Metric System Prefixes and Conversions

Metric System

• Giga (G) is 10^9, meaning billion.
• Mega (M) is 10^6, meaning million.
• Kilo (k) is 10^3, meaning thousand.
• Hecto (h) is 10^2, meaning hundred.
• Deca (da) is 10^1, meaning ten.
• Deci (d) is 10^-1, meaning tenth.
• Centi (c) is 10^-2, meaning hundredth.
• Milli (m) is 10^-3, meaning thousandth.
• Micro (µ) is 10^-6, meaning millionth.
• Nano (n) is 10^-9, meaning billionth.

Complimentary Metric System

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

Graphs

• Diagnostic ultrasound information is often displayed graphically.
• The two axes of a graph have special names.
  • Vertical axis, or y-axis, runs up and down representing depth.
  • Horizontal axis, or x-axis, runs side to side representing time.

Sound Wave

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

Acoustic Parameters

• Seven acoustic parameters describe sound waves:
  • Period
  • Frequency
  • Amplitude
  • Power
  • Intensity
  • Wavelength
  • Propagation Speed

Sound Wave 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 Sounds in Materials

• Air has a speed of 330 m/s.
• Water has a speed of 1,480 m/s.
• Metals have a speed between 2,000 to 7,000 m/s.

In-Phase & Constructive Interference

• In-phase waves have peaks (maximum values) and minimum values occurring at the same time and location.
• Constructive interference of in-phase waves results in a single wave with greater amplitude.

Out-of-Phase & Destructive Interference

• Out-of-phase waves have peaks and troughs occurring at different times and are "out of step".
• Destructive interference of out-of-phase waves results in a single wave with lesser amplitude.

Sound Wave Anatomy

• Sound consists of compression areas (squeezed together molecules) and rarefaction areas (stretched apart molecules).
• Compression areas have high density and high pressure.
• Rarefaction areas have low density and low pressure.

Sound Wave Parameters

• Amplitude, power, and intensity describe the 'bigness' or magnitude of a sound wave.
• Cycle, one complete variation in pressure or other acoustic variable (compression and rarefaction).
• Period, the time it takes for one cycle to occur
• Frequency, the number of cycles that occur in 1 second.
• Amplitude, the "bigness" of a wave, difference between maximum/minimum value and average.
• Peak-to-Peak Amplitude, the difference between maximum and minimum values of an acoustic variable.
• Power, rate of energy transfer or rate at which work is performed, measured in Watts.
• Intensity, concentration of energy in a sound beam.
• Propagation speed, distance sound travels through a medium in 1 second, depends on the medium only, unit is m/s.
• Stiffness, the ability of an object that resists compression, stiffness and speed are directly related.
• Density, the relative weight of a material, density and speed are inversely related.
• Speed is determined by density and stiffness of the medium
  • Increased stiffness increases speed
  • Increased density decreases the speed

Parameters Description

• Period and frequency determined and changed by sound source
• Amplitude, power and intensity can be changed by the sonographer
• Speed and wave length determined by the medium.

Tissue Speeds

• Lung has a speed of 500 m/s.
• Fat has a speed of 1,450 m/s.
• Soft tissue (average) has a speed of 1,540 m/s.
• Liver, blood both have speeds of 1,560 m/s.
• Muscle has a speed of 1,600 m/s.
• Tendon has a speed of 1,700 m/s.
• Bone has a speed of 3,500 m/s.

Units of Measure

• Wavelength measured in Millimeters
• Frequency measured in Hertz
• Intensity measured in Watts/cm²
• Propagation speed measured in Meters/second
• Period measured in Seconds
• Power measured in Watts

Determinants of Speed

• Wavelength relies on to both
• Frequency, Intensity (initial), Period, Power (initial), Amplitude (initial) rely sound source
• Propagation speed relies on the medium

Relationship Between Parameters

• How parameters relate:
  • 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 the ultrasound vocabulary.

