Term
| What does the Beamformer do? |
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Definition
- For transmit and receive beams it does the following:
> the appropriate phase delay (steer and focusing)
> pulse sequencing (depth)
- Apodization technique is used.
~ Tells pulser WHEN to generate electrical impulses
~ Beamformer is part of the Master synchronizer
~ By using pulse delays it can STEER, FOCUS, and adjust focus to different DEPTHS. |
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Term
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Definition
| - A technique that controls which elements in an array are active and which ones are not. |
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Term
| What are the pulser modes? |
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Definition
- Continous Wave (CW)
> Pulser produces continuous electrical signal which in turn produces continous US wave.
- Pulsed Wave (PW)
> Pulser creates an electrical "spike" which the crystal later transfers into a single US pulse. |
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Term
| What happens in a pulsed wave with an array of crystals? |
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Definition
| - In an array of crystals each crystal recieves a "spike." Therefore it takes multiple "spikes" from the pulser to generate an acoustic wave. The timing between these "spikes" is what determines FOCUSING and STEERING. |
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Term
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Definition
- Steering (Linear Steer)
- Focus (Focus)
- Number of focal points (Focal No.)
- Image shape and size (Scan Range and Wide view)
- Line Density (Frame Rate) |
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Term
| What does a low line density image mean? |
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Definition
- High FR (good temporal resolution)
- Bad LATA |
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Term
| What does a high line density image mean? |
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Definition
- Low FR (Bad temporal resolution)
- Good LATA |
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Term
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Definition
- The pulser receives timed signals from the master synchronizer and produces voltages based on those signals and then transmitted to the transducer.
> Voltage ~ Power ~ Intensity of the US wave
- Therefore transducer output is regulated by excitation voltage from the pulser and can be regulated by the sonographer. |
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Term
What is the control for power?
What are all the possible names for it? |
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Definition
- Acoustic Power
- Other names for Acoustic Power (TOPET)
1. Transducer Output
2. Output gain
3. Pulser Power
4. Energy Output
5. Transmitter Power |
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Term
| What can output power be expressed in? |
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Definition
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Term
| How many dB is the maximum power? |
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Definition
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Term
| Formula for output power? |
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Definition
The formula is the Mechanical Index (MI) formula.
MI is proportional to amplitude which is proportional to power.
( P ~ I ~ A^2 ) |
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Term
| What can the output power be expressed in? |
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Definition
- dB, where 0dB is the MAXIMUM power
- Mechanical Index, MI |
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Term
| What are the functions of the transducer? |
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Definition
- Turns electric into acoustic pulse (converse piezoelectric effect)
- Sends US signal into tissues
- Receives echoes
- Turns acoustic waves into electrical pulse (piezoelectric effect) |
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Term
| How should a sonographer choose their transducer? |
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Definition
1) SHAPE AND SIZE
2) FREQUENCY
> Higher f = BETTER LARD
> Lower f = BETTER DEPTH (penetration) |
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Term
| What is the function of the receiver? |
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Definition
| - The receiver RECEIVES an ELECTRICAL SIGNAL from the TRANSDUCER, PROCESSES it, and PREPARES it for DISPLAY. |
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Term
| What are the 5 major steps in processing? |
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Definition
(ACCRD = A Cat Can't Really Die)
- Amplification
- Compensation
- Compression
- Rejection
- Demodulation |
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Term
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Definition
| - The received electrical signal is VERY SMALL in comparison to the transmitted signal. It needs to be adjusted. |
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Term
| What are the controls for Amplification? |
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Definition
Controls are: 2D GAIN (TRACKBALL ROTATION) = OVERALL GAIN
Look at the pictures on the lecture notes. |
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Term
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Definition
| - Echoes returning from DEEP structures are SMALLER than echoes returning from SUPERFICIAL structures (due to attenuation) |
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Term
| What is the control for compensation? |
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Definition
| The control for compensation is: TGC = TIME GAIN COMPENSATION = DEPTH GAIN COMPENSATION |
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Term
| Explain relationship between how TGC settings should be due to attenuation. |
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Definition
- Think of the attenuation formula:
Ba= Mdf
This means:
Higher f --> TGC's should be steep sloped due to bigger amount of attenuation
Deeper depth --> TGC's should be steep sloped due to bigger amount of attenuation |
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Term
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Definition
| - The difference between the biggest returning echo and the smallest returning echo is too much, so the highest returning echo needs to be COMPRESSED, to better match the size of the smaller returning echoes. |
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Term
| What is the control for compression? |
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Definition
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Term
What is the user's dynamic range?
