Doppler Ultrasound, Using High-frequency Sound Waves to Measure the Amount of Blood - Report Example

Doppler Ultrasound Your name Subject Date Abstract Conventional ultrasound imaging is used widely in the medical setting. Ultrasound imaging uses high frequency sound waves to look at organs and structures within the body. Ultrasound imaging is used to evaluate to important organ structures in the body and is therefore a critical tool in medical diagnosis. Doppler ultrasound on the other hand is a type of ultrasound imaging that uses shifts in frequency from the ultrasound beam to the area of interest, known as Doppler Effect, to evaluate flow within the blood vessels in the body. Doppler ultrasound is used to diagnose blockages, clots and other medical phenomena within the blood vessels. It has numerous advantages and certain limitations but is an imaging modality that is immensely valuable as a diagnostic tool. Introduction Doppler Ultrasound is an ultrasound technique used in observing fetuses in the womb, internal body organs, and blood flow through blood vessels in the abdomen, arms, legs and neck. The use of ultrasound in medical imaging is ubiquitous in the healthcare setting. The Ultrasound imaging the intended picture is sometimes needed to be a motion picture, sometimes referred to as a 4D image. Sometimes the color of the object needs to be clear, and sometimes the spectral displays are needed. The movement of an object brings the necessity of a robust imaging system that can accommodate the various parameters need. Structural engineers trying to get to know the internal structure of anything may have as many options as they can think of. It is easier to take any option from MRI (magnetic resonance imaging), CT scans; X-rays to gamma radiation, though these options get limited or narrow when you consider movement. The use of Doppler ultrasound which is a subset of diagnostic ultrasound imaging has also risen invariably. Ultrasound imaging utilizes reflected sound waves to produce diagnostic images of the relevant organs and structures in the body including vessels, joints and muscles. Ultrasound generally refers to the frequencies above the audible range of human hearing. This is generally thought to about 20Khz. Frequencies used in diagnostic ultrasound imaging are generally between 2 MHz and 8Mhz. A computer converts these frequencies or sound waves into two dimensional black and white moving pictures on your computer screen. Doppler ultrasound however, uses the reflected sound waves in the evaluation of moving structures like blood vessels in the body. It is usually ordered to check blood flow in the major arteries and veins. Narrowing or blocking of blood vessels can be revealed through the use of Doppler ultrasound. It is also commonly used to detect problems during pregnancy especially in the unborn fetus. This report will focus on the physics, processes and equipment used in Doppler ultrasound. It will also focus on the results, clinical indicators, advantages, limitations and applications of Doppler ultrasound. The Physics of Doppler Ultrasound The basis of Doppler ultrasound is what is known as the Doppler Effect. It is named after an Australian physicist Christian Doppler who theorized it in 1842. It states that the reflected waves from a moving object will undergo a change in frequency. For example when a vehicle with a siren moves toward an observer the frequency received by the observer is higher than that emitted from the siren and this is also the case as the source of the siren moves away. The magnitude and direction of this change is able to provide information about the moving object. In the medical realm, the movement of blood cells causes changes in the pitch of reflected sound waves from the Doppler ultrasound machine. This hand-held machine is known as a transducer and is lightly applied on the skin over a blood vessel. Information from the reflected sound waves is then processed by a computer into two dimensional color images and graphs as well. Figure 1: Doppler ultrasound measures the movement of scatters in the blood through the beam. As blood velocity increases so does Doppler frequency There a few basic types of Doppler ultrasound including continuous or pulsed wave Doppler, duplex Doppler and color Doppler ultrasound. Continuous Wave Doppler Also known as bedside Doppler, in this kind of Doppler ultrasound, there is continuous transmission and reception of ultrasound. Deane (2002) states Doppler signals are obtained from all vessels in the path of the ultrasound beam. The change in pitch of the sound waves produced is what is used to provide information about flow of blood in the vessels. The beam has to become sufficiently attenuated to provide information about the blood vessel. As the name suggest in can be done at the bedside in a hospital with a portable machine. Figure 2: Continuous wave Doppler transducer. Continuous wave Doppler can therefore detect high velocity flows however, is unable to pinpoint where along the line the high velocity is coming from. Pulse wave Doppler can achieve this. Pulse Wave Doppler Pulse wave Doppler allows measurement of velocity along a single point on the line. The radiographer sends a signal or to a specific depth and then listens for frequency at that depth. Duplex Doppler In duplex ultrasound, a picture of the blood vessels and surrounding organs is produced usually using standard ultrasound methods. It therefore combines conventional imaging information and Doppler flow imaging information to allow the structure of the blood vessels to be seen. During a duplex ultrasound exam the radiographer uses two forms of ultrasound together, conventional ultrasound to show