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CT Exam (CT or CAT Scan)

To diagnose certain injuries and conditions, a doctor may order CT exam (commonly called a "CAT scan") to obtain two-dimensional images of bones, organs or other body tissues. Learn mor about CT exams and how they are used.


What is a CT exam?

A computed tomography examination (often abbreviated as CT scan or CAT scan), is a type of advanced, noninvasive X-ray exam that obtains multiple digital images of the body using a series of thin X-ray beam. A CT exam is used to diagnose abnormalities of bone and soft tissues by producing images of the body much like the slicing of a loaf of bread. It is a highly sensitive method of accurately viewing internal anatomy and detecting extremely small lesions. Utilizing high speed computers, the CT obtains 360-degree of X-ray information.The HSS radiologists performing and interpreting these examinations are uniquely qualified in that they are sub-specialized in conditions of the musculoskeletal system and orthopaedic conditions.

What are the benefits of a CT examination?

  • CT exams have shown to be a cost-effective imaging tool for a wide range of clinical problems.
  • CT scanning is painless, noninvasive and accurate.
  • New state of the art CT scanners produce superior exams using a fraction of time and radiation exposure. At HSS, we practice ALARA for all our patients including pediatric.New technologies make faster scanning possible. For children this means shorter imaging times and less time required to hold still in order to produce clear, crisp images. Also, shorter scan times will make it easier for children and adults to hold their breath during critical parts of the exam. Scanning helps to reduce the need for sedation in children.
  • A major advantage of CT is its ability to image bone, soft tissue and blood vessels all at the same time.
  • Compared to MRI, CT is less sensitive to patient movement and can be performed if you have an implanted medical device of any kind.
  • CT imaging provides real-time imaging, making it a good tool for guiding minimally invasive procedures such as needle biopsies and needle aspirations. Sometimes ultrasound is substituted for CT as a method of image guidance for procedures especially in children.
  • A diagnosis determined by CT scanning may eliminate the need for exploratory surgery and surgical biopsy.

Why did my doctor order the CT exam?

A CT exam may be requested to be performed in order to assess bones, soft tissue, such as cartilage, muscle, and tendons, and joints for damage, lesions, fractures, or other abnormalities, particular when another type of examination, such as X-ray, MRI or physical examination are not conclusive.

CT provides hightly detailed information about bony structures, joints and soft tissue. At HSS most advanced technology is used to diagnose abnormalities of the spine, the bones, joints, in addition to abnormalities of the abdomen, pelvis and head. CT provides highly detailed information about bony structures, joints, soft tissue and soft tissue calcifications.

Special protocols are used for detailed imaging of the spine, the pelvis, the hips, the shoulders, the bones and joints of the extremities. CT is used to gain additional detailed information after myelograms, discograms, and after selected types of arthrograms. CT is also used to guide procedures such as biopsies, aspirations of fluid collections, to guide facet joint injections and nerve root blocks.

Who performs and interprets the CT exam?

The CT examination is ordered by your referring physician and is interpreted by a radiologist. A radiologist is a physician with dedicated training in the safe utilization of imaging equipment and cross-sectional image interpretation. The radiologist will protocol (prescribe) the specific examination parameters. A specially trained technologist will operate the CT scanner according to the prescribed protocol. The radiologist will supervise and confirm that the examination is performed accurately, interpret the study, and provide a written report to your physician. All radiologists at HSS are certified by the American Board of Radiology and have experience and/or fellowship training in orthopaedic conditions.

What is special about CT scans at HSS?

  • The radiologists protocoling and interpreting your examination are sub-specialized in conditions of the musculoskeletal system and orthopaedic conditions
  • Customized orthopedic protocols have been developed due to the nature of each referring physicians' specialized surgical needs
  • Specialized in fine osseous (bony) and soft tissue detail scanning
  • Specialized studies are performed to evaluate rotation abnormalities and limb length discrepancy (anterversion studies)
  • Special protocols are performed for biomechanics to design custom implants.
  • Stealth scanning for virtual spine surgery is performed upon request
  • 3D images are created upon physician request to enhance anatomical visualization of fractures/dislocations. This technology can be used to optimize visualization of complex fractures and or dislocations
  • Same day service is available, and accommodation of patients into the appointment schedule on an as-needed basis
  • Immediate/stat/wet reading results available
  • Highly skilled technologists performing the prescribed musculoskeletal scans

How is a CT exam performed?

