Contrast X-rays

Images produced using radiation and a substance that makes hollow or fluid-filled structures visible.

Hollow or fluid-filled body structures, such as the intestines or blood vessles, do not show up well on an ordinary x-ray image. A substance called a contrast medium or dye can be introduced into these structures to make them visible. Contrast media are opaque to radiation in the same way as dense body tissues, such as bone. X-rays cannot pass through the media, and areas containing these substances will appear white on an x-ray image.

The contrast medium is injected into the body or introduced orally or rectally.

Contrast X-ray procedures are increasingly being replaced by other techniques, in particular CT scanning, MRI, and ultrasound scanning.

Contrast x-rays may be used to image the blood vessles, urinary system and digestive tract. 

Different types of contrast media that may be used include iodine (soluble) and barium sulphate (insoluble).

Water-soluble iodine dyes can be carried around the body in the bloodstream. For this reason, and because they show up well on x-rays, they can be used to check whether blood is flowing normally in the blood vessles. 

Imaging of blood vessles by using x-rays is known as angiography. 

In this techniques, the dye is injected through a catheter that has been guided into a blood vessel until its tip is near the vessel to be studied. 

The dye flows into the appropriate vessles, making abnormalities, such as blockages, visible on x-rays.

When injected into a vein, dye circulates in the bloodstream and becomes concentrated in the kidneys before it is excreted in urine. The dye can therefore be used to image various parts of the urinary system. As the dye passes through the urinary tract, it outlines the urethra and bladder.

Contrast x-rays may be used to look for suspected kidney disease and obstructions in the urinary system due to kidney stones or tumors.

Barium sulphate is a thick, insoluble, chalky liquid that does not allow x-rays to pass through it and shows up well on the x-ray image. It moves slowly through the digestive tract and is not absorbed by the body; therefore it is a good contrast medium for examining the digestive tract.

Injecting contrast media carries a minor risk of serious complications such as anaphylaxis. People who have asthma triggered by an allergy or who have a known sensitivity to iodine are advised not to have contrast x-rays or are pretreated with drugs such as antihistamines ot corticosteriods, or other contrast media may be used.

Most people experience a flushing sensation as dye is injected. Barium sulphate may also cause constipation.