Magnetic resonance imaging in primary care
Published in MedicineWise News
Date published: About this date
New MBS funding for GP referred MRI | Why recommend MRI? | MRI safety issues and considerations | Using imaging in patients with back pain | Using imaging in patients with headache | Discuss options and findings in partnership with radiologists
Diagnostic imaging landscape in Australia
Over the last decade there has been increased use of imaging services with the greatest increases in nuclear medicine and magnetic resonance imaging (MRI; Figure 1).1 MRI use is likely to increase further as updated radiological guidelines generate a better understanding of its appropriate use. There is also more awareness and concerns around ionising radiation with the use of X-ray and computed tomography (CT) scans.2 New Medicare Benefits Schedule (MBS) items to fund referral for MRI by GPs3 mean MRI use is likely to change even further. Appropriate use of imaging technologies will provide benefits for patients and the community.1
Encounters commonly seen in general practice when imaging may be considered include: headache, back pain and other musculoskeletal conditions.4,5
Figure 1: Average annual imaging growth rate in Australia (2006–2011).1 Click image to enlarge.
New MBS funding for GP referred MRI
- Scan of the head for unexplained seizures, unexplained headache where significant pathology is suspected and paranasal sinus pathology which has not responded to conservative therapy.
And following plain X-ray for:
- Scan of the spine for unexplained neck or back pain including for significant trauma, unexplained neck or back pain with associated neurological signs or unexplained back pain where significant pathology is suspected.
- Scan of the knee for internal joint derangement.
- Scan of the hip for certain indications for suspected septic arthritis, slipped capital femoral epiphysis or Perthes disease.
- Scan of the elbow where significant fracture or avulsion injury is suspected that will change management.
- Scan of the wrist where scaphoid fracture is suspected.
It is anticipated that the eligibility criteria for these items will be extended in the future.
For MBS item numbers visit the MBS Online A-Z database
The Western Australian Department of Health Diagnostic Imaging Pathways (DIP) group, in collaboration with the Paediatric Imaging Reference Group of the Royal Australian and New Zealand College of Radiologists are developing guidelines for the new MBS items. For an evidence-based and consensus-based education and decision-support tool to guide diagnostic examinations refer to the DIP application.
Because of the higher risk of cancer in children exposed to CT, MRI should be the imaging modality of choice for all people under 20 years of age, unless an X-ray or CT is clinically indicated.2,6A. Please note: The information provided in this publication is not specific to a paediatric population. Radiological standards and guidelines referenced are predominantly for an adult population.
A systematic review showed that using imaging as a screening tool does not improve clinical outcomes, compared with imaging only when clinically indicated.7
Figure 2: Guidelines on requests for MRI, CT, X-ray or ultrasoundB Click image to enlarge.
Why recommend MRI?
MRI is superior to other imaging modalities for determining some body tissue characteristics.24 MRI can detect soft tissues such as organs and muscles that are not well imaged by X-ray or CT scan, enabling abnormalities that might be obscured by bone to be identified.24,25
Absence of ionising radiation
There are concerns about inducing cancer in individuals exposed to ionising radiation.2,16,26 MRI does not use ionising radiation – consider it first in situations where it provides better or similar information to CT scan or X-ray, and where both modalities are available.2,3
Comparative radiation doses
Effective radiation doses of imaging investigations of the chest (Figure 3), result in 8 milliSieverts (mSv) from a CT scan and 0.02 mSv from an X-ray. This is equivalent to 3.6 years and 3 days respectively, of background radiation.26
Any dose of ionising radiation carries risk
The ‘linear / no lower threshold’ model estimates the average lifetime risk of fatal cancer from 5 mSv to be approximately 1 in 4000. This is especially important in children and young adults who are at greater risk from ionising radiation than older adults.26
For effective doses of ionising radiation refer to the Ionising radiation page of the Diagnositic Imaging Pathways website.
Figure 3: Ionising radiation levels in imaging tests (ultrasound uses no ionising radiation).25 Click image to enlarge.
MRI safety issues and considerations
A quality MRI image relies on the patient remaining immobile for the duration of the scan.23 Special consideration needs to be given to:
- Patients who need sedation
Some patients (e.g. children) may need to be sedated or undergo anaesthesia to ensure image quality but whenever possible, sedation should be avoided.23
- Patients who suffer claustrophobia
People who experience claustrophobia may require anxiolytics. Conscious sedation is commonly used, some facilities may use anaesthesia.23 Some MRI scanners have a more ‘open’ or ‘wide bore’ design which may help such patients remain calm.27
Contraindications to MRI include, but are not limited to:
- Patients with prostheses or other implanted devices
Pacemakers, implanted defibrillators, nerve stimulators, cochlear, orthopaedic and dental implants. Newer prostheses are usually manufactured to be MRI compatible.23
- Patients carrying foreign bodies
For example, metallic foreign bodies in the eye.23,28 Note that injuries have also been sustained from metal objects becoming projectiles during MRI.2,29
Other reported safety issues
Thermal burns, including skin burns from medication patches.30
- Hearing loss
Hearing loss has been reported although acoustic noise levels are anticipated to be well within limits set by standards.2,31
Keep in mind the limitations
Increased use of diagnostic imaging such as MRI has not always been reflected in improved outcomes.32 Investigations, including imaging of any kind, should be requested only when the findings may alter treatment.2
In some clinical scenarios, other types of diagnostic imaging remain more appropriate than MRI (see Figure 2).
