Term
| Basic Processes of Real Time |
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Definition
| 1.Transmit Beam-F 2.Receive Beams-F 3.Process the returned data-F/B 4.Performs Measurements on data-B 5.Display the processed data-B 6.Store the processed data-B |
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Term
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Definition
| The transmit power knob controls the amplitude of the excitation voltage which drives the transducer crystals. Aka:acoustic power, output power, transmit gain, power gain transmit voltage. Changes power, amplitude & intensity. If the image is too bright turn this down. |
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Term
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Definition
As Low AS Reasonably Achievable.
Refers to transmit power. |
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Term
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Definition
| Ratio of the maximum to the minimum signal strength that each component processes. Use Amplitude dB equation. |
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Term
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Definition
| What the sonographer is trying to measure. |
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Term
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Definition
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Term
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Definition
| The amplitude level below which no signals are visible due to noise. |
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Term
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Definition
A measure of how strong a signal is relative to the background noise.
Amplitude of the signal divided by the amplitude of the noise. A high signal to noise ratio means a more trustworty image. |
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Term
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Definition
1.Electronic: From the electronics.
2.Clutter: Large specular reflectors.
3.Haze: Poor skin contact, different tissues, side lobes.
4.Electrical Interference: From other electrical devices. |
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Term
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Definition
| Occurs upon acquisition of the ultraound reflections. Takes place before scan conversion and cannot be changed on data that has been stored in the internal system memory. System must rescan ROI. |
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Term
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Definition
| Any process that can be changed after the data is acquired . Takes place after scan conversion and can be changed after the data has been stored in the internal system memory (cine memory). |
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Term
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Definition
Creates the voltage needed for a particular wave. Aka: Pulser,Beamformer
PW-certain freq. voltage.
CW-continuous voltage. |
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Term
| Operations of a Receiver (5) |
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Definition
| 1.Amplification 2.Compensation 3.Compression 4.Demodulation 5.Rejection |
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Term
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Definition
| Receiver Gain or Gain. Amplifies the returning echoes. If the image is to dark turn this up. We can adjust this. |
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Term
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Definition
| TGC's. Refers to the application of extra amplification (gain) to compensate for increasing attenuation due to depth. Aka: Depth compensation, swept compensation. We can adjust this. |
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Term
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Definition
Dynamic Range. Ratio of max to min.
Compresses this lager ratio in to a smaller one so we can display it. Gray scale maps. We can adjust this. |
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Term
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Definition
Recticifation:Turns all negative signals into positive ones.
Smoothing:Enveloping of the signal or averaging the signal to make them more smooth. We CAN NOT change this! |
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Term
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Definition
| Sets a threshold below which signals will not be displayed. Signals below the noise floor are masked by the noise in the image. We can adjust this. |
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Term
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Definition
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Term
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Definition
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Term
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Definition
| Transmitter. The transmit beamformer is reponsible for creating all of the timing, phase delays and transmit signals which create each individual beam and, over time, a scan. |
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Term
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Definition
| Apparent Signal to Noise Ratio. |
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Term
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Definition
1.Increase transmit power 2.Use a lower freq. transducer for deeper Imaging Depths 3.Use a different imaging plane 4.Help reduce attenuators
like air 5.Move transmit focus deeper
6.Use a larger aperture transducer (deeper focus) |
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Term
| Grayscale & Visual Dynamic Range |
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Definition
| The dynamic range of the human eye is less than 36 dB, which is equal to 64 shades of gray at the same time. The range returning signals must be compressed so we can see it. High amplitudes show up bright, no reflection is black. |
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Term
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Definition
| Presents an image as the combination of two interlaced fields,an odd field and an even field. |
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Term
| Interlaced Monitors & Frame Rate |
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Definition
| Needs 1/60th of a sec. to dsplay each field, the entire frame needs 1/30 of a sec. Frame rate is 30Hz. or 30 frames/sec. |
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Term
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Definition
| Displays both fields in an image simultaneously. The image is produced in half the time, so the rate is doubled. 60Hz or 60 frames/sec. |
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Term
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Definition
Pixel size up-Resolution down.
