Computed Tomography

CT scans, also called CAT scans, have been valuable tools in the diagnosis and treatment of diseases and injuries since 1974. CT stands for computed tomography. These scanners create very detailed two- and three-dimensional pictures of the organs, bones, and blood vessels inside the body. CT scanning is unique in that it can scan different types of tissues at the same time. The physician can then select the type of tissue to be viewed.

CT scanning can be done on most any part of the body, and is often used to study trauma and diagnose types of cancer. It is used to view vascular functions, diagnose heart disease or strokes, and measure bone density as a way of identifying osteoporosis. It can produce images of the head and brain to aid in the diagnosis and treatment of tumors, blood clots, or to view nerves and blood vessels. It is often used in emergency situations because of its versatility. Almost all trauma departments have CT scanners to more quickly identify internal injuries. Because of its great detail, CT is also used extensively to image small body parts and sinuses.

Fluoroscopic CT is used in interventional procedures so the physician can see their progress as they perform needle biopsies or drainages. This type of imaging enables the physician to provide a more minimally invasive treatment.

How CT works

Computed tomography uses x-rays to produce images. As with traditional x-rays, the technology is based on the fact that different types of tissues absorb the x-rays at different levels. This creates variations in the exposures of the images that are formed and results in pictures that have amazing detail and resolution. The difference in the CT scan and a traditional x-ray is that rather than using film, the CT data is sent digitally to a computer. (Although, x-ray machines can also produce digital images now.)

The way the information is gathered is also very different with a CT. Instead of taking a picture from one position, the CT scanner has a large circular opening where the patient can lie down. Inside there is a rotating frame with an x-ray tube on one side and a detector on the other. This frame rotates 360 degrees around the patient. Each time it makes a rotation it gathers another "slice" of information. These slices are anywhere from 1mm to 10mm thick and are made up of over 1000 pictures of the area the x-ray beam is hitting. The information that is gathered is sent to a computer where it is manipulated to produce a two-dimensional image of the slice. As each slice is collected, the table the patient is lying on slowly moves through the opening of the scanner until the entire area has been scanned. The computer puts all of the slices together to create the complete image.

New spiral CT scanners make the process even easier. Rather than spinning in a circle in one direction and then stopping to spin in the other direction, they move in a continuous spiral motion around the patient creating a three dimensional image. Spiral CT is quicker as well, taking only 20-30 seconds for an average region to be scanned. Since patients typically need to hold their breath in order to get clear scans for this type of imaging, the quicker the scan the better the image.

What to expect when you have a CT scan
The CT scan is a safe and painless scan that simply requires that you lie very still. The only part of the scan that may be uncomfortable is the oral or injected contrast material you may need if you are having a scan of the abdomen or pelvic region.

IMPORTANT: Make sure you tell the RRA technician or radiologist if you are allergic to iodine, because most contrast agents contain iodine.

Because the CT scan uses x-rays, it is also very important that you tell the technician or radiologist if you are pregnant – or even if you think you might be pregnant. While x-rays are safe for you, they can be very harmful to the embryo.

When you arrive for the CT scan, allow plenty of time for preparation and paperwork. You may have a questionnaire to fill out about your medical history, allergies, etc. If your scan is of the abdomen or pelvis it will probably require contrast material. If so, you will need to be there at least an hour before your scheduled scan. (You may also be given contrast material to take the night before your exam.)

When it is time for the exam, you will go into the CT scan room and the RRA technician will determine the best position based on the part of your body that is being scanned. In most instances, you will be placed on the table that slides into the center of the doughnut-shaped CT scanner. Make sure you are comfortable before the scan begins because you cannot move once the scan starts. While the scans are taking place you may be asked to hold your breath to prevent the images from blurring with the movement of your chest.

The entire exam should only take 10-15 minutes. Once it is complete and the CT staff has ensured that all of the information has been collected accurately then you are free to go. There are no further restrictions.

An RRA radiologist will review the exam and results will be communicated to your physician.