Basic physical principles of ultrasound

# Sound Waves
- Ultrasound uses high frequency energy to create sound waves, characterized by
frequency: number of cycles per second (Hz)
wavelength: distance between excitations (mm)
amplitude: height of sound wave (decibels)
- frequency: number of cycles per second (Hz)
- wavelength: distance between excitations (mm)
- amplitude: height of sound wave (decibels)

# Ultrasound And Tissue Interaction
- Reflection
- occurs when an ultrasound wave hits tissue.  Part of the wave is reflected back to the transducer
tissues with greater density reflect a greater portion of the beam
tissues at a 90 degree angle to the beam reflect a greater portion of the beam
- occurs when an ultrasound wave hits tissue.  Part of the wave is reflected back to the transducer
- tissues with greater density reflect a greater portion of the beam
- tissues at a 90 degree angle to the beam reflect a greater portion of the beam
- Acoustic impedance
- tissues can be defined by their individual acoustic impedance
AI = density x acoustic velocity
- tissues can be defined by their individual acoustic impedance
- AI = density x acoustic velocity
- Scatter
- small structures lead to scattering of the ultrasound signal
scattering radiates the beam in all directions, very little reaches back to the transducer
- small structures lead to scattering of the ultrasound signal
- scattering radiates the beam in all directions, very little reaches back to the transducer
- refraction: ultrasound waves can be deflected as they pass into a medium of different acoustic impedance
- Attenuation
when sound travels through a medium, intensity diminishes with distance
caused by absorption of the energy by the tissues, and conversion to heat
also affected by acoustic impedance and mismatch in impedance between adjacent structures
- when sound travels through a medium, intensity diminishes with distance
- caused by absorption of the energy by the tissues, and conversion to heat
- also affected by acoustic impedance and mismatch in impedance between adjacent structures

# Ultrasound Set-Up
- Energy source
- Transducer
- Piezoelectric crystals
- It is found inside the transducer
- It compresses and expand the electric current that is applied, generating a sound wave
- Same crystals also act as receivers.  An electric current is generated when a reflected wave hits a crystal.
Image formation: based on the time interval between the ultrasound transmission and the arrival of the sound wave back to the transducer

# Resolution
- Axial- along the length of the ultrasound beam
- Lateral- side to side resolution of the 2D image
- Elevational- the thickness of the tomographic slice

# Basics of Echocardiography

## Basics of Echocardiography-Part 1
Basics of Echocardiography-Part 1-Series 1
Basics of Echocardiography-Part 1-Series 2

## Basics of Echocardiography-Part 2
Basics of Echocardiography-Part 2--Series 1
Basics of Echocardiography-Part 2--Series 2

# Fetal Echocardiography

## A Descriptive Case Presentation
- A Descriptive Case Presentation

## Transposition
- Transposition

## Fetal Cardiac Myxoma
- Fetal Cardiac Myxoma

# The Guide to Pediatric Echocardiography

## Pediatric Echocardiography