Table of ContentsView AllTable of ContentsWhat Is a CT Scan?What Is a PET Scan?ComparisonsPET-CT Scanning
Table of ContentsView All
View All
Table of Contents
What Is a CT Scan?
What Is a PET Scan?
Comparisons
PET-CT Scanning
Computed tomography (CT)andpositron-emission tomography (PET)scans are two medical imaging techniques that differ in several key ways. The main difference is that a CT scan creates a detailed image of organs, bones, and tissues, while a PET scan shows how the tissues in your body work on a cellular level.
Both can be used to diagnose or evaluate many different medical conditions. The two techniques can also be combined into a PET-CT scan to provide more detailed information about cancer.
This article will review the basics of PET and CT scanning, including their differences and their medical uses.
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A CT scan uses multipleX-raybeams from different locations to create a detailed image of the internal structures of the body. The cross-sectional images generated during the scan can be viewed as multiple “slices” of an organ, bone, or tissue, or reformatted to create a three-dimensional image.
As with X-rays, CT involves exposure to low-dose ionizing radiation. The devices, called CT scanners, can vary in their designs but are comprised of a table and a rotating X-ray tube.
A CT scan has many different medical uses, including the diagnosis and monitoring of diseases as well as preventive screening of diseases. This includes:
A CT scan can detect abnormalities based on the ability of different tissues to attenuate (block) X-rays to different degrees. For example, bone blocks more X-rays than fat, causing bones to appear white on CT scans.
A PET scan is a medical imaging technique that uses radioactive substances, called radiotracers, to visualize and measure changes inmetabolism(the chemical processes that take place in cells to keep the body functioning normally). This includes evaluating where energy is being consumed or detecting types of cells that place specific proteins (receptors) on their surface.
A PET scanner is comprised of a table that moves in and out of a doughnut-shaped or tube-shaped port that houses the detection apparatus.
PET scans have several different medical uses, including:
By way of example, cancer cells have a higher metabolic rate as they grow faster than other cells and cause theformation of new blood vesselsto feed them. These metabolic changes will appear as bright-colored spots on the PET scan.
Comparing CT Scans to PET Scans
CT scans and PET scans are important tools for medical imaging with specific benefits, uses, risks, and limitations.
From the broadest perspective, CT scans help detect structural abnormalities in the body, while PET scans detect functional abnormalities in the body.
CT ScanUsed to create detailed images of bones, organs, and tissuesPasses X-rays through the body to create imagesCan be used to diagnose, monitor, and screen many medical conditionsCan be performed in 10 to 30 minutes, depending on whether contrast is neededRadiation does not stay in the body after the scan is completeMay be less sensitive in detecting very small or early-stage cancersCan be used to guide certain medical proceduresAre less costlyPET ScanUsed to visualize and detect changes in metabolismUses a radioactive material that emits energy to create imagesCan be used to diagnose and/or monitor cancer, brain disorders, or cardiovascular concernsCan take 20 minutes to several hours based on the radiotracer and the aims of imagingA small amount of radiation may persist for a short time after the scanCan often detect cancer sooner based on subtle changes in metabolismHas no use in guided medical proceduresCan be very costly
CT ScanUsed to create detailed images of bones, organs, and tissuesPasses X-rays through the body to create imagesCan be used to diagnose, monitor, and screen many medical conditionsCan be performed in 10 to 30 minutes, depending on whether contrast is neededRadiation does not stay in the body after the scan is completeMay be less sensitive in detecting very small or early-stage cancersCan be used to guide certain medical proceduresAre less costly
Used to create detailed images of bones, organs, and tissues
Passes X-rays through the body to create images
Can be used to diagnose, monitor, and screen many medical conditions
Can be performed in 10 to 30 minutes, depending on whether contrast is needed
Radiation does not stay in the body after the scan is complete
May be less sensitive in detecting very small or early-stage cancers
Can be used to guide certain medical procedures
Are less costly
PET ScanUsed to visualize and detect changes in metabolismUses a radioactive material that emits energy to create imagesCan be used to diagnose and/or monitor cancer, brain disorders, or cardiovascular concernsCan take 20 minutes to several hours based on the radiotracer and the aims of imagingA small amount of radiation may persist for a short time after the scanCan often detect cancer sooner based on subtle changes in metabolismHas no use in guided medical proceduresCan be very costly
Used to visualize and detect changes in metabolism
Uses a radioactive material that emits energy to create images
Can be used to diagnose and/or monitor cancer, brain disorders, or cardiovascular concerns
Can take 20 minutes to several hours based on the radiotracer and the aims of imaging
A small amount of radiation may persist for a short time after the scan
Can often detect cancer sooner based on subtle changes in metabolism
Has no use in guided medical procedures
Can be very costly
Despite their differences, CT scans and PET scans have certain similarities, namely that:
PET-CT Scan
CT and PET technology can be combined into a single scanner, called a PET-CT scanner. Combined PET-CT scanners perform almost all PET scans today. Together, they may be able to provide a more accurate diagnosis than the two scans performed separately.
