Magnetic Resonance Imaging (MRI) is a non-invasive medical imaging technique that utilizes strong magnets and radio waves to generate detailed images of internal body structures. For a knee MRI, this scan is performed to diagnose injuries, evaluate pain, assess swelling, or investigate other issues within the knee joint. This advanced imaging method provides a comprehensive view of the knee’s intricate components without using ionizing radiation.
Positioning for a Knee MRI
When undergoing a knee MRI, patients typically lie on their back on a movable table that slides into the machine. The patient is usually positioned feet first into the scanner’s bore, so only the lower body, particularly the leg and knee area, enters the narrow tunnel of the MRI machine.
The patient’s head and upper body generally remain outside the bore, which can be reassuring for those who experience anxiety in enclosed spaces. A specialized knee coil or brace is often used to stabilize the leg and position the knee precisely within the magnetic field. This positioning ensures that the knee joint is centered, optimizing image quality.
Understanding Different MRI Machines
How far a patient goes into the machine for a knee MRI varies by scanner type. Traditional “closed” MRI machines have a longer, narrower tunnel. Even with these machines, for a knee MRI, the patient’s head and upper body usually remain outside the main bore, as only the lower extremities need to be inside for the scan. These systems often have powerful magnets, ranging from 1.5 to 3.0 Tesla, which contribute to high-quality images.
“Open” MRI machines are designed with a less enclosed structure, often featuring open sides or two flat magnets positioned above and below the patient. This design can make the scan feel less restrictive, which is beneficial for patients with claustrophobia or larger body types. However, open MRI systems generally have lower magnetic field strengths, typically ranging from 0.2T to 1.0T, which can result in images of slightly lower quality compared to closed systems, though often sufficient for knee diagnostics.
“Wide-bore” MRI machines offer a compromise, providing a larger opening (around 70 centimeters in diameter) than traditional closed systems while still maintaining strong magnetic fields for good image quality. This type of machine balances patient comfort with diagnostic capabilities, offering more space within a tunnel-like design.
What to Expect During Your Scan
Once positioned, the MRI machine produces loud knocking, thumping, or banging noises during operation. These sounds are a normal part of the imaging process, generated by the magnetic field interacting with radio waves to create images. To mitigate the noise, patients are consistently provided with ear protection, such as earplugs or headphones, which are important for comfort.
Remaining still throughout the scan is crucial for clear images. Even minor movements can blur the results, potentially requiring sections of the scan to be repeated, which prolongs the examination. A typical knee MRI takes 30 to 60 minutes to complete, though this can vary based on the specific injury or the clarity of images obtained. Patients can communicate with the technologist, who operates the machine from an adjoining room, via a two-way intercom system. A call button is also available for immediate assistance if any discomfort arises or if the scan needs to be paused.