Quantitative computed tomography (QCT) uses X-ray images to create a 2D or 3D model of a body part, with QCT software analyzing the images to generate numerical values for bone volume, mass, and density. QCT is commonly used in bone densitometry and can distinguish between cortical and trabecular bone.
Quantitative computed tomography is a form of medical imaging in which data from a series of x-ray images creates a two- or three-dimensional model of a body part. In general, computed tomography (CT) refers to the practice of using this type of X-ray image to create a more complete image. QCT, often abbreviated, the term “quantitative computed tomography” distinguishes the type of analysis used in this method. Quantitative computed tomography is most common in the field of bone densitometry, the measurement of bone mineral density (BMD), but it has other applications as well.
In quantitative computed tomography, the patient or subject places the body part to be scanned inside a CT scanner. Most QCT involves the spine or an extremity such as the forearm. In spinal scans, the patient or subject lies down inside the scanner. In peripheral quantitative computed tomography (pQCT), the patient or subject places their forearm in a smaller scanner while sitting or standing.
The CT scanner contains an X-ray tube and sensor, which rotate around the body part in a circular or spiral pattern. The X-ray device takes a series of pictures of the body part, then transmits them to a computer. Special QCT software analyzes the images, creating a model of the scanned area. This image can be three-dimensional or two-dimensional, depending on the scanner and the purpose of the scan.
The main difference between quantitative computed tomography and other forms of computed tomography lies in the analysis performed by the computer. In most computed tomography, the software produces a composite visual image that the doctor or researcher can examine. The purpose of this type of visual examination is to detect fractures, injuries, or other symptoms in the scanned bone or soft tissue. QCT takes the data provided by the scanner and uses it to generate numerical values for bone volume, mass and density.
Quantitative computed tomography has a number of advantages over other forms of bone density measurement. One of the most important is its ability to distinguish between cortical bone, which lines the outside of bones, and trabecular bone, the softer tissue that forms the center of the bone. Trabecular bone is much more metabolically active than cortical bone, meaning that the two types of bone are replaced at different rates. As a result, the two types of bone will show different rates of change in bone mineral density.
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