By: Dr. Laura Hays

Medical imaging has revolutionized the diagnosis and treatment of various medical conditions, offering healthcare professionals invaluable insights (pun intended) into the human body’s inner workings. From broken bones, infections to tumors, medical imaging modalities play a crucial role in detecting, diagnosing, and monitoring diseases. Sometimes, your physician may order a specific test but you may not be sure why or what the test will entail.  In this post, we’ll explore some of the most common medical imaging modalities, including Computed Tomography (CT), Magnetic Resonance Imaging (MRI), X-ray, Ultrasound, and Positron Emission Tomography (PET).


X-ray imaging is one of the oldest and most commonly used medical imaging techniques. It involves passing a small amount of ionizing radiation through the body to create images of bones, tissues, and organs. X-rays are particularly useful for detecting fractures (broken bones), dental issues, infections like pneumonia, and foreign objects within the body. While X-rays provide quick results and are relatively affordable, they offer limited (2-dimensional) detail compared to other modalities like CT and MRI.  They are more widely available than other imaging modalities, offered in most emergency departments, urgent care facilities, and many outpatient doctor’s offices, often making them the initial study of choice.  

Computed Tomography (CT) 

Computed Tomography, commonly known as CT or CAT scan, utilizes X-rays to create detailed cross-sectional images of the body. CT scans are particularly useful for imaging bones, organs, and soft tissues simultaneously. They are widely used in diagnosing conditions such as fractures, tumors, kidney stones, and internal bleeding. 

Not only are CTs quick and informative, they are also non-invasive and provide high-resolution images, making them a preferred choice in emergency situations and for detecting acute injuries.  Sometimes, your physician may start with an X-ray, then decide that a CT is needed for a more thorough assessment.  But, oftentimes, X-ray is enough. 

During a CT scan, you will lie still on a table that moves slowly through a large, doughnut-shaped machine.  This is an “open” machine and generally will not induce feelings of claustrophobia.  In some cases, you may be asked to drink contrast or receive contrast through an intravenous (IV) line in order for certain details or body parts to “light up” differently, aiding in diagnosis.  If IV contrast dye is used, you may experience a warm sensation, metallic taste in your mouth or the feeling like you need to pee!  These are all normal effects and will subside quickly.   If you experience shortness of breath, lightheadedness or rash, these may be signs of a more serious reaction and you should alert the technician immediately.  CT scans typically take only a few minutes to complete.  However, more complex scans may take a bit longer.  CT scanners are available for use in most emergency departments for emergency conditions.  In many cases, your outpatient physician may send you to a separate imaging center for a CT scan, then schedule a later time to discuss results with you.  

Magnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging, or MRI, is really pretty cool!  This modality employs powerful magnets and radio waves to generate detailed images of the body’s internal structures. Unlike CT scans, MRI does not use ionizing radiation, making it safer for certain populations, such as pregnant women and children. MRI is highly adept at imaging soft tissues, such as the brain, spinal cord, muscles, and organs like the heart and liver. It is invaluable in diagnosing neurological disorders, spinal injuries, joint problems, and conditions affecting internal organs.  Due to the unique mechanisms, MRI takes much longer than an X-ray or CT.  As a more specialized study, it is not available everywhere or all the time.  It may be available in some emergency departments, used selectively for specific patients and conditions.  However, MRI is generally performed in the outpatient setting.

During an MRI scan, you’ll lie on a table that slides into a large, tube-like machine. Some people find MRIs uncomfortable and feel a bit claustrophobic at first, but closing your eyes and taking some deep breaths will help to keep you calm.  As the scan begins, you’ll need to remain still to ensure clear images.  The machine may produce loud tapping or knocking sounds which is normal.  You’ll be given earplugs or headphones to help soften the noise.  The length of the test depends on which body part(s) are being imaged.  Certain studies may require the administration of IV contrast.  Note that this contrast is different from the type used in CT scans.  Most MRI scans take about 20 to 60 minutes, but some may take longer.  


Ultrasound imaging, also known as sonography, utilizes high-frequency sound waves to produce real-time images of internal organs and structures. It is widely used in obstetrics to monitor fetal development during pregnancy but has applications in various medical specialties and is being used more and more for bedside procedures, especially in the Emergency Department. Ultrasound is non-invasive, safe, and does not involve ionizing radiation, making it suitable for repeated examinations and imaging vulnerable populations. It is commonly used to evaluate the heart, abdomen such as gallbladder, pelvic organs, and blood vessels.  We also use it to look under the skin, the backs of the eyes and even the spaces between your back bones! 

Positron Emission Tomography (PET)

Positron Emission Tomography, or PET imaging is an advanced medical imaging technique that allows us to visualize the function and metabolism of organs and tissues within your body.  PET scans are particularly useful for detecting diseases at the molecular level.  They are mostly used in oncology for detecting cancerous tumors, assessing their metabolic activity, and monitoring treatment response. They are also utilized in neurology to evaluate brain function and detect abnormalities.  They may even be used to diagnose certain heart conditions.  

PET scans are often used in combination with CT or MRI to provide more comprehensive information about your health.  However, this is not a study ordered in the emergency setting and PET scans are not available in an emergency department.  

During a PET scan, a small amount of radioactive tracer is injected through an IV line.  You may feel a slight sensation at the injection site, but it is generally well-tolerated.  

After the tracer is injected, you’ll be asked to rest quietly for a short period of time to allow it to circulate throughout your body.  You’ll then lie on a table that moves slowly through the PET scanner, which typically takes between 30 to 60 minutes.  


In conclusion, more and more advances are made in the world of medicine each day and imaging modalities continue to evolve.  Medical imaging plays a crucial role in diagnosing and treating a wide range of medical conditions. Each modality offers unique advantages and is suited to specific clinical scenarios. 

Keep in mind, the value of imaging is not always to find something, but at times to exclude something or rule it out.  So, the next time your physician orders an imaging study, consider it another piece of the diagnostic puzzle.  

By understanding the differences between modalities such as X-ray, CT, MRI, ultrasound, and PET, you and your physician can effectively utilize these tools to provide accurate diagnoses, exclude others, and develop personalized treatment plans. 


Dr. Laura Hays is an emergency physician with MEMA and co-founder of Lasting Impact Wellness Group- a health & well-being coaching and consulting company. Check out her website at and tune in to her podcast “Lasting Impact Wellness” for more valuable insight and tips for optimal well-being.