Uptake Of 18F Research Articles

Can Na18F PET/CT bone scans help when deciding if early intervention is needed in patients being treated with a TSF attached to the tibia: insights from 41 patients

PurposeTo demonstrate the usefulness of positron emission tomography (PET)/computed tomography (CT) bone scans for gaining insight into healing bone status earlier than CT or X-ray alone.MethodsForty-one prospective patients being treated with a Taylor Spatial Frame were recruited. We registered data obtained from successive static CT scans for each patient, to align the broken bone. Radionuclide uptake was calculated over a spherical volume of interest (VOI). For all voxels in the VOI, histograms and cumulative distribution functions of the CT and PET data were used to assess the type and progress of new bone growth and radionuclide uptake. The radionuclide uptake difference per day between the PET/CT scans was displayed in a scatter plot. Superimposing CT and PET slice data and observing the spatiotemporal uptake of 18F− in the region of healing bone by a time-sequenced movie allowed qualitative evaluation.ResultsNumerical evaluation, particularly the shape and distribution of Hounsfield Units and radionuclide uptake in the graphs, combined with visual evaluation and the movies enabled the identification of six patients needing intervention as well as those not requiring intervention. Every revised patient proceeded to a successful treatment conclusion.ConclusionNumerical and visual evaluation based on all the voxels in the VOI may aid the orthopedic surgeon to assess a patient’s progression to recovery. By identifying slow or insufficient progress at an early stage and observing the uptake of 18F− in specific regions of bone, it might be possible to shorten the recovery time and avoid unnecessary late complications.

Precise preoperative diagnosis of struma ovarii with pseudo-Meigs\u2019 syndrome mimicking ovarian cancer with the combination of 131I scintigraphy and 18F\u2013FDG PET: case report and review of the literature

BackgroundStruma ovarii is a rare ovarian neoplasm that often appears malignant on conventional imaging. Pseudo-Meigs’ syndrome with ascites, pleural effusion, and elevated serum CA 125 levels is much rarer and leads to misdiagnosis of ovarian cancer and unnecessary extended surgery.Case presentationA 50-year-old woman with abdominal distention and dyspnoea was referred to our hospital. Ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) showed a polycystic ovarian tumor with a solid component, pleural effusion, and massive ascites with negative cytology. Her serum CA 125 level was 1237 U/ml, indicating the presence of ovarian cancer. Based on increased uptake of 131I but no uptake of 18F–FDG in the tumor, the preoperative diagnosis was struma ovarii with pseudo-Meigs’ syndrome, which was confirmed histologically. She had no evidence of ascites and pleural effusion six months after surgery.ConclusionsTo date, there have been no systematic reviews focused on preoperative diagnosis with imaging modalities. The combination of 131I scintigraphy and 18F–FDG PET/CT in addition to conventional imaging modalities can provide the precise preoperative diagnosis of struma ovarii with pseudo-Meigs’ syndrome mimicking ovarian cancer, leading to the appropriate treatment strategy.

Imaging of isoproterenol-induced myocardial injury with 18F labeled fluoroglucaric acid in a rat model

