The utility of PET imaging in depression

Abstract

This educational review article aims to discuss growing evidence from PET studies in the diagnosis and treatment of depression. PET has been used in depression to explore the neurotransmitters involved, the alterations in neuroreceptors, non-neuroreceptor targets (e.g., microglia and astrocytes), the severity and duration of the disease, the pharmacodynamics of various antidepressants, and neurobiological mechanisms of non-pharmacological therapies like psychotherapy, electroconvulsive therapy, and deep brain stimulation therapy, by showing changes in brain metabolism and receptor and non-receptor targets. Studies have revealed alterations in neurotransmitter systems such as serotonin, dopamine, GABA, and glutamate, which are linked to the pathophysiology of depression. Overall, PET imaging has furthered the neurobiological understanding of depression. Despite these advancements, PET findings have not yet led to significant changes in evidence-based practices. Addressing the reasons behind inconsistencies in PET imaging results, conducting large sample size studies with a more standardized methodological approach, and investigating further the genetic and neurobiological aspects of depression may better leverage PET imaging in future studies.

Keywords: FDG; PET; amyloid; antidepressant; deep brain stimulation (DBS); depression; electroconvulsive therapy (ECT); serotonin.

Figure 1

Voxel-wise, statistical parametric mapping unimodal analysis for [¹¹C]-PiB and [¹¹C]-DASB. Voxel-wise, statistical parametric mapping and separate unimodal analysis for [¹¹C]-PiB and [¹¹C]-DASB showed higher beta-amyloid (left, hot-colored areas) and lower serotonin transporter availability (right, cool-colored areas) observed in Late-Life Depression (LLD) patients when compared to normal controls. Here, the Monte-Carlo Simulation Method is used to address the issue of multiple comparison correction in this study [with permission from reference (42)].

Figure 2

PET images of ketamine-treated patients. PET images of patients zooming in on the hippocampi (red boxes) before (left) and after (right) ketamine treatment. [¹¹C]AZ10419369 radiotracer was used in this study. During PET imaging analysis, the regional binding potential for non-displaceable binding (BP_ND) was calculated using the simplified reference tissue model (SRTM) (74), with the cerebellum as the reference region. [with permission from reference (73)].

Figure 3

PET images of the serotonin_1B receptor effect of electroconvulsive therapy for severe major depressive episodes. Average parametric [¹¹C]AZ10419369 PET images overlaid over MR images, showing decreased 5-HT_1B receptor binding in the hippocampus before ECT (top) when compared with images taken within one week of (bottom) ECT in major depressive disorder patients [with permission from reference (81)].