Positive Emission Tomography Scan Research Articles

Comparison of brown adipose tissue activation detected by infrared thermography in men with vs without metabolic syndrome

BackgroundBrown adipose tissue (BAT) high density of mitochondria and its thermogenic characteristics promote the dissipation of chemical energy in the form of heat, increasing body caloric expenditure, decreasing plasma levels of lipids and glucose (GL). This makes BAT a potential therapeutic target of Metabolic Syndrome (MetS). Position Emission Tomography Scanning (PET-CT) is the gold standard for estimating BAT, but it has several limitations, including high cost and high emission of radiation. On the other hand, Infrared Thermography (IRT) is considered a simpler, cheaper and non-invasive method to detect BAT. ObjectiveThe aim of this study was to compare BAT activation through IRT and cold stimulation in men diagnosed without and with MetS. MethodsSample of 124 (35.3 ± 9.4 years old) men was evaluated of body composition, anthropometric measurements and dual X-ray absorptiometry (DXA) hemodynamics, biochemical tests and body skin temperature acquisition. The Student t-test with subsequent effect size by (d) Cohen and two-way repeated measures ANOVA with Tukey post-hoc comparisons were conducted. Level of significance was p < 0.05. ResultsThere was significant interaction between group factor (MetS) vs group moment (BAT activation) in supraclavicular skin temperatures right side (maximum (F(1,122) = 10.4, p < 0.002, η2 = 0.062), mean (F(1.122) = 13.0, p < 0.001, η2 = 0.081) and minimal (F(1,122) = 7.9, p < 0.006, η2 = 0.052)) and left side maximum (F(1,122) = 7.7, p < 0.006, η2 = 0.048), mean (F(1.122) = 13.0, p < 0.037, η2 = 0.007) and minimal (F(1,122) = 9.8, p < 0.002, η2 = 0.012)). The MetS risk factor group didn't present significant increase of SCV temperature BAT after cold stimulation. ConclusionMen diagnosed with MetS risk factors seem to activate less BAT, when exposed to cold stimulation, compared to group without MetS risk factor.

Bone marrow adiposity in diabetes and clinical interventions.

This study aims to review bone marrow adipose tissue (BMAT) changes in people with diabetes, contributing factors, and interventions. In type 1 diabetes (T1D), BMAT levels are similar to healthy controls, although few studies have been performed. In type 2 diabetes (T2D), both BMAT content and composition appear altered, and recent bone histomorphometry data suggests increased BMAT is both through adipocyte hyperplasia and hypertrophy. Position emission tomography scanning suggests BMAT is a major source of basal glucose uptake. BMAT is responsive to metabolic interventions. BMAT is a unique fat depot that is influenced by metabolic factors and proposed to negatively affect the skeleton. BMAT alterations are more consistently seen in T2D compared to T1D. Interventions such as thiazolidinedione treatment may increase BMAT, whereas metformin treatment, weight loss, and exercise may decrease BMAT. Further understanding of the role of BMAT will provide insight into the pathogenesis of diabetic bone disease and could lead to targeted preventive and therapeutic strategies.

Quantitative determination of 64Cu-liposome accumulation at inflammatory and infectious sites: Potential for future theranostic system

BackgroundTherapeutic interventions for infectious and inflammatory diseases are becoming increasingly challenging in terms of therapeutic resistance and side-effects. Theranostic systems to ameliorate diagnosis and therapy are therefore highly warranted. The pathophysiological changes in inflammatory lesions provide an attractive basis for extravasation and accumulation of PEGylated liposomes. The objective of this study was to provide direct quantitative information on the theranostic potential of radiolabeled liposome for accumulation in inflammatory models using position emission tomography (PET). MethodPreclinical murine models of inflammation (turpentine and LPS), infection (Staphylococcus aureus) and collagen-induced arthritis (CIA) was established and monitored using bioluminescence imaging (BLI). Across all models PET imaging using radiolabeled PEGylated liposomes (64Cu-liposomes) were performed and evaluated in terms of accumulation properties in inflammatory and infectious lesions. ResultsBLI demonstrated that the inflammatory and infectious models were successfully established and provided information on lesion pathology. Activity of 64Cu-liposomes were increased in inflammatory and infectious lesions between early (10-minute or 3-hour) and late (24-hour) PET scans, which validates that a continuous extravasation and accumulation of long circulation PEGylated liposomes occurs. ConclusionThe theranostic potential of long circulating PEGylated radiolabeled liposomes was shown in multiple preclinical models. Impressive accumulation was seen in both inflammatory and infectious lesions. These results are encouraging towards advancing PEGylated liposomes as imaging and drug delivery systems in inflammatory and infectious diseases.

