Metric System and Diagnostic Ultrasound Graphs

Metric System

• The prefixes for powers of ten:
• Giga (G): 10^9 (Billion)
• Mega (M): 10^6 (Million)
• Kilo (k): 10^3 (Thousand)
• Hecto (h): 10^2 (Hundred)
• Deca (da): 10^1 (Ten)
• Deci (d): 10^-1 (Tenth)
• Centi (c): 10^-2 (Hundredth)
• Milli (m): 10^-3 (Thousandth)
• Micro (µ): 10^-6 (Millionth)
• Nano (n): 10^-9 (Billionth)

Complimentary Metric System

• Billions and billionths use the prefixes giga and nano, abbreviated as G & n.
• Millions and millionths use the prefixes mega and micro, abbreviated as M & µ.
• Thousands and thousandths use the prefixes kilo and milli, abbreviated as k & m.
• Hundreds and hundredths use the prefixes hecto and centi, abbreviated as h & c.
• Tens and tenths use the prefixes deca and deci, abbreviated as da & d.

Graphs

• Information in diagnostic ultrasound is displayed in graphical form.
• Graphs have two axes:
• Vertical axis (y-axis) displays depth and runs up and down.
• Horizontal axis (x-axis) displays time and runs side to side.

Acoustic Variables

• Acoustic variables:
• Pressure is measured in Pascals (Pa).
• Density is measured in Kg/cm³.
• Distance is measured in cm or mm.

Seven Acoustic Parameters

• The seven acoustic parameters are period, amplitude, power, intensity, wavelength, propagation speed and frequency.

Frequencies

• Infrasound has a frequency less than 20 Hz.
• Audible Sound has a frequency between 20 Hz and 20 kHz.
• Ultrasound has a frequency greater than 20 kHz.

Speed of Sound in Different Materials

• Air: 330 m/s
• Water: 1,480 m/s
• Metals: 2,000 to 7,000 m/s

In-Phase Waves & Constructive Interference

• In-phase waves have their peaks (maximum values) and minimum values occurring at the same time and location.
• Constructive interference occurs when in-phase waves combine to form a single wave with a greater amplitude than the original waves.

Out-of-Phase Waves & Destructive Interference

• Out-of-phase waves have their peaks and troughs occurring at different times.
• Destructive interference occurs when out-of-phase waves combine to form a single wave with a lesser amplitude than the components.

Sound

• Sound is made up of areas of compression (squeezed together)
• Sound is made up of rarefaction (stretched apart) of vibrating molecules.
• Areas of compression have high density and high pressure.
• Areas of rarefaction have low density and low pressure.

Frequency Spectrum of Sound

• The bigness parameters are Amplitude, Power and Intensity
• These parameters describe the size, or magnitude, or strength of sound wave.
• Infrasound has a frequency less than 20 Hz.
• Audible Sound has a frequency between 20 Hz and 20 kHz.
• Ultrasound has a frequency greater than 20 kHz.

Cycle

• A cycle is one complete variation in pressure or other acoustic variable (compression and rarefaction).

Period and Frequency

• Period measured as the time it takes a wave to vibrate a single cycle to occur, or the time from the start of a cycle to the start of the next cycle.
• Frequency is the number of cycles in a wave that occur in 1 second.

Amplitude

• Amplitude is the "bigness" of a wave.
• The difference between the maximum value and the average or undisturbed value of an acoustic variable.
• The difference between the minimum value of the acoustic variable.
• Peak-to-Peak Amplitude is the difference between maximum and minimum values of an acoustic variable.

Power

• The rate of energy transfer/the rate at which work is performed.
• Like amplitude, describes the "bigness" of a wave.
• Measured in Watts.

Intensity

• The concentration of energy in a sound beam.
• Like power and amplitude, describes the "bigness" of a wave.
• Relates to how the power in a wave spreads or is distributed in space.
• Depends on both, the power in the beam and the area over which the power is applied.

Propagation Speed

• Propagation speed is the distance that a sound wave travels through a medium in 1 second.
• Speed is determined only by the medium through which the sound is traveling.
• Speed is not affected by the nature of the sound wave.
• Propagation speed= frequency x wavelength

Stiffness & Density

• Stiffness describes the ability of an object to resist compression.
• Stiffness and speed are directly related.
• Elasticity or compressibility describes stiffness.
• Density describes the relative weight of a material; density and speed are inversely related.
• Speed is determined by density and stiffness of the medium.
• Stiffness increased = speed increase.
• Density increase = speed decrease.

