed1997

18-Fluorodeoxyglucose uptake and survival of patients with suspected recurrent malignant glioma.

BACKGROUND: After intensive initial radiation therapy for malignant glioma, magnetic resonance imaging (MRI) and computerized tomography (CT) cannot distinguish tumor progression from radiation injury. METHODS: The authors studied the prognostic value of 18-fluorodeoxyglucose positron emission tomography (FDG-PET) in 55 patients with malignant glioma for whom MRI obtained after initial surgery and radiation therapy demonstrated enlarging, enhancing lesions consistent with either tumor progression or radiation necrosis. Forty patients (73%) had an initial diagnosis of Grade 4 malignant glioma and 15 (27%) had Grade 3 malignant glioma. The FDG-PET scans were graded visually on a four-level scale at the time of acquisition. RESULTS: In univariate analysis, the FDG-PET score was a significant predictor of survival time after FDG-PET scanning (P = 0.005). Median survival was 10 months for patients with FDG-PET scores of 2 or 3 (glucose uptake > or = adjacent cortex) and 20 months for those with scores of 0 or 1 (glucose uptake < adjacent cortex). In multivariate proportional hazards analysis, the FDG-PET score was a significant predictor of survival (P = 0.019) in a model that included patient age, recurrence number, and FDG-PET score. There was no significant difference in the FDG-PET score hazard ratio for patients with Grade 3 or 4 tumors at initial diagnosis, first or later suspected recurrence, initial photon irradiation given with standard fractions or hyperfractionation, or stereotactic irradiation prior to FDG-PET scanning. CONCLUSIONS: This analysis demonstrates that FDG-PET scanning has prognostic value in a cohort limited to patients with suspected recurrent high grade glioma.

Adolescent↗
PubMed1997

Abnormal temporal lobe metabolism in violent subjects: correlation of imaging and neuropsychiatric findings.

PURPOSE: To search for metabolic correlates of clinical and electrophysiological abnormalities in violent subjects. METHODS: Seven subjects with histories of extremely violent behavior were studied with positron emission tomography (PET) with fludeoxyglucose F 18 (FDG), brain electrical area mapping, MR imaging, neuropsychiatric and neuropsychological testing, and clinical examination during medical evaluation associated with legal proceedings. Nine control subjects without evidence of organic brain disease were also studied with FDG-PET. Quantitative PET data were calculated as standardized uptake values comparing the highest occipital region with the lowest temporal region. RESULTS: Temporal lobe metabolism was decreased in the study group relative to the control subjects. Medial temporal lobe metabolism was 39% lower than that in the occipital cortex in study subjects and only 27% lower than that in control subjects. These groups differed by Mann-Whitney U test and Wilcoxon's two-sample test. Metabolic differences correlated with limbic neuropsychiatric and electrophysiological abnormalities in the violent group. CONCLUSION: In this selected population of violent subjects, FDG-PET scans showed metabolic abnormalities in the temporal lobes. These abnormalities correlated with limbic abnormalities seen at electrophysiological and neuropsychiatric evaluation.

Adolescent↗
PubMed1996

Cost-effectiveness of PET imaging in clinical oncology.

To be cost-effective, PET must be diagnostically accurate and effective in improving management without increasing treatment cost. To evaluate diagnostic accuracy, we performed prospective evaluations of whole-body PET imaging in staging of non-small-cell lung cancer (99 patients), detection of recurrent colorectal cancer (57 patients), diagnosis of metastatic melanoma (36 patients), and staging of advanced head and neck cancer (29 patients). In each case, PET was more accurate than anatomic imaging for determination of the presence and extent of tumor and demonstration of nonresectable disease. PET was also more accurate than conventional imaging in staging Hodgkin's disease (30 patients). We evaluated the management impact of PET retrospectively, by reviewing the treatment records of 72 patients with solitary pulmonary nodules or non-small-cell lung cancer, 68 patients with known or suspected recurrent colorectal cancer, 45 patients with known or suspected metastatic melanoma, and 29 patients with advanced head and neck tumors. PET improved patient management by avoiding surgery for nonresectable tumor and for CT abnormalities that proved to be benign by PET imaging. For determining cost impact, the costs of surgical procedures were determined from Medicare reimbursement rates, and the cost of a PET study was taken to be $1800. The savings from contraindicated surgical procedures exceeded the cost of PET imaging by ratios of 2:1 to 4:1, depending on the indication. PET was decisively more accurate and cost-effective than anatomic imaging by CT, combining improved patient care with reduced cost of management.

Cost-Benefit Analysis↗
PubMed1995

Staging non-small cell lung cancer by whole-body positron emission tomographic imaging.

BACKGROUND: A need exists for an accurate, noninvasive means of staging non-small cell lung cancer. METHODS: A prospective evaluation of regional and whole-body positron emission tomography (PET) imaging for staging lung cancer was carried out in 99 patients. Mediastinal PET and computed tomography findings were compared with results of surgical staging in 76 patients. Those PET and computed tomography findings that indicated possible distant metastasis were compared with biopsy results and the results of clinical and imaging follow-up. RESULTS: Sensitivity and specificity for the diagnosis of N2 disease were 83% and 94% for PET and 63% and 73% for computed tomography, respectively. Positron emission tomography showed previously unsuspected distant metastasis in 11 patients (11%), with no demonstrated false-positive results. Normal PET findings were obtained at distant sites of computed tomography abnormality in 19 patients (19%). Clinical and imaging follow-up in 14 of these patients showed no evidence of metastasis. In 1 case, the PET result proved to be falsely negative. CONCLUSIONS: Imaging with PET was more accurate than computed tomography for diagnosis of mediastinal and distant metastasis. Detection of unsuspected metastatic disease by PET may permit reduction in the number of thoracotomies performed for nonresectable disease.

