Lesson 1 - CT

Question 1

2 limitations to conventional radiography

Answer 1

low in contrast
superimposition

Question 2

is the tomographic angle increases does the exposure angle increase

Answer 2

yes

Question 3

does a small tomographic number or a large tomographic number blur out more

Answer 3

a large tomographic angle blurs out more

Question 4

What does SSCT mean

Answer 4

single slice per evolution

Question 5

interpolation

Answer 5

take and slant and blur out of helical scainning

Question 6

3 steps of image formation with CT

Answer 6

data acquisition
image reconstruction
image display

Question 7

how does data aquisition work

Answer 7

electronic detectors measure the attenuated values and convert into digital input

Question 8

what is DAS

Answer 8

data acquisition system

Question 9

how does image reconstruction work

Answer 9

image in numerical form converted into electrical signals

Question 10

whats the software that sores all the images

Answer 10

PACS

Question 11

whats involved in CT detector efficicency 3

Answer 11

ability to capture, absorb, and convert X-ray photons to an electrical signal

Question 12

what does capture efficicency depend on

Answer 12

distance and size of the detector array

Question 13

What is absorption efficiency dependent on

Answer 13

atomic number, physical density, size, and thickness of the detector face

Question 14

response time ( resolving time)

Answer 14

recovery time between X-ray events

Question 15

dynamic range

Answer 15

The ratio of the largest to the smallest signal that can be measured, most are 1 million to one

Question 16

what does a photodiode do

Answer 16

convert light to electrons

Question 17

what scintillation materials are currently used with photodiodes

Answer 17

cadmium tungstate
gadolinium oxysulfide

Question 18

categories of multi row ct detectors 2

Answer 18

matrix array detectors
adaptive array detectors

Question 19

what are matrix array detectors

Answer 19

cells have equal dimentions
isotropic

Question 20

what are adaptive array detectors

Answer 20

cells have unequal dimensions
anisotropic

Question 21

whats the formula for pixel size

Answer 21

pixel size= FOV/ matrix size

Question 22

what does ART stand for

Answer 22

algebraic reconstruction technique

Question 23

whats iterative recontruction

Answer 23

start with an assumed value then comapre with measured ones
square calculation

Question 24

whats the advantages to iterative reconstruction

Answer 24

reduced image noise and artifacts
lower patient dose
disadvantage is it takes a long time

Question 25

whats the current method of reconstruction

Answer 25

filtered back projection

Question 26

what filters are used woth filtered back projection or convolution method

Answer 26

convolution filter or a kernel

Question 27

what do sharpening filters do

Answer 27

reduce blurring but accentuates noise

Question 28

what does a smoothing filter do

Answer 28

decreases noise but increases blur

Question 29

when to use sharp or smooth filters

Answer 29

sharp when contrast is hig smooth when contrast is low

Question 30

What is interpolation

Answer 30

data estimated by interpolation

Question 31

whats the pitch

Answer 31

1:1 scans everything 2:1 means the table will move. twice the distance of the slice thickness

Question 32

whats the Ct number/Hounsfield unit of water

Answer 32

0

Question 33

what the CT numbers for bone, soft tissue, fat and air

Answer 33

bone = 1000 sift tissue = 50 fat = -100 air = -1000

Question 34

whats beam hardening

Answer 34

polychromatic beans increase in quality as they penetrate

Question 35

whats the cupping artifact

Answer 35

darker in the middle due to beam hardening