1-11C-acetate versus 18F-FDG PET in detection of meningioma and monitoring the effect of gamma-knife radiosurgery

Dural involvement in central nervous system langerhans cells histiocytosis (LCH) on FDG PET/CT: Case report and review of CNS manifestations of LCH on PET/CT

We report a case of multisystem Langerhans cell histiocytosis in a pediatric patient with central nervous system involvement, highlighting F-18(FDG) uptake characteristics of dural sites of disease. We also highlight the advantages of functional data offered by FDG-PET as a useful follow-up tool to assess viability and, therefore, treatment response of previously known central nervous system lesions. The utility of recognizing characteristic patterns of FDG uptake in dural disease is also applicable in cases of diagnostic uncertainty, such as when evaluating isolated dural lesions or when distinguishing between Langerhans cell histiocytosis and similar appearing lesions such as meningiomas.

Meningioma grading based on positron emission tomography: A systematic review and meta-analysis

Introduction

Meningiomas are the most common central nervous system tumor in adults. Knowledge of the tumor grade can guide optimal treatment timing and shape personalized follow-up strategies. Positron emission tomography (PET) has been utilized for the metabolic assessment of various intracranial space-occupying lesions. Herewith, we set out to evaluate the diagnostic accuracy of PET for the noninvasive assessment of meningioma's grade.

Materials and methods

The Medline, Scopus and Cochrane databases were systematically searched in March 2022 for studies that evaluated the sensitivity and specificity of PET compared to the gold standard of histological diagnosis in the grading of meningiomas. Summary statistics will be calculated and scatter plots, summary curve from the HSROC model and posterior predictions by empirical Bayes estimates will be presented.

Results

Five studies consisting of 242 patients with a total of 196 low-grade (Grade 1) and 46 high grade (Grade 2/3) meningiomas were included in our analysis. Three of the included studies used ¹⁸F-FDG, one study used ¹⁸F-FLT and one used(Whiting et al., 2011) 18 F-FET as PET tracers. The pooled sensitivity was 76% (95% CI: 52%-91%) and the pooled specificity was 89% (95% CI: 83%-93%). The diagnostic odds ratio was 27.17 (95% CI: 9.22-80.06), the positive likelihood ratio was 7.18 (95% CI: 4.54-11.34) and the negative likelihood ratio was 0.26 (95% CI: 0.11-0.61).

Conclusion

PET is a promising and viable option as a noninvasive imaging tool to differentiate the meningioma grades. However, currently it cannot overtake the gold standard of histological grade confirmation. More studies are required for further validation and refinement of this imaging technique and assessment of other radiotracers as well.

Imaging Characteristics of Meningiomas

Contemporary neuroimaging of meningiomas has largely relied on computed tomography, and more recently magnetic resonance imaging. While these modalities are frequently used in nearly all clinical settings where meningiomas are treated for the routine diagnosis and follow-up of these tumors, advances in neuroimaging have provided novel opportunities for prognostication and treatment planning (including both surgical planning and radiotherapy planning). These include perfusion MRIs, and positron emission tomography (PET) imaging modalities. Here we will summarize the contemporary uses for neuroimaging in meningiomas, and future applications of novel, cutting edge imaging techniques that may be routinely implemented in the future to enable more precise treatment of these challenging tumors.

Automated production of [11C]butyrate for keto body PET imaging

The report describes an updated, fully automated method for the production of [¹¹C]butyrate, validated for use in clinical studies. A commercially available GE Tracerlab FX_M synthesis module was reconfigured to allow for air-free introduction of n-propyl magnesium chloride and to incorporate Sep-Pak cartridges to simplify and shorten the purification process, as compared to purifying the product using traditional HPLC. The method takes 20 min from end-of-bombardment and reliably produces injectable doses of [¹¹C]butyrate (8029 ± 1628 MBq (217 ± 44 mCi), 14 % radiochemical yield based on [¹¹C]CO_2, non-decay corrected) in high radiochemical purity (>97 %), n = 3. With radiotracer in hand, PET scans of rats confirmed uptake of the radiopharmaceutical in the brain. Rat biodistribution data was obtained and used in conjunction with OLINDA software to determine an estimated human total body effective dose of 3.20 × 10^-3 mSv/MBq (1.19 × 10^-2 rem/mCi), along with preliminary rodent PET imaging that confirmed brain uptake. Lastly, our first human [¹¹C]butyrate PET studies using a dynamic bolus injection technique (n = 5), with a graphical Logan analysis using a white matter reference region, confirmed good radiotracer uptake in the brain and with relatively more prominent uptake in the cerebellar hemispheres, vermis, cingulum cortex and the thalami.

Use of advanced neuroimaging and artificial intelligence in meningiomas

Anatomical cross‐sectional imaging methods such as contrast‐enhanced MRI and CT are the standard for the delineation, treatment planning, and follow‐up of patients with meningioma. Besides, advanced neuroimaging is increasingly used to non‐invasively provide detailed insights into the molecular and metabolic features of meningiomas. These techniques are usually based on MRI, e.g., perfusion‐weighted imaging, diffusion‐weighted imaging, MR spectroscopy, and positron emission tomography. Furthermore, artificial intelligence methods such as radiomics offer the potential to extract quantitative imaging features from routinely acquired anatomical MRI and CT scans and advanced imaging techniques. This allows the linking of imaging phenotypes to meningioma characteristics, e.g., the molecular‐genetic profile. Here, we review several diagnostic applications and future directions of these advanced neuroimaging techniques, including radiomics in preclinical models and patients with meningioma.

