How Long It Takes: MRI Scans
An MRI exam looks at the body from many different angles without having to move the patient. Because there is so much information to gather, it takes the computer system time to record all of the details. The actual length of an MRI scan can take between 15 and 90 minutes depending on what part of the body is being scanned and what is needed for diagnosis. Before the scan begins, the radiographer can tell you approximately how long your scan will take and what you should expect.
MRI does not use ionizing (X-ray) radiation. Instead, to create an image, MRI scanners must determine which radio signals are coming from which hydrogen protons and plot them in their proper locations. To distinguish protons from one another, MRI scanners manipulate both the magnetic field and the radio energy so that protons in different parts of the patient emit slightly different radio signals. The MRI machine automatically knows where each of the different signals originated from and can then build a three-dimensional image.
The MRI machine also reads how strong the radio signals are in each area and can discriminate between body substances based on their physical properties; for example, differences between water- and fat-containing tissues and bone. The different strengths of the radio signal create the shades of gray in the final image based on the patient’s anatomy. Magnetic resonance imaging (MRI) is therefore particularly useful at providing highly detailed images of soft tissues in various planes.
An MRI scan can create clear pictures of most parts of the body without changing the position of the patient, so it is useful for all sorts of reasons where other tests (such as X-rays) are unable to image as accurately. It is commonly used to get detailed pictures of the brain and spinal cord to detect abnormalities and tumors. Even torn ligaments around joints can be detected by an MRI scan.
MRI can also detect certain diseases much earlier than other medical imaging techniques can, making it the diagnostic tool of choice for many physicians. In some cases, an injection of a special contrast dye is given into the bloodstream via a vein on the arm. This helps to give more information about certain tissues or organs being examined.