Can the standardized uptake value characterize primary brain tumors on FDG-PET?

The Clinical Role of CXCR4-Targeted PET on Lymphoproliferative Disorders: A Systematic Review

Background/Objectives: We conducted a comprehensive investigation to explore the pathological expression of the CXCR4 receptor in lymphoproliferative disorders (LPDs) using [68Ga]Ga-Pentixafor PET/CT or PET/MRI technology. The PICO question was as follows: What is the diagnostic role (outcome) of [68Ga]Ga-Pentixafor PET (intervention) in patients with LPDs (problem/population)? Methods: The study was written based on the reporting items for systematic reviews and meta-analyses (PRISMA) 2020 guidelines, and it was registered on the prospective register of systematic reviews (PROSPERO) website (CRD42024506866). A comprehensive computer literature search of Scopus, MEDLINE, Scholar, and Embase databases was conducted, including articles indexed up to February 2024. To the methodological evaluation of the studies used the quality assessment of diagnosis accuracy studies-2 (QUADAS-2) tool. Results: Of the 8380 records discovered, 23 were suitable for systematic review. Fifteen studies (on 571 LPD patients) focused on diagnosis and staging, and eight trials (194 LPD patients) assessed treatment response. Conclusions: The main conclusions that can be inferred from the published studies are as follows: (a) [68Ga]Ga-Pentixafor PET may have excellent diagnostic performance in the study of several LPDs; (b) [68Ga]Ga-Pentixafor PET may be superior to [18F]FDG or complementary in some LPDs variants and settings; (c) multiple myeloma seems to have a high uptake of [68Ga]Ga-Pentixafor. Overall, this technique is probably suitable for imaging, staging, and follow-up on patients with LPD. Due to limited data, further studies are warranted to confirm the promising role of [68Ga]Ga-Pantixafor in this context.

Rewiring of cortical glucose metabolism fuels human brain cancer growth

The brain avidly consumes glucose to fuel neurophysiology. Cancers of the brain, such as glioblastoma (GBM), lose aspects of normal biology and gain the ability to proliferate and invade healthy tissue. How brain cancers rewire glucose utilization to fuel these processes is poorly understood. Here we perform infusions of 13 C-labeled glucose into patients and mice with brain cancer to define the metabolic fates of glucose-derived carbon in tumor and cortex. By combining these measurements with quantitative metabolic flux analysis, we find that human cortex funnels glucose-derived carbons towards physiologic processes including TCA cycle oxidation and neurotransmitter synthesis. In contrast, brain cancers downregulate these physiologic processes, scavenge alternative carbon sources from the environment, and instead use glucose-derived carbons to produce molecules needed for proliferation and invasion. Targeting this metabolic rewiring in mice through dietary modulation selectively alters GBM metabolism and slows tumor growth.

Significance

This study is the first to directly measure biosynthetic flux in both glioma and cortical tissue in human brain cancer patients. Brain tumors rewire glucose carbon utilization away from oxidation and neurotransmitter production towards biosynthesis to fuel growth. Blocking these metabolic adaptations with dietary interventions slows brain cancer growth with minimal effects on cortical metabolism.

Usefulness of dual isotope 123I-IMP and 201Tl SPECT for the diagnosis of primary central nervous system lymphoma and glioblastoma

BACKGROUND

Preoperative differential diagnosis between primary central nervous system lymphoma (PCNSL) and glioblastoma (GBM) is important because these tumors require different surgical strategies. This study investigated the usefulness of dual isotope, iodine-123-labeled N-isopropyl-p-iodo-amphetamine (¹²³I-IMP) and thallium-201 chloride single-photon emission computed tomography (²⁰¹Tl SPECT) for the differential diagnosis.

METHODS

Twenty-five PCNSL patients and 27 GBM patients who underwent dual isotope imaging, ¹²³I-IMP and ²⁰¹Tl SPECT, are included. Tumor-to-normal (T/N) ratio was calculated from the ratio of maximum tracer counts in the lesion to the mean counts in the contralateral cerebral cortex. The mean and minimum apparent diffusion coefficient values (ADC_mean and ADC_min, respectively) on magnetic resonance imaging were also analyzed.

RESULTS

Delayed phase ¹²³I-IMP SPECT was the most useful imaging examination for the differentiation between PCNSL and GBM compared with early phase ¹²³I-IMP SPECT, early and delayed phase ²⁰¹Tl SPECT, ADC_mean, and ADC_min. However, the median T/N ratios of PCNSL and GBM were 1.32 and 0.83, respectively, in the delayed phase ¹²³I-IMP SPECT. On the other hand, the median T/N ratios of PCNSL and GBM were 3.10 and 2.34, respectively, in the delayed phase ²⁰¹Tl SPECT, with excellent tumor detection.

CONCLUSION

Delayed phase ¹²³I-IMP SPECT could differentiate between PCNSL and GBM with high accuracy, but T/N ratio was low and tumor detection was poor. ²⁰¹Tl SPECT was useful for estimation of the malignancy and localization of the tumors with high T/N ratio. Dual isotope ¹²³I-IMP and ²⁰¹Tl SPECT was useful for the preoperative diagnosis of PCNSL and GBM.

CXCR4-Directed PET/CT with [68Ga]Pentixafor in Central Nervous System Lymphoma: A Comparison with [18F]FDG PET/CT

PURPOSE

This study aimed to evaluate the value of [⁶⁸ Ga]Pentixafor PET/CT for the detection of lesions in central nervous system lymphoma (CNSL) patients before chemotherapy, during treatment and suspected CSNL recurrence, compared with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) positron emission tomography/computed tomography (PET/CT).

PROCEDURES

Twenty-six patients with newly or previously diagnosed CNSL who underwent [⁶⁸ Ga]Pentixafor PET/CT were included retrospectively. Histopathological results, magnetic resonance imaging (MRI), and follow-up were used as the standard reference. The accuracy of lesion detection, maximum standardized uptake value (SUV_max) of tumors, and ratio of tumor-to-normal brain (T/N) with [⁶⁸ Ga]Pentixafor PET/CT were calculated and compared to those obtained with [¹⁸F]FDG PET/CT. CXCR4 expression was analyzed through immunohistochemistry.