Intracranial neuroendocrine tumour simulating meningioma for several years: an overview of diagnosis and treatment

Metastatic neuroendocrine tumour (NET) to brain has been reported in 1.5–5% of patients with NETs. Differentiation between intracranial NET metastasis and meningiomas can cause a diagnostic dilemma. We present a symptomatic case of a 66-year-old male with a history of left-sided skull base mass. The diagnosis of a meningioma was made based on the MRI findings and clinical presentation. The patient received radiation and the mass remained stable on serial MRI images at follow-up visits. Five years after his initial presentation, the patient’s mass showed further growth. He also complained of worsening of his recent diagnosis of irritable bowel syndrome and fluctuations in his blood pressure. Surgical resection was performed, and histopathological features were consistent with moderately differentiated neuroendocrine tumour. Further evaluation with 68 Gallium-DOTATATE positron emission-computed tomography (Ga-68 PET/CT) showed metastatic disease involving the bones, lymph nodes, and liver without convincing evidence of the location of primary malignancy within the bowel loops or the pancreas. The patient was started on combination of capecitabine and temozolomide with partial response and significant improvement of his symptoms. This case highlights the clinical and radiological behaviour of intracranial NET that can mimic the diagnosis of meningioma.

Cellular and Molecular Imaging with SPECT and PET in Brain Tumors

This review highlights the 2 major molecular imaging modalities that are used in clinics, namely single-photon emission computed tomography (SPECT) and positron emission tomography (PET), and their added value in management of patients with brain tumors. There are a variety of SPECT and PET radiotracers that can allow imaging of different molecular processes. Those radiotracers target specific molecular features of tumors, resulting in improved specificity of these agents. Potential applications include staging of brain tumors and evaluating post-therapeutic changes.

Case Report: Long-Term Chemotherapy With Hydroxyurea and Prednisolone in a Cat With a Meningioma: Correlation of FDG Uptake and Tumor Grade Assessed by Histopathology and Expression of Ki-67 and p53

A 15.5-year-old, neutered, male, domestic shorthair cat was presented with neurologic dysfunctions. At presentation, an obtunded mental status and vestibular ataxia were identified. On neurologic examination, postural reactions were decreased-to-absent in all four limbs, and pupillary light reflexes showed bilaterally delayed results. Magnetic resonance imaging was performed, and a demarcated lesion was identified in the third ventricle. The cat was tentatively diagnosed with a brain tumor, which was suspected to be a meningioma. The cat was treated with hydroxyurea and prednisolone. Mental status was considered more alert, and ataxia improved following treatment. On the 106th day after the commencement of treatment, a ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) scan was performed. On the PET images, a hypermetabolic region was found in the lesion. The average standardized uptake value of FDG was 2.47, and the tumor-to-normal-tissue ratio was 1.25. The cat died 408 days following the commencement of treatment, and a grade 1 meningioma was confirmed by postmortem histopathology. Immunohistochemistry for Ki-67 and p53 was performed. The labeling indices of Ki-67 and p53 were 2.56 and 0%, respectively. This case shows that chemotherapy with hydroxyurea and prednisolone may be considered in the treatment of feline meningiomas. Furthermore, this is the first case describing the application of FDG-PET to visualize a naturally occurring meningioma in a cat.

Prediction of Meningioma WHO Grade Using PET Findings: A Systematic Review and Meta-Analysis

BACKGROUND AND PURPOSE

World Health Organization (WHO) grading of meningiomas reflects recurrence rate and prognosis. Positron emission tomography (PET) investigates metabolic activity, allowing for distinction between low- and high-grade tumors. As preoperative suspicion for malignant meningioma will influence surgical strategy in terms of timing, extent of resection, and risks taken to achieve a total resection, we systematically reviewed the literature on PET-imaging in meningiomas and relate these findings to histopathological analysis.

METHODS

Searches in PubMed, EMBASE, and The Cochrane Library, from inception to September 2019, included studies of patients who had undergone surgery for a histologically verified intracranial meningioma, with a PET-scan prior to surgery and description of (semi)quantitative PET values for meningiomas from two different WHO groups. Studies comparing more than 1 patient per WHO group were included in the meta-analysis.

RESULTS

Twenty-two studies (432 patients) were included. 18fluor-fluorodesoxyglucose (18F-FDG) PET was mostly described to differentiate benign from malignant meningiomas. Pooled data showed differences in mean (95% CI) Standardized Uptake Value (SUV) for WHO II/III compared to WHO I of 2.51 (1.36, 3.66), and in tumor-to-normal (T/N) ratio (T/N ratio) for WHO II/III versus WHO I of .42 (.12, .73).

CONCLUSIONS

We found that SUV and T/N ratio in 18F-FDG PET may be useful to noninvasively differentiate benign from malignant meningiomas. T/N ratio seems to have a high specificity for the detection of high-grade meningiomas. Other PET tracers were studied too infrequently to draw definitive conclusions. Before treatment strategies can be adapted based on 18F-FDG PET, prospective studies in larger cohorts are warranted to validate the optimal T/N ratio cutoff point.

Multifocal Meningioma Recurrence Detected on Ga68-DOTANOC Scan

Meningiomas arise from meningothelial cells of the arachnoid membranes. They are classified into three grades according to the WHO criteria, Grade I (Benign), Grade II (atypical), and Grade III (anaplastic). Radiological and structural imaging computed tomography (CT) and magnetic resonance imaging are done routinely for defining the location, extent, and follow-up. However, these imaging techniques have their limitations. Since meningiomas have overexpression of somatostatin receptor 2, DOTANOC positron-emission tomography (PET)/CT scan is suggested for their delineation and distinguish postradiotherapy necrosis from recurrence. Here, we present a case where DOTANOC PET/CT scan helped in confirming recurrence postsurgery and radiotherapy.

