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Pulsed-wave Doppler, in physics, is an ultrasound technique that precisely measures blood flow velocity at a specific location. It emits short bursts of ultrasound waves and then listens for echoes from moving red blood cells. By analyzing the time delay between pulses and the frequency shift (Doppler effect) of the returning echoes, the system can…

In physics, propagation speed in medical ultrasound refers to the rate at which sound waves travel through a medium. This crucial parameter is determined by the density and stiffness of the tissue; sound propagates faster through denser, stiffer tissues like bone than through fluid or fat. Understanding propagation speed is fundamental to accurate depth perception…

In physics, aliasing is a distortion or artifact that occurs when a continuous signal is sampled at a rate too low to accurately capture its true characteristics. This fundamental concept is particularly relevant in medical imaging and ultrasound, where it manifests when the sampling rate (pulse repetition frequency) is insufficient to accurately measure high-velocity blood…

In physics, acoustic impedance mismatch describes the difference in acoustic impedance between two media at their boundary. When sound waves encounter this mismatch, a portion of the wave is reflected, and the remaining portion is transmitted. This principle is fundamental to understanding how ultrasound works in medical imaging. In ultrasound, significant acoustic impedance mismatches, such…

In physics, the Nyquist limit is a fundamental concept in digital signal processing, particularly crucial in medical ultrasound. It states that to accurately reconstruct a signal, the sampling rate must be at least twice the highest frequency component of the original signal. Exceeding this limit leads to aliasing, where high-frequency information is misrepresented as lower…

In physics, Snell's Law describes the relationship between the angles of incidence and refraction of a wave passing through the boundary between two different isotropic media, such as sound waves traveling through various body tissues. This fundamental principle dictates how ultrasound beams bend when encountering interfaces between structures with different acoustic impedances, impacting image quality…

Time-gain compensation (TGC), a critical concept in ultrasound physics, is an adjustable control that allows sonographers to compensate for the attenuation of sound waves as they travel deeper into tissues. This function selectively amplifies echoes returning from greater depths, ensuring a uniform brightness across the entire ultrasound image. Without proper TGC adjustment, deeper structures would…

The Mechanical Index (MI) in medical ultrasound physics quantifies the potential for mechanical bioeffects, such as cavitation, in tissues. It's calculated as the peak negative pressure divided by the square root of the ultrasound frequency. A higher MI indicates a greater likelihood of these effects, crucial for patient safety. Sonographers closely monitor MI to ensure…

The Thermal Index (TI) is a crucial safety parameter in medical ultrasound, quantifying the potential for tissue heating due to the absorption of acoustic energy. Representing the ratio of acoustic power to the power required to raise tissue temperature by 1°C, TI helps sonographers and clinicians monitor and minimize thermal bioeffects, especially during prolonged or…