SPECT reveals aspects of clinical depression and its treatment
Caren B. Les
Researchers have used single-photon emission computed tomography (SPECT) to study blood flow in the brain as it is related to depression and its treatment, confirming earlier findings that cerebral blood flow in depressed individuals is lower than in healthy control subjects, especially in the frontal, limbic and subcortical regions. The purpose of the study was to address whether the reversal of decreased regional cerebral blood flow is dependent on the type of antidepressant treatment.
The images show brain regions that exhibited increased blood flow in depressed patients who responded to ECT. A pre- vs. posttreatment comparison of the sagittal plane (A), coronal plane (B) and transaxial plane (C) through voxel maximal difference (44, –60, –20) is presented.
Depression, a debilitating disease that affects an estimated 19 million Americans, is thought to be related to a chemical imbalance in the brain that negatively affects intercellular communication. Treatment options include antidepressant medications, psychotherapy and, for severe cases, electroconvulsive therapy (ECT).
Headed by Dr. Omer Bonne, the group at Hadassah-Hebrew University Medical Center in Jerusalem found that antidepressant medicines normalized the decreased brain blood flow in patients with depression who responded to treatment, whereas ECT was associated with additional decreases in blood flow even in patients whose clinical condition improved.
The researchers studied 33 patients who were assessed to have moderate major depressive disorder before undergoing six weeks of treatment with tricyclic antidepressants, with selective serotonin reuptake inhibitors or with a course of ECT; 31 patients were studied after treatment. Inclusion criteria for this group included a score of at least 18 on the 21-item Hamilton Depression Rating Scale. A control group of 25 healthy individuals was studied once.
In both groups, regional cerebral blood flow was evaluated using SPECT and the injectable radiotracer 99mTc-hexamethylpropyleneamine oxime. The first SPECT assessment of the depressive patients was made immediately before their treatments with antidepressants or ECT, and the second SPECT, along with psychometric evaluation, was performed one week after their respective courses of treatment. The researchers defined treatment response as a reduction of at least 50 percent in the patient’s score on the Hamilton scale.
Using the SPECT neuroimaging technique and statistical parametric mapping analysis, scientists studied regional cerebral blood flow in individuals who were clinically depressed and in those in a healthy control group. These brain regions exhibited increased blood flow in depressed patients who responded to medication. Shown is a post- vs. pretreatment comparison of the sagittal plane (A), coronal plane (B) and transaxial plane (C) through voxel of maximal difference (42, –32, 46). Images reprinted with permission of the Society of Nuclear Medicine Inc.
Images of regional cerebral blood flow were obtained with an Elscint Helix dual-head gamma camera with two rectangular 540 × 400-mm-field-of-view detectors, equipped with low-energy ultraflared fan beam collimators. Statistical parametric mapping software implemented on a Matlab platform was used to analyze the images, which were prepared for analysis by realignment to the Montreal Neurological Institute brain atlas. The SPECT molecular imaging/nuclear medicine procedure provides three-dimensional computer-reconstructed images that reveal both structure and function in brain areas.
The investigators determined that the baseline regional cerebral blood flow was lower in the depressed patients than in the control group. In patients who responded to the two classes of medicines, each targeting different neurotransmitters, the researchers determined an improvement in cerebral blood flow. In patients who responded to ECT, they noted an additional decrease in blood flow in the parietotemporal and cerebellar regions bilaterally.
They concluded that the blood flow normalizes in major depressive disorder following a response to drug therapy; blood flow changes after a response to ECT, however, may progress differently.
Further studies could explore the use of functional imaging techniques to determine the most effective course of treatment for an individual, as there could be more than one mechanism involved in the process of therapeutic response. Future investigations also could determine whether the cerebral blood flow differences between medication and ECT responders found at the acute aftermath of treatment persist or cease to exist at later times, according to Bonne.
The Journal of Nuclear Medicine, August 2007, pp. 1273-1278.
- single-photon emission computed tomography (spect)
- A medical imaging method in which gamma camera heads rotate about the patient to detect radionuclides, enabling physicians to monitor functions within the body such as metabolism or blood flow.
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