Imaging tests are procedures that produce images of internal body organs, tissues, structures and pathways. They may be used to diagnose health conditions and manage diseases. Imaging tests may also be used to assist certain procedures and surgeries.

The most commonly used imaging tests for diagnosing neurological conditions include:

• Angiography. Uses a dye that shows up well on x-rays (radiopaque) and travels through the bloodstream. It is used to identify blood vessel obstructions throughout the body, including in the brain, head or neck.
  
  
• Brain scan. Imaging techniques used to reveal tumors, blood vessel malformations or hemorrhages in the brain. Various technologies can be used to create brain scans.
  
  
• Computed axial tomography. Also known as a CAT scan or CT scan. It uses a rotating x-ray device to create detailed cross-sectional images (or slices) of different body parts.
  
  
• Magnetic resonance imaging (MRI). Test that uses computer-generated radio waves to produce clear, cross-sectional or three-dimensional images of the body’s tissues, even through bone and other obstructions.

• Myelography. Procedure in which a dye is injected into the spinal canal to help highlight abnormalities in the spine during x-rays.
  
  
• Positron emission tomography (PET) scans. Radioactive isotopes are injected into the bloodstream to provide two- and three-dimensional images of brain activity.
  
  
• Single photon emission computed tomography (SPECT) scan. Radionuclide imaging test that evaluates brain function by highlighting blood flow to brain tissue.
  
  
• Thermography. Infrared sensing devices are used to detect changes in temperature between the two sides of the body or within a single organ.
  
  
• Ultrasound. Test that uses high frequency sound waves rather than radiation to create images of internal organs or tissues.
  
  
• X-ray. Creates an image of part of the body using low doses of electromagnetic radiation that are reflected on film or fluorescent screens.

A radiology technician in a hospital or outpatient clinic generally performs imaging tests. Patient preparation differs depending on the nature of the test to be performed. In some instances, the patient may need to drink or be injected with a dye known as a contrast medium. This solution makes certain organs and tissues in the body more visible.

The imaging test procedures are different depending on which test is performed. Generally, patients are able to return home the same day of the test. Imaging tests carry very few risks.

Imaging tests produce pictures of internal body organs, tissues, structures and pathways. Some tests can be performed with external devices. Other tests require that a device be inserted into a body opening.

Imaging tests are used to diagnose conditions and manage diseases. They may also be used to assist certain procedures and surgeries. In some cases, a dye known as a contrast medium is used as part of an imaging test. This solution contains a liquid that makes targeted organs and tissues in the body more visible by highlighting the structure. This helps reveal the presence of disease or injury.

There are several types of imaging tests that can be used to view internal structures of a patient’s body. The tests most widely used to diagnose neurological conditions include:

• Angiography. A cerebral angiogram may be able to detect blood vessel abnormalities in the brain, head or neck. In this test, a catheter is inserted into the leg near the groin and threaded through the body and into an artery in the neck. After the catheter is in place, a guide wire is inserted and a dye that shows up well on x-rays (radiopaque) is released to travel through the bloodstream. When x-rays are taken, the dye helps reveal any obstructions. Angiography is most often used to diagnose narrowing or obstruction of blood vessels and to help find the size and location of a brain tumor, aneurysm or vascular malformation.
  

  
  

• Brain scan. Imaging technique used to reveal tumors, blood vessel malformations or hemorrhages in the brain. Various technologies can be used to create brain scans (e.g., CAT scan, MRI), which reveal information about organ function and injury or disease involving tissue or muscle.
  
  
• Computed axial tomography. Also known as a CAT scan or CT scan. It uses a rotating x-ray device to create detailed cross-sectional images (or slices) of different body parts. It may be performed alone or with the use of a special dye (contrast medium). A CAT scan is used to view the brain and spine to diagnose neurological disease. Conditions that can be revealed include bone and vascular abnormalities, certain brain tumors and cysts, herniated discs, encephalitis, epilepsy, intracranial bleeding in stroke patients and spinal stenosis (narrowing of the spinal canal). An intrathecal contrast-enhanced CT scan is used to detect problems with the spine and spinal nerve roots. A discography (CAT scan of the back) can identify damage to the discs of the spine.
  