structure of blood vessels and Doppler ultrasound to show flow of blood through the vessels. Color Doppler In this type of Doppler, a color image of the blood vessel is produced. Doppler sounds are then converted into colors that are overlaid on the blood vessel to come up with information about the speed and direction of the blood flow through the blood vessel. The image viewed in grayscale is difficult to read and color Doppler improves the image. It assigns color values that depend on whether the blood is moving towards or away from the transducer. Figure 3: Color flow Doppler image There are several factors that affect Doppler ultrasound imaging including blood velocity, ultrasound frequency, the choice of frequency and angle of isonation. Generally as blood velocity increases, Doppler frequency increases as well. Higher ultrasound frequencies yield higher Doppler frequencies. The choice of frequency is a choice between sensitivity to flow or better penetration. The angle of isonation affects in that as the ultrasound beam becomes more aligned to the flow of blood the Doppler frequency increases. Doppler ultrasound has a variety of clinical uses or indications. Clinical Uses for Doppler Ultrasound Doppler ultrasound is used by medics to diagnose or evaluate a host of medical conditions. It used to evaluate pain in the leg pain that occurs in the leg during exercise like going up a hill or climbing up the stairs. This pain could be caused by atherosclerosis Blood flow after a stroke or other medical condition can be evaluated with Doppler ultrasound It can be used evaluate grafts used to bypass blockage in veins or grafts The health of unborn baby especially flow of blood in the unborn fetus can be checked. Blood flow in the heart, placenta or brain may be evaluated. It can be used to monitor blood flow after surgery Abnormal veins that can cause varicose veins can also be evaluated Doppler ultrasound is also used to guide treatments like laser ablation of abnormal veins The location and amount of arterial plaque can be evaluated using Doppler ultrasound Doppler ultrasound can be used to find blood clots in most parts of the body including in the arms, legs and neck The Doppler ultrasound has its own purpose ranging from monitoring blood flow to pinpointing sterosis and further in detecting deep venous thrombosis better known as DVT which is a determinant in angioplasty procedures. Monitoring blood flow- The use of Doppler ultrasound makes sure ones blood flow normally to throughout the body. Pinpoint of sterosis- These are tiny particles of stones found in the kidney. In some cases, operation is the only way to do away with sterosis. Ultrasound detects these stones when they are still at the infant stage thus doing away with them in proper time. In most kidney related diseases, a considerable percentage is because of sterosis. Doppler ultrasound is the only surest way to cure sterosis. Detection of deep venous thrombosis (DVT) - Detection of deep venous thrombosis is a dangerous type of infection that one can have and which have fatal consequences if not detected early. Doppler ultrasound is one of the most sophisticated treatments is used in detecting deep venous thrombosis. It’s a simple detecting method which involves holding a detector and pointing to the infected area and the presence of venous thrombosis is either detected or not. Advantages of Doppler Ultrasound There are various advantages of Doppler ultrasound. First and foremost, Doppler ultrasound is the only ultrasound examination that can be used to evaluate blood vessels in a noninvasive manner. It also a fairly straightforward and can be easily performed. Studies have shown that Doppler ultrasound can be effective in high-risk pregnancies in reducing caesarian sections and the number who may die because of this. When Doppler ultrasound is used to evaluate blood flow in the unborn fetus, medics can decide which high risk pregnancies need assistance during delivery and those that can be delivered unassisted. Doppler ultrasound instrumentation is also relatively inexpensive compare to other methods of diagnostic imaging evaluation like CT scans and conventional x-ray machines. Certainly it is more portable than other methods (Science Daily 2010). Other Benefits of Doppler ultrasound Cautious and highly safe- ultrasound is one of the best mode of treatments as far as health safety is concerned. This is simply to give best and reliable results not to mention its efficiency. Well and carefully distributed picture elements or pixels give a doctor conducting ultrasound a clearer view of what is happening on a patient’s infected part his/her body. Therapeutic applications Stone breakage- sometimes the stones in a patient’s kidney can be bigger than expected. As an alternative to operation or surgery, breakage of kidney stones is made easier by using Doppler ultrasound. Doppler ultrasound helps in Heat generation and mechanical changes in tissues. These include change in iron and vitamins, carbohydrates in the blood circulation system. The general idea of this application is to make changes that occur in a particular patient suit the diagnosis of the disease at hand. Generation of heat comes in whereby a patient is sick boosting the temperature to an optimum point. The magical aspect of this idea is that generation of heat is done within a short time as compared to other methods. Rise in temperature also assists in efficient flow of blood. Doppler Ultrasound limitations Just like any other imaging technique in diagnostic imaging, Doppler ultrasound has its limitations. Depth ambiguity is one of the limitations of Doppler ultrasound. Reflections deep in the field of view or area being