Ultrasound Instrumentation Flashcards
What does analog refer to?
Variable which can contain a number of variables
What does the CRT consist of?
Glass vessel that contains an electron gun that is heated and produces free electrons from the cathode filament
How are electrons accelerated across the glass container?
High voltage
How is the electron beam focused?
By vertical and horizontal deflection plates
What is the electron beam focused to hit?
Phosphor screen
What is emitted by the phosphor screen when the electron beam hits it?
Light- proportional to intensity/amp of electrons
What was the oscilloscope initially used for?
A-mode
What type of CRT allows the image to be viewed directly during and after image build up?
Special purpose storage CRT
What type of scanning used special purpose storage CRT?
B-mode scanning
What is the most basic way of displaying US information?
CRT
What replaced the use of special purpose storing CRT?
TV screen
What is the positive end within the glass envelope?
Phosphor end
What contains the 10000volts with in the glass envelope that applied across the tube?
Vacuum
What happens when there is an increase in the amount of electrons liberated at the filament?
Brighter picture
What does the control grid do?
Method of controlling the amount of electrons which proceed to the phosphor end of the tube
Why is a large size of dot not the best for creating an image?
A large dot size will eradicate the benefits of even the best axial resolution
What is the purpose of the focusing lens?
Focuses a wide stream of electrons into a narrow tightly coiled beam
What is the purpose of the x and y focusing plates?
Also you to steer the electrons toward the imaging plate
What is the storage mesh?
Electrons pass through the collector mesh and hit the storage mesh knocking the electrons off leaving a positively charged latent image
What is the collector mesh?
Grounding device- attracts those little old dislodged electrons and safely grounds them out
What are the flood gun(s)?
Spray a gentle flood of electrons towards the phosphor
How does the latent image leave the storage mesh?
Electrons from the gun are attracted to the areas of positive charge on the storage mesh, and it is at these places that these electrons get through the storage mesh and to the phosphor
What were the 2 main disadvantages of CRTs?
- Image deterioration was rapid
2. Few shades of grey - bistable
What is a analog scan converter?
Stores an image in one form and displays it in another form
How does the ASC work?
Stores the image as a series of electrical charges on a dielectric matrix and then reads out this information for display as dots of light on a conventional television monitor
What was the major advantage of the analog scan concerted?
Grey scale
Are their flood guns in the analog scan converter?
No
What is the purpose of the field mesh/anode?
Cause electrons to strike the target at right angles, and also to collect the stray electrons which are deposed from the dielectric matrix
What is another name for dielectric matrix?
Storage target
What is the dielectric matrix made of?
Silicon wafer
What occurs to the electrons when they reach the target?
Dislodge electrons from the matrix leaving a positive charge forming the latent image
How is the latent image read in the ASC?
Signal plate placed behind matrix- medium energy level electrons are accelerated through the positively charged areas on the matrix in a raster scan fashion
What occurs after passing through the positively charged areas of the matrix?
The electron beam carries with it information regarding the relative signal amplitudes
What controls the level of brightness or spot brightness of the US signal in the TV monitor?
Video signal
How many scan lines are there in each conventional frame on a TV?
525
What is the FR of a conventional TV?
30
How long is each field (odd and even) formed in?
1/60th of a second
What is the FR when our eyes can detect flicker?
20
In A mode what does the height of deflection measure?
Strength of returned echo
When is A Mode useful?
- Determine whether an echo –free structure is fluid-filled or contains solid homogenous material
- If a structure is pulsatile
- Aid in cyst puncture
- Use in echoencephalography
How are echo signals represented in B-mode?
Brightened dots corresponding to echo intensity/amp
What is B-mode used to display?
Static and real time scanners
M-mode
What is the advantage of static B scanning?
Large FOV
What are the disadvantages of static b scanning?
Long imaging distance
Scan arm was difficult to maneuver
Very operator dependent
Image was static
What is m-mode?
A series of B mode dots being displayed on a moving time basis
What is a limiting factor of m-mode?
Represents only one anatomical plane
What is c-mode (constant depth scanning)?
Incorporation of static b scanning using additional electronics
What is PRF?
Number of voltage pulses sent to the transducer each second
What are the PRF ranges?
4-15kHz (5-30 in Doppler)
How should you PRF be sent to receive information for display at a rapid rate?
High PRF
What can improve the reduction of acoustic output (reduced echo amplitude)?
An increase of amplifier gain!
What are the operations occurring in pulse delay?
Steering, scanning, transmission focusing, aperture and apodization
What is a channel?
Independent signal path consisting of a transducer element, delay and possibly other electronic components
Define gain as a ratio
Ratio of the amplifier output to the electric power input
What functions accomplish reception apodization and dynamic aperture function?
Part of the summer (adder) process