RESULTS

Of 26 patients, 18 were newly diagnosed with a total of 23 lesions, 4 had recurrent with 4 lesions, and 4 underwent a mid-term treatment assessment after 4 cycles of chemotherapy (3 achieved complete response (CR), 1 experienced progressive disease (PD) with a total of 8 lesions). Thirty-five lesions were all clearly detected with favorable contrast by [⁶⁸ Ga]Pentixafor PET/CT (accuracy, 100%), consistent with the results of contrast-enhanced magnetic resonance imaging (CE-MRI). The SUV_max of positive lesions in [⁶⁸ Ga]Pentixafor PET/CT was correlated with tumor size (r = 0.555, P = 0.001). In 21 patients, compared with [¹⁸F]FDG PET/CT, [⁶⁸ Ga]Pentixafor PET/CT showed a remarkably higher T/N ratio (21.93 ± 10.77 vs 4.29 ± 2.16, P = 0.000) and detected 5 more lesions in the mid-term treatment assessment of patients (P = 0.026). The CXCR4 expression of CNSL lesions was correlated with SUV_max of [⁶⁸ Ga]Pentixafor PET/CT (r = 0.772, P = 0.000).

CONCLUSIONS

CXCR4-directed PET/CT using [⁶⁸ Ga]Pentixafor, with excellent tumor-to-background contrast, might be a more promising agent for the detection of lesions in CNSL patients than [¹⁸F]FDG PET/CT.

Brain [F-18]FDG PET for Clinical Dementia Workup: Differential Diagnosis of Alzheimer's Disease and Other Types of Dementing Disorders

PET imaging with [F-18]FDG has been used extensively for research and clinical applications in dementia. In the brain, [F-18]FDG accumulates around synapses and represents local neuronal activity. Patterns of altered [F-18]FDG uptake reflecting local neuronal dysfunction provide differential diagnostic clues for various dementing disorders. Image interpretation can be accomplished by employing statistical brain mapping techniques. Various guidelines have been published to support the appropriate use of [F-18]FDG PET for clinical dementia workup. PET images with [F-18]FDG demonstrate distinct patterns of decreased uptake for Alzheimer's disease (AD), Dementia with Lewy bodies (DLB), and frontotemporal dementia (FTD) as well as its multiple subtypes such as behavioral variant FTD, primary progressive aphasia (PPA), progressive supranuclear palsy, and corticobasal degeneration to aid in the differential diagnoses. Mixed dementia, not only AD + Vascular Dementia, but also AD + other neurodegenerative disorders, should also be considered when interpreting [F-18]FDG PET images. Brain PET imaging with [F-18]FDG remains a valuable component of dementia workup owing to its relatively low cost, differential diagnostic performance, widespread availability, and physicians' experience over more than 40 years since the initial development.

Subretinally injected semiconducting polymer nanoparticles rescue vision in a rat model of retinal dystrophy

Inherited retinal dystrophies and late-stage age-related macular degeneration, for which treatments remain limited, are among the most prevalent causes of legal blindness. Retinal prostheses have been developed to stimulate the inner retinal network; however, lack of sensitivity and resolution, and the need for wiring or external cameras, have limited their application. Here we show that conjugated polymer nanoparticles (P3HT NPs) mediate light-evoked stimulation of retinal neurons and persistently rescue visual functions when subretinally injected in a rat model of retinitis pigmentosa. P3HT NPs spread out over the entire subretinal space and promote light-dependent activation of spared inner retinal neurons, recovering subcortical, cortical and behavioural visual responses in the absence of trophic effects or retinal inflammation. By conferring sustained light sensitivity to degenerate retinas after a single injection, and with the potential for high spatial resolution, P3HT NPs provide a new avenue in retinal prosthetics with potential applications not only in retinitis pigmentosa, but also in age-related macular degeneration.

Clinicopathological characteristics of primary central nervous system lymphoma with low 18F-fludeoxyglucose uptake on brain positron emission tomography

Primary central nervous system lymphoma (PCNSL) typically shows a strong uptake of F-fludeoxyglucose (FDG) imaged by positron emission tomography (PET). Uncommonly, PCNSL demonstrates a low uptake on FDG PET. We investigated the clinicopathological characteristics of the unusual cases of PCNSL with low FDG uptake.We retrospectively enrolled 104 consecutive patients with newly diagnosed PCNSL who underwent baseline brain FDG PET. The degree of FDG uptake of PCNSL was visually scored by 4 grades (0, ≤contralateral white matter; 1, >contralateral white matter and <contralateral gray matter; 2, = contralateral gray matter; 3, >contralateral gray matter). Grades 0-2 were considered as PCNSL with low uptake. We investigated association of low uptake of PCNSL with the following clinicopathological factors: age, sex, steroid treatment, lactate dehydrogenase level, cerebrospinal fluid protein level, condition of PET scanning, immunohistochemical markers (cluster of differentiation 10 [CD10], B-cell lymphoma 6 [BCL-6], B-cell lymphoma 2 [BCL-2], multiple myeloma oncogene 1 [MUM1], Epstein-Barr virus [EBV] protein, and Ki67), location of lesions, tumor size, multiplicity of lesions, involvement of deep brain structures, and cystic or necrotic appearance of lesions.Of the 104 patients with PCNSL, 14 patients (13.5%) showed PCNSL with low FDG uptake on PET. Among various clinicopathological factors, MUM1 negativity was the only factor associated with low FDG uptake PCNSL by univariate (P = .002) and multivariate analysis (P = .007).This study suggests that the different clinicopathological characteristics between patients with high uptake and low uptake of PCNSL on FDG PET is closely associated with lack of MUM1, a protein known to be a crucial regulator of B-cell development and tumorigenesis.

Contribution of Different Positron Emission Tomography Tracers in Glioma Management: Focus on Glioblastoma

Although rare, glioblastomas account for the majority of primary brain lesions, with a dreadful prognosis. Magnetic resonance imaging (MRI) is currently the imaging method providing the higher resolution. However, it does not always succeed in distinguishing recurrences from non-specific temozolomide, have been shown to improve -related changes caused by the combination of radiotherapy, chemotherapy, and targeted therapy, also called pseudoprogression. Strenuous attempts to overcome this issue is highly required for these patients with a short life expectancy for both ethical and economic reasons. Additional reliable information may be obtained from positron emission tomography (PET) imaging. The development of this technique, along with the emerging of new classes of tracers, can help in the diagnosis, prognosis, and assessment of therapies. We reviewed the current data about the commonly used tracers, such as 18F-fluorodeoxyglucose (18F-FDG) and radiolabeled amino acids, as well as different PET tracers recently investigated, to report their strengths, limitations, and relevance in glioblastoma management.

Diagnostic value of fusion of metabolic and structural images for stereotactic biopsy of brain tumors without enhancement after contrast medium injection

BACKGROUND

The heterogeneous nature of glioma makes it difficult to select a target for stereotactic biopsy that will be representative of grade severity on non-contrast-enhanced lesion imaging. The objective of this study was to evaluate the benefit of fusion of metabolic images (PET 18F-DOPA) with magnetic resonance imaging (MRI) morphological images for cerebral biopsy under stereotactic conditions of glioma without contrast enhancement.