What is the systems DR? |
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Definition
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Term
| Explain the ranges in Dynamic range |
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Definition
- The Dynamic range contains all of the ranges in amplitude from the min. amplitude to the max amplitude.
- The emitted signal has a 10^10 - 10^15 times the received echoes amplitude (100-150 dB drop)
- The signal is compressed at various stages to reduce this difference:
Amplitude of received signal: 100-150 dB drop --> Receiver: 80 dB drop --> Scan converter: 60 dB drop --> Display: 20-40 dB drop --> Recording: 10-20 dB drop |
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Term
| Explain what REJECTION does |
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Definition
| Rejection gets rid of low amplitudes since they are associated with "noise" and have no clinical significance. |
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Term
| What is the control for rejection? |
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Definition
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Term
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Definition
- The purpose of demodulation is to change the SHAPE of the electrical signal so it can be accepted by display.
- It does this in two steps:
> RECTIFICATION: Turns negative voltage into positive
> SMOOTHING: Places an envelope over the bumps. |
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Term
| What is the control for demodulation? |
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Definition
- NO CONTROL;
system performs automatically. |
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Term
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Definition
- The purpose of the scan converter is to receive information from the receiver, STORE it and then PROCESS IT.
- Received in analog format
- Stored and processed in Digital format
- Displayed in analog format
- The information is received from the receiver in analog format, so then goes through a AD converter and is then saved and processed and then before it is displayed it has to go through a DA converter. |
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Term
| Explain what is analog and digital as information makes its way around |
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Definition
| Transducer (analog) --> Receiver (analog) --> AD Converter --> Memory (digital) --> DA Converter --> Display (Analog) |
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Term
| What is the limit of values in Analog format? |
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Definition
| - Analog format has an INFINITE number of values. |
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Term
| What is the limit of values for Digital format? |
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Definition
| Digital format has a limit, or set number of values. |
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Term
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Definition
| - An analog to digital converter converts analog information into digital information so it can be stored. |
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Term
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Definition
| - A Digital to Analog converter converts information that has been in the memory to analog format so it can be displayed. |
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Term
| Why is Data storage necessary? |
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Definition
| Because the way it is acquired, and the way it is displayed. |
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Term
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Definition
- The display is divided up into small squares known as PIXELS.
- Most display systems used a 525 x 525 pixel display.
- The more pixels on a image, the better details that are seen in the picture. |
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Term
| Memory contains ________ for each pixel. |
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Definition
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Term
| Explain the pixels y-coordinate, x-coordinate, and color |
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Definition
- The pixels vertical position (y-coordinate) reprints the depth of the reflector.
- The pixels horizontal position (x-coordinate) represents the line of sight it was taken from.
- The color of the pixels represent the amplitude of the returning signal (represent how well it reflects, or the Z mismatch of surrounding tissues). |
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Term
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Definition
- The computer memory stores CHARGE in small capacitors, or BITS.
- Each capacitor (bit) can encode two values (digital)
> For charge = 1
> No charge = 0
If we want to use more than 2 shades we have to incorporate more bits per pixel.
