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Aim: To study the clinical yield of diagnostic whole body 131 I scintigraphy (DxWBS) in the follow-up of differentiated thyroid carcinoma (DTC) patients in relation to stimulated thyroglobulin (sTg) in the initial post-ablation setting, as well as in the setting of repeated monitoring in course of further DTC follow-up., Methods: Data of 1420 thyroidectomized and radioiodine remnant-ablated DTC patients following a well-defined therapy and standardized follow-up protocol were evaluated. DxWBS and sTg were evaluated separately and in combination for various follow-up time points. The factual administration of the recorded indication for further oncologic therapy (excluding radioiodine therapies given for minimal normal remnants) within the following 4 months after follow-up served as the standard of reference. Furthermore, DxWBS was compared to post therapy WBS and SPECT(/CT) if available. Subgroup analysis was carried out for DTC patients < 45 years old at diagnosis without distant metastasis. The diagnostic impact of cervical ultrasound was not assessed., Results: sTg can identify the patients at risk better than DxWBS. Furthermore, the most sensitive time point to assess response appears to be a time point beyond 3 months after RRA. When information received from both imaging and laboratory measurements are concordant, i.e. both construe absence of remaining disease, only a small fraction of patients (<2%) required treatment in the future. The strongest effect was observed 12 months after RRA. Only 0.9% of the negative DxWBS patients with concordant sTg below the functional sensitivity at this time point required treatment thereafter., Conclusion: A complete omission of DxWBS in the post-RRA surveillance of DTC is justified once DxWBS is negative and sTg is below the functional sensitivity (with no evidence of thyroglobulin antibodies), as patients showing this combination of test results (especially 12 months after RRA) show an at worst marginal risk of recurrence. In all other cases DxWBS may still be justified.

Purpose: Coronary artery calcium scoring can complement myocardial perfusion imaging (MPI). The purpose of this study was to evaluate the feasibility and accuracy of using the CalciumScore-CT derived from a combined SPECT/CT device also for SPECT attenuation correction (AC)., Methods: The study group comprised 99 patients who underwent both post-stress and rest MPI using a two-slice SPECT/CT system. For AC, one of the two scans was accompanied by a CalciumScore-CT scan (CalciumScore-CTAC) and the other by a conventional spiral CT (AttenCorr-CT) scan (AttenCorr-CTAC). In 48 patients the CalciumScore-CT scan was acquired with the post-stress scan and the AttenCorr-CT scan with the rest scan, and in 51 patients the order was reversed. The accuracy of the images based on AC was determined qualitatively by consensus reading with respect to the clinical diagnoses as well as quantitatively by comparing the perfusion summed stress scores (SSS) and the summed rest scores (SRS) between attenuation-corrected and uncorrected images., Results: In comparison to the uncorrected images CalciumScore-CTAC led to regional inaccuracies in 14 of 51 of studies (27.5%) versus 12 of 48 studies (25%) with AttenCorr-CTAC for the stress studies and in 5 of 48 (10%) versus 1 of 51 (2%) for the rest studies, respectively. This led to intermediate and definite changes in the final diagnosis (ischaemia and/or scarring) in 12% of the studies (12 of 99) and in 7% of the studies (7 of 99) with CalciumScore-CTAC and in 9% of the studies (9 of 99) and 4% of the studies (4 of 99) with AttenCorr-CTAC. Differences in SSS and SRS with respect to the uncorrected images were greater for the CalciumScore-CTAC images than for the AttenCorr-CTAC images (ΔSSS 4.5 ± 5.6 and 2.1 ± 4.4, p = 0.023; ΔSRS 4.2 ± 4.9 and 1.6 ± 3.2, p = 0.004, respectively)., Conclusion: Using the same CT scan for calcium scoring and SPECT AC is feasible. Image interpretation must, however, include uncorrected images since CT-based AC relatively often introduces artefacts into the myocardial perfusion images. This effect is somewhat more pronounced with CalciumScore-CTAC than with AttenCorr-CTAC.

