Positron emission tomography using [18F] fluorodeoxyglucose in brain tumors. A powerful diagnostic and prognostic tool

Role of Molecular Imaging with PET/MR Imaging in the Diagnosis and Management of Brain Tumors

Gliomas are the most common primary brain tumors. Hybrid PET/MR imaging has revolutionized brain tumor imaging, allowing for noninvasive, simultaneous assessment of morphologic, functional, metabolic, and molecular parameters within the brain. Molecular information obtained from PET imaging may aid in the detection, classification, prognostication, and therapeutic decision making for gliomas. ¹⁸F-fluorodeoxyglucose (FDG) has been widely used in the setting of brain tumor imaging, and multiple techniques may be employed to optimize this methodology. More recently, a number of non-¹⁸F-FDG-PET radiotracers have been applied toward brain tumor imaging and are used in clinical practice.

Mitochondrial Generated Redox Stress Differently Affects the Endoplasmic Reticulum of Circulating Lymphocytes and Monocytes in Treatment-Naïve Hodgkin’s Lymphoma

Background. The redox stress caused by Hodgkin’s lymphoma (HL) also involves the peripheral blood mononucleated cells (PBMCs) even before chemotherapy. Here, we tested whether lymphocytes and monocytes show a different response to the increased mitochondrial generation of reactive oxygen species (ROS). Methods. PBMCs, isolated from the blood of treatment-naïve HL patients and control subjects, underwent assessment of malondialdehyde content and enzymatic activity of both hexose- and glucose-6P dehydrogenase (H6PD and G6PD) as well as flow cytometric analysis of mitochondrial ROS content. These data were complemented by evaluating the uptake of the fluorescent glucose analogue 2-NBDG that is selectively stored within the endoplasmic reticulum (ER). Results. Malondialdehyde content was increased in the whole population of HL PBMCs. The oxidative damage matched an increased activity of G6PD, and even more of H6PD, that trigger the cytosolic and ER pentose phosphate pathways, respectively. At flow cytometry, the number of recovered viable cells was selectively decreased in HL lymphocytes that also showed a more pronounced increase in mitochondrial ROS generation and 2-NBDG uptake, with respect to monocytes. Conclusions. PBMCs of HL patients display a selective mitochondrial and ER redox stress most evident in lymphocytes already before the exposure to chemotherapy toxicity.

Role of Peptides in Diagnostics

The specificity of a diagnostic assay depends upon the purity of the biomolecules used as a probe. To get specific and accurate information of a disease, the use of synthetic peptides in diagnostics have increased in the last few decades, because of their high purity profile and ability to get modified chemically. The discovered peptide probes are used either in imaging diagnostics or in non-imaging diagnostics. In non-imaging diagnostics, techniques such as Enzyme-Linked Immunosorbent Assay (ELISA), lateral flow devices (i.e., point-of-care testing), or microarray or LC-MS/MS are used for direct analysis of biofluids. Among all, peptide-based ELISA is considered to be the most preferred technology platform. Similarly, peptides can also be used as probes for imaging techniques, such as single-photon emission computed tomography (SPECT) and positron emission tomography (PET). The role of radiolabeled peptides, such as somatostatin receptors, interleukin 2 receptor, prostate specific membrane antigen, αβ3 integrin receptor, gastrin-releasing peptide, chemokine receptor 4, and urokinase-type plasminogen receptor, are well established tools for targeted molecular imaging ortumor receptor imaging. Low molecular weight peptides allow a rapid clearance from the blood and result in favorable target-to-non-target ratios. It also displays a good tissue penetration and non-immunogenicity. The only drawback of using peptides is their potential low metabolic stability. In this review article, we have discussed and evaluated the role of peptides in imaging and non-imaging diagnostics. The most popular non-imaging and imaging diagnostic platforms are discussed, categorized, and ranked, as per their scientific contribution on PUBMED. Moreover, the applicability of peptide-based diagnostics in deadly diseases, mainly COVID-19 and cancer, is also discussed in detail.

A picture is worth a thousand words: a history of diagnostic imaging for lymphoma

The journey from early drawings of Thomas Hodgkin's patients to deep learning with radiomics in lymphoma has taken nearly 200 years, and in many ways, it parallels the journey of medicine. By tracing the history of imaging in clinical lymphoma practice, we can better understand the motivations for current imaging practices. The earliest imaging modalities of the 2D era each had varied, site-dependent sensitivity, and the improved accuracy of imaging studies allowed new diagnostic and therapeutic techniques. First, we review the initial imaging technologies that were applied to understand lymphoma spread and achieve practical guidance for the earliest lymphoma treatments. Next, in the 3D era, we describe how anatomical imaging advances replaced and complemented conventional modalities. Afterward, we discuss how the PET era scans were used to understand response of tumors to treatment and risk stratification. Finally, we discuss the emergence of radiomics as a promising area of research in personalized medicine. We are now able to identify involved lymph nodes and body sites both before and after treatment to offer patients improved treatment outcomes. As imaging methods continue to improve sensitivity, we will be able to use personalized medicine approaches to give targeted and highly focused therapies at even earlier time points, and ideally, we can obtain long-term disease control and cures for lymphomas.

[Phosphorus MR spectroscopy and 18F-FDG PET/CT in the study of energy metabolism of glial tumors]

OBJECTIVE

To study energy metabolism in glial tumors using dynamic MR spectroscopy and ¹⁸F-FDG PET/CT.

MATERIAL AND METHODS

The study included 19 patients (9 women and 10 men) with newly diagnosed supratentorial glial tumors WHO Grade I-IV (diffuse astrocytoma - 4 cases, oligodendroglioma - 4 cases, anaplastic astrocytoma - 5 cases, glioblastoma - 6 cases). All patients underwent examination and surgical treatment at the Burdenko Neurosurgery Center. Dynamic MR spectroscopy and ¹⁸F-FDG PET/CT were applied in each patient.

