Electromyography (EMG)

Definition

Electromyography (EMG) is a diagnostic procedure to assess the health of muscles and the nerve cells that control them (motor neurons).

Motor neurons transmit electrical signals that cause muscles to contract. An EMG translates these signals into graphs, sounds or numerical values that a specialist interprets.

An EMG uses tiny devices called electrodes to transmit or detect electrical signals. During a needle EMG, a needle electrode inserted directly into a muscle records the electrical activity in that muscle.

A nerve conduction study, another part of an EMG, uses surface electrodes — electrodes taped to the skin — to measure the speed and strength of signals traveling between two or more points.

EMG results can reveal nerve dysfunction, muscle dysfunction or problems with nerve-to-muscle signal transmission.

Why it's done

Your doctor may order an EMG if you have signs or symptoms that may indicate a nerve or muscle disorder. Such symptoms may include:

• Tingling
• Numbness
• Muscle weakness
• Muscle pain or cramping

EMG results are often necessary to help diagnose or rule out a number of conditions:

• Muscle disorders, such as muscular dystrophy or polymyositis
• Diseases affecting the connection between the nerve and the muscle, such as myasthenia gravis
• Disorders of nerves outside the spinal cord (peripheral nerves), such as carpal tunnel syndrome or peripheral neuropathies
• Disorders that affect the motor neurons in the brain or spinal cord, such as amyotrophic lateral sclerosis or a herniated disk in the spine

Risks

EMG is a low-risk procedure, and complications are rare. There's a very small risk of bleeding, infection and nerve injury where a needle electrode is inserted. When muscles along the chest wall are examined with a needle electrode, there's a very small risk that it could cause air to leak into the area between the lungs and chest wall, causing a lung to collapse (pneumothorax).

How you prepare

Precautions
The nervous system specialist (neurologist) conducting the EMG will need to know if you have certain medical conditions. Tell the neurologist and other EMG lab personnel if you:

• Have a pacemaker or any other electrical medical device
• Take blood-thinning medications
• Have hemophilia, a blood-clotting disorder that causes prolonged bleeding

Questions to ask
When you schedule your EMG, you may want to ask the following questions:

• What time do I need to arrive?
• Where is the EMG lab, and what's the best way to find it in the hospital or clinic?
• Do I need to stop taking any prescription or over-the-counter medications before the exam?
• Can a friend or relative be with me during the exam?

Bathing
Take a shower or bath shortly before your exam to remove oils from your skin. Do not apply lotions or creams before the exam.

What you can expect

During your EMG
You'll likely be asked to change into a hospital gown for the procedure and lie down on an examination table. The following explanations can help you understand what will happen during the exam:

• Electrodes. The neurologist or a technician places surface electrodes at various locations on your skin depending on where you're experiencing symptoms. Or the neurologist may insert needle electrodes at different sites depending on your symptoms.
• Sensations. The electrodes will at times transmit a tiny electrical current that you may feel as a twinge or spasm. The needle electrode may cause discomfort or pain that usually ends shortly after the needle is removed. If you're concerned about discomfort or pain, you may want to talk to the neurologist about taking a short break during the exam.
• Instructions. During the needle EMG, the neurologist will assess whether there is any spontaneous electrical activity when the muscle is at rest — activity that isn't present in healthy muscle tissue — and the degree of activity when you slightly contract the muscle. He or she will give you instructions on resting and contracting a muscle at appropriate times. Depending on what muscles and nerves the neurologist is examining, he or she may ask you to change positions during the exam, such as rolling onto your side.

After your EMG
You may experience some temporary, minor bruising where the needle electrode was inserted into your muscle. This bruising should fade within several days. If it persists, contact your primary care doctor.

Results

The neurologist will interpret the results of your exam and prepare a report. Your primary care doctor, or the doctor who ordered the EMG, will discuss the report with you at a follow-up appointment.

