11 The amount of overall blackening on a radiograph, or of a certain part of the image, is referred to as density.Density results from two things:the amount of radiation that reaches a particular area of the film,and the amount of black metallic silver deposited when the film is developed.
19 Creating the IMAGEWhen x-rays pass through a patient's body, three things can happen:(1) the x-ray photon is transmitted, passing through the body, interacting with the film, and producing a dark area on the film;(2) the x-ray photon is absorbed in an area of greater tissue density, producing lighter areas on the film; and(3) the x-ray photon is scattered and reaches the film causing an overall gray fog.
22 Radiographic Prime factors The factors principally responsible for x-ray quality and quantity.These are mAs,kVp,distance (SID).
23 PRIME FACTORS SID - ADJUSTED IN THE ROOM KVP - “intensity of beam” CONTAST RANGE FOR PARTMAS – “density of image”CHANGES WITH PT SIZE
24 Introduction to Technical Factors to Create an image mAs & kVpIntroduction toTechnical Factors toCreate an image
25 X-ray quantity (mAs)is a measure of the number of x-ray photons in the beam.Also called x-ray output, intensity or exposure.X-ray quality (kVp)is a measure of the penetrating ability of the x-ray beam
26 The quantity of electron flow, or current, in the X-ray tube is described in units of milliamperes (mA).The maximum kinetic energy of the accelerated electrons is defined in terms of kilovolts peak potential (kVp).
27 IMAGES DENSITY = THE AMOUNT OF BLACKENING “DARKNESS” ON THE RADIOGRAPH CONTRAST – THE DIFFERENCES BETWEEN THE BLACKS TO THE WHITES
28 Film Screen Overexposed Referring to a radiograph that is too dark because too much x-radiation reached the image receptorUnderexposedReferring to a radiograph that is too light because too little x-radiation reached the image receptor
32 Density on Image When a radiologist looks at a radiograph, they looks for any anatomic or pathologic change that causes a change from the normal density.That could be, a solid mass in the lung that stops x-rays from reaching the film and decreases the amount of film darkening in that area (appears “light or white on image”Or excessive “AIR” – looks BLACK
35 MilliamperagemAOne milliampere is equal to one thousandth of an ampere.The amount of current supplied to thex-ray tubeRange 10 to 1200 mA
36 Tube current (mA)Tube current is equal to the number of electrons flowing from the cathode to the anode per unit timeExposure of the beam for a given kVp and filtration is proportional to the tube current
37 TimeIn secondsHow long x-rays will be produced0.001 to 6 seconds
38 mAs Changesat least % mas change needed to see a visible change in density
42 Kilovoltage Peak kVp One kilovolt is = to 1000 volts The amount of voltage selected for thex-ray tubeRange 45 to 120 kVp (diagnostic range)kVp controls contrast
43 Tube voltage (kVp) Determines the maximum energy in the beam spectrum and affects the quality of the output spectrumEfficiency of x-ray production is directly related to tube voltage
44 Contrast- the differences between blacks to whites Kilovolts to anode side – kVp ( )Kilovolts controls how fast the electrons are sent across the tubekVp – controls CONTRAST on imagesLow kVp – more absorbed – black - whiteHigh kVp - more grays on image
46 Influencing factors: kVp 15% rule:15% kVp = doubling of exposure to the film 15% kVp = halving of exposure to the film15% rule will always change the contrast of the image because kV is the primary method of changing image contrast.Remember :15% change ( ) KVP has the same effect as doubling or ½ the MAS on density
48 CONTROL PANEL CONTROLS kVp SELECTIONmA SELECTIONTIME (sec.)
49 The Control ConsoleThe control console is device that allows the technologist to set technical factors (mAs & kVp) and to make an exposure.Only a legally licensed individual is authorized to energize the console.
