PET imaging for brain tumor diagnostics

Intracranial myeloid sarcoma as the first presentation of acute myeloid leukemia and literature review

INTRODUCTION

Intracranial myeloid sarcoma is a rare extramedullary presentation of acute myeloid leukemia (AML). It can involve the meninges and ependyma presenting as extra-axial mass lesion. Rarely, it can also invade the brain parenchyma. It is commonly seen in children. It is usually misdiagnosed due to its close resemblance to other intracranial tumors (meningioma, metastasis, Ewing's sarcomas, and lymphoma). These are underdiagnosed if they precede the diagnosis of leukemia.

CASE REPORT

A 7-year-old boy with isolated intracranial myeloid sarcoma who presented with raised intracranial pressure (ICP) which was successfully managed by surgical excision.

CONCLUSION

Isolated intracranial myeloid sarcoma is a rare presentation of AML. Leukemia can be diagnosed early during the postoperative period and can be started on therapy timely. These patients requires regular follow-ups (clinical, laboratory and radiological) to detect relapses early.

Recent Advances in Liquid Biopsy of Brain Cancers

Brain cancers are among the top causes of death worldwide. Although, the survival rates vary widely depending on the type of the tumor, early diagnosis could generally benefit in better prognosis outcomes of the brain cancer patients. Conventionally, neuroimaging and biopsy are the most widely used approaches in diagnosis, subtyping, and prognosis monitoring of brain cancers, while emerging liquid biopsy assays using peripheral blood or cerebrospinal fluid have demonstrated many favorable characteristics in this task, especially due to their minimally invasive and easiness in sampling nature. Here, we review the recent studies in the liquid biopsy of brain cancers. We discuss the methodologies and performances of various assays on diagnosis, tumor subtyping, relapse prediction as well as prognosis monitoring in brain cancers, which approaches have made a big step toward clinical benefits of brain cancer patients.

Advanced Magnetic Resonance Imaging of the Skull Base

Magnetic resonance (MR) imaging is a crucial tool for evaluation of the skull base, enabling characterization of complex anatomy by utilizing multiple image contrasts. Recent technical MR advances have greatly enhanced radiologists' capability to diagnose skull base pathology and help direct management. In this paper, we will summarize cutting-edge clinical and emerging research MR techniques for the skull base, including high-resolution, phase-contrast, diffusion, perfusion, vascular, zero echo-time, elastography, spectroscopy, chemical exchange saturation transfer, PET/MR, ultra-high-field, and 3D visualization. For each imaging technique, we provide a high-level summary of underlying technical principles accompanied by relevant literature review and clinical imaging examples.

Isolated intracranial myeloid sarcoma: report of a case and review of the literature

Myeloid sarcoma is a rare malignant tumor of primitive myeloid cell origin often associated with hematologic disorders. The central nervous system is rarely involved and differentiating between myeloid sarcoma and other tumors is not possible on imaging. Here we present the rare case of an isolated intracranial myeloid sarcoma, initially misdiagnosed radiologically as a meningioma, treated with surgical total resection and subsequent chemotherapy, with no signs of any hematological disorder at follow up. Differential diagnosis and management strategies, as well as follow-up implications are discussed along with literature review, which pointed out that only five cases with no further signs of hematological disorders at follow up have been described in the literature so far and this case has the longest follow up of them at 9 years.

The Diagnostic Value Of Using 18F-Fluorodeoxyglucose Positron Emission Tomography To Differentiate Between Low- And High-Grade Meningioma

Objective

This study aims to evaluate the potential role of ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) in detecting high-grade meningiomas and predicting the prognosis of patients after meningioma surgery.

Patients and methods

A total of 124 patients met the final inclusion criterion. Tumor to gray ratio (TGR) was compared with Ki-67 labeling index, and its correlations with pre-operative neurological function and treatment status were also evaluated. Receiver-operating characteristic (ROC) curve was drawn to determine a cut-off value which could discriminate meningioma of different grades. Prognostic factors including TGR were analyzed using Kaplan-Meier survival curve and cox proportional model.

Results

The TGR of higher World Health Organization (WHO) grade meningioma was significantly higher than that in lower grade (p < 0.001), and it was correlated with the Ki-67 labeling index (p < 0.001, r = 0.1545). The TGR of 1.30 was the best cutoff value for the detection of high grade (WHO grade II&III) meningioma from low grade (WHO grade I) according to ROC analysis, with a sensitivity of 61.5%, the specificity of 86.7%, and accuracy of 81.5%. The TGR (p < 0.001), treatment status (p = 0.035), tumor grade (p < 0.001) and Ki-67 labeling index (p < 0.001) were significantly associated with progression-free survival (PFS). Cox proportional hazards model demonstrated that TGR (p = 0.013) was an independent prognostic factor for PFS.