PATIENTS AND METHODS

This single-center prospective observational study conducted between January 2016 and April 2018 included 20 consecutive patients (mean age: 45±19.5 years; range, 9-80 years) who underwent cerebral biopsy for a tumor without MRI enhancement but with hypermetabolism on ¹⁸F-FDOPA PET (positron emission tomography). Standard ¹⁸F-FDOPA uptake value (SUV_max) was determined for diagnosis of high-grade glioma, with comparison to histomolecular results.

RESULTS

Histological diagnosis was made in all patients (100%). Samples from hypermetabolism areas revealed high-grade glial tumor in 16 patients (80%). For a SUV_max threshold of 1.75, sensitivity was 81.2%, specificity 50%, PPV 86.7% and VPN 40% for diagnosis of high-grade glioma. No significant association between SUV_max and histomolecular mutation was found.

CONCLUSION

¹⁸F-FDOPA metabolic imaging is an aid in choosing the target to be biopsied under stereotactic conditions in tumors without MR enhancement. Nevertheless, despite good sensitivity, ¹⁸F-FDOPA PET is insufficient for definitive diagnosis of high-grade tumor.

Interplay between spinal cord and cerebral cortex metabolism in amyotrophic lateral sclerosis

We recently reported the potential of Hough transform in delineating spinal cord metabolism by ¹⁸F-fluorodeoxyglucose PET/CT scanning in amyotrophic lateral sclerosis. The present study aimed to verify the relationship between spinal cord and brain metabolism in 44 prospectively recruited patients affected by amyotrophic lateral sclerosis submitted to ¹⁸F-fluorodeoxyglucose brain and whole-body PET/CT. Patients were studied to highlight the presence of brain hypo- or hypermetabolism with respect to healthy controls, and multiple regression analysis was performed to evaluate the correlation between spinal cord and brain metabolism. Our results confirmed higher ¹⁸F-fluorodeoxyglucose uptake in both cervical and dorsal spinal cord in patients with amyotrophic lateral sclerosis with respect to controls. This finding was paralleled by the opposite pattern in the brain cortex that showed a generalized reduction in tracer uptake. This hypometabolism was particularly evident in wide regions of the frontal-dorsolateral cortex while it did not involve the midbrain. Bulbar and spinal disease onset was associated with similar degree of metabolic activation in the spinal cord. However, among spinal onset patients, upper limb presentation was associated with a more pronounced metabolic activation of cervical segment. Obtained data suggest a differential neuro-pathological state or temporal sequence in disease progression.

Metabolic regional and network changes in Alzheimer's disease subtypes

Clinical variants of Alzheimer's disease (AD) include the common amnestic subtype as well as subtypes characterised by leading visual processing impairments or by multimodal neurocognitive deficits. We investigated regional metabolic patterns and networks between AD subtypes. The study comprised 9 age-matched controls and 25 patients with mild to moderate AD. Methods included clinical and neuropsychological assessment, high-resolution FDG PET and T1-weighted 3D MR imaging with PET-MR coregistration, grey matter segmentation, atlas-based regions-of-interest, linear mixed effects and regional correlation analysis. Regional metabolic patterns differed significantly between groups, but significant hypometabolism in the posterior cingulate cortex (PCC) was common to all subtypes. The most distinctive regional abnormality was occipital hypometabolism in the visual subtype. In controls, two large clusters of positive regional metabolic correlations were observed. The most pronounced breakdown of the normal correlation pattern was found in amnestic patients who, in contrast, showed the least regional focal metabolic deficits. The normal positive correlation between PCC and hippocampus was lost in all subtypes. In conclusion, PCC hypometabolism and metabolic correlation breakdown between PCC and hippocampus are the common functional core of all AD subtypes. Network alterations exceed focal regional impairment and are most prominent in the amnestic subtype.

18F-FDG PET/CT in primary brain lymphoma

The actual role of 18F-FDG PET/CT in evaluating primary brain lymphoma is still an open issue. Brain lymphoma usually show elevated 18F-FDG uptake, often higher than other brain tumors or inflammatory processes, but the metabolic behavior of this lymphoma is not still understood. Our aim was to investigate the particular metabolic behavior of this lymphoma. Forty six patients (21 female, 25 male) with histologically-confirmed brain lymphoma who underwent 18F-FDG PET/CT from vertex to the mid-thigh for initial staging were retrospectively evaluated. The PET images were analyzed visually and semi-quantitatively by measuring the maximum standardized uptake value (SUVmax), lesion-to-liver SUVmax ratio, lesion-to-blood pool SUVmax ratio and the tumor to normal brain uptake ratio (T/N ratio) and compared with epidemiological (age, sex, HIV infection) and morphological (tumor size, MRI appearance) characteristics. Thirty-eight patients (83%) had positive 18F-FDG PET/CT (average SUVmax was 15.6 ± 9.2; lesion-to-liver SUVmax ratio 5.8 ± 2.8; lesion-to-blood pool SUVmax ratio 7.1 ± 3.8, T/N ratio 3.1 ± 1.7) at the corresponding brain lesion; the remaining 8 (17%) were not 18F-FDG avid. 18F-FDG avidity was significantly associated with morphological appearance and tumor size and not correlated with other features. 18F-FDG PET/CT detected extracranial disease in two cases (4%) with negative bone marrow biopsies and CT. In conclusion, brain lymphomas are 18F-FDG avid in 83% of cases showing high 18F-FDG uptake and 18F-FDG avidity is correlated with tumor size and morphological appearance of the lesion. PET/CT helped to recognize extracranial disease in two patients.

A new diagnostic marker for differentiating multicentric gliomas from multiple intracranial diffuse large B-cell lymphomas on 18F-FDG PET images

Intracranial gliomas and lymphomas may share similar radiological manifestations, while the treatment strategies for them are different. The aim of the study was to investigate the diagnostic value of fluorine-18-fluoro-2-deoxy-D-glucose (F-FDG) positron emission computed tomography (PET) for differentiation of multicentric gliomas and intracranial multiple diffuse large B-cell lymphomas (DLBCLs) as a study of diagnostic accuracy.A total of 32 patients with multiple intracranial tumors visualized on contrast-enhanced magnetic resonance imaging (MRI) were retrospectively evaluated. Histopathological findings confirmed multicentric gliomas and multiple DLBCLs in 17 and 15 patients, respectively. All patients underwent F-FDG PET with or without C-methionine PET. Maximum standardized uptake values (SUVmax) and tumor-to-normal tissue (T/N) ratios were compared between the 2 tumors. The diagnostic value of F-FDG PET for differentiating multicentric gliomas from multiple DLBCLs was evaluated by receiver operating characteristic (ROC) analysis.The SUVmax of multiple DLBCLs was significantly higher than that of multicentric gliomas (P = .009). However, the percentage of maximum difference-value of SUVmax (or T/N ratio) of multiple DLBCLs was significant lower than that of multicentric gliomas (P < .001). The ROC curve demonstrated that the percentage of maximum difference-value of SUVmax (or T/N ratio) on F-FDG PET images could effectively differentiate multicentric gliomas from multiple DLBCLs, with a cut-off value of 44.4%, sensitivity of 64.7%, and specificity of 100% (P < .001).Percentage of maximum difference-value of SUVmax (or T/N ratio) on F-FDG PET images might be a potential indicator for distinguishing multicentric gliomas from intracranial multiple DLBCLs, which might help determine the treatment strategy.

