Imaging

Question 1

how do X-rays work?

Answer 1

• current passed through a tungsten cathode for a known period of time
• potential difference between cathode and anode measured
• anode receives e- from cathode (current)
• e- leave through opening to be absorbed by tissue

Question 2

what does increasing X-ray current do? what is the downside to this?

Answer 2

• increase number of e- leaving machine
• increase X-ray quantity
• increases image contrast
• greater X-ray quantity means patient should be exposed to a fewer number of images

Question 3

what does increasing potential difference in an X-ray do? when may it be used?

Answer 3

• increases speed of e- leaving X-ray
• increases energy of e- at impact with target
• beam becomes more penetrating
• reduces contrast as the beams can penetrate more tissue types
• used in larger animals

Question 4

what is X-ray film made of? how does it work?

Answer 4

• clear plastic base coated with thin gelatin emulsion containing AgBr
• x-rays which penetrate soft tissue hit AgBr and e- exchanged from Br- to Ag+
• black metallic silver ppt produced
• film rinsed, fixed, washed and dried in dark room to wash off emulsion without ppt
• ppt shows up as black and (washed off emulsion shows up as white under light box)

Question 5

what do intensifying screens do? why do we use them?

Answer 5

• placed either side of digital films
• produce light when x-rays pass through them –> light interacts with film (produces ppt)
• allow shorter exposure times (fewer x-rays needed to produce ppt) –> reduce motion blur from breathing etc

Question 6

what can we use to reduce motion blur of x-rays? how do they work?

Answer 6

• grids
• block any x-rays which aren’t incident at 90° (perpendicular to the film)

Question 7

list the following from radio opaque to radiolucent:
- fat
- bone
- metal
- soft tissue
- gas
- fluid

Answer 7

• metal
• bone
• soft tissue + fluid
• fat
• gas

Question 8

what is underexposure? what causes it?

Answer 8

• image too white
• mA too low (not enough e- creating ppt)

Question 9

what is overexposure? what causes it?

Answer 9

• image too black
• mA too high (too many e- creating ppt)

Question 10

what does ultrasound record?

Answer 10

time lag between release and detection of high frequency sound being reflected (as opposed to transmitted like in x-rays)

Question 11

what creates the high frequency sound in ultrasound?

Answer 11

voltage applied to piezoelectric crystals which cause vibration

Question 12

what do piezoelectric crystals do?

Answer 12

convert vibrations (kinetic energy) into voltage (electrical energy) and vice versa

Question 13

where does most clear reflection of high frequency sound waves occur? why is this useful?

Answer 13

• interfaces between soft tissue
• useful because soft tissue and fluids are indistinguishable on radiographs but not ultrasound

Question 14

echogenic/hyperechoic

Answer 14

produce lots of reflections of ultrasound

Question 15

echopoor/hypoechoic

Answer 15

produce few reflections of ultrasound

Question 16

anechoic

Answer 16

doesn’t reflect ultrasound at all

Question 17

modes of ultrasound

Answer 17

• A-mode
• B-mode
• M-mode
• Doppler

Question 18

what are the two types of B-mode ultrasound?

Answer 18

• linear array
• sector array

Question 19

what is linear array ultrasound? what use is it good for?

Answer 19

• row of many piezoelectric crystals
• generates rectangular image
• good for rectal ultrasounds in larger animals

Question 20

what is sector array ultrasound?

Answer 20

• probe scanned across a field of view many times a second
• 2D sector-shaped image
• single point of contact/”steerable”

Question 21

A-mode ultrasound

Answer 21

plotting echoes on a graph of intensity against distance

Question 22

B-mode ultrasound

Answer 22

echoes represented as segments of a line (high intensity shows white, low intensity shows black)

Question 23

M-mode ultrasound

Answer 23

one B-mode line graphed over time

Question 24

doppler ultrasound

Answer 24

frequency increases or decreases when moving towards or away

Question 25

what is a CT scan? what type of image does it produce?

Answer 25

- x-ray head and detector rotate around patient - creates a 3D cross-sectional image

Question 26

what types of images do MRIs create?

Answer 26

cross-sectional images

Question 27

what waves do MRIs use?

Answer 27

radiowaves

Question 28

what does MRI stand for?

Answer 28

magnetic resonance imaging

Question 29

what does CT stand for?

Answer 29

computer tomography

Question 30

what does PET stand for?

Answer 30

positron electron tomography

Question 31

what is used in PET scans? what do they emit? what do the emissions do?

Answer 31

- short-lived radioisotopes (injected into patient) - emit positrons - positrons annihilate e- in patient's body to release y-waves (detected by surrounding detectors)

Question 32

what are PET scans usually used to detect?

Answer 32

areas of high metabolism e.g. tumours using glucose tracers

Question 33

what images do PET scans produce?

Answer 33

3D images

Question 35

what is scintigraphy? what images does it produce?

Answer 35

- radioisotopes injected into patient like in PET scans - generate 2D images