Magnetic resonance imaging (MRI) is a non-invasive diagnostic tool that uses powerful magnets and radio waves to generate highly detailed cross-sectional images of the body’s internal structures. This technology is particularly effective for visualizing soft tissues like ligaments, tendons, cartilage, and muscles, making it a common procedure for evaluating knee problems. Individuals often require a knee MRI to investigate pain, swelling, deterioration, or injuries such as meniscal or ligament tears. This frequently leads to the question of whether a patient experiencing bilateral symptoms can have both knees scanned at the same time.
The Feasibility of Simultaneous Knee Scans
The direct answer to whether both knees can be scanned simultaneously is yes, but the possibility depends on patient anatomy and the specific MRI equipment available. Simultaneous imaging presents a logistical challenge because both joints must fit within the machine’s central magnetic field and a single field-of-view (FOV). The patient’s size, specifically the girth of their legs, must be accommodated by the machine’s bore, which is the tunnel the patient slides into.
Most modern MRI scanners, such as the 1.5 Tesla (T) or 3T machines, are designed with a wider bore, often around 70 centimeters, which increases the likelihood of fitting both knees. Beyond the bore size, the machine requires specialized radiofrequency coils to capture the signal from both joints effectively. Traditional knee coils only accommodate a single limb, necessitating the development of flexible, phased-array coils or a dedicated bilateral coil-array setup. These specialized coils enable the simultaneous acquisition of high-resolution images from both joints with minimal signal interference. If a patient is unable to comfortably fit, or if the available equipment cannot maintain sufficient image quality, the technologist will have to perform the scans sequentially.
Clinical Reasons for Imaging Both Knees
A physician orders a bilateral knee MRI because there is a specific medical reason to examine both joints concurrently. One major indication is the evaluation of systemic conditions that inherently affect both sides of the body. Diseases like rheumatoid arthritis or widespread osteoarthritis often manifest bilaterally, and a single scan provides a comprehensive view of the disease’s extent in both knees.
Bilateral imaging is also valuable when a patient presents with vague symptoms in one knee, and the physician needs a baseline for comparison. By scanning the asymptomatic knee alongside the painful one, the radiologist can distinguish between normal variations and true pathology. Furthermore, simultaneous pain or suspected injury in both joints, such as bilateral meniscal tears, makes a dual scan the most efficient approach for diagnosis and treatment planning.
What to Expect During the Dual Knee Procedure
Preparation for a dual knee MRI begins similarly to any single MRI scan, requiring the patient to remove all metal objects and change into a provided gown. Patients will then be asked to lie on their back (supine) on the MRI table. Positioning is particularly important for a bilateral scan, as both knees must be placed side-by-side and centered within the specialized bilateral radiofrequency coils.
The technologist will use pads, cushions, or specialized wedges to keep the knees still and properly aligned throughout the procedure. Maintaining immobility is important because any movement during the scan can cause motion artifacts, which blur the image and may necessitate repeating the sequence. The table will then slide into the magnet bore, positioning the knees at the center of the magnetic field.
Because the machine is acquiring data from two joints instead of one, the overall scan time is significantly longer than a standard single-knee MRI, which typically takes 15 to 20 minutes. A simultaneous bilateral knee MRI can take anywhere from 45 to 90 minutes, depending on the complexity of the required imaging sequences. If the physician requires a contrast agent, typically Gadolinium, an intravenous line will be started to inject the material partway through the exam, which helps to highlight specific structures or areas of inflammation.