The Added Value of Diagnostic and Theranostic PET Imaging for the Treatment of CNS Tumors

This review highlights the added value of PET imaging in Central Nervous System (CNS) tumors, which is a tool that has rapidly evolved from a merely diagnostic setting to multimodal molecular diagnostics and the guidance of targeted therapy. PET is the method of choice for studying target expression and target binding behind the assumedly intact blood-brain barrier. Today, a variety of diagnostic PET tracers can be used for the primary staging of CNS tumors and to determine the effect of therapy. Additionally, theranostic PET tracers are increasingly used in the context of pharmaceutical and radiopharmaceutical drug development and application. In this approach, a single targeted drug is used for PET diagnosis, upon the coupling of a PET radionuclide, as well as for targeted (nuclide) therapy. Theranostic PET tracers have the potential to serve as a non-invasive whole body navigator in the selection of the most effective drug candidates and their most optimal dose and administration route, together with the potential to serve as a predictive biomarker in the selection of patients who are most likely to benefit from treatment. PET imaging supports the transition from trial and error medicine to predictive, preventive, and personalized medicine, hopefully leading to improved quality of life for patients and more cost-effective care.

The Diagnostic Value Of Using 18F-Fluorodeoxyglucose Positron Emission Tomography To Differentiate Between Low- And High-Grade Meningioma

Objective

This study aims to evaluate the potential role of ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) in detecting high-grade meningiomas and predicting the prognosis of patients after meningioma surgery.

Patients and methods

A total of 124 patients met the final inclusion criterion. Tumor to gray ratio (TGR) was compared with Ki-67 labeling index, and its correlations with pre-operative neurological function and treatment status were also evaluated. Receiver-operating characteristic (ROC) curve was drawn to determine a cut-off value which could discriminate meningioma of different grades. Prognostic factors including TGR were analyzed using Kaplan-Meier survival curve and cox proportional model.

Results

The TGR of higher World Health Organization (WHO) grade meningioma was significantly higher than that in lower grade (p < 0.001), and it was correlated with the Ki-67 labeling index (p < 0.001, r = 0.1545). The TGR of 1.30 was the best cutoff value for the detection of high grade (WHO grade II&III) meningioma from low grade (WHO grade I) according to ROC analysis, with a sensitivity of 61.5%, the specificity of 86.7%, and accuracy of 81.5%. The TGR (p < 0.001), treatment status (p = 0.035), tumor grade (p < 0.001) and Ki-67 labeling index (p < 0.001) were significantly associated with progression-free survival (PFS). Cox proportional hazards model demonstrated that TGR (p = 0.013) was an independent prognostic factor for PFS.

Conclusion

A high uptake of FDG was correlated with a more proliferative biological behavior and is a risk factor for tumor recurrence.

Theragnostic Use of Radiolabelled Dota-Peptides in Meningioma: From Clinical Demand to Future Applications

Meningiomas account for approximately 30% of all new diagnoses of intracranial masses. The 2016 World Health Organization's (WHO) classification currently represents the clinical standard for meningioma's grading and prognostic stratification. However, watchful waiting is frequently the chosen treatment option, although this means the absence of a certain histological diagnosis. Consequently, MRI (or less frequently CT) brain imaging currently represents the unique available tool to define diagnosis, grading, and treatment planning in many cases. Nonetheless, these neuroimaging modalities show some limitations, particularly in the evaluation of skull base lesions. The emerging evidence supporting the use of radiolabelled somatostatin receptor analogues (such as dota-peptides) to provide molecular imaging of meningiomas might at least partially overcome these limitations. Moreover, their potential therapeutic usage might enrich the current clinical offering for these patients. Starting from the strengths and weaknesses of structural and functional neuroimaging in meningiomas, in the present article we systematically reviewed the published studies regarding the use of radiolabelled dota-peptides in surgery and radiotherapy planning, in the restaging of treated patients, as well as in peptide-receptor radionuclide therapy of meningioma.

Cluster-Like Headache Secondary to Anamnesis of Sphenoid Ridge Meningioma: A Case Report and Literature Review

Cluster headache is generally considered to be a primary headache; secondary cluster-like headache is quite rare, while cluster-like headache secondary to meningioma is even rarer. Here, we describe an unusual case with cluster-like headache 2.5 years after sphenoid ridge meningioma surgery. The cluster-like headache and meningioma were on the same side, and even at the same position. Furthermore, the cluster-like headache lasted for 6 months. In addition, the patient did not respond well to conventional treatments for cluster headache, such as oxygen inhalation, carbamazepine, and tramadol. Brain magnetic resonance imaging demonstrated a softening lesion, glial hyperplasia, and localized thickening and enhancement of the dura in the left frontal-temporal lobe. However, positron-emission computed tomography showed reduced metabolism in the left frontal-temporal lobe. Although the possibility of a primary headache cannot be completely eliminated, the association between cluster-like headache and probable tumor recurrence or postoperative changes should be considered.

11C-Methionine Positron Emission Tomography/Computed Tomography Versus 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Evaluation of Residual or Recurrent World Health Organization Grades II and III Meningioma After Treatment

OBJECTIVE

The aim of this study was to determine the assessment of positron emission tomography-computed tomography using C-methionine (MET PET/CT) for World Health Organization (WHO) grades II and III meningiomas; MET PET/CT was compared with PET/CT using F-fluorodeoxy glucose (FDG PET/CT).

