Physics

Question 1

How is sound loudness measured?

Answer 1

In decibels which has a logarithmic relationship to amplitude

I.e. dB = 20 log (V/R)

V represents acoustic pressure and R a reference value

Question 2

Wavelength calculation

Answer 2

Speed of sound in blood (1540m/s)
= wavelength x frequency

Therefore frequency of 5MHz has a wavelength if 0.31mm

Question 3

What is the maximum depth of ultrasound?

Answer 3

Maximum depth is approximately 200 wavelengths
E.g. 0.31mm wavelength has 6cm max depth

Question 4

Blood velocity calculation

Answer 4

Doppler equation

V = c (Frequency change) / 2 x transducer frequency x cos (theta)

C = speed of sound in blood 1540m/s
Transducer freq = 1-5MHz
Theta = angle between jet and US beam

Question 5

Parasternal short axis mitral valve assessment

Answer 5

• Can clearly see the valve cusps
• Also allows for clear visualisation of any eccentric jets as they are often away or towards the transducer

Question 6

Acoustic impedance calculation

Answer 6

= tissue density x propagation velocity through that tissue

Question 7

DP/DT equation

Answer 7

Modified Bernoulli equation

4 ( V1^2 - V1^2) / Dt

BUT because it is the time from 1m/s to 3 m/s every time
4x (3x3-1x1) / Dt = 32 / Dt

Question 8

Calculate LVEDP from AR jet and blood pressure

Answer 8

Max velocity AR can be used in a Bernoulli equation to calculate pressure gradient across the AV.

4 x (AR Vmax ^2) = gradient across AV

Diastolic blood pressure - gradient across AV = LVEDP

Question 9

PISA equation

Answer 9

2 x pi x r^2 = surface area of PISA

Question 10

Maximum instantaneous regurgitation flow equation

Answer 10

PISA surface area x aliasing velocity

Question 11

Mitral valve area calculations

Answer 11

Simple method: 220 / PHT = MVA

Continuity equation
Stroke volume (e.g. RVOT area x RVOT VTI) / MV VTI = MVA