Medical Imaging (C27)

Question 1

How do you produce x-rays

Answer 1

thermionic emission of electron
electron is accelerated
hit target metal and emit photons

Question 2

max energy of x-ray photon =

Answer 2

max KE of electron

Question 3

define attenuation

Answer 3

decrease in intensity as EM radiation passes through matter

Question 4

4 possibilities when an x-ray collides with an atom

Answer 4

simple scatter
Photoelectric effect
Compton scattering
Pair production

Question 5

What is Compton scattering

Answer 5

Incident X-ray collides with electron and removes it and a lower energy EM photon is also emitted

Question 6

Why is simple scatter bad for hospitals

Answer 6

Creates blurriness

Question 7

What is a CAT scan in simple terms

Answer 7

3D X-ray

Question 8

Describe a cat scan

Answer 8

360 rotation
X-ray
Computer stitches together images

Question 9

Advantage of a CAT scan

Answer 9

allows you to determine foreground and background

Question 10

What does PET stand for

Answer 10

Positron emission Tomography

Question 11

How does PET work

Answer 11

Uses a beta plus source
emitted positron annihilates with electron giving off antiparallel gamma rays
these are recorded and time delay can be used to find location.

Question 12

How does the scanner work in PET

Answer 12

Incident photon hits scintillator (which amplifies signal) and then photomultiplier produces a voltage

Question 13

Advantages of PET scanning

Answer 13

Non-invasive

Can see where respiration is occurring

Question 14

disadvantages of PET scanning

Answer 14

very expensive

high radiation dose

Question 15

What device is used in PET

Answer 15

radiopharmaceutical or medical tracer

Question 16

what method of medical imaging is non-invasive and non-ionising

Answer 16

ultrasound

Question 17

What is the name of the device that makes and receives ultrasound

Answer 17

transducer

Question 18

What is the piezoelectric effect

Answer 18

Crystals that change shape under voltage (or the reverse)

Question 19

How does a transducer make ultrasound

Answer 19

alternating p.d. causing crystal to vibrate via the piezoelectric effect

Question 20

What is an A-scan

Answer 20

records ultrasound reflections in a line

Question 21

What is a B-scan

Answer 21

Creates 2d images by plotting intensity as brightness

Question 22

what is Z

Answer 22

acoustic impedance

Question 23

what is acoustic impedence

Answer 23

a material propety that affects how much sound is reflected and refracted

Question 24

what must be true to get a small proportion reflected

Answer 24

z1 ~ z2

Question 25

What is used in ultrasound

Answer 25

coupling gel

Question 26

why is a coupling gel used

Answer 26

ensures acoustic matching which reduces reflection

Question 27

What can be said between the air skin boundary compared to the skin gel boundary

Answer 27

there is impedance matching in the skin gel, whereas almost all the sound would be reflected at the air skin

Question 28

What is the intensity reflection coeffecient

Answer 28

ratio of the reflected to the initial intensities

Question 29

what effect is used to measure blood flow

Answer 29

doppler effect

Question 30

what happens to the frequency if the blood is moving towards the transducer

Answer 30

the frequency is high, the wavelength is lower

Question 31

what happens to the ultrasound if the blood is moving away

Answer 31

the frequency lowers the wavelength is larger

Question 32

what does a blood flow scan look like

Answer 32

different colours for different directions

Question 33

What medical tracer is used in PET

Answer 33

Fluorine 18 attached to fluorodeoxyglucose (FDG)

Question 34

what tracer is used in the gamma camera

Answer 34

Technetium-99m (Tc-99m)

Question 35

half life of Tc-99m

Answer 35

6 hours

Question 36

What does tc-99m emit

Answer 36

gamma radiation

Question 37

What is a key advantage of Tc-99m as a tracer

Answer 37

decays into a stable isotope

Question 38

Five key parts of a gamma camera

Answer 38

``` Source in organ collimator scintillator photomultiplier computer ```

Question 39

What is a collimator

Answer 39

long thin lead tubes

Question 40

what does a scintillator do

Answer 40

turns gamma photon into many visible photons

Question 41

What does a photomultiplier do

Answer 41

turns photon into an electric pulse

Question 42

Why does a gamma camera use a collimator

Answer 42

means only radiation travelling along axis of lead tubes is recorded, giving a clear image

Question 43

What is a gamma camera used for

Answer 43

Used to measure the function of organs like the kidney