Conclusion

A high uptake of FDG was correlated with a more proliferative biological behavior and is a risk factor for tumor recurrence.

Application of siemens SMART neuro attenuation correction in brain PET imaging

Siemens SMART neuro attenuation correction (SNAC) is a new type of calculated attenuation correction (CAC) method. This article aimed to evaluate the effect of SNAC on the quantitative analysis of brain positron emission tomography (PET) imaging.Brain PET images of 52 healthy participants after reconstructed by SNAC and CT attenuation correction (CTAC) were analyzed qualitatively by visual analysis, and quantitatively by Scenium software to compare their contrast, signal-to-noise ratio (SNR) as well as the mean standardized uptake value (SUVmean) of different brain regions.Compared with CTAC, reconstruction of images by SNAC significantly reduced the SNR by 17.3% (P < .001), but not affected the contrast (P = .440). In addition, the SUVmean of different brain regions in images reconstructed by SNAC is increased, but still significantly correlated with that by CTAC (r = 0.988, P < .001), with a coefficient of R = 0.976 in linear regression analysis. Moreover, the mean percent difference of SUVmean between images reconstructed with SNAC and CTAC was 8.03% ± 5.38%, varying significantly in the range of -7.56% to 75.31% among 10 different brain regions (F = 35.702, P < .001) and showed greater percent difference in the peripheral brain regions than in the mesial brain regions.Image reconstruction by SNAC has greater effect on quantitative analysis by increasing SUVmean of different brain regions to varying degrees, but has little influence on the brain PET image quality. Moreover, it simplifies examination process and reduces radiation dose, which is beneficial to pediatric patients as well as serial scans to monitor therapy.

The Role of Advanced Brain Tumor Imaging in the Care of Patients with Central Nervous System Malignancies

OPINION STATEMENT

T1-weighted post-contrast and T2-weighted fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI) constitute the gold standard for diagnosis and response assessment in neuro-oncologic patients but are limited in their ability to accurately reflect tumor biology and metabolism, particularly over the course of a patient's treatment. Advanced MR imaging methods are sensitized to different biophysical processes in tissue, including blood perfusion, tumor metabolism, and chemical composition of tissue, and provide more specific information on tissue physiology than standard MRI. This review provides an overview of the most common and emerging advanced imaging modalities in the field of brain tumor imaging and their applications in the care of neuro-oncologic patients.

Carbon-11 and Fluorine-18 Labeled Amino Acid Tracers for Positron Emission Tomography Imaging of Tumors

Tumor cells have an increased nutritional demand for amino acids (AAs) to satisfy their rapid proliferation. Positron-emitting nuclide labeled AAs are interesting probes and are of great importance for imaging tumors using positron emission tomography (PET). Carbon-11 and fluorine-18 labeled AAs include the [1-¹¹C] AAs, labeling alpha-C- AAs, the branched-chain of AAs and N-substituted carbon-11 labeled AAs. These tracers target protein synthesis or amino acid (AA) transport, and their uptake mechanism mainly involves AA transport. AA PET tracers have been widely used in clinical settings to image brain tumors, neuroendocrine tumors, prostate cancer, breast cancer, non-small cell lung cancer (NSCLC) and hepatocellular carcinoma. This review focuses on the fundamental concepts and the uptake mechanism of AAs, AA PET tracers and their clinical applications.