examined may arrive at the transducer after the next pulse has been emitted. Deep Doppler shifts may therefore record in an area where there is no flow. This may occur with low frequency transducer but is usually not a clinical issue because tissue usually attenuates the beam sufficiently causing shifts to go below depiction threshold. An additional limitation is angle of isolation (Mitchell 1990). Generally, in conventional ultrasound, the angle transducer is almost perpendicular to the reflecting surface. This usually produces the strongest reflections. However, in Doppler ultrasound Doppler shift is greatest when flow is aligned parallel to the ultrasound beam. As the angle of isolation approaches 90 degrees, the Doppler shifts may fall below the level of detection. But sometimes a larger angle of isonation may be appropriate as determined by the radiographer. Transducer geometry may also be a limitation. The ultrasound beam from a linear array transducer usually has constant angle relative to the skin surface. This angle however, can be altered mechanically using a wedge as well as electronically. However, steering the beam at angles other than 90 degrees to the transducer can cause degradation and increase artifacts on the Doppler images (Mitchell 1990). Another limitation of Doppler ultrasound can be the need to follow up exams because of variation in data from different ultrasound instruments. However, sometimes this can be expensive especially when the follow up exams do not yield the expected. It is therefore important to improve QA systems within health facilities to counter this limitation (Strope & Conti 2011) Conclusion The human perception of an object in space gives human the idea of the distance. For ultrasound gadgets, physical properties of sound like the speed of sound, frequency and wavelength is used to gauge the distance. The speed of sound is based on the medium with which the sound is conveyed. Ultrasound technology in general and Doppler ultrasound in particular has come a long way. The first quantitatively accurate Doppler ultrasound instruments became available in the 1980s and since then there has been continuous improvement in instrumentation and therefore quality of diagnostic images and thereby improving medical outcomes. It is the safest, lowest cost and simplest way to evaluate blood vessels. Recent developments including the ability to view colored images and Power ultrasound are among the recent development in this field. Doppler ultrasound is a widely embraced method for imaging, medically it is a less costly method, and has less harmful risks compared to other electromagnetic methods of imaging. The future lies in continuously the quality and accuracy of data of the Doppler instruments and improving access to these technologies in the developing world where the dire need for these instruments is being realized with changing disease patterns. References American Roentgen Ray Society. 2008. Ultrasound First, Not CT, For Diagnosing Suspected Acute Appendicitis. ScienceDaily. Viewed 25 October 2012, from Canadian Medical Association Journal (2010, January 5). Prenatal ultrasonography has increased 55 percent for pregnant women, even in low-risk pregnancies. ScienceDaily. Viewed October 25, 2012, http://www.sciencedaily.com­ /releases/2010/01/100105170932.htm Conti, J, Strope, E 2011, ‘How Accurate Doppler Ultrasound Can Reduce Health Care Costs and Increase Patient Safety’, viewed 24 October 2012, < http://dynateklabs.com/how- accurate-doppler-ultrasound-can-reduce-health-care-costs-and-increase-patient-safety/>. Deane, C 2002, ‘Doppler Ultrasound Principles and Practice’, 2002, viewed 24 October 2012, . Doppler Ultrasound in Pregnancy Reduces Risk in High Risk Groups n.d., viewed 20 October 2012, < http://www.sciencedaily.com/releases/2010/01/100119213045.htm>. Doppler Ultrasound Principles and Practice, images, viewed 24 October 2012, . Eberhard M. 2006, ‘Ultrasound in Obstetrics and Gynecology, Volume 2. NY: Thieme pp. 212 Evans DH, McDicken WN, Skidmore R, Woodcock JP. Doppler Ultrasound: Physics, Instrumentation, and Clinical Applications. Chichester: Wiley, 1989. Goldberg BB, Merton DA, Deane CR. An Atlas of Ultrasound Color Flow Imaging. London: Martin Dunitz, 1997. Gill RW. Measurement of blood flow by ultrasound: accuracy and sources of error. Ultrasound Med Bio, 1985;7: 625–42. Gosling RG, King DH. Continuous wave ultrasound as an alternative and complement to X- rays in vascular examination. In Reneman RS, ed. Cardiovascular Applications of Ultrasound. Amsterdam: North Holland, 1974:266–82. Mitchell, G, D 1990, ‘Color Doppler Imaging: Principles, Limitations and Artifacts’, State of the Art, vo. 177, no. 1, pp. 1-10. Powis RL, Schwartz RD. Practical Doppler Ultrasound for the Clinicia. Williams and Wilkins, 1991. Rourke C, Hendrickx P, Roth U, Brassel F, Creutzig A, Alexander K. Color and conventional image-directed ultrasonography: accuracy and sources of error in quantitative blood flow measurement.J Clin Ultrasound 1992;20:187–93 Thompson RS, Trudinger BJ, Cook CM. A comparison of Doppler ultrasound waveform indices in the umbilical artery. II. Indices derived from the mean velocity and first moment waveforms.Ultrasound Med Biol 1986;12:845–54. Wiley B. 2010, Doppler ultrasound in pregnancy reduces risk in high-risk groups. ScienceDaily. , viewed 24 October 2012,< http://www.sciencedaily.com­ /releases/2010/01/100119213045.htm> Dubose, T. J. (1985). "Fetal Biometry: Vertical Calvarial Diameter and Calvarial Volume". Journal of Diagnostic Medical Sonography 1 (5): 205. doi:10.1177/875647938500100504. ^ "3D BPD Correction". July 2000. http://www.obgyn.net/us/cotm/0007/3d-bpd-correction.htm. Read More