Pixel size up-# of pixels down.
# of pixels up-Resolution up. |
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Term
| Brightness Levels & Binary |
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Definition
(Binary)2^2(#of Bits)=4(shades of gray)
2^3=8
2^4=16
2^5=32 etc. |
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Term
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Definition
Aka:(High)Resolution Mode,
Magnification. A technique designed to accommodate the desire to visualize regions of images in a larger format. Two ways: Acoustic Zoom (write zoom) & Non-acoustic Zoom (read zoom). |
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Term
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Definition
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Term
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Definition
| Re-transmits acoustic lines, potentially using different line density, to achieve better resolution. |
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Term
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Definition
Transmit multiple lines with different foci. Improves Lateral Resolution.
Slows frame rate, decreasing temporal resolution. |
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Term
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Definition
| Changes focus during receive. Improves lateral resolution. There can only be one focus per transmitted line. Receiving is passive so there can be continuous, dynamic, focusing. |
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Term
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Definition
Transmits a less focused "fatter" beam then receives multiple simultaneous
"narrow" beams. Increases frame rate, thus improving temporal resolution or increases line density. |
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Term
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Definition
SNR Improvement=n/√n.
Take multiple signals then average them. Transmit signals are in phase and will get bigger, noise is only partly in phase and won't get as big. |
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Term
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Definition
| Constructive Interference. |
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Term
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Definition
| Destructive Interferance. |
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Term
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Definition
| Sometimes pixels reflect noise, look around and change the grayscale based on neighbors. |
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Term
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Definition
| Used in cardiac imaging and for fetal heart rates. Non-scanned modality. Displays grayscaled values of each line over time, motion can be discerned. |
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Term
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Definition
| Axial, Lateral, and Elevational Resolution. |
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Term
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Definition
Determined by: Scan Converter,# Bits/Pixel, Post Processing Curves, Monitor Settings(Contrast/Brightness),
Ambient Light, Acoustic Impedance Mismatch. |
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Term
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Definition
Determined by: Depth,Packet Size(Color),Image Size,Line Density,
Parallel Processing,# Foci/Line,
Persistence(Averaging),Compound Imaging,Monitor Frame Rate. |
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Term
| Standard Doppler Modalities(3) |
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Definition
| 1.CW Doppler 2.PW Doppler 3.Color Doppler |
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Term
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Definition
| The apparent change in frequency as a result of a change in wavelength caused by a motion of a wave source relative to an observer. |
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Term
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Definition
| Soundwaves compressed, hear a higher frequency. |
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Term
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Definition
| Soundwaves decompressed, sounds like a lower frequency. |
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Term
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Definition
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Term
| Doppler Shift(Change in Frequency) |
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Definition
| f(Dop)=f(received)-f(transmitted)=Δf |
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Term
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Definition
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Term
| Doppler Shift & Propagation Velocity |
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Definition
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Term
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Definition
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Term
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Definition
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Term
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Definition
| Red Blood Cell Aggregation,seen as spontaneous contrast,"smoke". Abiltiy to visualize the blood. Happens in high frequency situations or from disease. |
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Term
| Doppler(Insonification) Angle |
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Definition
| θ. Always measured between the direction of the flow and the line of observation (Doppler steered line). |
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Term
| Doppler Insonification Angle=0° |
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Definition
| Flow directly toward the transducer. Positive Shift. cos=1 |
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Term
| Doppler Insonification Angle=90° |
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Definition
| Flow is not traveling closer or farther away. cos=0 |
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Term
| Doppler Insonification Angle=180° |
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Definition
Flow directly away from the transducer. Negative Shift. cos=-1
True Doppler Shift, Parallel to flow. |
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Term
| Doppler Insonification Angle for Vascular |
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Definition
60° is ok. cos=.5
Less is good, lower error, but not usually possible.
