Contrast is the difference between the light and dark areas of this X-ray.
Contrast in radiography makes the image on an X-ray or other scan visible. Contrast is the difference in image density between two areas. For instance, one area of a scan may be very dark and another very light. Radiographers need contrast in order to spot broken bones or defects on organs.
Levels of Contrast
Images can have a high level of contrast or a low level. The difference in the density of two parts of an image is greater in high-contrast images. The higher the contrast, the easier it is to spot problems and abnormalities in a scan.
Subject Contrast
According to the NDT (Nondestructive Testing) Resource Center, subject contrast deals with the "ratio of radiation intensities transmitted" through the subject being imaged. If areas of the subject vary in thickness, the contrast will be greater between those two thicknesses. Additionally, taking an X-ray using low voltage will create an image with high contrast.
Film Contrast
The way radiographers process an image's film as well as the type of film and its exposure also determine the level of contrast in an image.
Contrast Agent
Radiographers may inject a contrast agent, such as iodine or gadolinium, in the patient to increase the contrast between internal organs, such as the intestines, with the area around them.
Warnings
Patients with kidney problems face an increased risk for nephrogenic systemic fibrosis if they receive gadolinium contrast, according Carl Anderson, MD, of the Mayo Clinic. Gadolinium contrast is commonly used in MRIs. A doctor can decide to give an at-risk patient an MRI without contrast instead.
Tags: Contrast difference, level contrast
