CT Scan vs. PET Scan

Difference between CT Scan and PET scan

A CT scan, which stands for Computed Tomography, uses X-rays to take an axial film of a part of the body. Although it uses X-ray it gives a much better image because it provides more details about the tissue. The way in a CT scan works is that the X-ray passes through one side and the sensor catches the rays as they pass through the other side and this can happen for any part of the body.

The probes in the scanner can move in a circular rotation and the 360 degree view will help give a clearer image than an ordinary X-ray. The computer calculates the image and according to the radiation it will give the image of the tissue. The radiation in a CT scan comes from the X-rays.

PET is the shortened form of Positron Emission Tomography and is a procedure that uses nuclear reactions. Positron is similar to an electron that has a positive charge. Atoms in the isotopes can divide and emit the rays that are used in this type of scan, and FDG (fluro deoxy glucose) is often used. This is what emits the positrons.

Glucose is the fuel that provides energy to the tissues as it is absorbed by the active tissues. Radioactive substances attach to the glucose. The metabolically active tissue takes up the FDG. When the active tissue takes the glucose, the radioactive substance is also taken inside the tissue. The amount that is taken in helps to identify the manner in which the tissue behaves. The emission amount varies according to the amount that the tissues take. Positrons react with the electrons in the tissue. The electron is negatively charged and the positron is positively charged.  The computer calculates the reaction and delivers the final image.

A PET scan is very helpful in diagnosing cancer. This is because the cancer tissue divides very quickly because they are so active. Therefore they will take much more glucose out of the blood.

Because a PET scan takes longer than a CT scan to complete, there is a waiting period between the time you receive the injection and the time it takes for the tissues to take the glucose. This usually takes about an hour.  This procedure can also be combined with a CT scan and an MRI.


  1. Medical professionals use the imaging techniques of CT scan and PET scan.
  2. Both techniques are used to diagnose whether or not cancer has spread.
  3. Because they both use radiation they can increase the risk of cancer.
  4. PET scan is better than CT scan because it shows the metabolic activity of the tissues.
  5. It takes longer to have a PET scan.
  6. CT scan uses X-rays and a PET scan uses radioactive isotopes.
  7. CT scan is a simpler procedure than PET scan.


  • Edward Osler

    I am chronic claustrophobic plus I suffer from chronic failed back syndrome and cannot lie flat on my back for longer than 5-8 min. An MRI is not possible and if I have to lie flat on my back, the CT Scan won’t be possible either. I tried an OPEN MRI but the space is too tight for me to withstand and cope with,  What other options do I have?  My problem is a swollen and painful right foot.

  • Anonymous

    I suffer from Peripheral Neuropathy, Failed Back Syndrome, Claustrophobia and I cannot lie flat on my back for longer than 5-8 minutes. I have attempted an open MRI but the tight space problem kicked in and the test had to be aborted. I tried a Gastric Emptying Scan to try to determine why I have been nauseus for the last 4 months but I couldn’t lie flat. Are there any scans or x-rays that can be done that I can complete.  I tried taking Ativan to deal with the anxiety to no avail.  My foot pain persists. Any suggestions would be appreciated.