Radiation Dose Reduction in CT Flashcards
when mAS increases, what happens to noise
noise decreases
what can be optimized in CT to reduce dose
detector, DAS, beam filters, collimators
what are some scanning technique optimization for dose reduction
it is AEC, optimal tube potential, EKG pulsing and dose efficient scanning modes
what can reconstruction and data processing do to dose reduce
denoising projection data or images and iterative reconstruction
what are the sources of noise in CT
quantam and electronic noise
what is qunatam noise for CT
noise from photon statistics, random nautre of photons interaction, poisson distribution
what is the source of electronic noise in CT
originate from the detector system, unrelated to the number of photons detected, and they are additive to the quantam noise
is noise better for integrated detectors or conventional detectors
integrated detectors have less noise
what kind of filters are used for CT
bowtie ilter. match bowties filters to the size and shape of patietn
are there collimators for CT and how are they different
early scanners had post patietn collimation to define slice width, reduce scatter, adn improve spatial resolution. Current scanners rarely use post-patient collimation.
what collimation is used for multi-slice CT
4 slice MSCT scanners use of narrow z collimations required a larger penumbral region and wasted more dose. Adaptive z colimation addresses spiral overranging
what is the goal of AEC
it is to adjust the tibe current as the attenutaion level changes so that the minimum total radiation dos cna be used to achieve the image
what is the noise level usually determined by in CT
noise level in the reconstructed image is primarily determined by teh number of photons exiting the patient
what are the effects of constant tube current
projection data are noiser at higher attenutationsmoother at lower attenuation. After reconstruction, noise on final image. The noise level in the final image is primary determined by the noisiest slcie. The lower the noise, and the larger number of detected photons alng the less attenuated projections are just a waste of dose
what is angular modulation
as the angle of the CT changes, the tube adjusts the current
what is z modulation
it is the adjustment of the current as the anatomic thickness changes
what is x,y,z modulation
automatically adjust the tube current as projection angle and anatomic level changes
energy dependent linear attenujation coefficient
as kev goes up, the attenuation decreases
what is tube potential optimization
automattically adjust to task and patient more powerful tubes allow higher mA so that you an use lower KV
what happens to noise with and KVP
noise decreases as KVP increases, especially for larger patients
what is the relationship between CNR and KVP
it is decreasing so increased KVP means decreased CNR
optimal Kv?
optimal kv is the kv that uses the minimum radiation dose to acheive the desired image quality. It is dependeny onpatient size and diagnostic task
what is the optimal Kv dependent on
patient size and diagnostic task
what can be done to decrease noise during reconstruction
filtering in analytical reconstruction, and noise control in iterative reconstruction, post reconstruction image-space noise reduction