• Five parameters describe Pulsed sound; Spatial Pulse Length, Pulse Duration, Pulse Repetition Period, Pulse Repetition Frequency, and Duty Factor.

Pulse Duration

• The time from the start of the pulse to the end of the pulse.
• Determined by the source- cannot be adjusted.
• Pulse duration (µs) = # cycles x period (µs)

Spatial Pulse Length

• The length or distance that a pulse occupies in space (mm) = # cycles x wavelength (mm).
• SPL is directly proportional to wavelength
• Determined by the source & the medium; cannot be adjusted.

Pulse Repetition Period

• The time from the start of one pulse to the start of the next pulse.
• Determined by source and depth and can be adjusted.

Pulse Repetition Period & Depth

• By increasing the depth of the sound we are increasing the time the sound beam takes to return.

Pulse Repetition Frequency

• The number of pulses that an ultrasound system transmits into the body each second.
• Pulse repetition = number of Pulses
• Frequency = cycles occurring in one second
• Meaning how often can the pulse be repeated and how often is related to depth of viewing
• The more shallow you are on the sonogram the more frequent the pulse can be repeated
• The deeper you are on the sonogram, the less frequent pulse can be repeated.
• Pulse repetition frequency is determined by source and depth and can be adjusted
• PRP depth are inversley proportional to each other and HZ (units) .
• The deeper the reading (less listening time); more frequent the pulse can be repeated. If too shallow reading the less listening time for image and less frequent to repeat

Duty Factor

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

• It is also called duty cycle

• Maximum value = 1.0 or 100 % (CW)

• Minimum value = 0.0 or 0% (machine off)

• Units of measurements: unitless

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

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

• Duty factor equation : PD/PRP x 100

• The time of the start of one pulse to start of next pulse is PRF

• Percent of time that sends a pulse is duty factor

• High duty factor = more shallow you must be

Intensities

• Spatial refers to distance or space/The ultrasound can't be intense at the same distances
• Peak-maximum value
• Averages- mathematical middle value
• Temporal refers to all time transmit( pulse duration and recive)
• Pulsed is for transit time only/not have intense times
• Temporal peak -max intensity values that are pulsed
• Spatial intensity is measured during the transit time duration(pulse) only
• Temporal Average Intensity( red)
• Average during the duration.

"Ten Commandments" of Intensity

• Intensities may be reported in various ways respect to time and space.
• The different measurements of intensities are important in the study of bioeffects.
• SPTA intensity is the most relevant intensity with respect to tissue heating.
• All intensities have units of watts/cm².
• Average and continuous wave pulsed beams with same SPTP, continue wave is more than the intensity
• All beams SATA intensity is higher - continue wave beam Is average over most intense half cycle the pulse
• If Puls Average Intensity (Ipa) is averaged and only do during " on timed pulses".

Methods of Measuring Intensity

• SPTP Spatial peak, temporal peak
• SATP Spatial average, temporal peak
• SPTA Spatial peak, temporal average
• SATA Spatial average, temporal average
• SPPA Spatial peak, pulse average
• SAPA Spatial average, pulse average

Largest to smallest intensities = SPTP, Im SPPA, SPTA, SATA.

Attenuation

• Sound waves weaken as they propagate in a medium.
• Decrease in intensity, power, and amplitude as sound travels is called attenuation.
• Measured in negative units of dB due to the decrease in signal strength
• Determined by Sound and Distance , and unrelated to propagation.
• Longer distances = more weakened strength is greater
• High Frequency-more strength is weaker
• Shorter distance; Less weakens strength
• Lower Frequency; less weakend strength
• Attenuation Process

1. reflection, scattering, absorption
2. Organized and Disorganized - organization (specular),

• Sound back to a Transducer

Specular- disorganized is diffuse or in backscatter, is scattered!