Endoscopy

Definition

Endoscopy is a procedure used to visually examine your upper digestive system with a tiny camera on the end of a long, flexible tube. A doctor who specializes in diseases of the digestive system (gastroenterologist) uses endoscopy to diagnose and, sometimes, treat conditions that affect the esophagus, stomach and beginning of the small intestine (duodenum).

An endoscopy procedure involves inserting a long, flexible tube (endoscope) down your throat and into your esophagus. A tiny camera on the end of the endoscope lets your doctor examine your esophagus, stomach and the beginning of your small intestine (duodenum).

Doctors often refer to endoscopy as esophagogastroduodenoscopy (EGD) or upper endoscopy. Endoscopy may be done in your doctor's office, an outpatient surgery center or a hospital.

Why it's done

Endoscopy is used to diagnose and, sometimes, treat conditions that affect the upper part of the digestive system, including the esophagus, stomach and beginning of the small intestine (duodenum).

Your doctor may recommend an endoscopy procedure to:

• Investigate causes of digestive signs and symptoms. Endoscopy may help your doctor determine what's causing signs and symptoms, such as nausea, vomiting, abdominal pain, difficulty swallowing and gastrointestinal bleeding.
• Diagnose digestive diseases and conditions. Your doctor may use endoscopy to collect tissue (biopsy) samples to test for diseases and conditions, such as anemia, bleeding, inflammation, diarrhea or cancers of the digestive system.
• Treat certain digestive system problems. Using special tools during endoscopy allows your doctor to treat certain problems in your digestive system, such as bleeding from the esophagus or stomach and difficulty swallowing caused by a narrow esophagus, or to remove polyps. Endoscopy can also be used to remove foreign objects lodged in your upper digestive tract.

Your digestive tract stretches from your mouth to your anus. It includes the organs necessary to digest food and process waste.

Endoscopy is sometimes combined with other procedures, such as ultrasound. An ultrasound probe may be attached to the endoscope to create specialized images of the wall of your esophagus or stomach. An endoscopic ultrasound may also help your doctor create images of hard-to-reach organs, such as your pancreas.

Risks

Endoscopy is a safe procedure. However it carries a very small risk of complications, including:

• Bleeding. Your risk of bleeding complications after endoscopy is increased if the procedure involves removing a piece of tissue for testing (biopsy) or for treating a digestive system problem. In rare cases, such bleeding may require a blood transfusion.
• Infection. An infection caused by an endoscopy procedure may require antibiotics.
• Tearing of the gastrointestinal tract. A tear in your esophagus or another part of your upper digestive tract may require hospitalization, and sometimes surgery to repair it.

You can reduce your risk of complications by carefully following your doctor's instructions for preparing for endoscopy, such as fasting and stopping certain medications.

Signs and symptoms that could indicate a complication
Signs and symptoms to watch for after your endoscopy include:

• Fever
• Chest pain
• Shortness of breath
• Black or very dark colored stool
• Difficulty swallowing
• Severe or persistent abdominal pain
• Vomiting

Call your doctor immediately or go to an emergency room if you experience any of these signs or symptoms.

How you prepare

Your doctor will give you specific instructions to prepare for your endoscopy. In some cases your doctor may ask that you:

• Fast before the endoscopy. You may be asked to stop drinking and eating six to eight hours before your endoscopy. This is to ensure your stomach is empty for the procedure.
• Stop taking certain medications. You may be asked to stop taking certain blood-thinning medications in the days before your endoscopy. Blood thinners may increase your risk of bleeding if certain procedures are performed during endoscopy. If you have chronic conditions, such as diabetes, heart disease or high blood pressure, your doctor will give you specific instructions regarding your medications.

Tell your doctor about all the medications and supplements you're taking before your endoscopy.

Plan ahead for your recovery
Most people undergoing endoscopy will receive a sedative to make them relaxed and more comfortable during the procedure. If you'll be sedated during the procedure, plan ahead for your recovery. For instance, find someone to drive you home since it won't be safe for you to drive. You may also need to take the day off from work.