A fully organic retinal prosthesis restores vision in a rat model of degenerative blindness

The degeneration of photoreceptors in the retina is one of the major causes of adult blindness in humans. Unfortunately, no effective clinical treatments exist for the majority of retinal degenerative disorders. Here we report on the fabrication and functional validation of a fully organic prosthesis for long-term in vivo subretinal implantation in the eye of Royal College of Surgeons rats, a widely recognized model of retinitis pigmentosa. Electrophysiological and behavioural analyses reveal a prosthesis-dependent recovery of light sensitivity and visual acuity that persists up to 6-10 months after surgery. The rescue of the visual function is accompanied by an increase in the basal metabolic activity of the primary visual cortex, as demonstrated by positron emission tomography imaging. Our results highlight the possibility of developing a new generation of fully organic, highly biocompatible and functionally autonomous photovoltaic prostheses for subretinal implants to treat degenerative blindness.

Application of PET/CT in treatment response evaluation and recurrence prediction in patients with newly-diagnosed multiple myeloma

Multiple myeloma (MM) causes osteolytic lesions which can be detected by 18F-fluorodeoxyglucose positron emission tomography/Computed tomography (18F-FDG PET/CT). We prospectively involve 96 Newly diagnosed MM to take PET/CT scan at scheduled treatment time (figure 1), and 18F-FDG uptake of lesion was measured by SUVmax and T/Mmax. All MM patients took bortezomib based chemotherapy as induction and received ASCT and maintenance. All clinical features were analyzed with the PET/CT image changes, and some relationships between treatment response and FDG uptakes changes were found: Osteolytic lesions of MM uptakes higher FDG than healthy volunteers, and this trend is more obvious in extramedullary lesions. Compared to X-ray, PET/CT was more sensitive both in discoering bone as well as extramedullary lesions. In newly diagnosed MM, several adverse clinical factors were related to high FDG uptakes of bone lesions. Bone lesion FDG uptakes of MM with P53 mutation or with hypodiploidy and complex karyotype were also higher than those without such changes. In treatment response, PET/CT showed higher sensitivity in detecting tumor residual disease than immunofixation electrophoresis. But in relapse prediction, it might show false positive disease recurrences and the imaging changes might be influenced by infections and hemoglobulin levels. Conclusion: PET/CT is sensitive in discovering meduallary and extrameduallary lesions of MM, and the 18F-FDG uptake of lesions are related with clinical indictors and biological features of plasma cells. In evaluating treatment response and survival, PET/CT showed its superiority. But in predicting relapse or refractory, it may show false positive results.

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.

Glucose-corrected standardized uptake value in the differentiation of high-grade glioma versus post-treatment changes

Background

Standardized uptake values (SUVs) of fluorine-18 fluorodeoxyglucose PET (¹⁸F-FDG PET) are used widely to differentiate residual or recurrent high-grade gliomas from post-treatment changes in patients with brain tumors. The aim of this study is to assess the accuracy of SUV corrected by blood glucose level (SUV_gluc) compared with various quantitative methods in this role.

Materials and methods

In 55 patients with dynamic ¹⁸F-FDG PET scans, there were 97 glioma lesions: glioblastoma (n=60), grade III gliomas (n=22), grade III or IV gliomas (n=6), grade I/II (n=7), and prebiopsy lesions (n=2). The final actual diagnosis was made on the basis of pathology (n=33) and clinical outcome (n=64). Dynamic ¹⁸F-FDG PET scans were processed to generate parametric images of SUV_gluc, SUV_max, and glucose metabolic rate (GMR). Lesion to cerebellum ratios (SUV_Rc) and contralateral white matter ratios (SUV_Rw) were also measured. The SUV_gluc was calculated as SUV_max×blood glucose level/100.

Results

Using the thresholds of SUV_max>4.6, SUV_Rc>0.9, SUV_Rw>1.8, SUV_gluc>4.3, and GMR>12.2 μmol/min/100 g to represent positivity for viable tumors, the accuracies were the same for the SUV_gluc and SUV_Rw (80%) and were higher than the conventional SUV_max (72%). The area under the receiver operating characteristic curve for the SUV_gluc (0.8933) was better than that for the SUV_max (0.8266) (P<0.01) and was similar to those of the GMR (0.8622), SUV_Rc (0.8606), and SUV_Rw (0.8981).

Conclusion

These results suggest that SUV_gluc may aid in the differentiation of residual or recurrent high-grade tumor from post-treatment changes in patients with abnormal blood glucose levels. The simplicity of the SUV_gluc avoids the complexity of kinetic analysis or the requirement of a reference tissue.

The use of 18F-FDG PET ratios in the differential diagnosis of common malignant brain tumors

OBJECTIVE

This study examined the use of positron emission tomography (PET) ratios to improve the diagnostic ability of 18F-FDG PET/computed tomography (CT) in the differentiation of enhancing brain metastases, central nervous system lymphomas, and gliomas.

MATERIALS AND METHODS

Seventy-six patients with malignant brain tumors and available magnetic resonance imaging and PET/CT examinations were included.

RESULTS

Among standardized uptake value (SUV)-related parameters tested, tumor maximum SUV to ipsilateral cortex maximum SUV ratio (Tmax:WMimax) and maximum SUV (SUVmax) proved to be the two most valuable parameters for differential diagnosis.

CONCLUSION

In addition to SUVmax, Tmax:WMimax also seems to provide helpful information for the differential diagnosis of lymphomas from other malignant brain tumors.

