← Section I · Physical Principles, Instrumentation, Examination Principles

I.D

Cross-Sectional Echocardiographic Examination

4 cards

Notes

Boundary types

Specular reflectors - large (> λ) and smooth surfaces (chamber walls, valve leaflets, pericardium, diaphragm). Return strong signals. Best imaging when beam is perpendicular.
Non-specular / scatterers - small or rough (RBCs, tissue). Return weak signals in all directions (basis for backscatter and Doppler).

Backscatter

The dominant signal used to form a 2-D image (it returns energy in many directions, so the transducer catches some regardless of orientation).

Refraction

At 90° incidence, no refraction. At oblique angles across an interface between tissues of different propagation speeds (Snell's law), the beam bends → duplicated/displaced structures.

Reflection basics

Angle of incidence = angle of reflection.
Reflection amplitude depends on acoustic impedance mismatch at the interface.

Higher frequency → more scatter

Scatter cross-section scales with frequency; explains why higher-frequency imaging shows more speckle.

Cards

basicI.D-001
Give three examples of specular reflectors in the heart.
→ Chamber walls, valve leaflets, pericardium, diaphragm — large (> λ), smooth surfaces that produce strong reflections.
basicI.D-002
Give two examples of non-specular reflectors (scatterers) and their significance.
→ Red blood cells and soft tissue — small or rough. They scatter US in multiple directions; scattering off RBCs is the physical basis of Doppler.
basicI.D-003
Under what geometric condition does refraction NOT occur at an interface?
→ When the beam is at normal incidence (90°) to the interface — no oblique component to refract.
basicI.D-004
How does higher transducer frequency affect scattering?
→ Higher frequency = more scatter (scatter cross-section increases with frequency). This is why high-frequency imaging shows more speckle.