RESULTS

We found multiple correlations between the ratio of bioorganic phosphate peaks and parameters of glucose uptake by tumor tissue. These relationships were more significant in patients with high-grade tumors: positive significant correlation between SUVtumor and PME/PCr ratio (R_S=0.75, p=0.01), T/Nmix and βATP/Pi ratio (R_s=0.76, p=0.02), SUVpeaktumor and aATP/Pi ratio (R_S=0.77, p=0.008). Moreover, there were negative correlations between SUVtumor and PCr/bATP ratio (R_S= -0.66, p=0.05), T/Nmix and PDE/bATP ratio (R_S= -0.83, p=0.006), SUVpeaktumor and PDE/aATP ratio (R_S= -0.76, p=0.009).

CONCLUSION

High-grade gliomas were characterized by higher glucose consumption, ATP release (intensification of energy metabolism) and faster cell membrane synthesis. These processes indicate enhanced proliferation of tumor cells (intensification of plastic metabolism).

PET Molecular Imaging: A Holistic Review of Current Practice and Emerging Perspectives for Diagnosis, Therapeutic Evaluation and Prognosis in Clinical Oncology

PET/CT molecular imaging has been imposed in clinical oncological practice over the past 20 years, driven by its two well-grounded foundations: quantification and radiolabeled molecular probe vectorization. From basic visual interpretation to more sophisticated full kinetic modeling, PET technology provides a unique opportunity to characterize various biological processes with different levels of analysis. In clinical practice, many efforts have been made during the last two decades to standardize image analyses at the international level, but advanced metrics are still under use in practice. In parallel, the integration of PET imaging with radionuclide therapy, also known as radiolabeled theranostics, has paved the way towards highly sensitive radionuclide-based precision medicine, with major breakthroughs emerging in neuroendocrine tumors and prostate cancer. PET imaging of tumor immunity and beyond is also emerging, emphasizing the unique capabilities of PET molecular imaging to constantly adapt to emerging oncological challenges. However, these new horizons face the growing complexity of multidimensional data. In the era of precision medicine, statistical and computer sciences are currently revolutionizing image-based decision making, paving the way for more holistic cancer molecular imaging analyses at the whole-body level.

Multimodal Molecular Imaging of the Tumour Microenvironment

The tumour microenvironment (TME) surrounding tumour cells is a highly dynamic and heterogeneous composition of immune cells, fibroblasts, precursor cells, endothelial cells, signalling molecules and extracellular matrix (ECM) components. Due to the heterogeneity and the constant crosstalk between the TME and the tumour cells, the components of the TME are important prognostic parameters in cancer and determine the response to novel immunotherapies. To improve the characterization of the TME, novel non-invasive imaging paradigms targeting the complexity of the TME are urgently needed.The characterization of the TME by molecular imaging will (1) support early diagnosis and disease follow-up, (2) guide (stereotactic) biopsy sampling, (3) highlight the dynamic changes during disease pathogenesis in a non-invasive manner, (4) help monitor existing therapies, (5) support the development of novel TME-targeting therapies and (6) aid stratification of patients, according to the cellular composition of their tumours in correlation to their therapy response.This chapter will summarize the most recent developments and applications of molecular imaging paradigms beyond FDG for the characterization of the dynamic molecular and cellular changes in the TME.

Does 2-FDG PET Accurately Reflect Quantitative In Vivo Glucose Utilization?

2-Deoxy-2-¹⁸F-fluoro-d-glucose (2-FDG) with PET is undeniably useful in the clinic, being able, among other uses, to monitor change over time using the 2-FDG SUV metric. This report suggests some potentially serious caveats for this and related roles for 2-FDG PET. Most critical is the assumption that there is an exact proportionality between glucose metabolism and 2-FDG metabolism, called the lumped constant, or LC. This report describes that LC is not constant for a specific tissue and may be variable before and after disease treatment. The purpose of this work is not to deny the clinical value of 2-FDG PET; it is a reminder that when one extends the use of an appropriately qualified imaging method, new observations may arise and further validation would be necessary. The current understanding of glucose-based energetics in vivo is based on the quantification of glucose metabolic rates with 2-FDG PET, a method that permits the noninvasive assessment of various human disorders. However, 2-FDG is a good substrate only for facilitated-glucose transporters (GLUTs), not for sodium-dependent glucose cotransporters (SGLTs), which have recently been shown to be distributed in multiple human tissues. Thus, the GLUT-mediated in vivo glucose utilization measured by 2-FDG PET would be masked to the potentially substantial role of functional SGLTs in glucose transport and use. Therefore, under these circumstances, the 2-FDG LC used to quantify in vivo glucose utilization should not be expected to remain constant. 2-FDG LC variations have been especially significant in tumors, particularly at different stages of cancer development, affecting the accuracy of quantitative glucose measures and potentially limiting the prognostic value of 2-FDG, as well as its accuracy in monitoring treatments. SGLT-mediated glucose transport can be estimated using α-methyl-4-deoxy-4-¹⁸F-fluoro-d-glucopyranoside (Me-4FDG). Using both 2-FDG and Me-4FDG should provide a more complete picture of glucose utilization via both GLUT and SGLT transporters in health and disease states. Given the widespread use of 2-FDG PET to infer glucose metabolism, it is relevant to appreciate the potential limitations of 2-FDG as a surrogate for glucose metabolic rate and the potential reasons for variability in LC. Even when the readout for the 2-FDG PET study is only an SUV parameter, variability in LC is important, particularly if it changes over the course of disease progression (e.g., an evolving tumor).

New metabolic imaging tools in neuro-oncology

PURPOSE OF REVIEW

The current treatment of gliomas dovetails results of decades-old clinical trials with modern trends in chemotherapy. Molecular characterization now plays a pivotal role, and IDH mutations are key characteristics and the subject of active debate. IDH-mutant tumors produce the 'onco-metabolite', 2-hydroxyglutarate. Metabolic changes have become central to the understanding of tumor biology, and tumors display a fundamental metabolic change called the Warburg Effect. The Warburg Effect represents a preference for glycolysis, as opposed to oxidative phosphorylation. The present review details the clinical context and discusses clinical and preclinical metabolic imaging tools to characterize the Warburg Effect.

