Basics of Ultrasound
These are the potential harmful effects that ultrasound can have on tissues, such as heating or cavitation, which are considered when determining safe exposure levels.
What are biological effects?
The unit used to measure frequency, representing the number of sound wave cycles that occur per second.
What is a Hertz (Hz)?
Ultrasound, or ultrasonic sound, has a frequency higher than this number of kilohertz.
What is 20 kHz?
This is the time from the start of one pulse to the start of the next, including both the pulse duration and the listening time.
What is pulse repetition period (PRP)?
Continuing to lose energy as the ultrasound waves pass through tissues.
What is attenuation.
In ultrasound, when one parameter increases and another also increases proportionally, the two are said to be this.
What is directly related?
This is the speed of sound in soft tissues.
What is 1540 m/s OR 1.54 mm/µs ?
When the maximum imaging depth is increased during an exam, this parameter of the sound wave remains unchanged.
What is frequency?
For continuous wave ultrasound, this is the maximum value the duty cycle can reach.
What is 1 (or 100%)?
This occurs when a sound wave bounces off a boundary between two tissues with different acoustic impedances.
What is reflection?
In ultrasound, when one parameter increases and another decreases proportionally, the two are said to be this.
What is inversely related?
Power and intensity are proportional to this quantity squared.
What is amplitude?
Power and Intensity are proportional to amplitude²
These three parameters, often called the “bigness” parameters, describe the magnitude of a sound wave.
What are amplitude, power, and intensity?
Less listening time, a shorter pulse repetition period, a higher pulse repetition frequency, and a higher duty factor are all characteristics of this type of imaging.
What is shallow imaging?
This type of reflection occurs when a sound wave hits a smooth, large interface at an angle, producing a strong, mirror-like echo.
What is specular reflection?
This occurs when two sound waves meet in phase, combining to produce a wave with greater amplitude than either original wave.
What is constructive interference?
This is the relationship between period and frequency, where one equals the reciprocal of the other.
What is the inversely related?
This type of wave involves particles of the medium vibrating back and forth around a fixed position as it propagates.
What is a mechanical wave (or sound wave)?
This parameter represents the fraction or percentage of time that the ultrasound system is actively transmitting a pulse.
What is duty factor?
When predicting potential bioeffects in diagnostic ultrasound, this type of intensity, which considers both the highest value in space and the average over time, is most relevant.
What is Spatial Peak, Temporal Average (SPTA) intensity?
These are the measurable properties of a medium that change as a sound wave travels through it, including pressure, density, and particle motion.
What are acoustic variables?
If a beam has a power of 15 Watts and spreads over an area of 3 cm², this is the beam’s intensity in W/cm².
What is 5 W/cm²?
This parameter is the distance or length of one complete cycle of a wave.
What is wavelength?
If the attenuation coefficient in dB/cm equals half the frequency in MHz, a transducer with a frequency of 10 MHz has this attenuation coefficient.
What is 5 dB/cm?
Atten. Coeff.(dB/cm) = frequency (MHz) / 2
Atten. Coeff. = 10 MHz / 2
Atten. Coeff. = 5 db/cm
A wave’s intensity is initially 2 mW/cm². It experiences a +9 dB change. By approximately how many times does the intensity increase?
What is 8 times?
Rule: Every +3 dB change ≈ 2× increase in intensity.
You have +9 dB, which is 3 dB + 3 dB + 3 dB.
Each 3 dB doubles the intensity:
2×2×2=8
So the intensity increases by 8 times.