Purpose: Respiratory gating is an established approach to overcoming respiration-induced image artefacts in PET. Of special interest in this respect are raw PET data-driven gating methods which do not require additional hardware to acquire respiratory signals during the scan. However, these methods rely heavily on the quality of the acquired PET data (statistical properties, data contrast, etc.). We therefore combined external radioactive markers with data-driven respiratory gating in PET/CT. The feasibility and accuracy of this approach was studied for [(18)F]FDG PET/CT imaging in patients with malignant liver and lung lesions., Methods: PET data from 30 patients with abdominal or thoracic [(18)F]FDG-positive lesions (primary tumours or metastases) were included in this prospective study. The patients underwent a 10-min list-mode PET scan with a single bed position following a standard clinical whole-body [(18)F]FDG PET/CT scan. During this scan, one to three radioactive point sources (either (22)Na or (18)F, 50-100 kBq) in a dedicated holder were attached the patient's abdomen. The list mode data acquired were retrospectively analysed for respiratory signals using established data-driven gating approaches and additionally by tracking the motion of the point sources in sinogram space. Gated reconstructions were examined qualitatively, in terms of the amount of respiratory displacement and in respect of changes in local image intensity in the gated images., Results: The presence of the external markers did not affect whole-body PET/CT image quality. Tracking of the markers led to characteristic respiratory curves in all patients. Applying these curves for gated reconstructions resulted in images in which motion was well resolved. Quantitatively, the performance of the external marker-based approach was similar to that of the best intrinsic data-driven methods. Overall, the gain in measured tumour uptake from the nongated to the gated images indicating successful removal of respiratory motion was correlated with the magnitude of the respiratory displacement of the respective tumour lesion, but not with lesion size., Conclusion: Respiratory information can be assessed from list-mode PET/CT through PET data-derived tracking of external radioactive markers. This information can be successfully applied to respiratory gating to reduce motion-related image blurring. In contrast to other previously described PET data-driven approaches, the external marker approach is independent of tumour uptake and thereby applicable even in patients with poor uptake and small tumours.

Purpose: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a nonischaemic cardiomyopathy and leading cause of sudden death in the young. It has been shown that microvascular dysfunction reflected by an impaired myocardial blood flow (MBF) response to stress is present in patients with other forms of nonischaemic cardiomyopathy, e.g. dilated cardiomyopathy, and that the reduced MBF may be related to a poor prognosis. Therefore, we quantified MBF, coronary flow reserve and coronary vascular resistance in patients with nonfailing ARVC using H(2)(15)O and PET., Methods: In ten male patients with ARVC (mean age 49 ± 14 years), MBF was quantified at rest and during adenosine-induced hyperaemia using H(2)(15)O PET. Results were compared with those obtained in 20 age-matched healthy male control subjects (mean age 46 ± 14 years)., Results: Resting MBF was not significantly different between patients with ARVC and controls (MBF(rest) 1.19 ± 0.29 vs. 1.12 ± 0.20 ml/min/ml). However, hyperaemic MBF was significantly lower in patients with ARVC than in controls (2.60 ± 0.96 vs. 3.68 ± 0.84 ml/min/ml; p = 0.005). Consequently, patients with ARVC had a significantly lower coronary flow reserve than control subjects (2.41 ± 1.34 vs. 3.39 ± 0.93; p = 0.030). In addition, hyperaemic coronary vascular resistance was increased in patients with ARVC (36.79 ± 12.91 vs. 26.31 ± 6.49 mmHg × ml(-1) × min × ml; p = 0.007), but was found to be unchanged at rest., Conclusion: In this small well-characterized cohort of patients with nonfailing ARVC, we found a significantly reduced hyperaemic MBF and increased coronary vascular resistance. Further studies are necessary to corroborate this potential new functional aspect of the pathophysiological mechanisms underlying ARVC.

Purpose: Increased sympathetic activation is a key modifier for arrhythmogenesis in patients with long QT syndrome (LQTS), a congenital channelopathy. Therefore, we investigated cardiac sympathetic function using 123I-metaiodobenzylguanidine (MIBG) single photon emission computed tomography (SPECT) in a cohort of symptomatic LQTS patients and correlated these findings with the underlying genotype., Methods: [123I]MIBG SPECT was performed in 28 LQTS patients. Among these, 18 patients (64%) had a previous syncope and 10 patients (36%) survived sudden cardiac arrest. Patients were characterized in terms of genetic subtypes and QTc interval on surface ECGs. SPECT images were analysed for regional [123I]MIBG uptake in a 33-segment bullseye scheme and compared to those obtained from 10 age-matched healthy control subjects (43±12 years)., Results: An abnormal 123I-MIBG scan was found in 17 of 28 LQTS patients (61%) with a tracer reduction mainly located in the anteroseptal segments of the left ventricle. This finding was independent of the genetic LQTS subtype. In addition, no differences were found between LQTS patients with a QTc>500 ms vs <500 ms or those suffering from syncope vs VF (p>0.05)., Conclusion: A distinct regional pattern of impaired cardiac sympathetic function was identified in the majority of symptomatic LQTS patients. This innervation defect was independent of the underlying genotype and clinical disease expression.

