Positron Emission Tomography Procedures Research Articles

NUCLEAR MEDICINE PROCEDURE VOLUME AND ESTIMATION OF COLLECTIVE EFFECTIVE DOSE IN TAMIL NADU TOWARDS THE ESTABLISHMENT OF DIAGNOSTIC REFERENCE LEVEL.

With an objective to establish adult diagnostic reference levels in the practice of nuclear medicine (NM) in the state of Tamil Nadu (TN), data on the predominant NM procedures carried out in the state are analyzed. In this study, data on total NM diagnostic procedures during the years 2015-19 along with patient-specific diagnostic NM procedure data for the period April-June 2021 from all centers in Tamil Nadu are collected and analyzed using SPSS statistical software. Nine predominant types of NM scans are analyzed. Collective effective dose from NM scans and per capita dose for the TN population are estimated. The 75th percentile of the distribution and average administered activity (AAA) has been derived and local reference levels are reported. Based on the statistical analysis, it is observed that the whole-body positron emission tomography (PET), renal diethylenetriamine pentaacetate (DTPA) scan, bone methylene diphosphonate (MDP) scan, iodine-131 whole body scan, thyroid studies using Technetium per technetate, renal dimercaptosuccinic acid (DMSA), myocardial perfusion methoxyisobutyl isonitrile sestamibi (MIBI), mebrofenin, Galium-68 prostate-specific membrane antigen (PSMA) are the most common procedure covering >90% of the practices carried out. The collective effective dose is 410 man-Sv in the year 2019, leading to a mean effective dose of 0.006mSv per capita of the TN state population. The 75th percentile of the distribution of AA is slightly higher than diagnostic reference level (DRL) as compared with Australian DRL (310MBq). It is also observed that F-18 PET procedures are primarily responsible for most of the collective effective dose, local DRL is 316MBq and it is important to establish national DRLs for NM diagnostic scans to optimize the NM examinations.

Occupational exposures in PET procedures with 18F-FDG in adult and pediatric patients

Diagnosis through positron emission tomography (PET) is an increasingly used procedure in cerebral, cardiac and especially oncology diseases. It is performed in nuclear medicine clinics, mainly using 18F-Fluorodeoxyglucose (18F-FDG), which has one of the longest half-lives among positron emitters. The gamma rays, produced in the annihilations, require strict radiation control to guarantee the safety of the occupationally exposed individuals working in PET exam facilities. To evaluate occupational exposures, in this study, the MCNPX2.7.0 radiation transport code was used. The professionals were represented by the FASH3 (female) and MASH3 (male) adult virtual anthropomorphic phantoms, which have anthropometric characteristics like those of real individuals. Four exposure scenarios were modeled: radiopharmaceutical preparation, administration to the patient, patient follow-up, and patient placement in PET equipment. The results are presented in terms of the mean effective dose by PET procedure (μSv/procedure) and the mean effective dose by radiopharmaceutical activity (nSv/MBq). Using the set of conversion coefficients presented in this study, it is possible to calculate the absolute values of effective doses for nuclear medicine professionals who are in contact with the radioactive material or the patient. The differences between our study and the literature were only 3%. The effective occupational doses, with an adult patient, were 14% higher than those with pediatric patients.

Effective doses and associated age-related risks for common paediatric diagnostic nuclear medicine and PET procedures at a large Australian paediatric hospital.

Effective dose alone cannot be used to specify and communicate the radiation risk for an individual as risks are dependent on many factors including age and gender. There are limited published data regarding age-specific effective doses and the associated lifetime risk of developing cancers for paediatrics. In this study, we have estimated the typical effective doses for six commonly performed paediatric nuclear medicine and positron emission tomography (PET) studies at the Royal Children's Hospital, Melbourne, Australia. Effective doses were used to estimate and categorise associated stochastic risks with commonly used risk terminology. Paediatric protocols for common nuclear medicine and PET studies and the World Health Organization (WHO) 50th percentile weight-for-age data for females and males aged up to 18 years were used to estimate typical organ and effective doses using ICRP dosimetric tables for radiopharmaceuticals and lifetime risk of cancer incidence using BEIR VII Phase 2 report data. Results were used to determine standardised levels of risk. Organ doses, effective doses, corresponding lifetime risk of cancer incidence and level of risk category from six common nuclear medicine and PET studies for paediatric patients were calculated and presented for ease of communication. Typical effective doses from common paediatric nuclear medicine and PET studies and the associated lifetime risk of cancer incidence and level of risk have been established for our institution. This can be used to convey risks to health professionals, patients and carers in ways that are easy to understand and compare with other everyday risks.