Number of shades calculated by:
# shades = 2^n
n = number of bits |
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Term
| To represent 2 shades of gray we need ___ bits. |
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Definition
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Term
| To represent 8 shades of gray, we need ___ bits. |
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Definition
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Term
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Definition
| - Data that is PROCESSED before it is STORED in scan converter. |
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Term
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Definition
| Data that HAS been PROCESSED and STORED in the SCAN CONVERTER, but before it is DISPLAYED. |
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Term
| Pre and Post processing as signal starts off and finishes flow chart |
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Definition
PREPROCESSING: Transducer (analog) --> Receiver (analog) --> AD converter -->
Memory (digital)
POSTPROCESSING: DA Converter --> Display (analog) |
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Term
| What are the different types of ZOOM? |
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Definition
- Write Magnification
- Read Magnification |
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Term
| Explain Write Magnification |
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Definition
- Preprocessing
- Occurs when data is ACQUIRED. The sonographer chooses an area to be rescanned using more lines (line density), that allows for a better SPATIAL RESOLUTION. |
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Term
| Explain Read Magnification |
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Definition
- Post processing
- Occurs with data that has already been stored, and is being magnified. The sonographer chooses an area on the image and machine assigns more PIXELS to be received from echoes from location x. |
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Term
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Definition
- The system CAN generate up to 60 frames per second. Since the difference between each frame is so SMALL, the system will AVERAGE SEVERAL FRAMES to reduce "NOISE", which will improve image quality.
- By doing this in a step-down fashion, the number of frames displayed remains almost the same.
- Postprocess function
- Seems like the temporal resolution is changing, however it's not. |
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Term
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Definition
E.E. = AVERAGES SEVERAL PIXELS to either give a sharper or smoother image.
- DECREASE to get a SMOOTHER image, with better CONTRAST resolution.
- INCREASE to give a SHARPER, grainy, speckled image with better DETAIL resolution. |
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Term
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Definition
- Combining (ApliPure) of ELECTRICAL SIGNALS obtained with:
- different frequency (frequency compounding)
- different lines of sight (spatial compounding)
- compounding on both the sending and receiving side |
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Term
| Explain Spatial Compounding |
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Definition
- Sequentially COMBINES ultrasonic lines ACQUIRED from scanning in DIFFERENT DIRECTIONS in REAL TIME.
- The result is a UNIFORM image with CONTINUOUS boundaries that may eliminate some ARTIFACTS. |
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Term
| Explain frequency compounding |
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Definition
- Simultaneously but seperately processes SIGNAL'S with different FREQUENCIES of the bandwidth.
- Higher f = better LARD
- Lower f = better penetration
- Combines this data in a SINGLE IMAGE to give better PENETRATION and RESOLUTION. |
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Term
| What does the postprocess (gamma) function allow us to do? |
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Definition
| - The postprocess (gamma) function allows us to choose different gray scale curves. |
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Term
| What does Contrast (gray scale) resolution depend on? |
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Definition
- Acoustic Impedance Mismatch
- Scan Converter (#bits/pixel)
- Postprocess (Gamma) curves
- Monitor setting (contrast and brightness)
- Ambient light (light in the room) |
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Term
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Definition
- The original frequency (fo) is called the FUNDAMENTAL frequency.
- Double, triple, etc. of the fundamental frequency is called HARMONIC FREQUENCY. |
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Term
| What is a non-sinusoidal wave the sum of? |
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Definition
| - A non-sinusoidal wave is a sum of the central frequency (fo) and its harmonics. |
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Term
| Explain HARMONIC IMAGING and how a sinusoidal wave become's non-sinusoidal |
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Definition
- Recall that ultrasound waves are mechanical waves consisting of compressions and rarefactions.
- In the area of compression the MEDIUM is more STIFF.
- Stiffness (incompressibility) affects the velocity of the sound wave:
v~ 1/k
- (decrease k, v increases)
- Only intensities in the CENTER of the beam are high enough to make a notable difference in the velocity.
This is what creates a distortion of the pulse, that makes a sinusoidal wave --> non-sinusoidal.
