Medical Imaging Explained – The Different Types of Medical Imaging Available and Their Uses
In an ideal world, we’d be able to diagnose and treat patients without any harmful side effects. Medical imaging remains one of the best ways to achieve that aim, being able to see what’s going on inside the body without the need for surgery or other invasive procedures. Indeed, it’s something we’re perhaps guilty of taking for granted at times.
Medical imaging can be used for both diagnosis and therapeutic purposes, making it one of our most powerful resources available to effectively care for our patients.
In terms of diagnosis, common imaging types include:
- CT (Computer Tomography)
- MRI (Magnetic Resonance Imaging)
They each work slightly differently to create images of what’s going on inside the body, so let’s look at them a little closer.
Ultrasound is the safest form of medical imaging and has a wide range of applications.
There are no harmful effects when using ultrasound and it’s one of the most cost-effective forms of medical imaging available to us, regardless of our speciality or circumstances.
Ultrasound uses sound waves rather than ionising radiation. High-frequency sound waves are transmitted from the probe to the body via the conducting gel, those waves then bounce back when they hit the different structures within the body and that is used to create an image for diagnosis.
Another type of ultrasound commonly used is the ‘Doppler’ – a slightly different technique of using sound waves that allows the blood flow through arteries and veins to be seen.
Due to the minimal risk of using Ultrasound, it’s the first choice for pregnancy, but as the applications are so wide – emergency diagnosis, cardiac, spine and internal organs – it tends to be one of the first ports of call for many patients.
X-ray imaging – the oldest but one of the most frequently used imaging types. We all know, and have probably had at least one X-ray over the course of our lives.
Discovered back in 1895, X-rays are a form of electromagnetic radiation.
X-rays work on a wavelength and frequency that we’re unable to see with the naked, human eye, but can penetrate through the skin to create a picture of what’s going on beneath.
Typically used for diagnosing issues with the skeletal system, X-rays can also be used to detect cancer through mammography and digestive issues through barium swallows and enemas.
X-rays are widely used as they are low cost, quick and relatively easy for the patient to endure. However, there are risks associated with the use of radiation for X-ray imaging.
Every time a patient has an X-ray they receive a dose of radiation. This can go on to cause radiation-induced cancer or cataracts later in life or cause a disturbance in the growth of an embryo or foetus in a pregnant patient.
Most of these risks are mitigated by only using X-rays when strictly necessary, and correct shielding of the body.
Computer Tomography (CT)
CT or ‘CAT’ scans are a form of X-ray that creates a 3D picture for diagnosis.
Computer tomography (CT) or computed axial tomography (CAT) uses X-rays to produce cross-sectional images of the body. The CT scanner has a large circular opening for the patient to lie on a motorised table. The X-ray source and a detector then rotate around the patient producing a narrow ‘fan-shaped’ beam of X-rays that passes through a section of the patient’s body to create a snapshot.
These snapshots are then collated into one, or multiple images of the internal organs and issues.
CT scans provide greater clarity than conventional X-rays with more detailed images of the internal organs, bones, soft tissue and blood vessels within the body.
The benefits of using CT scans far exceed the risks which, like with X-rays, include the risk of cancer, harm to an unborn child or reaction to a contrast agent or dye that may be used. In many cases, the use of a CT scan prevents the need for exploratory surgery.
It is crucial that when scanning children, the radiation dose has been lowered than that used for adults to prevent an unreasonable dose of radiation for the necessary imaging to be obtained. In many hospitals you’ll find a paediatric CT scanner for that reason.
Magnetic Resonance Imaging (MRI)
MRI scans create diagnostic images without using harmful radiation
Magnetic Resonance Imaging (MRI) uses a strong magnetic field and radio waves to generate images of the body that can’t be seen well using X-rays or CT scans, i.e. it enables the view inside a joint or ligament to be seen, rather than just the outside.
Commonly used to examine internal body structures to diagnose strokes, tumours, spinal cord injuries, aneurysms and brain function.
As we know, the human body is made mostly of water, and each water molecule contains a hydrogen nucleus (proton) which becomes aligned in a magnetic field. An MRI scanner uses a strong magnetic field to align the proton ‘spins’, a radio frequency is then applied which causes the protons to ‘flip’ their spins before returning to their original alignment.
Protons in the different body tissues return to their normal spins at different rates so the MRI can distinguish between various types of tissue and identify any abnormalities. How the molecules ‘flip’ and return to their normal spin alignment are recorded and processed into an image.
MRI doesn’t use ionising radiation and is increasingly being used during pregnancy with no side effects on the unborn child reported. However, there are risks associated with the use of MRI scanning and it isn’t recommended as a first stage diagnosis.
As strong magnets are used, any kind of metal implant, artificial joint, etc., can cause a hazard – they can be moved or heated up within the magnetic field. There have been several reported cases where patients with pacemakers have died through the use of MRI. The loud noise from the scanner also necessitates the need for ear protection.
One thing we do have to be aware of as medical professionals in a time of escalating medical costs and increasing demand is that we’re using the best resources available to meet the needs of our patients. That means a careful decision on the right medical imaging to be used for the patient and their potential diagnosis.
- Medical Imaging and Technology Alliance 2018, Medical Imaging Modalities, MITA, Arlington, VA, viewed 12 January 2018, http://www.medicalimaging.org/about-mita/medical-imaging-primer/
- Nordbeck, P, Ertl, G & Ritter, O 2015, ‘Magnetic resonance imaging safety in pacemaker and implantable cardioverter defibrillator patients: how far have we come?’, European Heart Journal, vol. 36, no. 24, pp. 1505-11, viewed 12 January 2018, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4475571/
- NPS MedicineWise 2017, Imaging Explained, NPS MedicineWise, Surry Hills, NSW, viewed 11 January 2018, https://www.nps.org.au/medical-info/consumer-info/imaging-explained
- Understanding Medical Radiation 2011, Overview, Siemens Healthcare, Erlangen, Germany, viewed 12 January 2018, https://www.medicalradiation.com/types-of-medical-imaging/
- World Health Organization 2018, Diagnostic Imaging, WHO, Geneva, viewed 12 January 2018, http://www.who.int/diagnostic_imaging/en/