Discovery of Xrays Xrays were discovered on November
Discovery of X-rays � X-rays were discovered on November 8, 1895, by Dr. Wilhelm Conrad Roentgen. � Accidental discovery � First radiograph of Mrs. Roentgen's hand � Roentgen received the first Nobel Prize presented for physics in 1901. � Public viewed discovery as a novelty � Radiographic imaging and therapy important to the medical sciences Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 1
X-rays as Energy � � � A form of electromagnetic radiation Behave both like waves and like particles Move in waves that have wavelength and frequency Wavelength and frequency are inversely related X-rays also behave like particles and move as photons Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 2
Properties of X-rays � � � � X-rays are invisible. X-rays are electrically neutral. X-rays have no mass. X-rays travel at the speed of light in a vacuum. X-rays cannot be optically focused. X-rays form a polyenergetic or heterogeneous beam. X-rays can be produced in a range of energies. X-rays travel in straight lines. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 3
Properties of X-rays (cont. ) � � � X-rays can cause some substances to fluoresce. X-rays cause chemical changes to occur in radiographic and photographic film. X-rays can penetrate the human body. X-rays can be absorbed or scattered by tissues in the human body. X-rays can produce secondary radiation. X-rays can cause chemical and biologic damage to living tissue. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 4
Birth of Radiology � Dry plate- used to record x-ray images � exposure required were extremely long. � Glass plate easily broken. Thomas Edison developed the first intensifying screen WWI x-ray film was produced the cellulose nitrate film base and was highly flammable and a fire hazard Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 5
X-ray Production � The production of x-rays requires a rapidly moving stream of electrons that are suddenly decelerated or stopped. � The negative electrode (cathode) is heated, and electrons are emitted (thermionic emission). � The electrons are attracted to the anode, move rapidly towards the positive electrode, and are stopped or decelerated. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 6
X-ray Tube Housing � � � Metal or glass envelope Negatively charged electrode Positively charged electrode Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 7
Cathode � Filament � Source of electrons Filament current Thermionic emission � Coiled tungsten wire Large and small � Focusing cup Space charge effect Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 8
Anode � Rotating anode Requires a stator and rotor to rotate � Tungsten metal High melting point Efficient x-ray production � Target Decelerates and stops electrons Energy converted to heat and x-rays Bremsstrahlung and characteristic interactions � Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 9
Target Interactions � Bremsstrahlung interactions � Braking or slowing down � 85% of x-ray beam � radiation Characteristic interactions � Projectile electron energy at � Inner shell electron ionized � 15% of x-ray beam � least 69. 5 ke. V X-ray properties the same Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 10
Review of Interactions in the xray tube � � Bremsstrahlung- electrons interacts with the atomic nucleus, more energy is lost and a stronger x-ray is produced; account for the majority of the x-ray beam. Characteristic Radiation - electrons interact with an orbital electron from the atom, the pulling down of another electron from an outer shell causes an x-ray to be produced; account for a small majority of the x-ray beam Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 11
Target Interactions (cont. ) Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 12
Heterogeneous Beam � � Contains low energy rays which will be absorbed by the x-ray tube Average energy of the beam is 1/3 of the maximum energy X-rays are an inefficient process 99% heat, 1% converted to x-rays Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 13
X-ray Beam � Primary Radiation (PR)- portion of beam from tube to the patient; radiation before it enters the patient � Remnant Radiation (RR)- radiation emerging from patient’s body to expose the film; image forming radiation Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 14
Primary Beam Distribution � 5% of primary beam passes through the patient without any interactions � 15% of the primary beam interacts with atoms and produce secondary radiation, they make it out of the patient and expose the film. � 80% will be totally absorbed by patient Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 15
Distribution of Remnant Radiation � 20% or 1/5 of the intensity of the original beam exposes the film � With remnant radiation about 75% to 80% of the beam is made up of secondary radiation Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 16
Prime Factors of Radiography � m. A- milliampere � S- seconds time � k. Vp- kilovoltage peak � SID- source to image distance These are all controlled by the technologist Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 17
X-ray Emission Spectrum The range and intensity of x-rays emitted changes with different exposure technique settings on the control panel. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 18
