Computed Tomography (CT or CAT) Scan of the Kidney

(Renal CT Scan)

Procedure Overview

What is a CT or CAT scan of the kidney?

Computed tomography (CT or CAT scan) is a noninvasive diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce both horizontal and vertical cross-sectional images (often called slices) of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than standard x-rays.

In standard x-rays, a beam of energy is aimed at the body part being studied. A plate behind the body part captures the variations of the energy beam after it passes through skin, bone, muscle, and other tissue. While much information can be obtained from a standard x-ray, a lot of detail about internal organs and other structures is not available.

In computed tomography, the x-ray beam moves in a circle around the body. This allows many different views of the same organ or structure. The x-ray information is sent to a computer that interprets the x-ray data and displays it in a two-dimensional (2D) form on a monitor.

CT scans may be done with or without "contrast." Contrast refers to a substance taken by mouth or injected into an intravenous (IV) line that causes the particular organ or tissue under study to be seen more clearly. Contrast examinations may require you to fast for a certain period of time before the procedure. Your physician will notify you of this prior to the procedure.

CT scans of the kidneys can provide more detailed information about the kidneys than standard kidneys, ureters, and bladder (KUB) x-rays, thus providing more information related to injuries and/or diseases of the kidneys. CT scans of the kidneys are useful in the examination of one or both of the kidneys to detect conditions such as tumors or other lesions, obstructive conditions such as kidney stones, congenital anomalies, polycystic kidney disease, accumulation of fluid around the kidneys, and the location of abscesses.

Other related procedures that may be used to diagnose kidney problems include KUB x-rays, kidney biopsy, kidney scan, kidney ultrasound, renal angiogram, and renal venogram. Please see these procedures for additional information.

How do the kidneys work?

The body takes nutrients from food and converts them to energy. After the body has taken the food that it needs, waste products are left behind in the bowel and in the blood.

The kidneys and urinary system keep chemicals, such as potassium and sodium, and water in balance, and remove a type of waste, called urea, from the blood. Urea is produced when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea is carried in the bloodstream to the kidneys.

Two kidneys, a pair of purplish-brown organs, are located below the ribs toward the middle of the back. Their function is to:

  • Remove liquid waste from the blood in the form of urine

  • Keep a stable balance of salts and other substances in the blood

  • Produce erythropoietin, a hormone that aids the formation of red blood cells.

  • Regulate blood pressure

The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule.

Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.?

Reasons for the Procedure

A CT scan of the kidney may be performed to assess the kidneys for tumors and other lesions, obstructions such as kidney stones, abscesses, polycystic kidney disease, and congenital anomalies, particularly when another type of examination, such as x-rays or physical examination, is not conclusive. CT scans of the kidney may be used to evaluate the retroperitoneum (the back portion of the abdomen behind the peritoneal membrane). CT scans of the kidney may be used to assist in needle placement in kidney biopsies.

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