Pulsed Echo Instrumentation and Receiver Functions

Comprehensive vocabulary flashcards covering pulsed echo instrumentation, system components, pulser types, and the five main receiver functions (Amplification, Compensation, Compression, Demodulation, and Reject) as described in the ultrasound physics notes.

Transducer

A major component of an ultrasound system that transforms electrical energy into acoustic energy during transmission and converts returning acoustic energy back into electrical energy during reception.

Pulser

A component that creates electrical signals that excite the transducer's PZT crystals; it determines the amplitude, pulse repetition period ($PRP$), and pulse repetition frequency ($PRF$).

Beam Former

A sophisticated electronic device that receives the pulser's single electrical spike and distributes it to the numerous active elements of an array transducer, coordinating firing delay patterns.

Receiver

The component that transforms the electrical signals produced by reflected sound into a form suitable for display on the monitor.

Display

The system component that presents processed data in various formats, such as a flat screen monitor, spectral plot, or transparency.

Storage

The component used to archive ultrasound studies, including media like hard drives, CD, DVD, and videotape.

Master Synchronizer

The component that maintains and organizes the proper timing and interaction of all the ultrasound system's components.

Continuous Wave (CW) Pulser

A type of pulser that generates a constant electrical signal in the form of a sine wave.

Pulsed Wave, Single Crystal Pulser

A pulser that creates a single electrical signal that excites the transducer to create a single acoustic pulse.

Pulsed Wave, Phased Array Pulser

A pulser that emits numerous electrical spikes to excite numerous crystals in an array, ultimately creating only a single acoustic pulse.

Channel

A components consisting of a single PZT element in the transducer, the electronics in the beam former/pulser, and the wire connecting them.

Apodization

The process by which the beam former adjusts electrical spike voltages to reduce lobe artifacts.

Transmit-Receive Switch

A device that protects sensitive receiver components from high voltages during transmission and directs low-voltage signals from the transducer to the receiver during reception.

Amplification

Also called receiver gain, the first receiver function where each electronic signal returning from the transducer is made larger by an equal amount.

Preamplification

The process of improving the quality of a signal before it is amplified, often occurring within the transducer to prevent electronic noise contamination.

Compensation

The second receiver function, also known as time gain compensation ($TGC$), depth gain compensation ($DGC$), or swept gain, which corrects for attenuation by treating echoes differently based on depth.

Near Gain

The portion of a typical $TGC$ curve where reflections at superficial depths undergo a small, constant amount of compensation.

Delay (TGC)

The specific depth on a $TGC$ curve at which variable compensation begins.

Slope (TGC)

The region of a $TGC$ curve where compensation corrects for the effects of increasing attenuation resulting from increased path length.

Knee (TGC)

The depth at which reflections are maximally compensated by the ultrasound system.

Far Gain

The maximum amount of compensation that the receiver can provide on a $TGC$ curve.

Compression

The third receiver function, also called log compression or dynamic range; it is measured in $dB$ and adjusts the gray scale mapping to suit human vision and system electronics.

Demodulation

The fourth receiver function, a two-part process consisting of rectification and smoothing that changes electrical signals into a form suitable for display; it is not user-adjustable.

Rectification

The first part of demodulation that converts all negative voltages into positive voltages.

Smoothing (Enveloping)

The second part of demodulation that places a smooth line around the voltage signal bumps to even them out.

Reject

The fifth receiver function, also called threshold or suppression, which allows the sonographer to eliminate low-level noise while keeping meaningful diagnostic information.

Dynamic Frequency Tuning

A feature that uses the high frequency part of a pulse's bandwidth for superficial imaging and the lower frequency portion for deeper imaging to optimize axial resolution.

Output Power

A user-controlled setting that adjusts the strength of the sound pulse sent into the body, affecting image brightness and patient exposure.

Signal-to-Noise Ratio

A comparison of the meaningful diagnostic information (signal) to the amount of random disturbance (noise) in an image.

ALARA Principle

Stands for 'As Low As Reasonably Achievable,' stating that sonographers should choose settings that minimize patient exposure when improving image quality.