PET imaging with the most widely available PET tracer, 2-deoxy-2-[18F]fluoro-d-glucose (FDG), is a powerful tool in the differential diagnosis of numerous neurologic and psychiatric disorders, particularly in early disease stages. It also plays an important role in the longitudinal evaluation of treatment effects and the depiction of disease courses. A selection of established and eligible application areas of FDG PET in neurology and psychiatry, such as different types of dementia, epilepsy, schizophrenia, and bipolar disorder, are reviewed in this article. A general methodology for clinical FDG PET examinations and typical diagnostic criteria and pitfalls are addressed.

Keywords

Fluorodeoxyglucose positron emission tomography

[18F]-Fluorodeoxyglucose

Neurology

Psychiatry

Dementia

Key points

Introduction

The synthesis of 2-deoxy-2-[18F]fluoro-d-glucose (FDG) at the Brookhaven National Laboratory in 1976 was a groundbreaking development in nuclear medicine imaging.1

FDG has developed since then into the most widely available tracer for PET and is used extensively in clinical and research settings.

The first application of FDG PET in humans was to measure glucose metabolism in the brain,2 and although most clinical FDG PET examinations are performed in oncology, its application in the assessment of disorders of the central nervous system (CNS) is of cardinal importance.

In neurology and psychiatry, focal lesions in the highly plastic CNS can lead to complex symptoms, and neuroimaging by means of computed tomography (CT) and magnetic resonance (MR) imaging plays an important role in the in vivo detection of structural lesions. However, it was with the advent of PET that the ability was provided to understand the underlying molecular mechanisms that often precede structural changes, allowing an early diagnosis as well as targeted treatment management based on functional rather than structural measures.

The great diversity of existing PET tracers allows the study of numerous brain functions in normal and pathologic conditions, such as the measurement of regional blood flow, glucose metabolism, enzyme activity, protein accumulation, or receptor density in the CNS. However, in this article, the focus is on selected established and eligible applications of FDG PET in neurology and psychiatry (Box 1).

Imaging technique

The technical aspects of FDG PET and its application are covered in the article “The basic principles of FDG-PET/CT imaging” in this issue and are thus only sketchily described here.

FDG PET in the study of the CNS is safe for the patient and a straightforward procedure, which generally is as follows (for European Association for Nuclear Medicine [EANM] guidelines, see Ref.3): the patient does not need any preparation except for at least 4 hours of fasting and abstention from coffee, tea, alcohol, and nicotine, and in case of diabetes, normalization of glycemia. A dose of approximately 3.0 MBq/kg (Box 2 for detailed information) of FDG is administered intravenously once the patient is in a condition of neurosensory relaxation, lying on a bed in a dimmed room with eyes closed and no external auditory stimuli. If a patient is unable to cooperate, mild sedation may be used shortly before image acquisition. After 30 to 60 minutes under these conditions, images are acquired with the patient supine and the head stabilized in the center of the field of detection. In three-dimensional acquisition mode of modern PET scanners, offering a spatial resolution of 3 to 6 mm, a static emission scan commonly lasts about 30 minutes, including transmission scans for tissue attenuation correction, whereas dynamic imaging, meaning the collection of a temporal series of frames, can last up to 90 minutes. In addition to studies of resting state, acquisition can also be performed in the course of a pharmacologic or cognitive stimulation.