More is bad because high error is squared in the pressure gradient calculation. |
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Term
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Definition
| Reduces "clutter" signals, reducing the dynamic range. High pass filter. Rejects low freqs., keeps high freqs. compared to corner freq. |
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Term
| Typical Wall Filter Settings |
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Definition
Less than 25-50 Hz: Venous
50-100 Hz: Arterial
200-600 Hz: Adult Echo
600-800 Hz: Pediatric Echo |
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Term
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Definition
| In order to visualize the range of Doppler frequences it is necessary to seperate the collection of shifts into individual bins. |
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Term
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Definition
Aliasing occurs when the Nyquist criterion is violated. Can't determine velocity if Doppler shift is greater than the Nyquist limit.
f(Dop)[max]=PRF/2 |
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Term
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Definition
f(Dop)up= f(0)up,v up,θ close to 0° or 180°.
PRF down=PRP up, Image Depth up. |
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Term
| Spectral(Spread) Broadening |
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Definition
Filling in of the Spectral Window.
CW:Looks everywhere-no window.
PW close to wall-no window.
PW turbulent flow after stenosis-no window. |
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Term
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Definition
Doppler Shift=+/-∑ f(Dop)
Spectrum of shifts.
Peak Velocity. |
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Term
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Definition
Too Low(Freq.):"Clutter" is left over.
Too High(Freq.): Loss of data. |
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Term
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Definition
| Not true aliasing, can be adjusted by shifting the baseline down. |
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Term
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Definition
Scales are decreased to make accurate peak velocity measurements. PRP is increased by adding "dead time".
PRF is decreased, too much can cause aliasing. |
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Term
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Definition
Present:Laminar Flow
Not Present:May or may not be disease. |
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Term
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Definition
| Range ambiguity will occur when echoes are received as a result of previous transmits arriving from locations deeper than the desired depth gate. |
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Term
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Definition
| A form of Doppler which uses the artifact of range ambiguity. Creates a tradeoff between standard PW and CW. |
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Term
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Definition
| Provides an estimate of the mean velocity of flow. Has multiple sample gates (4-12). Good sensitivity, bad temporal resolution. |
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Term
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Definition
| Most systems do not have seperate controls for the color wall filters. The are usually set at about 10% of the color scales. When you change the scales you change the wall filters. If you want to see lower velocity flow you have lower your scales. |
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Term
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Definition
Aka:Power Doppler
Cannot determine flow, but is very sensitive to lower velocities. |
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Term
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Definition
Occurs when:
Low color scales (low PRF)
High velocity flow (like center stream)
Regions of acceleration (bends,kinks,narrowings,convergence)
Angles close to 0°-180°
Higher frequency transducers
[f(Dop)∝f(o)] |
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Term
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Definition
Weighted averaging technique, improves SNR, decreases temporal resolution.
Short duration events could disappear.
Long duration events seem longer. |
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Term
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Definition
You can give priority to color or grayscale.
Low: more gray less color.
Higher: more color less gray. |
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Term
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Definition
1.Look at color bar & see what color is going toward the transducer.
2.Determine steering.
3.Draw flow lines.
4.Assign direction-angles less than 90° should match the toward color.
5.Watch out for aliasing. |
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Term
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Definition
| Any perturbation of a signal which distorts a display from "truth". Errors in imaging. Can be useful or bad. |
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Term
| Detail Resolution Artifacts |
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Definition
| Inability to correctly visualize structures: axially, laterally or elevationally. |
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Term
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Definition
| Result in structures appearing in an incorrect position. Refraction, Reverberation(Comet Tail,Ring Down), Multipath, Grating and Side Lobes, Speed Error, Range Ambiguity, Mirror Image. |
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Term
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Definition
| Results in a lateral displacement of the structure within the image. Machine assumes straight lines. |
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Term
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Definition
| Results in "ladders" Sound bouncing between two or more surfaces. When: large impedance mismatch and relatively specular reflection. Highly angle dependent. Worst when sound is perpendicular to the interface. Causes structures to replicated. |
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Term
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Definition
| Type of reverberation artifact, caused by air. A similar artifact called Comet Tail is created by metal or calcifications. |
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Term
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Definition
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Term
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Definition
| Results in a structure appearing deeper than it is because of an elongated return path length. |
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Term
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Definition
Grating Lobes: Multi-element
Side Lobes: Single element
Lateral displacement. |
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Term
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Definition
System assumes 1540 m/s.