Attenuation of Ultrasound in Media

• Extremely low-water

• Low-blood urine fluids/fat

• Intermediate -tissue

• Higher level- Muscle

• Even -High-bone/lung

• Air- Extremely high

• THIN HALF VALUE*

• High frequency sounds

• Media with high attenuation rate

• THICK HALF VALUE*

• Low frequency sound

• Rate Of attenuation from the media - the lower it is

• Rayleigh Scattering: Frequency with exponent 4

• Total Attenuation: attenuation and distance

• Attenuation coefficient: frequency over 2 mhz

• Impedance= density plus propagation speed

Transmission Laws

• Normal incidence sound wave hits boundary at exactly 90 degrees
  • Also called perpendicular
• Oblique incidence-sound wave hits at and angle not other than 90 degrees -Refraction is the change in direction
  • The law of physics is called Snell's Law

Transducers

• Time of Flight:
  • Transducers determine depth by knowing that the speed of sound goes out and returns
    • Transducer is directly related to depth (speed)

PRP

• PRP measures depth by knowing that soft tissue is 13 micro sec/ cm -imaging = depth at 13 cm

• If the view is at 10 cm the PRP = .130 mircosec / 10 or a depth view = 13 mircosec

• Pulse Repetition -Period is directly related to maximum depth.

PRF

PRF measures the time at soft tissue which is 1.540 s or 15400/s, In One Second = can travel and return depth at 7700cm 7.7cm; A total of 1000 times in seconds

PRF = 7cm / measuring depth

• The more shallow the pulse is more repeating, and the deeper it is measured is less repeating as you are traveling slow but deep, more energy used

Transducers Chapter 8

• 7 parameters measured plus new defintions

• The different types of transducers; Imaging + non

  • The types: high-frequency imaging transducers that are more thin , and those that are frequency pTZ,
  • Low-frequency are thicker Formula Frequency = PZT/ 2 Thickness(mm)

• The best images have wide bandwidth and are called broadband.

• High bandwidth uses backing and is bad sensistivty

• Quality factors has main Frequency Bandwidth

• Electrical frequency = Acoustic frequency*

• Formula:Sound speed / 2 Thickness(mm)*

Transducers cont

• Anatomy of a Sound Beam Five terms that describe the shape and regions of a sound are as follows:

1. Focus 2 NeAr Zone
2. Focal length near zone line
3. Far Zone 5 Zone High Quality transducer create more efficient beam The ability to resolve are two structure that are side by side or perpendicular to a sound beam = is called resolution is called

Better images are those made at resolution are best at the focus. *axial * + Lateral

• ShAlloW FOCUS
• SmAlLER PZTs * the deep focus* are larger

The high frequency has images that are longer

More divergence is smalls and less a wider dameteer as the frequency is higher

Huygens principle is used to determine image transducer based upon in / out phase 10: High-Quality transducer create more efficient beam The ability to resolve are two structure that are side by side or perpendicular to a sound beam = is called *axial * axial images are front to back on an image and one must be deeper than others Super images will have;

Super good resolution images are those with small special pulse

Fewer cycles per pulses equals less ring

lower numerical values on a graph

• *FORMULLA: resolution = length/2 mm

The following: images longitudinal actual radial depth resolve good AXIAL and is used in LARRD and latA and are best and small * high res/ frequency as the being are narrowest

Method high images, with Lens * Curved * PAA

11 Chapter of displays are Amplification: is horizontal + Amplitude is vertical is display

Brightness: Vertical the displays the depth

Motion mode x axis

• Measures Time the displays with

12 Chapter IMaging + TraNsducers

Loss of entire image = mechanical

DrOp off image = linear converted aaray

Eratical is phases rays

Horizontal are aunarial

Transducer to a perfect images

Steep Techniques = Mechanics All elctronis

Focus Techniq The only fixed one is mechanics Types to Arrangement

This lesson covers the prefixes used in the metric system, ranging from giga to nano, and their corresponding powers of ten. It also explains relationships between billions/billionths, millions/millionths, etc. Includes information about graphs.