Sarcoidosis: Involvement of Genetic Factors

Sarcoidosis affects people of all racial and ethnic groups and occurs at all ages, although it usually develops before the age of 50 years, with the incidence peaking at 20 to 39 years. The incidence of Sarcoidosis varies widely throughout the world. The modern history of Sarcoidosis disease goes back to 1899 when the pioneering Norwegian dermatologist coined the term to describe skin nodules characterized by compact, sharply defined foci of epithelioid cells with large pale nuclei and also a few giant cells. Thinking this resembled sarcoma, he called the condition “multiple benign sarcoid of the skin”. This review article has focused on the underlaying mechanism which is responsible for occurance of Sarcoidosis. It also involved the genetic factors (genes) that are responsible for Sarcoidosis. Sarcoidosis has no known cause; although none of potential causes has been definitely confirmed, there is increasing evidence to support that one or more infectious agents may cause Sarcoidosis, although this organism may no longer be viable in the patient. The diagnosis of Sarcoidosis has been significantly aided by new technology. This includes the endobronchial ultrasound, which has been shown to increase the yield of needle aspiration of mediastinal and hilar lymph nodes. The positive emission tomography scan has proven useful for selecting possible biopsy sites by identifying organ involvement not appreciated by routine methodology. Emerging technologies and advances in genomics and proteomics will help to find the causes of Sarcoidosis in future, with the better understanding of pathogenesis of Sarcoidosis and to test new therapy for it

Primary Gastrointestinal Follicular Lymphoma: When Lymphoid Infiltrate is not Benign

Background Primary gastrointestinal follicular lymphoma is a rare variant of follicular lymphoma. The most common location of involvement is the second portion of the duodenum and detection is often incidental during upper endoscopy. The clinical course is usually indolent. Dissemination is rare and transformation into high-grade lymphoma almost never occurs even without treatment. Histologically, diagnosis can be difficult, appearing as a benign lymphoid infiltrate prior to immunohistochemical staining. We present the case of a patient with a rare primary gastrointestinal follicular lymphoma. Case A 54-year-old Caucasian female previously healthy was referred for evaluation of intermittent epigastric pain associated with reflux. There were no fevers, chills or weight loss. Upper endoscopy performed at an outside facility was significant for a nodular duodenal mucosa in the bulb and second portion with biopsy showing atypical lymphoid infiltrate. A repeat upper endoscopy at our facility had identical endoscopic findings with extensive duodenal biopsy showing lymphoid infiltrate. A second pathologic opinion noted lymphoid nodules with small and large cells that were CD20 positive B-cells which co-expressed Bcl-2, Bcl-6 and CD10 consistent with follicular lymphoma. Staging position emission tomography scan showed no hypermetabolic areas and bone marrow biopsy showed no lymphoma but did note an incidental chronic lymphocytic leukemia. Discussion Follicular lymphoma comprises only 1-3% of primary gastrointestinal lymphomas. When follicular lymphoma does involve the gastrointestinal tract, the duodenum is most often affected (89% of cases). Endoscopically, follicular lymphoma usually manifests as multiple white nodules < 10 mm in size. The diagnosis of follicular lymphoma requires identification of a neoplastic infiltrate forming nodular follicles. The majority of primary gastrointestinal follicular lymphomas express Bcl-2 and CD-20. Treatment options include: watch and wait, radiation, rituximab monotherapy or chemotherapy with or without radiation. Conclusions Primary gastrointestinal follicular lymphoma is a rare, indolent neoplasm that may appear as a benign lymphoid infiltrate. Immunohistochemical staining is critical in making the diagnosis particularly in the setting of atypical lymphoid infiltrates that are nodular. In patients with localized disease, clinical outcomes are excellent even without therapy.Figure: Follicular lymphoma duodenal bulb.

Quantitative Evaluation of Therapeutic Response by FDG-PET-CT in Metastatic Breast Cancer.

