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67 Cards in this Set
- Front
- Back
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what is registration
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Registration is the spatial orientation of the beam.
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explain the SUAR system?
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-consists of two rowes of fine wires imbedded in a perspex block which mimics sound transmission through the human body.
-two rows of wires converge -3 parameters evaluated=axial resolution, system uniformity, -initially, we take care of the uniformity(set parameters to penetrate deepest wire(shouldn't change much from month to month if output and ampitude are functioning properly)) -by scanning and finding the point of convergence(where 2 rows are now distinguished as one)-this shows axial resolution -system uniformity determines weather all transducers in a linear array are firing properly(should see an unbroken line). If several transducers are not firing, there will be a gap.-consists of two rowes of fine wires imbedded in a perspex block which mimics sound transmission through the human body. -two rows of wires converge -3 parameters evaluated=axial resolution, system uniformity, -initially, we take care of the uniformity(set parameters to penetrate deepest wire(shouldn't change much from month to month if output and ampitude are functioning properly)) -by scanning and finding the point of convergence(where 2 rows are now distinguished as one)-this shows axial resolution -system uniformity determines weather all transducers in a linear array are firing properly(should see an unbroken line). If several transducers are not firing, there will be a gap. |
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Calorimeter
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-uses physical properties of wave propegation
-The rise in temperature is proportional to the increase in the power of the beam. -In this gadget we have an absorbing liquid encased in an insulating tank (so that heat is not easily lost -Temperature is accurately asssessed. -THis temperature reading will indicate the power in the beam. |
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# Why are cylindrical objects placed in some phantoms?
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Cylindrical objects are placed in test objects to evaluate contrast resolution.
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explain how the tissue equivilant phantom tests axial resolution?
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-pin arrangements similar to the AIUM test object, but often placed in near, medium and far distances from the transducer to test axial resoution at various depths.
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What parameters are generally tested for 2D, and doppler imaging?
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2D;
-detail resolution(axial, latereral, and elevational) -contrast resolution -penetration -range accuracy Doppler: -Penetration(sensistivity) of PW, CW, and Color -Range accuray of PW and Color -Peak or mean velcity accuracy of PW, CW, and COlor -Spectral broadening-PW -Lateral resolution-Color |
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explain how the tissue equivilant phantom tests lateral resolution?
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-determined by evaluatine line widths corrisponding to equally spaced rods within the test object
-measurement of the narrowest line corrisponds to the best possible lateral resolution of that system -will indicate at what distance from the transducer the optimal lateral resolution will occur(w/ a static focal zone) -will provide an indication of a transducer's fixed focal zone. |
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# How can slice thickness be evaluated?
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A diagonal reflector in a test object is scanned. The width of the demonstrated beam at a given depth is the slice thickness at that depth.
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# What do string test objects evaluate?
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String phantoms are used to test for -beam penetration,
-determine flow directions, -accuracy of sample volume, and -determining flow speed. |
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Explain the hypdrophone
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-small piezoelectric element mounted on the end of a narrow tube or hollow needle. --crystal is placed in the beam path
-Varying intensities encountered in different sections of the beam produce a corresponding varying voltage which can be displayed on an oscilloscope |
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# Describe the construction of a SUAR test object and what information can be provided.
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-consists of an acrylic or Perspex block incorporating a wedge at the bottom. (One reference describes this as a water-filled wedge.) -Sensitivity is determined when one notes the settings needed to just penetrate the back of the block. -Uniformity is judged by looking at the back of the block (acrylic/air interface) or the wedge to see if image is the same across the rectangle.
-Axial resolution is determined by the point at which one no longer identifies the anterior and posterior edges of the wedge as separate structures. |
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PIRTO
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-particle image resolution test object
-tissue equivalent phantom in which cystic spheres are randomly placed |
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What are the problems with non-fluid based phantoms.
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-strong specular reflectors createm blossoming causing an overestimation of peak velocity, so gains and power need to be turned down.
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explain how the tissue equivilant phantom tests dot formation?
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-no single dot should be >3 wavelengths in diameter
(no large blobby dots) -large dots indicate informtion processing problems |
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which is the worst measrure of spacial resoluation?
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lateral and elevational resolution is typically worse than axial resoluation
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of what use is a beam profiler
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allows evaluation of bam focusing characteristics
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Name 4 ways of measuring intensity and power?
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-hydrophone
-radiation force measurements -calorimeter -schleirin photography |
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# What is a hydrophone and what is its main use?
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-large piezoelectric crystal which is placed in the path of the ultrasound beam
-voltage generated is directly proportional to the energy in the beam -better in house method than radiation force measurements of output evaluation |
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what information does a calirimeter provide?
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-indicates the output.
