Magnetic Resonance Imaging (MRI) uses strong magnetic fields and radio waves to create detailed pictures of organs and tissues without using ionizing radiation. It is a common diagnostic tool for examining soft tissues, cartilage, and bone structures in the joints. When a wrist injury requires detailed investigation, patients often worry about confinement. This article clarifies the positioning and equipment used for a localized wrist MRI.
Body Placement for a Wrist Scan
For an MRI focused exclusively on the wrist, the entire body does not need to enter the machine. The imaging requires the target area—the wrist and a portion of the forearm—to be positioned precisely at the isocenter, which is the uniform magnetic sweet spot within the machine’s bore. Technologists achieve this by carefully sliding the patient onto the table so that only the arm is fully inside the main cylinder of the scanner.
In most standard procedures using a whole-body scanner, the patient is positioned feet-first into the machine. This allows the head, shoulders, and torso to remain outside the opening, maximizing patient comfort and significantly reducing feelings of enclosure.
Understanding MRI Machine Types
The exact positioning experience depends heavily on the specific type of MRI equipment utilized by the imaging center.
Closed-Bore Scanners
The standard closed-bore MRI machine features a tube-like structure. Even with this common design, entering feet-first ensures the patient’s head is not enclosed for a wrist scan. This approach utilizes the machine’s full magnetic strength while keeping the patient’s upper body in open air.
Open MRI Systems
A more accommodating option is the open MRI system, which uses a design featuring two flat magnets with a wide, open space between them. This configuration eliminates the traditional cylindrical tube entirely, providing significantly more space around the patient. Open MRI machines are frequently used for patients who experience high levels of anxiety, though they sometimes offer a slightly lower magnetic field strength.
Dedicated Extremity Scanners
The most specific option for extremity imaging is the dedicated extremity scanner, a smaller, specialized unit designed only for limbs like the hand, wrist, foot, or ankle. These compact machines are significantly smaller than whole-body scanners, often only requiring the patient to insert the arm or leg into a small opening. This focused technology concentrates the magnetic field specifically on the limb, making the experience non-claustrophobic since the rest of the body remains completely outside the machine room.
The Wrist MRI Procedure and Positioning
Once the arm is correctly positioned at the magnetic isocenter, a specialized radiofrequency (RF) coil is placed directly around the wrist. This coil transmits and receives the radio signals that generate the detailed images. These specialized coils are necessary for obtaining high-resolution pictures needed to accurately diagnose small tendons, ligaments, and fine bone structures in the wrist.
Maintaining stillness is required throughout the scan, which typically lasts between 30 and 45 minutes, depending on the number of different image sequences the radiologist needs to acquire. Even minor movements of the wrist or hand can blur the resulting images, necessitating the use of straps or supportive padding to immobilize the arm securely during the procedure. The patient must remain as motionless as possible to ensure the clarity and diagnostic quality of the resultant cross-sectional images.
During data acquisition, the patient will hear loud, repetitive banging and knocking noises that are a normal byproduct of the rapid switching of magnetic field gradients. Because these sounds can reach high decibel levels, the imaging center always provides earplugs or specialized headphones to protect the patient’s hearing effectively. Communication with the technologist is maintained via an intercom system, and the patient is given a signaling device or call button to press if they need assistance or need to stop the examination at any point.