A Computed Tomography (CT) scan of the abdomen and pelvis is a common medical imaging procedure used to create detailed pictures of the internal organs and structures in the mid and lower torso. This examination utilizes X-rays and computer processing to generate cross-sectional “slices” of the body, offering a detailed view compared to a standard X-ray. The addition of a contrast agent allows for clearer differentiation between soft tissues, blood vessels, and organs. This non-invasive method investigates the source of various symptoms, injuries, or suspected diseases.
Understanding the Imaging Technology
Computed Tomography captures numerous images from different angles as the X-ray tube and detector array move around the patient. Powerful computer software processes these data points to assemble detailed, two-dimensional cross-sectional images, often called slices. These reconstructed images provide a comprehensive look at bones, soft tissues, and blood vessels, offering greater clarity than conventional X-ray techniques.
The “Abdomen and Pelvis” portion of the scan defines the large anatomical region being examined. The abdomen includes organs such as the liver, kidneys, spleen, pancreas, gallbladder, and most of the intestinal tract. The pelvis covers the bladder, reproductive organs, colon, and the major vascular structures that extend into the lower extremities. Scanning both areas simultaneously is often performed when a patient’s symptoms are vague or could originate from either region, such as generalized abdominal pain.
The CT scanner is a large, doughnut-shaped machine where the patient lies on a motorized table that slides through the opening. These scanners are fast, capable of scanning large sections of the body in seconds, which minimizes the time a patient needs to lie still. This speed is beneficial for emergency situations or for patients who have difficulty holding their breath.
The Function of Contrast Agents
The term “with contrast” signifies the administration of a substance designed to enhance the visibility of specific tissues on the CT images. Without contrast, soft tissues and blood vessels often appear similar in density, making it difficult to distinguish between a normal structure and a disease process. The contrast highlights areas that would otherwise blend into the background.
For CT scans, the contrast material used is iodine-based, which is radiopaque and absorbs X-rays. This increased absorption causes the structures containing the iodine to appear bright white on the final images, clearly outlining their shape and boundaries. The contrast is administered through different routes depending on the structures the physician needs to visualize.
Intravenous (IV) contrast is injected directly into a vein to circulate through the bloodstream and highlight blood vessels and organs with high blood flow, such as the liver, kidneys, and spleen. This is used for assessing organ perfusion and identifying masses like tumors, which often have increased blood supply. Oral contrast is a liquid solution swallowed by the patient to coat and fill the gastrointestinal tract, making the esophagus, stomach, and intestines visible. This helps delineate the bowel walls and distinguish them from surrounding structures or fluid collections. Rectal contrast may also be administered as an enema to enhance the lower colon and rectum.
Preparing for and Experiencing the Procedure
Preparation for a CT Abdomen and Pelvis with Contrast involves optimizing the internal environment for clear images. Patients are typically required to refrain from eating or drinking anything for a few hours before the exam (NPO). This fasting period ensures the stomach is empty and allows for clear visualization of the abdominal organs.
Preparation involves consuming the oral contrast agent, which is drunk over a specified period, sometimes up to two hours before the scan. This allows the contrast material time to travel through the gastrointestinal tract. Before the IV contrast is administered, a blood test may be required to check the patient’s kidney function, ensuring the body can safely filter and eliminate the iodine compound.
A technologist will place an IV line to administer the intravenous contrast. When the IV contrast is injected, patients often experience a warm, flushed sensation that spreads throughout the body, along with a temporary metallic taste in the mouth. The scan itself is painless and lasts only a few minutes. Patients lie on the table and are asked to remain perfectly still and hold their breath for short intervals to prevent image blurring. After the procedure, patients who received IV contrast are advised to drink extra fluids to help flush the iodine from their system.
What Conditions This Scan Identifies
The CT Abdomen and Pelvis with Contrast provides information to diagnose a wide array of conditions. The scan is frequently used to investigate the causes of unexplained or severe abdominal and pelvic pain. Its ability to visualize soft tissues and inflammation aids in diagnosing acute conditions like appendicitis, diverticulitis, and abscesses.
This scan is used to detect, stage, and monitor cancers, including those of the:
- Colon
- Liver
- Kidneys
- Pancreas
- Reproductive organs
The contrast helps to delineate tumors and assess their relationship to surrounding structures and blood vessels. The scan is also used to evaluate the urinary system, identifying kidney stones and bladder stones, and assessing inflammatory bowel diseases. Vascular issues, including abdominal aortic aneurysms and blood clots, are visible due to the enhancement provided by the IV contrast.