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the five components of the imaging system
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Terms in this set (31)
small voltages boosted to make them stronger,user adjustable.
units of amplification =-decibels
operator adjustable through overall gain control key.
preamplifier-clips large voltages spikes on amplifies very weak signals prior to amplification.
goes between transducer and receiver-on tail of transducer.
TGC,compensation,swept gain,depth gain compensation,overall gainpurpose to compensate for attenuation due to depth operator adjustable of TGC. GOAL-ultrasound image of uniform brightness. the deeper the target, the more compensation needed reduction of strong signal.log compression,dynamic range,compressionpurpose to squeeze signal amplitudes into a narrower range. definition-ratio of the greatest to smallest amplitude that ultrasound instrument can handle.dynamic range,log compression, compression-relationshipslower dymanic range-less shades of gray-greater contrast Higher dynamic range-more shades of gray-less contrast Inverse relationship between Dynamic Range and CompressionDynamic range of componentsTransducer/receiver -100-200 Memory (scan converter) 40-45 the Display/printer-20-30 Action in rangeDemodulationPurpose- change voltages into another form NOT USER ADJUSTABLERECTIFICATIONnegative signals changed to positive for image generationSMOOOTHINGsignal AVERAGE to reduce spikes or fill voidsREJECTION-SUPPRESSION,THRESHOLD,FILTERPURPOSE-suppressing or elimnating small votltage amplitudes to reduce noise. sonographer controlled through filter control keySCAN CONVERTER-AKA MEMORYFUNCTION-storage of information coming from receiver METHODS OF STORAGE- Analog-infinitely variable Digital-discreet binary numbers-numbers storedanalog scan converterELECTRIC CHARGES stored on silicon wafer advantage-provides excellent resolution, infinitely variable disadvantage-unstable imageDigital scan convertersignals stored as binary numbers in random access memory function-converts analog signals into digital format =, then back for output devices,stable storage numbers are stored as binary numbers on-1,off-0 eight bits-one byte-ability to make alphanumeric characters specific sequence of zeros ans ones are combined to represent any base 10 numberspixelpicture element, a dot on the screen information is stored as a bit within a pixel. increased pixel density improves spatial resolution decreased pixel density lowers spatial resolution location of pixel relationship with echo arrival time,depth and beam orientation-laterallyvoxelpicture element in three dimensional imaging-3Drelationship of number of bits and contrastadditional of bits,bit depth increases the number of shades of gray the ultrasound unit can display. calculation of shades of gray, raise number 2 to exponential power of bits present in system example 3 bit resolution=2 raised to the 3rd power=2x2x2=8 shades of gray. bistable image=off-0 on-1preprocessing functiononly available while image is live. allows change,alteration,or manipulation of echoes PRIOR to storage in computer memory. not available afterimage is frozen examples-TGC,DYNAMIC RANGE,RES OR WRITE ZOOM,LOG COMPRESSIONRES OR WRITE ZOOMRESCANS the specified area,ROI-REGION OF INTEREST WITH MORE SCAN LINES,INCREASING SPACIAL RESOLUTIONRESREGION EXPANSION SELECTION RESCANS ONLY THAT AREA, MORE PIXELS, LARGER AREAPOSTPROCESSING FUNCTIONFUNCTIONS AVAILABLE AFTER FREEZING THE IMAGE ALLOWS CHANGE,MANIPULATION, OR ALTERATION OF ECHOES AFTER STORAGE IN COMPUTER MEMORY CHANGE IMAGE APPERANCE AFTER FRAME IS FROZENPROCESS OF PRE-POSTPRE-PROCESSING,MEMORY,POST-PROCESSING EXAMPLES-CALIPER PLACEMENT,BLACK AND WHITE INVERSION,CHANGE BACKGROUND FROM BLACK TO WHITE, READ MAGNIFICATION,REGULAR ZOOM, POST PROCESSING CURVE-CHANGES THE GRAYSCALE MAP BRIGHTNESS OF PIXELS.PERSISTANCETYPE OF FRAME AVERAGING,SMOOTHER IMAGE,LOWERS FRAME RATE MOSTLY USED FOR THYROID SCANSEDGE ENHASMESNT