CLINICAL HANDBOOK OF SCHIZOPHRENIA

36 I. CORE SCIENCE AND BACKGROUND INFORMATIONSTRUCTURAL BRAIN IMAGINGComputed TomographyCT was one of the earliest brain imaging techniques to be applied to the study of schizophrenia.In CT scanning, X-rays passing through the brain strike detectors that rotateslowly about the head. The differential absorption of X-rays by different tissue types createscontrast between gray matter, white matter, cerebrospinal fluid (CSF), and bone tocreate an image of the brain in multiple two-dimensional slices. Early in vivo studies ofbrain structure in schizophrenia used hand measurement or qualitative judgments basedon CT scans, often on a predetermined single slice located by an anatomical landmark. Ingeneral, these studies found enlargement of the lateral ventricles of patients with schizophreniacompared to healthy participants. Although the finding of a mean difference betweengroups was fairly consistent, there was considerable overlap of the distribution ofventricular size between patients and comparison participants, and ventricular enlargementwas also observed in other psychiatric conditions. The modest nature of the deficitsrevealed by using CT, combined with limitations of the technique as a research tool, suchas poor gray–white matter contrast, artifacts due to bone, and concerns about repeatedexposure to X-radiation, motivated a switch to the use of the newly developed MRI technique.Magnetic Resonance ImagingMRI creates images by capitalizing on the inherent magnetic properties of atoms in thebody. The most abundant, and most commonly visualized, is the hydrogen atom. By alteringthe energy state of protons in the brain through a combination of (1) placement ina static magnetic field, (2) introduction of radiofrequency energy, and (3) recording as theprotons relax back to their initial state after the energy pulse, the signals detected vary dependingon the local environment. This allows for good visualization of tissue types thatdiffer in their water concentration, such as gray matter, white matter, and CSF. The lackof ionizing radiation in this technique means that scans can be repeated, allowing for longitudinalstudies of the course of brain abnormalities in schizophrenia. Magnet strengthsof 1.5 Tesla are commonly available in most medical centers and allow for spatial resolutionof 1 mm × 1mm× 1 mm.Initial psychiatric studies using MRI replicated the finding of ventriculomegaly inschizophrenia. Third ventricle enlargement has also been frequently observed. The promiseof MRI, however, was more fully realized when it was used to examine the size of individualcortical and subcortical regions within the brain. The most consistent observationin this regard has been reduced temporal lobe volume. In particular, more than 80%of studies have found reduced volume of the hippocampus and superior temporal gyrus.Frontal lobe volume has also been frequently examined, and the majority of studies havefound overall volume decrements in patients with schizophrenia compared to healthy individuals.Slightly less consistent results have been found in the smaller number of investigationsof parietal lobe, occipital lobe, and cerebellar volumes. Among subcortical structures,the basal ganglia have most consistently shown volume reductions, although someevidence exists for abnormalities of the thalamus and corpus callosum.Thus, the MRI evidence that patients with schizophrenia, on average, have largerventricles and smaller subcortical and cortical structures, particularly in the temporallobes, is strong. The widespread nature of the structural abnormalities has led to severaltheories about the etiology of these deficits. The theories commonly emphasize the idea ofa disconnection between areas that are normally coordinated, and several postulate aneurodevelopmental origin to the disconnection and subsequent volume loss. There has