Parameters That Describe Sound Waves

• All determined by the source - Period Frequency
• Cannot be changed by sonographer - Period Frequency
• Reciprocals - Period Frequency
• Can be change by sonographer - Amplitude Power Intensity
• Determined by medium - Speed
• Determined by both: Source and Medium – Wavelength

Tissue Type

• Lung - 500 m/s
• Fat - 1,450 m/s
• Soft Tissue (average) -1,540 m/s
• Liver - 1,560 m/s
• Blood - 1,560 m/s
• Muscle - 1,600 m/s
• Tendon - 1,700 m/s
• Bone - 3,500 m/s
• Air - 330 m/s
• Water - 1,480 m/s
• Metals - 2,000 to 7,000 m/s

Parameters for Continuous Wave

• Period - Adjustable No - measure in Seconds, μs, time - Determined by Source-Typical Value 0.1 to 0.5 μs
• Frequency - Adjustable No - measure Per second, Hz - Determined by Source - Typical Value 2 to 10 Mhz
• Amplitude - Adjustable Yes - measure Pascals, cm, g/cm 3, dB - Determined by Source-Typical Value 1 Mpa to 3 Mpa
• Power - Adjustable Yes - measure in Watts - Determined by Source - Typical Value 4 to 90 mw
• Intensity- Adjustable Yes - measure in Watts/cm2 - Determined by Source - Typical Value 0.01 to 300 w/cm 2
• Wavelength -Adjustable No - measure in mm, distance - Determined by Both -Typical Value 0.15 to 0.8 mm
• Speed - Adjustable No - measure in m/s - Determined by Medium - Typical Value 1,500 to 1,600 m/s

Units of:

• Wavelength - Millimeters
• Frequency - Hertz
• Intensity- Watts/cm2
• Propagation speed - Meters/second
• Period - Second
• Power - Watts

Determined by Source

• Wavelength - Both
• Frequency - Sound source
• Intensity (initial) - Sound source
• Propagation speed - Medium
• Period - Sound source
• Power (initial) - Sound source
• Amplitude (initial) - Sound source

Operator Cannot Change?

• Wavelength - Cannot
• Frequency - Cannot
• Intensity - Can
• Propagation speed - Cannot
• Period - Cannot
• Power - Can
• Amplitude (initial) - Can

Parameters How Related

• Frequency and period - Inversely
• Amplitude and power - Directly
• Amplitude and intensity - Directly
• Power and intensity - Directly
• Wavelength and intensity - Unrelated
• Wavelength and frequency - Inversely
• Acoustic velocity and density - Inversely
• Elasticity and speed of sound - Inversely
• Acoustic velocity and compressibility - Inversely
• Stiffness and sound speed - Directly
• Frequency and sound speed - Unrelated
• Frequency and intensity - Unrelated
• Power and frequency - Unrelated

Pulsed Waves

• In addition to the seven parameters that describe continuous waves, new terms and their definitions must be added to our vocabulary with pulsed waves.

Five Parameters Describe Pulsed Sound

• Pulse Duration - µs
• Spatial Pulse Length - mm
• Pulse Repetition Period
• Duty Factor - %
• Pulse Repetition Frequency - Hz

Pulse Duration

• The TIME from the START of the PULSE to the END of the PULSE.
• Pulse duration (μs) = # cycles x period (µs)
• Determined by the source, and cannot be adjusted.

Spatial Pulse Length

• The LENGTH or DISTANCE that a PULSE occupies in space.
• SPL IS DIRECTLY PROPORTIONAL TO WAVELENGTH (LONGER WAVELENGTH, LONGER SPL)
• Spatial pulse length (mm) = # cycles x wavelength (mm)
• Determined by the source & MEDIUM, and cannot be adjusted

Pulse Repetition Period

• The TIME from the START of one pulse to the START of the next pulse.
• Can Be Adjusted
• Use your depth button to adjust your PRP!

Pulse Repetition Period & Depth

• Increase the DEPTH, INCREASE the TIME

Pulse Repetition Frequency

• Number of PULSES that an ultrasound system transmits into the body EACH SECOND.
• Meaning, how often the PULSE can be REPEATED!
• THE MORE SHALLOW YOU ARE THE MORE FREQUENT THE PULSE CAN BE REPEATED (LESS LISTENING TIME)
• THE DEEPER YOU ARE THE LESS FREQUENT THE PULSE CAN BE REPEATED (LONGER LISTENING TIME)

Duty Factor

• Duty Factor is the percentage or fraction of time that the ultrasound machine is producing a pulse or transmitting sound.

• Maximum value = 1.0 or 100 % (CW) is the percentage or fraction of time

• Minimum value = 0.0 or 0% (machine off), of course no fraction is the duty

• Units of measurements: unitless, no fractions

• Duty factor (%) = pulse duration (sec) x 100 / PRP (sec)

• Clinical imaging duty factor ranges = 0.002 to 0.005 (0.2% to 0.5 % )

Intensities Definitions

• Spatial: refers to distance or space; an ultrasound beam intensity varies at different locations.
• Peak: the maximum value.
• Average: the mathematical middle value.
• Temporal: refers to all time, transmit (pulse duration) and receive; a pulsed ultrasound beam's intensity varies at different times.
• Pulsed: refers only to the transmit time; for pulsed ultrasound, it's the average intensity for the pulse duration only (ignore listening time).

