Physical Principles Behind Pulsed and Continuous Wave Doppler Ultrasound - Research Paper Example

?Physical Principles behind Pulsed and Continuous Wave Doppler Ultrasound In physics, ultrasound relates to sound that has a frequency higher than the upper limit that human ears can detect. Simply stated, ultrasound has a frequency beyond audible sound and therefore cannot be heard by humans (Bates, 2004). The physical principles underlying ultrasound solely are founded on the frequency of sound transmission. In the study of ultrasound, keen reflection is dedicated to the behavior of sound when transmitted in different media. The most prevalent media used are water and air which are easy to work with. Scientists have to scrutinize on the compression and decompression of ultrasound in the transmitting medium, such as water or air. This is only done successfully when the velocity of the traveling sound is constant while in the transmitting medium. Therefore, a simple explanation denotes that around is the epitome of longitudinal waves considered to be in an oscillating movement, which goes back and forth. The oscillation is considered to be in the same direction as the traveling sound waves, thereby encompassing successive zones of compression (Gent 1997). Similarly, the indulgence of successive zones of compression leads to rarefaction. Fig. 1 Courtesy of Hendrick, W., Hykes, D. and Stachman D. (2005) Ultrasound Physics and Instrumentation. New York: Elsevier-Mosby. In the figure above, it is evident that there is a consistent flow of waves, as reflected from the compression and transverse waves. In this figure above, the top waves denote the compression wave, while the bottom denotes the transverse wave. This is a consistent flow of sound waves, used in the physical examination of the principles underlying sound waves. The audible frequency in this diagram is considered to be in a kind of consistent frequency, which is used as one of the physical principles of ultra sound. The audible frequency in this diagram is therefore a frequency between 15, 000 Hz to 20, 000 Hz (Callen, 2000). On the other hand, in such a frequency, the ultrasound is in a range of 1 to 12 Hz. A physical principle underlying the Doppler ultrasound is a detection of a change in frequency of sound, when there is a change in the reflection. Basically, Doppler ultrasound solely relies on a change in the frequency of sound, depending on how the sound has been reflected. Movement in Doppler ultrasound is detected when there is a change in the sound frequency. The sound frequency change is evidently seen as the movement reflects visible change. When sound is exposed to different mediums, it is duly reflected, depending on the reflecting surface. After a reelection, the surface will detect the direction of the sound. In addition to this, the reflecting surface will dictate change in the frequency of sound, thereby changing its frequency over time. Transducers have the ability of generating electric charges when there is an applied mechanical stress or energy to their physics. Therefore, when there id a continuous operation mode in a transducer, then the voltage will have a directly proportional sound wave. However, this only depends on one principle. The basic principle in this part is that, the voltage should never be turned off. In the end, the voltage on a transducer will generate an equal sound wave. On the other hand, some transformers are not operated in a continuous mode. This is the pulsed mode, where the frequency has change over time. When the pulses are introduced to the transducer, it produces different wave lengths, depending on the pulsed frequency. In moist cases, the wavelength produced by ringing a transducer is doubled by the thickness. One physical principle underlying ultrasound is that, sound travels around corners. Evidently, human beings and animals have the ability to hear sounds, even when the sound is at a far distance and around corners. This evidently shows that the basic physical principle of sound is negotiating corners. This is scientifically referred to sound diffraction (Bates, 2004). However, there is a course of concern when sound is travelling in a straight line. When sound is traveling in a straight line, higher frequencies tend to move at a faster rate, as opposed to sound travelling over corners. Examples of higher frequencies moving in a straight line include electromagnetic beams, which are also reflected as light beams. For easier calculations, the equation is denoted as follows. С = ? ? This shows that the wavelength in the equation is inversely proportional to the frequency ?, which is in effect by the initial sound velocity С (Callen, 2000). In a further reaction to the same, the equation could be enhanced to bring a better approach about ultrasound calculations. For instance, the