Pitfalls in the neuroimaging of glioblastoma in the era of antiangiogenic and immuno/targeted therapy - detecting illusive disease, defining response

Glioblastoma, the most common malignant primary brain tumor in adults is a devastating diagnosis with an average survival of 14–16 months using the current standard of care treatment. The determination of treatment response and clinical decision making is based on the accuracy of radiographic assessment. Notwithstanding, challenges exist in the neuroimaging evaluation of patients undergoing treatment for malignant glioma. Differentiating treatment response from tumor progression is problematic and currently combines long-term follow-up using standard magnetic resonance imaging (MRI), with clinical status and corticosteroid-dependency assessments. In the clinical trial setting, treatment with gene therapy, vaccines, immunotherapy, and targeted biologicals similarly produces MRI changes mimicking disease progression. A neuroimaging method to clearly distinguish between pseudoprogression and tumor progression has unfortunately not been found to date. With the incorporation of antiangiogenic therapies, a further pitfall in imaging interpretation is pseudoresponse. The Macdonald criteria that correlate tumor burden with contrast-enhanced imaging proved insufficient and misleading in the context of rapid blood–brain barrier normalization following antiangiogenic treatment that is not accompanied by expected survival benefit. Even improved criteria, such as the RANO criteria, which incorporate non-enhancing disease, clinical status, and need for corticosteroid use, fall short of definitively distinguishing tumor progression, pseudoresponse, and pseudoprogression. This review focuses on advanced imaging techniques including perfusion MRI, diffusion MRI, MR spectroscopy, and new positron emission tomography imaging tracers. The relevant image analysis algorithms and interpretation methods of these promising techniques are discussed in the context of determining response and progression during treatment of glioblastoma both in the standard of care and in clinical trial context.

Regional cerebral18FDG uptake during subarachnoid hemorrhage induced vasospasm

OBJECTIVES

The aim was to elucidate whether aneurysmal subarachnoid hemorrhage (SAH)-induced vasospasm induces changes of regional glucose uptake in surgically treated, asymptomatic cases.

METHODS

(18)FDG uptake (standardized uptake value, SUV) was analysed with PET in eight surgically treated aneurismal patients with a mean middle cerebral artery flow velocity >120 cm/seconds measured with transcranial Doppler ultrasound. Data were compared with a healthy control group using Statistical Parametric Mapping (SPM99b).

RESULTS

Six of the eight patients had no focal neurological signs. The inhomogeneous bilateral increase in SUV (p<0.0001) was asymmetrical, with an almost 70% larger volume on the operated side. Reduced glucose uptake was found in the frontal and temporobasal regions of the two patients with neurological deficits (p<0.0001); the affected volume was 40% larger on the operated side.

DISCUSSION

SAH-induced vasospasm results in widespread increase of glucose uptake-probably reflecting increased glycolysis. This was earlier than neurological focal signs appear. Decreased glucose uptake can be detected in severe cases of vasospasm reflected by neurological deficit. Although the changes are more prominent where surgery had taken place our results suggest that not only the surgery, but also subarachnoid blood might have resulted in our findings.

A meta-analysis on the diagnostic performance of (18)F-FDG and (11)C-methionine PET for differentiating brain tumors

SUMMARY

(18)F-FDG-PET has been widely used in patients with brain tumors. However, the reported sensitivity and specificity of (18)F-FDG-PET for brain tumor differentiation varied greatly. We performed this meta-analysis to systematically assess the diagnostic performance of (18)F-FDG-PET in differentiating brain tumors. The diagnostic performance of (11)C-methionine PET was assessed for comparison. Relevant studies were searched in PubMed/MEDLINE, Scopus, and China National Knowledge Infrastructure (until February 2013). The methodologic quality of eligible studies was evaluated, and a meta-analysis was performed to obtain the combined diagnostic performance of (18)F-FDG and (11)C-methionine PET with a bivariate model. Thirty eligible studies, including 5 studies with both (18)F-FDG and (11)C-methionine PET data were enrolled. Pooled sensitivity, pooled specificity, and area under the receiver operating characteristic curve of (18)F-FDG-PET (n = 24) for differentiating brain tumors were 0.71 (95% CI, 0.63-0.78), 0.77 (95% CI, 0.67-0.85), and 0.80. Heterogeneity was found among (18)F-FDG studies. Subsequent subgroup analysis revealed that the disease status was a statistically significant source of the heterogeneity and that the sensitivity in the patients with recurrent brain tumor was markedly higher than those with suspected primary brain tumors. Pooled sensitivity, pooled specificity, and area under the receiver operating characteristic of (11)C-methionine PET (n = 11) were 0.91 (95% CI, 0.85-0.94), 0.86 (95% CI, 0.78-0.92), and 0.94. No significant statistical heterogeneity was found among (11)C-methionine studies. This meta-analysis suggested that (18)F-FDG-PET has limited diagnostic performance in brain tumor differentiation, though its performance may vary according to the status of brain tumor, whereas (11)C-methionine PET has excellent diagnostic accuracy in brain tumor differentiation.

18F-FDG PET in the diagnosis and treatment of primary central nervous system lymphoma

This paper summarizes the usefulness and limitation of positron emission tomography (PET) with (18)F-fluorodeoxyglucose ((18)F-FDG) in the diagnosis and treatment of primary central nervous system lymphoma (PCNSL). The (18)F-FDG uptake in typical PCNSL is about 2.5 times higher than that in the normal gray matter, and the tumor can usually be identified visually. The (18)F-FDG uptake pattern and value provide useful information for differentiating PCNSL from other enhancing malignant brain tumors especially glioblastoma (GB). The (18)F-FDG uptake in typical PCNSL is usually homogenous, and the uptake value is significantly higher than that in GB. However, (18)F-FDG PET often fails to show the presence of tumor in the brain as (18)F-FDG uptake is faint in atypical PCNSL such as disseminated or nonenhancing lesions. (18)F-FDG PET is also useful for evaluating the treatment response at a very early stage after the initial treatment. Pretreatment and posttreatment (18)F-FDG uptake values may have a prognostic value in patients with PCNSL. In conclusion, (18)F-FDG PET is very useful in the diagnosis of typical PCNSL and can differentiate PCNSL from other malignant brain tumors. However, the usefulness of (18)F-FDG PET is limited in the diagnosis of atypical PCNSL.

Role of (18)F-fluorodeoxyglucose Positron Emission Tomography scan in differentiating enhancing brain tumors

Aim:

To determine whether F-18-fluorodeoxyglucose positron emission tomography (F-18-FDG PET) can be used to differentiate among common enhancing brain tumors such as gliomas, metastatic brain tumors, and lymphoma.

Materials and Methods:

We evaluated 20 patients with an enhancing brain tumor on magnetic resonance imaging (MRI). FDG PET scan was done in all patients pre operatively. For PET image analysis, regions of interest were placed over the tumor (T), contralateral cortex (C), and white matter (WM). Average and maximum pixel values were determined at each site. On the basis of these measurements, average and maximum standard uptake values (SUV _avg and SUV _max ) were calculated, and comparisons among lesions were then made.

