Uncoupling of hexose transport and phosphorylation in human gliomas demonstrated by PET

Parametric Imaging With Dynamic PET for Oncological Applications: Protocols, Interpretation, Current Applications and Limitations for Clinical Use

Nuclear medicine imaging modalities, and in particular positron emission tomography (PET), provide functional images that demonstrate the mean radioactivity distribution at a defined point in time. With the help of mathematical model's, it is possible to depict isolated parameters of the radiotracers' pharmacokinetics and to visualize them. These so called parametric images add a new dimension to the existing conventional PET images and provide more detailed information about the tracer distribution over time and space. Prerequisite for the calculation of parametric images, which reflect specific pharmacokinetic parameters, is the dynamic PET (dPET) data acquisition. Hitherto, PET parametric imaging has mainly found use for research purposes. However, it has not been yet implemented into clinical routine, since it is more time-consuming, it requires a complicated analysis and still lacks a clear benefit over conventional PET imaging. However, the recent introduction of new PET-CT scanners with an ultralong field of view, which allow a faster data acquisition and are associated with higher sensitivity, as well as the development of more sophisticated evaluation software packages will probably lead to a renaissance of dPET and parametric maps even of the whole body. The implementation of dPET imaging in daily routine with appropriate acquisition protocols, as well as the calculation, interpretation and potential clinical applications of parametric images will be discussed in this review article.

[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).

The current role of PET-CT in the characterization of hepatobiliary malignancies

BACKGROUND

Surgery has become heavily dependent on accurate imaging in the assessment and treatment of suspected or confirmed intra-abdominal malignancy. Positron emission tomography-computed tomography (PET-CT) fuses uptake of a radiotracer combined with CT images to assess both functional tissue activity and anatomical detail. Since its introduction it has offered new ways of treating gastrointestinal cancers.

METHODS

The review analyses the present literature regarding the use of PET-CT in the assessment, diagnosis, staging and treatment of hepatobiliary malignancies.

RESULTS

PET-CT is widely used in pre-operative tumours staging for colorectal liver metastases. There is convincing data that it may also be applicable for neuroendocrine tumours, assessment of indeterminate pancreas lesions and clinical drug trials. PET-CT is of limited value in hepatocellular cancers, although new techniques in dual-tracer PET-CT may change this.

CONCLUSION

Knowledge of the strengths and limitations of PET-CT is important for all surgeons managing cancer of the hepatobiliary system. More clinical data are required on PET-CT, particularly its effect on long-term survival in PET-CT-staged patients undergoing resection.

Positron emission tomography for neurologists

This short review focuses on practical, present day, clinical application of FDG PET, a technology available to practicing neurologists for managing their patients. Indications in the disease states of dementia, neuro-oncology, epilepsy, parkinsonism, and other less common settings are reviewed. Many third-party payers currently make reimbursements based on these indications. By measuring an aspect of brain function, PET provides information that often is unobtainable from other sources, thus facilitating more rationale and cost-effective management, which can only benefit the patient, the referring physician, and the health care system as a whole.

Application of PET/CT in the development of novel anticancer drugs

Combined positron emission tomography/computed tomography (PET/CT) is a relatively new imaging modality, combining the functional images of PET with the anatomical information of CT. Since its commercial introduction about 5 years ago, PET/CT has become an important tool in oncology. Currently, the technique is used for primary staging and restaging of cancer patients, as well as for surgery and radiation therapy planning. The abilities of PET/CT to measure early treatment response as well as drug distribution within the body make this technique very useful in the development of novel anticancer drugs. In this paper, the recent literature on the current role of PET/CT in drug development is reviewed.

Determination of regional cerebral function with FDG-PET imaging in neuropsychiatric disorders

Functional brain imaging using 18F fluorodeoxyglucose (FDG) and positron emission tomography (PET) has greatly enhanced our understanding of brain function both in normal conditions as well as in a wide variety of neuropsychiatric disorders. We review the uses of FDG PET in the diagnosis, management, and follow-up of patients with neuropsychiatric disorders. This article will also explore what FDG-PET imaging has revealed in these neuropsychiatric disorders and how these findings relate to both research and clinical applications.