METHODS

This study was performed in 17 cases with residual and/or recurrent WHO grades II and III meningiomas. Two neuroradiologists reviewed both PET/CT scans. For agreement, the κ coefficient was measured. Difference in tumor-to-normal brain uptake ratios (T/N ratios) between 2 PET/CT scans was analyzed. Correlation between the maximum tumor size and T/N ratio in PET/CT was studied.

RESULTS

For agreement by both reviewers, the κ coefficient was 0.51 (P < 0.05). The T/N ratio was significantly higher for MET PET/CT (3.24 ± 1.36) than for FDG PET/CT (0.93 ± 0.44) (P < 0.01). C-methionine ratio significantly correlated with tumor size (y = 8.1x + 16.3, n = 22, P < 0.05), but FDG ratio did not CONCLUSIONS: C-methionine PET/CT has superior potential for imaging of WHO grades II and III meningiomas with residual or recurrent tumors compared with FDG PET/CT.

Correlation of 18F-FDG and 11C-methionine uptake on PET/CT with Ki-67 immunohistochemistry in newly diagnosed intracranial meningiomas

OBJECTIVE

We evaluated the uptake of 2-deoxy-2-¹⁸F-fluoro-D-glucose (FDG) and L-[methyl-¹¹C]-methionine (MET) in patients with newly diagnosed intracranial meningiomas and correlated the results with tumor proliferation.

METHODS

Data from 22 patients with newly diagnosed intracranial meningioma (12 grade I and 10 grade II) who underwent both FDG and MET brain PET/CT studies were retrospectively analyzed. The PET images were evaluated by a qualitative method and semiquantitative analysis using standardized uptake value (SUV) (SUV_max and SUV_peak) and tumor-to-reference tissue ratio (T_max/N ratio and T_peak/N ratio). Proliferative activity as indicated by the Ki-67 index was estimated in tissue specimens.

RESULTS

MET PET/CT showed a higher detection rate of meningioma than did FDG PET/CT (100 vs. 46%, respectively). The T_max/N ratio and T_peak/N ratio on MET PET/CT were significantly higher than those on FDG PET/CT (p < 0.001 and p < 0.001, respectively). There was a significant difference between grades I and II with respect to FDG SUVmax (p = 0.003), FDG SUV_peak (p = 0.003), FDG T_max/N ratio (p = 0.02), FDG T_peak/N ratio (p = 0.006), MET SUV_max (p = 0.002), MET SUV_peak (p = 0.002), MET T_max/N ratio (p = 0.002), and MET T_peak/N ratio (p = 0.002). There was a significant correlation between Ki-67 index and FDG PET/CT for SUV_max (p = 0.02), SUV_peak (p = 0.005), and T_peak/N ratio (p = 0.05) and between Ki-67 index and MET PET/CT for SUV_max (p = 0.004), SUV_peak (p = 0.007), T_max/N ratio (p = 0.002), and T_peak/N ratio (p = 0.004).

CONCLUSION

MET PET/CT showed a high sensitivity compared with FDG PET/CT for detection of newly diagnosed WHO grades I and II intracranial meningiomas. Both FDG and MET uptake were found to be useful for evaluating tumor proliferation in meningiomas.

PET imaging in patients with meningioma-report of the RANO/PET Group

Meningiomas are the most frequent nonglial primary brain tumors and represent about 30% of brain tumors. Usually, diagnosis and treatment planning are based on neuroimaging using mainly MRI or, rarely, CT. Most common treatment options are neurosurgical resection and radiotherapy (eg, radiosurgery, external fractionated radiotherapy). For follow-up after treatment, a structural imaging technique such as MRI or CT is used. However, these structural imaging modalities have limitations, particularly in terms of tumor delineation as well as diagnosis of posttherapeutic reactive changes. Molecular imaging techniques such as PET can characterize specific metabolic and cellular features which may provide clinically relevant information beyond that obtained from structural MR or CT imaging alone. Currently, the use of PET in meningioma patients is steadily increasing. In the present article, we provide recommendations for the use of PET imaging in the clinical management of meningiomas based on evidence generated from studies being validated by histology or clinical course.

Organic Semiconducting Nanoparticles as Efficient Photoacoustic Agents for Lightening Early Thrombus and Monitoring Thrombolysis in Living Mice

Acute venous thrombosis is prevalent and potentially fatal. Accurate diagnosis of early thrombus is needed for patients in timely clinical intervention to prevent life-threatening conditions. Photoacoustic imaging (PAI) with excellent spatial resolution and high optical contrast shows more promise for this purpose. However, its application is dramatically limited by its signal-off effect on thrombus because of the ischemia in thrombus which lacks the endogenous photoacoustic (PA) signal of hemoglobin. To address this dilemma, we herein report the feasibility of using organic semiconducting nanoparticles (NPs) for contrast-enhanced PAI of thrombus in living mice. An organic semiconducting NP, self-assembled by amphiphilic perylene-3,4,9,10-tetracarboxylic diimide (PDI) molecules, is chemically modified with cyclic Arg-Gly-Asp (cRGD) peptides as a PA contrast agent (cRGD-PDI NPs) for selectively lightening early thrombus. cRGD-PDI NPs presents high PA intensity, good stability in light and serum, and sufficient blood-circulating half-life. In living mice, PA intensity of early thrombus significantly increases after tail vein injection of cRGD-PDI NPs, which is 4-fold greater than that of the control, blocking, and old thrombus groups. Pathological and immunohistochemical findings show that glycoprotein IIb/IIIa abundant in early thrombus is a good biomarker targeted by cRGD-PDI NPs for distinguishing early thrombus from old thrombus by PAI. Such a lightening PAI effect by cRGD-PDI NPs successfully provides accurate information including the profile, size and conformation, and spatial distribution of early thrombus, which may timely monitor the obstructive degree of thrombus in blood vessels and the thrombolysis effect.

