Despite what you may think, Doctors and Allied Health Professionals are not superheroes. We do not possess X-ray vision, nor can we read minds and figure out what is going on underneath the skin without proper assessment. Assessment includes what you tell us about your injury or condition and the assessment of physical movements that stimulate your symptoms. From this we develop theories of potential causes influencing your injury or condition. In some cases, we would send you for a scan to assess your internal structures to confirm or deny our theories.
Scans, otherwise known as medical imaging assists in looking beneath the surface and identifying affected structures within the body causing your injury. They are relatively cheap and accessible due to the number of practices offering imaging services and the improvement in medical technology. Most images range between bulk-billed ($0) to $350 depending on the type and nature of the image required. Physiotherapists as Allied Health Providers are qualified to send their patients for medical imaging to assist in the diagnosis process or to aid management of their patient’s injury.
The question is, if we have such great access to medical imaging in the 21st century, why don’t all patients’ get sent for a scan? The simple answer is that most patients do not require getting imaging due to the nature of their injury/condition. Only a minority of patient requires additional medical imaging to assist in the diagnosis/management process. This depends on a number of things that the patient has said about the history of the condition and what they have shown us with movement. The reason for referral for medical imaging could be for a suspected broken bone, a serious muscle/tendon/ligament injury or for potential nerve related conditions.
Before sending a patient for medical imaging we as physiotherapists must first determine if the patient fits the criteria for medical imaging. This is done by weighing up a number of important factors:
1) Imaging algorithm
Does this injury tick the boxes indicated for this series of images to be performed? For example in the case for a sprained ankle. Before an X-ray can be taken the patient must describe pain over the bony edges of the ankle or unable to stand on the affected ankle either immediately after the injury occurred or when they present for medical assessment. If the patient doesn’t meet the recommended criteria it is unlikely the image requested will be of any benefit to the diagnosis process. The algorithm also directs the next course of treatment if the image comes back positive or negative for an ankle fracture. Your Physiotherapist would usually describe this process to you before sending you off for an image otherwise you can check out the pathway process on the WA health webpage.
2) Type of image
Depending on the type of injury a different type of image may be necessary. The types of tissues we are interested in observing are bone, muscle, ligament, tendon, cartilage and nerve. Each type of image is specific to certain tissues compared to another type of medical imaging.
X-ray: The image is formed by exposing the target area to electromagnetic radiation called X-rays. The X-rays pass through the body and leave a shadow of bony tissue as they cannot pass through the dense structure of bone. X-ray is useful for diagnosing dislocation or fracture of bones, they are often used as a first step to rule out serious injury which may require surgical intervention.
Ultrasound: Ultrasound is produced by introducing a sound wave to the structures immediately beneath the skin. Much the same as whales and dolphins use echolocation, the soundwave produces an image of the structures beneath the skin. This image assists in identifying breaks in normal tissues and or swelling in the affected area. This works best for soft tissues such as ligaments and tendons, but is not as accurate as other forms of images. Ultrasound is often appropriate because it is a cheaper alternative to MRI.
CT (computed tomography): CT scans are a 3D representation of multiple X-ray scans. The machine performs multiple X-Rays around the affected area in a circular fashion to produce a 3D image on a computer. The images are shown as cross sectional ‘slices’ that show different tissues in different shades of grey. CT’s are useful at showing small fractures in bone tissue and changes in soft tissue consistency identifying damage to tissue. CT is often used as an alternative to MRI as there is no magnetic field produced by the machine and its operation.
MRI (magnetic resonance imaging): MRI imaging uses a magnetic field to identify structures within the body. Patients are required to lay still as they are introduced to a narrow tube containing the scanning equipment which highlights water and fat molecules within the body. These molecules in different proportions represent separate tissues within the body. Damage and injury can be observed as disruptions to the consistency of these tissues and inform clinicians of abnormality within the tissue. This results in better image quality and more accurate diagnosis in internal structures than other forms of medical imaging. MRI may not be suitable for patients with certain metallic implants as the magnetic field produced by the machine can potentially cause harm if specific implants are brought within the magnet’s field.