Results:

SUV_avg and SUV_max are significantly higher for central nervous system (CNS) lymphoma than for other tumors (P < 0.01). High-grade gliomas showed significantly higher SUV_avg and SUV_max than the low grade gliomas (P < 0.05) and metastatic tumor showed higher SUV_avg and SUV_max than all gliomas, both low and high grade (P < 0.05). When the lowest values of CNS lymphoma parameter were used as cutoff levels to distinguish CNS lymphomas from other tumors (i.e. 100% sensitivity), SUV_max was the most accurate parameter. Using a SUV_max of 15.0 as a cutoff for diagnosing CNS lymphoma, only one case of metastasis (SUV _max , 16.3) was found to be false positive in this study.

Conclusion:

FDG PET appears to provide additional information for differentiating common enhancing malignant brain tumors, namely lymphoma versus high grade glioma and metastatic tumor, particularly when differential diagnoses are difficult to narrow using MRI alone.

Brain tumors

This review addresses the specific contributions of nuclear medicine techniques, and especially positron emission tomography (PET), for diagnosis and management of brain tumors. (18)F-Fluorodeoxyglucose PET has particular strengths in predicting prognosis and differentiating cerebral lymphoma from nonmalignant lesions. Amino acid tracers including (11)C-methionine, (18)F-fluoroethyltyrosine, and (18)F-L-3,4-dihydroxyphenylalanine provide high sensitivity, which is most useful for detecting recurrent or residual gliomas, including most low-grade gliomas. They also play an increasing role for planning and monitoring of therapy. (18)F-fluorothymidine can only be used in tumors with absent or broken blood-brain barrier and has potential for tumor grading and monitoring of therapy. Ligands for somatostatin receptors are of particular interest in pituitary adenomas and meningiomas. Tracers to image neovascularization, hypoxia, and phospholipid synthesis are under investigation for potential clinical use. All methods provide the maximum of information when used with image registration and fusion display with contrast-enhanced magnetic resonance imaging scans. Integration of PET and magnetic resonance imaging with stereotactic neuronavigation systems allows the targeting of stereotactic biopsies to obtain a more accurate histologic diagnosis and better planning of conformal and stereotactic radiotherapy.

Biopsy validation of 18F-DOPA PET and biodistribution in gliomas for neurosurgical planning and radiotherapy target delineation: results of a prospective pilot study

BACKGROUND

Delineation of glioma extent for surgical or radiotherapy planning is routinely based on MRI. There is increasing awareness that contrast enhancement on T1-weighted images (T1-CE) may not reflect the entire extent of disease. The amino acid tracer (18)F-DOPA (3,4-dihydroxy-6-[18F] fluoro-l-phenylalanine) has a high tumor-to-background signal and high sensitivity for glioma imaging. This study compares (18)F-DOPA PET against conventional MRI for neurosurgical biopsy targeting, resection planning, and radiotherapy target volume delineation.

METHODS

Conventional MR and (18)F-DOPA PET/CT images were acquired in 10 patients with suspected malignant brain tumors. One to 3 biopsy locations per patient were chosen in regions of concordant and discordant (18)F-DOPA uptake and MR contrast enhancement. Histopathology was reviewed on 23 biopsies. (18)F-DOPA PET was quantified using standardized uptake values (SUV) and tumor-to-normal hemispheric tissue (T/N) ratios.

RESULTS

Pathologic review confirmed glioma in 22 of 23 biopsy specimens. Thirteen of 16 high-grade biopsy specimens were obtained from regions of elevated (18)F-DOPA uptake, while T1-CE was present in only 6 of those 16 samples. Optimal (18)F-DOPA PET thresholds corresponding to high-grade disease based on histopathology were calculated as T/N > 2.0. In every patient, (18)F-DOPA uptake regions with T/N > 2.0 extended beyond T1-CE up to a maximum of 3.5 cm. SUV was found to correlate with grade and cellularity.

CONCLUSIONS

(18)F-DOPA PET SUV(max) may more accurately identify regions of higher-grade/higher-density disease in patients with astrocytomas and will have utility in guiding stereotactic biopsy selection. Using SUV-based thresholds to define high-grade portions of disease may be valuable in delineating radiotherapy boost volumes.

PET Parametric Response Mapping for Clinical Monitoring and Treatment Response Evaluation in Brain Tumors

PET parametric response maps (PRMs) are a provocative new molecular imaging technique for quantifying brain tumor response to therapy in individual patients. By aligning sequential PET scans over time using anatomic MR imaging information, the voxel-wise change in radiotracer uptake can be quantified and visualized. PET PRMs can be performed before and after a particular therapy to test whether the tumor is responding favorably, or performed relative to a distant time point to monitor changes through the course of a treatment. This article focuses on many of the technical details involved in generating, visualizing, and quantifying PET PRMs, and practical applications and example case studies.

Independent prognostic value of pre-treatment 18-FDG-PET in high-grade gliomas

The prognostic value of PET with (18F)-fluoro-2-deoxy-D: -glucose (FDG) has been shown in high-grade gliomas (HGG), but not compared with consensual prognostic factors. We sought to evaluate the independent predictive value of pre-treatment FDG-PET on overall (OS) and event-free survival (EFS). We retrospectively analyzed 41 patients with histologically-confirmed HGG (31 glioblastomas and 10 anaplastic gliomas). The pre-treatment uptake of FDG was assessed qualitatively by five-step visual metabolic grading, and quantitatively by the ratio between the tumor and contralateral maximal standardized uptake value (T/CL). EFS and OS following PET were compared with FDG uptake by univariate analysis, and by two multivariate analyses: one including main consensual prognostic factors (age, KPS, extent of surgery and histological grade), and the other including the classification system of the Radiation Therapy Oncology Group (Recursive Partitioning Analysis, RPA). Median OS and EFS were 13.8 and 7.4 months, respectively, for glioblastomas, and over 25.8 and 12 months, respectively, for anaplastic gliomas (P = 0.040 and P = 0.027). The T/CL ratio predicted OS in the entire group [P = 0.003; Hazard Ratio (HR) = 2.3] and in the glioblastoma subgroup (P = 0.018; HR = 2), independently of age, Karnofsky performance status, histological grade, and surgery, and independently of RPA classification. T/CL ratio tended to predict EFS in the whole group (P = 0.052). The prognostic value of visual metabolic grade on OS was less significant than T/CL ratio, both in the entire group and in the glioblastoma subgroup (P = 0.077 and P = 0.059). Quantitative evaluation of the ratio between the maximal tumor and contralateral uptake in pre-treatment FDG-PET provides significant additional prognostic information in newly-diagnosed HGG, independently of consensual prognostic factors.