Positron emission tomography (PET) of myocardial infarction (MI) by infarct avid imaging has the potential to reduce the time to diagnosis and improve diagnostic accuracy. The objective of this work was to synthesize 18F–labeled glucaric acid (FGA) for PET imaging of isoproterenol-induced cardiomyopathy in a rat model. MethodsWe synthesized 18F–FGA by controlled oxidation of 18F–fluorodeoxy glucose (FDG), mediated by 4-acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) in presence of NaBr and NaOCl in highly-buffered reaction conditions. After ascertaining preferential uptake of 18F–FGA in necrotic as compared to normal H9c2 myoblasts, the biodistribution and circulation kinetics of 18F–FGA was assessed in mice. Moreover, the potential of 18F–FGA to image myocardial damage was investigated in a rat model of isoproterenol-induced cardiomyopathy. Isoproterenol-induced myocardial injury was verified at necropsy by tissue staining and plasma cardiac troponin levels. ResultsSynthesis of radiochemically pure 18F–FGA was accomplished by a 5 min, one step oxidation of 18F–FDG. Reaction yield was quantitative and no side-products were detected. Biodistribution studies showed rapid elimination from the body (ke = 0.83 h−1); the major organ of 18F–FGA accumulation was kidney. In the rat model, isoproterenol-treatment resulted in significant increase in cardiac troponin. PET images showed that the hearts of isoproterenol-treated rats accumulated significant amounts of 18F–FGA, whereas healthy hearts showed negligible uptake of 18F–FGA. Target-to-nontarget contrast for 18F–FGA accumulation became significantly more pronounced in 4 h images as compared to images acquired 1 h post-injection. Conclusion18F–FGA can be easily and quantitatively synthesized from ubiquitously available 18F–FDG as a precursor. The resultant 18F–FGA has a potential to serve as an infarct-avid agent for PET imaging of MI. Advances in knowledge and implications for patient care18F–FGA/PET will complement existing perfusion imaging protocols in therapeutic decision making, determination of revascularization candidacy and success, differentiation of ischemia from necrosis in MI, discrimination of myocarditis from infarction, and surveillance of heart transplant rejection.

Glutamine Addiction in Kidney Cancer Suppresses Oxidative Stress and Can Be Exploited for Real-Time Imaging.

Many cancers appear to activate intrinsic antioxidant systems as a means to counteract oxidative stress. Some cancers, such as clear cell renal cell carcinoma (ccRCC), require exogenous glutamine for growth and exhibit reprogrammed glutamine metabolism, at least in part due to the glutathione pathway, an efficient cellular buffering system that counteracts reactive oxygen species and other oxidants. We show here that ccRCC xenograft tumors under the renal capsule exhibit enhanced oxidative stress compared with adjacent normal tissue and the contralateral kidney. Upon glutaminase inhibition with CB-839 or BPTES, the RCC cell lines SN12PM-6-1 (SN12) and 786-O exhibited decreased survival and pronounced apoptosis associated with a decreased GSH/GSSG ratio, augmented nuclear factor erythroid-related factor 2, and increased 8-oxo-7,8-dihydro-2'-deoxyguanosine, a marker of DNA damage. SN12 tumor xenografts showed decreased growth when treated with CB-839. Furthermore, PET imaging confirmed that ccRCC tumors exhibited increased tumoral uptake of 18F-(2S,4R)4-fluoroglutamine compared with the kidney in the orthotopic mouse model. This technique can be utilized to follow changes in ccRCC metabolism in vivo Further development of these paradigms will lead to new treatment options with glutaminase inhibitors and the utility of PET to identify and manage patients with ccRCC who are likely to respond to glutaminase inhibitors in the clinic. Cancer Res; 77(23); 6746-58. ©2017 AACR.

Can Spatiotemporal Fluoride (18F\u2212) Uptake be Used to Assess Bone Formation in the Tibia? A Longitudinal Study Using PET/CT