Additional Assessment of Fecal Corticosterone Metabolites Improves Visual Rating in the Evaluation of Stress Responses of Laboratory Rats

Simple SummaryAssessment of animal welfare is an important aspect of preclinical studies to minimize suffering and burden and to improve scientific data. In a standard preclinical setup, such an assessment is normally done via so-called score sheets, which are part of the official documentation and approval of a preclinical study. These score sheets contain different categories, including objective parameters such as animals’ body weight, as well as more subjective criteria such as general status, behavior, and appearance, by which the animal is assessed and given a score reflecting the burden. However, very little is known about whether this mainly visual-based and subjective evaluation of the animals’ welfare reliably reflects the status of the animal and correlates well with more objective parameters used for assessment of animal welfare. To this end, the current study investigates the concordance of parameters obtained via standardized score sheets and fecal corticosterone metabolites in a preclinical neuroscientific setup. Determination of fecal corticosterone metabolites as response parameter of adrenocortical activity is thereby a well-validated parameter often used to determine animals’ stress levels. Our data reveal that specific but subjective scores did not mirror the stress response assessed via fecal corticosterone metabolites in the same animals.Since animal experiments cannot be completely avoided, the pain, suffering, and distress of laboratory animals must be minimized. To this end, a major prerequisite is reliable assessment of pain and distress. Usually, evaluation of animal welfare is done by visual inspection and score sheets. However, relatively little is known about whether standardized, but subjective, score sheets are able to reliably reflect the status of the animals. The current study aimed to compare visual assessment scores and changes in body weight with concentrations of fecal corticosterone metabolites (FCMs) in a neuroscientific experimental setup. Additionally, effects of refinement procedures were investigated. Eight male adult Sprague-Dawley rats underwent several experimental interventions, including electroencephalograph electrode implantation and subsequent recording, positron emission tomography (PET), and sleep deprivation (SD) by motorized activity wheels. Additional 16 rats were either used as controls without any treatment or to evaluate refinement strategies. Stress responses were determined on a daily basis by means of measuring FCMs, body weight, and evaluation of the animals’ welfare by standardized score sheets. Surgery provoked a significant elevation of FCM levels for up to five days. Increases in FCMs due to PET procedures or SD in activity wheels were also highly significant, while visual assessment scores did not indicate elevated stress levels and body weights remained constant. Visual assessment scores correlate with neither changes in body weight nor increases in FCM levels. Habituation procedures to activity wheels used for SD had no impact on corticosterone release. Our results revealed that actual score sheets for visual assessment of animal welfare did not mirror physiological stress responses assessed by FCM measurements. Moreover, small changes in body weight did not correlate with FCM concentration either. In conclusion, as visual assessment is a method allowing immediate interventions on suffering animals to alleviate burden, timely stress assessment in experimental rodents via score sheets should be ideally complemented by validated objective measures (e.g., fecal FCM measured by well-established assays for reliable detection of FCMs). This will complete a comprehensive appraisal of the animals’ welfare status in a retrospective manner and refine stressor procedures in the long run.

Cardiac PET-CT: A Brief Review of Indications and Feasibility in the Indian Scenario

AbstractCardiac positron emission tomography (PET) is a functional imaging modality with the predominant indications being an assessment of myocardial perfusion and viability using short-lived positron emitters. PET procedures are used for perfusion assessment only when single-photon emission computed tomography is equivocal. Perfusion agents are ultra short-lived and have limited availability in our country, that is, only at centers with onsite cyclotron. Viability assessment with fluorodeoxyglucose (FDG) is widely performed in many centers across the country due to the availability of FDG. The other important indication is in the detection of inflammatory myocarditis, the most common being cardiac sarcoidosis done with special dietary instructions and FDG as a tracer. This indication is widely used for early detection of myocardial inflammation which would be reversible if treated early. It is also used in the assessment of treatment response. Newer tracer 68 Ga Dotapeptide is also used in this application.