To assess the therapeutic response for metastatic breast cancer with (18)F-FDG position emission tomography (PET), this retrospective study aims to compare the performance of six different metabolic metrics with PERCIST, PERCIST with optimal thresholds, and an image-based parametric approach. Thirty-six metastatic breast cancer patients underwent 128 PET scans and 123 lesions were identified. In a per-lesion and per-patient analysis, the performance of six metrics: maximum standardized uptake value (SUVmax), SUVpeak, standardized added metabolic activity (SAM), SUVmean, metabolic volume (MV), total lesion glycolysis (TLG), and a parametric approach (SULTAN) were determined and compared to the gold standard (defined by clinical assessment and biological and conventional imaging according RECIST 1.1). The evaluation was performed using PERCIST thresholds (for per-patient analysis only) and optimal thresholds (determined by the Youden criterion from the receiver operating characteristic curves). In the per-lesion analysis, 210 pairs of lesion evolutions were studied. Using the optimal thresholds, SUVmax, SUVpeak, SUVmean, SAM, and TLG were significantly correlated with the gold standard. SUVmax, SUVpeak, and SUVmean reached the best sensitivity (91, 88, and 83%, respectively), specificity (93, 95, and 97%, respectively), and negative predictive value (NPV, 90, 88, and 83%, respectively). For the per--patient analysis, 79 pairs of PET were studied. The optimal thresholds compared to the PERCIST threshold did not improve performance for SUVmax, SUVpeak, and SUVmean. Only SUVmax, SUVpeak, SUVmean, and TLG were correlated with the gold standard. SULTAN also performed equally: 83% sensitivity, 88% specificity, and NPV 86%. This study showed that SUVmax and SUVpeak were the best parameters for PET evaluation of metastatic breast cancer lesions. Parametric imaging is helpful in evaluating serial studies.

Sebocyte-Like Cell Primary Cutaneous Melanoma

Although rising incidence rates of cutaneous melanoma have been observed during the last 4 decades in white populations worldwide, the sebocyte-like cell variant has been described only twice in the literature to date. In our case, a 64-year-old man presented for evaluation of a changing pigmented lesion on the left upper back. Excision of the lesion revealed an invasive melanoma with a Breslow depth of 3.3 mm. Microscopic sections showed a predominantly dermal-based tumor composed of sheets and nests of enlarged epithelioid melanocytes, most of which showed an uncommon phenotype with multivacuolated cytoplasms and scalloped nuclei, features that gave them a strong resemblance to mature sebocytes. The lesional cells expressed S100 protein, Melan-A, and p16, whereas adipophilin was positive only within the sebocyte-like component of the neoplasm and showed focal nonspecific staining. The patient's sentinel lymph node biopsy was positive for micrometastases, although a subsequent position emission tomography scan was unremarkable. Sebocyte-like melanocytes are a rare distinctive type of melanocytes that can be found mostly in benign but also in malignant melanocytic lesions. They usually present focally within the lesions and, therefore, do not represent a diagnostic problem in nevus or primary cutaneous melanoma. However, when sebocyte-like melanocytes are the main cellular component of a melanocytic lesion or when they are found in the context of metastatic melanoma, they may create a potential diagnostic pitfall; for this reason, awareness of this cell type is important.

A Concise Review of Pulmonary Sarcoidosis

This is an update on sarcoidosis, focusing on etiology, diagnosis, and treatment. In the area of etiopathogenesis, we now have a better understanding of the immune response that leads to the disease as well as genetic factors that modify both the risk for the disease and its clinical outcome. Several groups have also identified possible agents as a cause for sarcoidosis. Although none of these potential causes has been definitely confirmed, there is increasing evidence to support that one or more infectious agents may cause sarcoidosis, although this organism may no longer be viable in the patient. The diagnosis of sarcoidosis has been significantly aided by new technology. This includes the endobronchial ultrasound, which has been shown to increase the yield of needle aspiration of mediastinal and hilar lymph nodes. The positive emission tomography scan has proven useful for selecting possible biopsy sites by identifying organ involvement not appreciated by routine methodology. It has also helped in assessing cardiac involvement. The biologic agents, such as the anti-tumor necrosis factor antibodies, have changed the approach to refractory sarcoidosis. There is increasing evidence that the clinician can identify which patient is most likely to benefit from such therapy. As new and more potent antiinflammatory agents have been developed, it is clear that there are other factors that burden the patient with sarcoidosis, including fatigue and sarcoidosis-associated pulmonary hypertension. There have been several recent studies demonstrating treatment options for these problems.