BackgroundWhen a bone is broken for any reason, it is important for the orthopaedic surgeon to know how bone healing is progressing. There has been resurgence in the use of the fluoride (18F−) ion to evaluate various bone conditions. This has been made possible by availability of positron emission tomography (PET)/CT hybrid scanners together with cyclotrons. Absorbed on the bone surface from blood flow, 18F− attaches to the osteoblasts in cancellous bone and acts as a pharmacokinetic agent, which reflects the local physiologic activity of bone. This is important because it shows bone formation indicating that the bone is healing or no bone formation indicating no healing. As 18F− is extracted from blood in proportion to blood flow and bone formation, it thus enables determination of bone healing progress.Questions/purposesThe primary objective of this study was to determine whether videos showing the spatiotemporal uptake of 18F− via PET bone scans could show problematic bone healing in patients with complex tibia conditions. A secondary objective was to determine if semiquantification of radionuclide uptake was consistent with bone healing.MethodsThis study investigated measurements of tibia bone formation in patients with complex fractures, osteomyelitis, and osteotomies treated with a Taylor Spatial FrameTM (TSF) by comparing clinical healing progress with spatiotemporal fluoride (18F−) uptake and the semiquantitative standardized uptake value (SUV). This procedure included static and dynamic image acquisition. For intrapatient volumes acquired at different times, the CT and PET data were spatially registered to bring the ends of the bones that were supposed to heal into alignment. To qualitatively observe how and where bone formation was occurring, time-sequenced volumes were reconstructed and viewed as a video. To semiquantify the uptake, the mean and maximum SUVs (SUVmean, SUVmax) were calculated for the ends of the bones that were supposed to heal and for normal bone, using a spherical volume of interest drawn on the registered volumes. To make the semiquantitative data comparable for all patients with multiple examinations, the SUVmean and SUVmax difference per day (SUVmeanDPD and SUVmaxDPD) between the first PET/CT scan and each subsequent one was calculated. Indicators of poor healing progress were (1) uneven distribution of the radionuclide uptake between ends of the bones that were supposed to heal as seen in the video or, (2) low absolute magnitude of the SUV difference data. Twenty-four patients treated between October 2013 and April 2015 with a TSF gave informed consent to be examined with 18F− PET/CT bone scans. Twenty-two patients successfully completed treatment, one of whom had only one PET/CT scan.ResultsObservation of 18F− uptake was able to identify three patients whose healing progress was poor, indicated by uneven distribution of radionuclide uptake across the ends of the bones that were supposed to heal. An absolute magnitude of the SUVmaxDPD of 0.18 or greater indicated good bone formation progress. This was verified in 10 patients by the days between the operation to attach and to remove the TSF being less than 250 days, whereas other SUVmaxDPD values were ambiguous, with 11 patients achieving successful completion.ConclusionsObservation of the spatiotemporal uptake of 18F− appears to be a promising method to enable the clinician to assess the progress of bone formation in different parts of the bone. Bone uptake which is uneven across the ends of bone that were supposed to heal or very low bone uptake might indicate impaired bone healing where early intervention may then be needed. However, semiquantification of 18F− uptake (SUVmaxDPD), SUVmeanDPD) was ambiguous in showing consistency with the bone-healing progress.Level of EvidenceLevel III, diagnostic study.

18F-AV1451 PET DETECTS TAU PATHOLOGY IN MAPT MUTATION CARRIERS AND CORRELATES STRONGLY WITH IMMUNOHISTOCHEMISTRY OF TAU AGGREGATES

Background: The Tau PET ligand 18F-AV1451 has been shown to reliably detect paired helical filaments of tau in Alzheimer's disease, but it is not yet known whether it binds to the tau aggregates present in patients with mutations in the gene (MAPT) coding for the tau protein. Further, no study has yet compared the cerebral retention of 18F -AV1451 with the tau aggregates revealed using neuropathology. Methods: Three patients from a Swedish family carrying the R406W mutation of MAPT were assessed with cognitive tests and subjects underwent 18F-AV1451 and 18F-Flutemetamol PET scans. Further one of younger subjects also underwent an 18F-FDG PET scan. The oldest subject died two weeks after the scan and the brain was processed for neuropathology. Tau immunohistochemistry was performed on brain sections from affected and unaffected brain regions. Results: Two mutation carriers, aged 56 and 60 years, had disease durations of 5-10 years and still only exhibited mild-moderate episodic memory impairment and no clear behavioural deficits. The MRI revealed only slight cortical atrophy and 18F-AV1451 PET imaging showed uptake in the hippocampus and the temporal lobes, especially in the inferior and anterior parts (Fig 1A, B). The uptake of 18F - AV1451 correlated well with hypometabolism revealed with FGD PET in one of the subjects. The third case, 76 years, had a disease duration of ≥20 years and exhibited clear cognitive impairment, behavioural disturbances, mutism and dysphagia. The CT scan showed generalised cortical atrophy with a pronounced temporal lobe atrophy and 18F -AV1451 PET imaging revealed uptake in the temporal and frontal lobes, as well as in the basal ganglia (Fig 1 C). The regional uptake of 18F -AV1451 correlated strongly with the tau aggregates revealed using immunohistochemistry (R2 = 0.80, P <0.01; Fig 2). All cases exhibited negative amyloid (18F -flutemetamol) PET scans. Conclusions: The in vivo uptake of 18F-AV1451 reflects the regional amount of tau aggregates revealed by neuropathological examination. Further, tau pathology in MAPT mutation carriers is accurately detected with 18F -AV1451 PET, which consequently can be used to track the effects of anti-tau therapies in this patient group. (Figure Presented) . (Less)

