Yola



Electrostatics & Energy:Matter – The substance that comprises all living objectsPrinciple characteristic = mass/weightEnergy - The ability to do workPrinciple characteristic is movement/motionWork – The result of force acting on an object over a distancePower – incorporates time into equationSame amount of work to lift puppy to certain height (5 mins or 5 seconds)More power lifts quickerMany types energy – mechanical, chemical, nuclear, electromagnetic, electricalCombination of matter & energy is a constantThey can convert to each other but can’t be destroyedEnergy:Electrical energy – Can be converted:Light bulb – electrical to radiant/lightHair dryer – electrical to thermalElectromagnetic spectrumElectromagnetic radiation/energy placed on a continuum based on type of electrical excitationRainbow is a small portion in the middleVisible light in the middleUltraviolet – above violet on the spectrumInfrared – below redHuman eye can see very littleElectromagnetic waves can travel through a vacuum without losing energyVacuum – space entirely devoid of matterSemi-vacuum x-ray tube used in radiologyParticle Wave TheoryEnergy described as a wave – high, low, frequent, infrequentWaves:Measurable height & frequencyWavelength is distance between wave crestsShorter wavelength = higher frequencyCrest – wave highpointTrough – wave low pointFrequency - Rapidity with which waves hit the shore (symbol is hertz/Hz)Period – Time taken to complete one whole waveCycle – One crest & troughAmplitude – height of wave from crest to troughSine wave – tracing of waves as they travelHave a high and low point with time as a constantImportant in choosing radiology time settingsSound waves – travel invisibly through spaceEnergy in RadiologyEnergy is thought of as particles (x-rays or gamma rays)Mathematic quantification of amount of energy needed to do workPhoton particle carries a specific energy that depends on frequencyEnergy & frequency are directly proportionalEnergy doubled = frequency doubledRoentgen’s Properties of x-rays – still the original listWon Nobel Prize in Physics in 1901 for producing/detecting x-raysX-Ray Properties – Very importantHighly penetrating invisible rays that are a form of electromagnetic radiationElectrically neutral – not affected by electric or magnetic fieldsCan be produced over a wide variety of energies & wavelengthsRelease small amount heat as pass through matterTravel in straight linesTravel at speed of light – 3 X 108 meters/sec in vacuumCan ionize matterCause fluorescence (light emission) of certain crystalsCannot be focused by a lensAffect photographic filmUse ionization & excitation to produce chemical/biological changesProduce secondary & scatter radiationMagnetism & ElectricityElectricity becomes x-raysAtoms:Protons in nucleus positiveTightly boundElectrons orbiting are negativeVulnerable to outside forcesCharges can be weakBonds can be brokenElectrons can be cast offIf not replaced, atom stays positively chargedCan float freely (free electrons) or join other atomsStrives for balance of pos/negElectricity concerns the movement of the electronsElectrostaticsStatic electricity/electrostatic charge – Radiant energyCharge of free electrons builds up & dissipates when an object that will accept a charge (conductor) is encounteredStatic electricity in hair – Hairs build up excess electrons so are negatively charged & repel each otherShocking others – Feet scoop up extra electrons, then discharge and lose them when touches something that conductsCold, dry atmospheres enhance build-upWetting a comb allows electrons to redistribute appropriatelyRadiation works this way on a greater scaleElectrification – The process of electron charges being added/subtracted from an objectLaws of electrostatics – Very ImportantElectricity called packets of electron energy5 laws:Like charges repel; unlike attractFundamental basis of magnetismPrinciple of an electric circuitHow an x-ray tube prepares to make an exposureInverse square law [Flashlight]One of the most important concepts in the field of imagingImpacts set-up of x-ray unit & technical factorsThe intensity of the x-ray beam is inversely proportional to the square of the distance from the sourceMoving tube closer to subject intensifies the radiationAnd illumination? distance = radiation X 4Distribution – The charges reside on the outside surfaces of conductors but all through nonconductorsConcentrationGreatest concentration of charges is on surface where curvature is steepestNot as applicable in radiology but governs voltage from taser or cattle prodMovement – Only negative charges move along solid conductorsPositive charges tightly boundElectrification – Object electrified in 3 waysContact – Shocking a friendElectrons collect on body surface, giving you negative chargeElectrons concentrate on point of fingerFinger close enough – spark discharges into electrical neutral or slightly posStatic electricity can build up on an x-ray tray in a very dry atmosphereFilm records exact amount of dischargeFriction – Occurs when one object rubs against anotherElectrons travel based on availability of electrons in each objectInduction – Most important for radiologyElectrical fields act upon each other without actual contactUses the force fields of the electrons of one object to cause a reaction in an opposing objectPrinciple directly applies to x-ray productionAlso transformers, x-ray tubes, electric motorsLightning:Clouds build up excess electrons when form thunderheadsGround is neutralDischarge of electrons from cloud to ground is instant, loudElectric current is generated between cloud & ground Conductors & InsulatorsSome objects conduct easilyWater – no appliances in bathCopper – Used in household wiringSome don’t conductRubber, plastic, and