RECENT FINDINGS

A clinical Warburg Index is proposed, defined as the lactate concentration measured by H-MRSI over the SUV measured by FDG-PET, to measure the Warburg Effect. A preclinical technique called deuterium metabolic imaging has successfully imaged the Warburg Effect in vivo in glioblastoma.

SUMMARY

Metabolic imaging provides an opportunity to measure the Warburg Effect and other metabolic changes in brain tumors. An increased understanding of metabolic shifts integral to brain cancer has the potential to address multiple contemporary debates on glioma pathophysiology and treatment. Metabolic imaging tools thus have the potential to advance research findings, clinical trial development, and clinical care.

Prognostic Value of MTV, SUVmax and the T/N Ratio of PET/CT in Patients with Glioma: A Systematic Review and Meta-Analysis

Background: In the past decade, positron emission tomography/computed tomography (PET/CT) has become an important imaging tool for clinical assessment of tumor patients. Our meta-analysis aimed to compare the predictive value of PET/CT parameters regard to overall survival (OS) and progression-free survival (PFS) outcomes in glioma.

Methods: Relevant articles were systematically searched in PMC, PubMed, EMBASE and WEB of science. Studies involving the prognostic roles of PET/CT parameters with OS and PFS in glioma patients were evaluated. The impact of metabolic tumor volume (MTV), maximal standard uptake value (SUVmax), and the ratio of uptake in tumor to normal (T/N ratio) on survival was measured by calculating combined hazard ratios (HRs) and 95% confidence intervals (CIs).

Results: A total of 32 articles with 1715 patients were included. The combined HRs of higher MTV, higher SUVmax and higher T/N ratio for OS were 1.14 (95% CI: 0.98-1.32, P heterogeneity<0.001), 1.69 (95% CI: 1.18-2.41, P heterogeneity<0.001) and 1.68 (95% CI: 1.40-2.01, P heterogeneity< 0.001), respectively. Regarding PFS, the combined HRs were 1.04 (95% CI: 0.97-1.11, P heterogeneity=0.002) with higher MTV, 1.45 (95% CI: 1.11-1.90, P heterogeneity<0.001) with higher SUVmax and 2.07 (95% CI: 1.45-2.95, P heterogeneity<0.001) with higher T/N ratio. Results remained similar in the sub-group analyses.

Conclusion: PET/CT parameters T/N ratio may be a significant prognostic factor in patients with glioma. Evidence of SUVmax and MTV needed more large-scale studies performed to validate. PET/CT scan could be a promising technique to provide prognostic information for these patients.

The Role of Fluorine-18-Deoxyglucose (Fdg) Positron Emission Tomography (Pet) Whole Body Scan (Wbs) in the Staging and Follow-Up of Cancer Patients: Our First Experience

We report the results of FDG PET whole body scan in 75 cancer patients in whom tumor extent was defined by surgical, histological or cytological findings and clinical follow-up. Twenty-five had malignant lymphomas, 24 lung carcinomas, and 26 other types of solid tumors. Twenty-three patients were evaluated at disease onset, before therapy, and 37 at the moment of tumor recurrence; the remaining 15 patients were in complete remission after treatment and were taken as controls. Visual and quantitative PET results were compared with conventional imaging (US, CT scan and/or MRI, and Tc99m MDP bone scan).

In the 60 patients with active disease, PET as well as conventional imaging were able to locate the primary tumor in all 23 patients studied at disease onset. However, with regard to lymph node and distant metastases, PET provided the same information as conventional imaging in 31 cases (51.6%), but revealed further neoplastic foci in 29 cases (48.4%), 21 in lymph nodes and 8 at distant sites. The sensitivity of PET, in comparison with conventional imaging, was 100% versus 100% for the detection of the primary tumor, 97.6% versus 55.8% for the localization of node metastases, and 100% versus 55.5% for the visualization of distant metastases. The specificity, calculated in the group of 15 disease-free patients, was 100% for PET and 86.6% for conventional imaging. The therapeutic approach was modified in 12 patients (20%) on the basis of the PET results. Furthermore, in 14 cases (23.3%) with advanced disease, PET provided complete information on tumor spread, otherwise obtainable only by taking together the results of all other diagnostic procedures. Our data indicate a higher accuracy of FDG PET whole body scan compared to conventional imaging techniques in the evaluation of metastatic spread both at initial diagnosis and during follow-up, with an important impact on therapeutic decision-making. Moreover, by providing complete information on tumor spread in some cases, PET can become a profitable tool in terms of cost reduction.

Quantitative assessment of brain glucose metabolic rates using in vivo deuterium magnetic resonance spectroscopy

Quantitative assessment of cerebral glucose consumption rate (CMR_glc) and tricarboxylic acid cycle flux (V_TCA) is crucial for understanding neuroenergetics under physiopathological conditions. In this study, we report a novel in vivo Deuterium (²H) MRS (DMRS) approach for simultaneously measuring and quantifying CMR_glc and V_TCA in rat brains at 16.4 Tesla. Following a brief infusion of deuterated glucose, dynamic changes of isotope-labeled glucose, glutamate/glutamine (Glx) and water contents in the brain can be robustly monitored from their well-resolved ²H resonances. Dynamic DMRS glucose and Glx data were employed to determine CMR_glc and V_TCA concurrently. To test the sensitivity of this method in response to altered glucose metabolism, two brain conditions with different anesthetics were investigated. Increased CMR_glc (0.46 vs. 0.28 µmol/g/min) and V_TCA (0.96 vs. 0.6 µmol/g/min) were found in rats under morphine as compared to deeper anesthesia using 2% isoflurane. This study demonstrates the feasibility and new utility of the in vivo DMRS approach to assess cerebral glucose metabolic rates at high/ultrahigh field. It provides an alternative MRS tool for in vivo study of metabolic coupling relationship between aerobic and anaerobic glucose metabolisms in brain under physiopathological states.