18F–FLUORIDE UPTAKE AS A NOVEL BIOMARKER OF CORONARY PLAQUE RUPTURE

Active calcification occurs within atherosclerotic plaque. Using positron emission (PET) and computed tomography (CT), we investigated coronary uptake of 18F–fluoride (18F–NaF) and 18F–fluorodeoxyglucose (18F–FDG) in patients with stable angina and acute coronary syndrome (ACS). We

Evaluation of a Novel 18 F-Labeled Positron-Emission Tomography Perfusion Tracer for the Assessment of Myocardial Infarct Size in Rats

Background— The goal of this study was to evaluate a new 18 F-labeled positron-emission tomography (PET) perfusion tracer, 18 F BMS747158-02, for the assessment of myocardial infarct (MI) size. Methods and Results— Wistar rats were studied 24 hours after ligation of the left coronary artery either permanently (n=15) or transiently (n=16) for 30 minutes. Seven nonoperated rats were studied as controls. The rats were injected with 37 MBq of 18 F BMS747158-02 and imaged with a small animal PET scanner for 20 minutes. Polar maps were generated for measurement of PET defect size, and left ventricular systolic and diastolic volumes were assessed in gated images. As a reference, MI size was determined by 2,3,5-triphenyltetrazolium chloride staining of left ventricular tissue samples. Permanent or transient ligation of the left coronary artery produced transmural or subendocardial MI of variable sizes, respectively. In normal rats, PET imaging demonstrated intense and homogeneous uptake of 18 F BMS747158-02 throughout the myocardium. After ligation, sharply defined perfusion defects were present. Throughout the imaging period, the defect size correlated closely with the MI size either after permanent ( r =0.88; P &lt;0.01; mean difference, 1.86%) or transient ( r =0.92; P &lt;0.01; mean difference, 2.16%) ligation of the left coronary artery. Moreover, reduction of left ventricular systolic function measured with PET correlated with the MI size ( r =−0.81; P &lt;0.01; n=23). Conclusions— Myocardial 18 F BMS747158-02 PET imaging provides excellent image quality and uptake properties, enabling accurate evaluation of MI size and left ventricular function in rats. It is a promising technique for evaluation of MI size in clinical trials.

18F and 18FDG PET imaging of osteosarcoma to non-invasively monitor in situ changes in cellular proliferation and bone differentiation upon MYC inactivation