The X-ray tube and a series of detectors are contained in a doughnut shaped machine; you lie on a platform that will move you slowly through the doughnut. Some CT examinations will require an injection of an iodinated contrast agent into your vein. If contrast is needed, an intravenous line will be placed for the injection if you do not already have a functioning intravenous line. Patients undergoing CT guided biopsies, joint injections and/or aspirations, facet and/or nerve root injections may have local anesthesia and needle placement, as required, for performing these specific procedures.

What should I do to prepare for the examination?

If your CT examination is part of a procedure, follow the instructions for that procedure. If the CT examination is to include an injection of a contrast agent, it is advisable that you do not eat or drink for a several hours before the procedure. If you have any allergies, especially allergies to medications, contrast agent, local anesthesia, Betadine soap, or latex, be sure to inform your physician at the time of scheduling of the procedure, and also inform the CT technologist and the radiologist before the start of the procedure.

If you are pregnant or think you may be pregnant, be sure to inform your physician, the technologist, and the radiologist prior to the procedure. Most procedures/examinations using X-rays will not be performed on pregnant women unless the benefits of the procedure/examination outweigh the risks of radiation exposure to the fetus.

What are the risks of a CT scan?

Our equipment is monitored daily by highly trained technologists and a radiation physicist. When appropriate, radiation-sensitive areas will be shielded during the examination.

Although many slices may be obtained of a portion of your body, each slice is obtained with a very thin X-ray beam in order to minimize exposure and scatter radiation. The X-ray exposure you receive is within the limits determined to be acceptable (safe) by the National Radiation Safety Commission.

  • Contrast Reaction:
    If intravenous contrast is used, there is a risk for an allergic reaction to the dye. Contrast reactions vary from nausea, vomiting, itching, or hives, to more serious reactions including anaphylactoid reaction (severe allergic reaction) with hypotension (low blood pressure); shock, and in rare cases, death.
  • Allergies:
    If you have a history of prior reaction to a contrast agent, be sure to inform your physician at the time of scheduling of the CT exam. Also, at the time of the examination, be sure to inform the technologist and the radiologist performing the exam prior to the injection of any contrast. Individuals with a history of prior severe contrast reaction will either have the exam performed without contrast or in certain cases will have it performed with contrast after a course of premedication with steroids and antihistamine. The premedication is started the day before the exam.
  • Bleeding/Soreness at the Injection Site:
    Bleeding may occur at the puncture site for the intravenous line or at the sight of needle placement for biopsy, joint injection and/or aspiration, facet injection, or nerve root block.

What are the alternatives?

Your physician has ordered a CT examination because the specific information a CT offers will be useful in making a diagnosis, planning treatment, or following the progress of treatment. Routine radiographs, ultrasound examination, nuclear medicine scanning, or magnetic resonance imaging are possible alternatives.

What can I expect after the procedure?

If intravenous contrast was given, soreness at the site of the intravenous line can be expected to last for a few hours. If a biopsy, joint injection, and/or aspiration, or nerve root block was performed, soreness at the sight of needle placement may last up to a few days or a hematoma with swelling and a black and blue appearance can develop at the site of needle placement. If you had a therapeutic injection you will receive a discharge instruction form.

What happens with the results?

The radiologist will interpret your CT examination and generate a written report. of your CT examination. The report will become a part of your medical record and a copy will be sent to your referring physician. If an abnormality of urgent nature is discovered on your scan, your physician will be notified immediately. Copies of the report can be obtained through your referring physician's office. Your physician can call the file room at 212.606.1015 and a copy of the report can be faxed or mailed free of charge to their office. The images obtained are the property of the institution as are biopsy slides or blood samples. Copies of the images can also be obtained by contacting the file room. There is a charge for obtaining film copies and mailing them to your physician. To protect our patients private health information, all patients requesting images and/or reports are required to first complete a Request for Release of Information and fax it to 212.774.2327.

Will other tests be ordered?

Your physician may order additional types of imaging studies in order to further evaluate your condition.

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