​Computed tomography (CT) scan

A doctor orders a computed tomography (CT) scan, which is an X-ray study that uses a computer to produce 3D cross-sectional images of the body. It obtains detailed pictures of internal organs, bones and soft tissues—and differs from a medical X-ray image in that it uses a doughnut-shaped machine to emit X-ray beams at different angles.

3D CT

3D CT pinpoints the location of tumors and can determine whether the cancer has spread to other parts of the body, and assesses the effects of treatment.

Advantages may include:

• Providing more detailed images than those from magnetic resonance imaging (MRI) or ultrasounds 
• Most scans take less than 10 minutes

3D CT angiography

CT angiography (CTA) highlights the blood vessels of tumors and notes other abnormal blood vessels that may be a health concern.

Advantages may include:

• Less invasive evaluation of blood vessels than catheter angiography
• Capturing 3D images of almost every blood vessel in the body, as well as the brain, heart, lungs, pelvis, abdomen and extremities

Large bore CT scanner/radiation therapy (RT) with simulation

This health-care tool produces detailed images of areas inside the body for planning radiation therapy. It uses simulation, fluoroscopy and respiratory gating to plan and deliver radiation.

Advantages may include:

• Locating abnormalities and guiding precision radiation therapy
• Planning for treatment options based on a patient’s breathing patterns
• Allowing for varying patient sizes and positioning

Multi-detector CT scanner

This scanner provides multiple image slices in one rotation, allowing radiologists to view high-quality images in micro-level detail and faster. The CT machine's wide scanning space makes it a more comfortable experience for the patient.

PET/CT scan

This nuclear imaging technique uses both positron emission tomography (PET) and computerized tomography (CT), providing detailed information about the structure and function of cells and tissues in the body. The patient receives a glucose injection that has a small amount of radiation as a contrast agent. The radiation dose is absorbed by the organs or tissues being examined, making them visible in medical imaging. The radiation exposure from this procedure is minor.

Advantages may include:

• Locating damaged or cancerous cells where the glucose is being abnormally absorbed (cancer cells often use more glucose than normal cells)
• Determining the response to therapy by measuring the rate at which the tumor is using the glucose
• Providing a more detailed image of cancerous tissues than either test is able to do on its own
• Capturing both forms of diagnostic imaging in one scan

A patient lies on a table that slides into the CT scanner, where an X-ray tube rotates around the patient.. A technologist may inject a contrast material, usually an iodine contrast dye, into a vein in the arm for even more detailed CT images. Many abdominal and pelvic exams also require drinking a liquid to opacify the GI tract. This painless outpatient procedure typically takes about 10 minutes.

Before the scan

• Wear comfortable clothing. The technologist may ask you to change into a medical gown.
• Remove metal objects such as jewelry, eyeglasses, dentures and hairpins. If you have piercings, remove them as well.
• If you’re getting contrast, you may be asked to not eat or drink a few hours before the scheduled exam.
• If you’re on medications, ask your doctor whether to take them before the exam.
• If you have allergies, ask if there are medications to reduce the risk of a reaction to the contrast.
• If you have other medical conditions, such as diabetes, heart disease, asthma, kidney disease, thyroid problems, or may be pregnant, tell your care team.

During the scan

• A noninvasive procedure, a CT scan requires nothing to break the skin or enter the body. However, sometimes your doctor orders a CT with contrast dye to highlight specific areas of the body. In that case, the contrast agent may be injected into a vein or given orally or by enema.
• You may be asked to hold your breath, so you don’t move and blur the images. You’re not enclosed like you are in an MRI machine, so it’s unlikely you’ll feel claustrophobic.
• Most CT scans take anywhere from a few minutes to a half-hour and are available in different settings—whether that’s in the radiology department of a hospital or at an outpatient imaging facility.
• CT scans are typically painless and easy, but if you’re given contrast through an intravenous (IV) line, you may experience slight discomfort at the injection site.
• You may be asked to wait a few minutes for the technologist to check that the images are of the quality needed for an accurate interpretation.

CT scans play many different roles in the diagnosis and treatment of cancer.

• Screening: CT is sometimes used to screen for different types of cancer, such as lung and colorectal cancer.
• Diagnosis: Your doctor may order a CT scan to locate and size suspected tumors. It also may help determine whether a tumor has recurred.
• Planning and treatment guide: A CT scan may help your doctor identify and locate the tissue that needs to be biopsied. It may also be used to guide treatments such as cryotherapy, microwave ablation and the implantation of radioactive seeds, or to plan surgery or external-beam radiation.
• Treatment response: Sometimes doctors order a scan to see whether a tumor is responding to treatment.
• Tool for monitoring for other diseases: CT scans may be necessary to look for other conditions that may or may not be related to cancer, including:
  • Abnormal brain function
  • Coronary artery disease
  • Blood vessel aneurysms
  • Blood clots
  • Bone fractures
  • Emphysema or pneumonia
  • Kidney and bladder stones
  • Inflammatory diseases, such as ulcerative colitis and sinusitis
  • Injuries to your head or internal organs

As with any medical procedure, you and your doctor must weigh the risks and benefits.

The information your doctors may get from a CT scan may be critical to diagnosing and treating your cancer. Possible risks include:

Radiation. CT scans use low-level ionizing radiation. While it’s more radiation than emitted from an X-ray, it’s still low. Still, some concerns have been raised over whether even small doses of radiation from imaging could lead to cancer. In most cases, the information obtained from the scan far outweigh the minimal risks of the radiation used.

Allergic reactions. Though it’s rare, sometimes people have allergic reactions to the contrast agents. You may experience itching or hives. If you have a serious allergic reaction, where you experience shortness of breath and your throat swells, alert the technologist immediately so that you may be treated promptly.

Kidney function. If your kidneys are impaired in any way, the contrast dye may make it worse. About 2 percent of patients who are given dyes develop contrast induced nephropathy (CIN), according to the National Kidney Foundation. CIN may cause fatigue, swelling of the feet and ankles, and dry, itchy skin. CIN also may lead to serious kidney and heart problems.

You may not be a candidate for a CT scan if you:

• Are obese (usually more than 450 pounds)
• Are pregnant 

• The procedure is fast, simple, painless and accurate.
• CT scans provide a wealth of information: Your doctors may see bone, soft tissue and blood vessels with one scan. They also get very detailed images of your tissues and organs.
• Unlike MRI, CT scans may be performed on patients with implanted medical devices of any kind.
• The information from a CT scan may eliminate the need for surgery or biopsy.
• While it provides some radiation, no radiation remains in the body afterward.
• A CT scan may be used to guide minimally invasive procedures such as needle biopsies and needle aspirations in areas of the body such as the lungs, abdomen and pelvis.

A radiologist analyzes your scans and sends a report to the physician who ordered the exam. Your doctor then discusses the results with you.

Depending on what’s found, the radiologist and your doctor may recommend additional or different imaging exams.