Osteosarcoma is one of the most common pediatric cancers. Accurate imaging of osteosarcoma is important for proper clinical staging of the disease and monitoring of the tumor’s response to therapy. The MYC oncogene has been commonly implicated in the pathogenesis of human osteosarcoma. Previously, we have described a conditional transgenic mouse model of MYC-induced osteosarcoma. These tumors are highly invasive and are frequently associated with pulmonary metastases. In our model, upon MYC inactivation osteosarcomas lose their neoplastic properties, undergo proliferative arrest, and differentiate into mature bone. We reasoned that we could use our model system to develop non-invasive imaging modalities to interrogate the consequences of MYC inactivation on tumor cell biology in situ. We performed Positron Emission Tomography (PET) combining the use of both 18F-fluorodeoxyglucose (18FDG) and 18F-flouride (18F) to detect metabolic activity and bone mineralization/remodeling. We found that upon MYC inactivation, tumors exhibited a slight reduction in uptake of 18FDG and a significant increase in the uptake of 18F along with associated histological changes. Thus, these cells have apparently lost their neoplastic properties based upon both examination of their histology and biologic activity. However, these tumors continue to accumulate 18FDG at levels significantly elevated compared to normal bone. Therefore, PET can be used to distinguish normal bone cells from tumors that have undergone differentiation upon oncogene inactivation. In addition, we found that 18F is a highly sensitive tracer for detection of pulmonary metastasis. Collectively, we conclude that combined modality PET/CT imaging incorporating both 18FDG and 18F is a highly sensitive means to non-invasively measure osteosarcoma growth and the therapeutic response, as well as to detect tumor cells that have undergone differentiation upon oncogene inactivation

PET as a Diagnositic Tool in Unilateral Condylar Hyperactivity

PET as a Diagnositic Tool in Unilateral Condylar Hyperactivity

Skeletal metastases from breast cancer: uptake of 18F-fluoride measured with positron emission tomography in correlation with CT.

To characterise the uptake of 18F in skeletal metastases from breast cancer using positron emission tomography (PET) and to relate these findings to the appearance on CT. PET with 18F and CT were performed in five patients with multiple skeletal metastases from breast cancer. The CT characteristics were analysed in areas with high uptake on the PET study. Dynamic PET imaging of the skeletal kinetics of the 18F-fluoride ion were included. The areas of abnormal high accumulation of 18F correlated well with the pathological appearance on CT. Lytic as well as sclerotic lesions had markedly higher uptake than normal bone, with a 5-10 times higher transport rate constant for trapping of the tracer in the metastatic lesions than in normal bone. PET with 18F-fluoride demonstrates very high uptake in lytic and sclerotic breast cancer metastases.

Affinities of dopamine analogs for monoamine granular and plasma membrane transporters: Implications for PET dopamine studies

Affinities of dopamine (DA) analogs to both granular and plasma membrane uptake transporters were measured in vitro by inhibition of [ 3H]DA uptake in bovine chromaffin granule ghosts and C6 glial cells transfected with cDNA for the rat presynaptic dopamine transporter, respectively. Five amines were studied: DA, 6-fluorodopamine (6FDA), m-tyramine (MTA), 6-fluoro-m-tyramine (6FMTA), and β-fluoromethylene-m-tyramine (FMMTA). Direct uptake of 18F labeled 6FDA and 6FMTA was also measured in the chromaffin granule system and compared with [ 3H]DA uptake. Results show that the transporter affinities of 6FDA and MTA were similar to that of DA in both transport systems while affinities of 6FMTA and FMMTA were lower. Furthermore while the direct uptake of DA and FDA in chromaffin granules were essentially identical and significantly reserpine-inhibitable, the direct uptake of 6FMTA was about 15-fold less and only minimally sensitive to reserpine pretreatment. Thus, although vesicular protection and reuptake may influence the turnover of FDA in 6-fluoroDOPA studies, they are unlikely to be important determinants of the kinetics of the slowly clearing components in studies with either 6-fluoro-m-tyrosine (6FMT) or 6-fluoro-β- fluoro-methylene-m-tyrosine (6FFMMT), the bioprecursors of 6FMTA and 6-fluoro-FMMTA, respectively. These results are consistent with the finding that the longterm component in 6FMT PET studies is 6-fluoro-hydroxyphenylacetic acid (6FHPAC), which can be explained by the lack of vesicular protection of 6FMTA from MAO oxidation.

Positron emission tomographic imaging of cardiac sympathetic innervation and function.