This report will focus on the physics, processes and equipment used in Doppler ultrasound. It will also focus on the results, clinical indicators, advantages, limitations and applications of Doppler ultrasound. The Physics of Doppler Ultrasound The basis of Doppler ultrasound is what is known as the Doppler Effect. It is named after an Australian physicist Christian Doppler who theorized it in 1842. It states that the reflected waves from a moving object will undergo a change in frequency. For example when a vehicle with a siren moves toward an observer the frequency received by the observer is higher than that emitted from the siren and this is also the case as the source of the siren moves away.

The magnitude and direction of this change is able to provide information about the moving object. In the medical realm, the movement of blood cells causes changes in the pitch of reflected sound waves from the Doppler ultrasound machine. This hand-held machine is known as a transducer and is lightly applied on the skin over a blood vessel. Information from the reflected sound waves is then processed by a computer into two dimensional color images and graphs as well. Figure 1: Doppler ultrasound measures the movement of scatters in the blood through the beam.

As blood velocity increases so does Doppler frequency There a few basic types of Doppler ultrasound including continuous or pulsed wave Doppler, duplex Doppler and color Doppler ultrasound. Continuous Wave Doppler Also known as bedside Doppler, in this kind of Doppler ultrasound, there is continuous transmission and reception of ultrasound. Deane (2002) states Doppler signals are obtained from all vessels in the path of the ultrasound beam. The change in pitch of the sound waves produced is what is used to provide information about flow of blood in the vessels.

The beam has to become sufficiently attenuated to provide information about the blood vessel. As the name suggest in can be done at the bedside in a hospital with a portable machine. Figure 2: Continuous wave Doppler transducer. Continuous wave Doppler can therefore detect high velocity flows however, is unable to pinpoint where along the line the high velocity is coming from. Pulse wave Doppler can achieve this. Pulse Wave Doppler Pulse wave Doppler allows measurement of velocity along a single point on the line.

The radiographer sends a signal or to a specific depth and then listens for frequency at that depth. Duplex Doppler In duplex ultrasound, a picture of the blood vessels and surrounding organs is produced usually using standard ultrasound methods. It therefore combines conventional imaging information and Doppler flow imaging information to allow the structure of the blood vessels to be seen. During a duplex ultrasound exam the radiographer uses two forms of ultrasound together, conventional ultrasound to show structure of blood vessels and Doppler ultrasound to show flow of blood through the vessels.

Color Doppler In this type of Doppler, a color image of the blood vessel is produced. Doppler sounds are then converted into colors that are overlaid on the blood vessel to come up with information about the speed and direction of the blood flow through the blood vessel. The image viewed in grayscale is difficult to read and color Doppler improves the image. It assigns color values that depend on whether the blood is moving towards or away from the transducer. Figure 3: Color flow Doppler image There are several factors that affect Doppler ultrasound imaging including blood velocity, ultrasound frequency, the choice of frequency and angle of isonation.

Generally as blood velocity increases, Doppler frequency increases as well. Higher ultrasound frequencies yield higher Doppler frequencies. The choice of frequency is a choice between sensitivity to flow or better penetration. The angle of isonation affects in that as the ultrasound beam becomes more aligned to the flow of blood the Doppler frequency increases.

Read More