9848 Lecture Notes - Lecture 4: Radon Transform, Iterative Reconstruction, Radiography
19 Jun 2018
School
Department
Course
Professor
Overview of CT continued
Overview of Principles
Data Acquisition - this refers to the collection of x-ray transmission measurements from the
patient / object.
an x-ray tube produces x-ray photons as per general radiography, these then passes
through the patient or object, and is attenuated.
I = Io e ^–µx the linear attenuation equation (basic principle)
the attenuated beam exits the subject it comes into contact with a series of electronic
detectors, typically 900+ in an array, the information is recorded as a slice profile.
x-ray tube and detectors rotate through at least 180 degres , usually 360degrees
at each angle (typically < that 1degrees , so more than 360 angles), intensity values (data) is
collected by the detectors (forms the slice profile)
intensity values are converted to digital values via an ADC
slice profiles typically are “filtered” – eg in filtered back-projection
Image reconstruction
- converts raw data (slice profiles) to image data
- utilises image reconstruction algorithms; filtered back-projection ( taking profiles and
looking back ) technique – old method, adaptive statistical iterative reconstruction
(ASIR) – becoming more commonly used
Each algorithm can be varied to obtain tissue enhancement
- bone
- soft tissue
- brain
- lung
• Image display
- CT images are displayed on a monitor
- require altering (automatic or manual) of the displayed contrast and brightness
- done through the use of window width (WW) and window level (WL)
find more resources at oneclass.com
find more resources at oneclass.com
