medical physics

Question 1

what is the piezoelectric effect

Answer 1

The ability of particular materials to generate a potential difference by transferring mechanical energy to electric energy

Question 2

applications of a piezoelectric transducer

Answer 2

• Microphone
  -ultrasound

Question 3

what is an ultrasound

Answer 3

A high frequency sound above the range of human hearing.
-usually above 20,000Hz

Question 4

how are ultrasounds used to create a 2D image

Answer 4

1. transducer sends out a beam of ultrasound waves into the body using piezocrystal
2. sound waves are reflected back into the body by boundaries
3. echoes hit transducer and generate an electric signal sent to ultrasound scanner
4. distance and depth calculated using speed of sound and time between echoes
5. distances used to create a 3d image

Question 5

how does a higher frequency of ultrasound affect image

Answer 5

• higher resolution
• smaller structures can be distinguished

Question 6

what is specific acoustic impedance

Answer 6

the product of the speed of the ultrasound in a medium and the density of the medium

Question 7

how does the difference between the Specific acoustic impedance affect intensity

Answer 7

the larger the difference the more will be reflected

Question 8

what is intensity reflection coefficient

Answer 8

the ratio of the intensity of the reflected wave relative to the incident wave

Question 9

what is a coupling medium

Answer 9

medium used to reduce the difference between z as air and skin have a very large difference

Question 10

what is attenuation of ultrasound matter

Answer 10

the reduction of energy due to the absorption of ultrasound as it travels through a material
- the greater the value the faster the rate of decay

Question 11

how are X-rays produced

Answer 11

-electrons are accelerated nu the accelerating p.d
- the target is hit through electron bombardment
- x-rays are produced when the energy of the electrons is converted into photons

Question 12

why do the x-rays produced have a continuous spectrum of energies

Answer 12

-electrons decelerate on hitting the target
- there are a range of decelerations
-photon energy depends on the magnitude of deceleration

Question 13

what are the two aims when treating patients

Answer 13

• reducing exposure
• contrast and sharpness

Question 14

how can exposure be reduced in x-rays

Answer 14

using aluminium filters to absorb longer wavelength x-rays since x-rays are ionsing patients should recieve minimum dosage

Question 15

what is contrast and how can it be improved

Answer 15

the difference in the degree of blackening
-using the correct level x-ray hardness, using a contrast media

Question 16

how does the difference in the linear attenuation coefficients of different tissues affect contrast

Answer 16

the larger the difference (assuming thickness is equal) the different the amounts absorbed so there would be good contrast

Question 17

what is sharpness and how can be improved

Answer 17

how well defined the edges of the structures are
- using a narrower beam, reduce x-ray scattering

Question 18

what does CT and CAT scanning

Answer 18

Computed tomography (CT)
Computerised Axial Tomography (CAT)

Question 19

main features of CT scanning

Answer 19

-X-ray tube rotates around the stationary patient
- CT scanner takes x-ray images of the same slice, at many different angles
- the process is repeated with the successive slices being combined together
- a computer pieces the images together to build a 3D images

Question 20

Advantages of CT scanning

Answer 20

-Detailed images
-produced a 3D image

Question 21

disadvantages of CT scanning

Answer 21

patient recieves a higher dose of x-ray
possible side effects from contrast media

Question 22

what is a radioactive tracer

Answer 22

A substance containing radioactive nuclei that is introduced to the body and can be absorbed by tissues in order to study the structure and function of organs in the body

Question 23

why are radioactive substances like flourine-18 suitable for this purpose

Answer 23

-they bind to organic molecules
-they emit gamma radiation and decay into stable isotopes
- they have short half-lifes

Question 24

what does PET stand for

Answer 24

Positron Emission Tomograpgy

Question 25

what is PET

Answer 25

a type of medical procedure that images tissues and organs by measuring the metabolic activity of the cells of body tissues

Question 26

what type of tracers are used in PET scanning

Answer 26

Tracers that decay by emitting a positron
-common tracer Fluorodeoxyglucose (FDG)w

Question 27

what are tracers used for?

Answer 27

Cancer diagnosis
heart/brain injuries
detecting areas of decreased blood flow

Question 28

what is Annihilation

Answer 28

when a particle meets its equivalent antiparticle they are both destroyed and their mass is converted into energy

Question 29

what is conserved during annihilation

Answer 29

mass, momentum, energy
-mass becomes pure energy in the form of two gamma rays that move in opposite directions

Question 30

Process of PET scanning

Answer 30

-tracer injected or swallowed into the body
-positrons are emitted by the decay of the tracer
- travels a short distance and annihilate with electrons in the tissue
-annihilation produces a pair of gamma-ray photons which travel on opposite directions

Question 31

how are images created in PET scanning

Answer 31

1.gamma-rays travel in straight lines in opposite directions from annihilation
2. they hit the detectors in line
3.many gamma-rays are emitted simultaneously
4. the more photons from a particular point, the more tracer that is present in that area
5. image created through using arrival times of the gamma-ray photons