PET Scan VS CT Scan-What is the Difference？

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You’ve probably heard of CT scans and PET scans – but what exactly are they? Both procedures use special equipment to analyze the state of your body, but they show different metrics about your condition. In many cases, both a CT scan and PET scan will be ordered to get a complete picture. Here’s a look at the similarities and differences between these two procedures.

What is a Computed Tomography Scan?

Formerly known as a CAT scan, a CT scan is a medical test that, thanks to technological advances, now allows doctors to see inside the human body. A CT scan can produce cross-sectional images (often called "slices") of the body. This data can create three-dimensional images of specific areas within the body. A CT scan is often used to detect problems such as cancer, internal injuries, blood clots, and infections. Doctors can also use it to guide procedures such as biopsies or surgeries.

How Does it Work?

A CT scan takes X-ray measurements from different angles and processes them into cross-sectional images with a computer. This allows the examiner to see inside the body being scanned. The CT scanner is typically a large machine with a hole in the center. The patient lies on an examination table that moves into and out of this hole. During the procedure, an X-ray tube inside the machine rotates around the body, collects images, and then transfers them to a connected computer.

The computer processes these images into detailed pictures of organs, bones, and other tissues.

The radiologist then interprets these pictures and sends a report to a doctor.

A CT scan can be done with or without “contrast.”

A typical CT scan takes 10-30 minutes. Some scans require multiple pictures, meaning the patient might have to stay longer depending on how many images are needed.

What is a Positron Emission Tomography Scan?

A PET scan is a medical imaging procedure that uses small amounts of radiation to monitor metabolic processes in the body using three-dimensional images.

PET scans are performed in hospitals and clinics and usually take an hour to complete. The patient is injected with a radioactive tracer and placed inside a PET scanner during the procedure. The scanner detects the radiation from the tracer, and this information is used to form pictures showing the body's internals.

PET scans are often used to diagnose cancer because they can show where the cancer cells are located in the body. They can also be used for cardiac imaging, evaluation of brain disorders, and other conditions.

How Does it Work?

A PET scan begins with the patient getting an injection containing the radiotracer, the one commonly used is FDG (fluorodeoxyglucose), at least an hour before the scan. The patient then rests during this period to enable the radiotracer spread through the body and into the tissues. The tracer will then gather in bodily parts with higher metabolic or biochemical activity levels, frequently identifying the disease's site.

The patient is then taken into the scanning room and placed in a doughnut-shaped machine.

The machine then slowly scans over the body part being examined. The breakdown of the FDG results in the production of positrons. When elections collide with positrons near the decay process, annihilation photons are created. The scanner works by detecting photons that are emitted when gamma rays collide. Each detector receives photons in pairs, 180 degrees apart. The computer uses this information to create an image of the studied organ or tissue. The concentration of FDG in the tissue determines how brightly the tissue appears on an image, reflecting the organ or tissue function level.

PET Scan Compared to a CT Scan

While both PET and CT scans use radiation to create images of the body's internals, there are some critical differences between the two procedures.

Let's check them out.

Scope

One of the main differences is that a PET scan looks at metabolic activity while a CT scan looks at the anatomical structure. This means that a PET scan can show how well organs and tissues function, while a CT scan can show what they look like.

For example, a PET scan can check for cancer because it can show where the cancer cells are in the body. It can also help to check if there is any damage to the functioning of the heart or brain after a stroke.

A CT scan, on the other hand, cannot show how well organs and tissues are functioning. However, it can diagnose problems such as fractures, aneurysms, and tumors.

Material

Another difference between PET and CT scans is the material used for the scan. A PET scan uses a radioactive tracer, while a CT scan uses X-rays.

Cost

Another difference between PET and CT scans is that the former tend to be more expensive than the latter.

PET Scanners not only have a high upfront cost, but the ongoing operating costs can also be rather steep. Throw in the cost of the radioactive tracers used during the procedure, and you have a fairly pricey test.

CT Scanners, on the other hand, are not as expensive as PET Scanners. The CT machines are less expensive, and the procedure does not require using radioactive tracers.

Time

A PET scan takes longer to complete than a CT scan. While the former could take anything from 20 minutes to several hours, the latter can be completed in 10 minutes.

Accuracy

CT scans provide more accuracy when detecting problems such as tumors. CT scans provide a more detailed image of the body's anatomy. On the other hand, PET scans are better at detecting early signs of disease. This is because PET scans show how the body's cells function rather than their structure.

Ultimately, the best type of scan for a particular patient will depend on what needs to be diagnosed. For example, a CT scan will likely be ordered if a tumor is suspected. However, a PET scan may be recommended if a doctor tries to detect early signs of cancer.

Working Principle

Except in instances of contrast imaging, CT is generally considered to be more non-invasive than PET. CT scans do not require the administration of radioactive tracers, and the procedure is relatively quick and painless. In contrast, PET scans require injecting a small number of radioactive tracers, which can cause discomfort.

Prevalence

CT scans have greater prevalence than PET scans. This is because CT scans can diagnose many problems, while PET scans are mainly used to detect cancer despite how they can serve multiple purposes..

How Are CT and PET Scans Similar

Despite their differences, CT and PET scans share certain similarities. For one, they are relatively painless procedures and can be performed on an outpatient basis. Also, PET and CT scans use radiation, which can harm the body. However, the amount of radiation exposure from these procedures is generally low, and the risks are considered very small. Also, doctors and radiologists can use both procedures in combination with other tests to get a complete picture of a patient's condition.

FAQ

Is a PET scan the same as a CT scan?

No, CT and PET scans are not the same. They are both imaging tests that can detect various problems. However, there are several key differences between these two tests. For one, PET scans show how well organs and tissues function, while CT scans show what they look like. Also, PET scans use radioactive tracers, while CT scans use X-rays.

Will a PET scan detect all cancers?

No, PET scans are not able to detect all types of cancer. For example, tumors with low glycolytic activity, such as bronchioloalveolar carcinomas, adenomas, low-grade lymphomas, carcinoid tumors, and small-sized tumors, are not easily detected on PET scans.

Which has more radiation, CT or PET?

CT scans use just as much radiation as PET scans.

There is no radiation in the body after a CT scan. In contrast, a minimal amount of radiation may remain in the body for a brief time following a PET scan.

However, these procedures' radiation exposure is generally low, with minimal risks.

Which is better, CT scan or PET scan?

The best type of scan for a particular patient will depend on what needs to be diagnosed. For example, a CT scan will likely be ordered if a tumor is suspected. However, a PET scan may be recommended if a doctor tries to detect early signs of cancer.

Which is more accurate, PET scan or CT scan?

CT scans are more accurate than PET scans when detecting problems such as tumors. CT scans provide a more detailed image of the body's anatomy. On the other hand, PET scans are better at detecting early signs of disease. This is because PET scans show how the body's cells function rather than their structure.

Conclusion

PET and CT scans are two imaging tests that can diagnose various problems. PET scans show how well organs and tissues function, while CT scans show what they look like. PET scans use radioactive tracers, while CT scans use X-rays. Ultimately, the best type of scan for a particular patient will depend on what needs to be diagnosed.

Consult your doctor if you have questions or concerns about PET or CT scans. They can advise you on which type of scan is best for you and answer any other questions you may have.