LEARN It! Challenge 1, Topic 6
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dr-rob February 23, 2019
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As medicine evolved, understanding the patterns of images became a way to diagnose a problem. A series of different modes of imaging continues to evolve. This section will introduce you to some of the imaging technologies you may encounter in your life or work. One of the beauties of images is that it allows for telemedicine, which means that we can have the patient in one location with their caregiver and an expert somewhere else giving advice without the patient having to travel. 


Is the mole getting larger and changing color since the doctor last saw you in the office? Taking a picture is a common way to track subtle changes over time. Photos can be shared with experts to get their thoughts on those changes. Common areas for photography in medicine is the skin, back of the eye, or eardrum using special camera attachments.

Telemedicine with a Doctor and a senior woman with tablet

People can take pictures of a suspicious rash, mole, or injury with a dime or other object with a standard size so that they can compare the changes in size over time. Pictures become a tool for them to use with their doctor over the phone, in person or the future.

It's kind of like taking a "healthy selfie."


X-ray, a type of light radiation that we can't see with our eyes, can travel through the body and expose film or affect the image on a screen to make a picture of the shapes and densities inside the body. These are very useful and cost-efficient as it is a less expensive means of looking for major abnormalities such as broken bones, pneumonia of infection with pus filling up part of the lung, or massive heart enlargement.

While X-ray can pass through soft tissues such as muscles and organs, it is absorbed by bones and shows up as white or grey areas on X-ray images. Things such as metal and thick tissue areas also show up as white or grey. Air absorbs X-ray the least, so areas where there is air, such as outside of the body or in the lungs or colon, shows up as black.

See if you can identify the body parts below. ​

Collection of x-ray pictures of cervical spine, skull, shoulder, chest, abdomen, back, hand, ankle, foot, and knee

CT Scan (Computerized Tomography Scan)

CT Scan is a newer technology that allows for much more detailed images by taking a series of images using a computer and reconstructing them into a series of slices and 3D reconstructed images to see smaller or more subtle changes. It is not painful, and you have to lay still for a couple of minutes.

Some times pronounced as CAT scan, it is a test used on humans predominantly, although veterinarians also can use this test on animals. It should not be confused with a PET scan.  


This test uses sound waves to bounce off internal structures to create raw images representing the structures. It is like sonar in ships looking for fish, submarines, or measuring the depth of the water. With a feature called doppler, it can detect flowing fluids such as blood. Ultrasound is commonly used in pregnancy where they don't want any radiation exposure.

MRI (Magnetic Resonance Scan)

MRI uses magnetic resonance of the molecules in the body to simulate an image. It is like a CAT scan in that it uses a computer to create an image from a circular imaging device that surrounds the person. It is excellent for looking at soft tissue issues like muscle tears and tumor locations. It is not well suited for organs that move such as the heart and lungs but for joints and muscles.

PET Scan and Other Nuclear Tests

A PET scan stands for positron emitting tomography, which is done in conjunction with a CAT scan to see how a tumor uses radioactive sugar as a way to tell if it is likely cancer or not.

Nuclear tests use chemicals that have a low dose of radiation in them that stay in the body for a short period. They work by making an image based on sensing the presence of radiation in specific areas. It is like a giant Geiger counter camera. One usually gets an injection and then has to lay still for about 30 minutes on a device to create the images.

PET/CT of thyroid gland is a valuable imaging test, in the appropriate clinical context, for the management of thyroid cancers.

The mass in the upper left chest in the top image lights up on the PET scan at the same location. It does not match the other side, and which highly suggests that the mass seen in the scan is fast-growing cancer.

Angiography  ("Catheterization")

This technique involves using X-ray movies called fluoroscopy along with a thin tube or catheter inserted through a blood vessel into the body. A special type of dye that absorbs X-rays is inserted through the tube and helps create an image of the inside of blood vessels. Angiography is commonly used to diagnose blockages in blood vessels such as arteries to the brain or heart. Other uses include using devices called stents to place through the catheter to hold open the blood vessel, or using small coils to block blood flow to leaking areas or to starve tumors.

Instead of a large incision, a needle is used to puncture a vein or artery and then a dye, wire, laser, balloon, stent, coil, or other tool is inserted through the vessel with the guidance of X-rays. Below is the beginning of such a procedure with the needle ready to insert a wire. 

Surgeons Preparing Equipment For Surgery

During angiography, images are shown on a screen along with the heartbeat monitoring (electrocardiogram) and pressure measurements. You can see the images from the dye inserted into the vessel on the left, and the electrocardiogram on the top right side and the pressure measurements on the lower right of the video below.