Purpose: Respiratory motion of organs during PET scans is known to degrade PET image quality, potentially resulting in blurred images, attenuation artefacts and erroneous tracer quantification. List mode-based gating has been shown to reduce these pitfalls in cardiac PET. This study evaluates these intrinsic gating methods for tumour PET scans., Methods: A total of 34 patients with liver or lung tumours (14 liver tumours and 27 lung tumours in all) underwent a 15-min single-bed list mode PET scan of the tumour region. Of these, 15 patients (8 liver and 11 lung tumours in total) were monitored by a video camera registering a marker on the patient's abdomen, thus capturing the respiratory motion for PET gating (video method). Further gating information was deduced by dividing the list mode stream into 200-ms frames, determining the number of coincidences (sensitivity method) and computing the axial centre of mass of the measured count rates in the same frames (centre of mass method). Additionally, these list mode-based methods were evaluated using only coincidences originating from the tumour region by segmenting the tumour in sinogram space (segmented sensitivity/centre of mass method). Measured displacement of the tumours between end-expiration and end-inspiration and the increase in apparent uptake in the gated images served as a measure for the exactness of gating. To estimate the accuracy, a thorax phantom study with moved activity sources simulating small tumours was also performed., Results: All methods resolved the respiratory motion with varying success. The best results were seen in the segmented centre of mass method, on average leading to larger displacements and uptake values than the other methods. The simple centre of mass method performed worse in terms of displacements due to activities moving into the field of view during the respiratory cycle. Both sensitivity- and video-based methods lead to similar results., Conclusion: List mode-driven PET gating, especially the segmented centre of mass method, is feasible and accurate in PET scans of liver and lung tumours.

Purpose: Inflamed atherosclerotic plaques may rupture and cause acute myocardial infarction, stroke and other thrombotic events. Early detection of these unstable plaques could, in many cases, prevent such potentially fatal events. 11C-choline or 18F-labelled choline derivatives for visualizing the synthesis of phospholipids, are promising markers of plaque inflammation with potential advantages over 18F-FDG. Their potential for plaque characterization in humans is, however, unclear. In this study the prevalence and distribution of 11C-choline uptake in the aortic and common carotid arterial walls of elderly male patients was evaluated with combined PET/CT. Additionally, the localization of radiotracer uptake and calcification was correlated in various vessel segments., Methods: Image data from 93 consecutive male patients between 60 and 80 years old who had undergone whole-body 11C-choline PET/CT assessment for prostate cancer were evaluated retrospectively. 11C-choline uptake and calcification were analysed qualitatively and semiquantitatively and compared., Results: 11C-choline uptake was found in 95% of patients, calcification in 94% throughout all vessel segments. In 6% of the patients radiotracer uptake was colocalized with calcifications, whereas less than 1% of calcification sites showed increased radiotracer uptake., Conclusion: Both 11C-choline uptake and calcification in the aortic and common carotid arterial walls are common in elderly men. Radiotracer uptake and calcification are, however, only rarely colocalized. 11C-choline has the potential to provide information about atherosclerotic plaques independent of calcification measurement.

This highlight lecture was presented at the closing session of the Annual Congress of the European Association of Nuclear Medicine (EANM) in Munich on 15 October 2008. The Congress was a great success: there were more than 4,000 participants, and 1,597 abstracts were submitted. Of these, 1,387 were accepted for oral or poster presentation, with a rejection rate of 14%. In this article a choice was made from 100 of the 500 lectures which received the highest scores by the scientific review panel. This article outlines the major findings and trends at the EANM 2008, and is only a brief summary of the large number of outstanding abstracts presented. Among the great number of oral and poster presentations covering nearly all fields of nuclear medicine some headlines have to be defined highlighting the development of nuclear medicine in the 21st century. This review focuses on the increasing impact of molecular and multimodality imaging in the field of nuclear medicine. In addition, the question may be asked as to whether the whole spectrum of nuclear medicine is nothing other than molecular imaging and therapy. Furthermore, molecular imaging will and has to go ahead to multimodality imaging. In view of this background the review was structured according to the single steps of molecular imaging, i.e. from target description to clinical studies. The following topics are addressed: targets, radiochemistry and radiopharmacy, devices and computer science, animals and preclinical evaluations, and patients and clinical evaluations.