You may feel mentally alert after receiving a sedative, but your memory, reaction times and judgment may be impaired. Planning ahead for this can help keep you safe while the sedative wears off. Additionally, don't make any important personal or financial decisions for 24 hours.

What you can expect

During endoscopy
During your endoscopy procedure, you'll be asked to lie down on a table on your back or your side.

Monitors often will be attached to your body to allow your health care team to monitor your breathing, blood pressure and heart rate during the procedure. You may receive a sedative medication through a vein in your arm. This medication helps you relax during the endoscopy.

Your doctor may spray an anesthetic in your mouth to numb your throat in preparation for insertion of the long, flexible tube (endoscope) that will be used to see your digestive tract. You may be asked to wear a plastic mouth guard to hold your mouth open. Then the endoscope is inserted in your mouth. Your doctor may ask you to swallow as the scope passes down your throat. You may feel some pressure in your throat, but you shouldn't feel pain.

You can't talk after the endoscope passes down your throat, though you can make noises. The endoscope doesn't interfere with your breathing.

Your doctor then passes the endoscope down your esophagus toward your stomach. A tiny camera on the end of the endoscope transmits images to a video monitor in the exam room. Your doctor watches this monitor to look for abnormalities in your upper digestive tract. If abnormalities are found in your digestive tract, your doctor may record images for later examination.

To help the endoscope move through your upper digestive tract, gentle air pressure may be fed into your esophagus. This inflates your digestive tract so the endoscope can move freely and the folds of your digestive tract are more easily examined. But the air can also create a feeling of pressure or fullness.

If there's a need to collect a tissue sample or remove a polyp, your doctor will pass special surgical tools through the endoscope. Your doctor watches the video monitor to guide the tools.

When your doctor has finished the exam, the endoscope is slowly retracted through your esophagus and back out through your mouth. Endoscopy typically takes five to 20 minutes, depending on your situation.

After endoscopy
You'll be taken to a recovery area to sit or lie quietly after your endoscopy. You may stay for an hour or so, depending on your situation. This allows your health care team to monitor you as the sedative begins to wear off.

Once you're at home, you may experience some mildly uncomfortable signs and symptoms after endoscopy, such as:

• Bloating and gas
• Cramping
• Sore throat

These signs and symptoms will improve with time. If you're concerned or quite uncomfortable, call your doctor.

Take it easy for the rest of the day after your endoscopy. You may feel alert, but your reaction times and judgment are delayed after receiving a sedative.

Results

When you receive the results of your endoscopy will depend on your situation. If, for instance, your doctor performed the endoscopy to look for an ulcer, you may learn the findings right away after your procedure. If your doctor performed an endoscopy to collect a tissue sample (biopsy), it may be several days until results from laboratory testing are available. Ask your doctor when you can expect the results of your endoscopy.

Echocardiogram

Definition

An echocardiogram uses sound waves to produce images of your heart. This commonly used test allows your doctor to see how your heart is beating and pumping blood. Your doctor can use the images from an echocardiogram to identify various abnormalities in the heart muscle and valves.

Depending on what information your doctor needs, you may have one of several types of echocardiograms. Each type of echocardiogram has few risks involved.

Why it's done

Your doctor may suggest an echocardiogram if he or she suspects problems with the valves or chambers of your heart or your heart's ability to pump. An echocardiogram can also be used to detect congenital heart defects in unborn babies.

