Hybrid MR-PET of brain tumours using amino acid PET and chemical exchange saturation transfer MRI.

PURPOSE: PET using radiolabelled amino acids has become a promising tool in the diagnostics of gliomas and brain metastasis. Current research is focused on the evaluation of amide proton transfer (APT) chemical exchange saturation transfer (CEST) MR imaging for brain tumour imaging. In this hybrid MR-PET study, brain tumours were compared using 3D data derived from APT-CEST MRI and amino acid PET using O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET). METHODS: Eight patients with gliomas were investigated simultaneously with 18F-FET PET and APT-CEST MRI using a 3-T MR-BrainPET scanner. CEST imaging was based on a steady-state approach using a B1 average power of 1µT. B0 field inhomogeneities were corrected a Prametric images of magnetisation transfer ratio asymmetry (MTRasym) and differences to the extrapolated semi-solid magnetisation transfer reference method, APT# and nuclear Overhauser effect (NOE#), were calculated. Statistical analysis of the tumour-to-brain ratio of the CEST data was performed against PET data using the non-parametric Wilcoxon test. RESULTS: A tumour-to-brain ratio derived from APT# and 18F-FET presented no significant differences, and no correlation was found between APT# and 18F-FET PET data. The distance between local hot spot APT# and 18F-FET were different (average 20 ± 13 mm, range 4-45 mm). CONCLUSION: For the first time, CEST images were compared with 18F-FET in a simultaneous MR-PET measurement. Imaging findings derived from18F-FET PET and APT CEST MRI seem to provide different biological information. The validation of these imaging findings by histological confirmation is necessary, ideally using stereotactic biopsy.

Methods for molecular imaging of brain tumours in a hybrid MR-PET context: Water content, T2∗, diffusion indices and FET-PET.

The aim of this study is to present and evaluate a multiparametric and multi-modality imaging protocol applied to brain tumours and investigate correlations between these different imaging measures. In particular, we describe a method for rapid, non-invasive, quantitative imaging of water content of brain tissue, based on a single multiple-echo gradient-echo (mGRE) acquisition. We include in the processing a method for noise reduction of the multi-contrast data based on Principal Component Analysis (PCA). Noise reduction is a key ingredient to obtaining high-precision water content and transverse relaxation T2∗ values. The quantitative method is applied to brain tumour patients in a hybrid MR-PET environment. Active tumour tissue is identified by means of FET-PET; oedema, white and grey-matter segmentation is performed based on MRI contrasts. Water content information is not only relevant by itself, but also as a basis for correlations with other quantitative measures of water behaviour in tissue and interpreting the microenvironment of water. Water content in active tumour tissue (84%) and oedema (79%) regions is found to be higher than that of normal WM (69%) and close to that of normal GM (83%). Consistent with literature reports, mean kurtosis is measured to be lower in tumour and oedema regions than in normal WM and GM, whereas mean diffusivity is increased. Voxel-based correlations between water content and diffusion indices obtained with diffusion kurtosis tensor imaging, and between quantitative MRI and FET-PET are reported for 8 brain tumour patients. The effective transverse relaxation time T2∗ is found to be the MR parameter showing the strongest correlations with other MR indices derived here and with FET-PET.

Multimodal Fingerprints of Resting State Networks as assessed by Simultaneous Trimodal MR-PET-EEG Imaging.

Simultaneous MR-PET-EEG (magnetic resonance imaging - positron emission tomography - electroencephalography), a new tool for the investigation of neuronal networks in the human brain, is presented here for the first time. It enables the assessment of molecular metabolic information with high spatial and temporal resolution in a given brain simultaneously. Here, we characterize the brain's default mode network (DMN) in healthy male subjects using multimodal fingerprinting by quantifying energy metabolism via 2- [18F]fluoro-2-desoxy-D-glucose PET (FDG-PET), the inhibition - excitation balance of neuronal activation via magnetic resonance spectroscopy (MRS), its functional connectivity via fMRI and its electrophysiological signature via EEG. The trimodal approach reveals a complementary fingerprint. Neuronal activation within the DMN as assessed with fMRI is positively correlated with the mean standard uptake value of FDG. Electrical source localization of EEG signals shows a significant difference between the dorsal DMN and sensorimotor network in the frequency range of δ, θ, α and ß-1, but not with ß-2 and ß-3. In addition to basic neuroscience questions addressing neurovascular-metabolic coupling, this new methodology lays the foundation for individual physiological and pathological fingerprints for a wide research field addressing healthy aging, gender effects, plasticity and different psychiatric and neurological diseases.

