WHAT’S THE DIFFERENCE BETWEEN CT AND X-RAY?

Radiography (commonly referred to as “X-ray“) and computed tomography (CT) imaging examinations both use ionizing electromagnetic radiation in the form of X-ray photons (energy) to create images of your body.

In radiography, the X-ray source emits a small amount of radiation photons through the body part of interest. An X-ray detector is placed behind the area of interest to record the signal of the photons after their journey, resulting in a two-dimensional image.

In CT, a rotating X-ray source emits a beam of radiation photons through the body part of interest which is then recorded by an advanced detector on the other side. A specialized computer reconstructs the signal into 3D images that can be viewed from multiple directions.

In general, radiography is useful to image the heart and lungs, the abdomen, and various bones in your body. CT is more sophisticated, providing greater anatomic detail of the body. It also has the ability to evaluate the arteries, veins, and blood flow to organs when augmented with intravenous contrast.

WHAT CAN RADIOGRAPHY DIAGNOSE?

Radiography is one of the most frequently ordered types of imaging and is often the first step in using imaging to confirm a diagnosis and determine treatment options, such as for pain or swelling.

Your doctor might order an X-ray to identify injuries, fractures within the bone and tissues, and monitor how the bone is healing. X-rays are also good for seeing arthritis or bone diseases in your joints. They could be used to detect infection of the sinuses or lungs, obstruction of the intestines, gall and kidney stones, and foreign objects within the body.

X-rays are very good a looking at bones, however they don’t see cartilage, muscles, tendons, or ligaments very well.

WHAT CAN A CT SCAN HELP DIAGNOSE?

CT scans are also very good at imaging bone but can also provide detailed information about soft tissues in the chest or abdomen, and blood vessels. A CT may be preferred to evaluate fractures or look for cancers or blood clots.

CT lung screening can help examine suspicious lung nodules for lung cancer, as well as other serious illnesses. It could be appropriate for patients at high risk of lung cancer due to smoking, a family or personal history of lung cancer, or other risk factors. In these cases, CT screening can help detect early signs of lung cancer, as small as just a few millimeters in size.

For those at risk of coronary artery disease, a coronary CT angiography can be used to non-invasively examine the coronary arteries. It can detect both calcified or hard plaques and noncalcified or soft plaques. It is these soft plaque deposits, often invisible with standard imaging tools, that are more likely to cause heart attack related health issues.

CT virtual colonscopy is a minimally invasive CT scan that uses low-dose X-rays to produce two- and three-dimensional images of the large intestine (colon) and rectum, which can be used to screen for colon cancer. It differs from a colonoscopy in that an endoscope is not used and your rectum is inflated with CO2, which is more comfortable and more readily absorbed by the body than room air.

HOW DO I GET AN IMAGING EXAM?

Once your doctor has identified the need for an exam, you will be given a requisition form. X-rays are offered in the community on a walk-in basis at any medical imaging clinic, including 11 Mayfair Diagnostics locations in Calgary and one in Regina. Appointments are not required for general X-ray procedures; simply bring your form with you.

At Mayfair Diagnostics we provide CT lung screening as a private pay exam at our Mayfair Place location. These exams are not covered by Alberta Health Care. They can be purchased for single or multiple body areas. We also offer Health Assessment packages, which provide a discount on multiple imaging exams when purchased together.

Your health spending account or group medical insurance plan may cover the cost of a private CT that is prescribed by a qualified health care practitioner. You will need to check with your plan administrator for coverage details.

Whether public or private, a CT must be requested by a health care practitioner. To determine whether a CT is recommended, you will need to discuss with your doctor your medical and family history, risk factors, and if there are symptoms, how long symptoms have been present and how they affect daily activities.

If a private CT scan is indicated as a best next course of action, a requisition will be provided, and the appointment can be booked. It’s important to note that the exposure to radiation from a CT scan is higher than that of standard X-rays, but the associated risk is still small. For example, the radiation exposure from one low-dose CT scan of the chest is less than the exposure from the earth’s natural background radiation over six months. In most cases, the benefits of a CT, such as the early detection of a serious illness, outweigh the small increased risk from radiation exposure.

For more information, please visit our services page. Please note that our Cochrane, Saskatoon, Southcentre, and Sunpark locations do NOT offer X-ray services.

REFERENCES

Alberta Health Services (2023) “New screening program will use CT scans to detect early-stage lung cancer.” screeningforlife.ca/lung. Accessed December 18, 2023.

Canadian Cancer Society (2023) “Colorectal cancer statistics.” cancer.ca. Accessed December 18, 2023.

Canadian Cancer Society (2023) “Risk factors for colorectal cancer.” cancer.ca. Accessed December 18, 2023.

De Koning, H. J., et al. (2020) “Reduced Lung-Cancer Mortality with Volume CT Screening in a Randomized Trial.” New England Journal of Medicine, 2020; 382:503-513. Accessed December 18, 2023.

History.com Editors (2022) “German scientist discovers X-rays.” www.history.ca Accessed December 18, 2023.

Government of Alberta (2022) “X-Ray: About This Test.” myhealth.alberta.ca. Accessed December 18, 2023.

Radiological Society of North America (2022) “Bone X-ray.” www.radiologyinfo.org. Accessed December 18, 2023.

Toward Optimized Practice Working Group for Colorectal Cancer Screening. (2013) “Colorectal cancer screening: clinical practice guideline.” actt.albertadoctors.org. Accessed December 18, 2023.