Guide To Medical Imaging: X-Ray, Ultrasound, CT Scan, MRI Scan And PET Scan

What Is An X-Ray?

X-ray machines emit electromagnetic energy beams to produce images of tissues, bones, and organs Standard X-rays may be used for a variety of reasons, including diagnosing tumours or injuries to bones. X-ray scans expose patients to radiation.

• Soft body tissues such as blood, skin, fat, and muscle allow more X-ray to pass through, resulting in darker images on the film or digital media.
• Bones and tumours are denser and allow less of the X-rays to pass through, resulting in white images.
• For example, if there is a break in the bone, more of the X-rays pass through the broken area and the break is seen as a dark line against the white bone.

X-rays are also used in technology is used in other types of diagnostic imaging, such as CT scans.

What Is An Ultrasound?

Another diagnostic imaging technology is ultrasound. This non-invasive imaging test uses high-frequency sound waves to create pictures or videos of internal organs or other soft tissues in real-time. Ultrasound does not involve the use of radiation. Ultrasound can help the doctor investigate a variety of conditions, such as unexplained pains, lumps, or the causes of abnormal blood tests.

• During an ultrasound, a transducer is placed over an area of the body. The ultrasound waves are transmitted from the transducer into the body.
• The sound waves bounce off structures inside the body and back to the transducer. A computer then converts the signals into real-time images or videos.

What Is A CT Scan?

CT (computed tomography) scans use X-rays to produce detailed images of the inside of the body. They are often used to diagnose cancer, heart disease, injuries from trauma, and musculoskeletal disorders. Like standard X-Rays, radiation is used in CT scans.

• Multiple cross-sectional images of the body are taken and re-assembled in a computer to show the internal organs and other structures (e.g. bones, blood vessels).
• Can be rotated to allow the radiologist to view it from various angles.

What Is A MRI Scan?

MRI (magnetic resonance imaging) creates detailed images of organs and other structures inside the body using a powerful magnet and radio waves. Patients undergoing this test must remove metal items and inform the technician of any internal devices (e.g. pacemaker) that contain metal. MRI is used to diagnose conditions including ligament injuries and tumours.

• MRI scans may require a contrast agent that is injected through an IV line to allow a better view of the area under study.
• Like CT scan, MRI shows the structure of the body, but produces different set of information.
• Takes longer to perform than a CT and is more expensive.
• Does not expose patients to radiation.

What Is A PET Scan?

A PET (positron emission tomography) scan is used to visualise the metabolism or chemical activity within the body. Unlike CT and MRI scans that look at the form of structures inside the body, a PET scan looks at the functioning of the body and detected unusual cellular activity. A PET scan may be used to diagnose cancer, heart disease, and brain disorders such as dementia or Alzheimer’s.

• It involves injecting a small amount of radioactive substance (radiotracer) through an IV line into the body.
• The PET scanner detects and records the activity of the radiotracer as it moves through the body.
• Can detect abnormal changes before structural changes occur. E.g. Cancer may be detected before tumour formation, or before it can be seen via CT or MRI scan.

PET scans may often be combined with a CT scan for a more complete picture (PET-CT Scan).