18F-fluorothymidine PET imaging in gliomas: an update

Brain neoplasms constitute a group of tumors with discrete differentiation grades, and therefore, course of disease and prognosis. Magnetic resonance imaging (MRI) remains the gold standard method for the investigation of central nervous system tumors. However, MRI suffers certain limitations, especially if radiation therapy or chemotherapy has been previously applied. On the other hand, given the development of newer radiopharmaceuticals, positron emission tomography (PET) aims to a better investigation of brain tumors, assisting in the clinical management of the patients. In the present review, the potential contribution of radiolabeled fluorothymidine (FLT) imaging for the evaluation of brain tumors will be discussed. In particular, we will present the role of FLT-PET imaging in the depiction of well and poorly differentiated lesions, the assessment of patient prognosis and treatment response, and the recognition of disease recurrence. Moreover, related semi-quantitative and kinetic parameters will be discussed.

Preoperative Evaluation of Sellar and Parasellar Macrolesions by [18F]Fluorodeoxyglucose Positron Emission Tomography

OBJECTIVE

Various diseases can occur in the sellar and suprasellar regions. The potential of [¹⁸F]fluorodeoxyglucose (FDG) positron emission tomography (PET) for the preoperative evaluation of sellar and parasellar lesions was investigated.

METHODS

A total of 49 patients aged 8-82 years with sellar and parasellar macroscopic lesions (≥10 mm) underwent FDG PET. Twenty-two patients had pituitary adenomas, including 14 nonfunctioning and 8 growth hormone-secreting adenomas. Eleven patients had craniopharyngiomas, including 5 adamantinomatous and 6 squamous-papillary types. Eight patients had chordoma, 4 had meningioma, and 4 had a Rathke cleft cyst. The maximum standardized uptake value (SUV_max), and the ratio of the SUV_max in the tumor to the mean standardized uptake value in the normal cortex (T/N ratio) or in the normal white matter (T/W ratio) were calculated. The relationships between SUV_max, T/N ratio, and T/W ratio, and lesion disease were evaluated.

RESULTS

Uptakes of FDG, including SUV_max, T/N ratio, and T/W ratio, were lower in chordoma and Rathke cleft cyst compared with pituitary adenoma. SUV_max, T/N ratio, and T/W ratio of nonfunctioning adenoma were significantly higher than those of growth hormone-secreting adenoma. SUV_max, T/N ratio, and T/W ratio of squamous-papillary type were significantly higher than those of the adamantinomatous type of craniopharyngioma.

CONCLUSIONS

FDG PET is useful for the preoperative diagnosis of sellar and parasellar macrolesions. High uptake in nonfunctioning pituitary adenoma, and low uptake in chordoma are significant. The difference in FDG uptake dependent on the histologic subtype may be related to the specific genetics of the craniopharyngioma subtype.

Usefulness of positron emission tomographic studies for gliomas

Non-invasive positron emission tomography (PET) enables the measurement of metabolic and molecular processes with high sensitivity. PET plays a significant role in the diagnosis, prognosis, and treatment of brain tumors and predominantly detects brain tumors by detecting their metabolic alterations, including energy metabolism, amino acids, nucleic acids, and hypoxia. Glucose metabolic tracers are related to tumor cell energy and exhibit good sensitivity but poor specificity for malignant tumors. Amino acid metabolic tracers provide a better delineation of tumors and cellular proliferation. Nucleic acid metabolic tracers have a high sensitivity for malignant tumors and cellular proliferation. Hypoxic metabolism tracers are useful for detecting resistance to radiotherapy and chemotherapy. Therefore, PET imaging techniques are useful for detecting biopsy-targeting points, deciding on tumor resection, radiotherapy planning, monitoring therapy, and distinguishing brain tumor recurrence or progression from post-radiotherapy effects. However, it is not possible to use only one PET tracer to make all clinical decisions because each tracer has both advantages and disadvantages. This study focuses on the different kinds of PET tracers and summarizes their recent applications in patients with gliomas. Combinational uses of PET tracers are expected to contribute to differential diagnosis, prognosis, treatment targeting, and monitoring therapy.

(18)F-Flourodeoxy-Glucose PET/Computed Tomography in Brain Tumors: Value to Patient Management and Survival Outcomes

(18)F-flourodeoxy-glucose (FDG) PET/computed tomography (CT) is most useful in the evaluation of primary central nervous system (CNS) lymphoma, important in diagnosis, pretherapy prognosis, and therapy response evaluation. Utility in working up gliomas is less effective, and FDG PET/CT is most helpful when MR imaging is unclear. FDG avidity correlates with the grade of gliomas. FDG PET/CT can be used to noninvasively identify malignant transformation. Establishing this change in the disease process has significant effects on patient management and survival outcome.

Imaging metabolic heterogeneity in cancer

As our knowledge of cancer metabolism has increased, it has become apparent that cancer metabolic processes are extremely heterogeneous. The reasons behind this heterogeneity include genetic diversity, the existence of multiple and redundant metabolic pathways, altered microenvironmental conditions, and so on. As a result, methods in the clinic and beyond have been developed in order to image and study tumor metabolism in the in vivo and in vitro regimes. Both regimes provide unique advantages and challenges, and may be used to provide a picture of tumor metabolic heterogeneity that is spatially and temporally comprehensive. Taken together, these methods may hold the key to appropriate cancer diagnoses and treatments in the future.