Depending on what information your doctor needs, you may have one of the following kinds of echocardiograms:

• Transthoracic echocardiogram. This is a standard, noninvasive echocardiogram. A technician (sonographer) spreads gel on your chest and then presses a device known as a transducer firmly against your skin, aiming an ultrasound beam through your chest to your heart. The transducer records the sound wave echoes your heart produces. A computer converts the echoes into moving images on a monitor. If your lungs or ribs block the view, a small amount of intravenous dye may be used to improve the images.
• Transesophageal echocardiogram. If it's difficult to get a clear picture of your heart with a standard echocardiogram, your doctor may recommend a transesophageal echocardiogram. In this procedure, a flexible tube containing a transducer is guided down your throat and into your esophagus, which connects your mouth to your stomach. From there, the transducer can obtain more-detailed images of your heart. Your throat will be numbed, and you'll have medications to help you relax during a transesophageal echocardiogram.
• Doppler echocardiogram. When sound waves bounce off blood cells moving through your heart and blood vessels, they change pitch. These changes (Doppler signals) can help your doctor measure the speed and direction of the blood flow in your heart. Doppler techniques are used in most transthoracic and transesophageal echocardiograms, and can check blood flow problems and blood pressures in the arteries of your heart that traditional ultrasound might not detect.
• Stress echocardiogram. Some heart problems — particularly those involving the coronary arteries that supply blood to your heart muscle — occur only during physical activity. For a stress echocardiogram, ultrasound images of your heart are taken before and immediately after walking on a treadmill or riding a stationary bike. If you're unable to exercise, you may get an injection of a medication to make your heart work as hard as if you were exercising.

Risks

There are few risks involved in a standard transthoracic echocardiogram. You may feel some discomfort similar to pulling off an adhesive bandage when the technician removes the electrodes placed on your chest during the procedure.

If you have a transesophageal echocardiogram, your throat may be sore for a few hours afterward. Rarely, the tube may scrape the inside of your throat. Your oxygen level will be monitored during the exam to check for any breathing problems caused by sedation medication.

During a stress echocardiogram, exercise or medication — not the echocardiogram itself — may temporarily cause an irregular heartbeat. Serious complications, such as a heart attack, are rare.

How you prepare

No special preparations are necessary for a standard transthoracic echocardiogram. Your doctor will ask you not to eat for a few hours beforehand if you're having a transesophageal or stress echocardiogram. If you'll be walking on a treadmill during a stress echocardiogram, wear comfortable shoes. If you're having a transesophageal echocardiogram, you won't be able to drive afterward because of the sedating medication you'll receive. Be sure to make arrangements to get home before you have your test.

What you can expect

During the procedure

An echocardiogram can be done in the doctor's office or a hospital. After undressing from the waist up, you'll lie on an examining table or bed. The technician will attach sticky patches (electrodes) to your body to help detect and conduct the electrical currents of your heart.

An echocardiogram checks how your heart's chambers and valves are pumping blood through your heart. An echocardiogram uses electrodes to check your heart rhythm and ultrasound technology to see how blood moves through your heart. An echocardiogram can help your doctor diagnose heart conditions.

If you'll have a transesophageal echocardiogram, your throat will be numbed with a numbing spray or gel. You'll likely be given a sedative to help you relax.

During the echocardiogram, the technician will dim the lights to better view the image on the monitor. You may hear a pulsing "whoosh" sound, which is the machine recording the blood flowing through your heart.

Most echocardiograms take less than an hour, but the timing may vary depending on your condition. During a transthoracic echocardiogram, you may be asked to breathe in a certain way or to roll onto your left side. Sometimes the transducer must be held very firmly against your chest. This can be uncomfortable — but it helps the technician produce the best images of your heart.

After the procedure
If your echocardiogram is normal, no further testing may be needed. If the results are concerning, you may be referred to a heart specialist (cardiologist) for more tests. Treatment depends on what's found during the exam and your specific signs and symptoms. You may need a repeat echocardiogram in several months or other diagnostic tests, such as a cardiac computerized tomography (CT) scan or coronary angiogram.