Carcinoma, Non-Small-Cell Lung↗
PubMed1993

High-resolution (2.6-mm) PET in partial complex epilepsy associated with mesial temporal sclerosis.

Eleven patients with medically refractory partial seizures underwent positron emission tomography (PET) with a 600-crystal tomograph and fluorine-18 fluorodeoxyglucose. All patients had been selected for temporal lobe resection, and the side of the epileptogenic focus had been demonstrated with electroencephalography (EEG). Only patients in whom structural lesions had been excluded with magnetic resonance (MR) imaging were studied. Ten of 11 patients were found to have temporal cortical hypometabolism on the same side as the focal abnormality that was demonstrated with EEG. In two patients, PET showed hypometabolism in the mesial temporal cortex only. There were no incorrectly lateralizing PET results. MR imaging showed an abnormality in the corresponding temporal lobe in seven patients. In one patient, both PET and MR images were normal. All patients underwent anterior temporal resection, and histologic examination of resected tissue showed mesial temporal sclerosis in all cases.

Adult↗
PubMed1992

Hypoxia in human gliomas: demonstration by PET with fluorine-18-fluoromisonidazole.

Positron emission tomography (PET) with the hypoxic-cell tracer [18F]fluoromisonidazole presents a possible means of noninvasively demonstrating tumor hypoxia. PET studies using this tracer were performed in three patients with malignant glioma, and in all patients the tumor was clearly seen at 5 min postinjection and initial tumor activity exceeded cortical activity. In one patient, there was no tumor retention of [18F] fluoromisonidazole and tumor activity fell while cortical activity increased, with the two tissues reaching equality at 40-50 min. The tumor-to-plasma ratio was 0.71 at 3 hr. The other two patients showed variable tumor retention of [18F]fluoromisonidazole, with tumor-to-plasma ratios of 1.10 and 1.49 at 2 and 3 hr. These results demonstrate the feasibility of using [18F]fluoromisonidazole PET to detect hypoxia in human gliomas in vivo. Clinical trials are needed to determine whether a relationship exists between [18F]fluoromisonidazole uptake and tumor radiation response.

Adult↗
PubMed1991

MRI and PET of delayed heavy-ion radiation injury in the rabbit brain.

Magnetic resonance imaging (MRI) and positron emission tomography (PET) techniques were used to obtain in vivo scans of delayed (30 GyE helium ion, 230 MeV/u) radiation injury in rabbit brain. T2-weighted (T2W) MRI scans demonstrated alterations that were restricted primarily to the white matter tracts and the deep perithalamic and thalamic regions. Quantitative measurements of T2 and T1 values demonstrated wide variations in absolute values. However, paired comparisons in hemibrain-irradiated rabbits revealed significant increases in T2 (p less than 0.001) and T1 (p less than 0.01) in irradiated versus unirradiated brain. Gadolinium DTPA (GdDTPA) enhanced MRI and 82Rubidium (82Rb) PET detected focal regions of blood-brain barrier (BBB) disruption restricted to the deep white matter and thalamic regions. Sequential GdDTPA enhanced MRI scans showed the spreading of the tracer from the initial site of contrast enhancement. 18Fluorodeoxyglucose (18FDG) PET studies demonstrated the markedly depressed metabolic profiles of irradiated brain. Histological findings of tissue edema and necrosis correlated well with the in vivo imaging abnormalities. These initial studies demonstrate that the irradiated rabbit brain is a suitable animal model for examining the delayed effects of radiation injury in the brain.

Animals↗
PubMed1991

Diminished glucose transport in Alzheimer's disease: dynamic PET studies.

Dynamic positron emission tomography with [18F]fluorodeoxyglucose was used in six patients with Alzheimer's disease (AD) and seven healthy age-matched control subjects to estimate the kinetic parameters K1*, k2*, and k3* that describe glucose transport and phosphorylation. A high-resolution tomograph was used to acquire brain uptake data in one tomographic plane, and a radial artery catheter connected to a plastic scintillator was used to acquire arterial input data. A nonlinear iterative least-squares fitting procedure that included terms for the vascular fraction and time delay to the peripheral sampling site was used to fit a three-compartment model to the brain data. Regions studied included frontal, temporal, occipital, and the entire cortex and subcortical white matter. The values obtained for the individual rate constants and regional CMRglc (rCMRglc; calculated using regional values of the rate constants) were higher than those reported previously. A significant (p less than 0.05) decrease was found in K1* in frontal and temporal cortex in the AD patients compared with the controls, with values of 0.157 and 0.161 ml/g/min in frontal and temporal cortex, respectively, of controls and 0.127 and 0.126 ml/g/min in frontal and temporal cortex of the AD patients. rCMRglc was also significantly (p less than 0.02) lower in the AD patients than controls in all cortical brain regions. Lower values of k3* were found in all brain regions in the AD patients, although these were not statistically significant. These findings provide evidence of an in vivo abnormality of forward glucose transport in AD.(ABSTRACT TRUNCATED AT 250 WORDS)

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