PET in Brain Tumors

Evaluating gliomas, either at diagnosis or at recurrence, is among the historical indications of FDG positron emission tomography (PET) imaging. There is a clear relationship between the tumor grade, patient prognosis, and intensity of uptake. Yet the exact role of FDG PET imaging remains debated. PET and methionine labeled with the short-lived C11 also have been proposed, with the significant advantage of high tumor-to-cortex contrast and distinct bological properties that lead to specific indications. Clinical use of this tracer is hampered by the need for an on-site cyclotron, however. In recent years, the increased availability of fluorinated amino-acid analogs, in particular FET, has open the way to renewed scientific interest in the field of neuro-oncological PET and PET/CT. This article discusses FDG and alternative tracers for diagnosing and characterizing primary brain tumors, detecting their recurrences, helping to guide the radiation therapy, and for evaluating the response to treatments.

Normoglycemic plasma glucose levels affect F-18 FDG uptake in the brain

OBJECTIVE

The aim of this study was to investigate whether normoglycemic glucose concentrations interfere with cerebral F-18 FDG uptake.

METHODS

The analysis was based on 2 sets of paired PET scans in 94 patients who were in complete metabolic remission after the successful completion of treatment for lymphoma. For these 188 PET scans, 2 subgroups were defined according to the plasma glucose level at the time of scanning. Group 1 contained the PET images that were associated with the lower of both normoglycemic plasma glucose levels, whereas group 2 contained the PET images that were associated with the higher of both plasma glucose levels. SUVs (standard uptake values) in the cerebellum between both groups were compared using paired sample T test. Subsequently, SUVs were normalized to a standard glucose concentration and normalized SUVs were again compared. Further, we calculated the coefficient of variation of SUVs in group 1 and 2 both before and after the normalization step.

RESULTS

Mean plasma glucose level was 86 mg/dL (SD of 9 mg/dL) in group 1 and 97 mg/dL (SD of 10 mg/dL) in group 2. Mean SUV was 3.8 (SD of 1.1) for group 1 and 3.5 (SD of 1.1) for group 2. Mean SUV in group 1 was slightly but statistically significantly higher than the mean SUV in group 2 (p < 0.01). Mean normalized SUV was 3.6 (SD of 1.1) in group 1 and 3.7 (SD of 1.3) in group 2. A paired comparison between normalized SUVs in both groups indicated that there was no statistically significant difference (p < 0.31). The coefficient of variation for the SUVs in group 1 and 2 before normalization was 29 and 30%, respectively. The coefficient of variation for the normalized SUVs in group 1 and 2 was 30 and 34%, respectively.

CONCLUSIONS

Our results indicated that plasma glucose levels that are within the normoglycemic range have a small but systematic effect on F-18 FDG uptake in the brain (following an inverse relationship). Normalizing plasma glucose levels to a standard glucose concentration successfully reduced the intra-subject variability of SUV measures. Inter-subject variability, however, remained high suggesting that other factors have an influence as well.

Molecular imaging (PET) of brain tumors

Despite the recognized limitations of (18)Fluorodeoxyglucose positron emission tomography (FDG-PET) in brain tumor imaging due to the high background of normal gray matter, this imaging modality provides critical information for the management of patients with cerebral neoplasms with regard to the following aspects: (1) providing a global picture of the tumor and thus guiding the appropriate site for stereotactic biopsy, and thereby enhancing its accuracy and reducing the number of biopsy samples; and (2) prediction of biologic behavior and aggressiveness of the tumor, thereby aiding in prognosis. Another area, which has been investigated extensively, includes differentiating recurrent tumor from treatment-related changes (eg, radiation necrosis and postsurgical changes). Furthermore, FDG-PET has demonstrated its usefulness in differentiating lymphoma from toxoplasmosis in patients with acquired immune deficiency syndrome with great accuracy, and is used as the investigation of choice in this setting. Image coregistration with magnetic resonance imaging and delayed FDG-PET imaging are 2 maneuvers that substantially improve the accuracy of interpretation, and hence should be routinely employed in clinical settings. In recent years an increasing number of brain tumor PET studies has used other tracers (like labeled methionine, tyrosine, thymidine, choline, fluoromisonidazole, EF5, and so forth), of which positron-labeled amino acid analogues, nucleotide analogues, and the hypoxia imaging tracers are of special interest. The major advantage of these radiotracers over FDG is the markedly lower background activity in normal brain tissue, which allows detection of small lesions and low-grade tumors. The promise of the amino acid PET tracers has been emphasized due to their higher sensitivity in imaging recurrent tumors (particularly the low-grade ones) and better accuracy for differentiating between recurrent tumors and treatment-related changes compared with FDG. The newer PET tracers have also shown great potential to image important aspects of tumor biology and thereby demonstrate ability to forecast prognosis. The value of hypoxia imaging tracers (such as fluoromisonidazole or more recently EF5) is substantial in radiotherapy planning and predicting treatment response. In addition, they may play an important role in the future in directing and monitoring targeted hypoxic therapy for tumors with hypoxia. Development of optimal image segmentation strategy with novel PET tracers and multimodality imaging is an approach that deserves mention in the era of intensity modulated radiotherapy, and which is likely to have important clinical and research applications in radiotherapy planning in patients with brain tumor.

18F-fluorodeoxyglucose positron emission tomography imaging in brain tumours: the Western Australia positron emission tomography/cyclotron service experience

(18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) scans in the first 49 patients referred with either possible brain tumour or brain tumour recurrence were reviewed. FDG-PET imaging was reported with reference to anatomical imaging. Based on the report the FDG study was classified as either positive or negative for the presence of tumour. Thirty-eight cases were included in the analysis, 21 having pathological data and 17 with diagnostic clinical follow up. Eleven were excluded, as they had inadequate follow-up data. Of the 21 cases with pathology, 18 were shown to have tumour. In this group there were five false-negative scans and two false-positive PET scans. Seventeen cases were assessed by clinical follow up, nine were considered to have been tumour. There were two false negatives with one false positive. The overall sensitivity, specificity and positive and negative predictive values were 74, 73, 87 and 53% respectively. This is similar to figures previously quoted in published work. Despite relatively limited numbers, the utility of FDG PET imaging in our hands is similar to published reports. With a positive predictive value of 87%, a positive FDG study indicates a high likelihood that there is brain tumour present. A negative study does not exclude the presence of tumour.

Clinical Application of PET in Pediatric Brain Tumors

While rare in adults, central nervous system tumor is the most common solid tumor in childhood and is the leading cause of cancer death in children. Childhood brain tumors are different from those in adults in epidemiology, histologic features, and responses to treatment. Gliomas make up over one-half of all childhood brain tumors. Clinical application of PET imaging in brain tumors has demonstrated that it is helpful in tumor grading, establishing prognosis, defining targets for biopsy, and planning resection. This article emphasizes PET applications in childhood brain tumors, focusing on mainly gliomas with regard to tumor-grading and prognosis, distinguishing tumor recurrence from radiation necrosis, and PET guided diagnosis and treatment.