Bone regeneration induced by a 3D architectured hydrogel in a rat critical-size calvarial defect.

Bone regeneration can be stimulated by implantation of biomaterials, which is especially important for larger bone defects. Here, healing potency of the porous ArcGel was evaluated in a critical-size calvarial bone defect in rats in comparison with clinical standard autologous bone and Bio-Oss® Collagen (BioOss), a bone graft material frequently used in clinics. Bone healing and metabolic processes involved were monitored longitudinally by [18F]-fluoride and [18F]-FDG µ-PET/CT 1d, 3d, 3w, 6w, and 12w post implantation. Differences in quality of bone healing were assessed by ex vivo µ-CT, mechanical tests and histomorphometry. The amount of bone formed after implantation of ArcGel was comparable to autologous bone and superior to BioOss (histomorphometry). Furthermore, microarchitecture of newly formed bone was more physiological and better functional in case of ArcGel (push-out tests). [18F]-FDG uptake increased until 3d after implantation, and decreased until 12w for both ArcGel and BioOss. [18F]-fluoride uptake increased until 3w post implantation for all materials, but persisted significantly longer at higher levels for BioOss, which indicates a prolonged remodelling phase. The study demonstrates the potential of ArcGel to induce restitutio ad integrum comparable with clinical standard autologous bone and better bone regeneration in large defects compared to a commercial state-of-the-art biomaterial.

Multimodal Imaging in Malignant Brain Tumors: Enhancing the Preoperative Risk Evaluation for Motor Deficits with a Combined Hybrid MRI-PET and Navigated Transcranial Magnetic Stimulation Approach.

BACKGROUND AND PURPOSE: Motor deficits in patients with brain tumors are caused mainly by irreversible infiltration of the motor network or by indirect mass effects; these deficits are potentially reversible on tumor removal. Here we used a novel multimodal imaging approach consisting of structural, functional, and metabolic neuroimaging to better distinguish these underlying causes in a preoperative setting and determine the predictive value of this approach. MATERIALS AND METHODS: Thirty patients with malignant brain tumors involving the central region underwent a hybrid O-(2-[(18)F]fluoroethyl)-L-tyrosine-PET-MR imaging and motor mapping by neuronavigated transcranial magnetic stimulation. The functional maps served as localizers for DTI tractography of the corticospinal tract. The spatial relationship between functional tissue (motor cortex and corticospinal tract) and lesion volumes as depicted by structural and metabolic imaging was analyzed. RESULTS: Motor impairment was found in nearly all patients in whom the contrast-enhanced T1WI or PET lesion overlapped functional tissue. All patients who functionally deteriorated after the operation showed such overlap on presurgical maps, while the absence of overlap predicted a favorable motor outcome. PET was superior to contrast-enhanced T1WI for revealing a motor deficit before the operation. However, the best correlation with clinical impairment was found for T2WI lesion overlap with functional tissue maps, but the prognostic value for motor recovery was not significant. CONCLUSIONS: Overlapping contrast-enhanced T1WI or PET-positive signals with motor functional tissue were highly indicative of motor impairment and predictive for surgery-associated functional outcome. Such a multimodal diagnostic approach may contribute to the risk evaluation of operation-associated motor deficits in patients with brain tumors.

Applications of PET imaging of neurological tumors with radiolabeled amino acids.