Pulmonary Cryptococcosis: Imaging Findings in 23 Non-AIDS Patients

ObjectiveWe aimed to review the patterns of lung abnormalities of pulmonary cryptococcosis on CT images, position emission tomography (PET) findings of the disease, and the response of lung abnormalities to the therapies in non-AIDS patients.Materials and MethodsWe evaluated the initial CT (n = 23) and 18F-fluorodeoxyglucose (FDG) PET (n = 10), and follow-up (n = 23) imaging findings of pulmonary cryptococcosis in 23 non-AIDS patients. Lung lesions were classified into five patterns at CT: single nodular, multiple clustered nodular, multiple scattered nodular, mass-like, and bronchopneumonic patterns. The CT pattern analyses, PET findings, and therapeutic responses were recorded.ResultsA clustered nodular pattern was the most prevalent and was observed in 10 (43%) patients. This pattern was followed by solitary pulmonary nodular (n = 4, 17%), scattered nodular (n = 3, 13%), bronchopneumonic (n = 2, 9%), and single mass (n = 1, 4%) patterns. On PET scans, six (60%) of 10 patients showed higher FDG uptake and four (40%) demonstrated lower FDG uptake than the mediastinal blood pool. With specific treatment of the disease, a complete clearance of lung abnormalities was noted in 15 patients, whereas a partial response was noted in seven patients. In one patient where treatment was not performed, the disease showed progression.ConclusionPulmonary cryptococcosis most commonly appears as clustered nodules and is a slowly progressive and slowly resolving pulmonary infection. In two-thirds of patients, lung lesions show high FDG uptake, thus simulating a possible malignant condition.

Early Pre/Post Fluoro-Deoxyglucose Positive Emission Tomography (PET) Does Not Predict Outcome of Patients Undergoing Hematopoietic Stem Cell Transplantation in Hodgkins Disease and Non-Hodgkins Lymphoma.

This study was designed to investigate the predictive value of early pre/post stem cell transplant (SCT) FDG-PET on outcomes in non hodgkins (NHL) or Hodgkins lymphoma (HL). We analyzed patients who received SCT for treatment of relapsed or refractory NHL or HL at Duke Medical Center between the years of 1996–2007. Patients who had either a FDG-PET scan following salvage chemo- or radio- therapy and within 14 weeks of transplantation (pre-PET)or a FDG PET scan within 6–14 weeks following transplantation (post-PET) were included in the analysis. PET was determined to be positive or negative based on chart review of radiology reports. Survival times are estimated using Kaplan- Meier method. Hazard ratios (HR) are from univariate Cox proportional hazards models. Overall survival (OS) was measured from the time of transplant until death, and for those patients still alive, it was censored at the last follow up date. Disease free survival (DFS) was measured from the time of transplant until first progression or death, whichever occurred first, and was censored at the date of last follow up for those alive without progression. A total of 102 patients were identified with PET in the appropriate time period. Median age was 48.5 (18–78); 71 patients had NHL, 31 patients had HL. Ninety-eight (96%) of the patients had chemosensitive disease, and had a documented PR (62) or CR (36) prior to transplant. The median DFS and OS of this population was 55 and 73 mo respectively. Median time to follow up was 38 mo (1.5 – 145 mo). Of the 75 pre-PET scans, 32 (43%) were positive; of the 78 post-PET scans, 22 (28%) were positive. At the time of this analysis, 28 (27%) of the patients had died from disease progression. There were 8 (10.6%) pre-PET, and 7 (9%) post- PET readings that were not clear. Our analysis revealed that neither pre-PET nor post-PET results were predictive of DFS (HR 1.73 p=0.16, HR 1.97 p = 0.052) or OS (HR 1.92 p=0.13; HR1.65 p=0.21). Further, for the patients who had measurable disease at the entry to SCT, post-PET was not predictive for DFS (HR 1.62, p=0.29) or OS (HR 1.59 p=0.35). Exclusion of unclear PET readings did not have any effect on these results. In subset analysis, post- PET did predict DFS in patients with NHL (HR 2.6 p=0.034). Our results suggest that early pre/post SCT PET analysis is not beneficial in this algorithm for predicting overall survival in these patients. Negative post-PET may predict DFS in patients with aggressive NHL, however, did not predict OS in this group. Our analysis indicates that other methods of determining risk of relapse and transplant outcome are needed.

Commentary on “Diagnosis of Alzheimer's disease: Two decades of progress.” Central role of technology in the treatment and prevention of Alzheimer's disease

Commentary on “Diagnosis of Alzheimer's disease: Two decades of progress.” Central role of technology in the treatment and prevention of Alzheimer's disease

Current practice of patient follow-up after potentially curative resection of cutaneous melanoma.

