Written by in section: Medical Technology > Diagnostics
Medically Reviewed by Dr. Aj Thomas MS, MBA & Updated on Apr 3, 2016
What is a CAT scanner? Hint: It's not a machine to scan a Cat!
CAT scanner (Computerized Axial Tomography scan)
Faculty of Health & Social Care

A CAT scanner (Computerized Axial Tomography scan) is a diagnostic machine used to make internal images of the patient’s body in 3D. It’s also known as CT scan or X-ray CT. A modern CAT scanner is often called as a CT scanner because of its ability to make pictures in more angles than older Axial plane scanners that used to make image like bread slices in one particular direction and angle.


It is a noninvasive procedure and is a very important piece of technology used in diagnostic medicine and medical imaging. The name Tomography is derived from the Greek words "tomos" which means slice or sections and "graphia" meaning describing or writing.

The CAT scanner was invented in 1971. It was the results of contributions from English electrical engineer named Godfrey Hounsfield and South African born American physicist named Allan McLeod Cormack. For their individual contributions that led to the invention of the CAT scanner they shared the Nobel Prize in Physiology or Medicine in 1979.

Left: Godfrey Hounsfield Right: Allan McLeod Cormack
Left: Godfrey Hounsfield. Right: Allan McLeod Cormack

There is also hope that even in these days of increasing specialization there is a unity in the human experience.

- Allan McLeod Cormack

A Radiologist is medical doctor who specialize in medical imaging techniques. With the use of CT scanner radiologists can easily diagnose tumors, cancers, cardiovascular diseases, certain infectious diseases, trauma etc.


How does a CAT scan work?

A conventional X-ray machine is only able to generate a 2D image of a patient’s body. A CAT scan uses the same x-ray technology in a different way to generate a 3D image of the area being examined or even the whole body.

A CAT scanner works by rotating a conventional X-ray beam in a circular pattern around the patient’s body. This circular motion around the body creates what is known as slices.  A single slice is a 2D image similar to an image generated by a conventional X-ray machine. Then these slices are transferred to a computer which assembles the slices to create a complete 3D image of the area being examined or even the whole body.


CT scan working


Inside the circular tube, there is a X-ray emitter and 180 degree across from this emitter is the receiver that receives the X-ray images and transfers this data to a computer for processing.

X-rays are being constantly beamed and received while the emitter and receiver move in a circular motion around the patient’s body. The patients bed can move into the circular tube till the full length of the bed is reached, thus being able to bring the complete areas that is required to be examined.


What are the advantages of a CAT scanner?

  • It is a noninvasive, painless and quick diagnostic method that is able to produce very accurate images of the inside of the human body.
  • It can make very detailed images of internal organs unlike conventional X-rays. It can generate images of bones, soft tissues blood vessels simultaneously.
  • It is suitable for diagnosing muscle or bone disorders, locate tumors, blood clots and certain infections.
  • In cases of emergency like trauma, it can provide quick assessment of the internal organs and detect any possible internal bleeding in a quick and timely manner.
  • A diagnosis with the help of CAT scanners may also eliminate the need for performing unnecessary surgeries or biopsies (tissue sampling for detailed examination)
  • A CAT scan unlike MRI scan can be performed on a patient that has an implanted medical device like pacemakers, internal orthopedic fixation devices, bare-metals stents etc.
  • It can also provide real time information for guiding surgical procedures or performing a biopsy
  • CAT scan can also be used periodically to monition the effectiveness of cancer treatments like chemo and radiotherapy.


CT scan of the human brain. © Boogordoctor
CT scan of the human brain. © Boogordoctor


What are the risks associated with undergoing a CAT scan?

CTA scan is generally considered as a very low risk procedure. A CAT scanner uses a X-ray emitter that carries similar health risk like a conventional X-ray procedure.

However it is important to note the benefits of a CAT scan greatly exceeds the possible potential radiation risk due to the exposure to electromagnetic radiation during the procedure.

Some of the risk factors associated with CAT scanners are:

  • The resulting exposure to electromagnetic radiation is a CAT scan is comparatively much higher than a conventional 2D X-ray exposure. This is because of the fact that multiple X-ray images (slices) are taken from different angles in order to compose a 3D image on the computer. Multiple CAT scans may slightly increase a patient’s risk of developing cancers in the future.
  • CAT scan is generally not recommended for pregnant women due to the possibility of causing harm to the baby. However a scan is performed in case of an emergency using protective shielding to the abdominal area. The abdominal area is always excluded from the examination. Alternative imaging procedures like MRI or Ultrasound scanning is safer for pregnant women.
  • Certain types of CAT scans required the patient to be injected with a special dye (contrast material) through the veins in the arm. In some rare cases the patient may have an allergic reaction to this dye. Fortunately most reaction are mild and not life threatening.


What are the limitations of a CAT scanner?

Other medical imaging techniques like MRI is better suited for evaluation of soft tissue details of the brain, joints and the internal organs of the pelvic region.


How is a CAT scan done?

CAT scan reports are read by a radiologist. The person conducting the scanning procedure is usually a radiology technologist. The scan reports are stored in an electronic medium (like computer hard disk, USB flash disk, DVD) which can later be viewed by other specialist from the medical field.


The Royal Marsden Cancer Charity
© The Royal Marsden Cancer Charity


  • The patient has to change into a medical gown and remove all jewelries that may interfere with the scanning process.
  • The patient has to lie on a table that is attached to the donut shaped scanner. While the machine is working, it may produce a buzz or clicking sound while the table moves slowly to position the area to be examined inside the circular donut shaped scanner.
  • During the scan, the patient has to remain perfectly still in order for the machine to produce perfectly clear images. Small children who needs to undergo a CAT scan maybe given sedative to prevent the child from moving.
  • The patient is usually left alone on the table while the medical staff moves into the other room with a glass window facing the patient and the scanner. The staff can constantly observe the patient through the glass window during the entire procedure. It is possible to communicate with the staff through a two way microphones build into the scanner.

The entire test takes about 30 to 60 minutes. The scanning process itself is very quick with the actual process taking just a few seconds. Majority of the time is spent in preparation for the actual scan.

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  • Last Reviewed on:Apr 3, 2016
  • Medically Reviewed by:Dr. Aj Thomas MS MBA
  • References:


    1. CT scan - Mayo Clinic. http://www.mayoclinic.org/tests-procedures/ct-scan/basics/definition/prc-20014610
    2. Body CT (CAT Scan). http://www.radiologyinfo.org/en/info.cfm?pg=bodyct
    3. Brief History of CT | CT Scan | Imaginis - The Women’s Health & Wellness Resource Network. http://www.imaginis.com/ct-scan/brief-history-of-ct

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