Computed tomography in the assessment of protective helmet deformation.

Damage to a helmet worn by a motorcyclist or pedal cyclist involved in a crash can provide information of importance to those investigating impact responses of the helmeted head. In the past the retrieval of this information has been incomplete as it has involved the destructive dismantling of a helmet into its component layers. Conventional radiology, whilst being noninvasive, has the disadvantage that all structures traversed by the X-ray beam are superimposed in the final image. In an attempt to overcome the limitations of existing methods, computed tomography (CT) was evaluated in a study of 25 protective helmets. This was found to be an informative, noninvasive technique of investigation that provided faithful images of each helmet layer and delineated helmet damage that was not observed with other methods. Additional advantages of CT include the ease of computed data storage, the ability to reformat CT data into a variety of planes as either two- or three- dimensional images, and the facility to measure distance and density. Limiting factors include scanning cost and artefacts produced by metal in the helmet.