equation will be generated to reflect the following. ? = С/ ? This shows that the velocity of the frequency is equal to the wavelength, multiplied by the number of oscillations per second. However, there is a course of concern in such refraction. Different materials have different sound velocity at given temperatures, but are considered constant throughout the reaction. For instance, in a recent reaction procedure, air was considered to have a velocity of 330 meters per second, while water had a velocity of 1497 meters per second(Gent 1997). A basic principle of ultrasound is sampling using different levels of complexity. When ultrasound is exposed to different levels of complexity, there is a notable difference in the reaction. This shows that ultrasound behaves in a different manner, depending on the incumbent complexity (Bates, 2004). This shows that there is a different reaction when sound is exposed to different medium, though it may be the same. Fig 2: Courtesy of Hendrick, W., Hykes, D. and Stachman D. (2005) Ultrasound Physics and Instrumentation. New York: Elsevier-Mosby. In the figure above, the first diagram represents ultrasound pulse that is in wave form. Therefore, the waves are represented in terms of the full waveform that represents the data that is relayed. Therefore, if there is need to calculate the post processing, the amplitude and frequency of the data will be used (Gent 1997). In the second diagram, the pulse of the ultrasound has certain amplitude. The ultrasound revolves around the stated amplitude, making an oval revolution. In this diagram, it is considered that the sound is much less involving, as it revolves around a stipulated pulse. In this figure, it is evident that the amplitude is displayed in brightness at the point of the scattered sound that emanates. This is further reflected in the third diagram, as the amplitude is further given a dark coloring. The dark coloring is noted to give a clear representation of the amplitude, in which the ultrasound reacts. The reaction therefore is given a frequency depending on the surrounding medium. In the last diagram, it is evident that the amplitude and reaction has a given numerical figure. In a further analysis of the diagram, it if denoted as ? (Bates, 2004). This denotes that the ultrasound in production has a particular frequency, depending on the emanating sound. In the last diagram denoted with ?, it is evident that the frequency and amplitude in a sound effect can be measured, depending on the magnitude. In some images, it is possible to notice a spectrum of frequencies, which reflects a wide range of frequencies. This is particularly when there are more than two frequencies in ultrasound. Since the numerical refection can be computed, it is possible to indulge a numerical value that would represent the image pixel. For instance, in the fourth diagram, the frequency is denoted by ? (Hendrick, Hykes and Stachman, 2005). This numerical value represents the diagram about its frequency in the reaction. Therefore, any figure that has ultrasound reaction can be estimated by the use of numerical values, to note its frequency in reaction. Therefore, there will be a range of reaction when there are a number of reactions about sound and the frequency of sound. In most cases, the frequency of sound is considered to be in a constant movement, making it easier to denote the numerical value. In the end, the computation of such will be a lot easier as the consistency will not deter a successful recognition of the provided data. In actual sense, the physical consistency of frequency makes it easier to estimate the numerical value of a reaction, especially when in a particular image (Gent 1997). Physically, it is evident that sound will react according to the medium and external factors in the offing. For instance, in the above diagram, the sound reacts according to the external factors. When sound is generated in a frequency without external factors, it shows a different reaction as compared to the reaction that is seen when it is exposed to external factors. For instance, the sound is considered to show a different reaction in the dark colored diagram, making it invisible. The sound therefore reacts accordingly to the external factors. Lastly, the external factors and the reaction of sound have to note a difference ion the numerical value of the same. For instance, the last diagram is denoted as ?, which is a representation of its frequency. However, there is a difference for data relayed in the different mediums. For instance, in the diagram denoted by ?, the amount of data is far less than the RF data (Hendrick, Hykes and Stachman, 2005). This shows that there is a possible difference in the relay of data, depending on the pre-existing factors. Therefore, there is need to reflect on the possible factors that could generate