Purpose: Renal function can be quantified by both laboratory and scintigraphic methods. In the case of small animal diagnostics, scintigraphic image-based methods are ideal since they can assess split renal function, work noninvasively, and can be repeated. The aim of this study is to validate a (18)F-PET-based method to quantify renal function in rats., Materials and Methods: Fluoride clearance was calculated from a dynamic whole body listmode acquisition of 60 min length in a small animal PET scanner following an i.v. injection of 15 MBq (18)F-fluoride. Volumes of interest (VOIs) were placed in the left ventricle and the bladder as well as traced around the kidney contours. The respective time-activity curves (TAC) were calculated. The renal (18)F-clearance was calculated by the ratio of the total renal excreted activity (bladder VOI) and the integral of the blood TAC. PET-derived renal function was validated by intraindividual measurements of creatinine clearance (n = 23), urea clearance (n = 23), and tubular excretion rate (TER-MAG3). The split renal function was derived from the injection of the clinically available radionuclide (99m)Tc-mercaptotriglycine by blood sampling and planar renography (n = 8)., Results: In all animals studied, PET revealed high-quality TACs. PET-derived renal fluoride clearance was linearly correlated with intraindividual laboratory measures (PET vs. creatinine: r = 0.78; PET vs. urea: r = 0.73; PET vs. TER-MAG3: r = 0.73). Split function was comparable ((18)F-PET vs. MAG3-renography: r = 0.98). PET-derived measures were highly reproducible., Conclusions: (18)F-PET is able to noninvasively assess renal function in rats and provides a significant potential for serial studies in different experimental scenarios.

Purpose: This prospective single-centre phase II trial assessed the diagnostic impact of (18)F-FDG PET-CT in the evaluation of solid pancreatic lesions (phi >or= 10 mm) compared to endosonography (EUS), endoscopic retrograde cholangio-pancreatography (ERCP) with intraductal ultrasound (IDUS), abdominal ultrasound (US) and histopathological reference., Methods: Forty-six patients (32 men/14 women, phi 61.7 years) with suspected pancreatic neoplasms underwent PET-CT with contrast-enhanced biphasic multi-detector CT of the upper abdomen followed by a diagnostic work-up with EUS, ERCP with IDUS and US within 3 weeks. PET-CT data sets were analysed by two expert readers in a consensus reading. Histology from surgery, biopsy/fine-needle aspiration and/or clinical follow-up >or=12 months served as standard of reference., Results: Twenty-seven pancreatic malignancies were histopathologically proven; 19 patients had benign diseases: 36/46 lesions (78%) were detected in the head of the pancreas, 7/46 and 3/46 in the body and tail region, respectively. Sensitivity and specificity of PET-CT were 89% and 74%, respectively; positive predictive value (PPV) and negative predictive value (NPV) were 83% and 82%, respectively. Sensitivity (81-89%), specificity (74-88%), PPV (83-90%) and NPV (77-82%) achieved by EUS, ERCP and US were not significantly different. PET analysis revealed significantly higher maximum mean standardised uptake values (SUV(max) 6.5+/-4.6) in patients with pancreatic malignancy (benign lesions: SUV(max) 4.2+/-1.5; p<0.05). PET-CT revealed cervical lymphonodal metastasis from occult bronchogenic carcinoma and a tubular colon adenoma with intermediate dysplasia on polypectomy, respectively., Conclusions: (18)F-FDG PET-CT achieves a comparably high diagnostic impact evaluating small solid pancreatic lesions versus conventional reference imaging modalities. Additional clinical diagnoses are derived from concomitant whole-body PET-CT imaging.

Introduction: The introduction of hybrid imaging modalities such as combined positron emission tomography and computed tomography (PET-CT) has altered image analysis and reporting as well as the expectations of the referring physicians. The training in multimodality imaging is unsatisfactory at the moment because no specialisation is adequate for full analysis of the resulting image data. In the recent "White paper of the European Association of Nuclear Medicine (EANM) and the European Society of Radiology (ESR) on multimodality imaging", ways to adjust training opportunities and, thus, to improve the situation were proposed. We think that action is urgently required in order to provide optimal training in multimodality imaging., Opinion: Training in both nuclear medicine and diagnostic radiology should be restructured to allow for optional integrated training in multimodality imaging while maintaining the depth and detail of the individual specialties., Suggested Action: We propose criteria for the training in multimodality imaging that can be implemented locally and fast without precluding a yet to be defined regulatory framework.

