Dynamic 18F-FDOPA-PET/MRI for the preoperative evaluation of gliomas: correlation with stereotactic histopathology

Magnetic resonance spectroscopy for enhanced multiparametric MRI characterization of [18F]FET PET-negative gliomas

BACKGROUND

Approximately 30-36% of gliomas presented with [18F]fluoroethyl-L-tyrosine ([18F]FET) PET-negative at primary diagnosis, which interferes with the differentiation of gliomas from other isolated brain lesions. Preoperative noninvasive identification of [18F]FET PET-negative gliomas to aggressive surgical treatment could reduce ineffective treatment and improve prognosis. This study aimed to assess the potential utility of multiparametric MRI with 1H-magnetic resonance spectroscopy (1H-MRS) in the diagnosis of gliomas within [18F]FET PET-negative isolated cerebral lesions.

RESULTS

A total of 51 patients (mean age 44.35 ± 27.15 years, 26 males) with 37 gliomas and 14 non-gliomas were recruited for the study. More than half of PET-negative gliomas presented T2-FLAIR mismatch sign, whereas non-gliomas were more likely to present absence of T2-FLAIR mismatch sign (54.05% vs. 7.14%, p < 0.001). Choline to creatine (Cho/Cr) ratios in gliomas were significantly higher than those in non-gliomas (2.21 vs. 1.30, p < 0.001). Multiparametric MRI (AUC = 0.88) outperformed conventional MRI (AUC = 0.72) in differentiating gliomas from non-gliomas (NRI = 0.29, p = 0.02). And WHO grade was correlated with Cho/Cr and total lesion tracer standardized uptake (TLU) (r = 0.43 and 0.55; p = 0.007 and < 0.001; respectively). Low-grade PET-negative gliomas exhibit low levels of both TLU and Cho/Cr, but the distribution of TLU and Cho/Cr is more variable in high-grade gliomas. Furthermore, there was a moderated correlation between TLU and Cho/Cr in low-grade PET-negative gliomas (r = 0.54, p = 0.017), whereas there was no correlation in the high-grade PET-negative gliomas (r = -0.017, p = 0.95).

CONCLUSION

Multiparametric MRI with 1H-MRS demonstrates significant promise in enhancing the diagnosis and overall clinical management for [18F]FET PET-negative gliomas. Moreover, the correlation between TLU and Cho/Cr that was affected by tumor grading of 2021 WHO criteria provides a rationale for further research into the mechanisms of reduced [18F]FET uptake in gliomas.

Case Report: 18F-FDOPA PET in the clinical management of a dog with an intraventricular tumor suspected to be choroid plexus papilloma

An 8-year-old neutered male Miniature Poodle, weighing 6.7 kg, was presented with lethargy, anorexia, and single seizure episode. Neurological examination revealed bilaterally absent menace reflexes and an obtunded mental status. Magnetic resonance imaging showed a papilliform shaped mass measuring 1.2 × 1.4 × 1.3 cm in size, with a volume of 1.17 cm3 in the third ventricle. 3,4-dihydroxy-6-[18F] fluoro-l-phenylalanine (18F-FDOPA) positron emission tomography/computed tomography (PET/CT) was performed 53 days after presentation, revealing a hypermetabolic region in the intraventricular mass with mean and maximal standardized uptake values (SUVmean and SUVmax) of 1.2 and 1.42, respectively, and a tumor to normal tissue (T/N) ratio of 1.33. The mass lesion measured 1.3 × 1.4 × 1.2 cm in size, with a volume of 1.09 cm3 on contrast-enhanced CT images. The metabolic tumor volume (MTV) was 1.184cm . 3 No evidence of brain parenchymal metastases was observed. Therefore, the dog was tentatively diagnosed with a brain tumor, which was suspected to be a choroid plexus papilloma (CPP) and chemotherapy with prednisolone and cyclophosphamide was initiated. As worsening clinical signs were observed, a second 18F-FDOPA PET/CT scan was performed on day 183. The SUVmean, SUVmax, and T/N ratio of the lesion were 1.49, 1.85, and 1.62, respectively. The mass lesion measured 1.0 × 1.0 × 1.3 cm in size, with a volume of 0.68 cm3 on contrast-enhanced CT images, whereas the MTV was increased to 2.217 cm3. The dog died 186 days after the presentation. To the best of our knowledge, this is the first report describing the 18F-FDOPA PET/CT findings in a dog with an intraventricular brain tumor suspected of having CPP. In the present case, although the lesion size decreased on CT contrast imaging, an increase in the MTV was observed on follow-up 18F-FDOPA PET/CT after chemotherapy. Thus, an increase in MTV post-chemotherapy combined with the worsening clinical signs and limited survival period in dogs correlates with poor prognosis, as previously reported in a human study. This case offers significant diagnostic insights into canine intraventricular tumors within the field of veterinary medicine.

