Ch27 medical physics

Question 1

x ray tube

Answer 1

at cathode, an electric current heats a filament that produces electrons.
electrons are accelerated by pd towards the anode(targeted metal)
when electrons strike the metal, x rays are produced

Question 2

x ray absorption mechanism
simple scattering

Answer 2

x ray has energy less than work function.
so x ray performs a simple scatter in which it does not lose energy.

Question 3

x ray absorption mechanism
compton scattering

Answer 3

the incoming x ray has a high energy so it removes the electron
there is still some energy left and a lower energy photon is scattered.

Question 4

x ray absorption mechanism
pair production

Answer 4

incoming x rat has high energy and interact with the nucleus

an electron-positron pair is produced
they normally annihilate and produce a pair of low energy photons

Question 5

x ray absorption mechanism
photoelectric effect

Answer 5

x ray with high energy is absorbes
electron gain this energy and escape
electron released with some kinetic energy

Question 6

x ray characteristics

Question 7

x rays contrast media

Answer 7

barium and iodine are injected into the patient or digested.
the contrast media absorbs x rays duebto high num of protons.
x ray attenuation is proportional to z^3
contrast media allow outlines of soft tissue

Question 9

CAT Scan

Answer 9

• x ray tube rotates around the patient.
• a thin fan shaped beam pf x ray is used
• x rays are absorbed differently by different tissues and intensity of x rays is recorded by the detector
• images of slices pf patient are taken
• x ray tube moves along the patient
• computer software produce 3d images

Question 10

adv and dis of CAT Scan

Answer 10

• x-rays scan is quicker and cheaper than CAT
• CAT can be used to create 3D images
• harmful if exposed for long time

Question 11

medical tracers

Answer 11

medical tracers are radioactive substances, either injected or digested, used for diagnosis or treatment of patients.

Question 12

properties of medical tracers

Answer 12

• typically gamma sources.
• half life need to be long to be detected but short so it doesn’t stay in the patient for long time.
• activity must be large to be detected from outside the body
• must be non toxic

Question 13

examples of medical tracers

Answer 13

technitium 99m

flourine 18
used in pet scan