glassRubber covering over copper wireElectric Current:Andre-Marie Ampere – described electric current as a quantity of electrons flowing past a pt in timeAmpere is unit of currentMilliamperes (mA’s) – Diagnostic imaging uses these to regulate # of electrons to produce x-ray photonsmA setting determines number of electrons to flow past a given pointIncreasing mA will increase image density or darkenDecreasing mA will lightenDoubling mA’s doubles densityResistance – the opposite of current flowGeorge Ohm researched resistance & ohm is the unit of resistancePotential Difference:Causes electrons to travel from one end of the wire to then otherEmpty Garden hose – Little water in hose but lots of potential in faucetFaucet turned on to allow flow - potential difference along hoseOne end with none & one end has lots of water coming inPotential difference is measurement of empty hose compared to fullDiameter impactsSmall hose/wire has lots of resistanceLarger hose/wire has littleVoltageAlessandro Volta – identified unit of potential differenceElectromotive force – Force that draws electrons from area of excess to area deficient of electrons in circuitVolt - Strength of potential difference or strength of electron flowDiagnostic X-ray productionElectrical circuit requires:Potential difference (voltage)Resistance (ohms)Amperage (current)PowerWatt – unit of powerNamed after James WattColleagues with Ampere, Volta, and Ohm – aware of work1 watt = 1 ampere flowing through a circuit at 1 volt per secondCurrent in amperes (I) X volts (V) = Power (W or watts)I X V = WExample – Most x-ray units use a maximum of 125 volts & 300 milliamperes of electricityW = 0.3 X 125,000 = 37,500 watts or 37.5 kilowattsMost generators are rated at a minimum of 30 KW’sSo should be OKElectrical circuitPower originates at a power plant & is transmitted with periodic transformer stations that boost powerThe transformer nearest the clinic is most importantMay be an auxiliary just outside clinicClosing a switch completes the circle or circuitConnection is needed to turn the system on/offBreaking the circuit causes the light to go offBurnt out light bulb:Fine wire the forms the cathode of the lamp burns out in the heat of the electron flowCircuit is interrupted and light doesn’t functionMouse eats through cord:As cord is eaten through – mouse conducts electricity & diesOn-off switch – On all units, plusWall switch – usually required by law to be at eye level within reach of the generatorPower can be shut off as alternate meansLine Voltage Compensator – standard equipmentUsually automatic on newer unitsOlder ones have compensator mounted on control panelMeans for increasing/decreasing incoming line voltageCircuit BreakersPower supply to x-ray unitAccepts current (amperage) up to its limit/ratingWhen hits limit – circuit breaker disconnects & power is interruptedFuse works the same way except a small piece of metal melts to stop flowImportant factors to circuit:Current/amperageIf too much current is demanded by generator – overload light comes on and no exposure is possibleCurrent in generator is milliamperage (mA’s)Very important – should never be bypassedGroundCircuit must be grounded to be safeNeeds an alternate route for electricity to flow if circuit breaks inappropriatelyOriginal circuit is directed to a ground wire attached to an object that absorbs electronsFlow of electrons stops but excess go to ground wireDirect vs alternating currentDirect – batteries installed in a tube/line (flashlight, car battery)Orientation mattersRequires source situated close to end userIf energy needed to go large distances – need low current/high voltage (more efficient)Alternating current – produces 1 pos and 1 negative pulse (cycle)Most efficient way to transmit power = 100 cycles per secondRequires a transformer to step up power at one end and down at otherHeinrich Hertz – studied electromagnetismHertz is # cycles per second of oscillations of pos/neg1 Hertz = 1 pos and 1 neg cycleTransformers – Receive power from incoming power lines & transform power to x-ray tubeUse turns of wire around a central core or two close coresIncrease or decrease voltage in a circuitUses induction to electrify3 transformers in the x-ray circuit:AutotransformerIncreases incoming voltageKilovoltage selector – allows selection of KW’s to produce radiographCentral core & tapsHigh voltage transformer – very powerfulFinal step-up transformer to boost voltage to x-ray tubeRaises voltage from incoming 220 to maximum 125,000 voltsFilament transformer Smaller, step-down transformerProduces voltage to the filament of the x-ray tubeTube works like light bulbSmall wire visible in bulb is cathodeProduces light depending on wattage ratingProduces electrons in cloud governed by selection factorsFilament must reach certain temp for exposure to take placeFilament produces this tempRectifiersChanges current flow on negative part of AC cycle to positive so entire flow can travel to x-ray tube to produce radiationIf only half the current available, only half radiation producedX-ray tube can only receive positive charges, since current only can flow one wayAdditional feature added to ensure each exposure starts at beginning of pulse and finished at end – all current can be usedThree-phase circuitsAdd in 2 more pulses of power offset from 1st pulse to make the dips in power in the waveform less significantRequires a lot more powerOnly used in large hospitals needing to image large chests/abdomensHigh frequencyUses high-frequency pulses to keep ripple low with continuous outputMore x-rays per exposure reduces overall exposuresSaves wear & tear on unit & reduces overall doseOutside of X-ray unit3 items essential to every unitControl panel/generator – sometimes mounted above