Current Radiopharmaceuticals for Positron Emission Tomography of Brain Tumors

Brain tumors represent a diverse spectrum of histology, biology, prognosis, and treatment options. Although MRI remains the gold standard for morphological tumor characterization, positron emission tomography (PET) can play a critical role in evaluating disease status. This article focuses on the use of PET with radiolabeled glucose and amino acid analogs to aid in the diagnosis of tumors and differentiate between recurrent tumors and radiation necrosis. The most widely used tracer is ¹⁸F-fluorodeoxyglucose (FDG). Although the intensity of FDG uptake is clearly associated with tumor grade, the exact role of FDG PET imaging remains debatable. Additionally, high uptake of FDG in normal grey matter limits its use in some low-grade tumors that may not be visualized. Because of their potential to overcome the limitation of FDG PET of brain tumors, ¹¹C-methionine and ¹⁸F-3,4-dihydroxyphenylalanine (FDOPA) have been proposed. Low accumulation of amino acid tracers in normal brains allows the detection of low-grade gliomas and facilitates more precise tumor delineation. These amino acid tracers have higher sensitivity and specificity for detecting brain tumors and differentiating recurrent tumors from post-therapeutic changes. FDG and amino acid tracers may be complementary, and both may be required for assessment of an individual patient. Additional tracers for brain tumor imaging are currently under development. Combinations of different tracers might provide more in-depth information about tumor characteristics, and current limitations may thus be overcome in the near future. PET with various tracers including FDG, ¹¹C-methionine, and FDOPA has improved the management of patients with brain tumors. To evaluate the exact value of PET, however, additional prospective large sample studies are needed.

The use of amino acid PET and conventional MRI for monitoring of brain tumor therapy

Routine diagnostics and treatment monitoring of brain tumors is usually based on contrast-enhanced MRI. However, the capacity of conventional MRI to differentiate tumor tissue from posttherapeutic effects following neurosurgical resection, chemoradiation, alkylating chemotherapy, radiosurgery, and/or immunotherapy may be limited. Metabolic imaging using PET can provide relevant additional information on tumor metabolism, which allows for more accurate diagnostics especially in clinically equivocal situations. This review article focuses predominantly on the amino acid PET tracers 11C-methyl-l-methionine (MET), O-(2-[18F]fluoroethyl)-l-tyrosine (FET) and 3,4-dihydroxy-6-[18F]-fluoro-l-phenylalanine (FDOPA) and summarizes investigations regarding monitoring of brain tumor therapy.

Improving the Grading Accuracy of Astrocytic Neoplasms Noninvasively by Combining Timing Information with Cerebral Blood Flow: A Multi-TI Arterial Spin-Labeling MR Imaging Study

BACKGROUND AND PURPOSE

Systematic and accurate glioma grading has clinical significance. We present the utility of multi-TI arterial spin-labeling imaging and provide the bolus arrival time maps for grading astrocytomas.

MATERIALS AND METHODS

Forty-three patients with astrocytomas (21 men; mean age, 51 years) were recruited. The classification abilities of conventional MR imaging features, normalized CBF value derived from multi-TI arterial spin-labeling imaging, normalized bolus arrival time, and normalized CBF derived from single-TI arterial spin-labeling were compared in patients with World Health Organization (WHO) grade II, III, and IV astrocytomas.

RESULTS

The normalized CBF value derived from multi-TI arterial spin-labeling imaging was higher in patients with higher grade astrocytoma malignancies compared with patients with lower grade astrocytomas, while the normalized bolus arrival time showed the opposite tendency. The normalized CBF value derived from the multi-TI arterial spin-labeling imaging showed excellent performance with areas under the receiver operating characteristic curve of 0.813 (WHO II versus III), 0.964 (WHO II versus IV), 0.872 (WHO III versus IV), and 0.883 (low-grade-versus-high-grade gliomas). The normalized CBF value derived from single-TI arterial spin-labeling imaging could statistically differentiate the WHO II and IV groups (area under the receiver operating characteristic curve = 0.826). The normalized bolus arrival time effectively identified the WHO grades II and III with an area under the receiver operating characteristic curve of 0.836. Combining the normalized CBF value derived from multi-TI arterial spin-labeling imaging and normalized bolus arrival time improved the diagnostic accuracy from 65.10% to 72.10% compared with the normalized CBF value derived from multi-TI arterial spin-labeling imaging being applied independently. The combination of multi-TI arterial spin-labeling imaging and conventional MR imaging had the best performance, with a diagnostic accuracy of 81.40%.

CONCLUSIONS

Multi-TI arterial spin-labeling imaging can evaluate perfusion dynamics by combining normalized bolus arrival time and normalized CBF values derived from multiple TIs. It is superior to single-TI arterial spin-labeling imaging and conventional MR imaging features when applied independently and can improve the diagnostic accuracy when combined with conventional MR imaging for grading astrocytomas.