Kilovoltage � Creates potential difference Determines the speed of the electrons in tube current Greater speed results in greater quantity and quality of primary beam � Increasing electron speed will increase x-ray beam penetrability � � Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 19
Milliamperage � Unit to measure tube current or number of electrons flowing per unit time � � m. A directly proportional to quantity of x-rays produced Double the m. A will double the number of x-ray photons produced Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 20
Milliamperage and Time � Exposure time determines the length of time x-rays are produced. � Increasing time will increase the total number of x -rays produced. Exposure time and x-ray quantity are directly proportional. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 21
Beam Filtration � Aluminum filtration added to x-ray beam to absorb low-energy photons � Total filtration Inherent Added � Reduces patient exposure Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 22
Compensating Filtration � Added to primary beam to alter its intensity � � Wedge filter Trough filter Used to image nonuniform anatomic areas Thicker part of filter lined up with thinner part allowing fewer xray photons to reach anatomic area Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 23
Image Formation � Differential absorption � Anatomic tissues absorb and transmit x-rays differently based on their composition (atomic number and tissue density). � Bone absorbs more x-rays than muscle. � Attenuation: the primary x-ray beam loses some of its energy (number of photons) as it interacts with anatomic tissue. Absorption Scattering Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 24
Differential Absorption Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 25
X-ray Beam Absorption � During absorption, the energy of the primary beam is deposited within the atoms comprising the tissue. � Photoelectric effect: complete absorption of the incoming photon X-ray ionizes atom Low energy secondary x-ray photon created Probability of photoelectric effect dependent on the energy of the incoming x-ray photon and tissue atomic number Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 26
Determining Attenuation of the Beam � � Three essential aspects of tissues will determine their attenuation properties and the resulting subject contrast: Tissue Thickness Tissue density Tissue atomic number Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 27
X-ray interaction with matter � � When the primary x-ray beam interacts with anatomic tissues. Three processes occur during attenuation of the x-ray beam: Absorption Scattering Transmission Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 28
Transmission � � If the incoming x-ray photon passes through the anatomic part without any interaction with the atomic structures, it is called transmission. The combination of absorption and transmission of the x-ray beam will provide an image that represents the anatomic part. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 29
Scattering � The Compton effect occurs when an incoming photon loses some but not all of its energy, then changes its direction. � It can occur within all diagnostic x-ray energies and is dependent only on the energy of the incoming photon, not the atomic number of the tissue. � Higher k. Vp reduces the number of interactions overall, but the number of Compton interactions increases in comparison to the number of photoelectric interactions. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 30
Absorption versus Scattering Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 31
Photoelectric Effect � � � The secondary x-ray photon does not reach the film. The photoelectric effect is crucial to the formation of the radiographic image. The photoelectric effect is responsible for the production of contrast on the radiographic image. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 32
Photoelectric Effect � During attenuation of the x-ray beam, the photoelectric effect is responsible for total absorption of the incoming x-ray photon. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 33
Scattering/ Compton Effect � � � The Compton photon may be scattered in any direction. Scatter refers to any x-ray photon which has changed direction from the direction of the primary beam. The Compton Effect may be considered as scatter, since 99% of all scattered x-ray photons originate from Compton interactions in the patient. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 34
Where do interactions occur � Compton interactions occur only in the outer shells of an atom. � Photoelectric interactions occur only in the inner most shell of an atom. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 35
Factors Affecting Beam Attenuation � Tissue thickness � � Type of tissue � � Tissues composed of a higher atomic number will increase beam attenuation. Tissue density � � X-rays are attenuated exponentially and generally reduced by ~ 50% for each 4 to 5 cm (1. 6" to 2") of tissue thickness. Increasing the compactness of the atomic particles will increase beam attenuation. X-ray beam quality � Higher k. Vp increases the energy of the x-ray beam and will decrease beam attenuation. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 36