Routine diagnostics and treatment monitoring of brain tumors is usually based on contrast-enhanced magnetic resonance imaging (MRI). However, the capacity of structural MRI to differentiate neoplastic tissue from non-specific treatment changes may be limited especially after therapeutic interventions such as neurosurgical resection, radio- and chemotherapy. Metabolic imaging using PET may provide relevant additional information on tumor metabolism, which allows for more accurate diagnostics especially in clinically equivocal situations. In contrast to the widely used ¹8F-2-fluoro-2-deoxy-D-glucose, which exhibits a poor tumor-to-background contrast within the brain, amino acid tracers provide high sensitivity to detect primary tumors, recurrent or residual gliomas, including most low-grade gliomas. The method improves targeting of biopsy and provides additional information of tumor extent, which is helpful for planning neurosurgery and radiotherapy. In the further course of the disease, amino acid positron-emission tomography (PET) allows a sensitive monitoring of treatment response, the early detection of tumor recurrence, and an improved differentiation of tumor recurrence from treatment-related changes. In the past, the method had only limited availability due to the use of radiopharmaceuticals with a short half-life. In recent years, however, novel amino acid tracers labeled with positron emitters with a longer half-life have been developed and clinically validated which allow a more efficient and cost-effective application. These developments and the well-documented diagnostic performance of PET using radiolabeled amino acids suggest that its application continues to spread and that the method may be available as a routine diagnostic technique for certain indications in the near future.

Meningioangiomatosis in a patient with progressive focal neurological deficit-case report and review of literature.

Meningioangiomatosis (MA) represents a vascular hamartoma accompanied by meningothelial cell proliferation. It generally becomes symptomatic with difficult to control seizures, though in some patients it may be asymptomatic. We present the case of a 41-year-old male patient with a newly developed central distal monoparesis of the left leg. Cranial magnetic resonance imaging (MRI) and further diagnostic characterization via (18)F-Fluoro-Ethyl-Tyrosine positron emission tomography ((18)F-FET-PET) indicated a low-grade glioma. Histopathological diagnosis revealed a meningioangiomatosis. The clinical, radiological and neuropathological findings of this rare constellation are described and discussed with the actual literature.

Integrated boost IMRT with FET-PET-adapted local dose escalation in glioblastomas. Results of a prospective phase II study.

PURPOSE: Dose escalations above 60 Gy based on MRI have not led to prognostic benefits in glioblastoma patients yet. With positron emission tomography (PET) using [(18)F]fluorethyl-L-tyrosine (FET), tumor coverage can be optimized with the option of regional dose escalation in the area of viable tumor tissue. METHODS AND MATERIALS: In a prospective phase II study (January 2008 to December 2009), 22 patients (median age 55 years) received radiochemotherapy after surgery. The radiotherapy was performed as an MRI and FET-PET-based integrated-boost intensity-modulated radiotherapy (IMRT). The prescribed dose was 72 and 60 Gy (single dose 2.4 and 2.0 Gy, respectively) for the FET-PET- and MR-based PTV-FET((72 Gy)) and PTV-MR((60 Gy)). FET-PET and MRI were performed routinely for follow-up. Quality of life and cognitive aspects were recorded by the EORTC-QLQ-C30/QLQ Brain20 and Mini-Mental Status Examination (MMSE), while the therapy-related toxicity was recorded using the CTC3.0 and RTOG scores. RESULTS: Median overall survival (OS) and disease-free survival (DFS) were 14.8 and 7.8 months, respectively. All local relapses were detected at least partly within the 95% dose volume of PTV-MR((60 Gy)). No relevant radiotherapy-related side effects were observed (excepted alopecia). In 2 patients, a pseudoprogression was observed in the MRI. Tumor progression could be excluded by FET-PET and was confirmed in further MRI and FET-PET imaging. No significant changes were observed in MMSE scores and in the EORTC QLQ-C30/QLQ-Brain20 questionnaires. CONCLUSION: Our dose escalation concept with a total dose of 72 Gy, based on FET-PET, did not lead to a survival benefit. Acute and late toxicity were not increased, compared with historical controls and published dose-escalation studies.

[Use of amino acid PET in the Diagnostic and Treatment Management of cerebral gliomas]. / Anwendung der Aminosäure-PET in der Diagnostik und Therapie von zerebralen Gliomen.

