Plain radiographs of the skull give limited information about the brain, most of it indirect from the appearance of tissues calcified either naturally (bone) or fortuitously (pineal gland, membrane or falx separating major divisions of the brain.)

Fluid occurring normally (cerebrospinal fluid) or pathologically (collection of blood) may provide sufficient contrast with denser brain tissue to reveal distortions of gross structure. Finer detail is revealed when injected dye opaque to xrays enhances cerebrospinal fluid (myelography) or blood-supply (angiography).

Yet finer structural detail is provided by tomography, a technique for blurring out all but the image of a thin slice of tissue. Computed Tomography (C-T) electronically integrates a series of such slices into a three-dimensional image.

Magnetic Resonance Imaging (MRI) is more sensitive than C-T in detecting small brain lesions and abnormalities in the white matter.

These methods of identifying alterations in the structure of the brain are now being complemented by imaging studies which detect functional change. Positron Emission Tomography (PET) visually portrays variations in metabolic activity in different areas of the brain. This technique can thus distinguish tumour and blood-clot, and demonstrate otherwise invisible scars.

As noted in Medical Litigation News (Volume 1, Issue 3 and Volume 3, Issue 9), Single Photon Emission Computed Tomography (SPECT) demonstrates variations in blood supply to different regions of the brain[1]. Such changes in Regional Blood Flow are commonly seen after even Mild Traumatic Brain Injury[2],[3] and are currently the most sensitive method of visualising abnormal brain functioning in clients with a remote history of Traumatic Brain Injury[4]. The evidentiary admissibility of this technique is still being contested in some jurisdictions.

A fairly recent refinement is the superimposing[5],[6],[7] of images from two or three structural and functional techniques - C-T, MRI, PET, and SPECT - further to enhance resolution and interpretation.

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