Exit Radiation � � � Remnant or exit radiation is composed of transmitted and scattered radiation. The varying amounts of transmitted and absorbed radiation create an image that structurally represents the anatomic area of interest. Scatter radiation reaching the image receptor creates unwanted exposure called fog. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 37
Secondary Radiation vs. Scatter Radiation � � � Secondary Radiation refers to any radiation resulting from interactions within the patient. Scatter radiation refers only to that secondary radiation which has been emitted in a direction different than the original x-ray beam. Most secondary radiation is scattered. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 38
Radiographic Quality � A quality radiographic image accurately represents the anatomic area of interest, and its information is well visualized for diagnosis. � Visibility of anatomic structures Density Contrast � Accuracy of structural lines (sharpness) Resolution or recorded detail Distortion Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 39
Density � A film image is evaluated by the amount of density or overall blackness after processing. A radiographic image must have sufficient brightness or density to visualize the anatomic structures of interest. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 40
Image Contrast � The radiograph must exhibit differences in the brightness levels or densities (image contrast) in order to differentiate among the anatomic tissues. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 41
Subject Contrast Subject contrast is a result of the absorption characteristics of the anatomic tissue radiographed and the quality of the x-ray beam. � The ability to distinguish among types of tissues is determined by the differences in brightness levels or densities in the image or contrast. Contrast resolution describes an imaging receptor's ability to distinguish between objects similar in subject contrast. � Gray scale: number of different shades of gray that can be stored and displayed in a digital image � Scale of contrast: the range of densities visible on film � Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 42
Scale of Contrast Short scale or high contrast Long scale or low contrast Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 43
Recorded Detail � Anatomic details must be recorded accurately and with the greatest amount of sharpness. � Recorded detail refers to the distinctness or sharpness of the structural lines that make up the recorded film image. � All radiographic images have some degree of unsharpness. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 44
Distortion � Radiographic misrepresentation of either the size or shape of the anatomic part � Size distortion or magnification is an increase in the object's image size compared to its true or actual size. SID and OID affect magnification. � Shape distortion is a misrepresentation of an object's image shape. Elongation and foreshortening Central ray (CR) alignment of the x-ray tube, part, and image receptor affect distortion. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 45
Scatter � Unwanted exposure to the image receptor resulting in fog � A result of Compton interactions � Provides no useful information � Scatter or fog decreases image contrast. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 46
Modern x-ray film � Radiographic film is composed of two main parts � Base � Emulsion Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 47
Film Construction � Consists of emulsion of finely precipitated silver bromide crystals � Crystals are suspended in a gelatin and is coated on both sides with a transparent blue tinted polyester support called the base Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 48
Manifest Image � Visible image you see when the film is processed � What you see as your final radiograph Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 49
Film-screen Image Characteristics � Film used as medium for acquiring, processing, and displaying the radiographic image � Film emulsion: active layer of film that contains the crystals that serve as latent imaging centers � Intensifying screens: used to convert exit radiation intensities to visible light and expose the emulsion crystals � Film is chemically processed to display the range of densities created as a result of the x-ray attenuation characteristics of anatomic structures. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 50
Primary Exposure Factors � Milliamperage (m. A) � Directly proportional to radiation quantity � Inversely related to exposure time to maintain exposure to image receptor (IR) � Exposure time (time) � Directly proportional to radiation quantity � Inversely related to m. A to maintain exposure � � to IR m. A × time (seconds) = m. As Kilovoltage (k. Vp) � Directly related to radiation quality and quantity � Inversely related to radiographic contrast Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 51
Beam Attenuation � As the primary beam passes through the patient it will loose some of its’ original energy. � This reduction in the energy of the primary beam is known as attenuation. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 52