- A medium is placed in an insulated fluid-filled object containing a thermometer. -The beam is passed into the medium. - The degree of heating is directly related to the energy in the beam. |
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what are spacial measurements? temporal and pulse measurements
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the power distribution over physical dimensions
-temporal and pulse measuements-distribution of power over time |
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what factors determine TI and MI?
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TI:
-determined by output and transducer frequency MI: -determined by transducer frequency and peak rarefactional pressure(output) |
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what does MI depend on?
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frequency and output of the system
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what are the types of mechanical biological effects?
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-radiation force
-streaming -cavitation(stable and transient) |
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when does heating become significant in ultrasound?
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-significant if it exceeds 2 degrees celsius
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what is the threshold for fetal anomolies over extended periods of time?
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41 degrees
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explain streaming
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-excessive radiation can show flow within a medium
-can cause sheer(rectangular book becomes rhobic w/ sheer foce) or tearing stress |
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ODS
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output display standard
-displayed as MI and TI=take a number of factors into account to display potential heating and mechanical pressures |
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explain biological studies on cells?
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-some reports of cell damage due to the use of medical ultrasound, but these studies have not been able to be independently confimed
-cell studies are significantly different from human cells, so even w/ independant confirmation of harmful effects, reproducing this in the human population is extremely difficult -cells are particularly susceptible to changes in heat |
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explain transient cavivation
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aka collapse cavivation:
-bubble collapses as a reaction to the changing mechanical pressures possible results: -shock waves -extremely high temperatures -light emmision(in clear fluid) |
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epidemiological studies
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-evaluations of the effects of ultrasound in a stated population
-12 studies have been carried out, and have not revealed any adverse effects of u/s |
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explain biological studies on plants?
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-useful to study effects on plants because gas filled channels btw cell walls allow studying cavitation.
-the only irreversible effects on plant cells has been cell death. -other effects are: -chromosomal abnormalities -mitotic index reduction -growth rate reduction |
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what factors are used to calculate TI?
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-frequency, aperture, and internsity
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what ways can TI be expressed?
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TIS-thermal index in soft tissue
TIB-thermal index in bone(at or near the focus after travelling though soft tissue) TIC-thermal index in cranial tissue(when transducer is close to bone) |
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what are the wave variables? which variable are the main concern for biological effects?
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-pressure
-density -temp -distance (temperature and distance are the main concern for biological effects) |
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how is mechanical index calculated?
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-Peak rarafactinal pressure/ square root of center frequency of the bandwidth
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explain the development portion of transparency film processing?
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-converts exposed ares of the film to regions of concentration on the film
-phenidone, and hyproquinone are the active chemicals which accomplish this Chemicals which perform ancillary functions: -sodium carbonate-controls hydrogen ion concentration -sodium sulphate-inhibits oxidation -potassium bromide-restrainer-to limit reaction rate -a hardener to control swelling of the emulsion |
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explain photothermography
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-1995
-processed by a heating method -chemicals in emulsion are heat sensitive -when a latent image is generated in the normal fashion, film is carried across a heated drum |
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explain thermal silver behenate
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-heat sensitive coating on a base
-laser heats the coating which results in silver deposits in that region -intensity of laser determines optical density in a given region |
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explain heat-sensitive paper
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-Chemically-treated paper is transported past a CRT displaying a single echo train. --The echo train changes as paper moves past the CRT.
-Heat forms deposits of silver on the paper. -Variations in heat forms different shades of gray. |
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explain dye sublimation
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-dye is coated onto a ribbon
-as dye is heated, it transforms(sublimates) into gas and transfers to the films -density depends on how much dye was depositied which is dependant on how much heat is applied. |
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video printers
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-Dyes are heat activated and are transferred to paper without the need for chemical processing.
-Separate ribbons are needed for each of the primary colours and are placed on the paper separately. - colours are transferred to the paper by a sublimation process. |
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explain how the VHS works?
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-most common method of recording motion until DVD's came around
- A 1/2-inch diameter tape is coated with magnetic particles -This coating consists of dipoles which are subjected to a magnetic field. -When recording, the tape is transported past two writing heads which produces a magnetic field in the region of the tape. -The magnetic field varies according to the brightness changes on the image(variations are stored in oblique tracks on the tape) -Audio information is recorded on a linear track. -During playback, magnetic variations are read and changed into the varying brightnesses which make up the image. |
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explain dye sublimation
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-dye is coated onto a ribbon
-as dye is heated, it transforms(sublimates) into gas and transfers to the films -density depends on how much dye was depositied which is dependant on how much heat is applied. |
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multiformat camera?
