Abstract
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Objectives: Emphasizing the importance of adjusting window setting to improve the detection of brain metastases from extra-cranial neoplasms when the whole brain is included in the routine whole body 18F-FDG PET/CT scan.
Methods: Standard oncologic whole body PET imaging may include imaging of the brain. On routine PET windowing, brain uptake appears diffusely hyper-intense, limiting visualization of intracranial lesions. Detection of brain lesions on whole-body PET often requires adjusting window settings to reduce the intensity of normal brain FDG activity and improve detection of intracranial lesions [1]. We present several cases of brain metastases identified with this technique which could have otherwise be easily missed using routine PET windowing.
Results: Many patients with malignancies undergo whole body PET/CT to assess tumor spread. The brain is a common site of metastatic spread. In patients with solid extra-cranial tumors, brain metastases occur in 10%-35% of the cases [2]. MRI remains the gold standard for diagnosing brain lesions [3]. Brain scanning as a part of whole body scan can provide early and crucial information for further patient management, especially in asymptomatic patients with positive findings detected on whole body PET/CT, so that timely treatment could be offered [4]. The major drawback of brain scanning is the physiologically high brain 18F-FDG uptake, which may exceed the expected uptake of many malignant lesions, thus limiting visualization of these lesions. Several techniques have been proposed to overcome this problem, like dual time point imaging, or glucose loading [5-7]. However these techniques require specific dedicated brain protocols, are time consuming, and are difficult to use in routine whole body PET scans. The typical PET activity viewing range is an SUV value scale of 0-5, but when we examine the brain we typically use an SUV range of 0-15 or higher if needed. Applying this simple technique helped in identifying metastatic brain lesion in several patients with extra-cranial malignancies.
Conclusion: 18F-FDG PET is known to have poor sensitivity for malignant brain lesions [8], however if the brain is included in the scanned field during whole body PET/CT scan it can provide crucial information for patient management. An important step in the evaluation of brain PET imaging is to adjust the window setting to help decrease the physiologically high metabolic activity of the brain and allow metabolically active brain lesions to be readily identified. It is likely that incidental detection of brain metastases by whole body PET/CT can change the patient's management.