change for data relayed in a diagram and figure. A factoring principle in ultrasound is imaging. Ultrasound imaging is experienced when a pulse is emitted and partly reflected from a boundary, which is found between two tissues or structures. It is then transmitted to the various destinations, which forms the ultimate imaging. However, three transmission of the produced pulse depends on the difference in the impedance of the two tissues or structures. In actual reflection, basic imaging in ultrasound solely depends on the amplitude of information, which is found in the reflected signal (Hendrick, Hykes and Stachman, 2005). With such a consideration in ultrasound, one pulse is emitted and then reflected by the various tissues. Therefore, the reflected signal is subjected to more samples during the entire period, which are considered to be utterly multiple times. In this reaction, the velocity of sound in the tissues is considered constant. However, the time between the emissions of a pulse and the reception of the same is entirely dependent on the distance between the tissues (Hendrick, Hykes and Stachman, 2005). This is particularly about the depth of the reflecting structure, which is a considerable factor in the frequency and distance. To garner an appropriate approach in ultrasound, the reflected pulses are sampled at multiple intervals, which are solely dependent on the time lapse in between the pulses. This is scientifically referred to as multiple range gating, which is reflected in the time intervals used. In this multiple range gating, there is a possible correspondence to considerable depth before giving the ultimate time intervals. In addition to this, the images must be displayed with utter regard to their depth in the imaging. Physically, different structures will have a different reflection concerning the substantial amount of energy emitted. This will in turn reflect on the signal; that is reflected in different depths in the amplitudes. In actual sense, there could be a difference in the amplitude, depending on the release of the sound and the structures. Therefore, the time before a new pulse is released is dependent on the maximum desired depth that is reflected to the desired image. The figure below is used to explain further amplitude and reaction of emitted energy. a b c Q a b c Fig 3. Courtesy of Gent, R. (1997) Applied Physics and Technology of Diagnostic Ultrasound. South Australia: Openbook Publishers. This is a waveform showing Doppler shift versus time, however, the reaction depends on the physical properties in the experiment. In the figure above, it is shown that energy is initially transmitted from the focal point Q. The ultrasound in transmitted from the place of origin at point Q, and subjected to different structures, which are named, a, b and c (Bates, 2004). When the energy in released, it is exposed to the three structures. Part of the energy is transmitted to point a, part to point b, while the remainder is transmitted to point c (Bates, 2004). There is a notable difference in the reaction, as all the points have different structures. Scientifically, when the pulse returns to the initial point of release Q, it is given two measurements (Hendrick, Hykes and Stachman, 2005). The first measurement is considered the amplitude of the reflected signal, while the second reaction is the time taken in returning the same pulse. This is solely dependent on the distance between the transmitter and the reflector, as the sound is considered to be travelling back and forth. However, there are further courses of concern when the reflecting structures are not the same. There is a different effect when there is change in the direction and size of the reflection surfaces (Hendrick, Hykes and Stachman, 2005). These surfaces will factor in the reflection of the same, as the repulsion of the emitted energy will not be the same. Therefore, there is a physical principle that is dependent on the size and direction of the reflecting surfaces. This is further explained in the following diagrams. a b c d Fig 4. Courtesy of Gent, R. (1997) Applied Physics and Technology of Diagnostic Ultrasound. South Australia: Openbook Publishers In the figure above, there is a difference in the reflecting surfaces, based on shape and size. With a difference in the shape and size, it is evident that the reflection is different (Hendrick, Hykes and Stachman, 2005). In the first two images, the reflecting surface is perfect, giving most of the energy in one direction (Bates, 2004). However, in the last two images, the emitted energy is scattered as the surface is not even in shape and size. This shows the physical principle that the direction of reflection will depend on the reflecting surface, in terms of shape and size. There are various uses of the pulsed Doppler ultrasound in medical