Chapter 10: CT scan

Question 1

type of scanning pattern where scanning pattern corresponds to attenuation meausrements that are aprallel to each other

Answer 1

Parallel Beam Projection

Question 2

individual attenuation measurements that corresponds toa line thru the objects defined at one end of the xray source and at the other end by the detector

Answer 2

Rays

Question 3

data collected at specified angle of interogation of the object

Answer 3

projection/profile/view

Question 4

individual rays each correspond toa line integral that spans between the source and the detector

Answer 4

fan beam projection

Question 5

minimal divergence of xray beam trajectory

Answer 5

true fan beam

Question 6

non negligible beam divergence in the orthogonal direction

Answer 6

nrrow cone beam geometry concept

Question 7

fan angle and cone angle for fan beam projection

Answer 7

fan angle: >60 degrees

full cone angle 2.4 degrees

Question 8

seen in flat panel detector array

cone angle is almost equal to fan angle

Answer 8

full cone beam

Question 9

correction methods needed for the different distance from source to detector

Answer 9

planar detector system

Question 10

center of rotation of the CT gantry

Answer 10

isocenter

Question 11

defined by the physical extent of the curved detector arrays (fan angle)

Answer 11

Max FOV

Question 12

xray tube and detector are fixed rigidly to a rotating gantry

Answer 12

rotate rotate - 3rd gen

Question 13

gantry rotation speed

Answer 13

5 rotation per second

Question 14

HU of water, air, adipose, most organs, CM/Bone

Answer 14

Water = 0
air = -1000
Adipose = -80 to - 30
most organs = 30-220
contrast, bone = 3095

Question 15

reduces the intensity of the incident xray beam in the periphery of the xray field where the attenuation path thru the px is generally thinner

Answer 15

bow tie filter

Question 16

modern multidetector CT scanner uses _____ solid state detectors

Answer 16

indirect

Question 17

in a single array CT, what determine slice thickness

Answer 17

xray beam collimation

Question 18

in MDCT, what determines slice thickness and xray beam width

Answer 18

slice thickness = detector configuration

xray beam width = collimator

Question 19

table moves at a constant speed without stopping while the gantry rotates

Answer 19

Helical/spiral acquisition

Question 20

describe the relative advancement of CT table per rotation of the gantry

Answer 20

pitch

Question 21

pitch used for thoracic and pedia where speed is imp

Answer 21

1.5 pitch

1.0 = continguous axial CT 
<1 = overscanning, higher rad dose
>1 = underscanning, lower rad dose

Question 22

challenges related to cardiac CT

Answer 22

temporal resolution

Question 23

projection data are acquired over the enetire cardiac cycle using ECG gating info

Answer 23

retrospective construction

Question 24

ECG triggers the xray tube such that data are acquired only during END DIASTOLE

Answer 24

Prospective gating

Question 25

used to identify blockage in the coronary artery

Answer 25

retrospective gating

Question 26

Designed primarily for cardiac imaging

kV can be switched during acquisitionto achieve dual energy data

Answer 26

Dual energy CT

Question 27

allows a CT scanner to repeatedly image a volume of tissue wider than the detector array

Answer 27

Shuttle mode CT

Question 28

identifies regions in teh data with low signals

Answer 28

adaptive noise filtering algorithm

Question 29

projected value thru each line passing thru the patient is linear sum of the voxel values that each ray intersects

Answer 29

simple back projection

Question 30

creating projection from central data

Answer 30

forward projection

Question 31

computing the image matrix from the projection values can be achieved

Answer 31

back projection

Question 32

a CT reconstruction method used in nuclear medicine application, such as SPECT, and produce images with higher SNR at the same dose.

Answer 32

Iterative reconstruction

Question 33

presence of densestructures such as bones on xray path cause the lower energies in the xray spectrum to preferentially attenuate compared to the higher energy photons

Answer 33

beam hardening

Question 34

attenuation levels of a region in the patient are excessibe, which can exceed the dynamic range of the detector systems or the effective linear range of detectors

Answer 34

Streak artifact

Question 35

use of few projection images acquired to reconstruct high frequency objects in the image

Answer 35

View aliasing

Question 36

CT voxels are large enough to encompass several types of tissues, such as bone and tissue or tissues from different organs

Answer 36

Partial volume

Question 37

stack of alternating disks separated by low density material which can be used to evaluate cone beam artifacts

Answer 37

Defrise phantom

Question 38

angular sampling due to the relationship of the detectors and xray source

Answer 38

ring artifact

Question 39

Determine the generation
translate-rotate 
   pencil beam
   fan beam
rotate-rotate
rotate-stationary

Answer 39

1st gen
2nd gen
3rd gen
4th gen

Question 40

CT tubes has a power rate of

Answer 40

5-7MJ

Question 41

Sintered to increase physical density and light output

Answer 41

Intensifying screen:Gd2S2O

Question 42

Heart is most stationary

Answer 42

End diastole

Question 43

Allow the CT gantry to rotate freely and eliminates need to deal with gantry inertia between scans.
Eliminated cable connections

Answer 43

Slip ring