Depending on the expertise and MRI equipment available at a particular institution, specific MRI scanning protocols are designed to acquire the best possible images of certain body parts and diseases. A few of these indications are discussed below.
Patients with hydrocephalus (dilated fluid-filled ventricles in the brain) often undergo numerous brain CT examinations to determine if there has been any detrimental change in size of the ventricles in the setting of suspected ventriculoperitoneal shunt dysfunction. Very fast (<10 minute) brain MRI protocols have been designed as an alternative to CT so that the degree of hydrocephalus may be rapidly determined in children of all ages without the use of sedation or ionizing radiation.
Rapid brain MRI protocols are generally not appropriate when looking for intracranial hemorrhage, tumor, stroke, infectious disease, or a seizure focus. When hydrocephalus is not the primary concern, a complete brain MRI should be ordered instead. These are better addressed by more traditional length examinations.
Tumor Diagnosis, Therapy Response Assessment & Surveillance
In many cases, tumors are initially diagnosed by CT or US. MRI is then sometimes used to provide greater anatomic definition of the tumor and surrounding brain or other organ system or to characterize the type of tissue in the tumor. MRI is the imaging examination of choice for assessing tumor response to treatment (arrows in following figure) and for surveillance for recurrence of certain tumors, especially those of the brain, spinal cord, bone and muscle.
Inflammatory Bowel Disease
MRI is the preferred imaging examination for monitoring patients with inflammatory bowel disease (IBD). Inflammation of the bowel wall, abnormal connections between bowel loops, and infected fluid collections outside the bowel can be detected with MRI. Abnormal peristalsis (motion of the bowel) can even be detected with a technique known as cine MRI.
Ultrasound is most often used as the initial imaging examination for children with suspected appendicitis. When the ultrasound examination is inconclusive, computed tomography (CT) is often performed. However, MRI is emerging as a viable alternative to CT for the evaluation of appendicitis (enlarged inflamed appendix shown by arrow in following figure) in children with an inconclusive ultrasound examination.
Musculoskeletal Infectious and Inflammatory Conditions
MRI is the preferred imaging examination for diagnosing infections of the bone, growth cartilage, and muscle. While bone scintigraphy (nuclear medicine study) can also be used to diagnosis osteomyelitis, MRI better shows associated conditions such as septic arthritis and abscesses in and around bones and muscles that may require surgical drainage (arrows in figure below).
MRI is also very useful for demonstrating the extent of arthritis, such as juvenile idiopathic arthritis, and the extent of inflammation not due to infection in a setting such as juvenile dermatomyosis. This helps to guide treatment and monitor therapy response to anti-inflammatory drugs (see arrows in the following figures).
Tendon, Ligament, Cartilage and Bone Injury
Due to its excellent demonstration of different structures such as fat, blood vessels, muscles, tendons, ligaments, cartilage, bone and bone marrow, MRI is the preferred imaging examination to detect injury to these tissues (arrows in figure below). The extent and severity of these injuries can be graded by MRI to assist in treatment planning by the orthopedic surgeon or sports medicine physician.
MRI is also especially good for detecting bone bruises and stress injuries that are not evident on radiographs (arrows in figure below).