Validation of the Image Registration Technique from Functional Near Infrared Spectroscopy (fNIRS) Signal and Positron Emission Tomography (PET) Image

Functional near infrared spectroscopy (fNIRS) is an imaging system that can measure hemodynamic changes of the brain. However, the system incapability to measure beyond the brain cortex region make it usage less appealing for in-depth brain studies. To overcome this, many researchers combine fNIRS with other imaging modalities to gain better understanding of the brain activities. In this paper, we described the theory of the registering fNIRS signals and positron emission tomography (PET) image method and performed experiments to validate it. The registration method was validated using specially designed phantom for fNIRS and PET. Polaris system was used to track the position of the phantom which is based on the Polaris markers during fNIRS and PET procedures. The Polaris markers share the same coordinate, thus the fNIRS and PET were calibrated to each other through these markers. To register the fNIRS signal on the PET image, the phantom position in fNIRS coordinate is translated to PET coordinate which allow the probe and the markers being coordinated in PET. Polaris markers were used as the references marker to determine the transformation matrices. The result shows that the fNIRS channel can be viewed on the PET image of the phantom. The transformation error from Polaris to PET is less than 1.00 mm and the precision test is less than 0.1mm while the accuracy is less than 2.8 mm. This result suggests that our theory on the registration method could be used for multimodal image registration between fNIRS and other modalities.

Cost-Effectiveness of [18F] Fluoroethyl-L-Tyrosine for Temozolomide Therapy Assessment in Patients With Glioblastoma.

Background and Purpose: Glioblastomas are the most aggressive of all gliomas. The prognosis of these gliomas, which are classified as grade IV tumors by the World Health Organization (WHO), is poor. Combination therapy, including surgery, radiotherapy, and chemotherapy has variable outcomes and is expensive. In light of rising healthcare costs, there are societal demands for the justification of medical expenses. Therefore, we calculated the cost-effectiveness of follow-up [18F] fluoroethyl-L-tyrosine ([18F] FET) positron emission tomography (PET) scans performed on patients with glioblastoma after surgery and before commencing temozolomide maintenance treatment.Materials and Methods: To determine the cost-effectiveness of follow-up [18F] FET PET procedures, we examined published clinical data and calculated the associated costs in the context of Belgian healthcare. We subsequently performed one-way deterministic sensitivity analysis and Monte Carlo analysis on the calculated ratios.Results: The decision tree based on overall survival rates showed that the number of non-responders identified using PET was 57.14% higher than the number of non-responders identified using conventional MRI. Further, the decision tree based on progression-free survival rates revealed a comparable increase of 57.50% non-responders identified. The calculated cost of two required PET scans per patient during the follow-up treatment phase was 780.50 euros. Two cost-effectiveness ratios were determined for overall survival and progression-free survival rates. Both of these calculations yielded very similar results: incremental cost-effectiveness ratios of 1,365.86 and 1,357.38 euros, respectively, for each identified non-responder. The findings of the sensitivity analysis supported the calculated results, confirming that the obtained data were robust.Conclusion: Our comparative study of conventional MRI and [18F] FET PET revealed that the latter is a valuable tool for predicting the treatment responses of patients with glioblastomas to follow-up temozolomide maintenance treatment while considering its cost-effectiveness. Thus, [18F] FET PET scans enable clinical outcomes to be predicted accurately and at a low cost. Moreover, given the robustness of the data in the sensitivity analyses, the level of certainty of this outcome is acceptable.

Multi-Modal Signatures of Tau Pathology, Neuronal Fiber Integrity, and Functional Connectivity in Traumatic Brain Injury.