Image Receptor Exposure � � � To increase exposure to image receptor, increase m. A, exposure time, or k. Vp. To decrease exposure to image receptor, decrease m. A, exposure time, or k. Vp. To maintain exposure to image receptor � Increase m. A and proportionally decrease time � Increase time and proportionally decrease m. A � Increase k. Vp 15% and decrease m. As by half � Decrease k. Vp 15% and increase m. As by two times Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 53
Changing Kilovoltage � Kilovoltage affects � X-ray beam quality and quantity beam penetration and absorption in anatomic tissues Increasing k. Vp increases penetration and decreases absorption. Decreasing k. Vp decreases penetration and increases absorption. � Subject contrast Increasing k. Vp decreases subject contrast. Decreasing k. Vp increases subject contrast. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 54
k. Vp and Wavelength � KVP increases, wavelength gets shorter; penetrating ability increases. � KVP increases, wavelength decreases, indirect relationship � KVP increases, penetration increases, direct relationship Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 55
k. Vp and Wavelength � shorter the wavelength, stronger the penetration, higher the k. Vp � Higher the k. Vp, shorter the wavelength � Lower the k. Vp, longer the wavelength Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 56
Primary Factors: Film-screen � � Kilovoltage and m. As have a direct effect on radiographic density for film-screen imaging. Repeating a radiograph for a density error requires a change in m. As by a factor of 2 or a change in k. Vp by 15%. For insufficient density multiple the m. As by 2 or increase k. Vp by 15%. � For excessive density divide the m. As by 2 or decrease k. Vp by 15%. � The best factor to change for density errors is m. As, because k. Vp also affects radiographic contrast. � Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 57
OID � Distance between the anatomic part and image receptor will affect � Radiation intensity reaching the image receptor � Amount of scatter radiation reaching the image receptor � Magnification � Recorded detail/spatial resolution Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 58
OID (cont. ) � � � An air gap will decrease the intensity of radiation and scatter reaching the image receptor. Increasing the OID will decrease the exposure to the image receptor, increase contrast and magnification, and decrease recorded detail/spatial resolution. Decreasing the OID will increase the exposure to the image receptor, decrease contrast and magnification, and increase recorded detail/spatial resolution. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 59
OID (cont. ) Distance created between the object and image receptor will reduce the amount of scatter radiation reaching the image receptor. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 60
Magnification Factor (MF) = SID. SOD = SID – OID Object size = image size MF Source-to-object distance is the distance between the source of the x-ray and the object radiographed. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 61
Shape Distortion Any misalignment of the CR among these three factors—tube, part, or image receptor—will alter the shape of the part recorded on the image receptor. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 62
Grids � � Limiting the amount of scatter radiation that reaches the image receptor improves the quality of the radiograph. The effect of less scatter or unwanted exposure on the image is to increase the radiographic contrast. Much of the scatter radiation toward the image receptor will be absorbed when a grid is used. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 63
Grids (cont. ) � Grids also absorb some of the transmitted radiation exiting the patient and therefore reduce the amount of radiation reaching the image receptor. Grid conversion formula m. As 1 = grid ratio 1 m. As 2 grid ratio 2 Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 64
Beam Restriction � A larger field size (decreasing collimation) increases the amount of tissue irradiated, causing more scatter radiation to be produced and increasing the amount of radiation reaching the image receptor. The increased amount of scatter reaching the image receptor results in less radiographic contrast. � A smaller field size (increasing collimation) reduces the amount of tissue irradiated and reduces both the amount of scatter radiation produced and the amount of radiation reaching the image receptor. The decreased amount of scatter radiation reaching the image receptor results in higher radiographic contrast, but it requires an increase in m. As. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 65
Generator Output Generators with more efficient output, such as three-phase units or high frequency, require lower exposure technique settings to produce an image comparable to those of single-phase units. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 66
Patient Factors � Body habitus � Hypersthenic, � sthenic, hyposthenic, asthenic Part thickness affects � Beam attenuation � Exposure reaching image receptor � Scatter production and image contrast � Pediatric patients � Small size may require a reduction in exposure � Quicker exposure times may be necessary Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 67