Structural as well as functional imaging methods are of special importance in neurooncology. Improvements of radionuclide and magnetic resonance-based imaging modalities over the past decade have enabled clinicians to non-invasively assess the dynamics of disease-specific processes at the molecular level in patients with malignant gliomas. To date, a range of complementary imaging parameters have been established in the diagnostic work-up of patients with brain tumours. Magnetic resonance imaging (MRI) provides morphological information as well as functional information such as vascular permeability, cell density, tumour perfusion, and metabolic information by using magnetic resonance spectroscopy. The use of radiolabelled amino acids for positron emission tomography (PET) allows a better delineation of tumour margins and improves targeting of biopsy and radiotherapy, and planning surgery. In addition, amino acid imaging appears useful in distinguishing tumour recurrence from non-specific post-therapeutic scar tissue, in predicting prognosis in low-grade gliomas, and in monitoring metabolic response during treatment. Taken together, MRI and PET provide complementary information about tumour biology and activity, thereby resulting in an improved understanding of the kinetics of tumour growth and therefore allow new insights into the pathophysiology of malignant brain tumours. However, multimodal imaging studies comparing the value of amino acid PET and functional methods of MRI (e. g., perfusion and diffusion weighted imaging) are needed. From these studies, surrogate MRI and PET imaging techniques need to be derived to gain complementary structural and functional information of brain tumours that can be placed into common clinical practice which will optimise the clinical management of patients with malignant gliomas.

[German guidelines for brain tumour imaging by PET and SPECT using labelled amino acids]. / PET- und SPECT-Untersuchungen von Hirntumoren mit radioaktiv markierten Aminosäuren.

For the primary diagnosis of brain tumours, morphological imaging by means of magnetic resonance imaging (MRI) is the current method of choice. The complementary use of functional imaging by positron emitting tomography (PET) and single photon emitting computerized tomography (SPECT) with labelled amino acids can provide significant information on some clinically relevant questions, which are beyond the capacity of MRI. These diagnostic issues affect in particular the improvement of biopsy targeting and tumour delineation for surgery and radiotherapy planning. In addition, amino acid labelled PET and SPECT tracers are helpful for the differentiation between tumour recurrence and non-specific post-therapeutic tissue changes, in predicting prognosis of low grade gliomas, and for metabolic monitoring of treatment response. The application of dynamic PET examination protocols for the assessment of amino acid kinetics has been shown to enable an improved non-invasive tumour grading. The purpose of this guideline is to provide practical assistance for indication, examination procedure and image analysis of brain PET/SPECT with labelled amino acids in order to allow for a high quality standard of the method. After a short introduction on pathobiochemistry and radiopharmacy of amino acid labelled tracers, concrete and detailed information is given on the several indications, patient preparation and examination protocols as well as on data reconstruction, visual and quantitative image analysis and interpretation. In addition, possible pitfalls are described, and the relevant original publications are listed for further information.

High resolution BrainPET combined with simultaneous MRI.

UNLABELLED: After the successful clinical introduction of PET/CT, a novel hybrid imaging technology combining PET with the versatile attributes of MRI is emerging. At the Forschungszentrum Jülich, one of four prototypes available worldwide combining a commercial 3T MRI with a newly developed BrainPET insert has been installed, allowing simultaneous data acquisition with PET and MRI. The BrainPET is equipped with LSO crystals of 2.5 mm width and Avalanche photodiodes (APD) as readout electronics. Here we report on some performance characteristics obtained by phantom studies and also on the initial BrainPET studies on various patients as compared with a conventional HR+ PET-only scanner. MATERIAL, METHODS: The radiotracers [18F]-fluoro-ethyl-tyrosine (FET), [11C]-flumazenil and [18F]-FP-CIT were applied. RESULTS: Comparing the PET data obtained with the BrainPET to those of the HR+ scanner demonstrated the high image quality and the superior resolution capability of the BrainPET. Furthermore, it is shown that various MR images of excellent quality could be acquired simultaneously with BrainPET scans without any relevant artefacts. DISCUSSION, CONCLUSION: Initial experiences with the hybrid MRI/BrainPET indicate a promising basis for further developments of this unique technique allowing simultaneous PET imaging combined with both anatomical and functional MRI.

O-(2-[18F]fluorethyl)-L-tyrosine PET in the clinical evaluation of primary brain tumours.

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.

Multimodal target point assessment for stereotactic biopsy in children with diffuse bithalamic astrocytomas.