Intensities peak average temporal

• Temporal Peak Intensities is the maximum value.
• Imax : is derived from the most intense half cycle in the pulse (shade green area).
• Pulse Average Intensity (blue) is measured during the transmit only.
• Temporal Average (red) is measured during both the transmit and receive times.

Ten Commandments of Intensity

• Intensities may be reported in various ways respect to time and space. SP/SA FACTOR is unitless, with a value of 1 or greater.

Duty Factor is a unitless number with a value between 0 and 1.

SPTA intensity is the most relevant intensity with respect to tissue heating.

All intensities have units of watts/cm2.

For continuous wave ultrasound, the beam is always “on” and both types of Average intensities are the same.

SAPA, SA TA=SAPA.

Temporal considerations: Temporal Peak Intensity (Itp) is maximum in time.

Im Intensity is average over the most intense half-cycle.

Pulse Average Intensity (Ipa) is averaged only during the pulse duration (“on” time only).

• When pulsed and continuous wave sound beams have the higher SPTA intensity.

• and beams have SATA intensity Temporal Average Intensity (Ita) is average during the PRP (both the “on” and “off” times).

• Spatial considerations:Spatial Peak Intensity (Isp) is the maximum space.

• Spatial Average Intensity, (Isa) is average over the cross-sectional area of the beam.

Methods For Measuring Intensity SPTP, SPPA the largest to smallest are (spatial peak, temporal peak). SPPA,SPTA,SAPA,SATA,SATA.

Decibels

• 3 dB double
• 10 dB ten times larger
• 3 dB Half
• 10 dB One - tenth

Attenuation

• Reflection,scattering,absorption - Sound energy is where by extracted From A wave by Sound waves weaken as they propagate in a medium. decrease in intensity, power, and amplitude as sound travels is called attenuation.

Attenuation Average Attenuation in Soft Tissue: 5dB cm-1 ,mhz1

-dB, measured , db negative due to a

• Signal strength measured Attenuation = Frequency & travel Distance

Attenuation, Half Value Layer And Impedance

More Attenuation -longer distance Short Distance

High Acoustic Frequency; Long wavelength - Low Frequency Short wavelength

Half Value - Impedance

• Tissue Thickness is is the measure for High acoustic values
• Thin with the thin half value Attenuation coefficient (dB/cm)= frequency
• Attenuation coefficient (dB/cm) = Frequency / cm
• Rayis= Density * Propagation Speed (Density * speed)
• Incident Intensity = reflected Intensity + transmitted intensity

Three Components of a Sound Beam

• Reflection is the sound energy extracted
• Scattering Scattering
• Absorption Organized.

Attenuation Of Ultrasound In Media

Different for

• High value High frequency Sound, Short Distance Short Wavelength Thin

Normal Incidence Normal Incidence - sound beam strikes an incidence. The Boundary strikes with the incidence Ninety degrees angle, Any beam outside the boundary strikes the oblique Incidence

Snell's Law described the physics of refraction

• Micro Second Rule- Go Return the Time

• Time Of-Flight

• Time-of-Flight or Go – Return Time It depends on how fast the body is moving, Body moves in the machine will

Determines the Depth and Length of Image

For example: (go return time or time of flight) in 5ms

Note: Pulse repetition period

 Is  the  how images are formed during  a body examination

• PRF(HZ) –Depth and imaging

• cm/ Depth

Tranascuders

• Different Types of transducers
• It should be imaging or non imaging

PZT Material - half wave Matching Layer - wave Lengths wave

Frequency = is the one Speed of Sound in Pzt(mm , μs/per length) /mm 2 thickness

Quality - main frequency - Electrical - acoustic wave that is formed in Transducers

Mechanical and The crystal elements form soundwaves

Each component - Has crystal layers with different measurements, such as width, length and radius etc.

Near zone has a small region, where as farzone has large region

• Focal region with

• Near region with

• length Region

• The Beam Has, Near far

• Huygens Principe 2 The shape explains an emitted sound wave, in imaging transducers, based around in/ out phase and the interference between the transducers crystal, sound wave.

Axial and larteral resolution, they are both The two objects are both shown

Supieror excelence has 3

axial Excellent space. The speed decreases with less ringing. In the process of lower electrical activity

(mm) Space /

• is called- LARRD / Angular
• is called- LATA the side view with

Methods For focusing

3 different ways of focusing

• 3 with lens is called External - FIXED
• Curves that are internal and fixed
• and are in-Adjustablr that is the last mode The three Basic Modes of Display
• or

Display modes

Different modes

A mode B mode M mode

• called Time Motion,

• Display two types, a

Mechanical transducers A vertical with different types or levels and or sides

Shape, steer Linear The images all steer

An overview of the metric system, including prefixes for powers of ten. The lesson also covers complimentary metric system relationships. It also describes how information is displayed in graphical form in diagnostic ultrasound, explaining the usage of the vertical and horizontal axes.