Sites of uptake, storage, and metabolism of [18F]fluorodopamine and excretion of [18F]fluorodopamine and its metabolites were visualized using positron emission tomographic (PET) scanning after intravenous injection of the tracer into anesthetized dogs. Radioactivity was concentrated in the renal pelvis, heart, liver, spleen, salivary glands, and gall bladder. Uptake of 18F by the heart resulted in striking delineation of the left ventricular myocardium. Pretreatment with desipramine markedly decreased cardiac positron emission, consistent with dependence of the heart on neuronal uptake (uptake-1) for removal of circulating catecholamines. In reserpinized animals, cardiac positron emission was absent within 30 minutes after injection of [18F]-6-fluorodopamine, demonstrating that the emission in untreated animals was from radioactive labeling of the sympathetic storage vesicles. Decreased positron emission from denervated salivary glands confirmed that the tracer was concentrated in sympathetic neurons. Radioactivity in the gall bladder and urinary system depicted the hepatic and renal excretion of the tracer and its metabolites. Administration of tyramine or nitroprusside increased and ganglionic blockade with trimethaphan decreased the rate of loss of myocardial radioactivity. The results show that PET scanning after administration of [18F]fluorodopamine can be used to visualize sites of sympathetic innervation, follow the metabolism and renal and hepatic excretion of catecholamines, and examine cardiac sympathetic function.

Enhanced glucose metabolism and impaired placental function in hypoxic pregnant rats

Glucose metabolism using 2-deoxy-2-[18F]fluoro-D-glucose [( 18F]FDG) was studied in experimental hypoxia (10% oxygen concentration) of pregnant rats with special attention given to the placental function. After an i.v. injection of [18F]FDG, the uptake of 18F increased with time in the maternal brain, placenta and fetus of control rats. In the hypoxic condition, the uptake in these tissues was enhanced significantly, especially in the maternal brain and fetal heart, brain and lungs. A double-label autoradiography with [18]FDG and [14C]iodoantipyrine [( 14C]IAP) was performed to elucidate changes of the placental function in the hypoxic condition. The [18F]FDG image revealed a higher accumulation in the maternal side of the placenta of a control pregnant rat than in its fetal side. [18F]FDG uptake increased in the fetal brain and heart of hypoxic rats. The [14C]IAP image demonstrated that in the control rat there was a clear border zone on the maternal side of the placenta with very low permeability into the fetus. On the other hand, a high and heterogenous accumulation in both placenta and fetal organs was shown in hypoxic rats. We interpret this data to suggest that in a hypoxic condition the function of the placenta as a barrier system is impaired.

Synthesis and some characteristics of no-carrier added [ 18F]fluorotrimethylsilane

[ 18F]Fluorotrimethylsilane was prepared in 80% decay corrected yield by reaction of no-carrier added tetremethyl-ammonium fluoride (hydroxide as bulk anion) with chlorotrimethylsilane in 65% aqueous acetonitrile. The 18F gas was collected in a cold-trap at −130°C and found to have an Ostwald solubility coefficient of 11.5 in paraffin oil. Accurate measurement of its aqueous solubility was precluded by hydrolysis. When rats were allowed to inhale [ 18F]fluorotrimethysilane extensive uptake of 18F occurred in bone, demonstrating ready release of fluoride in vivo.

In-vitro study of the cellular control of 18F uptake in the enamel of developing rat molar teeth

Molar expiants from 6-day-old rats were cultured for 4 h in medium containing approx. 2μCi/ml 18F. Control-cultured expiants were compared to their contralateral pairs which had been subjected to: (1) the enamel organ removed prior to incubation; (2) the expiants heat-treated (65 °C for 10 min); or (3) a metabolic inhibitor, 5mM dinitrophenol (DNP), added to the medium. The Ca concentration of the medium indicated that the expiants became mineralized during incubation. Both removal of enamel organ and heat-treatment enhanced uptake of 18F from the medium. DNP had no consistent effect. As the pattern of 18F uptake was similar to that for net Ca uptake by mineralizing enamel, the findings suggest that there is no direct cellular control of F − flux through the enamel organ during the secretory phase of enamel formation.