[18F]AV-1451 (aka 18F-Flortaucipir, [18F]T807) was developed for positron-emission tomography (PET) imaging of paired helical filaments of hyperphosphorylated tau, which are of interest in a range of neuropathologies, including traumatic brain injury (TBI). Magnetic resonance imaging (MRI) techniques like diffusion tensor imaging (DTI) and resting state functional connectivity assess structural and functional characteristics of the brain, complementing the molecular information that can be obtained by PET. The goal herein was to explore the utility of such multi-modal imaging in a case series based on a population of TBI subjects. This study probes the interrelationship between tau deposition, white matter integrity, and gray matter functional connectivity across the spectrum of TBI. Nineteen subjects (11 controls, five former contact sports athletes, one automotive accident, and two with military-related injury) underwent [18F]AV-1451 PET and magnetic resonance scanning procedures. [18F]AV-1451 distribution volume ratio (DVR) was estimated using the Logan method and the cerebellum as a reference region. Diffusion tractography images and fractional anisotropy (FA) images were generated using diffusion toolkit and FSL. Resting-state functional MRI (fMRI) analysis was based on a graph theory metric, namely weighted degree centrality. TBI subjects showed greater heterogeneity in [18F]AV-1451 DVR when compared with control subjects. In a subset of TBI subjects, areas with high [18F]AV-1451 binding corresponded with increased FA and diminished white matter tract density in DTI. Functional MRI results exhibited an increase in functional connectivity, particularly among local connections, in the areas where tau aggregates were more prevalent. In a case series of a diverse group of TBI subjects, brain regions with elevated tau burden exhibited increased functional connectivity as well as decreased white matter integrity. These findings portray molecular, microstructural, and functional corollaries of TBI that spatially coincide and can be measured in the living human brain using noninvasive neuroimaging techniques.

FDG PET/CT Imaging in Diabetic Patients - A Special Emphasis on Imaging of Infection.

Nuclear Medicine (NM) imaging plays a major role in the assessment of infection and inflammation. Tracers, including single photon emitting radionuclides for Single Photon Emission Tomography (SPECT) and agents for positron emission tomography (PET), reflect primarily tissue and cellular function or metabolism. In the specific clinical setting of a patient with suspected infectious or inflammatory process, planar scintigraphy, SPECT or PET procedures are used to support a clinically suspected diagnosis. Integrating metabolic and anatomic information using a single SPECT/CT or PET/CT technique has substantially improved the diagnostic accuracy of these imaging tests and advanced the NM technology to be a significant and important tool in the field of infection and inflammation. Diabetes, one of the most prevalent diseases, has a direct relationship with the development of various infection related condition. Due to alterations in different metabolic pathways, imaging of the diabetic patient may be subject to specific pitfalls and obstacles which should be taken into consideration. This review aimed at describing the impact of diabetes and hyperglycemia on NM imaging, with an emphasis on FDGPET/ CT, in specific infectious conditions related to diabetes.

Implementation of diffusion-weighted magnetic resonance imaging in target delineation of central lung cancer accompanied with atelectasis in precision radiotherapy.

Radiotherapy, particularly the target delineation of cancer based on scanned images, plays a key role in the planning of cancer treatment. Recently, diffusion-weighted magnetic resonance imaging (DW-MRI) has emerged as a prospective superior procedure compared with intensified computed tomography (CT) and positron emission tomography (PET) in the target delineation of cancer. However, the implication of DW-MRI in lung cancer, the leading cause of cancer-associated mortality worldwide, has not been extensively evaluated. In the present study, the gross target volumes of lung cancer masses delineated using the DW-MRI, CT and PET procedures were compared in a pairwise manner in a group of 27 lung cancer patients accompanied with atelectasis of various levels. The data showed that compared with CT and PET procedures, DW-MRI has a more precise delineation of lung cancer while exhibiting higher reproducibility. Together with the fact that it is non-invasive and cost-effective, these data demonstrate the great application potential of the DW-MRI procedure in cancer precision radiotherapy.

Ultrasmall [(64)Cu]Cu nanoclusters for targeting orthotopic lung tumors using accurate positron emission tomography imaging.

Positron emission tomography (PET) imaging has received special attention owing to its higher sensitivity, temporal resolution, and unlimited tissue penetration. The development of tracers that target specific molecules is therefore essential for the development and utility of clinically relevant PET procedures. However, (64)Cu as a PET imaging agent generally has been introduced into biomaterials through macrocyclic chelators, which may lead to the misinterpretation of PET imaging results due to the detachment and transchelation of (64)Cu. In this study, we have developed ultrasmall chelator-free radioactive [(64)Cu]Cu nanoclusters using bovine serum albumin (BSA) as a scaffold for PET imaging in an orthotopic lung cancer model. We preconjugated the tumor target peptide luteinizing hormone releasing hormone (LHRH) to BSA molecules to prepare [(64)Cu]CuNC@BSA-LHRH. The prepared [(64)Cu]Cu nanoclusters showed high radiolabeling stability, ultrasmall size, and rapid deposition and diffusion into tumor, as well as predominantly renal clearance. [(64)Cu]CuNC@BSA-LHRH showed 4 times higher tumor uptake compared with that of [(64)Cu]CuNC@BSA by analyzing the (64)Cu radioactivity of tissues via gamma counting. The PET imaging using [(64)Cu]Cu nanoclusters as tracers showed more sensitive, accurate, and deep penetration imaging of orthotopic lung cancer in vivo compared with near-infrared fluorescence imaging. The nanoclusters provide biomedical research tools for PET molecular imaging.

