THE BASICS & SOUND
When one variable increases as the other decreases, they have this type of relationship.
What is an inverse relationship?
This parameter, measured in Hertz (Hz), describes the number of cycles a sound wave completes in one second.
What is frequency?
This is the general term for the decrease in sound intensity, power, and amplitude as sound travels through the body.
What is attenuation?
This component, bonded to the back of the active element, reduces the "ringing" of the PZT, which creates shorter pulses and a wide bandwidth.
What is the backing material (or damping element)?
This imaging parameter, determined by spatial pulse length, describes the ability to distinguish two structures that are parallel to the sound beam's main axis (one in front of the other).
What is axial resolution?
This parameter, the distance of one complete cycle, is the only one determined by both the source and the medium.
This is the difference between the maximum value and the average value of an acoustic variable, measured in units like Pascals or cm.
What is amplitude?
This property, measured in Rayls, is the resistance of a tissue to sound traveling through it and is calculated as density multiplied by speed.
What is acoustic impedance (Z)?
The region from the transducer to the focus, where the beam gradually narrows, is called this.
What is the near zone (near field or Fresnel zone)?
This type of resolution, determined by the width of the sound beam, is always worse than axial resolution in clinical imaging systems.
What is lateral resolution?
Sound waves are classified as this type of wave because the particles in the medium vibrate in the same direction that the wave is traveling.
What is a longitudinal wave?
This parameter describes the concentration of energy in a sound beam and is calculated by dividing power by the beam's cross-sectional area (W/cm²).
What is intensity?
This type of scattering occurs when the structure is much smaller than the wavelength and is proportional to frequency⁴.
What is Rayleigh scattering?
For a fixed-focus transducer, the focal depth is directly related to these two factors.
What are transducer diameter and frequency?
Higher frequency transducers provide better image quality but have reduced ability in this area, which is why lower frequencies are used for deeper structures.
What is penetration?
This phenomenon occurs when two waves combine. If their peaks occur at the same time and location, it results in a wave that is stronger than the individual waves.
What is constructive interference?
This parameter, which describes the strength of a wave, is directly proportional to the wave's amplitude squared.
What is power?
This is the change in direction of a sound wave when it travels from one medium to another at an oblique angle and the media have different propagation speeds.
Question: What is refraction?
This principle states that a large active element can be thought of as millions of tiny, distinct sound sources whose interference creates the hourglass-shaped beam.
What is Huygens' Principle?
The 13-microsecond rule states that for every 13 µs of go-return time, the reflector is located this distance deeper in the body.
What is 1 cm?
These two terms describe the areas in a longitudinal wave where particles are squeezed together (first term) and where they are stretched apart (second term).
What are compression and rarefaction?
Of the two factors that affect propagation speed, this one, also called bulk modulus, has the greatest influence.
What is stiffness?
This process, which converts ultrasound energy into heat, is the most sizeable component of attenuation.
Question: What is absorption?
The temperature at which a PZT crystal is polarized is called the Curie point. If a transducer is heated above this temperature, it will undergo this process and lose its piezoelectric properties.
What is depolarization?
This artifact occurs when a sound beam strikes a curved reflector (like a rib) at an oblique angle, causing the echo to miss the transducer and creating a shadow behind the structure.
What is shadowing (or edge shadowing)?