Diagnostic Imaging Techniques

X-rays are a standard tool in medical diagnosis. They help doctors see bones, teeth, and some soft tissues without surgery. The first X-ray image showed Wilhelm Röntgen’s wife’s hand, and it opened a new way to look inside the body.

Wilhelm Röntgen, a German physicist, discovered X-rays in 1895 while studying electrical current. He found that an invisible ray could pass through flesh but leave the bones outlined on a screen coated with a metal compound. His work led to the first durable record...

Computed tomography, or CT, creates detailed body slices using X-rays and computers. It is a non-invasive imaging method that helps reveal fine details inside the body. The word tomography means imaging by sections.

CT was developed in the 1970s. It works by measuring how X-rays pass through the body and are absorbed or reflected at different levels. During a scan, the patient lies on a motorized platform while a computerized axial tomography, or CAT, scanner rotates 360 degrees around the...

Magnetic resonance imaging, or MRI, is a noninvasive way to create detailed medical images. It uses strong magnetic fields and radio waves. When the body is exposed to them, it can emit radio signals that are used to build the image.

MRI became especially important after researchers saw that cancerous tissue gave off signals different from normal tissue. Raymond Damadian identified this difference in 1970 and later applied for a patent for the first MRI scanner used in clinical care. Early...

PET scans use radiopharmaceuticals to show how the body is working. PET, or positron emission tomography, is a medical imaging method that depends on short-lived radiation from these compounds. It gives doctors a way to see tissue activity instead of only body structure.

A PET scan starts with a positron-emitting radioisotope. This isotope is made in a cyclotron and then attached to a substance used by the body part being studied. The tagged compound is called a radiotracer. It can be given by...

Ultrasonography in medical imaging uses high-frequency sound waves to create images of internal body structures. It is a safe, non-invasive procedure. It does not use ionizing radiation, which is one reason it is widely used in medicine.

During an ultrasound exam, a handheld transducer is placed on the skin. A transducer is the device that sends sound waves into the body. When the waves hit different tissues, they bounce back as echoes. The transducer catches those echoes and sends them to a...

Microscopes have become more powerful by improving magnification, resolution, and contrast. Early pioneers such as van Leeuwenhoek used far simpler instruments than the microscopes used today. In 1830, Joseph Jackson Lister created an essentially modern light microscope. Later advances in the 20th century added nonvisible light, including fluorescence microscopy and electron microscopy.

Many microscopes used in schools and labs are light microscopes. These instruments use light to make images...