Chapter 6: Neuroimaging in Clinical Neuropsychiatry

INTRODUCTION

When used in the appropriate clinical context, neuroimaging is a useful tool in the evaluation of patients with neuropsychiatric disease and behavioral neurologic problems. Although primary psychiatric disorders such as depression, bipolar disorder, and schizophrenia do not have specific or pathognomonic diagnostic imaging findings, neuroimaging remains helpful in evaluating for secondary underlying causes of psychiatric symptoms. These underlying causes can include focal lesions such as tumors, strokes, or demyelination.

Perhaps the most widely used implementation of neuroimaging in neuropsychiatry is its use in the evaluation of patients with dementia. Therefore, a major focus of this chapter will be the application of neuroimaging in the diagnosis of dementing disorders including Alzheimer’s disease (AD), frontotemporal dementia (FTD), dementia with Lewy bodies (DLB), Parkinson’s disease dementia (PDD), vascular dementia (VD), and normal pressure hydrocephalus (NPH).

An important concept in the use of neuroimaging is that imaging captures only a snapshot in time. Neuropsychiatric disorders, particularly those resulting from neurodegeneration, generally evolve insidiously over months to years, and imaging thereby offers only a glimpse at a particular time point in the course of disease. The key to the effective use of neuroimaging in the diagnosis of neuropsychiatric disease is to correlate the snapshot that the imaging provides with the clinical narrative of the patient. A hypothesis about the diagnosis and the localization of the disorder needs to be generated clinically, after which neuroimaging can be used as a supplement to help support or refute that hypothesis. And when available, comparison of current to prior imaging findings can be highly informative as subtle changes in brain volume, for example, can be difficult to discern on a single study and are much more easily visualized by side-by-side comparison of old and new images.

There are several major categories of neuroimaging that will be covered in this chapter: structural imaging, functional imaging, and molecular imaging. Structural imaging includes computed tomography (CT) and magnetic resonance (MR) imaging. Functional and molecular imaging includes magnetic resonance spectroscopy (MRS), magnetic resonance perfusion (sometimes referred to as “perfusion imaging”), functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), positron emission tomography (PET), and single photon emission computed tomography (SPECT). Each of these imaging modalities will be discussed, with greater weight given to the more commonly used modalities and their utility in common neuropsychiatric disorders. It is important to remember that in neuroimaging, images are presented in “radiographic orientation” meaning that on axial and coronal images, the right side of the image is the left side of the patient’s brain, and vice versa.