Neuroimaging in Child and Adolescent Psychiatric Disorders
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412 Arch Dis Child 2000;82:412–419 CURRENT TOPIC Neuroimaging in child and adolescent psychiatric disorders Paramala Janardhanan Santosh Abstract detailed account of the physical basis of the Neuroimaging in child psychiatry is a various neuroimaging techniques. rapidly developing field and the number Brain imaging may be performed for a vari- of diVerent techniques being used is ety of reasons: to address needs in clinical increasing rapidly. This review describes research, patient management, or diagnosis. In the current status of neuroimaging in clinical practice, structural neuroimaging is childhood psychopathology and discusses indicated when one suspects intracranial limitations of the various studies. As yet, pathology—if the patient exhibits focal neuro- no specific and consistent abnormality logical signs on examination, or when there is a has been detected in childhood psychiat- history of significant head trauma (that is, with ric disorders. Obsessive compulsive dis- extended loss of consciousness, enduring neu- order has shown the most consistent rologic sequelae of any kind, or when there is a findings so far, with orbitofrontal cortex close temporal relation to the onset of psycho- and the caudate nucleus being impli- pathology), refractory epilepsy, childhood cated. Better understanding of the corti- onset psychoses, and when the disorder is costriatal neural networks will shed more refractory to an extensive array of conventional light on the neurodevelopmental disor- treatments. Apart from being indicated in ders of childhood. complicated epilepsy, functional neuroimaging (Arch Dis Child 2000;82:412–419) is currently only a research tool in psychiatry. Functional abnormalities are often picked up Keywords: neuroimaging; psychiatry; psychopathology in subjects with negative structural scans. Table 1 compares the diVerent techniques. Although structures may show group diVer- In the study of the human brain, a picture is ences, they need not show the same degree of worth a thousand words. In the past 20 years, diVerence in, for example, electron density technological advances have provided and (CT), phosphorylation (MRS), or oxygenation refined a variety of neuroimaging methods of blood (fMRI). Thus the fMRI cerebral acti- based on diVerent physical phenomena. There vation may not equate to the PET activation, is now considerable literature on the applica- and both may diVer from the anatomy depicted tion of neuroimaging to children with neurode- by visual inspection or tissue typing. velopmental disorders. At this stage in the Neurophysiological imaging refers to the use of field’s development, replicable findings are suf- cerebral blood flow radiotracers (15O labelled ficient to permit an appraisal of the progress water, 133Xe) or metabolic radiotracers (18F- made so far, while attempting to outline poten- fluorodeoxyglucose) to spatially resolve the tial pitfalls and diYculties faced. haemodynamic and metabolic correlates of Structural imaging measures anatomic neural circuit activity. Neuroreceptor imaging structure (radiographs, computed tomography refers to the use of PET or SPECT radionu- (CT), magnetic resonance (MR) imaging) clides bound to ligands possessing a high and while functional imaging measures the intrinsic selective aYnity for neurotransmitter receptors physical properties of tissues (for example, or transporters. Tracer kinetic models are used metabolism or blood flow) and changes that to convert local positron annihilations into occur in disease (magnetic resonance spectros- estimates of receptor or transporter density, copy (MRS), functional MR imaging (fMRI), distribution, or occupancy. Neurochemical im- positron emission tomography (PET), single aging refers to the use of PET or SPECT radionuclides bound to precursors (for exam- Institute of Psychiatry, photon emission CT (SPECT), magnetic Denmark Hill, London encephalography (MEG)). The nature of the ple, tryptophan, dihydroxyphenylalanine SE5 8AF, UK connection between the physical property (DOPA)) of enzymatic reactions that support P J Santosh measured (for example, radioactivity in some neurotransmitter synthesis. Correspondence to: areas) and the underlying physiological phe- Dr Santosh nomenon (for example, metabolism) estab- Normal neurodevelopmental changes email: lishes and limits the utility of diVerent that influence paediatric neuroimaging [email protected] methods, and the technical constraints of each Knowledge of the normal patterns of brain Accepted 26 January 2000 technique. Anderson and Gore1 giveavery development in the clinically relevant ages Neuroimaging in psychiatric disorders 413 Table 1 Comparison of diVerent neuroimaging techniques Neuroimaging technique