tableX-ray tubeHigh-tension transformerUnit requires dedicated power lineLarge Animal portable x-ray unitsSmaller version – not as powerfulLess milliamperageUsually only needed for legs & feetGenerator, transformer, and x-ray tube compressedDiagnostic x-ray productionAll in place:X-ray circuit receives incoming powerStep-up transformers supply power to cathode side of x-ray tubeCathode usually has 2 filaments made of thoriated tungstenCan withstand high temps without meltingElectrons are boiled off cathode filament in reaction called thermionic emissionCloud of emissions called a space chargeWhole process is space charge effectHas a large & small focal pointFilament circuit heats cathode to high temp (sometimes 3900 degrees F)Which filament is used is determined by mA settingFilaments positioned in cup-shaped focusing cup so aimed directly at anodeFocusing cups slightly negatively charged to focus electrons boiled off cathode filamentsBeveled edges also help focusFocal spot of anode is where x-rays are produced & where most heat must be dissipatedX-ray tube receives power, produces electrons, and converts them to x-raysProduces extreme heatDifferences in tubes have to do with cooling systemsRatio of heat to x-rays is 99-1Method of heat transfer enhances tube longevity & reliabilityTube consists of glass enclosure that houses specialized anode & cathodeGlass enclosure is heat-resistant (sometimes Pyrex)Standard tube is 30 cm long & about 20 cm diameter Anode2 types:Rotating – small animal unitsStationary – large animal unitsUsually made of tungsten or an alloy – high atomic number so can absorb electrons/heatTarget of the tube is mounted in rotating anode – prepared to accept electronsFunctions:Mechanically supports electron targetServes as thermal dissipater by directing heat emitted in x-ray productionRotates so photons aren’t always focused in same spotElectrical conductor – receives electrons & transmits them backRotor circuitActivated when the filament transformer starts to heat the cathodeRotor turns the rotating anodeContains stainless steel ball bearings to withstand high temperaturesBearings can distort as x-ray tube agesIncreases noise since move rapidly when rotor is turningIf bearings seize, rotor doesn’t turn, and the heat stays fixed on focal spotAnode overheats & cracks, safety interlocks kick inStationary anodeUsed in equine portable unitsNeeds a way of dissipating heat, absorbing photons, and converting to x-raysAnode made of copper w/a tungsten insertEnd is angled to direct the beam to the patientDoes not rotate so must watch warning/ready lightsThe Line Focus PrincipleEnsures the x-rays are directed onto object being radiographedDescribes how the electrons interact with the anode & change direction so x-rays are directed towards patientLine focus principle – Determines the width of the beam & resolutionInvolves the angle of the bevel on outer edge of anode & resulting change in direction of x-raysAngle < 15 degrees from vertical = beam narrow with high resolutionAngle > 15 degrees = beam wider, less heat focused, decreased bloom effectTypical angle is 11 degreesOff-focus radiationExposure switch is closed = electromagnetic function of circuit takes effectCloud of negatively charged particles drawn across to positively charged anodeElectrons interact with target + areas of anode adjacent to targetElectrons can bounce off the target, then be attracted back beyond the focal pointCollar of lead around tube normally prevents extra-focal radiationCan appear as artifactHeat BloomTarget exposed to radiation = anode can heat to 1000-2000 degreesHeat bloom - Repeated exposures can cause heat dissipation & enlargement of focal spotUsually not enough exposures in vet clinic to happenTube rating chartIndicates the x-ray tube limits based on the heat units equationmA X kV X timeDetermines suitability for size of animals clinic radiographsFocal spot bloomAffects the sharpness of the imageCan happen with old tubeAnode bombarded with radiation gets hotHeat dissipates into surrounding metal with timeIf tube not allowed to cool, outer edges of focal spot become hot enough to expand spotCauses image to lose sharpness, reducing resolutionIncreased focal spot size causes unsharpness Anode heel effectBevel of the anode limits the amount of x-rays produced on stem side of anodeIntensity of radiation is greater on cathode sideImportant when pt is thicker at one end than the otherThicker end should go at cathode sideHead end to right, foot to the leftExposure switchUnit that sets the sequence of events in motion to produce the x-ray exposureUsually 2-stageWait for the ready signal (especially in mobile units)Prolongs lie of unit1st activates the rotor & boosts the filament and transformersRotor noise should be evidentIf rotor doesn’t activate, don’t expose since tube can be damagedExposure could be directed to very small focal pointWill eventually melt the anodeIf hear boiling liquid – stopX-ray tube likely shorted out and filament circuit is overeating the cooling oil in the x-ray tube housingTube cold explode if exposure is attempted2nd activates the exposure through the x-ray tubeBe familiar with noises“Dead man” safety factor - Test at least annually to make sure disconnects when pedal releasedLegal requirement to make sure x-ray beam terminatesExposure switch variationsSingle-stage – wired so rotor begins when generator turned onNot ideal, should be activated only when exposure is about to be madeSingle-stage foot switch – initiates rotor when depressedSafety delay until unit picks up speedLessens flexibility in positioning fractious animalHand switch – most human unitsUsually behind wallReplace with foot for veterinary ................
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