Question: A carotid Doppler machine uses what change in frequency or wavelength of a wave for an observer who is moving relative to the wave source?

full_context: Document 1: Photoacoustic Doppler effect: The photoacoustic Doppler effect, as its name implies, is one specific kind of Doppler effect, which occurs when an intensely modulated light wave induces a photoacoustic wave on moving particles with a specific frequency. The observed frequency shift is a good indicator of the velocity of the illuminated moving particles. A potential biomedical application is measuring blood flow.
Document 2: Christian Doppler: Christian Andreas Doppler ( ; ] ; 29 November 1803 – 17 March 1853) was an Austrian mathematician and physicist. He is celebrated for his principle — known as the Doppler effect — that the observed frequency of a wave depends on the relative speed of the source and the observer. He used this concept to explain the color of binary stars.
Document 3: Franz–Keldysh effect: The Franz–Keldysh effect is a change in optical absorption by a semiconductor when an electric field is applied. The effect is named after the German physicist Walter Franz and Russian physicist Leonid Keldysh (nephew of Mstislav Keldysh).
Document 4: Tissue Doppler echocardiography: Tissue Doppler echocardiography (Also called Tissue Doppler Imaging - TDI or Tissue Velocity Imaging - TVI) is a Medical ultrasound technology mainly used in Echocardiography that measures the velocity of the heart muscle or myocardium through the phases of one or more heartbeats by the Doppler effect (frequency shift) of the reflected ultrasound. The technique is the same as for Doppler echocardiography, measuring flow velocities. Tissue signals however, have higher amplitude and lower velocities, and the signals are extracted by using different filter and gain settings. Like Doppler flow, Tissue Doppler can be acquired both by spectral analysis (Spectral density estimation) as pulsed Doppler and by the Autocorrelation technique as colour Tissue Doppler (Duplex ultrasonography). While pulsed Doppler only acquires the velocity at one point at a time, colour Doppler can acquire simultaneous pixel velocity values across the whole imaging field. Pulsed Doppler on the other hand, is more robust against noise, as peak values are measured on top of the spectrum, and are unaffected of the presence of clutter (stationary reverberation noise).
Document 5: Carotidynia: Carotidynia is a syndrome characterized by unilateral (one-sided) tenderness of the carotid artery, near the bifurcation. It was first described in 1927 by Temple Fay. The most common cause of carotidynia may be migraine, and then it is usually self-correcting. Common migraine treatments may help alleviate the carotidynia symptoms. Recent histological evidence has implicated an inflammatory component of carotidynia, but studies are limited. Carotid arteritis is a much less common cause of carotidynia, but has much more serious consequences. It is a form of giant cell arteritis, which is a condition that usually affects arteries in the head. Due to this serious condition possibly causing carotidynia, and the possibility that neck pain is related to some other non-carotidynia and serious condition, the case should be investigated by a medical doctor. Because carotidynia can be caused by numerous causes, Biousse and Bousser in 1994 recommended the term not be used in the medical literature. However, recent MRI and ultrasound studies have supported the existence of a differential diagnosis of carotidynia consistent with Fay's characterization.
Document 6: Transcranial Doppler: Transcranial Doppler (TCD) and transcranial color Doppler (TCCD) are types of Doppler ultrasonography that measure the velocity of blood flow through the brain's blood vessels by measuring the echoes of ultrasound waves moving transcranially (through the cranium). These modes of medical imaging conduct a spectral analysis of the acoustic signals they receive and can therefore be classified as methods of active acoustocerebrography. They are used as tests to help diagnose emboli, stenosis, vasospasm from a subarachnoid hemorrhage (bleeding from a ruptured aneurysm), and other problems. These relatively quick and inexpensive tests are growing in popularity. The tests are effective for detecting sickle cell disease, ischemic cerebrovascular disease, subarachnoid hemorrhage, arteriovenous malformations, and cerebral circulatory arrest. The tests are possibly useful for perioperative monitoring and meningeal infection. The equipment used for these tests is becoming increasingly portable, making it possible for a clinician to travel to a hospital, to a doctor's office, or to a nursing home for both inpatient and outpatient studies. The tests are often used in conjunction with other tests such as MRI, MRA, carotid duplex ultrasound and CT scans. The tests are also used for research in cognitive neuroscience (see Functional transcranial Doppler, below).