  
• Magnetic resonance imaging (MRI). Test that uses computer-generated radio waves to produce clear, cross-sectional or three-dimensional images of the body’s tissues, even through bone and other obstructions. Because of its safety and clarity, the MRI is a valuable tool that can help diagnose a wide range of conditions in nearly every part of the body, particularly in the brain, neck, spinal cord and soft tissues. Central nervous system disorders such as multiple sclerosis may be diagnosed using MRI. Other neurological conditions that can be diagnosed with an MRI include brain and spinal cord tumors, brain injury, eye disease, inflammation, infection and vascular irregularities. A variation called a functional MRI uses the blood’s magnetic properties to produce images of blood flow to particular areas of the brain. This is done in real time and can help reveal damage associated with head injury or degenerative disorders such as Alzheimer’s disease. Functional MRI also is used to diagnose or monitor neurological disorders such as brain tumors, multiple sclerosis and stroke.

• Myelography. Procedure in which a dye is injected into the spinal canal to help highlight abnormalities in the spine during x-rays. It is used to diagnose back or leg pain, fractures, herniated discs, spinal nerve injury and spinal tumors.
  
  
• Positron emission tomography (PET) scan. Radioactive sugars are injected into the bloodstream to provide two- and three-dimensional images of brain activity. The sugar can highlight diseased tissue, measure cellular and tissue metabolism, reveal tumors and show blood flow. PET scans are used to detect the presence and spread of cancer. It also is used to evaluate patients with seizure disorders that do not respond to treatment. Finally, PET scans can reveal brain changes that result after injury or drug abuse. Despite the use of radioactive isotopes, this procedure presents few risks.
  
  
• Single photon emission computed tomography (SPECT). Radionuclide imaging test that evaluates brain function by highlighting blood flow to brain tissue. It sometimes is used as a follow-up test to an MRI in diagnosing diseases such as Alzheimer's, epilepsy and tumors. A radioactive isotope is used, and areas of increased blood flow collect more of the isotope.
  
  
• Thermography. Infrared sensing devices are used to detect changes in temperature between the two sides of the body or within a single organ. Conditions that can be detected include complex regional pain syndromes such as reflex sympathetic dystrophy and causalgia.
  
  
• Ultrasound. Test that uses high frequency sound waves rather than radiation to create images of internal organs or tissues. In an ultrasound test, a small wand-like instrument called a transducer is passed over the patient’s body as it sends low energy sound waves against tissue. Some waves pass through and others bounce back. As sound waves bounce back, they are recorded and displayed on a monitor. Neurosonography is ultrasound of the brain and spinal column. It analyzes blood flow in the brain to help reveal the presence of brain tumors, hydrocephalus (fluid buildup in the brain), stroke and vascular problems. Transcranial Doppler ultrasound is used to view arteries and blood vessels in the head and neck and determine blood flow and stroke risk.
  
  
• X-rays. Oldest form of imaging test. In this procedure, an image is created of part of the body by using low doses of electromagnetic radiation that are reflected on film paper or fluorescent screens. The absorption of x-rays differs depending on the type of tissue being x-rayed. Bones absorb x-rays and appear white, soft tissues pass more x-rays and appear gray, and tissues containing air (e.g., lungs, intestines) appear dark. Chest and skull x-rays are most often used during neurological examinations.

Patients are urged to follow all preparatory steps recommended by the physician prior to the imaging test. They are also urged to inform the physician and the technician about any implanted metal or electronic devices, such as prostheses and pacemakers.

Immediately before the test, patients may be asked to change into a hospital gown. All metallic objects, such as watches and jewelry, should be removed so they do not interfere with test results. In fact, patients may want to leave these objects at home on the day of the test. Patients receiving the test may be given a sedative in some circumstances to ensure they are relaxed and remain still during testing.