Overview of PET Tracers for Brain Tumor Imaging

This article provides an overview of the key considerations for the development and application of molecular imaging agents for brain tumors and the major classes of PET tracers that have been used for imaging brain tumors in humans. The mechanisms of uptake, biological implications, primary applications, and limitations of PET tracers in neuro-oncology are reviewed. The available data indicate that several of these classes of tracers, including radiolabeled amino acids, have imaging properties superior to those of (18)F-fluorodeoxyglucose, and can complement contrast-enhanced magnetic resonance imaging in the evaluation of brain tumors.

Positron Emission Tomography Imaging of Tumor Cell Metabolism and Application to Therapy Response Monitoring

Cancer cells do reprogram their energy metabolism to enable several functions, such as generation of biomass including membrane biosynthesis, and overcoming bioenergetic and redox stress. In this article, we review both established and evolving radioprobes developed in association with positron emission tomography (PET) to detect tumor cell metabolism and effect of treatment. Measurement of enhanced tumor cell glycolysis using 2-deoxy-2-[(18)F]fluoro-D-glucose is well established in the clinic. Analogs of choline, including [(11)C]choline and various fluorinated derivatives are being tested in several cancer types clinically with PET. In addition to these, there is an evolving array of metabolic tracers for measuring intracellular transport of glutamine and other amino acids or for measuring glycogenesis, as well as probes used as surrogates for fatty acid synthesis or precursors for fatty acid oxidation. In addition to providing us with opportunities for examining the complex regulation of reprogramed energy metabolism in living subjects, the PET methods open up opportunities for monitoring pharmacological activity of new therapies that directly or indirectly inhibit tumor cell metabolism.

MRI and FDG PET/CT Uncovered the Cause of a Paraneoplastic Leukemoid Reaction

An 18-year-old man with progressive headache and vomiting for 2 weeks had significantly elevated levels of WBC count, which kept on rising over time during in-hospital evaluation. Exhaustive examinations did not reveal infection or any other explanations of increased WBC count. Instead, brain MRI and FDG PET/CT identified a malignant lesion in the brain without abnormality elsewhere. The pathological examination revealed a rhabdoid meningioma. The level of the WBC counts returned to normal promptly after surgical resection of the tumor, which confirmed the diagnosis of paraneoplastic leukemoid reaction.

Uptake and tracer kinetics of O-(2-(18)F-fluoroethyl)-L-tyrosine in meningiomas: preliminary results

PURPOSE

O-(2-[(18)F]Fluoroethyl)-L-tyrosine ((18)F-FET) is a well-established PET tracer for the imaging of cerebral gliomas, but little is known about (18)F-FET uptake in meningiomas. The aim of this study was to explore (18)F-FET kinetics and tumour-to-background contrast in meningiomas of various histologies.

METHODS

A group of 24 patients with suspected cerebral meningioma on MRI/CT had an additional dynamic (18)F-FET PET scan prior to surgery. Time-activity curves (TAC) of (18)F-FET uptake in the tumours and tumour-to-brain ratios (TBR) for early (3 - 14 min after injection) and late (18)F-FET uptake (20 - 40 min after injection) were analysed and compared with histological subtypes and WHO grade. (18)F-FET uptake in critical structures in the skull base was also evaluated in terms of tumour-to-tissue (T/Tis) ratio.

RESULTS

TBR of (18)F-FET uptake in meningiomas was significantly higher in the early phase than in the late phase (3.5 ± 0.8 vs. 2.2 ± 0.3; P < 0.001). The difference in TBR between low-grade meningiomas (WHO grade I, 18 patients) and high-grade meningiomas (WHO grade II or III, 6 patients) was significant in the late phase of (18)F-FET uptake (2.1 ± 0.2 vs. 2.5 ± 0.2, P = 0.003) while there was no significant difference in the early phase. ROC analysis showed that TBR of (18)F-FET uptake in the late phase had significant power to differentiate low-grade from high-grade meningiomas (AUC 0.87 ± 0.18, sensitivity 83 %, specificity 83 %, optimal cut-off 2.3; P < 0.01). Evaluation of TAC yielded three different curve patterns of (18)F-FET PET uptake. Combination of TBR (cut-off value 2.3) and TAC pattern slightly improved the differentiation of high-grade from low-grade meningiomas (accuracy 92 %; P = 0.001). Analysis of background radioactivity in the skull base indicated that (18)F-FET uptake may be helpful in distinguishing meningioma tissue in the late phase. T/Tis ratios were >1.2 in all patients for the periorbita, sphenoidal sinus, pituitary gland, tentorium, bone and brain, in more than 90 % of patients for the mucosa and dura, but in only 63 % of patients for the cavernous sinus.

CONCLUSION

(18)F-FET PET may provide additional information for noninvasive grading of meningiomas and possibly for the discrimination of tumour in critical areas of the skull base. A further evaluation of (18)F-FET PET in meningiomas appears to be justified.

