Computed Tomography (CT)
CT scans are relatively quick and can be completed within minutes. During a CT scan the patient lies on a table that moves through a large ring-shaped machine as it takes multiple X-ray images from different angles. The computer then uses these X-rays to create detailed 3D images of the body.
CT scans are generally considered safe, but they do expose the patient to ionizing radiation, which can increase the risk of cancer over time. The amount of radiation exposure during a CT scan is generally higher than that of traditional X-ray, so CT scans should be used only when needed to avoid unnecessary exposure to radiation. The amount of radiation exposure from a CT scan can vary depending on the type of scan and body part being imaged. For example, a chest CT scan typically results in higher radiation exposure than a head CT scan.
Figure A (Right): Axial view of contrast-enhanced CT of the chest
There are several different types of CT scans, each with its own imaging parameters that are tailored to specific anatomical areas or diagnostic purposes and challenges. These different types of scans are commonly categorized as but not limited to:
Abdominal CT: An abdominal CT scan provides images of the organs within the abdominal cavity, including the liver, spleen, pancreas, kidneys, adrenal glands, gastrointestinal tract, and blood vessels. It is useful in diagnosing conditions such as liver disease, kidney stones, abdominal tumors, or inflammatory bowel disease.
Chest CT: A chest CT scan examines the chest area, including the lungs, heart, mediastinum, and thoracic spine. It helps diagnose lung diseases, evaluate pulmonary embolism, or detect abnormalities in the chest wall or lymph nodes.
Extremity CT: Extremity CT scans are conducted to evaluate specific regions of the arms, legs, hands, or feet. They help assess fractures, joint abnormalities, soft tissue masses, or other localized conditions.
Head CT: This scan focuses on the head and brain, providing detailed images of the skull, brain, and structures within the cranium. It is used to evaluate head injuries, strokes, brain tumors, hemorrhages, and other neurological conditions.
Neck CT: A neck CT scan focuses on structures within the neck, including the thyroid gland, lymph nodes, salivary glands, and blood vessels. It is used to assess neck masses, infections, tumors, or trauma, and are typically combined with a head CT.
Pelvic CT: This scan focuses on the pelvis and reproductive organs, including the bladder, uterus, ovaries, prostate, and rectum. It is used to evaluate pelvic pain, assess tumors or infections, or detect abnormalities in the pelvic structures.
Spine CT: A spine CT scan is performed to visualize the bony structures of the spinal column. It helps diagnose spinal fractures, degenerative disc disease, spinal stenosis, or spinal infections.
Specialized techniques have been designed to provide additional information beyond what a standard CT can offer. Each technique has its own unique imaging parameters, contrast protocols, and post-processing algorithms, allowing for more targeted and comprehensive evaluations in specific clinical scenarios. Some examples include:
Cardiac CT: Cardiac CT scans are tailored specifically for imaging the heart and coronary arteries. They involve ECG gating to acquire images at specific phases of the cardiac cycle, allowing for the assessment of coronary artery disease, cardiac function, valve abnormalities, and other pathology.
CT Angiography (CTA): This technique involves injection of a contrast agent into the bloodstream to visualize blood vessels throughout the body. It is commonly used to evaluate the arterial and venous systems in various regions such as the brain, chest, or neck.
CT Enterography: CT enterography is used to evaluate the small intestine. It involves the ingestion of a contrast material and the use of intravenous contrast to enhance the visualization of the bowel wall and surrounding structures.
CT Myelography: CT myelography combines a CT scan with the injection of contrast material into the space around the spinal cord and nerve roots, known as the subarachnoid space. This technique is used to evaluate the spinal cord and nerve roots in cases where an MRI (magnetic resonance imaging) is inadvisable.
CT Urography: CT Urography focuses on visualizing the urinary tract, including the kidneys, ureters, and bladder. It involves administering contrast material orally or intravenously to enhance the urinary system’s visualization.
Dental CT (Cone Beam): Cone beam CT is a specialized CT technique primarily used in dental and maxillofacial imaging. It provides high-resolution images of the teeth, jaws, and surrounding structures. Cone beam CT scans are useful for dental implant planning, orthodontic evaluation, and assessing facial fractures.
Dual Energy CT: Dual-energy CT uses two different X-ray energy levels to obtain images with enhanced material differentiation. By analyzing the differential absorption of X-rays, it can help differentiate tissues with similar densities.