A note from history: Landmarks in history of cancer, part 7

In the 2 and half decades reviewed (1970-1995), research established that chromosomal translocation, deletion, and DNA amplification are prerequisites to cancerogenesis and that oncogenes, tumor-suppressor genes, growth factors, and cytokines play crucial roles in the pathomechanism of cancer. Human papillomavirus, human immunodeficiency virus, herpes virus, and hepatitis B virus were identified as cancer-causing viruses. Several laboratory tests were developed for the detection of primary and recurrent cancers, and cancer prevention by screening methods was popularized. Sonography, computerized tomography, magnetic resonance imaging, positron emission tomography, excision of sentinel lymph nodes, and immunohistochemical techniques became routine procedures. Clinicopathologic staging and classification of tumors were standardized. Limited surgery, adjuvant and neoadjuvant chemoradiation, and the therapeutic use of monoclonal antibodies, tumor vaccines, and targeted chemotherapy became routine practice. The decline in cancer incidence and mortality demonstrated that cancer prevention and advancement in oncology are pivotal to success in the crusade against cancer. Above all, it was clearly established that the care of patients with cancer can be accomplished best in a multidisciplinary setting involving surgical oncologists, radiologists, radiation therapists, medical oncologists, surgical pathologists, and laboratory scientists. In conclusion, the 25 years from 1970 and 1995 are the high-water mark in clinical oncology, and this is the period when oncology turned from art to science.

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.

PET/CT imaging in cancer: current applications and future directions

Positron emission tomography (PET) is a radiotracer imaging method that yields quantitative images of regional in vivo biology and biochemistry. PET, now used in conjunction with computed tomography (CT) in PET/CT devices, has had its greatest impact to date on cancer and is now an important part of oncologic clinical practice and translational cancer research. In this review of current applications and future directions for PET/CT in cancer, the authors first highlight the basic principles of PET followed by a discussion of the biochemistry and current clinical applications of the most commonly used PET imaging agent, (18) F-fluorodeoxyglucose (FDG). Then, emerging methods for PET imaging of other biologic processes relevant to cancer are reviewed, including cellular proliferation, tumor hypoxia, apoptosis, amino acid and cell membrane metabolism, and imaging of tumor receptors and other tumor-specific gene products. The focus of the review is on methods in current clinical practice as well as those that have been translated to patients and are currently in clinical trials.

Brain and whole-body FDG-PET in diagnosis, treatment monitoring and long-term follow-up of primary CNS lymphoma

Background

Positron emission tomography (PET) with F-18-labeled fluorodeoxyglucose (FDG) provides remarkable accuracy in detection, treatment monitoring and follow-up of systemic malignant lymphoma. Its value in the management of patients with primary central nervous system lymphoma (PCNSL) is less clear.

Patients and methods

In a prospective trial, 42 FDG-PET examinations were performed in ten immunocompetent patients with newly diagnosed or recurrent PCNSL before and repeatedly during and after the treatment. Brain and whole body FDG-PET were compared to brain MRI and extra-cerebral CT, respectively.

Results

Before the treatment, 6 of 10 patients had congruent findings on FDG-PET and MRI of the brain. Three patients had lesions on brain MRI, not detected by FDG-PET. One patient had additional FDG-PET positive lesions inconspicuous in MRI. The follow-up suggested FDG-PET to be false positive in these lesions. After the treatment, brain PET was in agreement with MRI in 6 of 8 patients. In the remaining 2 patients there were persistent lesions in brain MRI whereas FDG-uptake was reduced to normal values. In the long-term follow-up of 5 patients (63–169 weeks), 3 patients retained normal in both PET and MRI. In 2 patients a new focal pathologic FDG-uptake was detected 69 and 52 weeks after the end of the treatment. In one of these patients, recurrence was confirmed by MRI not until 9 weeks after PET.

Conclusions

Brain FDG-PET may contribute valuable information for the management of PCNSL, particularly in the assessment of the treatment response. Integration of FDG-PET into prospective interventional trials is warranted to investigate prognostic and therapeutic implications.

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.

Molecular imaging of pediatric brain tumors: comparison of tumor metabolism using ¹⁸F-FDG-PET and MRSI

Magnetic resonance spectroscopic imaging (MRSI) and (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) are non-invasive imaging techniques routinely used to evaluate tumor malignancy in adults with brain tumors. We compared the metabolic activity of pediatric brain tumors using FDG-PET and MRSI. Children (n = 37) diagnosed with a primary brain tumor underwent FDG-PET and MRSI within two weeks of each other. Tumor metabolism was classified as inactive, active or highly active using the maximum choline:N-acetyl-asparate (Cho:NAA) on MRSI and the highest tumor uptake on FDG-PET. A voxel-wise comparison was used to evaluate the area with the greatest abnormal metabolism. Agreement between methods was assessed using the percent agreement and the kappa statistic (κ). Pediatric brain tumors were metabolically heterogeneous on FDG-PET and MRSI studies. Active tumor metabolism was observed more frequently using MRSI compared to FDG-PET, and agreement in tumor classification was weak (κ = 0.16, p = 0.12), with 42 % agreement (95 % CI = 25-61 %). Voxel-wise comparison for identifying the area of greatest metabolic activity showed overlap in the majority (62 %) of studies, though exact agreement between techniques was low (29.4 %, 95 % CI = 15.1-47.5 %). These results indicate that FDG-PET and MRSI detect similar but not always identical regions of tumor activity, and there is little agreement in the degree of tumor metabolic activity between the two techniques.

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.

Clinical applications of positron emission tomography in sarcoma management

Positron emission tomography (PET) with the fluorine-18-labeled glucose analog FDG is a technique that noninvasively visualizes glucose metabolism in the human body. In oncology, the addition of FDG-PET to the conventional anatomical imaging techniques provides very useful clinical information in diagnosis, staging, treatment response monitoring and follow-up. In the heterogeneous group of patients with sarcoma, FDG-PET has been shown to be of great value in improving patient care. In this article we will discuss the current role of FDG-PET in the management of patients with sarcoma and its value in assessing tumor grade, guiding biopsy, staging, monitoring treatment response, restaging and prognostication. Our future expectation is that the value of PET will only augment owing to the implementation of FDG-PET in clinical guidelines, the increasing availability worldwide, and the development of new tracers and new hybrid imaging techniques.

