Topic 6. How CT's work Flashcards
Computed Tomography’s (CT) is Volumetric imaging modality based on
X-ray absorption
spatial resolution on CT is ____ than a plain film radiography (plain X-ray imaging)
lower
Contrast resolution on CT is ____ than a plain film radiography (plain X-ray imaging)
higher
CT’s require an X-ray source that produces an ______ beam thats in the shape of a _____ or a _____
X-ray beam
fan or a cone
What is data acquisition of CT’s
a collection of X-ray transmission measurements through the patient
The two perpendicular projections are used to determine the exact position, the projections are
lateral and anterior-posterior
When an X-ray beam passes through the patient, some photons are ______ or ________
absorbed or scattered
the reduction of X-ray transmission is dependant on 3 things what are they?
Atomic composition of crossed tissues (does the tissues composition make it difficult to transmit into)
Density of crossed tissue (is the tissue too dense?)
Energy of photons
(are they strong enough to go through?)
after passing through the patient where do the X-rays go?
they are absorbed by the detector on the opposite side
after the X-rays photons are absorbed by the detector they turn into
electrical signals which are then converted into digital data
when do we calculate attenuation value
when we have digital data
How do X-ray tube and detectors work
X-ray tube and detectors rotate around the patient, collecting many consecutive angular projections
what is the aim of CT?
Image Formation: To obtain a spatially resolved map of absorption coefficients in one slice of the patient’s body
Lambert Beer’s law, we obtain a linear equation system that we can only solve if
one of the absorption coefficients is known
Pixels that make up each cross sectional image in a CT are known as a
voxels
