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Sights and Sounds: Medical Imaging and Ultrasonography

By: Jose Maria M. Villarama IISights and Sounds: Medical Imaging and Ultrasonography

Linda woke up one day with excruciating pain on her left cheek. At the hospital, she was subjected to a series of tests which included a transcranial Doppler ultrasound and a magnetic resonance imaging (MRI) scan. The doctor suspected the pain may have something to do with an irritated facial nerve. Even if Linda had her wisdom teeth extracted years before, an x-ray of her upper and lower jaws was also done to rule out any dental problems. After these and several other tests, the results yielded trigeminal neuralgia, a condition brought about by the irritation of the trigeminal nerve, which carries sensation from the face to the brain.

In diagnosing the condition, the doctor ordered an MRI scan to rule out possible causes of pain such as the presence of tumor in the face, nasal inflammation or even tooth decay. A transcranial probe was performed on her jaw area to check on the flow of blood in the vessels around the brain, to see if this is causing irritation to the nerve.

Aside from diagnosing the cause of the symptoms, the goal of these imaging tests is to detect a disease before its onset. Later on, these same tests can be used to track the progress of the medical condition and treatment prescribed to address it and to check for any side effects of the treatment given.

Visualizing the Problem

Medical imaging techniques can fall under two main categories: those that create images using radiation or those that visualize internal structures in the body using sound waves. Radiation-driven modalities include the following: 

Radiography – It utilizes x-ray beams to generate a static image of organs, muscles or bones to help diagnose or treat any disease or damage, aberration or the presence of foreign objects in specific parts of the body. It is used in dentistry, orthopedia, pulmonology, etc.

Computerized Tomography (CT) scan  – Like x-rays, CT scans use radiation to generate internal images of the body.  The main difference is that CT scans are taken from different angles so that a computer can generate cross-sectional images of organs, tissues, bones, and blood vessels. This is especially helpful in detecting tumors or fractures in bones.

Magnetic Resonance Imaging (MRI) – This makes use of magnets and radio waves to visualize parts of the body to diagnose damage or injury, infection or cancer or to assess response to ongoing treatment. MRIs are especially useful to probe the brain, spinal cord, the heart, blood vessels, etc. especially after a blow to the head or the body, a stroke, or a heart attack.

Nuclear medicine imaging – It uses radiotracers (i.e. radioactive materials that are injected into the bloodstream), inhaled or ingested.  These tracers give off gamma rays which are detected by a machine that help generate images of internal organs and structures. Nuclear medicine is advantageous over other imaging modalities in that it can give doctors information on both function and structure of the organ being examined. It is especially useful in determining the extent of cancer in various parts of the body. A common type of nuclear imaging is positron emission tomography (PET) scan which detects diseases before it shows up on other imaging tests.

Optical Imaging – This uses a light/laser to probe into deep tissue layers. The visualization of tissue abnormalities or pathologic process is due to the interaction of light with different tissue components. Common applications for this include breast cancer detection.

Endoscopy – It makes use of a camera attached to a flexible tube (i.e. an endoscope) to examine the upper and lower parts of the digestive tract. In an upper endoscopy, the endoscope is passed through the mouth to view the structures and organs from the mouth to the upper part of the small intestine. In a colonoscopy, the probe enters through the rectum to examine the large intestine.  Specialized endoscopes can explore the gallbladder, pancreas, reproductive organs, etc. to get tissue samples for biopsies. Endoscopes can also be used for minimally invasive or ‘keyhole’ surgeries to remove polyps, tumors or growths.

Sounds Like a Plan

Meanwhile, the class of medical imaging techniques that make use of sound waves is called ultrasound. Ultrasounds utilize high-frequency sound waves to view internal organs and structures. Most people are familiar with a fetal ultrasound, which helps an obstetrician evaluate the unborn during the trimesters of pregnancy. They produce live images of organs or structures as opposed to static images. They are non-invasive and safe in that they do not involve any radioactive materials. Different ultrasound tests are used to diagnose specific conditions in the body. They include: 

Doppler ultrasound - Utilizing the Doppler effect (i.e. the change in frequency of a wave relative to a moving object), it is used to monitor blood flow through the circulatory system. Among other things, it can detect blockages in arteries or veins or the narrowing of these blood vessels.

Abdominal ultrasound – This is used to detect the source of pain or diagnose the enlargement of organs in the abdominal area. It helps diagnose kidney stones or gallstones in particular.

Echocardiography – It is used to determine the state of heart muscles to see if there are clots in the heart and problems with the aorta. Echocardiography is also known as cardiac ultrasound.

Elastography – This makes use of sound waves to produce a map or image of how stiff an organ is. Stiffness and elasticity are possible indicators of the presence of disease in the liver. Elastography is being used specifically to diagnose liver fibrosis and fatty liver disease. Clinicians opt for elastography especially when a patient wants non-invasive tests to diagnose these liver diseases. Today, there are two types of liver elastography widely being used: ultrasound elastography, which measures the stiffness of liver tissue and magnetic resonance elastography (MRE), a combination of ultrasound and MRI technology that generates a map which shows how stiff the liver is.

While radiation levels in the first class of medical imaging techniques mentioned above are within safe limits, some patients are still wary of the slightest exposure to radioactive rays or isotopes. Ultrasounds are, therefore, a wise alternative for people who have such a concern.  It is important to consider, however, that the health care provider’s goal is to accurately visualize the cause of the medical concern.  Ultimately, doctor and patient cooperation will spell the difference in determining the right imaging procedure for proper diagnosis and treatment. 

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