Body Habitus � � Hypersthenic: The hypersthenic body is of massive build with a broad and deep thorax. The diaphragm is high and the stomach and gallbladder also occupy high positions. An extreme body type, the hypersthenic classification accounts for only about 5% of all people (large- stocky build). Sthenic: Means active or strong. The sthenic body is the one we usually associate with the athletic type. The body is rather heavy with large bones. The sthenic body type is the predominant type, with about 50% all people falling into this classification( normal or average build). Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 68
Body Habitus � � Hyposthenic: Slender and light in weight with the stomach and gallbladder situated high in the abdomen. About 35 %of all people fall into this classification( slender, taller build). Asthenic: Extremely slender, light build, with a narrow, shallow thorax, and the gallbladder and stomach situated low in the abdomen. An extreme type, the asthenic classification accounts for only about 10% of all people. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 69
Special Considerations � � � Projections and positions Casts and splints Pathology Soft tissue imaging Contrast media Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 70
The 5 X-ray densities � � Low density material such as air is represented as black on the final radiograph. Very dense material such as metal or contrast material is represented as white. Bodily tissues are varying degrees of grey, depending on density, and thickness. Air –fat-soft tissue-bone-metal Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 71
Positive Contrast Agents � Iodine or barium � Because of their high atomic number(ability to attenuate the beam) not there density, viscosity, or weight Iodine is 53 Barium 56 Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 72
Rules to Remember � � � Changes in the average thickness of your patient still exist, and the changes in part thickness affects the x-ray absorption of photons in an exponential way. For every 4 centimeter change in patient thickness, change the m. As by a factor of 2. Scatter radiation exists in every radiograph, it increases as patient thickness increases Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 73
Diseases which affect Radiographs � Degenerative disease � This disease breaks bone down; you need less kvp to penetrate it Arthritis, emphysema � Additive disease � With this disease, you may need more kvp to penetrate it. pneumonia, pleural effusion- fluid retention Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 74
exposure latitude � � With higher kvp’s you have greater exposure latitude. With larger body parts there is greater exposure latitude. thicker the body part, the greater the kvp As kvp decreases, the exposure latitude decreases making it narrow latitude. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 75
Scatter Radiation � Scatter radiation is detrimental to radiographic quality, because it adds unwanted exposure (fog) to the image without adding any patient information. � Radiographic contrast for both film-screen and digital images will be decreased. � Increased scatter radiation either produced within the patient or higher energy scatter exiting the patient will affect the exposure to the patient and anyone within close proximity. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 76
Scatter Production � Increasing the volume of tissue irradiated results in increased scatter production. � Patient thickness Increased thickness will increase the volume of tissue. � X-ray beam field size Increased field size will increase the volume of tissue. � Higher k. Vp increases the energy of scatter radiation exiting the patient. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 77
Scatter Control � Beam restriction � Beam-restricting devices decrease the x-ray beam field size and the amount of tissue irradiated, thereby reducing the amount of scatter radiation produced. � Grids � Radiographic grids are used to improve radiographic image quality by absorbing scatter radiation that exits the patient, reducing the amount of scatter reaching the image receptor. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 78
Beam Restriction � � Limits patient exposure Reduces the amount of scatter radiation produced within the patient. � � A beam-restricting device changes the shape and size of the primary beam. Collimation � Increasing collimation means decreasing field size, and decreasing collimation means increasing field size. Less scatter radiation is produced within the patient, and less scatter radiation reaches the image receptor. To maintain exposure to the image receptor, m. As must be increased. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 79
Types of Beam Restrictors � Aperture diaphragm �A flat piece of lead (diaphragm) that has a hole (aperture) in it and is placed directly below the x-ray tube window � Cones and cylinders � An aperture diaphragm that has an extended flange attached that varies in length and shape � Collimator � Located immediately below the tube window, has two or three sets of lead shutters that limit the x-ray beam Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 80
Radiographic Grids � � A device that has very thin lead strips with radiolucent interspaces, intended to absorb scatter radiation emitted from the patient Construction � Radiolucent interspace � Grid frequency � Grid ratio material Grid ratio = h/D Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 81
