CT (Computed Tomography)


What is a CT?

A "CT Scan," "Computerized Tomogram," or CAT scan is a noninvasive type of x-ray that helps physicians diagnose and treat medical conditions that may not be visible on other types of studies.

A CT scanner is a doughnut shaped machine (the doughnut shape is known as the gantry) that uses advanced x-ray technology to take pictures of your body. Immediately after it scans your body, a computer in the scanner reconstructs the data into cross-sectional pictures of your body, called slices or sections. CT technology allows radiologists and your referring physician the ability to see more than what a regular x-ray would provide.

NYU Radiology offers patients the most advanced scanner technology available, providing images of exceptional quality and lowest possible radiation dose. Higher quality images mean more information for your physician to diagnose and plan the treatment for your medical condition. Lower dose means increased safety for you.

Why did my doctor order a CT?

Because CT provides detailed information about the bones, joints, and internal soft tissues, your physician may request a CT for various reasons including to assess for fracture characterization and healing, joint and cartilage abnormalities, vertebral body abnormalities and disc herniations in the spine, and to assess bone and soft tissue tumors. A CT can be performed to make the initial diagnosis, or can be utilized to provide additional information when another type of exam, such as standard x-rays, ultrasound, MRI, or nuclear medicine is inconclusive.  CT can give information about tendons and ligaments when another exam such as an MRI cannot be performed.

CT can also provide guidance for procedures such as arthrograms, steroid joint injections such as facet joint and sacroiliac joint injections, myelograms, discograms, bone and soft tissue mass biopsies, and fluid/abscess aspirations.

How should I prepare for the CT?

What should I eat or drink?

You may be asked not to eat or drink anything for several hours beforehand, especially if a contrast material is going to be used in your exam. You should inform your physician of any medications you are taking and if you have any allergies. If you have a known allergy to contrast material, your doctor may prescribe medications to reduce the risk of an allergic reaction.

Also inform your doctor of any recent illnesses or other medical conditions, such as a history of heart disease, asthma, diabetes, kidney disease, or thyroid problems. Any of these conditions may increase the risk of an unusual adverse effect.

What if I am allergic to IV contrast material?

If you think you may be allergic to IV contrast material or have experienced a prior reaction to IV contrast material, please notify your referring physician prior to scheduling your CT scan appointment. If you have a known allergy to contrast material, your doctor may prescribe medications to reduce the risk of an allergic reaction. Allergies to other foods and medications may increase your propensity to a contrast allergy, but no food in particular (e.g. shellfish) is any riskier.

If contrast is administered, certain medications (e.g. metformin) may need to be temporarily stopped before or after the scan. If you have any questions, you may speak to one of our radiology nurses. Please notify your doctor if you are concerned about stopping any medications.

What should I wear?

You should wear comfortable, loose-fitting clothing to your exam. Certain exams may require you to wear a gown, which we will provide. We have private dressing rooms with lockers for your clothes and valuables, although you may want to leave your valuables at home if you don't need them that day. Metal objects including jewelry, eyeglasses, dentures, and hairpins may affect the CT images and should be left at home or removed prior to your exam. You may also be asked to remove hearing aids and removable dental work.

I am claustrophobic, will I be able to have a scan?

That shouldn't be a problem. A CT Scanner is an open machine, not a tunnel like an MRI scanner. You are not enclosed in the scanner and, as a result, you see completely around yourself.

What should I bring to my appointment?

In order for us to perform your test, you will need to bring your prescription, insurance card, and any related insurance forms or pre-approvals.

When should I arrive for my appointment?

When you schedule your appointment, our scheduling associate will let you know how soon before your appointment time you should arrive. Depending on the exact type of exam, this may be 30-60 minutes before your scheduled appointment. This will allow time for registration and to complete all necessary paperwork, forms, and questionnaires.

To save time, you may download, print, and fill out the appropriate forms at home and bring them with you on the day of your appointment.

What if I might be pregnant?

Women should always inform their physician and the CT technologist if there is any possibility that they are pregnant.

Will I need an IV (Intravenous) for CT scan?

Your physician and the radiologist will determine if IV contrast material will be needed for your CT scan. IV contrast material containing iodine is used to highlight organs and blood vessels that are otherwise difficult to visualize. If IV contrast material is required for your CT scan, a small IV will be placed in your arm or hand prior to the CT scan.

How is the CT performed and who interprets the CT?

The CT machine is essentially a sliding table with a gantry (doughnut) around it, in which are housed an X-ray tube and an array of X-ray detectors. When it is time for your exam, the technologist will place you on the table lying down on your back (for the most part) or if the exam dictates on your belly or side (much less commonly). The technologist will utilize the protocol that has been established prior to the exam by the radiologist. This will ensure that the exam is the correct one, tailored for your medical indication with the lowest possible radiation dose. Once the protocol is set in the machine, the table will move you slowly through the gantry, in which X-rays are taken and detected.  The whole exam usually takes only a few minutes, from start to finish, with scanning times measured in seconds. The computer then analyzes the information from the X-ray detectors and reconstructs images. The technologist looks at the images at the console to make sure the images are satisfactory. If so, then the technologist will get you off the table. Then, the images will be sent to the musculoskeletal radiologist to interpret.

The musculoskeletal radiologist is a physician trained in radiology with sub-specialty training in conditions of the musculoskeletal system including sports medicine injuries, spinal disorders, arthritis, and tumors. The MSK radiologists at NYU combine a comprehensive knowledge base of these various conditions with a deft understanding of CT imaging to produce high-quality, accurate interpretations of your imaging studies. The findings that the radiologist sees on your study are summarized and organized into a report that is immediately sent to your doctor for review. If there is an emergent finding (ex. acute fracture) that needs urgent attention, the radiologist will call your doctor directly to explain what is found on the CT examination.

What can I expect after the examination?

If no contrast was given and no injection was made, you should feel nothing at all after the exam. If intravenous contrast was administered, you might have some discomfort or bruising at the site of the IV injection for a few hours. Once your scan is completed, you may resume your regular diet and activities. We recommend that you drink plenty of non-alcoholic, decaffeinated fluids, such as water or juice, to help your body flush out any IV or oral contrast material.