Purpose: Radioligand binding studies show that beta(1)-adrenoceptor (beta(1)-AR) density may be reduced in heart disease without down regulation of beta(2)-ARs. Radioligands are available for measuring total beta-AR density non-invasively with clinical positron emission tomography (PET) but none are selective for beta(1)- or beta(2)-ARs. The aim was to evaluate ICI 89,406, a beta(1)-AR-selective antagonist amenable to labelling with positron emitters, for PET., Methods: The S-enantiomer of an [O-methyl-(11)C] derivative of ICI 89,406 ((S)-[(11)C]ICI-OMe) was synthesised. Tissue radioactivity after i.v. injection of (S)-[(11)C]ICI-OMe (< 2 nmol x kg(-1)) into adult Wistar rats was assessed by small animal PET and post mortem dissection. Metabolism was assessed by HPLC of extracts prepared from plasma and tissues and by measuring [(11)C]CO(2) in exhaled air., Results: The heart was visualised by PET after injection of (S)-[(11)C]ICI-OMe but neither unlabelled (S)-ICI-OMe nor propranolol (non-selective beta-AR antagonist) injected 15 min after (S)-[(11)C]ICI-OMe affected myocardial radioactivity. Ex vivo dissection showed that injecting unlabelled (S)-ICI-OMe, propranolol or CGP 20712A (beta(1)-selective AR antagonist) at high dose (> 2 mumol x kg(-1)) before (S)-[(11)C]ICI-OMe had a small effect on myocardial radioactivity. HPLC demonstrated that radioactivity in myocardium was due to unmetabolised (S)-[(11)C]ICI-OMe although (11)C-labelled metabolites rapidly appeared in plasma and liver and [(11)C]CO(2) was detected in exhaled air., Conclusion: Myocardial uptake of (S)-[(11)C]ICI-OMe after i.v. injection was low, possibly due to rapid metabolism in other tissues. Injection of unlabelled ligand or beta-AR antagonists had little effect indicating that binding was mainly to non-specific myocardial sites, thus precluding the use of (S)-[(11)C]ICI-OMe to assess beta(1)-ARs with PET.

Purpose: The segmentation algorithm ESM based on an elastic surface model was validated for the assessment of left ventricular volumes and ejection fraction from ECG-gated myocardial perfusion SPECT. Additionally, it was compared with the commercially available quantification packages 4D-MSPECT and QGS. Cardiac MRI was used as the reference method., Methods: SPECT and MRI were performed on 70 consecutive patients with suspected or proven coronary artery disease. End-diastolic (EDV) and end-systolic (ESV) volumes and left ventricular ejection fraction (LVEF) were derived from SPECT studies by using the segmentation algorithms ESM, 4D-MSPECT and QGS and from cardiac MRI., Results: ESM-derived values for EDV and ESV correlated well with those from cardiac MRI (correlation coefficients R=0.90 and R=0.95, respectively), as did the measurements for LVEF (R=0.86). Both EDV and ESV were slightly overestimated for larger ventricles but not for smaller ventricles; LVEF was slightly overestimated irrespective of ventricle size. The above correlation coefficients are comparable to those for the 4D-MSPECT and QGS segmentation algorithms. However, results obtained with the three segmentation algorithms are not interchangeable., Conclusion: The ESM algorithm can be used to assess EDV, ESV and LVEF from gated perfusion SPECT images. Overall, the performance was similar to that of 4D-MSPECT and QGS when compared with cardiac MRI. Results obtained with the three tested segmentation methods are not interchangeable, so that the same algorithm should be used for follow-up studies and control subjects.

