A Computed Tomography (CT) scan is a medical imaging procedure that uses X-rays and computer processing to generate detailed cross-sectional pictures of the body. This technique, also formerly called a CAT scan, allows medical professionals to visualize internal organs, bones, soft tissues, and blood vessels. The scan produces a three-dimensional representation of the body’s internal structure by digitally creating many two-dimensional “slices.”
How CT Scans Create Images
A CT scanner operates by directing a narrow beam of X-rays through the patient’s body while simultaneously rotating 360 degrees around the patient. Detectors positioned opposite the X-ray source measure the amount of radiation that passes through the different tissues. Tissues with varying densities, such as bone versus soft tissue, absorb the X-rays at different rates.
This data, collected from hundreds of different angles, is transmitted to a computer. The computer uses mathematical algorithms to reconstruct the measurements into cross-sectional images, or “slices,” a process known as tomography. These slices can be digitally “stacked” to form a complete, high-resolution three-dimensional view of the area being examined. This provides significantly more detail than a standard X-ray, which produces a single, flat, two-dimensional image.
Preparing for and Undergoing the Scan
Preparation depends on the specific body part being imaged and whether a contrast agent will be used. Patients must remove metal objects, such as jewelry or clothing with zippers, as these materials can interfere with the X-ray beams and distort the images. If the scan involves the abdomen or pelvis, fasting (avoiding food and drink) may be required for a few hours beforehand to minimize the risk of nausea or vomiting if a contrast agent is administered.
A special substance called a contrast agent is often used to enhance the visibility of blood vessels, organs, or tumors on the images. This agent may be swallowed as a liquid for digestive tract scans, administered rectally, or, most commonly, injected into a vein through an intravenous (IV) line. When the IV contrast is injected, patients often experience a temporary, intense sensation of warmth spreading throughout the body, and some may notice a distinct metallic taste in their mouth.
During the scan, you lie on a narrow table that slides into the large, doughnut-shaped opening of the CT machine, called the gantry. The technologist operates the scanner from an adjacent room but communicates with you through an intercom system. The machine makes buzzing and whirring sounds as the X-ray tube rotates, and you will be instructed to remain completely still and sometimes to hold your breath briefly. Remaining motionless is essential because any movement can blur the images.
When Doctors Use CT Scans
CT scans are widely used across medicine for their speed and detailed anatomical information, making them invaluable in emergency situations and for diagnosing complex conditions. In trauma cases, a CT scan quickly identifies internal injuries, such as organ damage, internal bleeding, and complex bone fractures, especially in the head, spine, and chest. It is a primary tool for diagnosing and monitoring cancer, allowing doctors to detect tumors, determine the cancer’s stage, and assess treatment effectiveness over time.
The technology is also adapted for specialized uses, such as Computed Tomography Angiography (CTA), which uses the contrast agent to create detailed three-dimensional images of blood vessels. CTA helps diagnose vascular issues, including blockages, aneurysms, and blood clots in the lungs or elsewhere, aiding in the prevention of heart attack or stroke. Beyond diagnostics, the real-time imaging capability of the CT scanner is used to precisely guide minimally invasive procedures, such as performing a biopsy or draining an abscess or fluid collection.