Edelman Physics Ch 7-9

Time of Flight

The elapsed time from pulse creation to pulse reception is called 'time-of-flight' or the 'go-return time'

Range Equation

Depth = 1.54 x go-return time/2

Range

The distance from the transducer to an echo-generating structure

Speed of Sound in Soft Tissue

1.54 mm/µs is the average speed.

13 Microsecond Rule

Time-of-flight doubles as depth doubles.

PRP (Pulse Repetition Period)

Go-return time for one pulse cycle.

PRF (Pulse Repetition Frequency)

Inversely related to imaging depth.

Imaging Depth

Depth determined by PRP and time-of-flight.

Piezoelectric Effect

Voltage generated by mechanical deformation of materials.

Reverse Piezoelectric Effect

Material changes shape when voltage is applied.

PZT

Lead Zirconate Titanate, a piezoelectric material.

Acoustic Insulator

Reduces interference in transducer performance.

Matching Layer

Enhances sound transmission between transducer and tissue.

Backing Material

Dampens vibrations to improve image resolution.

Crystal/Active Element

Converts electrical energy to sound and vice versa.

Electrical Shield

Prevents electrical interference in transducer.

Reflector Depth Calculation

Depth = 0.77 x Time(µs) for soft tissue.

Speed Calculation Example

Speed = distance/time; 10 cm/2 sec = 5 cm/s.

Impedance Difference

Larger reflections occur with greater impedance differences.

Transducer Functions

Converts energy during transmission and reception.

PZT Impedance

Impedance is 20 times greater than skin.

Wave Reflection

Direct wave travel causes significant intensity reflection.

Matching Layer

Designed between PZT and skin to improve transmission.

Ultrasound Gel Impedance

Impedance lies between matching layer and skin.

Matching Layer Thickness

Thickness is 1/4 wavelength of sound in layer.

Backing Material

Essential for pulse creation in transducers.

Pulse Duration

Without backing, pulse length increases due to ringing.

Axial Resolution

Enhanced by limiting PZT ringing and shortening pulse.

Sound Absorption

Backing material has high sound absorption characteristics.

Acoustic Impedance

Impedance similar to PZT for effective transmission.

Sensitivity Decrease

Reduced crystal vibration affects signal reception quality.

Wide Bandwidth

Range between highest and lowest frequencies in pulse.

Resonant Frequency

Main frequency emitted, also called center frequency.

Natural Frequency

Another term for resonant frequency of transducer.

Vibration Restriction

Backing material limits PZT vibration, causing frequency variation.

Brake Pedal Analogy

Backing material restricts vibration like a brake pedal.

Bandwidth

Range of frequencies in ultrasound signals.

Narrow Bandwidth

Smaller range of frequencies utilized.

Wide Bandwidth

Larger range of frequencies utilized.

Quality Factor (Q-factor)

Main frequency divided by bandwidth, unitless.

Low-Q

Indicates low sensitivity and wide bandwidth.

High-Q

Indicates high sensitivity and narrow bandwidth.

Imaging Probes

Short pulse, wide bandwidth, low-Q characteristics.

Non-imaging Probes

Long pulse, narrow bandwidth, high-Q characteristics.

PZT

Ceramic material used in transducers.

Polarization

Creating piezoelectric properties via heat and electric field.

Curie Temperature

Temperature at which PZT is polarized.

Depolarization

Loss of piezoelectric properties when heated above Curie.

Sterilization

Destruction of all microorganisms using heat or chemicals.

Disinfection

Reduction of infectious organisms on an object.

Cleaning Protocols

Use CidexTM for disinfection, avoid extreme temperatures.

Continuous Wave Frequency

Electrical frequency equals acoustic frequency in CW mode.

Pulsed Wave Frequency

Short electrical spike excites the crystal.

PZT Speed

Directly related to frequency; faster equals higher frequency.

PZT Thickness

Inversely related to frequency; thinner equals higher frequency.

High Frequency PW Probes

Thinner PZT crystals with higher speeds.

Low Frequency PW Probes

Thicker PZT crystals with lower speeds.

Sound Beam Focus

Narrowest beam diameter location in ultrasound.

Near Zone (Fresnel Zone)

Region from transducer to focus in ultrasound.

Far Zone

Region where sound beam diverges after focus.

Fraunhofer Zone

Another term for Far Zone in acoustics.

Focal Zone

Area around focus with narrow beam.

Focal Length

Distance from transducer to focus point.

Focal Depth

Distance from transducer to focal point.

Transducer Diameter

Size of the crystal affecting focal depth.

Frequency of Sound

Rate of sound wave oscillation impacting focus.

Beam Divergence

Gradual spread of beam in far field.

Shallow Focus

Focus achieved with smaller diameter and lower frequency.

Deep Focus

Focus achieved with larger diameter and higher frequency.

Less Divergence

Occurs with larger diameter and higher frequency.

More Divergence

Occurs with smaller diameter and lower frequency.

Diffraction Pattern

V-shaped divergence from small sound sources.

Huygen's Principle

Large element acts as many tiny sound sources.

Constructive Interference

Waveforms combine to enhance sound intensity.

Destructive Interference

Waveforms combine to reduce sound intensity.

Lateral Resolution

Ability to distinguish two structures side by side.

Clinical Dilemma

High frequency probes provide shallow focus imaging.

Active Element

Part of transducer that generates sound waves.

Sound Beam Shape

Influenced by crystal size and frequency.

High Frequency Crystals

Used for shallow focus in imaging.