Radiation Dose Reduction in CT

Question 1

when mAS increases, what happens to noise

Answer 1

noise decreases

Question 2

what can be optimized in CT to reduce dose

Answer 2

detector, DAS, beam filters, collimators

Question 3

what are some scanning technique optimization for dose reduction

Answer 3

it is AEC, optimal tube potential, EKG pulsing and dose efficient scanning modes

Question 4

what can reconstruction and data processing do to dose reduce

Answer 4

denoising projection data or images and iterative reconstruction

Question 5

what are the sources of noise in CT

Answer 5

quantam and electronic noise

Question 6

what is qunatam noise for CT

Answer 6

noise from photon statistics, random nautre of photons interaction, poisson distribution

Question 7

what is the source of electronic noise in CT

Answer 7

originate from the detector system, unrelated to the number of photons detected, and they are additive to the quantam noise

Question 8

is noise better for integrated detectors or conventional detectors

Answer 8

integrated detectors have less noise

Question 9

what kind of filters are used for CT

Answer 9

bowtie ilter. match bowties filters to the size and shape of patietn

Question 10

are there collimators for CT and how are they different

Answer 10

early scanners had post patietn collimation to define slice width, reduce scatter, adn improve spatial resolution. Current scanners rarely use post-patient collimation.

Question 11

what collimation is used for multi-slice CT

Answer 11

4 slice MSCT scanners use of narrow z collimations required a larger penumbral region and wasted more dose. Adaptive z colimation addresses spiral overranging

Question 12

what is the goal of AEC

Answer 12

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

Question 13

what is the noise level usually determined by in CT

Answer 13

noise level in the reconstructed image is primarily determined by teh number of photons exiting the patient

Question 14

what are the effects of constant tube current

Answer 14

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

Question 15

what is angular modulation

Answer 15

as the angle of the CT changes, the tube adjusts the current

Question 16

what is z modulation

Answer 16

it is the adjustment of the current as the anatomic thickness changes

Question 17

what is x,y,z modulation

Answer 17

automatically adjust the tube current as projection angle and anatomic level changes

Question 18

energy dependent linear attenujation coefficient

Answer 18

as kev goes up, the attenuation decreases

Question 19

what is tube potential optimization

Answer 19

automattically adjust to task and patient more powerful tubes allow higher mA so that you an use lower KV

Question 20

what happens to noise with and KVP

Answer 20

noise decreases as KVP increases, especially for larger patients

Question 21

what is the relationship between CNR and KVP

Answer 21

it is decreasing so increased KVP means decreased CNR

Question 22

optimal Kv?

Answer 22

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

Question 23

what is the optimal Kv dependent on

Answer 23

patient size and diagnostic task

Question 24

what can be done to decrease noise during reconstruction

Answer 24

filtering in analytical reconstruction, and noise control in iterative reconstruction, post reconstruction image-space noise reduction

Question 25

does iterative reconstruction decrease dose

Answer 25

for msot but not all, the user has to manually decrease the dose

Question 26

dose iterative reconstruction improve lesion detection

Answer 26

IR degrades edges of low constrast lesions