51 X-Ray Machine Purpose: provide a specific current (mA) & voltage (kV) to the x-ray tubeconvert electrical energy to electromagnetic energy (x rays) in a controlled mannercontrol the energy of the x-ray photonscontrol the number of photons
52 kVp & mAskVp = quality of beam – the “intensity of how much tissue it can penetratemAs – the amount of time the beam is left on
53 THE X-RAY TUBEThe ANODE (+) attracts the electrons that are “boiled offFrom the ---Negative CATHODE (--)
60 INVERSE SQAURE LAW Applies basic rules of geometry The intensity of radiation at a given distance from the point source is inversely proportional to the square of the distance.Doubling the distance decreases intensity by a factor of four.
61 INVERSE SQUARE LAW The inverse square law – Used for RADIATION PROTECTIONWhen you change your distance from the “radiation source”The intensity of radiation will be reduced by a square of the distance (MOVING AWAY FROM THE SOURCE)OR INCREASED – CLOSER TO SOURCE
62 DISTANCEDistance from the radiation source should be kept as great as possiblePhysical Law:Inverse Square Law
63 Application of inverse square law principles can yield significant reductions in patient and operator radiation exposure.
81 TRANSFORMERS (Step Up or Step Down) Increases the VOLTAGE going to the ANODE side of the tube OR110 volts to 110,000 voltsDecreases the CURRENT going to the CATHODE side of the tube5 Amps to 50 milliamps
87 Circuitry: Source: Carlton & Adler (1996) Circuitry: Source: Carlton & Adler (1996). Principles of radiographic imaging: An art and a science. (96-99).MAIN CIRCUIT Modifies incoming current to produce x-raysBoosts voltage to range necessary producex-rays. Modifies incoming line power to produce thermionic emission from the filament wire.FILAMENT CIRCUITFilament circuit adjusts to mA ratings (50, 100, 200, etc.).After mA selection, current sent to step down transformer to modify amps that reach filament on x-ray tube
88 Important Parts Of The Circuit Board TO ID MAINBREAKEREXPSOURE SWITCHAUTOTRANSFORMERTIMER CIRCUITHIGH VOLTAGE STEP UP TRANSFORMERRECTIFIERFILAMENT CIRCUIT VARIABLE SELECTPRFILAMENT STEP DOWN TRANSFORMERX-RAY TUBEROTOR / STATOR
94 56478#139mA selector102See Circuitry Review handout and chart for numbers
95 Important Parts Of The Circuit Board TO ID 1 Incoming Line Voltage2 Autotransformer3 KVP Selector4 TimerNo # Ma Selector5 Primary Side (Low Voltage)6 Secondary Side (High Voltage)7 X-ray Tube8 Rectifier9 STEP – Up Transformer10 STEP – Down Transformer
98 TRANSFORMERS (Step Up or Step Down) Increases the VOLTAGE going to the ANODE side of the tube OR110 volts to 110,000 voltsDecreases the CURRENT going to the CATHODE side of the tube5 Amps to 50 milliamps
99 Filament Current Current comes from Autotransformer Controls the Ma selectionFocal Spot Selector Switch located here
105 A few days after Roentgen's initial public announcement of his discoveries, a doctor in America took X-ray photographs of a person with gunshot wounds in his handsWhy can you see the bullet fragments?
107 they are electromagnetic waves of shorter wavelength and higher energy than normal light. But the debates over the nature of the rays – waves or particles? –Photons can be described both as waves and particles.
108 The Electromagnetic Spectrum X-rays have wavelengths much shorter than visible light, but longer than high energy gamma rays.
109 IMAGE CREATIONATOMSINTERACTION WITH “MATTER”ATOMIC NUMBER
110 Why you see what you seeThe films or images have different levels of density – different shades of grayX-rays show different features of the body in various shades of gray.The gray is darkest in those areas that do not absorb X-rays well – and allow it to pass throughthe images are lighter in dense areas (like bones) that absorb more of the X-rays.
111 Kinetic energy Energy of motion The electrons KINETIC energy is converted to PHOTON energy