Ultrasound System Review

Vocabulary flashcards for reviewing ultrasound system components and functions.

Transducer

Transforms electrical energy into acoustic energy and back.

Pulser & Beam Former

Creates and controls the electrical signals sent to the transducer that generate sound pulses.

Receiver

Transforms the electrical signals from the transducer (produced by reflected sound) into a form suitable for display.

Display

Presents processed ultrasound data; may be a flat screen monitor, transparency, spectral plot, or other format.

Storage

Archives ultrasound studies using devices like computer hard drives, CDs, DVDs, USB drives, etc.

Master Synchronizer

Maintains and organizes the proper timing and interaction of the ultrasound system's components.

Pulser

Creates electrical signals that excite the transducer's PZT crystals and create sound beams.

Power Output

Synonyms: gain, acoustic power, pulser power, energy output, transmitter output. Changes in voltage modify the brightness of the entire image.

Thermal Index (TI)

Describes the potential temperature rise of tissue due to ultrasound exposure.

Mechanical Index (MI)

Describes pressure fluctuations in tissue due to ultrasound, relating to potential bioeffects.

Pulse Repetition Frequency (PRF)

The number of electrical pulses sent to the transducer each second, which equals the number of ultrasound pulses transmitted per second.

Pulse Repetition Period (PRP)

The time between one voltage spike (pulse) and the next.

Apodization

A technique used by the pulser and pulse delays to improve image quality by reducing unwanted side lobes, which are artifacts.

Signal to Noise Ratio (SNR)

A comparison of the meaningful information (signal) in an image compared to the amount of contamination (noise).

Coded Excitation

A sophisticated method of improving image quality by transmitting a series of pulses instead of one pulse per scan line; also used for multiple focal zones, improving contrast, resolution, and B-flow imaging.

B-Flow Imaging

A real-time 2D grayscale image of blood flow providing higher SNR, improved axial/spatial/contrast resolution, and deeper penetration.

Beam Former

Functions with array transducers during transmission and reception to distribute electrical spikes, coordinate signals, adjust voltages (apodization), establish time delays (dynamic receive focusing), and control dynamic aperture.

Digital Beam Former

A state-of-the-art device using microprocessor technology to produce signals in digital format.

T/R Switch (Transmit-Receive Switch)

Protects the delicate receiver from the powerful signals during transmission and directs electrical signals to appropriate components.

Amplification (Receiver Gain)

Adjustable by the sonographer. Each electrical signal returning from the transducer is made larger. Doesn't improve SNR; units in decibels.

Preamplification

The process of improving image quality of a signal BEFORE it is amplified. Occurs close to the active elements, preventing electronic noise contamination.

Compensation (TGC/DGC)

Corrects for attenuation, creating images that are uniformly bright from top to bottom; adjustable by the sonographer; units in decibels.

Compression

Reduces the number of grays in the display (dynamic range), keeping electrical signal levels within the system's accuracy range and the image's gray scale content within the range of human detection.

Demodulation

A 2-part process that changes the electrical signals within the receiver into a form more suitable for display: rectification (converting negative voltages to positive) and smoothing/enveloping. NOT adjustable.

Rejection (Threshold/Suppression)

Allows the sonographer to control whether low-level gray scale information (potentially noise) will appear on the displayed image; adjustable by the sonographer.

Preprocessing

Processing performed on the image as part of the scan conversion process before the image is stored in memory (e.g., edge enhancement, pixel interpolation).

Postprocessing

Manipulation of data after it is stored in memory; functions are performed on frozen images and are operator-controlled (e.g., magnification, B-color).

Write Magnification

Rescans only the region of interest (ROI), writing new data into the scan converter, increasing the number of pixels or scan lines in the ROI, improving spatial resolution

Read Magnification

System 'reads' and displays the original data from the chosen ROI. The ROI is not rescanned, spatial resolution does not change.

Persistence

Aka frame averaging or smoothing. Removes noise and increases SNR by averaging multiple frames.

Panoramic Imaging

Gives a 'bigger picture'. Slide transducer along area to be visualized and New info is added to one end of the image.

Spatial Compounding

Scan lines are sent through one area in more than one direction. Frames are then averaged to produce a more accurate image reducing artifacts and speckle.

Analog-to-Digital Converter (ADC)

Converts analog voltages to digital form (numbers) by sampling the voltage and assigning a number value.

Echo Delays

Used to accomplish reception dynamic focus.

Summer

Signals are added together in the summer to produce a scan line.

Signal Processor

Functions include filtering useful echo signals, while rejecting frequencies that are not useful.

Tuned Amplifier

An amplifier with a bandpass filter.

Bandpass Filter

Allows frequencies within a certain bandwidth to pass through while rejecting frequencies outside of that range.

Harmonic Imaging

The fundamental (transmitted) frequency is eliminated and second harmonic frequencies (twice the fundamental frequency) are allowed to pass through.

Image Memory

Where images are stored after scan conversion and preprocessing.

Cine Loop

Allows us to review the last several frames that were acquired before the image was frozen.

Pixel

Picture Element. Smallest building block of a digital picture.

Bit

Binary Digit. Smallest amount of computer memory, bistable with values of 0 or 1.

Byte

A group of 8 bits of computer memory.

Voxel

Smallest part of a 3D image – a pixel with length, width, and thickness.

Cathode Ray Tube (CRT)

Funnel shaped, glass vacuum tube with an electron gun and phosphors, used as a display.

Liquid Crystal Display (LCD)

Works with a light source, polarized filters, and liquid crystals to display images.