SPI ULTRASOUND REGISTRY REVIEW

SPL

Defined as the product of the wavelength and the number of cycles in a pulse

Phased Array Transducers

Transmitted sound beam is steered by varying the timing of pulses to individual piezoelectric elements

Type of Sound Wave

Mechanical and longitudinal

Frequency Ranges for Ultrasound

> 20,000 Hz (20kHz)

Speed of Sound in Soft Tissue

1540 m/s

Linear Sequence Array

Transducer that fires the elements in groups

Unit for Wavelength

Millimeters

Enhancement Caused by

Weakly attenuating structures (such as a cyst)

Wavelength Calculation

0.3 mm Wavelength= c/f = 1.5mm/us ÷ 5MHz = 0.3mm

Ultrasound Transducer Conversion

Converts electrical energy into mechanical energy and vice versa

Order of Attenuation:

Fat, Muscle, Bone, Air

Propagation Speed Order:

Air, Fat, Muscle, Bone

Frequency Doubling Effect on Wavelength:

Decrease by one half/ Frequency and wavelength are inversely related

Amplitude Halving Effect on Intensity:

Quarted/ Intensity is proportional to the amplitude squared

Definition of Duty Factor:

Percentage of time sound is transmitted

3dB Gain Intensity Increase:

2 times (A gain of 3dB results in doubling of intensity)

Reason for Higher Intensity at Focal Zone:

Smaller beam diameter

Attenuation Definition:

Weakening of beam strength from absorption, reflection, or scattering

SATA Intensity Level:

Lowest intensity

Beam Uniformity Ratio Formula:

BUR= SP/SA

Continuous Wave Doppler Duty Factor

100%

SPTP Intensity Level

Highest

Unit for Impedance

Rayl

ALARA Acronym

As Low As Reasonably Achievable

Snell's Law Description

Refraction at an Interface

Matching Layer Function

Enhances Sound Energy Transmission

Quality Factor Formula

Operating Frequency divided by Bandwidth

Spatial Resolution Definition

Ability to Discern Individual Reflectors

Infrasound Frequency Range

Less than 20 Hz

Unit for Pressure Amplitude

Pascual (Pa)

W/cm2

Unit for Intensity

Pulse Repetition Frequency

Number of Pulses Per Second

Spatial Pulse Length (SPL)

Distance a Pulse Occupies in Space

Hydrophone

Used to Test Output Intensity

Huygen's Principle

Waves Result from Interference of Wavelets

A-mode

Reflector Amplitude along Y-axis

B-mode

Brightness Mode in Z-axis of Image

Axial Resolution Determined by

Spatial Pulse Length

Improve Axial Resolution

Decrease Pulse Cycles or Increase Frequency

Phased Array Transducers Beam Steering

Varying Timing of Pulses to Elements

New Gain with Power Reduced by Half

15 dB

Effect of Tripling Amplitude on Power

Increased Ninefold

Ultrasound Attenuation Rate

0.7 dB/cm/MHz

Intensity Reflection Coefficient with ITC of 0.74

0.26

Definition of Acoustic Impedance

Speed of Sound in Tissue x Tissue Density

Example of Rayleigh Scattering

Reflector Smaller than Wavelength

Impedance Matching Result

100% Intensity Transmission

Total Attenuation of 3.5 MHz Pulse in Soft Tissue

3.5 dB after 2 cm

Relationship Between Piezoelectric Element Thickness and Frequency

Thinner Element = Higher Frequency

Purpose of Decibel (dB)

Describes Ratio of Sound Intensities

Range Equation Explanation

Distance to Reflector

Intensity Transmission Coefficient (ITC)

1 - Intensity Reflection Coefficient

Attenuation Coefficient in Soft Tissue

Frequency/2

Attenuation Coefficient for 6MHz Ultrasound in Soft Tissue

3 dB/cm

Calculation of Distance to Reflector

Requires Travel Time and Propagation Speed

Specular Reflections

Occur with Interface Larger than Wavelength

Matching Layer in Transducer

Intermediate Impedance between Transducer Element and Tissue

Bandwidth and Operating Frequency Relationship

Quality Factor

Piezoelectric Effect Description

Mechanical Deformation from High Voltage Generating Pressure Wave

Common Material in Ultrasound Transducers

Lead Zirconate Titanate

Diffraction

Spreading out of the ultrasound beam

Sterilization Method for Transducers

Cold sterilization

Transducer Frequency for Thickest Element(s)

2 MHz

Spatial Resolution

Ability to discern two closely spaced reflectors as individual reflectors

Focusing Improves

Lateral resolution

Bandwidth

Range of frequencies produced by the transducer

Effect of Decreasing Wavelength

Increase frequency, decrease divergence in the far field

Acoustic Impedance of Matching Layer

Chosen to improve transmission into the body

Effect of Decreasing Damping on Bandwidth

Decreases

Region Where Sound Beam is Smallest

Focus

Near Zone Length Determination

Transducer Frequency

Transducer Type with Concentric Rings

Annular Array

Curved Shape Transducer

Curvilinear

Echo Storage Control

Scan Converter

Attenuation Compensation Control

TGC

Transducer Driving Component

Pulser

Digital-to-Analog Converter Location

Scan Converter

Human Eye Shades of Gray Perception

100

Shades of Gray in Current Ultrasound Systems

256

Bits per Pixel with 4 Bits of Memory

16

Main Factors Affecting Spatial Resolution

Transducer

Purpose of Preprocessing in Scan Converter

Determines Echo Assignment to Gray Levels

Signal Dynamic Range Reduction in Grayscale Systems

Compression

Effect of Increasing Compression

Reduction in Dynamic Range

Unit for Area Measurement

cm2

Relationship Between Transducer Frequency and Wavelength

Inverse Relationship

Advantage of Tissue Harmonic Imaging

Decreased Near Field Artifacts

Frequency Range of Audible Sound

20 to 20,000 Hz

Operator-Adjustable Parameter

Pulse Repetition Frequency

Adjustment of Pulse Repetition Frequency

Depth Control

Time for One Cycle:

Period

Length of Pulse:

Spatial Pulse Length

Propagation Speed Determined by:

The Medium

Slowest Propagation Speed in:

Air

Beam Strength:

Intensity

Pressure Amplitude Unit:

Pascal

Intensity Unit:

W/cm2

Change in Amplitude Affects:

Output Power

Increased Acoustic Exposure

increased output gain

Output Gain Impact

increases exposure to the patient