Complex Diagnostic Challenges in Glioblastoma: The Role of 18F-FDOPA PET Imaging

Glioblastoma multiforme (GBM) remains one of the most aggressive and lethal forms of brain cancer, characterized by rapid proliferation and diffuse infiltration into the surrounding brain tissues. Despite advancements in therapeutic approaches, the prognosis for GBM patients is poor, with median survival times rarely exceeding 15 months post-diagnosis. An accurate diagnosis, treatment planning, and monitoring are crucial for improving patient outcomes. Core imaging modalities such as Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are indispensable in the initial diagnosis and ongoing management of GBM. Histopathology remains the gold standard for definitive diagnoses, guiding treatment by providing molecular and genetic insights into the tumor. Advanced imaging modalities, particularly positron emission tomography (PET), play a pivotal role in the management of GBM. Among these, 3,4-dihydroxy-6-[18F]-fluoro-L-phenylalanine (18F-FDOPA) PET has emerged as a powerful tool due to its superior specificity and sensitivity in detecting GBM and monitoring treatment responses. This introduction provides a comprehensive overview of the multifaceted role of 18F-FDOPA PET in GBM, covering its diagnostic accuracy, potential as a biomarker, integration into clinical workflows, impact on patient outcomes, technological and methodological advancements, comparative effectiveness with other PET tracers, and its cost-effectiveness in clinical practice. Through these perspectives, we aim to underscore the significant contributions of 18F-FDOPA PET to the evolving landscape of GBM management and its potential to enhance both clinical and economic outcomes for patients afflicted with this formidable disease.

A Systematic Review of Amino Acid PET Imaging in Adult-Type High-Grade Glioma Surgery: A Neurosurgeon's Perspective

Amino acid PET imaging has been used for a few years in the clinical and surgical management of gliomas with satisfactory results in diagnosis and grading for surgical and radiotherapy planning and to differentiate recurrences. Biological tumor volume (BTV) provides more meaningful information than standard MR imaging alone and often exceeds the boundary of the contrast-enhanced nodule seen in MRI. Since a gross total resection reflects the resection of the contrast-enhanced nodule and the majority of recurrences are at a tumor's margins, an integration of PET imaging during resection could increase PFS and OS. A systematic review of the literature searching for "PET" [All fields] AND "glioma" [All fields] AND "resection" [All fields] was performed in order to investigate the diffusion of integration of PET imaging in surgical practice. Integration in a neuronavigation system and intraoperative use of PET imaging in the primary diagnosis of adult high-grade gliomas were among the criteria for article selection. Only one study has satisfied the inclusion criteria, and a few more (13) have declared to use multimodal imaging techniques with the integration of PET imaging to intentionally perform a biopsy of the PET uptake area. Despite few pieces of evidence, targeting a biologically active area in addition to other tools, which can help intraoperatively the neurosurgeon to increase the amount of resected tumor, has the potential to provide incremental and complementary information in the management of brain gliomas. Since supramaximal resection based on the extent of MRI FLAIR hyperintensity resulted in an advantage in terms of PFS and OS, PET-based biological tumor volume, avoiding new neurological deficits, deserves further investigation.

The role of [18F]fluorodopa positron emission tomography in grading of gliomas

PURPOSE

Gliomas are the most commonly occurring brain tumour in adults and there remains no cure for these tumours with treatment strategies being based on tumour grade. All treatment options aim to prolong survival, maintain quality of life and slow the inevitable progression from low-grade to high-grade. Despite imaging advancements, the only reliable method to grade a glioma is to perform a biopsy, and even this is fraught with errors associated with under grading. Positron emission tomography (PET) imaging with amino acid tracers such as [18F]fluorodopa (18F-FDOPA), [11C]methionine (11C-MET), [18F]fluoroethyltyrosine (18F-FET), and 18F-FDOPA are being increasingly used in the diagnosis and management of gliomas.

