By James Flannery – Physiotherapist

In this newsletter, we’ll take a look at the three primary types of medical imaging that you might come across while under the care of your physiotherapist. I’ll look to outline what each is, what it shows us, and why it’s used.

First up, X-rays:

Most people are familiar with what an x-ray looks like, but I regularly have patients who aren’t really sure what they’re used for.
An x-ray machine works by firing x-rays, a type of electromagnetic radiation, through the target area, toward a detector plate on the other side. While this sounds somewhat scary at first, rest assured that the x-rays pass harmlessly through most tissues in the body, and are deflected away by harder tissue such as bone. The x-rays that hit the detector plate darken it, and image that is left behind after an x-ray is the shadow of the structures that could not be penetrated by the x-rays.
X-rays are an effective tool when there’s a need to check for bony injury; after a bad ankle injury, or a fall onto an outstretched wrist for instance. We can also use x-rays to check for some types of lung conditions, as fluid or other denser materials in the lungs shows up as lighter areas than air-filled areas of the lung.
X-rays do not show softer tissues like muscles and ligaments, and so can’t be used to directly diagnose damage to these structures; however, if an x-ray doesn’t show any bony injury, we can rule that out as a potential source of pain, which can help narrow down the diagnosis.

The second most commonly used imaging technique is diagnostic ultrasound. The most familiar use of an ultrasound scan to most people will be during pregnancy, during which a doctor can use ultrasound to look at a growing foetus and ensure that it’s healthy.
The same technique can be applied on other areas in order to check for things like muscle and ligament tears. The ultrasound probe emits high-frequency sound waves, which echo back off structures within the body, with different tissues reflecting at different levels. By picking up these echoes, the machine can create an image of the area within the body.
Ultrasound is a useful tool for early diagnosis of soft tissue injuries; it can be useful to tell whether something like a shoulder injury can be managed purely through physiotherapy, or whether the level of injury is such that it might need referral to a specialist.
One of the main limitations of ultrasound is that it is difficult to pick up injuries that are particularly deep, or that are surrounded by bony structures. Things like anterior cruciate ligament injuries in the knee can’t be reliably viewed by ultrasound.

The last main type of imaging is MRI, or magnetic resonance imaging. MRI is significantmy more complex than the other two forms of imaging, and involves creating a powerful magnetic field into which the patient is placed, then detecting the changes in vibrations of atoms throughout the patient’s body in response to the magnetic field; this is done by using concept known as nuclear magnetic resonance. Note that ‘nuclear’ in this sense refers to the core of the atoms; the process is actually free of any potentially harmful radiation.
The machines used for MRIs are very complex, very large, and very expensive. Because of this, and a few other reasons, there are limitations on who is able to refer patients for MRI scans. Neither physiotherapists nor GPs are able to refer directly for these scans, and will instead refer patients who might need them to a specialist, often an orthopaedic surgeon or a sports doctor.
An MRI scan gives us a very clear picture of all structures in the area scanned; ligaments, muscles, bones, nerves etc, and, for most things, is the best and most accurate form of imaging that we have available. MRIs are generally reserved for more serious injuries and/or for injuries that might need to be managed surgically.

Hopefully this has given a little more insight into an otherwise confusing area of medicine. If you have any questions about any imaging that’s been done for your injuries, ask your physiotherapist, and they’ll likely be happy to clear things up for you.