xray imaging

Question 1

what is an x-ray

Answer 1

high energy EM radiation
essentially the same as gamma radiation
Do not interact with matter much
find it hard to pass through dense materials

Question 2

formula for photon energy

Answer 2

plancks equation

E = hv

E= energy
h = placks constant 6.626x10-34 J.s
V = frequency in Hz

Question 3

wavelength of x-rays

Answer 3

0.01-10nm
hard x-rays are wavelengths under 0.2-0.1 nm

Question 4

energy of hard x-rays

Answer 4

have energies above 5-10 KeV

Question 5

4 parts of an Xray system

Answer 5

source
target
detector
signal processing/detection algorithm

Question 6

components of an X ray source

Answer 6

hot cathode
rotating anode (around 10,000 rpm, heat generated approx. 2000C)
tungsten target angled 12-15 degrees (though molybdenum or graphite can be used)
Rotator

Question 7

generation of xrays - how are K lines generated?

Answer 7

by high velocity electron from the anode knocking out an electron from the K (S) orbital and outer shell electrons dropping to lower energy states and releasing energy in the form of x rays as they do so.

Question 8

generation of xrays - what are the characteristic interaction alpha and beta peaks created from?

Answer 8

alpha from 2p (outer L) shell to 1s (K) (smaller peak)
beta from 3p (middle M) shell to 1s (K) (higher peak)

Question 9

generation of xrays - what is bremsstrahlung radiation?

Answer 9

where a high energy electron passes close to a nucleus, it does not interact with the electrons, but is deflected by the nucleus, this deflection slows the electron and bremsstrahlung radiation is emitted with energy being proportional to how close to the necleus it was (the closer the higher the energy)

Question 10

2 types of x ray detector/sensor

Answer 10

Scintillator
direct converstion

Question 11

define scintillator

Answer 11

these operate by converting packets of xray
radiation into wavelengths which can then just be
detected using CMOS/CCD devices that produce and
electrical signals

Question 12

define direct conversion (x-rays)

Answer 12

x-ray photons are directly converted to electrical signals

Question 13

Pros of direct conversion over scintillator

Answer 13

better energy resolution
better spatial resolution
higher signal conversion efficiencies

Question 14

steps of scintillator detection

Answer 14

Xray
scintillator (xray converted to light, causes scattering)
photodiode
electric circuit (TFT or CMOS)
image

Question 15

steps of direct detection

Answer 15

xray
CdTe (xray converted to electrical signal, minimal scattering)
CMOS circuit
Image

Question 16

Define CT scan

Answer 16

Computer tomography

table moves through sourve/detectors and they move around target taking slices over time whic are then used at the signal processing stage to build a 3d image

Question 17

Pros and cons of CT

Answer 17

pro

3d so can lead to better object identification
can hold certain scans on file for checking for addition/subtraction of material
comprehensive

con
higher dose rates, so may be unsuitable for circumstances where people might be exposed eg lorry backs

takes a lot longer