Incidental uptake of (18)F-fluorocholine (FCH) in the head or in the neck of patients with prostate cancer

Background

Positron emission tomography-computed tomography (PET/CT) with ¹⁸F-fluorocholine (FCH) is routinely performed in patients with prostate cancer. In this clinical context, foci of FCH uptake in the head or in the neck were considered as incidentalomas, except for those suggestive of multiple bone metastases.

Results

In 8 patients the incidental focus corresponded to a benign tumour. The standard of truth was histology in two cases, correlative imaging with MRI in four cases, ^99mTc-SestaMIBI scintigraphy, ultrasonography and biochemistry in one case and biochemistry including PTH assay in one case. The final diagnosis of benign tumours consisted in 3 pituitary adenomas, 2 meningiomas, 2 hyperfunctioning parathyroid glands and 1 thyroid adenoma.

Malignancy was proven histologically in 2 other patients: 1 papillary carcinoma of the thyroid and 1 cerebellar metastasis.

Conclusions

To the best of our knowledge, FCH uptake by pituitary adenomas or hyperfunctioning parathyroid glands has never been described previously. We thus discuss whether there might be a future indication for FCH PET/CT when one such tumour is already known or suspected: to detect a residual or recurrent pituitary adenoma after surgery, to guide surgery or radiotherapy of a meningioma or to localise a hyperfunctioning parathyroid gland. In these potential indications, comparative studies with reference PET tracers or with ^99mTc-sestaMIBI in case of hyperparathyroidism could be undertaken.

¹¹C-acetate PET/CT imaging: physiologic uptake, variants, and pitfalls

(11)C-acetate PET is used in the assessment of various cardiologic and oncologic diseases. This article describes the physiologic uptake of (11)C-acetate and presents the common benign findings in different anatomic parts of the body. Salivary glands, tonsils, thyroid, meningeal tuberculoma, meningiomas, and macroadenomas of pituitary gland are sites of mild to moderate tracer uptake in the head and neck region. Parenchymal diseases of the lung and reactive and/or inflammatory mediastinal lymphadenopathies cause benign (11)C-acetate uptake in the thorax. Liver, spleen, pancreas, and rectum show an increased uptake. Urinary tract and prostate gland show faint tracer uptake.

Exploiting metabolic differences in glioma therapy

Brain function depends upon complex metabolic interactions amongst only a few different cell types, with astrocytes providing critical support for neurons. Astrocyte functions include buffering the extracellular space, providing substrates to neurons, interchanging glutamate and glutamine for synaptic transmission with neurons, and facilitating access to blood vessels. Whereas neurons possess highly oxidative metabolism and easily succumb to ischemia, astrocytes rely more on glycolysis and metabolism associated with synthesis of critical intermediates, hence are less susceptible to lack of oxygen. Astrocytoma and higher grade glioma cells demonstrate both basic metabolic mechanisms of astrocytes as well as tumors in general, e.g. they show a high glycolytic rate, lactate extrusion, ability to proliferate even under hypoxia, and opportunistic use of mechanisms to enhance metabolism and blood vessel generation, and suppression of cell death pathways. There may be differences in metabolism between neurons, normal astrocytes and astrocytoma cells, providing therapeutic opportunities against astrocytomas, including a wide range of enzyme and transporter differences, regulation of hypoxia-inducible factor (HIF), glutamate uptake transporters and glutamine utilization, differential sensitivities of monocarboxylate transporters, presence of glycogen, high interlinking with gap junctions, use of NADPH for lipid synthesis, utilizing differential regulation of synthetic enzymes (e.g. isocitrate dehydrogenase, pyruvate carboxylase, pyruvate dehydrogenase, lactate dehydrogenase, malate-aspartate NADH shuttle) and different glucose uptake mechanisms. These unique metabolic susceptibilities may augment conventional therapeutic attacks based on cell division differences and surface receptors alone, and are starting to be implemented in clinical trials.

Combined PET/MR imaging using (68)Ga-DOTATOC for radiotherapy treatment planning in meningioma patients

Hybrid imaging is beneficial for improved medical diagnosis and therapy planning today. Hybrid imaging describes the prospective correlation of two or more complementary sets of imaging information, such as functional and anatomical image volumes. Correlation can be performed through physically combined imaging modalities, such as PET/CT, SPECT/CT, or PET/MR. Here we present first results from employing fully integrated PET/MR tomography for intensity-modulated radiotherapy (IMRT) treatment planning in patients with meningioma using [(68)Ga]-DOTATOC as the biomarker of choice. Combined PET/MR offers higher soft tissue contrast and the ability to add functional information to the plain combination of MR-based anatomy and PET-based metabolic and molecular information. Furthermore, fully integrated PET/MR employs novel PET technology that is neither available in PET-only nor PET/CT systems. Despite the current lack of broad clinical evidence, integrated PET/MR may become particularly important and clinically useful for improved, individualized RT therapy planning for brain lesions. In particular, logistical and diagnostic benefits of integrated PET/MR-based treatment planning over treatment planning based on PET/CT data may be expected in meningioma patients.

