X rays

Question 1

When an X-ray image is obtained of certain organs, image contrast enhancement is necessary. Explain why image contrast enhancement is needed and describe how this might be achieved.

Answer 1

For clear image need a large difference in densities between part being investigated and parts around it
when this is not natural, add material to part under investigation which has high density to provide good attenuation of X-rays.

Question 2

Purpose of glass tube

Answer 2

Evacuated, allows electrons to travel unimpeded

Question 3

Purpose of rotating anode

Answer 3

Rotation of anode to spread heated area

Question 4

Purpose of filament (or cathode)

Answer 4

Heat source to release electrons from surface of cathode by thermionic emission

Question 5

Purpose of lead housing

Answer 5

Prevent X-rays from escaping in unwanted directions

Question 6

Explain why it is important to use a point source of X-rays for imaging purposes.

Answer 6

point source gives a sharp image without the production of a penumbra

Question 7

Explain why the anode has a bevelled edge

Answer 7

gives larger target area but small source area (to produce sharp image)

Question 8

Define for a material the half-value thickness

Answer 8

the thickness of the material which will reduce the intensity to half its original level

Question 9

Define for a material the linear attenuation coefficient, μ,

Answer 9

the fraction of X-rays removed per unit thickness of the material

Question 10

(fluoroscopic image intensifier) purpose of the fluorescent screen

Answer 10

converts X rays to visible photons

Question 11

(fluoroscopic image intensifier) purpose of the photocathode

Answer 11

converts photons to emission of electrons

Question 12

(fluoroscopic image intensifier) purpose of the anodes

Answer 12

increases kinetic energy of electrons travelling from cathode to anode and focuses rays of electrons to produce a more detailed image

Question 13

(fluoroscopic image intensifier) purpose of the second fluorescent screen

Answer 13

Converts (increased) electron energy into light photons

Question 14

Give one example of a medical application for which a fluoroscopic image intensifier might be used. Explain why the use of an image intensifier is required

Answer 14

Cuts radiation dose whilst still providing good image

Question 15

State two methods which can be used to increase the intensity of the X-ray beam produced by the tube and the state the effect on the maximum X-ray photon energy

Answer 15

Increasing pd across the tube will increase the maximum photon energy and increasing tube current wont change the maximum photon energy

Question 16

Before taking an X-ray photograph, the X-ray beam emerging from the tube is passed through an aluminium filter. State and explain the reason for filtering the X-rays.

Answer 16

reduces intensity of low energy photons
hardly changes intensity of high energy photons
need high energy for picture
reducing low energy reduces dose received by patient

Question 17

(xray) State the use of the lead sheets

Answer 17

Provide aperture through which X-rays may pass, stopping others

Question 18

A patient is asked to swallow a suspension of barium sulfate before X-ray images are to be obtained. This is known as a barium meal technique.
Explain why the patient needs to swallow the barium sulfate

Answer 18

Barium meal proves high attenuation material at site to be investigated which provides much better contrast between the area to be investigated and surrounding tissue

Question 19

Explain the process which gives rise to spikes at certain photon energies for the X-ray spectrum for a certain X-ray tube target

Answer 19

electrons strike anode and ionise/excite the target atoms
excited/higher electrons fall to inner energy level
fixed energy gaps produce fixed energy photons

Question 20

What is fluoroscopy used for?

Answer 20

To create moving images

Question 21

Why are xray tubes operated between 30kV and 100kV

Answer 21

Photons of energies between about 30 keV and 100 keV are absorbed more readily
by bone than by soft tissue. This is because the elements in bone have higher
atomic numbers than the elements in soft tissues and therefore have deeper atomic
energy levels which can absorb photons in the 30–100 keV. X-ray photons in this
energy range are therefore used to distinguish between soft tissues and bone.

Question 22

Producing a sharp x-ray image

Answer 22

Xray plate close and tube fair away
Keep patient still
Put a lead grid between plate to reduce contrast and stop fogging
Image intensifier (fluorescence crystals absorb x-rays and emit visible light)

Question 23

X-rays are used in a CT scanner. Describe briefly how a CT scanner produces an image.

Answer 23

Narrow beam of X–rays
X ray generator rotated (in circular path) around patient
Detectors arranged around outside of the path
Detector opposite generator registers transmitted intensity
Detectors connected to computer which (over time) produces cross sectional
image

Question 24

How does an FTP work?

Answer 24

X-ray photons excite scintillator material in the detector, producing visible light. Light hits photodiode pixels than generate a voltage when light hits them. Thin-film transistors, one for every pixels, read the digital signal.

Question 25

Advantages of an FTP

Answer 25

Lightweight
Higher resolution
Less distortion 
Digital
Require lower exposure to produce a clear image