A longitudinal magnetic resonance elastography study of murine brain tumors following radiation therapy

An accurate and noninvasive method for assessing treatment response following radiotherapy is needed for both treatment monitoring and planning. Measurement of solid tumor volume alone is not sufficient for reliable early detection of therapeutic response, since changes in physiological and/or biomechanical properties can precede tumor volume change following therapy. In this study, we use magnetic resonance elastography to evaluate the treatment effect after radiotherapy in a murine brain tumor model. Shear modulus was calculated and compared between the delineated tumor region of interest (ROI) and its contralateral, mirrored counterpart. We also compared the shear modulus from both the irradiated and non-irradiated tumor and mirror ROIs longitudinally, sampling four time points spanning 9-19 d post tumor implant. Results showed that the tumor ROI had a lower shear modulus than that of the mirror ROI, independent of radiation. The shear modulus of the tumor ROI decreased over time for both the treated and untreated groups. By contrast, the shear modulus of the mirror ROI appeared to be relatively constant for the treated group, while an increasing trend was observed for the untreated group. The results provide insights into the tumor properties after radiation treatment and demonstrate the potential of using the mechanical properties of the tumor as a biomarker. In future studies, more closely spaced time points will be employed for detailed analysis of the radiation effect.

Static FET-PET and MR Imaging in Anaplastic Gliomas (WHO III)

OBJECTIVE

O-(2-[18F]-fluoroethyl)-L-tyrosine-positron emission tomography (FET-PET) imaging is an additional tool for tumor grading and surgery planning. Up to now, not much is known about FET-PET imaging in anaplastic gliomas. Our objective was to assess the FET uptake in anaplastic gliomas, compared with magnetic resonance imaging (MRI), histopathologic markers, and its prognostic value.

PATIENTS AND METHODS

Forty-six patients (27 males/19 females) with an anaplastic glioma (WHO III) who received MRI and FET-PET imaging before surgery were retrospectively analyzed. Tumor volume was calculated in MRI and FET-PET imaging using a tumor-to-background ratio (TBR), and maximum FET uptake (TBRmax) was calculated. Overall survival (OS) and histopathologic markers (isocitrate-dehydrogenase 1/2-mutation, oligodendrial differentiation, and Ki67 proliferation index) were assessed. Univariate and multivariate analysis was performed for OS.

RESULTS

In univariate analysis a significant correlation of TBRmax to OS was observed (P = 0.031). Tumor volume in FET-PET imaging (TBR > 2.0) (P = 0.028) showed a higher correlation to OS than the volume of the contrast-enhancing tumor part (P = 0.031). The highest correlation was observed for intersection of volume TBR > 1.3 and the volume of the contrast-enhancing tumor part (P = 0.005); fluid-attenuated inversion recovery volume showed no significant correlation to OS (P = 0.401) in the univariate analysis. Anaplastic glioma with oligodendrial differentiation showed significantly higher TBRmax values (P = 0.029), while no significant difference was observed for isocitrate hydrogenase 1/2-mutation (P = 0.752).

CONCLUSION

Static FET-PET provides significant prognostic information in anaplastic gliomas, which adds to the value of MRI, supporting the use of both modalities preoperatively to assess individual risks and estimate prognosis. Definition of the histopathologic subtype using static FET-PET remains challenging.

From the clinician's point of view - What is the status quo of positron emission tomography in patients with brain tumors?

The most common type of primary brain tumor is malignant glioma. Despite intensive therapeutic efforts, the majority of these neoplasms remain incurable. Imaging techniques are important for initial tumor detection and comprise indispensable tools for monitoring treatment. Structural imaging using contrast-enhanced MRI is the method of choice for brain tumor surveillance, but its capacity to differentiate tumor from nonspecific tissue changes can be limited, particularly with posttreatment gliomas. Metabolic imaging using positron-emission-tomography (PET) can provide relevant additional information, which may allow for better assessment of tumor burden in ambiguous cases. Specific PET tracers have addressed numerous molecular targets in the last decades, but only a few have achieved relevance in routine clinical practice. At present, PET studies using radiolabeled amino acids appear to improve clinical decision-making as these tracers can offer better delineation of tumor extent as well as improved targeting of biopsies, surgical interventions, and radiation therapy. Amino acid PET imaging also appears useful for distinguishing glioma recurrence or progression from postradiation treatment effects, particularly radiation necrosis and pseudoprogression, and provides information on histological grading and patient prognosis. In the last decade, the tracers O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET) and 3,4-dihydroxy-6-[(18)F]-fluoro-L-phenylalanine (FDOPA) have been increasingly used for these indications. This review article focuses on these tracers and summarizes their recent applications for patients with brain tumors. Current uses of tracers other than FET and FDOPA are also discussed, and the most frequent practical questions regarding PET brain tumor imaging are reviewed.