Certain types of medical imaging depend on the use of electromagnetic radiation to produce images. X-rays and CT require the use of X-Rays which sit at the high frequency end of the electromagnetic spectrum. Radiation at this end of the spectrum has greater energy than visible light, infrared or microwaves. With greater energy this form of radiation has the strength to affect normal atom behaviour within the body, this is known as ionising radiation. Changes in atom behaviour affect the electron cloud of the atom, changing the number of electrons attached to the atom. This can result in cell mutation which has the potential to increase the risk of cancerous cell development within the body.
As scary as ionising radiation sounds, the human body is exposed constantly to background ionising radiation in everyday life. Radiation is present in the air, in foods and in aeroplane travel, it is impossible to escape all forms of ionising radiation in everyday life. Between cosmic radiation from space (UV light to gamma rays) and naturally occurring radiation in the environment (Radon Gas, Potassium-40 and uranium) we are exposed to the equivalent of 75 chest X-rays per year (1.5mSv). The safe dose of exposure is suggested to be up to 10 mSv per year in humans.
4) Clinical relevance
It may sound silly but does the result of the medical image mean anything to my patient or my diagnosis? X does not always equal Y, and the same can be said regarding certain findings on medical images. The cornerstone of Physiotherapy is patient function, is the patient displaying signs of dysfunction or pain with their everyday lives? In many cases, patients can have underlying changes to joints and tissues which are completely unrelated or a non issue in the management of their condition. The most common example can be found in MRI images of the lumbar spine. A study (Kjaer, et al 2005)was performed on symptomatic (69% of subjects had experienced pain in the previous year) and asymptomatic patients alike who were sent for a MRI of their lumbar spine. The results showed 25-50% of patients had some form of hypointense disc signal, annular tears, high intensity zones, disc protrusions, endplate changes, zygapophyseal joint degeneration, asymmetry, and foraminal stenosis. Importantly it also found that disc herniation and nerve root compromise were not consistently associated with lower back pain.
The take home message is that just because it shows up on MRI or X-ray doesn’t mean that this is the cause of your pain. Firstly your subjective and movement assessment must add up to the imaging result and most importantly it must be stopping you from performing normally!
5) Will it change my management?
The last and arguably the most important factor to consider with medical imaging is what do I do with the information I have found? A specific image may mean the difference between having surgery or not, or it may be the difference between returning to sport this week and waiting another week. In other cases it may not change a great deal at all with your treatment, this depends on the nature of your injury and your progress to date with management. For example if you broke your ankle 6 weeks ago and now you are out of the cast and prepared to walk again, an X-ray wouldn’t always be ordered to confirm that you can walk on the leg. Pain and dysfunction govern whether or not there has been any disruption to the healing process. The case would change in the following 3 weeks if the patient was still experiencing ongoing pain and dysfunction which do not align with treatment expectations.
If what the patient displays does not follow what is expected at the stage of management that is when a scan might be necessary to change the treatment approach. As diagnosis is not always clear cut, physiotherapists usually employ differential diagnosis to account for other possible conditions that may mimic or contribute to your current presentation. If a test or a line of treatment is unable to split the other associated diagnosis’ an image may be requested to clearly define the injury.
So as you can see it is not as easy as saying ‘go get a scan’ to see what is going on with your injury. These are the factors that determine whether imaging is a useful addition to your assessment or a waste of your time and money. It may be a useful tool, but it’s what you do with the image that affects patient management, not the scan itself.
Kjaer, P., Leboeuf-Yde, C., Korsholm, L.,Sorensen, J.S., Bendix, T. (2005) Magnetic Resonance Imaging and Low Back Pain in Adults: A Diagnostic Imaging Study of 40-Year-Old Men and Women. Spine.30(10):1173-1180