What is a CT scan?
A CT scan, also known as computerized tomography or computed axial tomography, is an advanced X-ray scan that produces cross-sectional images of the bones, blood vessels, and soft tissues in your body. CT scans are far more detailed than a regular X-ray and can help aid in the diagnostic process. At The Iowa Clinic, we offer CT scans for both our pediatric and adult patients.
How does a CT scan work?
A CT scan works similar to an x-ray. The body casts a “shadow” on film when it is exposed to the x-ray, much like when you hold a flashlight up to your hand and cast a shadow on a wall. All of the tissue that the x-ray passes through overlap on the image, making it hard to isolate different elements. A CT scan works around this limitation by capturing one narrow slice of your body at a time. Inside the CT machine, the x-ray tube circles around the patient taking pictures as it rotates.
These slices can be viewed two-dimensionally or added back together to create a three-dimensional image of a body structure.
CT angiogram (CTA) can be used to view arteries and veins. Contrast dye injected into the bloodstream helps the computer “see” the vessels. CTA images can be 3-D reconstructed so that the cerebral vessels and accompanying pathology can be rotated and viewed from all angles.
What does a CT scan show?
CT scans are very good at showing bone, soft tissue, and blood vessels. While an MRI takes excellent pictures of soft tissue and blood vessels, a CT scan shows bone much better, so it’s often used to image the spine and skull. It’s also used to view the inner ear and sinuses because these areas are made of very fine bones.
What does a CT Scan help diagnose?
There are numerous conditions that a CT scan can help diagnose. However, it is most often the first procedure ordered when your healthcare team is looking to diagnose or rule out possible internal injuries.
CT scans especially excel at identifying:
- Internal injuries from car accidents or other physical trauma
- Broken bones
- Masses and tumors
- Joint issues
- Brain damage after a head injury
- Brain tumors
- Ruptured or leaking aneurysms
- Hydrocephalus, or enlarged brain cavities
- Spinal stenosis, or narrowing of the spinal canal
- Herniated discs
- Blood clots or bleeding associated with stroke
Outside of their excellent diagnostic usage, CT scans are also often used by healthcare teams to help plan, explain, and monitor treatment plans.
How should I prepare for a CT scan?
You should wear loose clothing and remove all objects that would get in the way of the scan, such as hairpins. You may need to change into a hospital gown, depending on what part of your body is being imaged.
If you are having a CT of your abdomen or pelvis you may be asked to:
- Arrive one hour prior to your exam to drink the oral contrast.
- Do not eat or drink for four hours prior to the exam.
- Only drink small amounts of water to take needed medications.
If you are having any other type of CT exam you may be asked to:
- Arrive 15 minutes early.
- As exams vary, please follow instructions provided to you at the time of scheduling.
Please let us know if you know or think you are allergic to iodine. In rare cases, the oral contrast medium can trigger anaphylaxis, a life-threatening allergic reaction in which the tissues of the airway become swollen enough to restrict breathing. In such cases, emergency treatment is immediately given.
Patients who have diabetes or renal disease require special care because the kidneys are involved in filtering iodine from the bloodstream. These patients should consult with their physician about proper scheduling of the CT scan.
What should I expect to happen during a CT scan?
You will lie on a moveable table. If your head is being imaged, the technologist may position your head in a special head-holder that keeps it from moving. When you are comfortably positioned, the table will slowly move into the CT machine. The technologist will stay in constant contact with you over an intercom. While each picture is taken, you will be asked to hold your breath and stay perfectly still for a few seconds.
The technologist will move the table with a remote control after each picture is taken. You may be given an injection of contrast dye into your arm or through an IV to enhance the images.
The machine may be quiet or noisy, depending on the brand. The noise you hear is the x-ray tube rotating around your body to produce the images. You will not feel any sensation from the scan. The scan can last from 5 to 15 minutes. After the test, the IV will be removed and you are free to go. You may be told to drink lots of fluids to help your kidneys remove the contrast dye from your body.
After your procedure, your physician will receive a copy of your report within 48 hours and communicate those results to you.
What are the risks of a CT scan?
There is a slight risk from X-ray radiation exposure, and some people are sensitive to the contrast agent. The most common side effects from the contrast are a brief metallic taste in your mouth and a feeling of warmth throughout your body. An allergic reaction to the contrast can cause severe hives and difficulty breathing. Medications such as antihistamines can reverse this reaction. If you have diabetes or kidney problems you may experience kidney failure, but this is very rare.
Be sure to tell you doctor if you are pregnant or have allergies (to medications, previous iodine injections, or shellfish), diabetes, asthma, a heart condition, kidney problems, or thyroid conditions.