18FDG synthesis and supply: a journey from existing centralized to future decentralized models.

Positron emission tomography (PET) as the functional component of current hybrid imaging (like PET/ CT or PET/MRI) seems to dominate the horizon of medical imaging in coming decades. 18Flourodeoxyglucose (18FDG) is the most commonly used probe in oncology and also in cardiology and neurology around the globe. However, the major capital cost and exorbitant running expenditure of low to medium energy cyclotrons (about 20 MeV) and radiochemistry units are the seminal reasons of low number of cyclotrons but mushroom growth pattern of PET scanners. This fact and longer half-life of 18F (110 minutes) have paved the path of a centralized model in which 18FDG is produced by commercial PET radiopharmacies and the finished product (multi-dose vial with tungsten shielding) is dispensed to customers having only PET scanners. This indeed reduced the cost but has limitations of dependence upon timely arrival of daily shipments as delay caused by any reason results in cancellation or rescheduling of the PET procedures. In recent years, industry and academia have taken a step forward by producing low energy, table top cyclotrons with compact and automated radiochemistry units (Lab- on-Chip). This decentralized strategy enables the users to produce on-demand doses of PET probe themselves at reasonably low cost using an automated and user-friendly technology. This technological development would indeed provide a real impetus to the availability of complete set up of PET based molecular imaging at an affordable cost to the developing countries.

Association of Adenosine Receptor Gene Polymorphisms and In Vivo Adenosine A1 Receptor Binding in The Human Brain

Adenosine A1 receptors (A1ARs) and the interacting adenosine A2A receptors are implicated in neurological and psychiatric disorders. Variants within the corresponding genes ADORA1 and ADORA2A were shown associated with pathophysiologic alterations, particularly increased anxiety. It is unknown so far, if these variants might modulate the A1AR distribution and availability in different brain regions. In this pilot study, the influence of ADORA1 and ADORA2A variants on in vivo A1AR binding was assessed with the A1AR-selective positron emission tomography (PET) radioligand [(18)F]CPFPX in brains of healthy humans. Twenty-eight normal control subjects underwent PET procedures to calculate the binding potential BPND of [(18)F]CPFPX in cerebral regions and to assess ADORA1 and ADORA2A single nucleotide polymorphism (SNP) effects on regional BPND data. Our results revealed SNPs of both genes associated with [(18)F]CPFPX binding to the A1AR. The strongest effects that withstood even Bonferroni correction of multiple SNP testing were found in non-smoking subjects (N=22) for ADORA2A SNPs rs2236624 and rs5751876 (corr. Pall<0.05). SNP alleles previously identified at risk for increased anxiety like the rs5751876 T-allele corresponded to consistently higher A1AR availability in all brain regions. Our data indicate for the first time that variation of A1AR availability was associated with ADORA SNPs. The finding of increased A1AR availability in regions of the fear network, particularly in ADORA2A risk allele carriers, strongly warrants evaluation and replication in further studies including individuals with increased anxiety.

Image-Derived Input Function Derived from a Supervised Clustering Algorithm: Methodology and Validation in a Clinical Protocol Using [11C](R)-Rolipram