Results

Your doctor will look for healthy heart valves and chambers, as well as normal heartbeats. Information from the echocardiogram may show:

• Heart size. Weakened or damaged heart valves, high blood pressure or other diseases can cause the chambers of your heart to enlarge. Your doctor can use an echocardiogram to evaluate the need for treatment or monitor treatment effectiveness.
• Pumping strength. An echocardiogram can help your doctor determine your heart's pumping strength. Specific measurements may include the percentage of blood that's pumped out of a filled ventricle with each heartbeat (ejection fraction) or the volume of blood pumped by the heart in one minute (cardiac output). If your heart isn't pumping enough blood to meet your body's needs, heart failure may be a concern.
• Damage to the heart muscle. During an echocardiogram, your doctor can determine whether all parts of the heart wall are contributing normally to your heart's pumping activity. Parts that move weakly may have been damaged during a heart attack or be receiving too little oxygen. This may indicate coronary artery disease or various other conditions.
• Valve problems. An echocardiogram shows how your heart valves move as your heart beats. Your doctor can determine if the valves open wide enough for adequate blood flow or close fully to prevent blood leakage. Abnormal blood flow patterns and conditions such as aortic valve stenosis — when the heart's aortic valve is narrowed — can be detected as well.
• Heart defects. Many heart defects can be detected with an echocardiogram, including problems with the heart chambers, abnormal connections between the heart and major blood vessels, and complex heart defects that are present at birth. Echocardiograms can even be used to monitor a baby's heart development before birth.

EEG (electroencephalogram)

Definition

An electroencephalogram (EEG) is a painless procedure that uses small, flat metal discs (electrodes) attached to your scalp to detect electrical activity in your brain. Your brain cells communicate via electrical impulses and are active all the time, even when you're asleep. This activity shows up as wavy lines on an EEG recording.

An EEG is one of the main diagnostic tests for epilepsy. An EEG may also play a role in diagnosing other brain disorders.

An EEG records the electrical activity of your brain via electrodes affixed to your scalp. EEG results show changes in brain activity that may be useful in diagnosing brain conditions, especially epilepsy and other seizure disorders.

Why it's done

An EEG can determine changes in brain activity that may be useful in diagnosing brain disorders, especially epilepsy. An EEG may be helpful to confirm, rule out or provide information that helps with management of the following disorders:

• Epilepsy or other seizure disorder
• Brain tumor
• Head injury
• Encephalopathy — diffuse brain dysfunction
• Inflammation of the brain (encephalitis)
• Stroke
• Sleep disorders
• Memory impairment

An EEG can't measure intelligence or detect mental illness. It may be used to confirm brain death in someone in a persistent coma.

Risks

EEGs are safe and painless. Sometimes people with epilepsy have a seizure intentionally triggered during the test, but appropriate medical care is provided if needed.

How you prepare

To prepare for an EEG:

• Wash your hair the night before or the day of the test, but don't use any conditioners, hair creams, sprays or styling gels.
• Avoid anything with caffeine six hours before the test.
• Take your usual medications unless instructed otherwise.

If you're supposed to sleep during your EEG test, your doctor may ask you to sleep less or even avoid sleep entirely the night before your EEG. If you have trouble falling asleep for the test, you might be given a sedative to help you relax.

What you can expect

During the test
You'll feel little or no discomfort during an EEG. The electrodes don't transmit any sensations. They just record your brain waves. If you need to sleep during the EEG, you might be given a sedative beforehand to help you relax.

A technician measures your head and marks your scalp with a special pencil, to indicate where to attach the electrodes. Those spots on your scalp may be scrubbed with a gritty cream to improve the quality of the recording.

During an EEG, flat metal discs (electrodes) are attached to your scalp. The electrodes are connected to the EEG machine with wires. Some people wear an elastic cap fitted with electrodes, instead of having the adhesive applied to their scalps.

Using a special adhesive, a technician affixes flat metal discs (electrodes) to your scalp. The electrodes are connected with wires to an instrument that amplifies — makes bigger — the brain waves and records them on computer equipment.

