RELEVANT TERMINOLOGIES

RT 215 Topic 2

Echogenic

the ability of a structure to produce echoes

Anechoic

the absence of echoes and sonolucent quality—appearing black on ultrasound

Hypoechoic

less reflective structures with a low amount of echoes when compared with neighboring structures, appearing as varying shades of darker gray

Hyperechoic

highly reflective and echo-rich structures compared with neighboring structures, appearing as varying shades of lighter gray; the term is often used interchangeably with echogenic

Homogeneous

organ parenchyma that is uniform in echogenicity

Inhomogeneous or Heterogeneous

organ parenchyma that is not uniform in echogenicity

Sound

mechanical energy transmitted by pressure waves through a medium, causing a mechanical disturbance in the form of molecule vibration

Medium

a substance containing molecules required for sound transmission; sound cannot travel through a vacuum

Vibrating Object

an essential requirement for the production of sound

Infrasound (subsonic)

sound frequencies below 20Hz

Audible Sound

sound frequencies between 20-20,000Hz

Ultrasound

sound frequencies exceeding 20,000Hz

Nondiagnostic Medical Applications

ultrasound applications using frequencies less than 1MHz

Medical Diagnostic Ultrasound

ultrasound applications using frequencies greater than 1MHz

Acoustic Variables

a group of variables including Period, Wavelength, Amplitude, Frequency, and Velocity

Period (T)

the time taken for one complete cycle to occur or the time required for one complete wavelength to pass, expressed in microseconds (µs)

Wavelength (λ)

length of space over which one cycle occurs or the distance between adjacent areas of rarefaction or compression, expressed in millimeters (mm)

Amplitude

the maximum displacement that occurs in an acoustic variable

Frequency (f)

the number of cycles (pressure oscillations) or wavelengths that pass a given point in one second, expressed in hertz (Hz)

Compression

the phase of the wave when molecules are pushed together

Rarefaction

the phase of the wave when molecules are apart

Wave Equation

the physical relationship where velocity (v) equals frequency (f) times wavelength (λ)

Attenuation

the process where an ultrasound beam travels through the body and loses energy, decreasing in intensity and amplitude

Attenuation Processes

the five main processes causing energy loss: absorption, reflection, scattering, refraction, and divergence

Absorption

the main factor causing attenuation where ultrasound energy is converted to heat; it is directly related to frequency and depends on a material's absorption coefficient

Reflection

occurs when sound waves strike an object larger than the wavelength, specifically at an interface between two structures of significantly different acoustic impedance

Scattering

occurs when an ultrasound wave strikes an object equal to or smaller than the wavelength, causing the wave to scatter in different directions

Refraction

the deviation of an ultrasound beam as it travels through tissue after encountering an interface at an oblique angle due to differences in wave velocity

Divergence

the reduction of beam intensity caused by power spreading over a larger area due to diffraction effects

Echoes

signals created when emitted sound waves encounter tissues with an acoustic mismatch, causing reflected waves to be converted into an image on a monitor

Acoustic Impedance (Z)

the property of a substance describing particle behavior under pressure, defined as the product of its density (p) and acoustic velocity (V)

Acoustic Impedance Mismatch

the difference in acoustic impedance between two substances, determining the proportion of energy reflected versus transmitted

Velocity of Ultrasonic Waves in Soft Tissue

an average speed of 1540 meters per second

Piezoelectric Effect

the ability of a material to generate an electrical charge in response to applied pressure, or to change shape when an electric field is applied

Piezoelectric Materials

crystalline materials composed of dipolar molecules used to convert electrical energy into mechanical energy (sound) and vice versa

Natural Piezoelectric Materials

substances like Quartz and Tourmaline

Synthetic Piezoelectric Materials

man-made ceramics like Lead Zirconate Titanate (PZT) and Barium Titanate

Curie Temperature

the temperature threshold above which materials must be heated in an electric field to permanently align dipolar molecules

Resonant Frequency

the natural frequency at which piezoelectric crystals produce oscillations of maximum amplitude, depending on crystal thickness

Beam Divergence Factors

factors such as crystal diameter, where decreasing diameter increases beam divergence

Importance of Ultrasound in Diagnosis

its crucial role in providing real-time, non-invasive imaging of internal organs and soft tissue