Uptake of iodine-123-alpha-methyl tyrosine by gliomas and non-neoplastic brain lesions

Using single-photon emission tomography (SPET), the radiopharmaceutical l-3-iodine-123-alpha-methyl tyrosine (IMT) has been applied to the imaging of amino acid transport into brain tumours. It was the aim of this study to investigate whether IMT SPET is capable of differentiating between high-grade gliomas, low-grade gliomas and non-neoplastic brain lesions. To this end, IMT uptake was determined in 53 patients using the triple-headed SPET camera MULTISPECT 3. Twenty-eight of these subjects suffered from high-grade gliomas (WHO grade III or IV), 12 from low-grade gliomas (WHO grade II), and 13 from non-neoplastic brain lesions, including lesions after effective therapy of a glioma (five cases), infarctions (four cases), inflammatory lesions (three cases) and traumatic haematoma (one case). IMT uptake was significantly higher in high-grade gliomas than in low-grade gliomas and non-neoplastic lesions. IMT uptake by low-grade gliomas was not significantly different from that by non-neoplastic lesions. Diagnostic sensitivity and specificity were 71% and 83% for differentiating high-grade from low-grade gliomas, 82% and 100% for distinguishing high-grade gliomas from non-neoplastic lesions, and 50% and 100% for discriminating low-grade gliomas from non-neoplastic lesions. Analogously to positron emission tomography with radioactively labelled amino acids and fluorine-18 deoxyglucose, IMT SPET may aid in differentiating high-grade gliomas from histologically benign brain tumours and non-neoplastic brain lesions; it is of only limited value in differentiating between non-neoplastic lesions and histologically benign brain tumours.

Metabolic patterns in malignant gliomas

Changes of mitochondrial and cytoplasm tumor metabolism were studied in malignant gliomas and normal cortex probes in vitro. By spectrophotometric methods marker enzymes of different mitochondrial (whole respiratory chain, citrate acid cycle, fatty oxidation) and cytoplasm (glycolysis, pentose phosphate shunt) metabolic energy pathways were analysed. Generally, the activities of intramitochondrial key enzymes were significantly decreased in gliomas when compared with enzyme activities of normal cortex tissue (p < 0.01). Glycolytic enzymes and a representative of the pentose phosphate shunt were unchanged or increased. Ratios of marker enzymes of the glycolytic pathway (lactate dehydrogenase) and glycose-6-P dehydrogenase revealed a significant difference between glioblastomas (p < 0.05) and grade III (p < 0.05) tumors in comparison to normal astrocytic tissue and astrocytomas WHO grade II. Thus, biochemical analyses allow metabolic grading of gliomas in vitro and may be a useful tool for understanding tumor biology.

Correlation of glucose consumption and tumor cell density in astrocytomas. A stereotactic PET study

To determine histological correlates of the variability of glucose consumption in astrocytomas, the authors performed positron emission tomography (PET) with 18F-2-fluoro-2-deoxy-D-glucose (FDG) and matched the PET scans three-dimensionally with computerized tomography scans obtained in a stereotactic frame before biopsy. Ten patients with astrocytomas of World Health Organization Grade 2 or 3 were studied; patients with glioblastomas, oligodendrogliomas, or oligoastrocytomas were excluded from the study to avoid any confounding effects of different cell types and necroses. In samples of pure tumor, glucose consumption correlated significantly with cell density, but not with nuclear polymorphism. It is concluded that tumor cell density is a major determinant of glucose consumption in astrocytomas. The use of PET with FDG may help to locate the highest cell density and thus improve the diagnostic yield of stereotactic biopsy.

Relationship between of blood flow, glucose metabolism, protein synthesis, glucose and ATP content in experimentally-induced glioma (RG1 2.2) of rat brain

In experimental RG1 2.2 glioma of rat brain, local blood flow, glucose utilization, protein synthesis, glucose and ATP content were measured by means of triple tracer autoradiography and bioluminescence technique, respectively, to determine hemodynamic and metabolic thresholds for local tumor energy failure. Perfusion thresholds were estimated at tumor blood flow values of 69.0 +/- 0.1 ml/100 g/min (estimate +/- standard error) and of 69 +/- 7.1 ml/100 g/min for the beginning of the decline in regional ATP and glucose content, respectively. Metabolic thresholds were derived at tumor glucose utilization values of 70.6 +/- 8.3 mumol/100 g/min for reduced protein synthesis, of 55.0 +/- 0.2 mumol/100 g/min for the decrease in glucose content, and 34.7 +/- 4.7 mumol/100 g/min for decline in ATP content. Our results suggest that blood flow limits glucose supply to tumor tissue at much higher flow rates than in normal brain which, in turn, is associated with a decrease in tumor glucose utilization. A reduction and not an increase in tumor glucose availability could be a more appropriate strategy for the induction of energy failure in tumors.

Non-stationary spatial filtering and accelerated curve fitting for parametric imaging with dynamic PET

A non-stationary spatial low pass filter was developed and implemented in combination with an accelerated non-linear curve fitting routine to create low noise-high contrast images of physiological parameters with dynamic positron emission tomography. The method was applied to 18F-2-fluoro-2-deoxyglucose (FDG) studies, and images of local blood volume, kinetic rate constants, precursor pool volume and glucose metabolism were generated. Noise reduction and contrast preservation was demonstrated in a simulated pie phantom and a study of a patient with a recent brain infarct. Considerably improvement in quantitative accuracy of pixel parameter values was observed in the phantom study in comparison with unprocessed or conventionally smoothed images.