C>1540 m/s then shallower
C<1540 m/s then deeper. |
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Term
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Definition
| The result of reflected data from the previous acoustic transmit adding to the current acoustic line. |
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Term
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Definition
| Results in an artificial structure symmetrical to the actual structure across the "mirroring structure". |
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Term
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Definition
| Caused by excessive reflection, absorption, or refraction. Can't see under it. |
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Term
| Refractive Edge Shadowing |
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Definition
| Type of shadowing, coming off the edges of a circular object. |
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Term
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Definition
| Caused by attenuation. Shadowing, Enhancement, Speckle. |
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Term
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Definition
| The image below a fluid filled area is displayed brighter because less attenuation occurs through the fluid than on either side of it. |
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Term
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Definition
| Aliasing,Range Ambiguity,Spectral Mirroring,Spectral Broadening, Blossoming, Circuit Saturation, Refraction. |
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Term
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Definition
| Results in an artificil Doppler signal to be displayed in the opposite direction of the true flow. These make it worse: too much transmit or gain, superficial Doppler with high freq. transducer,θ close to 90°, poor electronic design (I & Q channels). |
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Term
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Definition
| Results when the gain is too high, gives a higher than true peak velocity, could result in loss or decrease of spectral window in PW Doppler. |
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Term
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Definition
| When the dynamic range is not reduced enough circuit saturation occurs. |
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Term
| Principle Types of Bioeffects |
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Definition
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Term
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Definition
Temperature rise related to:
Temporal Average Intensity
Duty Factor
Scan Time
Scanned v. Unscanned Modalities |
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Term
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Definition
Cavitation related to:
Peak Rarefactionl Pressure |
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Term
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Definition
1. A peak is always greater than or equal to an average.
2. The 1st 2 letters spatial/2nd 2 temporal.
3.Pulse from PD.
4.Temporal from PRP. |
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Term
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Definition
DF=PD/PRP=TA/PA
Temporal Average/Pulse Average |
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Term
| Intensity Highest to Lowest |
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Definition
1.Isptp 2.Isppa 3.Ispta 4.Isatp 5.Isapa
6.Isata |
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Term
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Definition
| Refers to how the beam energy is distributed over physical space in the body. Mainly determined by the beam parameters. |
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Term
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Definition
| Refers to how energy is ditributed over time. Different for a PW than a CW. |
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Term
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Definition
| BUF=SP/SA. A measure of beam uniformity, 1=completely uniform. Usually greater than 1. |
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Term
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Definition
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Term
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Definition
CW Doppler
PW Doppler
M-Mode
A-Mode |
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Term
| Risk of Thermal Bioeffects High to Low |
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Definition
CW Doppler: Low Trans Voltage/High DF
PW Doppler
B-Mode: High Trans Voltage/Low DF |
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Term
| Risk of Mechanical Bioeffects |
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Definition
B-Mode: High Trans Voltage/Low DF
PW Doppler
CW Doppler: Low Trans Voltage/High DF |
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Term
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Definition
| A specialized ultrasound transducer used to measure acoustic power. |
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Term
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Definition
Best indicator for the risk of mechanical bioeffects.
MI=Peak Rarefactional Pressure/√ f(o) |
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Term
| Thermal Indices (TIS,TIB,TIC) |
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Definition
| Best indicator for the risk of thermal bioeffects. TI values indicate the worst case temperature rise(°C) based on the imaging parameters in use. |
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Term
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Definition
1. Used for a long time.
2.There are benefits.
3.No confirmed bioeffects for patients or sonographers.
4.Benefits of PRUDENT application outweigh the risks. |
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Term
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Definition
1.No needless scans.
2.No needlessly extended scan times
3.ALARA
4.If you could miss something you can increase transmitt power. |
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Term
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Definition
| The use of a contrast agent increases the acoustic impedance mismatch within the blood as a result of the high compressibility and low density of the gas. |
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Term
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Definition
| Transmit at the fundmental freq., receive at the higher 2nd harmonic freq.(2x f(t)) Better penetration and better resolution. Need wide bandwidth. May decrease axial reolution. |
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