Differentiation of tumor progression and radiation-induced effects after intracranial radiosurgery

A number of intracranial tumors demonstrate some degree of enlargement after stereotactic radiosurgery (SRS). It necessitates differentiation of their regrowth and various treatment-induced effects. Introduction of low-dose standards for SRS of benign neoplasms significantly decreased the risk of the radiation-induced necrosis after -management of schwannomas and meningiomas. Although in such cases a transient increase of the mass volume within several months after irradiation is rather common, it usually followed by spontaneous shrinkage. Nevertheless, distinguishing tumor recurrence from radiation injury is often required in cases of malignant parenchymal brain neoplasms, such as metastases and gliomas. The diagnosis is frequently complicated by histopathological heterogeneity of the lesion with coexistent viable tumor and treatment-related changes. Several neuroimaging modalities, namely structural magnetic resonance imaging (MRI), diffusion-weighted imaging, diffusion tensor imaging, perfusion computed tomography (CT) and MRI, single-voxel and multivoxel proton magnetic resonance spectroscopy as well as single photon emission CT and positron emission tomography with various radioisotope tracers, may provide valuable diagnostic information. Each of these methods has advantages and limitations that may influence its usefulness and accuracy. Therefore, use of a multimodal radiological approach seems reasonable. Addition of functional and metabolic neuroimaging to regular structural MRI investigations during follow-up after SRS of parenchymal brain neoplasms may permit detailed evaluation of the treatment effects and early prediction of the response. If tissue sampling of irradiated intracranial lesions is required, it is preferably performed with the use of metabolic guidance. In conclusion, differentiation of tumor progression and radiation-induced effects after intracranial SRS is challenging. It should be based on a complex evaluation of the multiple clinical, radiosurgical, and radiological factors.

SPECT and PET imaging of meningiomas

Meningiomas arise from the meningothelial cells of the arachnoid membranes. They are the most common primary intracranial neoplasms and represent about 20% of all intracranial tumors. They are usually diagnosed after the third decade of life and they are more frequent in women than in men. According to the World Health Organization (WHO) criteria, meningiomas can be classified into grade I meningiomas, which are benign, grade II (atypical) and grade III (anaplastic) meningiomas, which have a much more aggressive clinical behaviour. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are routinely used in the diagnostic workup of patients with meningiomas. Molecular Nuclear Medicine Imaging with Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) could provide complementary information to CT and MRI. Various SPECT and PET tracers may provide information about cellular processes and biological characteristics of meningiomas. Therefore, SPECT and PET imaging could be used for the preoperative noninvasive diagnosis and differential diagnosis of meningiomas, prediction of tumor grade and tumor recurrence, response to treatment, target volume delineation for radiation therapy planning, and distinction between residual or recurrent tumour from scar tissue.

13N-NH3 versus F-18 FDG in detection of intracranial meningioma: initial report

PURPOSE

Relatively high Tl-201 uptakes have been reported in all types of meningiomas, and it have been proposed that (201)TlCl SPECT could predict histologic types of meningiomas and differentiate the benign and aggressive meningiomas. Similar to Tl-201, (13)N-(13)NH(4)(+) is an analog of K(+) and could substitute K(+) in some cases. The aim of this study was to evaluate the capacity of PET with (13)N-NH(3) to discriminate meningioma from healthy tissue, and compare with F-18 FDG.

METHODS

Eleven patients with the neuroradiologic diagnosis of meningiomas were studied with (13)N-NH(3), and 10 of them were performed with F-18 FDG PET within 3 days. Ten of them were histologically confirmed (6 grade I, 4 grade II), and another one was proved by radiologic (computed tomography and magnetic resonance imaging) and clinical investigation.The PET images were evaluated by semiquantitative analysis using tumor-to-white matter ratio (T/W).

RESULTS

(13)N-NH(3) uptake was obviously increased in all 11 meningiomas with a good contrast to the surrounding normal brain tissues. Conversely, F-18 FDG uptake was decreased in comparison with the contralateral side in all 7 patients with grade I meningiomas and moderately increased in the remaining patient with grade II meningioma. The T/W ratio of (13)N-NH(3) was higher than that of F-18 FDG (7.03 ± 1.62 vs. 1.44 ± 0.57, P < 0.005). T/W of (13)N-NH(3) uptake was not useful for differentiating benign (Grade I) from atypical (Grade II) meningiomas (P = 0.88), whereas the T/W ratio of F-18 FDG uptake was better than that of N-NH3 for differentiating benign from malignant meningiomas (P = 0.037).

CONCLUSIONS

These preliminary results suggest that (13)N-NH(3) has relatively greater uptake in meningiomas in comparison with F-18 FDG. Clinical applications of (13)N-NH(3) PET for grading and follow-up of meningiomas need to be assessed in further studies.

Synthesis of oncological [11C]radiopharmaceuticals for clinical PET

Positron emission tomography (PET) is a nuclear medicine modality which provides quantitative images of biological processes in vivo at the molecular level. Several PET radiopharmaceuticals labeled with short-lived isotopes such as (18)F and (11)C were developed in order to trace specific cellular and molecular pathways with the aim of enhancing clinical applications. Among these [(11)C]radiopharmaceuticals are N-[(11)C]methyl-choline ([(11)C]choline), l-(S-methyl-[(11)C])methionine ([(11)C]methionine) and 1-[(11)C]acetate ([(11)C]acetate), which have gained an important role in oncology where the application of 2-[(18)F]fluoro-2-deoxy-d-glucose ([(18)F]FDG) is suboptimal. Nevertheless, the production of these radiopharmaceuticals did not reach the same level of standardization as for [(18)F]FDG synthesis. This review describes the most recent developments in the synthesis of the above-mentioned [(11)C]radiopharmaceuticals aiming to increase the availability and hence the use of [(11)C]choline, [(11)C]methionine and [(11)C]acetate in clinical practice.