This is particularly true with respect to cancer in which a PET-CT scan can:
By combining the two, areas of increased metabolism may be localized much more precisely.
The only major limitation is the cost of a PET-CT scan, which can cost upwards of $1,000 or more. A CT scan can cost one-half to two-thirds less.
Summary
CT scans and PET scans are both essential tools in the diagnosis and monitoring of many health conditions, including cancer. They use different types of radiation, with PET using radioactive tracers injected into a vein and CT scans using external X-rays.
PET scans detect functional changes in metabolism that indicate disease. CT scans detect structural changes in bones, organs, and tissues indicative of disease or injury. A PET-CT scan is a combination of these two techniques that offer more information and can help deliver more accurate diagnoses.
8 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.MedlinePlus.CT scan.National Institute of Biomedical Imaging and Bioengineering.Computed tomography (CT).Johns Hopkins Medicine.Computed tomography (CT scan).National Cancer Institute.PET scan.American Heart Association.Positron emission tomography.MedlinePlus.PET scan.National Cancer Institute.PET-CT scan.Kim CR, Kim B, Ning MS, et al.Cost analysis of PET/CT versus CT as surveillance for stage III non–small-cell lung cancer after definitive radiation therapy.Clin Lung Cancer. 2018 Jul;19(4):e517–28. doi:10.1016/j.cllc.2018.03.012
8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.MedlinePlus.CT scan.National Institute of Biomedical Imaging and Bioengineering.Computed tomography (CT).Johns Hopkins Medicine.Computed tomography (CT scan).National Cancer Institute.PET scan.American Heart Association.Positron emission tomography.MedlinePlus.PET scan.National Cancer Institute.PET-CT scan.Kim CR, Kim B, Ning MS, et al.Cost analysis of PET/CT versus CT as surveillance for stage III non–small-cell lung cancer after definitive radiation therapy.Clin Lung Cancer. 2018 Jul;19(4):e517–28. doi:10.1016/j.cllc.2018.03.012
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
MedlinePlus.CT scan.National Institute of Biomedical Imaging and Bioengineering.Computed tomography (CT).Johns Hopkins Medicine.Computed tomography (CT scan).National Cancer Institute.PET scan.American Heart Association.Positron emission tomography.MedlinePlus.PET scan.National Cancer Institute.PET-CT scan.Kim CR, Kim B, Ning MS, et al.Cost analysis of PET/CT versus CT as surveillance for stage III non–small-cell lung cancer after definitive radiation therapy.Clin Lung Cancer. 2018 Jul;19(4):e517–28. doi:10.1016/j.cllc.2018.03.012
MedlinePlus.CT scan.
National Institute of Biomedical Imaging and Bioengineering.Computed tomography (CT).
Johns Hopkins Medicine.Computed tomography (CT scan).
National Cancer Institute.PET scan.
American Heart Association.Positron emission tomography.
MedlinePlus.PET scan.
National Cancer Institute.PET-CT scan.
Kim CR, Kim B, Ning MS, et al.Cost analysis of PET/CT versus CT as surveillance for stage III non–small-cell lung cancer after definitive radiation therapy.Clin Lung Cancer. 2018 Jul;19(4):e517–28. doi:10.1016/j.cllc.2018.03.012
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