INTRODUCTION: Diffuse glial tumors with bithalamic involvement are rare in children. Diagnostic assessment can be difficult as the radiological findings can be unspecific. MATERIALS AND METHODS: In order to enhance the diagnostic yield metabolic imaging with MRS and PET using FET ( O-(2-[(18)F]fluoroethyl)- L-tyrosine) was performed in two children (2 and 10 years of age). Co-registered images were used for image-guided biopsy, which was planned with neuronavigation and stereotaxy simultaneously. RESULTS: Biopsies from the right thalamus were planned, but locations were changed in both cases after metabolic imaging was available. MRS (thalamic voxel) was typical for a glial tumor in one child. In the older girl FET-PET revealed an unexpected lesion in the left cerebellar hemisphere, with a tumor-to-cortex ratio of 3.8, as against 1.7 in the thalamus. Accordingly, a stereotactic biopsy specimen was taken from the left cerebellar hemisphere, and a final diagnosis of anaplastic astrocytoma was made. The other patient showed a higher uptake (tumor-to-cortex ratio 1.6) in the left dorsal thalamus, compared with bilateral homogeneous hyperintensity of the thalamus structures on MRI. Stereotactic biopsy revealed a low-grade diffuse astrocytoma. CONCLUSION: Stereotactic biopsy using metabolic imaging and image fusion can enhance the diagnostic yield in cases of diffuse pediatric gliomas disclosing unexpected 'hot spots'.

Monitoring isotretinoin therapy in thyroid cancer using 18F-FDG PET.

Treatment with isotretinoin (13-cis-retinoic acid, 13-cis-RA) is a recent additional option in advanced, otherwise intractable differentiated thyroid cancers. The aim of this study was to evaluate fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET) in the prediction and the monitoring of response to 13-cis-RA therapy. Twenty-one patients with advanced differentiated thyroid cancers were investigated using 18F-FDG PET and iodine-131 whole-body scans before and 3, 6 and 9 months after initiation of 13-cis-RA therapy. After 9 months, 13-cis-RA treatment was discontinued and imaging procedures repeated 3 months later. Average 18F-FDG uptake (SUV) decreased significantly during 13-cis-RA therapy but subsequently increased in five of eight patients after withdrawal of 13-cis-RA. 18F-FDG uptake (SUV) 3 months after onset of 13-cis-RA therapy was significantly lower in patients who developed increased 131I uptake in their tumour sites than in patients with no subsequent increase in 131I uptake. There was no relationship between serum thyroglobulin level on the one hand and simultaneously measured 131I or 18F-FDG uptake on the other hand. There was a tendency towards lower 18F-FDG uptake in tumour manifestations with a better outcome. Therefore, 18F-FDG PET at 3 months after the start of treatment promises to differentiate between those patients who will eventually benefit from 13-cis-RA and those who will not. In conclusion, these data indicate that 18F-FDG PET is a useful tool for the evaluation and monitoring of adjuvant therapy with 13-cis-RA in thyroid cancer.

MR imaging and single-photon emission CT findings after gene therapy for human glioblastoma.

BACKGROUND AND PURPOSE: Our goal was to evaluate MR imaging findings after local intracerebral gene therapy in patients with glioblastoma and differentiate postoperative contrast enhancement phenomena. METHODS: In all, 26 patients with supratentorial single lesion glioblastoma underwent tumor resection and intracerebral injection of murine retroviral vector-producer cells for gene therapy with the herpes simplex virus type I thymidine kinase gene/ganciclovir system. Serial contrast-enhanced MR studies were obtained before treatment and postoperatively on day 1 or 2; weeks 2, 4, 9, 13, 17, 25, and 33; and every 8 weeks thereafter. Iodomethyltyrosine single-photon emission CT (IMT-SPECT) investigations also were performed in selected cases. RESULTS: Twelve patients showed nontumorous enhancement of various intensities after treatment, arising within 18 to 72 hours and persisting at 3 to 10 months. It was characterized by a strong local enhancement up to 20 mm thick, which was initially nodular and later linear along the resection cavity wall and surrounded by massive perifocal edema. This "flare" enhancement had features that clearly differed from those of residual tumor enhancements and benign postsurgical enhancements. The IMT-SPECT investigations showed increased amino acid uptake in patients with enhancement from residual or relapsing tumor, but not in patients with flare. CONCLUSION: After local gene therapy, a unique dynamic, transient perifocal flare enhancement can occur on MR images. IMT-SPECT may help to differentiate between tumorous and nontumorous flare enhancements in patients with enhancing tissue on MR images after gene therapy for glioblastoma.

