- For those who are writing the SPI- Ultrasound physics exam. I have notes for sale it is about 1500 multiple choices sets for ARDMS -spi exam = 50 USA DOLLARS. I study those notes and passed my exam 670/700 . If you want to buy i can copy the notes and send them to you in e mail or by mail you can reach me atdrsteveramsey@gmail.com . I will also include some of the ideas about the 12 simulation questions. The payment with PayPal to drsteveramsey@gmail.com , fetal gender , Saad Ismail
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- Following is the content outline for ARDMS Sonography Principles and Instrumentation (SPI) Examination:
I. Patient care, safety and communication [5%]
Patient identification / documentation
- Patient interaction
- Verification of requested examination
- Emergency situations
- Universal precautions
- Bio effects and ALARA
II. Physics principles [20%]
Properties of ultrasound waves
- Interactions of sound with tissue
- Power, intensity, and amplitude
- Units of measurement
III. Ultrasound transducers [20%]
Transducer construction and characteristics
- Transducer types (sector, linear, phased arrays, etc.)
- Spatial resolution
- Transducer selection
IV. Pulse-echo instrumentation [30%]
Display modes and their formation (A-mode, B-mode, M-mode, 3-D, etc.)
- Transmission of ultrasound
- Reception of ultrasound (preprocessing)
- Beam former
- Post processing of ultrasound signals
- Pulse-echo imaging artifacts
- Tissue harmonic imaging
- Real time ultrasound instrumentation
- Recording and storage devices
V. Doppler instrumentation and hemodynamics [20%]
Ability to acquire color flow image
- Ability to acquire a Doppler spectral image
- Ability to take measurements from the spectral waveform
- Hemodynamics
VI. Quality assurance / quality control of equipment [5%]
Preventive maintenance
- Malfunctions
- Performance testing with phantoms
Ultrasound program students and Sonographers preparing to Pass Ultrasound Physics Exam should focus and spend more time on the areas with higher percentages such as:
Pulse-echo instrumentation [30%]
- Doppler instrumentation and hemodynamics [20%]
- Ultrasound transducers [20%]
- Physics principles [20%]
After you have prepared these Ultrasound Physics chapters, then spend some time on:
Patient care, safety and communication [5%]
- Quality assurance / quality control of equipment [5%]
Don’t spend your major time on these areas.
Source: The above information was obtained from ARDMS website: WWW.ARDMS.ORG. Basic Ultrasound Physics
- Sound is a mechanical wave, which requires a medium in which to travel. More accurately, it is a series of pressure waves propagating through a medium.
One cycle of the acoustic wave is composed of a complete positive and negative pressure change. The wavelength is the distance traveled during one cycle, the frequency of the wave is measured in cycles per second or Hertz (cycles/s, Hz), (illustration 1).
Illustration 1: The illustration shows a schematic drawing of wave length, pressure and amplitude.
For humans audible sound ranges between 16 Hz and 20.000 Hz (20 kHz). The hearing range of other species can be much higher than 20 kHz and is inaudible for us. These higher wave frequencies are referred to as “ultrasound” (Illustration 2).
Illustration 2: Hearing range in various animals and humans.
The speed with which an acoustic wave travels through a medium is determined by the density and stiffness of the medium. The greater the stiffness, the faster the wave will travel. This means that sound waves travel faster in solids than liquids or gases. Acoustic waves are calculated to travel through human tissue at body temperature at approximately 1540 m/s (about one mile per second).
When traveling through a medium the sound waves intensity and amplitude reduces. This is called attenuation and is the reason why echoes from deeper structures are weaker than echoes from superficial areas. The major source of attenuation in soft tissue is absorption, which is the conversion of acoustic energy into heat. Other mechanisms are reflection, refraction and scatter.
The sound wave encounters a boundary between two different media. Some of the wave bounces back towards the source as an echo (reflection). The angle of incidence is identical to the angle of the reflection. The remaining sound wave travels through the second medium (or tissue), but is “bent” from its path. The angle of incidence will be different from the angle of transmission. The amount of deflection is proportional to the difference in the two tissues ‘stiffness’. Scatter occurs when ultrasound waves encounter a medium with a non homogeneous surface. A small portion of the sound wave is scattered in random directions while most of the original wave continues to travel in its original path.
Illustration 3: Absorption, reflection, refraction. Scatter between the unhomogeneos border of two different mediums.
The production of ultrasound waves is based on the so-called ‘pulse-echo-principle’. The source of the ultrasound wave is the piezoelectric crystal, which is placed in the transducer. This crystal has the ability to transform an electrical current into mechanical pressure waves (ultrasound waves) and vice versa. Once the ultrasound wave is generated and travels through the medium, the crystal switches from ‘sending’ into ‘listening’ mode and awaits returning ultrasound echoes. Actually over 99% of the time is spent “listening”. This cycle is repeated several million times per second. This principle is called “pulsed-echo” principle. Returning sound waves are converted into images on the ultrasound monitor.