Document 7: Carotid Doppler machine: A carotid Doppler machine is a device which can be used to measure blood flow velocities within the cervical carotid arteries, as well as the vertebral arteries and sometimes the subclavian arteries by means of non-invasive ultrasonic scanning in which the Doppler effect is utilized. This can be useful for estimating the effects of atherosclerotic disease on the lumen in late stages; specifically the level of compromise in blood flow caused by reduction in arterial lumen diameter.
Document 8: Coronary artery ectasia: Coronary artery ectasia is a rare disease that occurs in only 0.3-4.9% of people in North America. Coronary artery ectasia is characterized by the enlargement of a coronary artery to 1.5 times or more than its normal diameter. The disease is commonly asymptomatic and is normally discovered when performing tests for other conditions such as coronary artery disease, stable angina and other acute coronary syndromes. Coronary artery ectasia occurs 4 times more frequently in males than in females and in people who have risk factors for heart disease such as smokers. While the disease is commonly found in patients with atherosclerosis and coronary artery disease, it can occur by itself and in both cases it can cause health problems. The disease can cause the heart tissue to be deprived of blood and die due to decreased blood flow, and blockages due to blood clots or spasms of the blood vessel. This blood flow disruption can cause permanent damage to the muscle if the deprivation is prolonged. Coronary artery ectasia also increases the chance of developing large weak spots in the affected coronary arteries, or aneurysms that can rupture and result in death. The damage can result in angina which is pain in the chest and is a common complaint in these patients.
Document 9: Cherenkov radiation: Cherenkov radiation, also known as Vavilov–Cherenkov radiation (named after Sergey Vavilov and Pavel Cherenkov), is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium at a speed greater than the phase velocity of light in that medium. The characteristic blue glow of an underwater nuclear reactor is due to Cherenkov radiation. It is named after Soviet scientist Pavel Alekseyevich Cherenkov, the 1958 Nobel Prize winner who was the first to detect it experimentally. A theory of this effect was later developed within the framework of Einstein's special relativity theory by Igor Tamm and Ilya Frank, who also shared the Nobel Prize. Cherenkov radiation had been theoretically predicted by the English polymath Oliver Heaviside in papers published in 1888–89.
Document 10: Phase contrast magnetic resonance imaging: Phase contrast magnetic resonance imaging (PC-MRI) is a specific type of magnetic resonance imaging used primarily to determine flow velocities. PC-MRI can be considered a method of Magnetic Resonance Velocimetry. Since modern PC-MRI is typically time-resolved, it can also be referred to as 4D imaging (three spatial dimensions plus time).
Document 11: Time dilation: According to the theory of relativity, time dilation is a difference in the elapsed time measured by two observers, either due to a velocity difference relative to each other, or by being differently situated relative to a gravitational field. As a result of the nature of spacetime, a clock that is moving relative to an observer will be measured to tick slower than a clock that is at rest in the observer's own frame of reference. A clock that is under the influence of a stronger gravitational field than an observer's will also be measured to tick slower than the observer's own clock.
Document 12: Doppler effect: The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave for an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.
Document 13: Magnetic resonance velocimetry: Magnetic resonance velocimetry (MRV) is an experimental method to obtain velocity fields in fluid mechanics. MRV is based on the phenomenon of nuclear magnetic resonance and adapts a medical magnetic resonance imaging system for the analysis of technical flows. The velocities are usually obtained by phase contrast tomography techniques. This means velocities are calculated from phase differences in the image data that has been produced using special gradient techniques. MRV can be applied using common medical MRI scanners. The term "magnetic resonance velocimetry" became current due to the increasing use of MR technology for the measurement of technical flows in engineering.
Document 14: Bruit: vascular murmur" ( ; from French, "noise"), or vascular murmur"', is the abnormal sound generated by turbulent flow of blood in an artery due to either an area of partial obstruction; or a localized high rate of blood flow through an unobstructed artery. The bruit may be heard ("auscultated") by pressing a stethoscope to the skin over the turbulent flow and listening. Most bruits occur only in systole, so the bruit is intermittent and its frequency dependent on the heart rate. Anything increasing the blood flow velocity such as fever, anemia, or hyperthyroidism, can increase the amplitude of the bruit.
Document 15: Relativistic Doppler effect: The relativistic Doppler effect is the change in frequency (and wavelength) of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect), when taking into account effects described by the special theory of relativity.
ground_truth: Doppler effect