The safety of MRI in pregnancy has not been established. The decision to scan during pregnancy should be made on an individual basis after considering the medical necessity and alternative imaging methods. This particularly applies to the first trimester.23
In patients who are hypersensitive to contrast media (gadolinium chelate), or for those with severe kidney or liver insufficiency, seek advice from the radiologist before requesting MRI.23
As with all tests, there are risks associated with interpreting MRI results (e.g. false positives and negatives) and there is potential for detecting abnormalities incidental to the reason for imaging. This may cause patient anxiety and clinical uncertainty, and lead to further unnecessary investigations or treatments with associated risks.33
MRI may lead to procedures that are of low value to patients. A study of 178 breast cancer patients found that those who had undergone MRI and mammography were more likely to have mastectomies that provided no or doubtful benefit than those who had mammography alone. The lesions detected by mammogram correlated more with pathologic lesions while MRI detected more incidental findings of non-cancerous lesions.2,34
For any imaging investigation the potential benefits must outweigh the possible risks.35
Using imaging in patients with back pain
For most people with back pain without ‘red flag’ symptoms an X-ray, CT or MRI scan is unlikely to help identify the cause of pain, or alter treatment or speed up recovery time.36,37 False-positive reports and incidental findings may even prolong recovery time due to subsequent unnecessary, invasive and expensive procedures.37
Carry out immediate imaging with X-ray when ‘red flags’C for serious underlying disease are present:
- age of onset < 20 years or > 55 years
- recent history of violent trauma
- constant progressive, non-mechanical pain (no relief with bed rest)
- thoracic pain
- past medical history of malignant tumour
- prolonged use of corticosteroids
- drug abuse, immunosuppression, HIV
- systemically unwell
- unexplained weight loss
- widespread neurological symptoms (including cauda equina syndrome)
- structural deformity
For possible spinal cord or cauda equina compression immediate imaging with MRI is prefered, but early referral to a tertiary centre is required.10C. There is no convincing evidence that the absence of these ‘red flags’ is sufficient to exclude serious underlying disease but they may help to reduce unnecessary use of X-ray.
Support patient self-management
Communicating incidental radiological findings
A systematic review has shown no direct link between degenerative MRI changes and chronic low back pain.38
"Is this just ‘wear and tear’?"
When explaining the results of images to patients, avoid labelling problems as ‘degeneration’ and ‘wear and tear’.39 These changes are incidental findings and may negatively impact the patient and place a barrier in the way of recovery.40 It may be helpful to explain that these changes are similar to those seen in others of the same age who are without any pain.40
Using imaging in patients with headache
Table 1: Some ‘red flags’ when diagnosing headache17, 33
|A ‘new-onset’ headache in a person||Headache associated with|
Use imaging in combination with a comprehensive history and targeted physical and neurological examination.33
Discuss options and findings in partnership with radiologists
Choose the right test
There are often a number of appropriate investigations in a particular clinical situation. Radiologists can provide guidance on selecting the right imaging pathway and give advice regarding when to refer onwards.35
Communicate background information about the patient to the radiologist to allow for a more definitive interpretation of test results.2
MRI use in primary care
James is a 15-year-old footballer who injured his right knee. He plays at school and for a local club.
DAY 1 - First consultation
James presented to you on the same day as his injury. He described being tackled from behind, falling onto his knee with another player falling onto the back of his leg. RICE (Rest, Ice, Compression, and Elevation) therapy was applied immediately after the injury.42 He was unable to walk from the field.
Since the injury, his knee has remained very painful, swollen and he is unable to bear weight. On examination he had a moderate effusion, posterior and lateral knee pain and tenderness over the joint line and proximal tibia.
- Anterior cruciate ligament (ACL) injury
- Lateral collateral ligament (LCL) injury
- Posterior cruciate ligament (PCL) injury
- Meniscal tear
- Bone bruising
Application of the Ottawa Knee and Pittsburgh Decision rules (Table 2) suggests James may benefit from plain X-ray.9
His X-ray shows no evidence of fracture/avulsion injury and no abnormality of the tibial plateau.44
You advised an initial period of conservative management including paracetamol and an NSAID for persisting pain.45 You counselled James to begin moving his knee as soon as pain permitted.45 You made a follow-up appointment to reassess the injury the following week.
DAY 7 - Second consultation
James reports residual swelling and discolouration of skin. Conservative treatment had partially relieved pain which allowed you to perform further examination. You find that he is now able to bear some weight, stand on one leg, hop and walk, though still with moderate pain. He reports instability walking downstairs. He demonstrated a negative Lachman’s test and full range of motion of the knee, positive posterior draw test and posterior sag.44 You are concerned about James’ slow recovery and suspect a possible PCL injury.44
Rationale for imaging
Following exclusion of fracture on X-ray, DIP guidelines recommend the use of MRI if a soft tissue injury is suspected.9,44 You request a MRI scan and images reveal a PCL sprain and subchondral tibial bone bruise in the lateral compartment.
