Ultrasound Transducers and Beam Physics

Comprehensive vocabulary flashcards covering ultrasound transducer components, beam zones, resolution types, and array operations based on the lecture material.

Transducer

A device that converts electrical energy into ultrasound and ultrasound echoes back into electrical energy.

Piezoelectric Effect

The process where certain materials produce electric voltage when pressure is applied ($\text{Pressure} \rightarrow \text{Electricity}$).

Reverse Piezoelectric Effect

The process where applying electricity causes the crystal to vibrate, producing ultrasound ($\text{Electricity} \rightarrow \text{Sound}$).

Lead Zirconate Titanate (PZT)

The most common material used for the active element inside the transducer that creates and receives ultrasound.

Operating (Resonance) Frequency

The natural frequency at which the crystal vibrates, determined by crystal thickness: thin crystals produce high frequency, and thick crystals produce low frequency.

Backing Material (Damping Material)

Material attached to the back of the crystal that stops it from vibrating too long, resulting in shorter pulses and better axial resolution.

Matching Layer

Material placed on the front of the crystal to reduce reflection and improve sound transmission into tissue; without it, $80\%$ of sound reflects back.

Coupling Gel

A substance that removes air between the transducer and skin, following the order: PZT (\rightarrow) Matching Layer (\rightarrow) Gel (\rightarrow) Skin.

Invasive Probes

Transducers used inside the body (e.g., Endovaginal, Endorectal, TEE) that provide higher frequency and better resolution due to proximity to anatomy.

Near Zone (Fresnel Zone)

The area from the transducer to the focus where the sound beam becomes narrower.

Focus (Focal Point)

The narrowest part of the sound beam where the best lateral resolution occurs.

Focal Zone

The region around the focus where the beam remains narrow, providing the best image quality.

Far Zone (Fraunhofer Zone)

The area beyond the focus where the beam widens or diverges, resulting in decreased image quality.

Near Zone Length (NZL)

Also called focal length; the distance from the transducer to the focus, which increases when frequency or aperture increases.

Lateral Resolution

The ability to distinguish two objects side-by-side, which is numerically equal to the beam width.

Axial Resolution

The type of resolution determined by the Spatial Pulse Length (SPL); improved by the use of backing material.

Linear Array

A transducer with elements in a straight line that produces a rectangular image; used for thyroid and vascular imaging.

Convex (Curvilinear) Array

A transducer with curved elements that produces a curved sector image; used for abdomen and OB imaging.

Phased Array

A transducer that uses electronic steering and focusing by firing almost all elements together with tiny time delays; produces a pie-slice image.

Vector Array

A transducer that combines linear and phased technology to produce a trapezoid image shape.

Annular Array

A transducer characterized by ring-shaped elements.

Sequential Array Operation

A method where elements fire one group after another, resulting in no steering and fixed focusing.

Variable Aperture

A technique that uses a larger aperture for deeper imaging to keep the beam narrow and improve lateral resolution.

Dynamic Aperture

A feature that automatically changes the receiving aperture with depth to maintain a narrow beam.

Grating Lobes

Weak, unwanted beams produced by array transducers that can be reduced by apodization and sub-dicing.

Apodization

The process of applying higher voltages to inner elements and lower voltages to outer elements to reduce grating lobes.

Diagnostic Frequencies

The range of ultrasound frequencies typically used in medical imaging, between $1\text{--}35\,MHz$.

Endovascular Frequency

High-frequency ultrasound used for internal vessel imaging, reaching up to $70\,MHz$.