Some people wear an elastic cap fitted with electrodes, instead of having the adhesive applied to their scalps.

A small amount of gel is placed between each electrode and your scalp, and the technician might use an instrument to rub the skin beneath each electrode to ensure a good connection. Once the electrodes are in place, an EEG typically takes 30 to 60 minutes.

During most of the test, you relax in a comfortable position with your eyes closed. At various times during the test, the technician may ask you to open and close your eyes, perform a few simple calculations, read a paragraph, look at a picture, breathe deeply (hyperventilate) for a few minutes, or look at a flashing light.

Your doctor may want you to undergo a video EEG, which may require you to be admitted to a hospital. During this test, your body motions are captured by a video camera while the EEG simultaneously records your brain waves during a seizure. This may help your doctor pinpoint the location in your brain where seizures begin.

After the test
After the test, the technician removes the electrodes or cap. If no sedative was given, you should feel no side effects after the procedure, and you can return to your normal routine.

If you used a sedative, it may take about an hour to partially recover from the medication. You'll need someone to take you home because it can take up to a day for the full effects of the sedative to wear off. Rest and don't drive for the remainder of the day.

Results

Technicians conduct the test. Doctors trained to analyze EEGs interpret the recording, and the results are sent to the doctor who ordered the EEG.

Your doctor may schedule an office appointment to discuss the results of the test. If possible, bring along a family member or friend. It can be difficult to absorb all the information provided to you during an appointment. The person who accompanies you may remember something that you forgot or missed.

Write down questions that you want to ask your doctor. Don't be afraid to ask questions or to speak up when you don't understand something your doctor says. Questions you may want to ask include:

• Based on the results, what are my next steps?
• What kind of follow-up, if any, should I expect?
• Are there any factors that might have affected the results of this test, and therefore may have altered the results?
• Will I need to repeat the test at some point?

Electrocardiogram (ECG or EKG)

Definition

An electrocardiogram is used to monitor your heart. Each beat of your heart is triggered by an electrical impulse generated from special cells in the upper right chamber of your heart. An electrocardiogram — also called an ECG or EKG — records these electrical signals as they travel through your heart. Your doctor can use an electrocardiogram to look for patterns among these heartbeats and rhythms to diagnose various heart conditions.

An electrocardiogram is a noninvasive, painless test. The results of your electrocardiogram will likely be reported the same day it's performed, and your doctor will discuss them with you at your next appointment.

Why it's done

An electrocardiogram is a painless, noninvasive way to diagnose many common types of heart problems. Your doctor may use an electrocardiogram to detect:

• Irregularities in your heart rhythm (arrhythmias)
• Heart defects
• Problems with your heart's valves
• Blocked or narrowed arteries in your heart (coronary artery disease)
• A heart attack, in emergency situations
• A previous heart attack

Risks

An electrocardiogram is a safe procedure. There may be minor discomfort, similar to removing a bandage, when the electrodes taped to your chest to measure your heart's electrical signals are removed. Rarely, a reaction to the electrodes may cause redness or swelling of the skin.

A stress test, in which an ECG is performed while you exercise or after you take medication that mimics effects of exercise, may cause irregular heartbeats or, rarely, a heart attack. These side effects are caused by the exercise or medication, not the ECG itself.

There isn't any risk of electrocution during an electrocardiogram. The electrodes placed on your body only record the electrical activity of your heart. They don't emit electricity.

How you prepare

No special preparations are necessary. However, avoid drinking cold water or exercising immediately before an electrocardiogram. Cold water can produce potentially misleading changes in one of the electrical patterns recorded during the test. Physical activity, such as climbing stairs, may increase your heart rate.

What you can expect

During the procedure
An electrocardiogram can be done in the doctor's office or hospital, and is often performed by a technician. After changing into a hospital gown, you'll lie on an examining table or bed. Electrodes — often 12 to 15 — will be attached to your arms, legs and chest. The electrodes are sticky patches applied with a gel to help detect and conduct the electrical currents of your heart. If you have hair on the parts of your body where the electrodes will be placed, the technician may need to shave the hair so that the electrodes stick properly.