Limitations of radioactive microspheres as tracers for bone blood flow and extraction ratio studies.

Radioactive microspheres have been used for measuring bone blood flow and the extraction ratios of bone-seeking radionuclides, but we have shown that the technique is not completely valid. Bone uptake of 18F and 85Sr was compared with that of microspheres simultaneously injected into the heart or aorta of rats and rabbits under a variety of conditions. In single-passage experiments with quick killing to avoid recirculation, attention was focused on the tibiae and femora which could be dissected quickly to avoid post-mortem migration. For the rest of the skeleton, the effect of the latter was minimized by allowing recirculation for 5 min and comparing blood flow determinations in conjunction wit a cardiac output measurement. The apparent extraction ratio of 18F was variable and always exceeded unity in the single-passage experiments. With recirculation, there were significant differences between the extraction ratios for some bones, and the ratios sometimes exceeded unity. Extraction ratios for 85Sr were similarly variable, but lower. When 85Sr was compared directly with 18F, the relative extraction ratio was 0.8, with little variation between bones or animals. It is concluded that the flux of microspheres entering the vasculature of bone is not representative of blood flow, owing to the removal of some microspheres in pre-osseous capillary beds. Microspheres are therefore not a satisfactory standard for the determination of extraction ratios.

18F-5-fluorouracil studies in humans and animals

Studies in animals showing that 18F from 18F-5-fluorouracil ( 18F-FU) concentrated in various transplanted tumors suggested to us that 18F-FU might be a useful tumor scanning agent in patients with cancer. We synthesized 18F-FU from radioactive fluorine gas produced on the University of Wisconsin Tandem Van de Graaf accelerator and studied 16 patients with a variety of malignant tumors. Patients were given 1.4–4.0 mCi of 18F-FU intravenously and studied with a rectilinear scanner two hours later. In two of seven patients with gastrointestinal cancer there was positive uptake of 18F in tumor locations. Two patients with head and neck cancer had positive scans. Seven other patients with non-gastrointestinal cancers were studied; in two 18F concentrated at the tumor site. We have shown that in 16 patients with cancer, sufficient uptake of 18F occurred in six to provide a positive rectilinear scan. These results suggest that 18F-FU might be a useful tumor scanning agent. Further investigation is necessary to confirm that positive scans represent increased concentrations of 18F in tumor tissue.

Post-mortem migration of bone-seeking radionuclides in the rat and rabbit and its effect on estimates of bone uptake.

1. The continued uptake of 18F, 85Sr and 47Ca by bone after death has been studied in rats and rabbits after aortic injection followed by quick killing, a period of recirculation of tracer before death, and perfusion of the carcase. In each case an approximately linear increase of bone radioactivity was observed during a period of 1 h at about the same rate. The proportionate increase depended on the initial concentration of bone-seeking nuclide, ranging from a factor of 1.5 to 4.5. Boiling the carcase did not increase the migration rate. 2. Delay between death and dissection may therefore lead to spuriously high bone concentrations of these radionuclides, leading to over-estimates of bone uptake, extraction ratio or bone blood flow.

The effect of artificially produced pellicle and plaque on the uptake of 18F by human enamel in vitro

The presence of artificial pellicle and plaque alters the mechanism of uptake of 18F by enamel from an acidulated phosphate fluoride solution (APF) labelled with 18F but has no apparent effect on the mechanism of uptake of the isotope from a labelled solution of NaF with a similar fluoride content (1.2 per cent). The presence of artificial plaque has no significant effect on the quantitative uptake of 18F by enamel from labelled solutions of either APF or NaF in 4 min. Results from a similar experiment using plaque formed in vivo support these findings.