Molecular imaging of gliomas with PET: opportunities and limitations

Neuroimaging enables the noninvasive evaluation of glioma and is considered to be one of the key factors for individualized therapy and patient management, since accurate diagnosis and demarcation of viable tumor tissue is required for treatment planning as well as assessment of treatment response. Conventional imaging techniques like MRI and CT reveal morphological information but are of limited value for the assessment of more specific and reproducible information about biology and activity of the tumor. Molecular imaging with PET is increasingly implemented in neuro-oncology, since it provides additional metabolic information of the tumor, both for patient management as well as for evaluation of newly developed therapeutics. Different molecular processes have been proposed to be useful, like glucose consumption, expression of amino acid transporters, proliferation rate, membrane biosynthesis, and hypoxia. Thus, PET might help neuro-oncologists gain further insights into tumor biology by "true molecular imaging" as well as understand treatment-related phenomena. This review describes the method of PET acquisition as well as the tracers used to image biological processes in gliomas. Furthermore, it considers the clinical impact of PET on the use of currently available radiotracers, which were shown to be potentially valuable for discrimination between neoplastic and nonneoplastic tissue, as well as on tumor grading, determinination of treatment response, and providing an outlook toward further developments.

Hypoxic stress and cancer: imaging the axis of evil in tumor metastasis

Tumors emerge as a result of the sequential acquisition of genetic, epigenetic and somatic alterations promoting cell proliferation and survival. The maintenance and expansion of tumor cells rely on their ability to adapt to changes in their microenvironment, together with the acquisition of the ability to remodel their surroundings. Tumor cells interact with two types of interconnected microenvironments: the metabolic cell autonomous microenvironment and the nonautonomous cellular-molecular microenvironment comprising interactions between tumor cells and the surrounding stroma. Hypoxia is a central player in cancer progression, affecting not only tumor cell autonomous functions, such as cell division and invasion, resistance to therapy and genetic instability, but also nonautonomous processes, such as angiogenesis, lymphangiogenesis and inflammation, all contributing to metastasis. Closely related microenvironmental stressors affecting cancer progression include, in addition to hypoxia, elevated interstitial pressure and oxidative stress. Noninvasive imaging offers multiple means to monitor the tumor microenvironment and its consequences, and can thus assist in the understanding of the biological basis of hypoxia and microenvironmental stress in cancer progression, and in the development of strategies to monitor therapies targeted at stress-induced tumor progression.

The role of f-fluorodeoxyglucose positron emission tomography in the treatment of brain abscess

OBJECTIVE

The purpose of this study was to evaluate whether (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) can be used to assess the therapeutic response of brain abscess.

METHODS

A study was conducted on 10 consecutive patients with brain abscess. Magnetic resonance imaging (MRI) with diffuse-weighted imaging (DWI) was performed at 3 and 6 weeks after surgical treatment and intravenous antibiotics therapy and FDG-PET at 6 weeks after treatment. The extent of the abscess, signal changes on MRI, and FDG-PET standardized uptake values were analyzed and correlated with the response to therapy.

RESULTS

Aspiration or craniotomy with excision of the abscess followed by intravenous antibiotics for 6-8 weeks resulted in good recovery with no recurrence. In 10 patients, two had low signal intensity on the DWI; one had no uptake on FDG-PET imaging after 6 weeks antibiotics and discontinued intravenous treatment, but the other patient had diffuse, increased uptake on FDG-PET imaging after 6 weeks antibiotics and underwent an additional 2 weeks of intravenous antibiotics. The remaining eight patients had high signals on the DWI. Four had no uptake on FDG-PET imaging and the treatment period varied from 6 to 8 weeks (mean, 6.75 weeks). Among the other four patients, FDG was accumulated in a diffuse or local area corresponding to a high signal area within the DWI and 2 weeks of intravenous antibiotics was added.

CONCLUSION

MRI plus FDG-PET improved the accuracy of assessing therapeutic responses to antibiotics treatment of brain abscess and aided in optimizing therapy.

Brain tumors

For most cancers, PET is essentially a diagnostic tool. For brain tumors, PET has got its main contribution at the level of the therapeutic management. Indeed, specific reasons render the therapeutic management of brain tumors, especially gliomas, a real challenge. Although some gliomas may appear well-delineated on conventional neuroimaging such as CT and MRI, they are by nature infiltrating neoplasms and the interface between tumor and normal brain tissue may not be accurately defined. Moreover, gliomas may present as ill-defined lesions for which various MRI sequences combination does not provide a unique contour for tumor delineation. Also, gliomas are often histologically heterogeneous with anaplastic areas evolving within a low-grade tumor, and contrast-enhancement on CT or MRI does not represent a good marker for anaplastic tissue detection. Finally, assessment of tumor residue, recurrence, or progression, may be altered by different signals related to inflammation or adjuvant therapies, and contrast enhancement on CT and MRI is not an appropriate marker at the postoperative or posttherapeutic stage. These limitations of conventional neuroimaging in detecting tumor tissue, delineating tumor extent and evidencing anaplastic changes, lead to potential inaccuracy in lesion targeting at different steps of the management (diagnostic, surgical, postoperative, and posttherapeutic stages). Molecular information provided by PET has proved helpful to supplement morphological imaging data in this context. F-18 FDG and amino-acid tracers such as C-11 methionine (C-11 MET) provide complementary metabolic data that are independent from the anatomical MR information. These tracers help in the definition of glioma extension, detection of anaplastic areas, and postoperative follow-up. Additionally, PET data have a prognostic value independently of histology. To take advantage of PET data in glioma treatment, PET might be integrated in the planning of image-guided biopsy, resection, and radiosurgery.