application. Medics have indulged the use of Doppler ultrasound in making appropriate treatment to patients. The most outstanding medical application of the pulsed Doppler ultrasound is non-invasive velocity measurement of blood flow. The pulsed Doppler frequency denotes the frequency that occurs in the velocity of flow of blood in the body. The ultrasound is transmitted into a vessel, followed by a detection of the blood flow, which is thereby detected (Rumack, 2005). Since the blood is in a constant movement, the sound is detected as it is undergoing a frequency shift. The diagram below gives an overview of the possible outcome when the Doppler ultrasound is used. Commonly known as Doppler sonography, the assessment of structures is initiated by scrutinizing the flow of the structures, as either from the probe or towards the probe. During the entire measurement, the relative velocity is a considerable factor that is vital. in this practice, the flow of blood in an artery is scrutinized, by observing the heat valve, the direction and its speed. They are then visualized to bring out visual images that can be used in the medical application. After the visual images, the information is then displayed by the use of graphs by assistance of spectral Doppler. To make a better display, medical practitioners have the choice between colors Doppler which is directional, to using the power Doppler, which is non directional. After usage of these directional and non-directional Doppler, the Doppler shifts are transformed into an audible range. Instantaneously after this, the gathered materials are usually presented using stereo speakers as audible files. With a keen scrutiny of the audio files, a synthetic and pulsating sound is derived, although it is very distinctive in nature. This can therefore be used to evaluate the medical procedure that should be approached, in case of need. Fig 5. Courtesy of Gent, R. (1997) Applied Physics and Technology of Diagnostic Ultrasound. South Australia: Openbook Publishers Medical application of continuous wave Doppler has accuracy in noting the outcome when used scientifically (Bates, 2004). The continuous wave Doppler is used in measuring high blood velocity, especially in valvular and congenital heart diseases. This figures any disorder presently in the body and blood vessels. The continuous wave Doppler is a process that indulges a continuous generation of waves (ultrasound), which are met with continuous reception (Rumack, 2005). With this two-sided approach, the continuous Doppler measurement is considered to have ultimate accuracy in the blood velocity measurement. With such an escalating accuracy in the measurement, this is considered to be the best approach in the measurement of blood velocity as it generates high accuracy, especially in frequencies exceeding 1.5 m/second (Rumack, 2005). This eventually shows that a person has a disorder, which should be considered a health issue. For instance, medical practitioners use a hand-held CW probe to measure ankle and brachial blood pressures. The physical principle behind this is that, the practitioners inflate a pressure cuff until the Doppler signal cuts out (Bates, 2004). Instantaneously after this, they embark on noting the frequency change and note the pressure at which this occurs. This is followed by a mathematical division of the ankle by the brachial pressure, to depict change in the process. During the process, a transmitter emits continuous ultrasound waves, which are continuously collected by the receiver, and placed at different angles. With this in action, the Doppler machine is used to detect the quadrature. This allows direction detection, including ultrasound waves reflected at 90 degrees as noted by Rumack, Wilson and Charboneau (2005). Signals from a wave Doppler, especially a continuous wave Doppler are displayed graphically (Bates, 2004). The graphs represent all the produced signals, though it is not considered quantitative. Initially, systole reflects an antegrade flow. Secondly, there is a retrograde flow experienced at diastole. This is basically due to high pressure experienced in the element. The ultimate point is experienced when there is forward flow of blood, which is pushed by a preceding cycle. This is basically experienced when a person’s legs are at rest. Reference List Bates, J. (2004). Abdominal Ultrasound – How, Why and When. London: Churchill Livingstone, London. Callen, P. (2000) Ultrasonography in Obstetrics and Gynaecology. New York: WB Saunders Company. Gent, R. (1997) Applied Physics and Technology of Diagnostic Ultrasound. South Australia: Openbook Publishers. Hendrick, W., Hykes, D. and Stachman D. (2005) Ultrasound Physics and Instrumentation. New York: Elsevier-Mosby. Rumack, C.,Wilson, S., and Charboneau, J. (2005) Diagnostic Ultrasound. New York: Mosby Publishers. Read More