Diagnostic ultrasound used for common medical imaging uses frequencies between 2 and 20 million Hertz (Megahertz, MHz).
Lower frequencies are able to penetrate deeper into tissue but show poorer resolution. In contrary higher frequency ultrasound will display more detail with a higher resolution in exchange for less depth penetration. This is a very important principle when choosing your probes and frequencies.
- es
A mode; A mode scan.
2- The most important mode for the ultrasound-beginner is the “B-mode”. B-mode stands for ‘brightness mode’ and provides structural information utilizing different shades of gray (or different ‘brightness’) in a two-dimensional image .
M-mode stands for ‘motion mode’. It captures returning echoes in only one line of the B-mode image but displays them over a time axis. Movement of structures positioned in that line can now be visualized. Often M-mode and B-mode are displayed together on the ultrasound monitor. M-Mode (lower portion of the image) combined with B-Mode image. the M-mode captures the movement of a particular part of the heart.The follows very sophisticated and complex laws of physics.
It utilizes a phenomenon called ‘Doppler shift’, which is a change in frequency from the sent to the returning sound wave. These changes or ‘shifts’ are generated by sound waves reaching moving particles. The change of frequency/amount of shift correlates with the velocity and direction of particle motion. In simplified terms, the Doppler mode examines the characteristics of direction and speed of tissue motion and blood flow and presents it in audible, color or spectral displays.
Color Doppler ultrasound is also called color-flow ultrasound. It is able to show blood flow or tissue motion in a selected two-dimensional area. Direction and velocity of tissue motion and blood flow are color coded and superimposed on the corresponding B-mode image.
Power Doppler: Unlike color Doppler, common power Doppler does not examine flow velocity or the direction of flow. It looks at the amplitudes of the returning frequency shifts and is able to detect even states of very low flow (Figure 4). This is of use when examining vascular emergencies such as testicular or ovarian torsion.
Spectral Doppler consists of a continuous and pulsed-wave form. Continuous wave Doppler is often available as a separate small hand-held unit containing discrete transmitting and receiving piezo-electric crystals. This allows for simultaneous transmitting of ultrasound waves and receiving of returning Doppler shift signals, which are converted to audible frequencies over a loudspeaker. No image is produced. This technique is often utilized at the bedside to demonstrate patent vessels or fetal heart tones in pregnancy. Pulsed-wave spectral Doppler shows the “spectrum” of the returned Doppler frequencies in a characteristic two-dimensional display. Venous flow demonstrates a more continuous, band like shape. Arterial flow shows a more triangular shape. III. Artifacts
Artifact refer to something seen on the ultrasound image that does not exist in reality. An artifact can be helpful interpreting the image or it can confuse the examiner. Several commonly encountered artifacts are mentioned below.Attention Artifacts:
Shadowing:
This artifact is caused by partial or total reflection or absorption of the sound energy. A much weaker signal returns from behind a strong reflector (air) or sound-absorbing structure (gallstone, kidney stone, bone).
Posterior Enhancement:
In posterior enhancement, the area behind an echo-weak or echo-free structure appears brighter (more echogenic) than its surrounding structures. This occurs because neighboring signals had to pass through more attenuating structures and return with weaker echoes
Edge Shadowing:
The lateral edge shadow is a thin acoustic shadow that appears behind edges of cystic structures. Sound waves encountering a cystic wall or a curved surface at a tangential angle are scattered and refracted, leading to energy loss and the formation of a shadow.
Edge artifact.
Propagation Artifacts:
Reverberation:
Reverberation occurs when sound encounters two highly reflective layers. The sound is bounced back and forth between the two layers before traveling back. The probe will detect a prolonged traveling time and assume a longer traveling distance and display additional ‘reverberated’ images in a deeper tissue layer
Sample of reverberation artifact.
Comet Tail:
A comet tail artifact is similar to reverberation. It is produced by the front and back of a very strong reflector (air bubble, BB gun pellet). The reverberations are spaced very narrowly and blend into a small band .
Comet tail artifact.
Mirror Imaging:
If a structure is located close to a highly reflective interface (such as the diaphragm), it is detected and displayed in its normal position. However, the strong reflector causes additional sound waves to bend towards the neighboring anatomy, from where they are bounced back towards the strong reflector and return to the transducer. These sound waves have a longer travel time and are perceived as an additional anatomic structure. The image is duplicated on the other side of the strong reflector Artifacts:
Ring Down:
The artifact is caused by a resonance phenomenon from a collection of gas bubbles. A continuous emission of sound occurs from the ‘resonating’ structure causing a long and uninterrupted echo. It appears very similar to the comet tail artifact.
