CT Principle 1

Question 1

Unlike X-rays, CT reconstructs ____ of internal structures according to ____ for almost every region in the body

Answer 1

cross sectional images; x-ray attenuation coefficients (tissue density)

Question 2

CT was previously known as

Answer 2

Computed Axial Tomography (CAT Scan)

Question 3

What imaging technique was used to visualize the brain before the invention of CT?

Answer 3

radiography

Question 4

Which mathematician introduced the transformation operator that laid the foundation for tomographic reconstruction?

Answer 4

Johann Radon

Question 5

After the injection of air in pneumoencephalography, the patient was rotated, somersaulted or placed in a ___________ position to depicts the entire ventricular system and subarachnoid spaces

Answer 5

Decubitus

Question 6

Who validated Allan Cormack’s work by building the first prototype CT scanner?

Answer 6

Sir Godfrey Hounsfield

Question 7

which gen uses pencil beam

Answer 7

1st Gen

Question 8

which gen uses narrow fan beam

Answer 8

2nd Gen

Question 9

which gen uses wide fan beam

Answer 9

3rd, 4th, 6th

Question 10

which gen uses electron gun firing beam

Answer 10

5th

Question 11

which gen uses cone beam

Answer 11

7th

Question 12

which gen uses translate-rotate

Answer 12

1st, 2nd

Question 13

which gen uses rotate-fixed

Answer 13

4th

Question 13

which gen uses rotate-rotate

Answer 13

3rd, 6th, 7th

Question 14

which gen uses stationary-stationary electron beam

Answer 14

5th

Question 15

which gen uses rotate-rotate (helical/spiral)

Answer 15

6th, 7th

Question 16

which gen uses slip ring technology

Answer 16

3rd, 6th, 7th

Question 17

What is the main advantage of CT over conventional radiography?

Answer 17

Elimination of superimposition of structures

Question 18

The first generation of CT scanners used which motion for scanning?

Answer 18

Translate – rotate

Question 19

In CT, what does the term ‘voxel’ refer to?

Answer 19

A volume element in 3D space

Question 20

pre-patient collimators is place between

Answer 20

filter & patient

Question 21

post-patient collimators is placed

Answer 21

on top of detector

Question 22

purpose of pre-patient collimators

Answer 22

lowers dose & over beaming

Question 23

purpose of post-patient collimators

Answer 23

reduces scatter, penumbra

defines slice thickness

Question 24

what are slip rings

Answer 24

alternatives to cabling system; power & control signals comms via rotating frame through slip ring

Question 25

what is the main benefit of slip rings

Answer 25

Allow scan frame to rotate continuously with no need to stop between rotations to rewind system cables

Question 26

CT Detector Image Formation Process

Answer 26

1. x-rays generates radiation 2. x-rays penetrate body & attenuated by tissue 3. attenuated x-rays processed by detector 4. detector converts radiation into electrical signals 5. converts digital data into high res images

Question 27

GOS

Answer 27

Gadolinium Oxysulfide

Question 28

Pr

Answer 28

Praesodynium-doped

Question 29

UFC

Answer 29

ultra fast ceramic

Question 30

CsI

Answer 30

Cesium Iodide

Question 31

Solid scintillator layer converts ___

Answer 31

x-ray photons to light photons

Question 32

photodiode converts __

Answer 32

light photons to electrical signals

Question 33

properties of solid state detectors

Answer 33

1. high detection 2. high geometry 3. small size of DELs

Question 34

DELs are important for

Answer 34

spatial resolution

Question 35

high detection & high geometry are important for

Answer 35

radiation dose

Question 36

what does beam shaping filtering do

Answer 36

Hardens x-ray by removing low energy x rays that do not contribute to image formation but increase patient dose

Question 37

as the x-ray energies become narrower, the beam becomes more ___

Answer 37

monochromatic

Question 38

what is the common beam filter used

Answer 38

bow-tie filter

Question 39

what happens if the iso-centering is off

Answer 39

off iso-centering > need to increase x-ray output due to filtering mismatch > increases dose

Question 40

what is related to couch top speed

Answer 40

pitch

Question 41

sequential scans are when the patient moves ___

Answer 41

gradually layer-by-layer through gantry during scan

Question 42

spiral scans are when the patient moves ___

Answer 42

continuously through gantry during scan

Question 43

advantages of multi-row detectors against single row detectors

Answer 43

- reduced scan time (more coverage + faster scans) - shorter breath holds - fewer motion artifacts - allows for multiphase contrast enhanced scanning - reduced dose - more efficient use of x-rays with increasing slices

Question 44

how many images are created per rotation when using single slice detectors

Answer 44

1 per rotation

Question 45

how many images are created per rotation when using multi slice detectors

Answer 45

hundred per rotation

Question 46

what controls slice thickness along z-axis for single slice detectors

Answer 46

collimation

Question 47

what controls slice thickness along z-axis for multi slice detectors

Answer 47

activating diff combo of detector rows along z-axis; by detector size

Question 48

detector pitch definition

Answer 48

distance table travels in 1 360 degrees gantry rotation divided by beam collimation / x-ray beam width

Question 49

pitch detector ranges from

Answer 49

0.75 to 1.5

Question 50

choice of pitch influences __

Answer 50

image quality + dose

Question 51

the higher the pitch, the ___ the dose & image quality

Answer 51

lower

Question 52

the lower the pitch, the ___ the dose & image quality

Answer 52

higher

Question 53

what does pitch fundamentally influence

Answer 53

1. dose 2. image quality 3. scan time