An electrocardiogram monitors your heart rhythm for problems. Electrodes are taped to your chest to record your heart's electrical signals, which cause your heart to beat. The signals are shown as waves on an attached computer monitor or printer.

You can breathe normally during the electrocardiogram. Make sure you're warm and ready to lie still, however. Moving, talking or shivering may distort the test results. A standard ECG takes just a few minutes.

If you have a heartbeat irregularity that tends to come and go, it may not be captured during the few minutes a standard ECG is recording. To work around this problem, your doctor may recommend another type of ECG:

• Holter monitoring. Also known as an ambulatory ECG monitor, a Holter monitor records your heart rhythms for an entire 24-hour period. Wires from electrodes on your chest go to a battery-operated recording device carried in your pocket or worn on a belt or shoulder strap. While you're wearing the monitor, you'll keep a diary of your activities and symptoms. Your doctor will compare the diary with the electrical recordings to try to figure out the cause of your symptoms.
• Event recorder. If your symptoms don't occur often, your doctor may suggest wearing an event recorder. This device is similar to a Holter monitor, but it allows you to record your heart rhythm just when the symptoms are happening. You can send the ECG readings to your doctor through your phone line.
• Stress test. If your heart problems occur most often during exercise, your doctor may ask you to walk on a treadmill or ride a stationary bike during an ECG. This is called a stress test. If you have a medical condition that makes it difficult for you to walk, medication may be injected to mimic the effect of exercise on the heart.

After the procedure
Usually, your doctor will be able to tell you the results of your ECG the same day it's performed. If your electrocardiogram is normal, you may not need any other tests. If the results show there's a problem with your heart, you may need a repeat ECG or other diagnostic tests, such as an echocardiogram. Treatment depends on what's causing your signs and symptoms.

Results

Your doctor will look for a consistent, even heart rhythm and a heart rate between 50 and 100 beats a minute. Having a faster, slower or irregular heartbeat provides clues about your heart health, including:

• Heart rate. Normally, heart rate can be measured by checking your pulse. But an ECG may be helpful if your pulse is difficult to feel or too fast or too irregular to count accurately.
• Heart rhythm. An ECG can help your doctor identify an unusually fast heartbeat (tachycardia), unusually slow heartbeat (bradycardia) or other heart rhythm irregularities (arrhythmias). These conditions may occur when any part of the heart's electrical system malfunctions. In other cases, medications, such as beta blockers, psychotropic drugs or amphetamines, can trigger arrhythmias.
• Heart attack. An ECG can often show evidence of a previous heart attack or one that's in progress. The patterns on the ECG may indicate which part of your heart has been damaged, as well as the extent of the damage.
• Inadequate blood and oxygen supply to the heart. An ECG done while you're having symptoms can help your doctor determine whether chest pain is caused by reduced blood flow to the heart muscle, such as with the chest pain of unstable angina.
• Structural abnormalities. An ECG can provide clues about enlargement of the chambers or walls of the heart, heart defects and other heart problems.

MRI (Magnetic Resonance Imaging)

Definition

Magnetic resonance imaging (MRI) is a technique that uses a magnetic field and radio waves to create detailed images of the organs and tissues within your body.

Most MRI machines are large, tube-shaped magnets. When you lie inside an MRI machine, the magnetic field temporarily aligns all the water molecules in your body. Radio waves cause these aligned particles to produce very faint signals, which are used to create cross-sectional MRI images — like slices in a loaf of bread.

The MRI machine can combine these slices to produce 3-D images that may be viewed from many different angles.

Why it's done

MRI is a noninvasive way for your doctor to examine your organs, tissues and skeletal system. It produces high-resolution images that help diagnose a variety of problems.