Follow-up care for patients who have undergone potentially curative resection of cutaneous melanoma varies widely among physicians, and the underlying rationale has not been assessed. To quantify current practice patterns and to discern motivation, a custom-designed questionnaire was mailed to U.S. and non-U.S. surgeons, all of whom were members of the American Society of Plastic and Reconstructive Surgeons (ASPRS). Surveys were mailed to 3,032 ASPRS members, chosen randomly from a total of 4,320 members. Of the 1,142 questionnaires that were returned, 395 were evaluable. Nonevaluability was usually due to lack of melanoma patients receiving follow-up in the surgeons' practices. Surveillance of patients after resection of melanoma relies most heavily on office visit, chest x-ray, complete blood count, and liver function tests. There was surprisingly little influence of elective node dissection on follow-up practices. Imaging tests such as computed tomography, magnetic resonance imaging, and position emission tomography scan were rarely employed. Surveillance is motivated by many factors, particularly early detection of recurrence of the index melanoma and second primary melanomas. This survey provides information regarding current follow-up strategies recommended by ASPRS surgeons after potentially curative resection of cutaneous melanoma. There is considerable variation in surveillance intensity and in motivation among practitioners, thus representing a lack of consensus.

Current Practice of Patient Follow-Up after Potentially Curative Resection of Cutaneous Melanoma

Follow-up care for patients who have undergone potentially curative resection of cutaneous melanoma varies widely among physicians, and the underlying rationale has not been assessed. To quantify current practice patterns and to discern motivation, a custom-designed questionnaire was mailed to U.S. and non-U.S. surgeons, all of whom were members of the American Society of Plastic and Reconstructive Surgeons (ASPRS). Surveys were mailed to 3032 ASPRS members, chosen randomly from a total of 4320 members. Of the 1142 questionnaires that were returned, 395 were evaluable. Nonevaluability was usually due to lack of melanoma patients receiving follow-up in the surgeons' practices. Surveillance of patients after resection of melanoma relies most heavily on office visit, chest x-ray, complete blood count, and liver function tests. There was surprisingly little influence of elective node dissection on follow-up practices. Imaging tests such as computed tomography, magnetic resonance imaging, and position emission tomography scan were rarely employed. Surveillance is motivated by many factors, particularly early detection of recurrence of the index melanoma and second primary melanomas. This survey provides information regarding current follow-up strategies recommended by ASPRS surgeons after potentially curative resection of cutaneous melanoma. There is considerable variation in surveillance intensity and in motivation among practitioners, thus representing a lack of consensus. (Plast. Reconstr. Surg. 106: 590, 2000.)

Reliability of a simple non-invasive method for the evaluation of 5-HT2 receptors using [18F]-setoperone PET imaging.

Position emission tomography (PET) imaging of 5-HT2 receptors can be potentially very useful in investigating neuropsychiatric disorders and their pharmacological treatments. [18F]-setoperone, a PET radio-ligand, has been shown to be useful for the delineation of 5-HT2 receptors in the cortex. However, there is no available data regarding the scan-rescan reliability of this technique. The purpose of this study was to assess the reliability of the [18F]-setoperone PET technique for assessing the binding potential (Bmax/ Kd) for 5-HT2 receptors. Ten healthy subjects had two [18F]-setoperone PET scans on two separate occasions 6-21 days apart. The average difference in the 5-HT2 binding potential (BP) as measured on the two occasions in the prefrontal, temporal, parietal and occipital region was between 5 and 7%. Thus 5-HT2 BP can be measured with a high reliability using a non-invasive technique that uses the cerebellum as a reference region. A power analysis based on the reliability data suggests that this technique can be used to detect within-subject differences of 10% or more, and between-group differences of 25% or more, with a reasonable number of subjects. It is concluded that [18F]-setoperone can be routinely produced and reliably used for the PET imaging of 5-HT2 receptors in clinical situations.