Unusually intense ¹⁸F-fluorodeoxyglucose (FDG) uptake by a mature ovarian teratoma: a pitfall of FDG positron emission tomography

We present a 32-year-old woman with an ovarian tumor. A large ovarian tumor with solid components was detected by ultrasonography and magnetic resonance imaging. Contrast enhanced magnetic resonance imaging showed strong enhancement within the solid component. ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography was performed for further evaluation and intense FDG uptake into the solid component was observed with standardized uptake values of 12.8 in the early phase and 14.8 in the delayed phase. Therefore, we could not rule out the possibility of a malignant ovarian tumor, and the patient underwent unilateral salpingo-oophorectomy through laparotomy. The tumor was pathologically diagnosed as a mature teratoma with no malignant elements. Histological examination revealed the solid component to be composed mainly of central nervous tissue, which was most likely to be responsible for the intense FDG uptake.

Prognostic significance of parameters derived from co-registered 18F-fluorodeoxyglucose PET and contrast-enhanced MRI in patients with high-grade glioma

OBJECTIVE

The aim of this study was to determine the prognostic significance of the volume and intensity of abnormal (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) accumulation within areas of contrast enhancement on post-therapeutic volumetric MRI.

METHODS

A total of 10 patients with Grade III or IV glioma were treated with resection followed by intracavitary radiation therapy with (131)I-labelled antitenascin monoclonal antibody. Patients underwent serial FDG-PET and 1.5 T MR imaging. For each patient, MR and FDG-PET image volumes at each time point were aligned using a rigid-body normalised mutual information algorithm. Contrast-enhancing regions of interest (ROIs) were defined using a semi-automated k-means clustering technique. Activity within the ROI on the co-registered PET scan was calculated as a ratio (mean activity ratio; MAR) to activity in contralateral normal-appearing white matter (NAWM). The PET lesion was defined as the portion of the ROI associated with activity greater than two standard deviations above the mean in NAWM. Survival was assessed using the logrank test.

RESULTS

Larger contrast-enhancing ROIs were strongly associated with an increased MAR (r = 0.51; p<0.002). Enhancing lesions with an MAR >1.2 were associated with decreased survival (p<0.016). In nine patients who died, the MAR on PET correlated inversely with survival duration (r = -0.43; p<0.01), whereas PET lesion volume did not.

CONCLUSION

Following intracavitary radiation therapy, the development of contrast-enhancing lesions that are associated with high mean FDG-PET accumulation suggests poor prognosis.

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

This study aimed to define the potential of 1-(11)C-acetate PET, compared with (18)F-FDG, in detecting meningiomas and monitoring the effect of gamma-knife radiosurgery.

METHODS

Twenty-two patients with the neuroradiologic diagnosis of meningioma were examined by 1-(11)C-acetate and (18)F-FDG PET on the same day. There were 12 cases of histopathologically proven meningioma (8 grade I, 2 grade II, and 2 grade III), 1 of tuberculous granuloma, and 1 of degenerative tissue. 1-(11)C-acetate PET scans of fasting patients were obtained 10 min after intravenous administration of 740 MBq of 1-(11)C-acetate. (18)F-FDG PET was performed at 2 h after 1-(11)C-acetate scanning. The PET images were evaluated by a qualitative method and semiquantitative analysis using standardized uptake value and tumor-to-cortex ratio.

RESULTS

The (18)F-FDG PET study revealed a hypometabolic focus in 17 meningiomas (8 grade I, 1 grade II, and 8 unknown grade) and hypermetabolism in 1 grade II and 2 grade III meningiomas. High uptake of 1-(11)C-acetate was observed in all 20 meningiomas, in contrast to the low uptake in surrounding normal brain tissue, allowing a clearer demarcation of the tumor boundary than that provided by (18)F-FDG. Dissociation of regional accumulation of 1-(11)C-acetate and (18)F-FDG within the tumor was also noted on the coregistered images. The standardized uptake value for 1-(11)C-acetate was not different from that for (18)F-FDG (mean +/- SD, 3.16 +/- 1.75 vs. 3.22 +/- 1.50, P = 0.601), but the tumor-to-cortex ratio for 1-(11)C-acetate was higher than that for (18)F-FDG (3.46 +/- 1.38 vs. 0.93 +/- 1.08, P < 0.005). (18)F-FDG was able to differentiate grade I from grade II-III meningiomas, whereas 1-(11)C-acetate was unable to do so. Tuberculous granuloma had a high 1-(11)C-acetate and (18)F-FDG uptake similar to that of grade II/III meningioma. Five patients received 1-(11)C-acetate and (18)F-FDG PET before and after gamma-knife surgery. 1-(11)C-acetate performed better than did (18)F-FDG in monitoring the response of tumor metabolism to radiosurgery.

CONCLUSION

1-(11)C-acetate was found to be useful for detecting meningiomas and evaluating the extent of meningiomas and potentially useful for monitoring tumor response to radiosurgery. However, 1-(11)C-acetate was not useful for evaluating the tumor grade. (18)F-FDG was found to be less useful than 1-(11)C-acetate for evaluating the extent of meningiomas and the response to radiosurgical treatment but may be useful for differentiating benign from malignant meningiomas. (18)F-FDG and 1-(11)C-acetate are complementary for assessing diverse cell metabolism of meningioma.

Clinical impact of integrating positron emission tomography during surgery in 85 children with brain tumors

OBJECT

In this paper, the authors' goal was to evaluate the impact of PET information on brain tumor surgery in children.

METHODS

Between 1995 and 2007, 442 children were referred to the authors' institution for a newly diagnosed brain lesion. Of these, 85 were studied with FDG-PET and/or L-(methyl-(11)C)-methionine -PET in cases in which MR images were unable to assist in selecting accurate biopsy targets (35 patients) or to delineate tumors for maximal resection (50 patients). In surgical cases, PET and MR images were combined in image fusion planning for stereotactic biopsies or navigation-based resections. The preoperative planning images were compared postoperatively with MR imaging and PET findings and histological data for evaluating the clinical impact on the diagnostic yield and tumor resection.