Image-derived input function (IDIF) obtained by manually drawing carotid arteries (manual-IDIF) can be reliably used in [11C](R)-rolipram positron emission tomography (PET) scans. However, manual-IDIF is time consuming and subject to inter- and intra-operator variability. To overcome this limitation, we developed a fully automated technique for deriving IDIF with a supervised clustering algorithm (SVCA). To validate this technique, 25 healthy controls and 26 patients with moderate to severe major depressive disorder (MDD) underwent T1-weighted brain magnetic resonance imaging (MRI) and a 90-minute [11C](R)-rolipram PET scan. For each subject, metabolite-corrected input function was measured from the radial artery. SVCA templates were obtained from 10 additional healthy subjects who underwent the same MRI and PET procedures. Cluster-IDIF was obtained as follows: 1) template mask images were created for carotid and surrounding tissue; 2) parametric image of weights for blood were created using SVCA; 3) mask images to the individual PET image were inversely normalized; 4) carotid and surrounding tissue time activity curves (TACs) were obtained from weighted and unweighted averages of each voxel activity in each mask, respectively; 5) partial volume effects and radiometabolites were corrected using individual arterial data at four points. Logan-distribution volume (V T/f P) values obtained by cluster-IDIF were similar to reference results obtained using arterial data, as well as those obtained using manual-IDIF; 39 of 51 subjects had a V T/f P error of <5%, and only one had error >10%. With automatic voxel selection, cluster-IDIF curves were less noisy than manual-IDIF and free of operator-related variability. Cluster-IDIF showed widespread decrease of about 20% [11C](R)-rolipram binding in the MDD group. Taken together, the results suggest that cluster-IDIF is a good alternative to full arterial input function for estimating Logan-V T/f P in [11C](R)-rolipram PET clinical scans. This technique enables fully automated extraction of IDIF and can be applied to other radiotracers with similar kinetics.

Suggestion of a national diagnostic reference level for 18F-FDG/PET scans in adult cancer patients in Brazil

Objective To suggest a national value for the diagnostic reference level (DRL) in terms of activity in MBq.kg–1, for nuclear medicine procedures with fluorodeoxyglucose (18F-FDG) in whole body positron emission tomography (PET) scans of adult patients. Materials and Methods A survey on values of 18F-FDG activity administered in Brazilian clinics was undertaken by means of a questionnaire including questions about number and manufacturer of the installed equipment, model and detector type. The suggested DRL value was based on the calculation of the third quartile of the activity values distribution reported by the clinics. Results Among the surveyed Brazilian clinics, 58% responded completely or partially the questionnaire; and the results demonstrated variation of up to 100% in the reported radiopharmaceutical activity. The suggested DRL for 18F-FDG/PET activity was 5.54 MBq.kg–1 (0.149 mCi.kg–1). Conclusion The present study has demonstrated the lack of standardization in administered radiopharmaceutical activities for PET procedures in Brazil, corroborating the necessity of an official DRL value to be adopted in the country. The suggested DLR value demonstrates that there is room for optimization of the procedures and 18F-FDG/PET activities administered in Brazilian clinics to reduce the doses delivered to patients. It is important to highlight that this value should be continually revised and optimized at least every five years.

The Development, Past Achievements, and Future Directions of Brain PET

The early developments of brain positron emission tomography (PET), including the methodological advances that have driven progress, are outlined. The considerable past achievements of brain PET have been summarized in collaboration with contributing experts in specific clinical applications including cerebrovascular disease, movement disorders, dementia, epilepsy, schizophrenia, addiction, depression and anxiety, brain tumors, drug development, and the normal healthy brain. Despite a history of improving methodology and considerable achievements, brain PET research activity is not growing and appears to have diminished. Assessments of the reasons for decline are presented and strategies proposed for reinvigorating brain PET research. Central to this is widening the access to advanced PET procedures through the introduction of lower cost cyclotron and radiochemistry technologies. The support and expertize of the existing major PET centers, and the recruitment of new biologists, bio-mathematicians and chemists to the field would be important for such a revival. New future applications need to be identified, the scope of targets imaged broadened, and the developed expertize exploited in other areas of medical research. Such reinvigoration of the field would enable PET to continue making significant contributions to advance the understanding of the normal and diseased brain and support the development of advanced treatments.

The radioprotection management of a PET department with a cyclotron and radiopharmacy laboratory, in accordance with Italian legislation

The possibility of setting up a positron emission tomography (PET) facility with a cyclotron and radiopharmaceutical laboratory in situ, at a feasible price and in a very restricted space, has led to a steady increase both in the use of the PET technique in diagnostic clinical routine imaging and in the number of cyclotrons for drug production. Owing to the progress made in the PET procedures, it is now possible to have not only a highly innovative system of diagnostic examination, with a remarkable improvement in the diagnostic quality and patient care, but also a considerable increase in the number of daily examinations. In this paper, the authors show how the acquired know-how, with respect to radioprotection, has applied to the planning, running and management of the PET/CT unit, installed in the Imaging Diagnostic Department of the Policlinico Tor Vergata (PTV), at Tor Vergata University, Rome.

