Radiation dose, safety, and patient imaging with X-ray and CT (part 3) Flashcards
Describe the characteristics of computerized tomography (CT) scan.
A CT scan combines a series of X-ray images taken from different angles around the body and uses computer processing to create cross-sectional images of the bones, blood vessels and soft tissues inside your body.
What is a conebeam CT?
A radiographic imaging device that focuses an X-ray beam into a cone shape. That beam is used to create a 3D image of a body region (usually mouth or head). The shape of the beam generates less radiation but still captures high-resolution radiographs compared to a conventional CT.
With CT, the attenuation coefficients are measured and depicted. What are these attenuation coefficients?
The attenuation coefficient is a measure of how easily a material can be penetrated by an incident energy beam (e.g. ultrasound or x-rays). It quantifies how much the beam is weakened by the material it is passing through and usually focuses on 1 voxel.
Describe the 3rd generation CT.
This CT scanner uses a fan-beam shaped X-ray beam acquiring all the data (for a slice) within each view. This acquisition mode can be termed rotate-rotate as both the x-ray source and x-ray detector are rotating together. Using a rigid ring the x-ray tube and detector can be mounted such that they rotate around the patient.
Backprojection means that the more pictures taken, the more sharp the image gets. Before backprojection, it is first important to use filters (i.e. kernels).
What are these kernels?
Note: this question is part of the slides that we do not need to learn.
Kernels refer to the process used to modify the frequency contents of projection data prior to back projection during image reconstruction in a CT scanner. This process corrects the image by reducing blurring. The kernel affects the appearance of image structures by sharpening the image. Different kernels have been developed for specific anatomical applications including soft tissue (standard kernel) and bone (bone kernel). Bone kernels produce a sharper image with higher spatial resolution.
Does the type of filter (smooth or sharp) influence the image reconstruction?
Yes
To reconstruct the CT image fully, the attenuation coefficients are trasnlated to hounsfield units (HU). Why is this done?
HU is the relative outcome where the attenuation coefficient is compared to water or air.
For example, the lungs have a lower HU compared to fat and bones have a higher HU compared to lungs. HU also differs for other tissues when being compared to each other.
What is the biggest advantage of a CT scanner compared to the use of X-rays for rontgen?
The generation of much more contrast and less overprojection (i.e. in rontgen there is low contrast of soft tissue structures due to the superposition of bones)