Bone bruise is a frequent finding on MRI imaging of post-traumatic knee injuries and can be indicative of significant articular cartilage damage.43 In patients with ACL rupture, bone bruise may alter the natural history of an isolated ACL tear.43
Table 2: Rationale for X-ray using Ottawa Knee and Pittsburgh Decision rules9
|Ottawa Knee Rules||Pittsburgh Decision Rules|
X-ray is indicated if any of the following apply
Blunt trauma or a fall plus either:
The MRI findings altered your treatment by lengthening the timing of the rehabilitation plan. While the PCL has a good blood supply and healing capacity44, bone bruise recovery is prolonged for most patients.46 James was advised to continue with simple pain relief when required, and to rest his knee by avoiding weight-bearing activity. This will help with pain relief and in severe cases reduce the risk of trabecular disruption caused by bone bruising, degrading into complete fracture.46
Bone bruises are often regarded as benign, self-limiting lesions.43 In most cases bone bruises will heal with conservative treatment. Complete resolution of bone bruises in the knee ranges from 88% to 100% after 2–16 months of follow-up.46
Only use MRI when it is clinically indicated9 – obtain a good history and examine the patient
Imaging can not and does not replace a clinical diagnosis based on history and examination. In conjunction with the history and clinical findings, imaging can help to confirm a suspected diagnosis and/or exclude important possible diagnoses, especially in complex injuries.47
Take care in predicting clinical outcomes from radiological findings
A European study of patients with conservatively treated knee injury in general practice found that observation of meniscal deterioration by follow-up MRI was not associated with improved clinical outcome. Fifty percent of patients with MRI showing deteriorated meniscus 1 year after trauma reported significant improvement or complete recovery.48
Increasing quality of MRI imaging, access to machines and funding make MRI an appropriate modality for the assessment of many paediatric sports injuries – to ensure the safe return of young people to sport.49
Clinical Professor Richard Mendelson, Consultant radiologist, Department of Diagnostic & Interventional Radiology, Royal Perth Hospital
Dr Nick Stephenson, Consultant radiologist, I-Med Regional Imaging, Wagga Wagga, NSW
Dr John Dowden, Editor, Australian Prescriber
Dr Graham Emblen, GP, Toowoomba, QLD
Dr Oliver Frank, GP, Hillcrest, SA
Dr Sarah Gani, GP and Medical Educator, Bella Vista, NSW
Benafsha Khariwala, Editor, Therapeutic Guidelines
A/Prof Jennifer Martin, Clinical Pharmacologist
Deborah Norton, QUM Pharmacist, West Vic DGP
Any correspondence regarding content should be directed to NPS. Declarations of conflicts of interest have been sought from all reviewers.
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- The Royal Australian and New Zealand College of Radiologists. Details on new GP referred paediatric MRI items. September 2012. (accessed 30 October 2012).
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- Department of Health Government of Western Australia Diagnostic Imaging Pathways. Non-traumatic hip and knee pain. 2012. (accessed 30 October 2012).
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- Moynihan R, Doust J, Henry D. Preventing overdiagnosis: how to stop harming the healthy. BMJ 2012;344:e3502.
- National Prescribing Service. NPS News 79: Headache - diagnosis, management and prevention. Sydney: National Prescribing Service Limited, 2012. (accessed 9 August 2012).
- Ayoola A, Alagarsamy S, Jaboin J, et al. Increase in mastectomies performed in patients in the community setting undergoing MRI. Breast J 2011;17:256–9.
- Department of Health Government of Western Australia Diagnostic Imaging Pathways. General Principles in Requesting Imaging Investigations. 2011. (accessed 26 October 2012).
- National Prescribing Service. NPS Back pain choices tool. 2012. (accessed 9 August 2012).
- Chou R, et al. Diagnostic imaging for low back pain: advice for high-value health care from the American College of Physicians. Annals Int Med 2011;154:181–9.
- Chou D, et al. Degenerative magnetic resonance imaging changes in patients with chronic low back pain: a systematic review. Spine (Phila Pa 1976). 2011;36(21 Suppl):S43–53. (accessed 26 October 2012).
- Maher CG, et al. Managing low back pain in primary care. Aust Prescr 2011;34:128–32.
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- Guidelines for all health professionals in the diagnosis and management of migraine, tension-type headache, cluster headache and medication overuse headache. Hull: British Association for the Study of Headache, 2010. (accessed 9 August 2012).
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- Crawford R, et al. Magnetic resonance imaging versus arthroscopy in the diagnosis of knee pathology, concentrating on meniscal lesions and ACL tears: a systematic review. Br Med Bull 2007;84:5–23.
- Oei EHG, et al. MRI follow-up of conservatively treated meniscal knee lesions in general practice. Eur Radiol 2010;20:1242–50.
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