Side Lobe:
This artifact is caused by low energy ‘side lobes’ of the main ultrasound beam. When an echo from such a side lobe beam becomes strong enough and returns to the receiver, it is ‘assigned’ to the main beam and displayed at a false location. Side-lobe artifacts are usually seen in hypoechoic or echo-free structures and appear as bright and rounded lines .
- Probes
Several different types of probes are commonly used in emergency departments. These transducers consist of the active element (the piezoelectric crystal), damping material and a matching layer. Different arrangements and forms of activation of the active element have lead to a variance of probes. The most common transducers utilized in the emergency department are listed below:Large Convex Probe:
Main ED utilization is trans abdominal sonography.
Produces a sector shaped image with a large curved top
The active element is arranged in a large curved line, also called large curved probe or transducer.Microconvex Probe:
Utilized for trans abdominal or trans thoracic sonography.
Produces a sector shaped image with a small curved top.
The active element is arranged in a small curved or “convex” line, the probe can be called small curved transducer.Linear Probe:
Main utilization is vascular sonography or evaluation of superficial soft tissue structures.
It produces a rectangular image. The active element is arranged in a straight line.Pobe:
Basically a microconvex probe on a large handle, it’s main utilization is endovaginal ultrasound.Sector Probe:
Other probes utilized in emergency departments, especially for trans thoracic sonography are sector probes. They produce a pie-shaped image with an angulated top. The active element is arranged in a circle and only parts of it are activated at a time and steered into the direction needed. This arrangement provides the sector probe with an overall lower resolution as fewer “crystals” are activated at one time. It has the advantage of requiring only very minimal skin contact or a very small sonographic window to obtain an image.
Terminology;
- Anechoic / Echolucent – Complete absence of returning sound waves, area is black.
- Hypoechoic – Structure has very few echoes and appears darker than surrounding tissue.
- Hyperechoic / Echogenic – Opposite of hypoechoic, structure appears brighter than surrounding tissue. Image Acquisition / Probe Positions:
- Transverse Plane – Also known as an axial plane or cross section, runs parallel to the ground separating the superior from the inferior, or, the head from the feet.
- Sagittal Plane – Oriented perpendicular to the ground, separating left from right. The “midsagittal plane” is a sagittal plane that is exactly in the middle of the body.
- Coronal Plane – Also known as the frontal plane, separates the anterior from the posterior or the front from the back.
Oblique Plane- The probe is oriented neither parallel to, nor at right angles from, coronal, sagittal or transverse planes. - Longitudinal Plane- The longitudinal plane is perpendicular to the transverse plane an can be either the coronal plane or sagittal plane.
Spatial orientation.
Gain – Changes overall strength of returning echoes, functions as an amplifier.
TGC – Changes strength of returning echoes in a certain depth.
Sample of some questions;
Units of length
distance or circumference = cm, feet
Units of area = cm^2 , ft^2
Units of volume = cm^3, ft^3
To increase by a factor = multiply , to decrease by a factor = divide
List the metric terms in increasing order; Micro , milli , deci, deca, hecto, meca
List the metric system ; Giga Deci, Mega Centi , kilo Milli, Hecto Micro ,Deca Nano
Sound waves are = Longitudinal and mechanical
Sound waves are identified by which acoustic variables? = Pressure, Density, and Distance (Pascals, Pa) (kg/cm^3) (cm,feet,mile)
What are the seven acoustic parameters? = -Period,-Frequency,-Amplitude,-Power,-Intensity,-Wavelength,-Propagation Speed
Transverse waves = move in a perpendicular direction (at right angles) to the direction that the wave propagates
Longitudinal waves =particles move in the same direction that the wave propagates. Sound is a LONGITUDINAL wave.
In-Phase waves = peaks (both maximum and minimum values) occur at the same time
Out-Of-Phase waves = Peaks occur at different times
Constructive Interference = The interference of a pair of in-phase waves.
This results in the formation of a single wave with a greater amplitude.
Destructive Interference = The interference of a pair of out-of-phase waves. This results in the formation of a single wave with a lesser amplitude.
Destructive interference with equal amplitude and complete destructive interference presents as a = flat-line, they cancel each-other out.
Interference with different frequencies =Both constructive and destructive interference occur.
What do waves transfer from one location to the other? =energy
Parameters =describe the features of a sound wave
what is the SOURCE of a sound wave? =the ultrasound system and transducer
Period = the time it takes a wave to vibrate a single cycle, or from the start of one cycle to the start of the next cycle.