> (hits a medium with high stiffness, velocity in the center of the beam is decreased, velocity in the rest of the beam doesn't change much --> causing that distortion) |
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Term
| If we filter out the fundamental frequencies and use the harmonic frequencies to image instead: |
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Definition
- LARD improves ( LARD = 1/2 SPL = nv/f ) (PRO)
- LATA improves ( High intensities only in the CENTER of the beam ) (PRO)
- Artifacts DECREASE (PRO)
- Attenuation INCREASES (Ba = Mdf) (CON)
- Frame rate MAY decrease (Because to filter out the Fo the machine often has to send out TWO pulses) |
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Term
| Why is LARD originally decreased with harmonic imaging? |
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Definition
- WIth a broad bandwidth, sometimes the fundamental frequeny, and harmonic frequencies will OVERLAP. (This creates noise)
- To avoid this a LONGER pulse is generated:
> It has a narrower bandwidth, so less overlapping = less noise
> However LARD = 1/2 SPL so if you increase the pulse length (SPL) you increase the LARD as well = :( |
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Term
| Explain Pulse (Phase) Inversion |
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Definition
- This is a technique used to improve LARD:
>Two pulses are sent out to interrogate each line, the 2nd pulse is a (pie) or 180 degrees out of phase (destructive interference)
> So then the harmonic frequencies generated by these pulses are in phase (constructive interference)
- ADVANTAGES:
> No need to narrow the bandwidth to eliminate noise.
> the signal with the fundamental frequency is eliminated.
> This improves LARD because:
>> LARD = nv/f --> by using constructive interference with the harmonic frequencies the frequency is actually increased decreasing LARD --> :) IMPROVED AXIAL RESOLUTION |
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Term
| Explain the TYPES of harmonic imaging |
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Definition
- Tissue Harmonic Imaging (THI) requires NO contrast agent.
- Harmonic Imaging uses contrast agent.
> Contrast agent containing micro gas bubbles (HUGE Z MISMATCH) is injected into blood vessels which generates MORE HARMONIC FREQUENCIES.
- POWER/COLOR doppler harmonic imaging uses contrast agent. |
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Term
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Definition
- A code of 1's and 0's are implanted on a sound beam.
- Some of the codes could code for maximum penetration and the other's are coded for maximum resolution.
- This technique allows for a sound beam to be generated that has maximum power and penetration while still maintaining a high frequency spatial resolution. |
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Term
| Explain the different types of VIDEO DISPLAY |
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Definition
- CRT (Cathode Ray Tube): A cathode ray tube emits electrons that are scanned across the phosphorescently coated screen. Still more common technique. (Think old bulky tv)
- LCD (Liquid Crystal Display): Starting to replace CRT monitors (think the new thin tv's)
- DLP (Digital Light Processing chips): A flat panel technology that uses millions of tiny mirrors. |
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Term
| Explain the different VIDEO FORMATS |
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Definition
- DICOM: Purest UNCOMPRESSED format used by ALL US SYSTEMS.
> requires A LOT of memory (uncompressed)
> Not compatibly for PC or labtop
- CODEC: Allows a COMPRESSION of data for storage (variety of algorithms exist)
- Various video formats are used for PC display
> AVI, MOV, MPEG-4, WMF, etc. |
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Term
| Explain the different types of STORAGE MEDIA |
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Definition
- HARD COPY
> photographs
> charts
> transparent film
- MAGNETIC
> magnetic tape
> computer memory
> floppy discs
> video tape
- OPTICAL
> laser discs
> compact discs (CD) |
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Term
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Definition
- RAID = REDUNDANT ARRAY OF INDEPENDENT DISKS
- It is a way of storing data that combines multiple disk drive components into one LOGICAL unit. Data is distributed across the drives called "RAID LEVELS" depending on the redundancy and performance required.
- This method of storing data HAS THE MOST AMOUNT OF MEMORY. |
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