Nuclear medicine procedures for the evaluation of male sexual organs: a brief review

Sexuality consists of three aspects that are interrelated and inseparable, biological, physiological and social. The biological aspect considers the individual's capability to give and to receive pleasure. In consequence, it covers the functionality of the sexual organs and the physiology of human sexual response cycle. Diagnostic imaging modalities, such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) have been used to evaluate clinical disorders of the male reproductive system. PET and SPECT procedures basically involve the administration of a radiopharmaceutical that has a higher uptake in a specific tumor or tissue. The aim of this brief review is to present some radiopharmaceuticals that have been used in the clinical evaluation of the male sexual organs (testes, prostate, seminal vesicles, penis) related with male sexuality. This information could be useful in better understanding the male sexual response cycle, as well as the sexual disorders, when considering the male sexual organs and the pelvic floor. Moreover, the findings obtained with PET and SPECT imaging could help to evaluate the efficacy of clinical results of therapeutic procedures. In conclusion, the knowledge from these images could aid in better understanding the physiology of the different organs related with sexuality. Furthermore, they could be important tools to evaluate the physiological integrity of the involved organs, to improve clinical strategies and to accompany the patients under treatment.

Positron Emission Tomography: Applications In Drug Discovery and Drug Development

Positron Emission Tomography (PET) is a sophisticated nuclear imaging modality that affords researchers the ability to conduct both functional and molecular imaging on biological and biochemical processes in vivo. In functional imaging, biological parameters such as metabolic rate and perfusion that can be altered by disease or treatment are monitored. In molecular imaging, PET can be used to examine and quantify cellular events such as cell trafficking, receptor binding and gene expression. Therefore, PET is an important tool to elucidate mechanisms associated with diseases and drug actions. In addition to PET, microPET is designed to image small animals. A great tool to facilitate preclinical studies and basic research, it can eliminate the need of sacrificing the animal by enabling noninvasive, longitudinal, and serial studies. The results from preclinical studies using microPET can be directly correlated with clinical studies using PET, thus bridging the chasm that used to separate the 2 pivotal phases in drug development. This review first describes the basic principles of PET and compares it to other imaging modalities. Then, PET procedures and PET isotopes and tracers synthesis are outlined. Next, functional and molecular PET imaging applications in the fields of oncology, neurology, and cardiology in both humans and animals are presented. Spanning a wide range, these applications demonstrate the versatility of PET and how it can be used to accelerate drug discovery and development. Finally, the advantages and limitations of PET and how it can be used in the future to minimize risks of drug development are discussed.

A survey of PET activity in Germany during 1999

Positron emission tomography (PET) is the most powerful molecular imaging technique currently available for clinical use. The aim of this study was to provide public health information on PET procedures carried out in Germany - a country with a very high number of PET installations. To this end, all facilities that in 1999 were running at least one dedicated PET system were contacted and requested to provide information in a questionnaire on the radiopharmaceuticals applied, the total number and age distribution of patients and volunteers examined, the main diagnostic applications and the range of administered activities. Based on the information provided by 48 of the 60 PET facilities in Germany, an annual frequency of about 0.34 PET procedures per 1,000 inhabitants was estimated, associated with an annual per capita effective dose of about 1.9 micro Sv. Averaged over all PET procedures, the mean effective dose to patients was 5.6 mSv. The age distribution of patients and volunteers was skewed markedly towards higher ages; only a very small fraction (<3%) of patients were children younger than 15 years while older patients, and especially those in the age group between 41 and 65 years, were overrepresented relative to the general population. In total, 28 different PET radiopharmaceuticals were used, with only half of these having been administered to more than 20 patients each. The most frequently applied radiotracer was the glucose analogue 2-[(18)F]fluoro-2-deoxy- D-glucose (FDG), which was utilised in more than 84% of all PET procedures. For this tracer, the median value for activities applied for examinations in the three-dimensional (3D) acquisition mode was only half of that used for two-dimensional (2D) measurements. Based on a statistical analysis of the distribution of mean FDG activities administered to patients in the 48 PET facilities who responded to our inquiry, diagnostic reference levels of 370 and 200 MBq are proposed for the 2D and the 3D mode, respectively.