3-[123I]Iodo-alpha-methyl-L-tyrosine uptake in cerebral gliomas: relationship to histological grading and prognosis.

3-[123I]Iodo-alpha-methyl-L-tyrosine (IMT) is employed clinically as a tracer of amino acid transport in brain tumours using single-photon emission tomography (SPET). This study investigates the role of IMT SPET in the non-invasive histological grading and prognostic evaluation of cerebral gliomas. The files of patients investigated by IMT SPET in our clinic between 1988 and 1996 were evaluated retrospectively. Complete follow-up was available for 58 patients with cerebral gliomas investigated by IMT SPET shortly after tumour diagnosis. Seventeen patients had low-grade gliomas (WHO grade II), 14 had anaplastic gliomas (WHO grade III) and 27 had glioblastomas (WHO grade IV). Thirty-six cases were primary tumours and 22 cases, recurrences. Maximal and mean tumour-to-brain (T/B) ratios of IMT uptake at the first IMT SPET investigation were related to histological grading and survival time. Patients with low-grade gliomas showed significantly longer survival than patients with high-grade (grade III or IV) tumours. Gliomas without contrast enhancement on computed tomography or magnetic resonance imaging scans were associated with longer patient survival than tumours with contrast enhancement. The T/B ratios of IMT SPET showed no differences in relation to histological grading [WHO grade II: 1.73+/-0.59; WHO grade III: 1.74+/-0.38; WHO grade IV: 1.59+/-0.35, (mean+/-SD, T/B ratios of mean tumour uptake)]. The median survival time of patients with a high T/B ratio on IMT SPET was not significantly different from that of patients with a low T/B ratio (T/B ratio <1.6, 14.8 months; T/B ratio > or =1.6, 13.0 months). Thus, no evidence could be found for a relationship between IMT uptake in cerebral gliomas and either histological grading or survival time. Nevertheless, IMT SPET constitutes a useful method for the detection of primary and recurrent gliomas, determination of tumour extent and individual follow-up.

Radiolabeled amino acids: basic aspects and clinical applications in oncology.

As the applications of metabolic imaging are expanding, radiolabeled amino acids may gain increased clinical interest. This review first describes the basic aspects of amino acid metabolism, then continues with basic aspects of radiolabeled amino acids, and finally describes clinical applications, with an emphasis on diagnostic value. A special focus is on (11)C-methionine, (11)C-tyrosine, and (123)I-iodomethyltyrosine, because these have been most used clinically, although their common affinity for the L-transport systems may limit generalization to other classes of amino acids. The theoretic and preclinical background of amino acid imaging is sound and supports clinical applications. The fact that amino acid imaging is less influenced by inflammation may be advantageous in comparison with (18)F-FDG PET imaging, although tumor specificity is not absolute. In brain tumor imaging, the use of radiolabeled amino acids is established, the diagnostic accuracy of amino acid imaging seems adequate, and the diagnostic value seems advantageous. The general feasibility of amino acid imaging in other tumor types has sufficiently been shown, but more research is required in larger patient series and in well-defined clinical settings.

Uptake of cis-4-[18F]fluoro-L-proline in urologic tumors.

UNLABELLED: Tumor uptake of the amino acid cis-4-[18F]fluoro-L-proline (cis-FPro) was studied with PET in eight patients with urologic tumors. METHODS: Three patients had primary renal cell carcinomas (RCCs), one had a local recurrence of RCC, one had squamous RCC, one had an adrenal hemangioma, one had inguinal metastases of penile squamous carcinoma, and one had suspected metastatic disease from prostate cancer. PET scans of the trunk were acquired at 1 and 3-5 h after intravenous injection of 400 MBq cis-FPro and compared with 18F-FDG PET scans and CT. RESULTS: None of the tumors or metastases showed significant uptake of cis-FPro. FDG uptake was seen in one of the three primary RCCs, in the local recurrence of RCC, in the squamous RCC, and in the metastases of penile cancer. CONCLUSION: Cis-FPro appears not to be a promising PET tracer in oncology.