The difference between imaging and diagnostic scans

14th December 2020 By Phoenix Hospital Group

Whilst doctors do their utmost to communicate well with patients, the endless stream of jargon and acronyms can be frustrating at times. In this article we give an overview and differences between the main types of scan you may encounter in our clinics.


X-rays themselves are a form of electromagnetic radiation, just like visible light. They are able to penetrate soft tissue like the human body because they are both higher in energy and wavelength. An X-ray source is placed on one side of the body with an imaging plate to collect the image on the other side.

X rays are absorbed at different rates by different body parts and tissue types, allowing clinicians to diagnose a range of conditions from broken bones to lung infections and heart failure.

You should tell your doctor or radiographer if there is any possibility that you are pregnant – x-rays are a greater risk to unborn children because they are still developing. Before your appointment you do not need to make any special preparations for your X-Ray. However, you may be requested to remove any jewellery that may interfere with the x-ray.


CT Scans

A CT or Computed Tomography scan is actually an advanced form of X-ray imaging, also referred to as a CAT scan (in the USA for example).

Rather than a single X ray source with an imaging plate, a CT scan takes multiple X ray images in a circular fashion. For this reason, CT machines look like a large ‘donut ring’ with the person being scanned lying in the middle of the ring.

They have a distinct advantage over traditional X-ray scans as they form a 3-dimensional image for clinicians to review and diagnose from. They do however expose patients to multiple doses of X-ray radiation at once, so their use is only employed when there is a clear clinical benefit to the patient.


MRI Machines

Magnetic Resonance Imaging or MRI machines look similar to the circular CT machines, but are longer tubes which patients can lie within.

MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body.

MRI does not involve X-rays or the use of ionizing radiation, which distinguishes it from CT and PET. Before having an MRI scan, you should tell medical staff if:

  • you think you have any metal in your body
  • you’re pregnant or breastfeeding

The strong magnets used during the scan can affect any metal implants or fragments in your body. You may not be able to have an MRI if there is any metal in your body, including artificial joints or a pacemaker. Having something metallic in your body doesn’t necessarily mean you can’t have an MRI scan, but it’s important for medical staff carrying out the scan to be aware of it.

They can decide on a case-by-case basis if there are any risks, or if further measures need to be taken to ensure the scan is as safe as possible.


DEXA Scans

Also known as bone density scans, these are a special type of X-ray that is tuned to pick up subtle differences in bone density that could be caused by conditions like osteoporosis.

During the scan, very low dose, dual energy X-ray absorptiometry (DEXA) is passed through your bones with a modified detector on the other side. These tests are routinely only available to those patients who are at risk of low bone density and further complications down the line such as fractures.

This would include post-menopausal women and those with an extensive smoking history amongst others.


Ultrasound Scans

Ultrasound scans as is a non-invasive procedure that uses high-frequency sound waves to create an image of part of the inside of the body.

Most famously known for pregnancy scans due to their good safety profile for the unborn infant, ultrasound scans have many medical applications from diagnosis to surgery.

Typically a jelly is applied to the skin before a small ultrasound probe is placed in the area of interest. An instrument called a transducer sends out high-frequency sound that humans can’t hear, and then records the echoes as the sound waves bounce back to determine the size, shape, and consistency of soft tissues and organs.


To book an appointment please call us on 0207 079 2102 or email [email protected].