Positron Emission Tomography Imaging of Meningioma in Clinical Practice

Meningiomas represent about 20% of intracranial tumors and are the most frequent nonglial primary brain tumors. Diagnosis is based on computed tomography (CT) and magnetic resonance imaging (MRI). Mainstays of therapy are surgery and radiotherapy. Adjuvant chemotherapy is tested in clinical trials of phase II. Patients are followed clinically by imaging. However, classical imaging modalities such as CT and MRI have limitations. Hence, we need supplementary imaging tools. Molecular imaging modalities, especially positron emission tomography (PET), represent promising new instruments that are able to characterize specific metabolic features. So far, these modalities have only been part of limited study protocols, and their impact on clinical routine management is still under investigation. It may be expected that their extended use will provide new aspects about meningioma imaging and biology.

In the present article, we summarize PET imaging for meningiomas based on a thorough review of the literature. We discuss and illustrate the potential role of PET imaging in the clinical management of meningiomas. Finally, we indicate current limitations and outline directions for future research.

Current molecular imaging of spinal tumors in clinical practice

Energy metabolism measurements in spinal cord tumors, as well as in osseous spinal tumors/metastasis in vivo, are rarely performed only with molecular imaging (MI) by positron emission tomography (PET). This imaging modality developed from a small number of basic clinical science investigations followed by subsequent work that influenced and enhanced the research of others. Apart from precise anatomical localization by coregistration of morphological imaging and quantification, the most intriguing advantage of this imaging is the opportunity to investigate the time course (dynamics) of disease-specific molecular events in the intact organism. Most importantly, MI represents one of the key technologies in translational molecular neuroscience research, helping to develop experimental protocols that may later be applied to human patients. PET may help monitor a patient at the vertebral level after surgery and during adjuvant treatment for recurrent or progressive disease. Common clinical indications for MI of primary or secondary CNS spinal tumors are: (i) tumor diagnosis, (ii) identification of the metabolically active tumor compartments (differentiation of viable tumor tissue from necrosis) and (iii) prediction of treatment response by measurement of tumor perfusion or ischemia. While spinal PET has been used under specific circumstances, a question remains as to whether the magnitude of biochemical alterations observed by MI in CNS tumors in general (specifically spinal tumors) can reveal any prognostic value with respect to survival. MI may be able to better identify early disease and to differentiate benign from malignant lesions than more traditional methods. Moreover, an adequate identification of treatment effectiveness may influence patient management. MI probes could be developed to image the function of targets without disturbing them or as treatment to modify the target's function. MI therefore closes the gap between in vitro and in vivo integrative biology of disease. At the spinal level, MI may help to detect progression or recurrence of metastatic disease after surgical treatment. In cases of nonsurgical treatments such as chemo-, hormone- or radiotherapy, it may better assess biological efficiency than conventional imaging modalities coupled with blood tumor markers. In fact, PET provides a unique possibility to correlate topography and specific metabolic activity, but it requires additional clinical and experimental experience and research to find new indications for primary or secondary spinal tumors.

Simultaneous 68Ga-DOTATOC-PET/MRI for IMRT treatment planning for meningioma: first experience

PURPOSE

To evaluate intensity-modulated radiotherapy (IMRT) treatment planning based on simultaneous positron-emission tomography and magnetic resonance imaging (PET/MRI) of meningioma.

METHODS AND MATERIALS

A meningioma patient was examined prior to radiotherapy with dedicated planning computed tomography (CT), MRI, PET/CT with gallium-68-labeled DOTATOC (68Ga-DOTATOC), and simultaneous 68Ga-DOTATOC-PET/MRI. The first gross target volume (GTV) was defined based on a combination of separate MR and 68Ga-DOTATOC-PET/CT imaging (GTVPET/CT+MR). Then, the simultaneous PET/MR images were used to delineate a second GTV (GTVPET/MR) by following exactly the same delineation strategy. After an isotropic expansion of those volumes by a 4-mm safety margin, the resulting planning target volumes (PTVs) were compared by calculating the intersection volume and the relative complements. A cross-evaluation of IMRT plans was performed, where the treatment plan created for the PTVPET/CT+MR was applied to the PET/MR-based PTVPET/MR.

RESULTS

Generally, target volumes for IMRT treatment planning did not differ between MRI plus 68Ga-DOTATOC-PET/CT and simultaneous PET/MR imaging. Only in certain regions of the GTV were differences observed. The overall volume of the PET/MR-based PTV was approximately the same as that obtained from PET/CT data. A small region of infiltrative tumor growth next to the main tumor mass was better visualized with combined PET/MR due to smaller PET voxel sizes and improved recovery. An IMRT treatment plan was optimized for the PTVPET/CT+MR. The evaluation of this plan with respect to the PTVPET/MR showed parts of the target volume that would not have received the full radiation dose after delineation of the tumor, based on simultaneous PET/MR.

CONCLUSION

This case showed that differences in target volumes delineated on the basis of separate MR and PET/CT and simultaneous PET/MR may be observed that can have significant consequences for an effectively applied radiotherapy treatment plan.

Automated production of [11C]acetate and [11C]palmitate using a modified GE Tracerlab FX(C-Pro)

As researchers explore new applications for positron emission tomography radiopharmaceuticals, the demand for effective and readily available radiopharmaceuticals continues to increase. The syntheses of two such radiopharmaceuticals, [(11)C]acetate and [(11)C]palmitate, can be automated on the GE Tracerlab FX(C-Pro) by utilizing Grignard reactions. Radiochemical purities of the [(11)C]acetate and the [(11)C]palmitate products were high (>98% and >99.9%, respectively) with average non-corrected yields of 18% (n = 3) and 10% (n = 5), respectively. These data comprise the validation trials for site qualification of clinical production of both radiopharmaceuticals.