Many CT scan tests require injection of IV contrast (dye). IV stands for intravenous which means the contrast is given through a vein. Generally a vein in your hand, lower arm, or near the elbow joint is used. The contrast is used to "highlight" internal organs such as the liver, kidneys, and pancreas. It helps detect and characterize tumors, infection and disease of the vessels.
Contrast scans are ordered either "with only", meaning contrast is given and then the images are taken or "with and without", which means images are taken before the contrast is administered and then immediately during or after the contrast is injected.
Into the scan room
Once you're in the CT scan room you'll be taken to a table and asked to lie down. The CT technologist may take a few images in preparation for the scan and/or do the "non-contrast" part of the scan first. That is, take images that are needed before the IV contrast injection is done.
The IV tray
Most facilities will have the IV materials on a metal tray near the CT scan machine. This will include a tourniquet, alcohol pad, IV catheter, gauze, tape, syringe with saline, and some tubing to connect to the injector (the part of the machine that injects the IV contrast - it looks like a big ray gun).
Getting the IV
Unlike a blood draw, the IV catheters used are larger and will need to stay in a vein. Larger IVs are used as the contrast is injected at a high rate. You'll be asked to straighten your arm and hand. The technologist will place the tourniquet around your upper arm or wrist.
The technologist will check for a vein, sometimes using a tapping or brushing movement across your arm. After finding a suitable vein, the technologist will clean the area with an alcohol pad and position the IV over the vein. The IV is advanced through the skin and into the vein. This might take a few tries, particulary for patients who may be dehyrated, have had multiple injections, or chemotherapy.
Once the IV is placed, a small amount of saline is sometimes injected to test it. The IV is then hooked via tubing to the injector. The table will move and the technologist will leave the room to begin the injection and scan.
The contrast will flow from the injector, through the tubing and into the IV and then the vein. You may feel a "pop" in the beginning of the injection right at the IV site. As the contrast goes into the vein you will feel the fluid rush up your arm. You shouldn't feel any pain - if you do alert the technologist immediately.
After a few seconds the contrast reaches your chest and heart and you'll feel an intense warm feeling. Some have described it as a "sunburst" or like drinking a hot cup of coffee in one gulp. You might also get a metallic taste in your mouth.
Usually the scanner begins taking pictures within 10-20 seconds after the injection begins and continues to take pictures after the injection is completed.
After the injection
The technologist will remove the IV and place a small piece of gauze with tape over the IV site.
What about side effects?
The most common side effect of contrast is a mild allergic reaction - sneezing, coughing, asthma-like symptoms and small hives. Severe allergic reactions can lead to heart and lung failure. Contrast can also damage the kidneys. If the contrast leaks from the IV and into the tissues of the hand or arm, it can cause pain and inflammation.
These are just some of the side effects of contrast. Your local Radiology center or hospital can give you more detailed information about the risks and benefits of IV contrast.
And remember, if you've had a side effect to contrast in the past, make sure you alert the Radiology facility and your doctor in advance.