Mechanism Advantages Disadvantages Computed tomography Collimated beams of x rays are rotated Excellent images of skull, sulci, and Artefacts often arise in regions containing around the head and pass through the brain, ventricles. Volumetric and dynamic images very dense structures, especially in posterior losing energy in proportion to the density of can be obtained if spiral CT is used. fossa and areas close to bony interfaces. the various tissues (grey matter, white Patient is exposed to ionising radiation. matter, and CSF). Only transverse slices obtained. Magnetic resonance Brief radiofrequency pulses activate the Primary method of choice for brain Pacemakers, shell injury, plates, screws, or imaging inherent distribution of hydrogen atoms in imaging. Superior images with high spatial metallic implants are contraindications. the brain, following which the hydrogen resolution. Safe, no exposure to radiation. Subjects have to remain relatively still. atoms align themselves in the strong Repeated scans possible even in very young Scanner noise is quite loud. Constrained magnetic field generated by the children. Arbitrary planes, environment within receiver coil. superconducting magnet around the head. transverse/coronal/ sagittal images can be The diVerent realignment times after the generated. burst of radiofrequency perturbation, are used to delineate the diVerent tissues of the brain. Functional magnetic Changes in blood flow (characterised by Can map brain’s functional responses to Image analysis techniques need to improve resonance imaging altered levels of oxygen or oxygenated specific stimuli. Non-invasive and safe. Will in children. Artefacts near skull base limit its blood) establish a new equilibrium of the help us learn more about neurophysiology use. Constrained environment within oxygen dependent magnetic properties of in both disease and health. Reference receiver coil. haemoglobin, detected through high field anatomic images are simultaneously magnets. acquired with the functional data. Positron emission Based on the detection of annihilation Exact quantification of cerebral blood flow Radionuclide scanning technique. Cannot tomography photons arising from the decay of injected and metabolism. Whole head imaging is be used repeatedly, or in pregnancy. radiotracer. Arrays of scintillation detectors more reliable. Neuroreceptor concentration Cyclotron is necessary to provide the are used as an electronic collimation system, and aYnity can be measured. radiotracers with very short half life. which transforms the photons into visible Constrained by need to inject isotope for light; this is ultimately filtered and each new task. Anatomic data need to be reconstructed to form the image showing obtained separately. either the blood flow or glucose metabolism, receptor occupancy or neurochemical binding in the brain (depending on the tracer). Single photon emission Similar to PET. Measures changes in blood Available in most departments of nuclear Radionuclide scanning technique. Cannot tomography flow, receptor activity using appropriate medicine. Large numbers of radiotracers be used repeatedly, or in pregnancy. radiotracers. Detectors specialised for available. Cost eVective. Absolute quantification is not possible, and localising photons (ã rays) emitted by bilateral symmetrical reduction is diYcult to positron annihilation are used. The data are recognise. processed to create images of slices of brain in the transaxial, coronal, and sagittal planes. Magnetic resonance This exploits the slight diVerences in Provides a direct investigation of Long procedure if one is interested in spectroscopy resonant frequency of protons (usually 1H phosphorhylated intermediate metabolites quantification at molecular level. Only and 31P) bound to diVerent cell associated and neurotransmitters such as GABA and limited substrates are measurable. structures. It characterises the molecular glutamate. state of both bound and free tissue water and the chemical microenvironment of cells and provides a profile of the status of intermediary metabolism within a selected tissue volume. Magnetic Uses specialised superconducting detectors Can help to locate and measure the strength Bias favours only some neurones and not all encephalography and sensory coils to measure magnetic fields of electrical impulses from the brain. Safe in a particular field and hence may not be that surround the currents which give rise to procedure, no exposure to radioactive accurate. Structural scans necessary EEGs and ERPs. The magnetic fields reflect compounds. separately, to transpose findings onto a brain currents induced within the dendrites of map. neurones oriented parallel to the sulci. from 4 to 18 years is necessary to interpret the profiles of developmental neuropsychiatric dis- subtle brain imaging findings