CT

Question 1

Is Compton scattering or the photoelectric effect responsible for more attenuation in CT?

Answer 1

Compton scattering

Question 2

What term describes the average attenuation of a photon beam through an area?

Answer 2

linear attenuation

Question 3

What symbol is used for linear attenuation in CT?

Answer 3

µ

Question 4

What factors influence the linear attenuation through a medium?

Answer 4

physical density
atomic number
energy (of the photons)

Question 5

What mathematical concept is utilised to calculate the incident energy of a photon beam that has travelled through something?

Answer 5

Beer’s law

Question 6

What is Beer’s law

Answer 6

I = Io * e ^ (-µ t)

Transmiitted Intensity (I)

Incident intensity (Io)

path length (t)

Question 7

How is Beer’s law utilised in CT?

Answer 7

Used to solve the linear attenuation where the intensity of the x-ray beam is known before and after patting through an object

Question 8

What is type of data array is CT data initially stored in (before processing into an image)

Answer 8

a sinogram

Question 9

How is data stored in a sinogram?

Answer 9

Each row represents all the x-rays that go through the patient from a certain angle (not for a certain point)

Question 10

What methods can be used to process a sinogram into a CT image?

Answer 10

Back Projection

Filtered Back Projeciton

Fourier Transformation

Iterative

Question 11

What characteristics are needed of CT x-ray generators (opposed to regular x-ray generators)?

Answer 11

high current
fast rotations
thin slices
long scan times
small focal spot size
robust (up to 13Gs at times)

Question 12

How are collimators used in CT?

Answer 12

used to define the slice that’s being CT’d, also used to restrict angle x-rays get through tot he detectors

Question 13

How do CT detectors measure incident x-ray photons?

Answer 13

scintillator crystals convert into electricity

current read

Question 14

What scintillator crystal is commonly used in CT

Answer 14

Na I

Question 15

What is the name of the device that allows the CT detectors and x-ray generator to rotate around the patient?

Answer 15

slip ring

Question 16

CTs that spin around the patient as they move through the machine?

Answer 16

helical CTs

Question 17

What generation of CTs are helical CTs?

Answer 17

6th generation

Question 18

What is the definition of pitch?

Answer 18

table travel per rotation/ normal slice width

Question 19

What pitch level indicates not every point is scanned from every angle?

Answer 19

pitch >1

Question 20

What are the advantages of pitch > 1 in CT scanning?

Answer 20

faster scan

lower dose

Question 21

What are the advantages of pitch < 1 in CT scanning?

Answer 21

better quality (at cost of higher dose)

Question 22

What are the advantages of helical CTs?

Answer 22

speed
potential dose reduction
reconstruction in any plane

Question 23

What are 6th generation CT scanners

Answer 23

helical CT scanners

Question 24

What are 7th generation CT scanners

Answer 24

multidetector CTs

Question 25

What are the advantages of multi-detector CTs?

Answer 25

better resolution (thinner slices)
speed
less tube loading