Cross-Sectional Imaging (Lamb)

Question 1

Properties of a piezoelectric crystal?

Answer 1

• change of shape initated by change in voltage, and change in voltage causes change of shape of the crystal
• so echo of “ping” can be transduced by same crystal that initiated it
• time this
• D=V*(t/2)

Question 2

How does the normal spleen and liver appear on ultrasound?

Answer 2

• liver hypoechoic

- spleen hyperechoic (produces more echoes)

Question 3

What factors influence echogenicity?

Answer 3

> increase/hyperechoic 
- fat
- glycogen
- collagen
- vascularity
- crystalline material 
> decrease/hypoechoic
- oedema

Question 4

3 main types of probe and their uses?

Answer 4

> linear
- flat eg. horses tendons
> sector
- heart (fans out so large range of view through small gap) 
> curvilinear
- best of both worlds 
- abdo

Question 5

What frequencies are necesary for small, superficial body parts? What is frequency measured in? Range of frequencies used?

Answer 5

• high frequency
• MHz
• Equine heart 2.5MHz - 13MHz

Question 6

Where is the controlled area for CT and MRI?

Answer 6

> CT = radiograph machine
- controlled area is teh room, but only when switched ON 
> MRI 
- always switched on
- access ALWAYS controlled

Question 7

How do grey and white mater appear on MRI?

Answer 7

Grey is white, white is grey

Question 8

What is CT digital matrix brightness measured in?

Answer 8

Hounsfield number

• darker = lower number
• measure of the attentuation of xrays compared to water (water = 0)
• if absorb less than water = negative

Question 9

What is narrow window and wide window CT?

Answer 9

> narrow window
- high contrast
- distinguish soft tissues
> wide window
- low contrast
- bone detail

Question 10

Outline MRI

Answer 10

• strong magnet aligned hydrogen nuclei
• these themselves create their own mini-magnetic fields -> net force created
• apply different magnetci fields to this
• nuclei align to new magnetic field
• as they move back, they release a radiowave
• tune the frequency of the transmitter to he frequency of hydrogen ions

Question 11

How do T1 and T2 weighting differ?

Answer 11

> T1
- high signal: Fat
- soft tissues
- water
- low signal: air, cortical bone 
> T2
- high signal: water
- soft tissue signal changes slightly

Question 12

What is sound?

Answer 12

• mechanical energy transmitted through a medium as a longitudinal wave (Compression and rarefaction)
• objects smaller than the ultrasound Wavelength cannot be detected so short wavelength required for small objects