Radiology Ultrasound physics

Explore pulse echo ultrasound parameters, including transmit and receive modes, range equation, speed of sound, and pulse duration, repetition period, and duty factor for depth-dependent imaging.

Explore acoustic impedance in ultrasound physics, linking tissue density and sound speed to boundary reflections, refractions, and scattering; learn how impedance differences govern how much sound reflects at tissue interfaces.

Explore how tissue acoustic impedance differences and incidence angle govern ultrasound reflection, producing specular or diffuse reflections that, with attenuation and transmission, shape image formation.

Explore how ultrasound refraction changes beam direction at tissue interfaces, with incident and transmitted angles adapting to tissue velocities, causing potential spatial distortions and artifacts in images.

Explain how ultrasound scatter occurs when tissue wavelength is smaller than the ultrasound wavelength, redirecting sound. Describe how attenuation increases with depth and frequencies, reducing beam intensity and image formation.

Describe the piezoelectric effect as the core mechanism for ultrasound generation, where piezoelectric crystals expand under voltage to produce sound and receive echoes from tissue, within a transducer assembly.

Examine how the damping block backed by tungsten-loaded zeolite dampens the piezoelectric crystal to produce a short pulse length and preserve axial resolution, noting tradeoffs with bandwidth and beam intensity.

Explore the three ultrasound modes—a-mode, b-mode, and m-mode—and how amplitude, brightness, and motion plots reveal tissue interfaces, echogenicity, and heart or brain measurements.

Apply time gain compensation to offset ultrasound attenuation as depth increases, adjusting the electrical signal so deeper tissues appear as echogenic as superficial ones.

Learn how ultrasound transducers, powered by piezoelectric crystals, generate and receive echoes to create sonograms, and compare linear, convex, phased array, pencil, and endocavitary probes across 2D and 3D imaging.

Explain how the ultrasound beam forms from the transducer, with near-field, focal, and far-field (Fresnel) zones, and how diameter and frequency influence divergence and focal distance.

Explore how ultrasound beam focusing shapes imaging quality by adjusting transducer surface area, transmit/receive elements, and frequency, with phased and linear arrays using delays and dynamic receive focusing.

Explore axial resolution, the minimum separation of two reflectors parallel to the ultrasound beam. It depends on spatial pulse length and improves with shorter pulses or higher frequency transducers.

Understand lateral resolution, the minimum separation of side-by-side reflectors perpendicular to the beam axis. Identify how beam width, frequency, focusing, and gain optimization affect resolution and penetration.

Explore how temporal resolution in ultrasound depends on frame rate to distinguish closely spaced moving structures, and how field of view and depth affect this capability.

Explore the Doppler shift in ultrasound, linking frequency changes to blood flow velocity through the Doppler equation and the critical role of the 30–60 degree insonation angle.

Compare continuous wave and pulsed wave Doppler in ultrasound physics, highlighting velocity assessment, depth localization, spectral analysis, and strategies to avoid aliasing.

Explore the three ultrasound doppler modes—color, power, and spectral—showing flow direction, velocity, and distribution. Learn how aliasing, laminar vs turbulent flow, and spectral indices inform haemodynamic assessment.

Tissue harmonic imaging enhances ultrasound image quality by using nonlinear propagation to generate harmonic signals, improving contrast resolution, reducing clutter, and sharpening lesion borders.

Identify key ultrasound artifacts such as reverberation, acoustic shadowing, enhancement, edge shadowing, beam width, side lobe effects, mirror and double images, slice thickness, and refraction, with practical mitigation tips.