Magnetic Resonance Imaging (MRI) offers a sophisticated way to visualize the internal structures of the body without using ionizing radiation. This diagnostic tool generates detailed images by leveraging powerful magnetic fields and radiofrequency pulses. To provide a comprehensive view, MRI scans can be captured and displayed in various orientations, known as planes. One particularly insightful orientation among these is the axial plane, which offers a unique cross-sectional perspective of the body.
Understanding the Axial View
The axial plane, also referred to as the transverse plane, essentially creates a “slice” through the body, much like cutting an apple horizontally. This orientation divides the body into upper and lower segments, running parallel to the ground when a person is lying down. This perspective differs from the sagittal plane, which divides the body into left and right halves, and the coronal plane, which separates the front from the back.
The benefit of the axial view lies in its ability to show structures in cross-section, revealing their relationships to surrounding tissues. This allows for a clear visualization of the full circumference of organs, the spinal cord, or specific brain structures. For instance, an axial image can display the entire cross-section of an intervertebral disc in the spine or demonstrate the full extent of a tumor within an organ. It is widely used in modern imaging techniques, including MRI and CT scans.
Common Applications of Axial MRI
Axial MRI is widely used across various anatomical regions to diagnose a range of medical conditions, providing detailed cross-sectional insights. For the brain and head, axial views are routinely employed to detect abnormalities such as tumors, assess the impact of strokes, identify lesions associated with multiple sclerosis, and evaluate the ventricles, which are fluid-filled spaces within the brain.
In the spine, axial MRI is particularly effective for evaluating disc herniations, where the soft inner material of a spinal disc protrudes. It also helps in diagnosing spinal stenosis, a narrowing of the spinal canal that can compress nerves, and assessing spinal cord compression or tumors.
For the abdomen and pelvis, axial MRI is valuable for imaging organs such as the liver, kidneys, pancreas, and reproductive organs. It aids in detecting tumors, inflammatory bowel disease, and assessing abnormal blood vessels.
When examining joints like the knee and shoulder, axial MRI contributes to assessing meniscal tears, ligament injuries, and cartilage damage. While often used in conjunction with sagittal and coronal views, the axial plane can provide unique insights into the full extent of these injuries. For example, specific accessory ligaments in the knee, such as the arcuate ligaments, are often best visualized on axial images. This comprehensive view helps clinicians understand the intricate details of joint pathologies.
Preparing for and Undergoing an Axial MRI
Preparing for an axial MRI involves several steps to ensure both patient safety and image quality. Patients are generally advised to remove all metal objects, including jewelry, piercings, hairpins, and eyeglasses, as these can interfere with the powerful magnetic field of the MRI scanner. It is also important to inform the medical staff about any implanted medical devices, such as pacemakers or aneurysm clips, as some metals can be hazardous or malfunction within the MRI environment.
Fasting instructions vary depending on the specific area being scanned and whether a contrast agent will be used. For abdominal or pelvic MRIs, or scans involving contrast dye, patients may be asked to avoid food and drink for a few hours before the procedure, typically around 4 to 6 hours. This helps reduce the risk of nausea or vomiting, and prevents digestive movements from blurring images. Patients should continue to take their usual medications unless otherwise instructed by their doctor.
During the scan, the patient will lie still on a movable table that slides into the MRI machine, which is a large, tunnel-like scanner. The machine produces loud knocking or humming sounds, so earplugs or headphones are typically provided to protect hearing. An intercom system allows two-way communication with the technologist throughout the procedure.
Some MRI exams may involve an intravenous (IV) injection of a contrast agent, most commonly gadolinium-based, which enhances the visibility of certain tissues, tumors, inflammation, or blood vessels by altering the magnetic properties of water molecules. The duration of an MRI scan can range from approximately 15 minutes to over an hour, depending on the body area and the number of images required.
After the scan, if no sedation was administered, patients can usually resume their normal activities immediately. If a contrast agent was used, drinking extra water for a few hours is often recommended to help flush it from the body. The images are then reviewed by a radiologist, and the results are shared with the referring physician, typically within a few hours to a few days.