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Imaging Techniques (MRI, CT)

Introduction

Some patients may require additional imaging techniques such as an MRI (magnetic resonance imaging) or a CT ( computerized tomography or CAT scan) to confirm their diagnosis.

Procedure

Magnetic Resonance Imaging (MRI)

hThe MRI exam is painless. You don't feel the magnetic field or radio waves. Most MRI machines consist of a large magnet shaped like a tunnel. You lie on a table that slides into the tunnel. The magnetic field aligns atomic particles in your cells. When radio waves are broadcast toward these aligned particles, they produce signals that vary according to the type of tissue they are. A computer then creates a composite, three-dimensional representation of your body from the collected signals. Two-dimensional slices can be electronically created from this representation and displayed on a monitor for examination. These images can be then be converted into photographic film for further viewing and analysis.

You should not receive an MRI scan if you have an implantable cardioverter defibrillator or a pacemaker. Its strong magnetic field may interfere with these devices. You should also mention if you think you may be pregnant, because the effects of MRIs on fetuses are not yet understood. Your doctor may recommend an alternative exam.

It's important that you remove any electronic devices and metal objects before your exam. The magnetic field may damage electronic items and metal can interfere with the magnetic field, affecting the quality of images.

CT, Computerized Tomography, or CAT Scan

hSome CT scans require that you to ingest a contrast medium before the scan. A contrast medium blocks X-rays and appears white on images. This can help emphasize blood vessels or other structures that need to be examined. Contrast mediums can be taken by mouth, enema, or an injection into a vein (intravenously).

During a CT scan, you lie on a table inside a round machine called a gantry. An X-ray tube inside the machine rotates around your body and sends small doses of radiation through it at various angles. As the X-rays pass through your body, different tissues absorb different amounts. Sensors inside the gantry measure the radiation leaving your body and convert it into electrical signals. A computer then gathers these signals and assigns them a color ranging from black to white depending on signal intensity. CT images are sent to an electronic data file and then reviewed on a computer. A radiologist than interprets these images and sends a report to your doctor.

Unlike MRI, CT scans can be done even if you have an internal cardioverter defibrillator or a pacemaker. However, if you're pregnant your doctor may suggest postponing the procedure or choosing an exam that doesn't involve radiation, such as an ultrasound or MRI.

As with an MRI exam, you will be asked to remove metal objects that might interfere with image results prior to your CT scan.