Sound Wave Parameters PDF

Sound Wave Parameters: Frequency Frequency (f): Frequency measures the occurrence rate of an event. In sound, it refers to the number of complete cycles of pressure variation (or any other acoustic variable) in one second. Sound Wave Parameters: Frequency A cycle is a full variation in pressure o...

Sound Wave Parameters: Frequency Frequency (f): Frequency measures the occurrence rate of an event. In sound, it refers to the number of complete cycles of pressure variation (or any other acoustic variable) in one second. Sound Wave Parameters: Frequency A cycle is a full variation in pressure or another acoustic variable, encompassing both compression (increased density) and rarefaction (decreased density). Units of Frequency: Measured in hertz (Hz), kilohertz (kHz), and megahertz (MHz), where one hertz is equivalent to one cycle per second, one kilohertz equals 1,000 Hz, and one megahertz is 1,000,000 Hz. Sound Wave Parameters: Frequency Typical Frequency Values in medical The frequency is determined by the ultrasound: Ranging from 2 to 15 MHz. sound source. Frequency-Period Relationship: The product of frequency and period equals 1 second. Frequency X Period = 1 second A, Frequency is the number of complete variations (cycles) that an acoustic variable (pressure, in this case) goes through in 1 second. B, Five cycles occur in 1 second; thus the frequency is five cycles per second, or 5 Hz. C, If five cycles occur within one millionth of a second, also known as a microsecond (1 μs) (i.e., five million cycles occurring in 1 second), the frequency is 5 MHz. Resonance Frequency in Ultrasound Transducers The resonance frequency of an ultrasound transducer is primarily determined by its piezoelectric crystals. Thinner crystals in the transducer vibrate at higher frequencies compared to thicker crystals Frequency plays a crucial role in determining the resolution and penetration of sonographic images. It is adjustable based on the transducer and sonographic instrument used. Sound Wave Parameters: Period The period value The period is The period is cannot be altered determined by represented by by the the sound source. the symbol (T). sonographer Each cycle occurs in 0.2 μs, so the period is 0.2 μs. If one cycle takes 0.2 (or 1⁄5) millionths of a second to occur, it means that five million cycles occur in 1 second, so the frequency is 5 MHz. Sound Wave Parameters: Wavelength Wavelength (λ) is the length of a cycle in space. Units for Wavelength: Measured in meters, millimeters, or any standard unit of length. Typical Values in Soft Tissue: Ranges from 0.1 to 0.8 mm.. Control by Sonographer: The wavelength cannot be modified by the sonographer. Factors Influencing Wavelength: 1. Transducer Frequency. 2. Speed of Sound in the Medium. Sound Wave Parameters: Wavelength Wavelength is calculated as Speed divided by Frequency Wavelength (λ) (mm) = c (mm/μs) ÷ f (MHz) Wavelength is a crucial parameter that influences the diagnostic quality of ultrasound images. Shorter-wavelength sound waves have superior spatial resolution but less penetration. In this figure, each cycle covers 0.31 mm. Thus the wavelength is 0.31 mm. This figure differs from for a propagation speed of 1.54 mm/μs and a frequency of 5 MHz, the wavelength is 0.31 mm. Sound Wave Parameters: Propagation speed Propagation speed (c) refers to the rate at which a sound wave moves through a medium. Within a specific medium, sound waves travel at a consistent speed, regardless of their frequency. This means that sound waves at 20 Hz and those at 20 MHz move at the same speed in the same medium. The speed of sound wave propagation varies across different mediums. It is generally fastest in solids, like bone, and slowest in gases or gas-containing structures, such as the lungs  The average propagation speed of sound in tissues Material speed (m/sec) Air 330 Fat 1450 Water 1480 Soft tissue 1540 Bone 4100 Sound Wave Parameters: Amplitude The amplitude of a sound is created by the number of molecules displaced by a vibration Amplitude is indicative of the strength or intensity of a sound wave. Amplitude is typically measured in units of pressure, such as Mega Pascals (MPa). Sound Wave Parameters: Power Power is the rate at which work is performed or energy is transferred. In ultrasound, power refers to the generation of ultrasound waves by the transducer and their propagation through tissues. These waves carry mechanical energy that facilitates the displacement of particles within the medium. The higher the power, the greater the wave's capacity to perform this work of displacing particles Sound Wave Parameters: Power The standard unit of power is the Watt (W). Power in diagnostic ultrasound is commonly expressed in milliwatts (mW). One milliwatt equates to one-thousandth of a Watt, meaning there are 1,000 milliwatts in a single Watt. Sound Wave Parameters: Intensity Intensity (I) is the rate at which energy passes through a unit area. It is equal to the power in a wave divided by the area (A) over which the power is spread. Ultrasound is generated by transducers in the form of beams. Beam area is expressed in centimeters squared (cm2). Intensity units include milliwatts per centimeter squared (mW/cm2) and watts per centimeter squared (W/cm2). An increase in area decreases intensity because power is less concentrated. A decrease in area (focusing) increases intensity because power is more concentrated. An ultrasound pulse is weakened (reduction of amplitude) as it travels through a medium (in this case from left to right). This weakening is called attenuation. A, Amplitude is the maximum amount of variation that occurs in an acoustic variable (pressure, in this case). In this figure, the amplitude is 2 megapascals (Mpa). B, Intensity is the power in a sound wave divided by the area over which the power is spread (the beam area). Pulsed wave A pulse, by definition, must have a distinct beginning and end Pulsed ultrasound comprises two main components: 1. The Cycle: This is the "on" or "transmit" time during which the ultrasound wave is emitted. 