##### Chapter 2 Ultrasound - Notes 2

Incident beam

starting beam

Reflected beam

after the incident beam hits a border part of the beam is reflected back

transmitted beam

after the incident beam hits a border part of the beam is transmitted through the next medium

Reflected angle

the angle in which the beam is reflected back

reflected angle = incident angle

What does the intensity of the reflected beam depend on?

incident beam

impedance formula

impedance = density * speed

Impedance

resistance to sound traveling through the medium.

What is likely when turning up output gain?

tissue damage

impedance symbol

z

Impedance units

rayl

What is the relationship between impedance and propagation speed?

directly

What is the relationship between impedance and density?

directly

IRC

% of the beam that is reflected back to the transducer

IRC formula 1

IRC = Reflected Intensity/ Incident Intensity

IRC - Ri/Ii

IRC formula 2

[(z2 - z1) / (z2 + z1)] squared

ITC

% of the beam that is transmitted through the medium

ITC formula 2

ITC = Transmitted Intensity/ Incident Intensity

ITC - Ti/Ii

IRC + ITC =

A) 0%

B) 1%

C) 1

D) 0 dB

E) 10 dB

C) 1

other names for 90 degrees

perpendicular

orthogonal

right angle

Normal

Impedance relationship with IRC

direct

Bone will always appear _________ due to high impedance mismatch

A) brighter

B) darker

A) brighter

Refraction

change of direction of the sound wave as it passes from one medium to another.

Refraction transmission angle

angle of transmission depends on change in propagation speed that exists between two media

Snells law

Sine i/ sine r = speed i / speed r

Snell's law 2

(New c / old c) * old angle = new angle

Is the angle higher or lower if the new speed is slower?

lower

Specular Reflections

when sound waves hit a large smooth surface at 90 degrees

bladder and vessels

Diffusion

boundary is not smooth

boundary smaller than the wavelength.

Light gets scattered (random and disorganized)

Scattering

non-specular reflection occurs at small, irregular of rough interfaces

It is not angle dependent

Relationship between frequency and scatter

directly related

Positive effects of scattering

scattering makes echo reception less dependent on incident angle

allows visualization of boundaries which specular reflection angle would miss

Effects of scatter

Two waves arriving at the same time either reinforce of cancel each other.

Negative effects of scattering

grainy images

Range equation

d = 1/2 ct

Distance can not be measured but time can if speed is known

How machine places image

How long will it take for u/s to detect a mass at a depth of 1 cm?

13 cm

More Amplitude

brighter dot.