Imaging studies are an important part of diagnosing most forms of cancer, including all types of lung cancer. Computed tomography (CT) is one of the most widely used imaging techniques for accurately locating tumors (or potential tumors) that lie deep within the body. In addition to their role in diagnosing lung cancer, CT scans are also important for evaluating the effectiveness of treatment and long-term monitoring for lung cancer recurrence.

How Does CT Work?

CT scan — also called computed axial tomography (CAT) scan — is an imaging technique that uses X-rays to construct images that are cross sections of a human body.

Traditional X-ray imaging can capture only a flattened view through the body from a single angle in two dimensions. CT, however, uses hundreds to thousands of narrow X-rays taken around the body from multiple angles to produce images that are a cross section of the body. Newer CT technology can produce 3D images.

Most CT scan images show a cross section in the axial plane, “cutting” through the body the way a magician saws their assistant in half. These slices, or sections, show detailed anatomy that is not visible on X-ray.

Typical CT scans used for lung cancer include:

• Chest scans to look at the lungs
• Abdominal scan to look for common sites of metastasis (spread of cancer), such as the liver
• CT scans of other parts of the body, such as the head, to look for metastatic lesions

Newer CT technology can produce very high-resolution images and produce cross sections from different planes. These types of CT images include the following:

• Coronal CT can show sections from front to back, similar to a standard chest X-ray.
• Sagittal CT can show sections that go from side to side.
• 3D reconstructions of the body can also be produced by some more advanced CT scanners.

What Do CT Scans Show?

Like traditional X-ray, CT can identify differences in radiodensity — that is, how well X-rays penetrate tissue. Bones and teeth are very radiodense and appear white on X-rays or CT scans. Soft tissue is less radiodense, and air-filled cavities, such as fully inflated lungs, appear darker on X-rays and CT scans. With a traditional X-ray, “shadows” cast by radiodense tissue can obscure soft tissue and hide important features. CT does not have this limitation. It can show clear distinctions between bone, soft tissue, fluid, and air.

A technique called contrast-enhanced CT, or CT with contrast, is used to produce additional detail and show specific structures during a CT scan. Contrast dye is radiopaque, meaning that it appears solid white on X-ray or CT, much like bone. Contrast is given as an intravenous injection. It may cause a temporary sensation of warmth or a strange taste in the mouth.

CT Scans and Lung Cancer Diagnosis

CT can be used to help diagnose suspected lung cancer by identifying tumors and enlarged lymph nodes. The detail provided by CT allows doctors to clearly see the size, shape, and location of abnormalities that would otherwise be difficult to detect using traditional X-ray images. CT scans are important to help determine the stage of lung cancer by identifying the size and extent of tumors, lymph node involvement, and metastases.

Once potential tumors are identified, CT can also be used to help obtain biopsies (tissue samples). Using CT-guided needle biopsies, doctors can precisely place a long needle into tumors to collect cells for analysis. This is especially useful for collecting biopsies from deep within the chest cavity and for very small tumors.

PET/CT Scans

Another type of imaging test used for lung cancer, positron emission tomography (PET), can also involve CT. PET can identify potential cancer cells based on how they metabolize a radioactive sugar that is injected before imaging. PET/CT combines this function with the 3D detail of a CT for more detail.

CT Scans for Lung Cancer Screening

CT scan can be used not only for diagnosing lung cancer but also screening for the condition. Low-dose computed tomography (LDCT) — which uses less radiation than a standard CT — is used to screen people for lung cancer who are at high risk due to smoking and age. LDCT is more sensitive than standard chest X-rays for lung cancer screening. LDCT is able to detect stage 1 cancer and has been proved to reduce cancer-specific mortality due to lung cancer.

CT Scans and Lung Cancer Treatment

Health care teams use repeated CT scans to assess the effectiveness of a person’s treatment, both while they’re being treated and afterward. They also use regular CT scans for long-term follow-up to monitor for signs of recurrence.

CT can also be used during specific lung cancer treatments. Similar to CT-guided needle biopsy, CT-guided ablation uses CT imaging to precisely place a needlelike electrode into small tumors. Radio waves or microwaves are then used to destroy cancer cells using heat. Similarly, CT-guided cryoablation uses cold to precisely kill cancer cells by freezing them.

How Accurate Are CT Scans?

CT scans are generally very accurate at identifying tumors, enlarged lymph nodes, and metastatic cancer. They can also assess the extent of cancer cell invasion into healthy tissue. Studies have shown that CT can be more than 90 percent accurate in identifying lung cancer tumors and 75 percent to 80 percent accurate at identifying lung cancer in lymph nodes.

Low-dose CT screening for lung cancer is used to detect potential tumors but can produce false-positive results, meaning they may incorrectly show that a person has a tumor when they don’t. As with any screening test, if a doctor finds a potential abnormality in a screening CT, they should follow up with further imaging and other testing, such as biopsy, to confirm a diagnosis.

Getting CT Scan Results

CT scans, like other imaging tests, must be interpreted by a doctor. While radiology technicians perform the actual scan, only a radiologist can “read” scan results to determine if there are abnormalities and what they may be.

CT results are typically available within one to two business days, not including weekends. After imaging, the data collected must be processed by a computer to produce images for a radiologist to examine. Once the radiologist reads the CT and writes their report, it may be immediately available electronically to you or your health care provider.

You probably will not have an immediate diagnosis as soon as the report results are available.

Your health care provider must interpret the CT report by correlating imaging results with clinical findings.

Reading a CT Report

To better understand your CT report, you should know what information it provides. A typical CT report contains a variety of information, including:

• Type of exam — For example, chest CT without contrast or chest and abdominal CT with contrast
• Comparison — Current scan may be compared with previous scans to look for changes
• Indication or clinical history — The reason for the scan, such as signs or symptoms of disease or a suspected diagnosis
• Findings — An objective description of what the scan shows including specific findings, either positive (what was seen in the scan) or negative (what was not seen on the scan)
• Impression or conclusion — A description of how the results could potentially correspond with clinical findings

The abbreviations and clinical terms used in reports may be difficult to understand. Keep in mind that the report may not provide a diagnosis but, rather, an assessment that the findings either are or are not consistent with one or more particular diagnoses.

Talk With Others Who Understand

MyLungCancerTeam is the social network for people with lung cancer and their loved ones. On MyLungCancerTeam, more than 6,700 members come together to ask questions, give advice, and share their stories with others who understand life with lung cancer.

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