2. The Dead Time: Also known as the "off" or "receive" time, this is the period during which the transducer awaits the return of the echoes. Pulsed transducers are designed to generate multiple, sequential, short pulses, allowing for the simultaneous use of the same crystal or group of crystals for both sound transmission and echo reception. Pulsed wave In pulsed mode, a singular crystal or a specific group of crystals is used for both the transmission of sound and the reception of echoes. A pulsed transducer emits ultrasound waves that span a variety of frequencies. This spectrum is referred to as the 'frequency bandwidth. Pulsed wave transducers are responsible for generating all types of ultrasound diagnostic images, including both real-time and static. Contentious wave (CW) Continuous wave (CW) ultrasound is It is important to note that predominantly employed continuous wave sound is in echocardiography for incapable of creating acquiring CW Doppler anatomic images information. Pulsed Repetition Frequency (PRF) Pulse Repetition Frequency (PRF) refers to the number of sound pulses generated by the transducer per second. The determination of PRF is attributed to the sound source and can be adjusted by the sonographer. There is an inverse relationship between imaging depth and PRF, meaning as imaging depth increases, PRF decreases. The sonographer can change PRF, and the adjustment is particularly relevant to achieve optimal imaging depth. Pulse repetition period (PRP) Pulse-repetition period (PRP) refers to the time from the beginning of one pulse to the beginning of the next one The pulse-repetition period decreases while PRF increases because, when more pulses occur in a second, the time between them decreases. Pulse Repetition Period (PRP) Pulse Repetition Period (PRP) is the reciprocal of Pulse Repetition Frequency (PRF), expressed in milliseconds or any unit of time. PRP = 1 / PRF The determination of PRP is influenced by the sound source, and it can be adjusted by the operator. In clinical imaging, typical values for PRP range from 100 microseconds to 1 millisecond. Pulse duration Pulse duration (PD) is the time that it takes for one pulse to occur PD is equal to the period (the time for one cycle) times the number of cycles in the pulse (n) and is expressed in microseconds. Sonographic pulses are typically two or three cycles long. Doppler pulses are typically 5 to 30 cycles long. PD(μs) = n ×T(μs) Pulse duration PD decreases if the number of cycles in a pulse is decreased or if the frequency is increased (reducing the period).  Consider a 3.5 MHz transducer with a 5-cycle pulse. Calculate the Pulse pulse duration: duration Answer Period = 1 ÷ frequency = 1 ÷ 3.5 MHz =0.28 µs PD = 0.28 µs × 5 = 1.4 µs. Duty factor (DF) The duty factor is the percentage of time that the ultrasound system transmits sound. DF is the fraction of the PRP that the sound is on. The remainder of the time to the next pulse is the listening time for reception of echoes that will form a scan line on the instrument display. DF = Pulse duration/pulse repetition period Continuous wave ultrasound is on 100% of the time. Duty factor (DF) Typical DFs for sonography are in the range of 0.1% to 1.0%. For Doppler ultrasound, because of longer pulse durations, the range of typical DFs is 0.5% to 5.0%. Changed by Sonographer? Yes, the sonographer can adjust it when changing imaging depth.  You are performing an ultrasound examination with a pulsed ultrasound system. The pulse duration is 2 microseconds (µs), Duty factor and the pulse repetition period is 1 (DF) millisecond (ms). Calculate the Duty Factor (DF) for this ultrasound examination. Answer Pulse Duration = 2 µs Pulse Repetition Period = 1 ms = 1000 µs DF = (2 µs) / (1000 µs) DF = 0.002 So, the DF for this ultrasound examination is 0.002 or 0.2%. This means that the ultrasound system is actively transmitting sound waves for only 0.2% of the time during the examination. Spatial pulse length (SPL) SPL is the length of a pulse from front to back SPL is equal to the length of each cycle times the number of cycles in the pulse. SPL(mm) = n × wavelength (mm) Because wavelength decreases with increasing frequency, SPL decreases with increasing frequency SPL determines axial resolution Spatial pulse length (SPL) A, Spatial pulse length (SPL) is the length of space over which a pulse occurs. SPL is equal to wavelength multiplied by the number of cycles in the pulse. In this figure, the wavelength is 0.5 mm, there are two cycles in each pulse, and the SPL is 0.5 × 2, or 1 mm.