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What's the difference between PET scan, CT scan, X-Ray and MRI?

September 23, 2021 | Farah Jassawalla

There are various imaging tests that the doctor can order after a patient undergoes an injury or an illness. Doctors can use techniques such as X-ray imaging to provide a clear picture of what is wrong so that the doctor can make a correct diagnosis and treatment plan. 

X-ray imaging, PET scans, CT scans, and MRIs are various imaging techniques that are used to capture images of the inside of the body. These images allow the doctor to view the bones, masses, muscles, and tendons. If they find something out of the ordinary, they can proceed with fixing the problem. 

There are several differences between the X-ray, MRI, CT scan, and PET scans; these have been broken down for you below. 

X-Ray Imaging and MRI Radiography

X-rays are the first resort for most cases after a problem has been spotted. X-ray images are also known as radiographs, as the machine uses radiation when the pictures are being taken. Radiation is used to transmit electromagnetic waves, which expose the structures of the body onto the film that shows the images. 

In an X-ray procedure, the patient is required to lie very still, hold their breath and not make any involuntary movements to get the best images. The patient is positioned between the X-ray and the film for the machine to capture images. X-ray imaging is taken from different angles so that the body part under scrutiny can be analyzed thoroughly. 

MRI radiography is also done after some kind of illness or injury. An MRI refers to magnetic resonance imaging. In MRIs, the images are taken using a magnetic field, which sends pictures of the body to the connected computer. You must inform the doctor if you have any metal inside your body prior to an MRI. Much like the X-ray, you should be still during the procedure. However, there are some differences between an X-ray and MRI:

  1. Location: X-rays target a specific body part, whereas, in MRIs, the patient is asked to lie down on a table and is glided into a tube. The machine surrounds the body and takes pictures.

  2. Radiation: MRIs do not use radiation. They use radio waves and magnetic fields. The waves pulse from the machine and cause the tissues to vibrate. The computer picks up on the vibration and pieces the image together. 

Much like the X-ray, this process is not harmful. However, it can take nearly an hour for the process to be complete. 

Is MRI an X-ray?

An MRI is not an X-ray. It is an imaging technique, like an X-ray. The key difference between them lies in the way images are captured, while the purpose of capturing the images may be the same. 

PET scan/CT scan

PET scans are also known as Positron Emission Tomography. Unlike MRIs and CT scans, this technique focuses on the organs instead of the bones. For this procedure, the patient is injected with a liquid containing small radioactive particles. When this spreads, the patient is glided through a scanner which picks up the particles and sends them to the computer to create images. 

PET is typically used for illnesses related to the brain, blood, and organs. They are helpful in determining the success of cancer treatments. They use small amounts of radiation compared to X-ray imaging and CT scans.

CT scans are also called computerized tomography scans. These are essentially an advanced form of X-ray, as it uses multiple angle and position X-rays to create a detailed image of the structure - creating a 3-D image of sorts. The different angles allow the doctor to understand the damage and analyze it better.

These are precise and detailed, which is why they are perfect for looking for small tumors, identifying internal bleeding, and weeding out cancer.

CT scan vs X-ray radiation

A CT scan employs a higher level of radiation in comparison to an X-Ray. In order to capture 3-dimensional views of the structures, larger doses of radiation are used. For example, if we take the example of chest X-ray vs chest CT scan, the former delivers 0.1 MSV, while the latter delivers 7 MSV.

What is a PET/CT scan?

PET scans are used for cancer treatments. In some cases, it is done alongside a CT scan. If both the tests are done together, it is called a PET/CT scan. However, most doctors just call it a PET scan regardless. The combination of these scans detects cancer and identifies its stage. 

Difference between MRI and CT Scan

An MRI uses radio waves, while a CT scan uses X-rays. MRIs also tend to be more expensive than CT scans. CT scans are often quieter and take less time. 

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