UNITS: time such as microseconds (µs), seconds, hours, days. -typical value between 0.06ms-0.5ms , Determined by SOUND source only.Adjustable? NO
Frequency =The number of particular events that occur in a specific duration of time,
UNITS: time such as per second,1/second, hertz,or Hz. -typical value between 2MHz-15MHz. Determined by SOUND source only. Adjustable? NO
Infrasound = the frequency is less than 20 Hz , *cannot be heard
Audible sound = the frequency is between 20 Hz-20 kHz ,*humans can hear
Ultrasound = the frequency is greater than 20 kHz , *too high for humans to hear
What is the relationship between frequency and period? =inversely related, the frequency increases and the period decreases (vice versa)
period and frequency have a reciprocal relationship =Period x Frequency= 1
What are the three “Bigness Parameters”? =Amplitude, Power, Intensity
Amplitude =is the “bigness” of the wave.
UNITS: (pressure) pascals, (density) g/cm^3, (particle motion) cm, inches-any distance. , -typical value between 1 million pascals (1 MPa)-3 million pascals (3 MPa). Determined by SOUND source only. amplitude decreases as sound propagates through the body. Adjustable? YES
How is amplitude measured? =from the baseline to the maximum or minimum value.
How is peak-to-peak measured? =it is twice the value of the amplitude.
Power = is the rate of energy transfer. Power also describes the “bigness” of a wave.
UNITS: watts = -typical value between 0.004-0.090 watts (4-90 milliwatts.
Determined by SOUND source only. Power decreases as sound propagates through the body. Adjustable? YES
How are amplitude and power related? =They are proportionally related. power ∞ amplitude^2
Intensity = is the concentration of energy in a sound beam. Intensity also describes the “bigness” of a wave.UNITS: watts/square centimeter, or W/cm^2-typical value between 0.01-300 W/cm^2, Determined by SOUND source only. Adjustable? YES
How is intensity related to power and amplitude? =-intensity and power are proportionally related, intensity ∞ power; -intensity is proportionally related to the waves amplitude squared. intensity ∞ amplitude^2
Wavelength = is the distance or length of one complete cycle. UNITS: meters, or any other unit of length. -typical value between 0.1-0.8 mm. Determined by BOTH sound source and the medium. Adjustable? NO
What is the relationship between wavelength and frequency? =Inversely related
Propagation Speed =is the rate at which a sound wave travels through a medium. UNITS: meters per second, mm/µs, or any distance divided by time. -typical value between 500 m/s- 4000 m/s. Determined by the MEDIUM. Adjustable? NO
The speed of sound in Biologic Media
Lung……………..500 m/s
Fat………………..1,450 m/s
Soft Tissue……1,540 (average) 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
Other materials
Air………………..330
Water…………..1,480
Metals………….2,000-7,000
***As a general rule…..Sound travels fastest in solids, slower in liquids, and slowest in gases. remember this question. Dont mix this with the attenuation of sound
speed (m/s) = frequency (Hz) x wavelength (m)
What characteristics of a medium determine the speed of sound in that medium? =stiffness and density
How are stiffness and speed related? =directly related
How are density and speed related? =inversely related
The wave properties of ultrasound
Using the following formula, it is possible to calculate the velocity, frequency or wavelength of a wave if the other two values are known:
v = fλ Where:
- The velocity (v) is the speed of the wave. It is measured in m s-1.
- The frequency (f) is the number of times a particle oscillates per second. It is measured in Hz.
- The wavelength (λ) is the distance between two compression or rarefactions. It is measured in m.
The amplitude is the distance a particle moves back or forth.
Compression are areas of the wave where particles are close together and there is high pressure. Rarefactions are areas of the wave where particles are far apart and there is low pressure.
The frequencies used in ultrasound diagnosis
Ultrasound uses high frequency sounds that are higher than the human ear can hear. ie. 20 000 Hz. Ultrasound can’t detect objects that are smaller than its wavelength and therefore higher frequencies of ultrasound produce better resolution. On the other hand, higher frequencies of ultrasound have short wavelengths and are absorbed easily and therefore are not as penetrating. For this reason high frequencies are used for scanning areas of the body close to the surface and low frequencies are used for areas that are deeper down in the body. These frequencies generally range between 1-50 MHz.
How ultrasound is produced and detected
To produce an ultrasound, a piezoelectric crystal has an alternating current applied across it. The piezoelectric crystal grows and shrinks depending on the voltage run through it. Running an alternating current through it causes it to vibrate at a high speed and to produce an ultrasound. This conversion of electrical energy to mechanical energy is known as the piezoelectric effect. The sound then bounces back off the object under investigation. The sound hits the piezoelectric crystal and then has the reverse effect – causing the mechanical energy produced from the sound vibrating the crystal to be converted into electrical energy. By measuring the time between when the sound was sent and received, the amplitude of the sound and the pitch of the sound, a computer can produce images, calculate depths and calculate speeds.
The nature of A-scans, B-scans, sector scans and phase scans;
Good luck to all of us . and thank you for reading part 1.
Steve Ramsey, PhD. Calgary, Alberta.