If a dye known as a contrast medium is to be used, the patient may be instructed not to eat or drink for several hours before the test.

Contrast mediums may be administered orally (by mouth), through an enema (fluid put into the rectum) or injected into a vein. Injection of the dye may produce a warm, flushed feeling for several minutes or a metallic taste in the mouth. Both sensations are normal and disappear quickly.

Patients undergoing a nuclear scan may receive an injected or oral radiopharmaceutical agent anywhere from a few minutes to several days before the actual procedure, depending on the type of scan. The agent travels to and remains in a particular body area and releases gamma rays that are detected and imaged by a device called a gamma camera.

Imaging tests are generally performed by a radiology technician in a hospital or outpatient clinic. The manner in which the test unfolds will depend upon the imaging procedure being used. It is typically important for patients to hold their breath at certain points during some of these imaging tests (e.g., CAT scan). This helps create a clearer image.

Depending on the nature of the test, the patient may sit, stand or lie down as images are taken. The test itself will unfold differently depending on the nature of the procedure being performed. Imaging tests can take anywhere from a few minutes to several hours to complete. Most imaging tests are painless.

In many cases, patients undergoing imaging tests should be able to leave the facility immediately following the imaging test with no side effects. However, if a sedative is administered, patients will be monitored at the facility until the effects of the sedative have passed. If the patient will be taking a sedative, it is advisable that someone drive the patient to and from the test.

Patients who have received radionuclide imaging tests may receive special instructions after their tests. The radioactive materials will decay and be flushed from their bodies over several days. The patient may need to flush the toilet immediately after using it. Physicians may offer other advice about limiting their time near children or refraining from sexual activity until the radioactive material is eliminated from the body.

After the imaging test is performed, the radiologist or physician will analyze the images. The results will then be reported to the patient.

Imaging tests are generally safe and present few risks. The levels of radiation used in these tests are very low and experts believe that they pose very little risk of long-term harm.

Still, exposure to any level of radiation has the potential to damage tissue, which in some cases may eventually result in cancer. It is important for patients to weigh the potential risks against the potentially lifesaving benefits of the information obtained from the test.

In rare cases, the special dye (contrast medium) used during a computed axial tomography (CAT) scan may cause nausea, a metallic or bitter aftertaste in the mouth, feeling of flushing or warmth or an allergic reaction in the form of mild itching or hives (small, raised, reddened areas of skin). In more severe reactions, shortness of breath, wheezing and swelling of the throat or other body areas that require treatment with allergy medication may occur. Patients who notice any of these symptoms developing during the procedure should immediately alert the technician performing the test.

Patients should also inform the physician of the following conditions before imaging tests are performed:

• Asthma or allergies. Contrast mediums can produce allergic reactions in some people, especially those with a history of asthma or allergies.
  
  
• Other medical conditions. Certain medical conditions may also increase the likelihood of an allergic reaction to contrast mediums. These include diabetes, heart disease, kidney problems and thyroid conditions.
  
  
• Presence of medical devices. Certain imaging tests should not be performed on patients with pacemakers and other types of implanted devices.

Preparing questions in advance can help patients have more meaningful discussions with healthcare professionals regarding their condition or test. Patients may wish to ask their doctor the following questions related to imaging tests:

1. Why do you recommend an imaging test?
   
   
2. Which type of imaging test is best to diagnose my condition? Why?
   
   
3. Can you explain the procedure to me in detail?
   
   
4. What information will my imaging test provide?
   
   
5. How should I prepare for my imaging test?
   
   
6. Will a contrast medium be used during my imaging test?
   
   
7. Will the imaging test cause any pain or discomfort?
   
   
8. Will I need to take a sedative for the discomfort?
   
   
9. Will I be able to return home the same day as the imaging test?
   
   
10. Should I have someone else drive me to and from the test?
    
    
11. When and from whom will I receive the test results?