One of the techniques to determine blood flow in a superficial blood vessel is to measure the frequency change by the Doppler effect of ultrasound. The mean velocity of blood flow in the aorta during systole is 1.5 × 10–2 m / s. What is the frequency change in an instrument with a signal frequency of 105 Hz? (speed of sound in blood, 1570 m / s).
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Answer:
Medical Doppler ultrasound is usually utilized in the clinical adjusting to evaluate and estimate blood flow in both the major (large) and the minor (tiny) vessels of the body. The normal and abnormal sign waveforms can be shown by spectral Doppler technique. The sign waveform is individual to each vessel. Thus, it is significant for the operator and the clinicians to understand the normal and abnormal diagnostic in a spectral Doppler show. The aim of this review is to explain the physical principles behind the medical Doppler ultrasound, also, to use some of the mathematical formulas utilized in the medical Doppler ultrasound examination. Furthermore, we discussed the color and spectral flow model of Doppler ultrasound. Finally, we explained spectral Doppler sign waveforms to show both the normal and abnormal signs waveforms that are individual to the common carotid artery, because these signs are important for both the radiologist and sonographer to perceive both the normal and abnormal in a spectral Doppler show.
The sound is a mechanical power (energy) which travel or propagate during flexible (elastic) continuous medium by the rarefaction and compression of elements that compose it. Rarefaction is an area where the elements furthest from each other, whereas the compression is an area where the elements are closest together. The energy (power) traveling occurs when the signal wave front in the direction of power propagate, called as a longitudinal wave. The distance between both of rarefaction and compression or between each two spots which regenerate on the sinusoidal signal wave known as the wavelength (λ). In contrast, the quantity of times the signal wave fluctuates (oscillates) during a cycle count each second known as the frequency (f).[1] When the frequency exceeds 20KHz, the human cannot hear it, and this process called ultrasound.[4] The speed of sound relies on both the compressibility and density of the medium and variates largely with materials variation.[5] The relationship between the wavelength (λ), frequency (f), and the velocity (c) given by this formula (
The probe or the transducer is a necessary component in an ultrasound system. The transducer has an ingredient that has the ability to produce ultrasound signal waves, and these signals occur when the electric current passes through the probe ingredient. This process called piezoelectric (PE) influence. Furthermore, the main function of the probe is sending ultrasound energy into body organs or into samples and then receiving the reflected signal echoes that may be processed via ultrasound unit into images displayed on a screen monitor. When a voltage utilized by PE element, this will produce a pressure signal wave. The ingredient utilized as a PE element made of crystal, like plastic and lead zirconate titanate which is the most common ingredient to be used basic components of an ultrasound probe are shown in Figure 1 In addition to the crystal which was described before, both of backing and matching materials are very significant components of the system. Matching layer is item situated between the PE material and the phantom sample or the patient. The acoustic resistance in matching layer is coming between PE material and the skin or the surface of the phantom sample, this help to produce a reflection of ultrasound power, then permits for larger energy of ultrasound to transporting through the tissues or blood vessels to produce images.[6] However, backing material, also called damping material, is placed behind the PE ingredient to reduce the pulse period. When the pulse period reduces, it becomes shortened, and this help to improve broadens bandwidth and resolution. The broadens bandwidth technique permits the probe to have a wide range of frequencies.[7] Choosing probes depend on the organ (structure) being tested and on the size of patient or phantom. Generally, the highest probable frequency should be applied because it will increase the resolution, while the lower frequency decrease the resolution and lead to increases the penetration.[8] However, linear probe with a frequency of more than 5 MHz is required in Doppler image scanning.[9,10,11,12,13]
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