CT Flashcards
what does CT measure
attenuation of tissue
how is a signal processed
same as x-ray
what are the components of CT
rotating x-ray tube, rotating detector array, grid, filter/bowtie, collimator, gantry adn slip ring for helical scanning
what can we control
anode/cathode axis with z axis to avoid heal effect, KVP, mas, focal spot, pitch, rotation time, detector configuration
what is a flying focal spot
allows increased sampling for detector size
what parameters are for image wuality of CT
spatial resolution, contrast, temporal resolution, noise proportional to 1/swuare root of photon number, HU
how does flying focal spot affect image quality
reduces artiface
how does mA affect image quality
number of photons-affects noise
how does kVP affect image quality
increased dose, decreased contrast
how does pitch/rotation time affect image quality
slower the better noise, more motion artifacts though
are thinner slices or thicker slices better
thin slices have more noise but better resolution
what is the noise proportional to in CT
1/square root of the photon number
what is the trade off on time
image quality vs. dose
what is the trade off with mA
noise vs. dose
what is the trade off on slice thickness
better resolution vs. noise
what is the trade off with kernal
spatial resolution vs. noise
what are the bioeffects
same as x-ray, but more burns
how is the image reconstructed
detectors-scintillator etc in array, filtered back projection, iterative recontruction
when is iterative reconstruction done
post processing
what are the strengths of CT
fast and good detail
what are the weaknesses of CT
expensive, higher dose, and weight limited
what are the special kinds of CT
dual energy, cardiac gating, prospective gating, and retrospective gating
what is special about dual energy
can show different attenuation to distinguish between tissues
what is cardiac gated trying to do
avoid motion
what is prospective gating
high pitch or step and shoot, only on low heart rate patients.
what is retrospective gaiting
record everything then remove the parts you dont want