RESULTS

The PET data influenced surgical decisions or procedures in all cases. The use of PET helped to better differentiate indolent from active components in complex lesions (in 12 patients); improved target selection and diagnostic yield of stereotactic biopsies without increasing the sampling; provided additional prognostic information; reduced the amount of tissue needed for biopsy sampling in brainstem lesions (in 20 cases); better delineated lesions that were poorly delineated on MR imaging and that infiltrated functional cortex (in 50 cases); significantly increased the amount of tumor tissue removed in cases in which total resection influenced survival (in 20 cases); guided resection in hypermetabolic areas (in 15 cases); improved early postoperative detection of residual tumor (in 20 cases); avoided unnecessary reoperation (in 5 cases); and supported the decision to undertake early second-look resection (in 8 cases).

CONCLUSIONS

The authors found that PET has a significant impact on the surgical decisions and procedures for managing pediatric brain tumors. Further studies may demonstrate whether PET improves outcomes in children.

Clinical interest of integrating positron emission tomography imaging in the workup of 55 children with incidentally diagnosed brain lesions

OBJECT

In this paper, the authors' goal was to evaluate the impact of PET data on the clinical management of incidental brain lesions in children.

METHODS

Between 1995 and 2007, 442 children with a newly diagnosed brain lesion were referred to the authors' department. Of these, 55 presented with an incidental brain lesion and were selected for study because MR imaging sequences revealed limitations in assessing the tumor, its evolving nature, and/or the malignant potential of the lesion diagnosed. Thirteen children were studied using FDG-PET and 42 with L-(methyl-(11)C)-methionine (MET)-PET; 3 children underwent both FDG-PET and MET-PET but only the MET-PET results were used in the analysis. The PET and MR images were combined in image fusion navigation planning. Drawing on their experience with PET in adults, the authors proposed the following treatment plans: 1) surgery in children with imaging evidence of increased PET tracer uptake, which is highly specific of tumor and/or malignant tumor tissue; or 2) conservative treatment in children in whom there was little or no tracer uptake on PET. The authors compared the PET data with the MR imaging-based diagnosis and either 1) the results of histological examination in surgically treated cases, or 2) the long-term outcome in untreated cases. They studied PET and MR imaging sensitivity and specificity in detecting tumor and malignant tissues, and evaluated whether PET data altered their clinical management.

RESULTS

Seventeen children had increased PET tracer uptake and underwent surgery. Tumor diagnosis was confirmed in all cases (that is, there were no false-positive findings). Cases in which there was little or no PET tracer uptake supported conservative treatment in 38 children. However, because PET was under evaluation, 16 of 38 lesions that were judged accessible for resection were surgically treated. Histological examination results demonstrated neither malignant nor evolving tumor tissue but yielded 9 indolent tumors (6 dysembryoplastic neuroectodermal tumors, 2 low-grade astrocytomas, and 1 low-grade astrocytoma and dysplasia) and 7 nontumoral lesions (3 cases of vasculitis, 3 of gliosis, and 1 of sarcoidosis). In 22 of the untreated 38 children, stable disease was noted during follow-up (range 18-136 months). Although an absence of PET tracer uptake might not exclude tumor tissue, PET did not reveal any false-negative findings in malignant or evolving tumor tissue detection in cases in which MR imaging showed false-positive and -negative cases in > 35 and 25% of the cases, respectively.

CONCLUSIONS

These data confirmed the high sensitivity and specificity of PET to detect tumor as well as malignant tissue. Regarding the treatment of the incidental brain lesions, the PET findings enabled the authors to make more appropriate decisions regarding treatment than those made on MR imaging findings alone. Therefore, the risk of surgically treating a nontumoral lesion was reduced as well as that for conservatively managing a malignant tumor. Nowadays, it is estimated that these data justify conservative management in incidental lesions with low or absent PET tracer uptake.

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.

[Imaging techniques in rheumatology: PET in rheumatology]

Positron emission tomography (PET) using F-18-fluoro-deoxyglucose (FDG) is suitable for many indications in oncology and can also be used in rheumatology to search for inflammatory foci and benign lesions with increased glucose metabolism in, for example soft tissue and joints (arthritis, vasculitis etc.) and fever of unknown origin. Usually a whole-body scanning technique is used for data acquisition in the search for foci of unknown localization or for the characterization of glucose metabolism of one or more known lesions - also for observation of the effect of, for example pharmacotherapy. Patients are admitted under fasting conditions and acquisition starts 1 h after i.v. injection of FDG with an acquisition time of 30-60 min. The method is sensitive and can measure glucose metabolism in an objective manner, but is not specific for inflammatory diseases (FDG also accumulates in malignant diseases).

Magnetic resonance spectroscopic imaging associated with analysis of fluid in cystic brain tumors

OBJECTIVE

There is a growing interest in cystic lesions of the brain. Examining the cyst content of brain tumors may contribute in determining the malignancy of the given tumor accompanied by a cyst.

METHODS

In this work, samples of cyst fluid from 18 patients with brain tumor were collected and studied biochemically regarding their protein, lactate contents and pH values; magnetic resonance spectroscopic images of these patients were also compared. We investigated the relation between the grade of malignancy and the lactate concentration and the discrepancy between the high levels of lactate in cysts and their alkaline environment.

RESULTS

There appears to be a positive relation between the grade of malignancy and the concentration of lactate in the cysts' fluid. A significant two-fold increase in lactate concentration in malignant tumors cysts has been found as compared with the more benign tumor cysts (p<0.001). This increase in lactate level is probably because of aerobic glycolysis, which causes lactate production by the tumor.

DISCUSSION

High lactate levels found through magnetic resonance spectroscopy are positively related to the grade of tumor malignancy. The pH values in the cyst fluids were above normal, resulting to a discrepancy in high levels of lactate in the cyst and the alkaline environment. This suggests efflux of H+ ions by a Na/H exchange mechanism to compensate for the change of pH.