Grading of brain glioma with 1-11C-acetate PET: comparison with 18F-FDG PET

The objective of this study is to reevaluate the clinical significance of 1-11C-acetate (ACE) positron emission tomography (PET) in patients with brain glioma, in comparison with 18F-fluorodeoxyglucose (FDG) PET.

METHODS

Ten patients with histologically proven glioma were included in this study. They underwent PET examination with both FDG and ACE on separate days. For ACE PET, 20-min data acquisition was performed just after the administration of 740 MBq of ACE; 10-20-min data were used for the analysis. FDG PET data acquisition for 10 min started 60 min postinjection of 370 MBq of FDG, approximately. Both reconstructed images were converted to standardized uptake value (SUV) images for patient body weight and injected dose. Regions of interest were placed on the tumor and the contralateral cerebral cortex, and SUV and tumor-to-cortex ratio (T/C) were calculated; these values were compared between high- and low-grade gliomas.

RESULTS

SUV and T/C of ACE PET showed significant difference (SUV: 2.63+/-0.46 vs. 1.85+/-0.56, P=.03; T/C: 2.36+/-0.63 vs. 1.14+/-0.36, P=.02). In contrast, FDG PET revealed no significant difference in SUV or T/C between high- and low-grade gliomas (SUV: 7.13+/-4.31 vs. 4.71+/-1.27, P=.31; T/C: 0.98+/-0.55 vs. 0.62+/-0.09, P=.22).

CONCLUSION

This preliminary study revealed that ACE PET is a promising tracer for the grading of brain glioma.

FDG-PET Evaluation of Response to Treatment

This article discusses evaluating response after and during therapy in various settings and for the types of cancers for which ample evidence demonstrates that PET imaging with flourodeoxyglucose provides a valuable surrogate for response to therapy. It also briefly discusses pitfalls in obtaining an optimal assessment of response and issues that need further attention for this modality to become established as an independent predictor of response to anticancer therapy.

Positron emission tomography of the brain

Positron emission tomography (PTE) is a technique that allows imaging of the temporal and spatial distribution of positron-emitting radionuclides. The purpose of this article is to outline the current clinical use for PET imaging in the brain and other radiopharmaceutical used for assessing various physiologic parameters pertaining to tumor metabolism.

Positron Emission Tomography of the Brain

Positron emission tomography (PET) is a technique that allows imaging of the temporal and spatial distribution of positron-emitting radionuclides. The purpose of this article is to outline the current clinical use for PET imaging in the brain and other radiopharmaceuticals used for assessing various physiologic parameters pertaining to tumor metabolism.

Uptake of 18F-fluorocholine, 18F-fluoro-ethyl-L-tyrosine and 18F-fluoro-2-deoxyglucose in F98 gliomas in the rat

INTRODUCTION

The positron emission tomography (PET) tracers (18)F-fluoro-ethyl-L: -tyrosine (FET), (18)F-fluorocholine (N,N-dimethyl-N-[(18)F]fluoromethyl-2-hydroxyethylammonium (FCH]) and (18)F-fluoro-2-deoxyglucose (FDG) are used in the diagnosis of brain tumours. The aim of this study was threefold: (a) to assess the uptake of the different tracers in the F98 rat glioma, (b) to evaluate the impact of blood-brain barrier (BBB) disruption and microvessel density (MVD) on tracer uptake and (c) to compare the uptake in the tumours to that in the radiation injuries (induced by proton irradiation of healthy rats) of our previous study.

METHODS

F98 gliomas were induced in 26 rats. The uptake of FET, FCH and FDG was measured using autoradiography and correlated with histology, disruption of the BBB and MVD.

RESULTS

The mean FET, FCH and FDG standardised uptake values (SUVs) in the tumour and the contralateral normal cortex (in parentheses) were 4.19+/-0.86 (1.32+/-0.26), 2.98+/-0.58 (0.51+/-0.11) and 11.02+/-3.84 (4.76+/-1.77) respectively. MVD was significantly correlated only with FCH uptake. There was a trend towards a negative correlation between the degree of BBB disruption and FCH uptake and a trend towards a positive correlation with FET uptake. The ratio of the uptake in tumours to that in the radiation injuries was 1.97 (FCH), 2.71 (FET) and 2.37 (FDG).

CONCLUSION

MVD displayed a significant effect only on FCH uptake. The degree of BBB disruption seems to affect the accumulation of FET and FCH, but not FDG. Mean tumour uptake for all tracers was significantly higher than the accumulation in radiation injuries.

PET and SPECT in low-grade glioma

Low-grade gliomas (LGG) account for 30-40% of all gliomas and are primarily treated with surgery. Since both timing and use of other oncological treatments in LGG are a matter of controversy, there has been a constantly increasing demand to characterize these often slowly growing neoplasms with functional imaging methods, such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). PET and SPECT yield information on growth rate and heterogeneity of LGG and are especially useful in follow-up since metabolic changes tend to precede structural changes detected with structure-based imaging methods. Furthermore, for planning of LGG surgery or radiotherapy coregistration of functional images with CT and MRI is invaluable. This is increasingly performed with a new generation of hybrid scanners with integrated PET or SPECT and CT.

PET imaging of brain astrocytoma with 1-11C-acetate

PURPOSE

The purpose of this study was to assess the use of 1-(11)C-acetate (ACE) as a metabolic tracer for the detection and characterisation of astrocytomas.

METHODS

Positron emission tomography (PET) studies with ACE and 2-(18)F-fluoro-2-deoxy-D-glucose (FDG) were performed sequentially in 26 patients with primary astrocytomas. Images were analysed by visual interpretation and determination of the tumour to cortex ratio (T/C ratio) and standardised uptake value (SUV). The tumour uptake was visually scored into three grades as compared with the contralateral cortex: clearly lower (-), almost equal (+) and clearly higher (++).

RESULTS

There were 85% of astrocytomas with ++ ACE uptake, 15% with + ACE uptake and none with - ACE uptake. Only 19% of astrocytomas had ++ FDG uptake. Thirty-seven percent of high-grade astrocytomas had + FDG uptake and 37% had - FDG uptake. The sensitivity and specificity of the FDG T/C ratio in discriminating high-grade from low-grade astrocytomas were 79% and 100%, respectively, at the cutoff value of 0.75. Using 2.33 as the cutoff value of the ACE T/C ratio, the sensitivity and specificity were 42% and 86%, respectively. FDG was better than ACE in discriminating high-grade from low-grade astrocytomas. T/C ratios and SUVs of FDG uptake of tumours correlated with the histological grades, but those of ACE uptake did not.

CONCLUSION

ACE appears to be a promising tracer for use in the detection of primary astrocytomas, but is of limited value in the differentiation of high- and low-grade astrocytomas. ACE is complementary to FDG for the diagnosis and characterisation of astrocytoma.