The data for thk in a CT film refers to the spacing between the layers of the scan, known as the layer spacing. A CT examination is a method of examining lesions by dividing the body into many layers in a cross-section through an X-ray scan. There are two main indicators that determine the method of layering, one is layer thickness, which is the thickness of each layer, commonly 5mm and 10mm, and the other is layer spacing, or thk, which indicates the distance between the upper layer and the lower layer, commonly 5mm and 8mm, etc. The size of the layers can determine the size of the examination. The size of the layer spacing can determine the fineness of the examination, the larger the layer spacing, the more parts that can not be inspected; while the smaller the layer spacing, the probability of detecting small lesions can be improved, but the same part of the radiation will be more. Usually, CT examination should be based on the specific condition to choose the appropriate layer spacing, if you have the need for CT examination, please consult the hospital in a timely manner, under the guidance of the doctor to standardize the diagnosis and treatment, in order to avoid adverse consequences.