Investigation of Cerebral O-(2-[18F]Fluoroethyl)-L-Tyrosine Uptake in Rat Epilepsy Models

Challenges, limitations, and pitfalls of PET and advanced MRI in patients with brain tumors: A report of the PET/RANO group

Brain tumor diagnostics have significantly evolved with the use of positron emission tomography (PET) and advanced magnetic resonance imaging (MRI) techniques. In addition to anatomical MRI, these modalities may provide valuable information for several clinical applications such as differential diagnosis, delineation of tumor extent, prognostication, differentiation between tumor relapse and treatment-related changes, and the evaluation of response to anticancer therapy. In particular, joint recommendations of the Response Assessment in Neuro-Oncology (RANO) Group, the European Association of Neuro-oncology, and major European and American Nuclear Medicine societies highlighted that the additional clinical value of radiolabeled amino acids compared to anatomical MRI alone is outstanding and that its widespread clinical use should be supported. For advanced MRI and its steadily increasing use in clinical practice, the Standardization Subcommittee of the Jumpstarting Brain Tumor Drug Development Coalition provided more recently an updated acquisition protocol for the widely used dynamic susceptibility contrast perfusion MRI. Besides amino acid PET and perfusion MRI, other PET tracers and advanced MRI techniques (e.g. MR spectroscopy) are of considerable clinical interest and are increasingly integrated into everyday clinical practice. Nevertheless, these modalities have shortcomings which should be considered in clinical routine. This comprehensive review provides an overview of potential challenges, limitations, and pitfalls associated with PET imaging and advanced MRI techniques in patients with gliomas or brain metastases. Despite these issues, PET imaging and advanced MRI techniques continue to play an indispensable role in brain tumor management. Acknowledging and mitigating these challenges through interdisciplinary collaboration, standardized protocols, and continuous innovation will further enhance the utility of these modalities in guiding optimal patient care.

Characterization of metabolic activity induced by kainic acid in adult rat whole brain at the early stage: A 18FDG-PET study

OBJECTIVE

Brain metabolic processes are not fully characterized in the kainic acid (KA)-induced Status Epilepticus (KASE). Thus, we evaluated the usefulness of ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) as an experimental strategy to evaluate in vivo, in a non-invasive way, the glucose consumption in several brain regions, in a semi-quantitative study to compare and to correlate with data from electroencephalography and histology studies.

METHODS

Sixteen male Wistar rats underwent FDG-PET scans at basal state and after KA injection. FDG-PET images were normalized to an MRI-based atlas and segmented to locate regions. Standardized uptake values (SUV) were obtained at several time points. EEGs and cell viability by histological analysis, were also evaluated.

RESULTS

FDG-PET data showed changes in regions such as: amygdala, hippocampus, accumbens, entorhinal cortex, motor cortex and hypothalamus. Remarkably, hippocampal hypermetabolism was found (mean SUV = 2.66 ± 0.057) 2 h after KA administration, while hypometabolism at 24 h (mean SUV = 1.83 ± 0.056) vs basal values (mean SUV = 2.19 ± 0.057). EEG showed increased spectral power values 2 h post-KA administration. Hippocampal viable-cell counting 24 h after KA was decreased, while Fluoro-Jade B-positive cells were increased, as compared to control rats, coinciding with the hypometabolism detected in the same region by semi-quantitative FDG-PET at 24 h after KASE.

CONCLUSIONS

PET is suitable to measure metabolic brain changes in the rat model of status epilepticus induced by KA (KASE) at the first 24 h, compared to that of EEG; PET data may also be sensitive to cell viability.

PET Imaging in Neurodegeneration and Neuro-oncology: Variants and Pitfalls

In neurodegenerative diseases, positron emission tomography (PET) imaging plays an important role in the early identification and differential diagnosis in particular in clinically challenging patients. ¹⁸F-FDG is still the most widely used and established tracer in this patient group, with different cortical and subcortical regions being preferentially affected in different neurodegenerative diseases, such as frontotemporal dementia, Alzheimer's disease or Lewy Body dementia, resulting in typical hypometabolic patterns. Over the last decades, however, the implementation of tracers specific for the pathological deposits characteristic of the different diseases, such as amyloid and tau, has revolutionized the way of classifying and reporting cases of cognitive impairment of neurodegenerative origin, providing complementary information to ¹⁸F-FDG PET. In neuro-oncology, PET imaging can be performed in several clinical indications, as highlighted in the joint European Association of Nuclear Medicine (EANM)/European Association of Neuro-Oncology (EANO)/Response assessment in neuro-oncology (RANO) practice guidelines on imaging in neuro-oncology. For assessment of glioma, amino-acid analogues, such as ¹¹C-methionine or ¹⁸F-FET, are used whenever clinically available, as they offer excellent tumor-to-background ratios in malignant tumors. Moreover, dynamic acquisition of amino-acid analogue tracers and assessment of the shape of the time-activity curve can be used to perform noninvasive grading of brain gliomas, differentiating low from high grade presentations. In both settings, however, thorough knowledge of the normal physiological tracer distribution and the variants and pitfalls that can occur during image acquisition, processing and interpretation is mandatory in order to provide optimal diagnostic information to referring physicians and patients. Especially in neuro-oncology, this process can be aided by the active use of coregistered magnetic resonance imaging to accurately identify the imaging correlates of developmental origin, acute and chronic stroke, inflammation, infection and seizure related activity.