MRI of the brain and spinal cord
MRI is the most sensitive imaging test of the brain and spinal cord. It's often performed to help diagnose:

• Tumors
• Developmental abnormalities
• Aneurysms
• Stroke
• Pituitary gland diseases
• Multiple sclerosis
• Dementia progression
• Spinal cord injuries

Functional MRI of the brain (fMRI) can be used to identify important language and movement control areas in the brain in people who are being considered for brain surgery.

MRI of the heart and blood vessels
An MRI that focuses on the heart or blood vessels can assess:

• The size and thickness of walls in the heart's chambers
• The extent of damage caused by heart attack or heart disease
• The buildup of plaques and blockages in the blood vessels
• Structural problems in the aorta, such as aneurysms or dissections

MRI of other internal organs
An MRI may be used to check for tumors or other abnormalities of the:

• Lungs
• Liver
• Kidneys
• Spleen
• Pancreas
• Uterus
• Ovaries
• Prostate
• Testicles

MRI of bones and joints
MRI may be used to help evaluate:

• Joint disorders, such as arthritis
• Joint abnormalities caused by traumatic or repetitive injuries
• Disk abnormalities in the spine
• Bone infections

MRI of the breasts
MRI may be used in addition to mammography to detect breast cancer, particularly in women who have dense breast tissue or who may be at high risk of the disease.

Risks

For most individuals, there are no known harmful effects from exposure to the magnetic field or radio waves used in making MRI images.

How you prepare

Before an MRI exam, eat normally and continue to take your usual medications, unless otherwise instructed. You will be asked to change into a gown and to remove:

• Jewelry
• Hairpins
• Eyeglasses
• Watches
• Wigs
• Dentures
• Hearing aids
• Underwire bras

The presence of metal in your body may be a safety hazard or affect a portion of the MRI image. Tell the technologist if you have any metal or electronic devices in your body, such as:

• Metallic joint prostheses
• Artificial heart valves
• An implantable heart defibrillator
• A pacemaker
• Metal clips to prevent aneurysms from leaking
• Cochlear implants
• A bullet, shrapnel or any other type of metal fragment

Also tell the technologist if you think you're pregnant, because the effects of magnetic fields on fetuses aren't well understood. Your doctor may recommend choosing an alternative exam or postponing the MRI.

It's also important to discuss any kidney or liver problems with your physician and the technologist, because problems with these organs may impose limitations on the use of injected contrast agents during your scan.

What you can expect

During the test
The MRI machine looks like a tunnel that has both ends open. You lie down on a movable table that slides into the opening of the tunnel. A technologist monitors you from another room. You can talk with him or her by microphone.

The MRI machine creates a strong magnetic field around you, and radio waves are directed at your body. The procedure is painless. You don't feel the magnetic field or radio waves, and there are no moving parts around you.

During the MRI scan, the internal part of the magnet produces repetitive tapping, thumping sounds and other noises. Earplugs or music may be provided to help block the noise. If you are worried about feeling claustrophobic inside the MRI machine, talk to your doctor beforehand. He or she may make arrangements for you to receive a sedative before the scan.

An MRI typically lasts about an hour. You must hold very still because movement can blur the resulting images. In some cases, contrast agents are injected into your veins to enhance the appearance of certain tissues or blood vessels in the images.

During a functional MRI, you may be asked to perform a number of small tasks — such as tapping your thumb against your fingers, rubbing a block of sandpaper or answering simple questions. This helps pinpoint the portions of your brain that control these actions.

After the test
If you haven't been sedated, you may resume your usual activities immediately after the scan. Nursing mothers shouldn't breast-feed for 36 to 48 hours after an MRI if a contrast material was used. Very rarely, the contrast material can cause hives and itching.

A radiologist — a doctor specially trained to interpret MRIs — will analyze the images from your scan and report the findings to your doctor. Your doctor will then discuss any important findings and next steps with you.