In planar projected images of the patient, important details may be hidden by over-laying tissues. By using slice-imaging techniques (tomography), selective demonstration of morphologic properties, layer by layer, may be performed.
Computerised tomography, CT, is an ideal form of tomography yielding sequence images of thin consecutive slices of the patient and providing the opportunity to localise in three dimensions. Unlike conventional, classical tomography, computerised tomography does not suffer from interference from structures in the patient outside the slice being imaged. This is achieved by irradiating only thin slices of the patient with a fan-shaped beam. Transaxial images (tomograms) of the patient’s anatomy can give more selective information than conventional planar projection radiographs. Compared to planar radiography, CT images have superior contrast resolution, i.e., they are capable of distinguishing very small differences in tissue-attenuation (contrasts), but have inferior spatial resolution. An attenuation difference of 0.4% can be visualised but the smallest details in the image that can be resolved must be separated at least 0.5 mm. In conventional planar radiography, the lowest detectable contrast is larger but details of smaller size can be separated.
Linköping: Linköping University Electronic Press , 1995. , 17 p.