Treatment of Advanced CNS Malignancies with the Recombinant Adenovirus H5.010RSVTK: A Phase I Trial. University of Pennsylvania Medical Center, Philadelphia

Primary CNS malignancies are responsible for approximately 12,000 deaths annually in the United States. There has been little change in the outcome for adults with malignant brain tumors over the past few decades, despite improvements in surgical techniques and advances in radiation therapy. These tumors are uniformly fatal one to two years after diagnosis. The morbidity and mortality of this disease arise from the effects of a locally invasive, non-metastasizing lesion. The patients may suffer from seizures, paralysis, incoordination, aphasia, confusion, memory loss, sensory deficits or visual loss, depending on the regions of the brain affected. In addition, they usually require large doses of corticosteroids early and late in their illness, and may experience disabling side effects of this treatment, such as edema, proximal myopathy, diabetes, fungal infections or deep vein thrombosis. Few patients in the older age group are able to work after the diagnosis. Most of the patients are incapable of self-care for several months before death. The localized transfer of new genes into cancer cells potentially permits the expression of proteins with specific biologic functions that may provide a means to alter the biology of tumor growth through a variety of mechanisms including increasing tumor immunogenicity, inducing the local expression of toxic agents, and sensitization of tumors to chemotherapeutic agents. Gene therapy with the transfer of the drug susceptibility gene Herpes virus thymidine kinase (HSV-TK) has shown promise in a number of animal models, including CNS tumors. This study will evaluate the use of adenovirus-mediated transfer of the HSV-TK gene into primary human brain tumors followed by systemic treatment with ganciclovir. The goals of this phase I study are to evaluate the overall safety and efficacy of this treatment and to gain insight into the parameters that may limit the general applicability of this approach. In this phase I study, patients with recurrent gliomas will receive stereotactic-guided injections of the virus into the brain tumor, followed by intravenous ganciclovir for 14 days. Patients eligible to undergo a palliative debulking procedure will receive the same treatment followed by resection on day 7. At the time of resection a second dose of virus will be administered intra-operatively into the residual, unresectable portion of the tumor, and intravenous ganciclovir will be continued for additional 14 days. Tissue removed at the time of resection will be analyzed for evidence of adenovirus infection, thymidine kinase expression and signs of inflammation. The size and metabolic activity of all tumors will be followed by volumetric MRI scans and Position Emission Tomography Scans, respectively. Patients will be enrolled in groups of three, with each group receiving successively larger doses of adenovirus. This study will quantify the toxicity of this therapy, and provide evidence as to the duration of transgene expression and virus induced inflammation.

μ Opiate receptors are selectively labelled by [ 3H]carfentanil in human and rat brain

[ 11C]Carfentanil is a potent opioid agonist currently in use as a specific PET (position emission tomography) scan radioligand for brain μ opioid receptors. In order to investigate the receptor interactions of carfentanil in detail [ 3H]carfentanil was used as a radioligand for labelling receptors in rat and human brain tissue homogenates. [ 3H]Carfentanil was found to bind saturably and with high affinity (K D = 0.08 ± 0.01 nM) to membranes prepared from human cortical (B max = 42 ± 3 fmol/mg) and thalamic (B max = 84 ± 3 fmol/mg) tissues and rat cortex (B max = 82 ± 4 fmol/mg) and deincephalon (B max = 105 ± 5 fmol/mg). Association (1.23 ± 0.19 × 10 10Mol −1 × min −1 and dissociation rate (0.19 ± 0.03 min −1) constants were determined in human cortical tissues; results from studies in rat cortical, and rat diencephalon tissue homogenates produced similar kinetic rate constants. Competition studies with a variety of drugs indicated that [ 3H]carfentanil interacts primarily with μ opioid receptors in the four tissues studied; the affinities of a series of non-radioactive opioid ligands were essentially identical in the four tissues (correlation coefficients = 0.88−0.93). Naloxone, morphine, DAGO ([D-Ala 2-MePhe 4-Gly-ol 5]enkephalin), DADL (D-Ala 2-D- Leu 5]enkaphalin) and EKC (ethylketazocine) potently displaced specific [ 3H]carfentanil binding with nM potency while the κ agonist U-69593, the σ agonists (+)-SKF 10047, (+)-3-PPP ((3-hydroxyphenyl)-N-propylpiperidine) and haloperidol and PCP (phencyclidine) were less potent displacing agents. The higher affinities of DAGO and morphine versus DADL for the [ 3H]carfentanil binding site indicates that δ opioid receptors are not being labelled. These data indicate that [ 3H]carfentanil is a high affinity, specific μ opioid receptor radioligand that may be of use in vitro for studying μ opioid receptors and supports the PET scanning data indicating the μ opioid receptor specificity of [ 11C]carfentanil. The molecular kinetic rate constants determined in vitro will be of assistance in using modelling procedures to interpret PET scanning information.