METHODS

In this review we discuss the literature available on the ability of 18F-FDOPA-PET to distinguish low- from high-grade in newly diagnosed gliomas.

RESULTS

In 2016 the Response Assessment in Neuro-Oncology (RANO) and European Association for Neuro-Oncology (EANO) published recommendations on the clinical use of PET imaging in gliomas. However, since these recommendations there have been a number of studies performed looking at whether 18F-FDOPA-PET can identify areas of high-grade transformation before the typical radiological features of transformation such as contrast enhancement are visible on standard magnetic resonance imaging (MRI).

CONCLUSION

Larger studies are needed to validate 18F-FDOPA-PET as a non-invasive marker of glioma grade and prediction of tumour molecular characteristics which could guide decisions surrounding surgical resection.

Case Report: 18F-Fluoro-L-Phenylalanine Positron Emission Tomography Findings and Immunoreactivity for L-Type Amino Acid Transporter 1 in a Dog With Meningioma

A 12-year-old intact female Miniature Pinscher dog weighing 5.4 kg presented with a history of seizures. On neurological examination, postural reactions were decreased in the left-sided limbs, and menace responses were bilaterally absent. Magnetic resonance imaging (MRI) of the brain was performed, and a solitary amorphous mass (2.7 × 1.9 × 2.2 cm) was observed on the right side of the frontal lobe. Based on the signalment, clinical signs, and MRI findings, a brain tumor was tentatively diagnosed, and meningioma was suspected. The dog was treated with hydroxyurea, prednisolone, and other antiepileptic drugs. One week after the treatment began, postural reactions returned to normal, and the menace response improved. At 119 days after treatment, 18F-fluoro-L-phenylalanine (18F-FDOPA) positron emission tomography (PET) was performed. Marked 18F-FDOPA uptake was observed in the lesion. The mean and maximal standardized uptake values of the lesion were 2.61 and 3.72, respectively, and the tumor-to-normal tissue ratio was 1.95. At 355 days after the initial treatment, a second MRI scan was performed and the tumor size had increased to 3.5 × 2.8 × 2.9 cm. The dog died 443 days after the initial treatment and was definitively diagnosed with grade 1 meningioma by histopathological examination. Immunohistochemical staining for Ki67 and L-type amino acid transporter 1 was positive and negative for p53, respectively. The labeling index of Ki67 was 2.4%. This is the first case to demonstrate 18F-FDOPA PET findings in a clinical case of a dog histologically diagnosed with a meningioma.

Update on the Use of PET/MRI Contrast Agents and Tracers in Brain Oncology: A Systematic Review

The recent advancements in hybrid positron emission tomography–magnetic resonance imaging systems (PET/MRI) have brought massive value in the investigation of disease processes, in the development of novel treatments, in the monitoring of both therapy response and disease progression, and, not least, in the introduction of new multidisciplinary molecular imaging approaches. While offering potential advantages over PET/CT, the hybrid PET/MRI proved to improve both the image quality and lesion detectability. In particular, it showed to be an effective tool for the study of metabolic information about lesions and pathological conditions affecting the brain, from a better tumor characterization to the analysis of metabolic brain networks. Based on the PRISMA guidelines, this work presents a systematic review on PET/MRI in basic research and clinical differential diagnosis on brain oncology and neurodegenerative disorders. The analysis includes literature works and clinical case studies, with a specific focus on the use of PET tracers and MRI contrast agents, which are usually employed to perform hybrid PET/MRI studies of brain tumors. A systematic literature search for original diagnostic studies is performed using PubMed/MEDLINE, Scopus and Web of Science. Patients, study, and imaging characteristics were extracted from the selected articles. The analysis included acquired data pooling, heterogeneity testing, sensitivity analyses, used tracers, and reported patient outcomes. Our analysis shows that, while PET/MRI for the brain is a promising diagnostic method for early diagnosis, staging and recurrence in patients with brain diseases, a better definition of the role of tracers and imaging agents in both clinical and preclinical hybrid PET/MRI applications is needed and further efforts should be devoted to the standardization of the contrast imaging protocols, also considering the emerging agents and multimodal probes.