Radiologist Questions X-Ray

What is the difference between an X-ray and a CT Scan?

My son is 3 years old and seems to be having a severe chest congestion followed by breathing difficulties. The X-ray shows a white patch on the lungs but no confirmed diagnosis. The doctor has now advised a CT scan. What is the difference between the two?

8 Answers

An X-ray (radiograph) yields a composite image with many overlying structures, which can result in less sensitivity to detection of abnormalities. CT uses X-rays to produce sectional cages through a body part of various thicknesses, so it is much more sensitive, specific and definitive.
Both X-rays & CT scans utilize ionizing radiation within permissible limits to penetrate tissues and bone to produce an image. An X-ray is a 2D image of the anatomical site which is produced after the rays which are emitted by an X-ray tube travel across the anatomical part/body & hit a specially coated film which detects the attenuation differences of various tissues in shades of gray & white. In case of CT, there is greater detail as the rays are picked up by multiple detectors as the patient moves through the circular tube-like structure called the gantry, which generates the X-rays. The images of present-day CT scanners can also be reconstructed in sagittal & coronal planes using a computer after scanning is complete; that's why the term "axial " or cross sectional has been omitted from the term C*A*T scan. CT is also expensive & not readily available, that's why initially X-ray is used to detect an abnormality.

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Dr. Himadri S. Das
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CT will give better visualization of the lung and can help narrow the diagnosis. If your son has infectious symptoms related to pneumonia, he should get a follow up X-ray only to ensure resolution. If it persists or your doctor feels it’s not infectious, then CT is recommended.

Dr Cox
CT scan is a computerized X-ray system that gives the radiologist a much more detailed look within the body. It requires a bit more radiation than a routine chest X-ray and is more expensive, but it gives a lot more useful information. That's the basic difference.
CT shows a lot more
A CT scan uses x-rays also. It is a specialized x-ray machine and demonstrates anatomy in a different manner than traditional x-ray machines.
The chest X-ray is a standard procedure which can show much, but CT is much more specific. It might help to have the CT and again, it may not. This is something that you need to weigh and discuss further with your doctor. Unfortunately, sometimes younger individuals will inhale a foreign body such as a small peanut or some other type of food product or item which may or may not be radiopaque. In this instance, CT is definitely an advantage, especially if the radiologist is carefully examining the main airways. The difference however is also involving the radiation dose. There are pediatric radiation dose schedules which are now mandatory on the newer CAT scanners.
The CT scan gives much more detailed information about what is going on in the lungs. Can be very helpful in making an accurate diagnosis.