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-photographic method which uses transparency film to place a selected number of images on a transparency film
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explain thermography
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-layer of heat-sensistve material consisting of devleloper and dye in separate minicapsules is coated onto a film base
-heat from laser causes walls of the devloper and dye capsules to become permeable -they combine to form a black blob -the amount of heat determines how dark the blob gets -when heat is removed, capsules become impermerable again -since this system is not light sensitive, a dark room is not required |
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Which are the two main components of transparency film.
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base and emulsion
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explain the fixing portion of transparency fild processing?
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-an acetic acid solution is used to stop the devlopment
-sodium thiosulfate helps remove underdevloped halide grains -aluminum chloride hardens -sodium sulfite preserves |
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name some dry processing systems
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-photothermography
-direct thermal silver behenate -thermography -dye sublimation |
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explain the basic function of a multiformat camera?
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-cathode ray tube directs the image toard a lens which positions an image over a designated section of the film
-the film/lens/CRT relative postitions are adjusted so that images are correctly placed on the film. |
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What is a 'true colour' memory?
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24-bit memory
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some have said that 2D has a 3rd non-spacial dimension. What are they talking about?
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brighness
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what 3 ways can 3D information be displayed?
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-Multiplanar formattting-viewing a single plane using perpendicular planes anywhere in the 3D volume
-surface rendering-depicts the surface of objects for display -volume rendering-a 2D image based on inside the 3D volume |
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What are the limitations of 3 and 4D? why has it been slow to be accepted in some cases
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-its time consuming to learn
-requires huge amount of computer memory -lack of orthogonal scan planes -slow frame rates -limited scan lines -long computational times -many factors contribute to the echo induced signal making data manipulations difficult to apply. |
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In transient echo imaging, what causes the chaotic appearances that helps track blood flow?
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The disintegration of the gas bubbles.
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Compare the terms linear and non-linear propagation
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Linear propegation:
-When low pressure fundamental frequencies are used, fundamental frequency echoes are returned. NOn-linear propegation: -When high pressure fundamental frequencies are used, various harmonic frequencies are generated. |
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why does the effective beam width narrow when harmonics are generated?
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-as pressures increase, output is increased, and there are more harmonics generated.
-only areas of the beam w/ sufficient energy will genreate harmonics -this results in a narrow effective beam. |
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What is the down-side of using non-pulse inversion harmonics?
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Because pulse lengths are increased to reduce bandwidths, there is a concomitant reduction in axial resolution.
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One type of harmonics is considered a filtering technique and the other a subtraction technique. Which is which.
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Regular, non-pulse inversion=a filtering technique because the fundamental is filtered out leaving only the harmonics.
Pulse inversion=a subtraction technique because the fundamental frequencies are removed from the bandwidth by cancellation. |
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what is another name for transient echo imaging?
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stimulated acoustic emision(SAE)
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what is transient echo imaging? what is it useful for?
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-under the influence of ultrasound, gas bubbles can break allowing gas to diffuse into the surrounding tissues quite easily
-useful for slow moving blood |
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There is something to be given up when using each of the two types of harmonics. What are they?
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-In regular harmonics axial resolution is worse than with pulse inversion.
-With pulse inversion, frame rate is lower due to the increased dwell time. |
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Why are longer pulse lengths generally used in non-pulse inversion harmonics?
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Both transmitted and received bandwidths must 'fit' within the transducer bandwidth.
- In order to cause a narrowing of these bandwidths, the pulse lengths are increased. |
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HOw is information w/ harmonics processed?
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-w/ regular harmonics, both fundamental and harmonic frequcny must fit into the transducer bandwidth w/out overlapping, so longer pulses are used
-as pulselength increases, bandwidth decreases. -amplifier is tuned to process higher frequencies, so it filters out the fundamental frequencies leaving the harmonics to be displayed |
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what are the advantages of harmonic imaging?
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-decreased clutter, grating lobes, side lobes, etc.
-decreased reverberation -reduction of acoustic noise -fluid spaces have less fill in -improved lateral resolution due to decreased effective beam width -effect of subcutaneous fat in lg. patients is reduced |
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what areas do not produce harmonics?
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-peripher of a wave
-low amplitude waves -first few centimeters -lower pressure regions in the far field |
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what does generation of harmonics depend on?
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-acoustic pressure
-frequency -non-linearity co-efficient -density of the medium -velocity in the medium -distance of propegation |
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Explain(in terms of the sinusoidal wave), how harmonics are produced?
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-sinusoidal wave propigates as a series of pressure variations
-higher pressure=faster wave which results in a change in the wave shape(it's now non-sinusoidal), and generation of harmonic frequencies. -as pressures increase(increased output), there are more harmonics genrerated. -only areas of the beem w/ sufficient energy will generate harmonics, so there is effective narrowing of the beam. |