Purpose: As primary osseous metastasis is the main adverse prognostic factor in patients with Ewing tumours, a NOD/scid mouse model for human Ewing tumour metastases has been established to examine the mechanisms of metastasis. The aim of this study was to evaluate the feasibility of diagnostic molecular imaging by small animal PET in this mouse model., Methods: Human Ewing tumour cells were transplanted into immune-deficient NOD/scid mice via s.c injection (n=17) or i.v. injection (n=17). The animals (mean weight 23.2 g) were studied 2-7 weeks after transplantation using a submillimetre resolution animal PET scanner. To assess glucose utilisation and bone metabolism, mice were scanned after intravenous injection of 9.6 MBq (mean) 2-[(18)F]fluoro-2-deoxy-D: -glucose (FDG) or 9.4 MBq (mean) [(18)F]fluoride. Whole-body PET images were analysed visually and semi-quantitatively [%ID/g, tumour to non-tumour ratio (T/NT)]. Foci of pathological uptake were identified with respect to the physiological organ uptake in corresponding regions., Results: Subcutaneously transplanted Ewing tumours demonstrated a moderately increased glucose uptake (median %ID/g 2.5; median T/NT 2.2). After i.v. transplantation, the pattern of metastasis was similar to that in patients with metastases in lung, bone and soft tissue. These metastases showed an increased FDG uptake (median %ID/g 3.6; median T/NT 2.7). Osseous metastases were additionally visible on [(18)F]fluoride PET by virtue of decreased [(18)F]fluoride uptake (osteolysis; median %ID/g 8.4; median T/NT 0.59). Metastases were confirmed immunohistologically., Conclusion: Diagnostic molecular imaging of Ewing tumours and their small metastases in an in vivo NOD/scid mouse model is feasible using a submillimetre resolution PET scanner.

Purpose: Idiopathic ventricular fibrillation (IVF) is defined as VF in the absence of any identifiable structural or functional cardiac disease. The underlying pathophysiological mechanisms are unknown. This study was performed to investigate the potential impact of sympathetic dysfunction, assessed by (123)I-meta-iodo-benzylguanidine scintigraphy ((123)I-MIBG SPECT), on the long-term prognosis of patients with IVF., Methods: (123)I-MIBG SPECT was performed in 20 patients (mean age 37+/-13 years) with IVF. Mean follow-up of patients after study entry was 7.2+/-1.5 years (range 4.9-10.5 years). Ten patients (five men, five women; mean age 43+/-12 years; p=NS versus study group) with medullary carcinoma of the thyroid gland served as an age-matched control group., Results: Abnormal (123)I-MIBG uptake was observed in 13 patients (65%). During follow-up, 18 episodes of VF/fast polymorphic ventricular tachycardias occurred in four IVF patients with abnormal (123)I-MIBG uptake whereas only two episodes of monomorphic ventricular tachycardia (and no VF) occurred in a single IVF patient with normal (123)I-MIBG uptake., Conclusion: Impairment of sympathetic innervation may indicate a higher risk of future recurrent episodes of life-threatening ventricular tachyarrhythmias in patients with IVF. Studies in larger cohorts are required to validate the significance of (123)I-MIBG SPECT during the long-term follow-up of these patients.

Purpose: The aim of this study was to evaluate the differential uptake of O-(2-[18F]fluorethyl)-L-tyrosine (FET) in suspected primary brain tumours., Methods: Positron emission tomography (PET) was performed in 44 patients referred for the evaluation of a suspected brain tumour. Acquisition consisted of four 10-min frames starting upon i.v. injection of FET. Tumour uptake was calculated as the ratio of maximal tumour intensity to mean activity within a reference region (FETmax)., Results: FET uptake above the cortical level was observed in 35/44 lesions. All histologically confirmed gliomas and many other lesions showed FET uptake to a variable extent. No uptake was observed in nine lesions (one inflammatory lesion, one dysembryoplastic neuroepithelial tumour, one mature teratoma, six lesions without histological confirmation). An analysis of uptake dynamics was done in the patients with increased FET uptake (22 gliomas, three lymphomas, three non-neoplastic lesions, three lesions with unknown histology and four other primaries). Upon classification of tumours into low (i.e. WHO I and II) and high grade (i.e. WHO III and IV), a significant difference in FETmax between the two categories was observed only in the first image frame (0-10 min p.i.), with FETmax=2.0 in low-grade and 3.2 in high-grade tumours (p<0.05); no significant differences were found in frame 4 (30-40 min p.i.), with FETmax=2.4 vs 2.7. Similar results were obtained when the analysis was applied only to astrocytic tumours (2.0 vs 3.1 in the first frame; 2.4 vs 2.6 in the fourth frame)., Conclusion: These initial results indicate that FET PET is a useful method to identify malignant brain lesions. It appears that high- and low-grade brain tumours exhibit a different uptake kinetics of FET. A kinetic analysis of FET PET may provide additional information in the differentiation of suspected brain lesions.