Grid Pattern Linear grid pattern Crossed/cross-hatched grid pattern Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 82
Grid Focus Comparison of transmitted photons passing through A, a parallel grid and B, a focused grid Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 83
Grid Focus (cont. ) Imaginary lines drawn above a linear focused grid from each lead strip meet to form a convergent point. The points form a convergent line along the length of the grid. The convergent line or point of a focused grid falls within a focal range. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 84
Reciprocating Grids � � Stationary grids produce visible grid lines on the radiography. Slightly moving the grid during the x-ray exposure will blur the grid lines, which will therefore be less visible. � Reciprocating grids are a part of the Potter-Bucky diaphragm. � Grid motion is controlled electronically. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 85
Grid Conversion Grid conversion factor (GCF) = m. As with grid. m. As without grid m. As 1 = GCF 1 m. As 2 GCF 2 Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 86
Grid Cutoff � A decrease in the number of transmitted photons that reach the image receptor because of some misalignment of the grid � Upside-down focused � Off-level grid � Off-center grid � Off-focus grid Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 87
Grid Selection � � � Used for anatomic parts 10 cm (4") or larger Examinations requiring higher than 60 -70 k. Vp Higher ratio grids will � Increase scatter absorption patient exposure potential for grid cutoff Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 88
Film-screen Image Receptors � Radiographic film serves as the medium for image acquisition, processing, and display. � Double emulsion screen film is placed between two intensifying screens, which will allow patient exposure to decrease. � Sensitivity specks within the film's emulsion serve as the focal point for the development of the latent image centers. These latent image centers appear as radiographic density on the manifest image after processing. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 89
Film Characteristics � Film speed: the degree to which the emulsion is sensitive to x-rays or light � The greater the film speed, the more sensitive it is. Increased film speed will require less exposure to produce a given density. � Film contrast: the ability of radiographic film to provide a level of contrast (density differences) � � � Film can be manufactured to display low, medium, or high contrast Exposure latitude: the range of exposure needed to produce diagnostic densities Films manufactured to display high contrast have a narrow exposure latitude compared to low-contrast films having a wider exposure latitude. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 90
Film-screen Imaging � Radiographic film must be sensitive to the light emission of the intensifying screen. � Spectral matching: correctly matching the color sensitivity of the film to the color emission of the intensifying screen � Spectral sensitivity: the color of light to which a particular film is most sensitive � Spectral emission: the color of light produced by a particular intensifying screen Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 91
Intensifying Screens � A device found in radiographic cassettes that contains phosphors to convert x-ray energy into visible light, which exposes the film � Phosphor layer: active layer that absorbs the transmitted x-rays and converts them to visible light Luminescence: the emission of light from the screen when stimulated by radiation Fluorescence: the ability of phosphors to emit visible light only while exposed to x-rays � Purpose is to intensify the action of the x-rays and permit lower patient radiation exposure Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 92
Intensifying Screen Speed � � Intensifying screens can be manufactured at different speeds (their capability to intensify the action of the x-rays). Faster speed screens emit more light for the same x-ray intensity. � Patient exposures will decrease. � Recorded detail decreases. Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 93
Intensifying Screen Speed (cont. ) � Factors � Absorption efficiency � Conversion efficiency � Thickness of phosphor layer � Size of phosphor crystal � Presence or absence of a reflecting layer, an absorbing layer, or dye in the phosphor layer Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 94
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 95
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 96
FILMSCREEN Image Quality Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 97
Variables affecting quality � � � Electrical Geometrical Patient status IR system Processing variable Viewing conditions Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 98
3 cardinal rules � � � Time Distance shielding Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 99
Image Instensification Tube Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 100
Conventional Fluoroscopy � � Allows imaging of the movement of internal structures Uses a continuous beam of x-rays to create images of moving internal structures � Uses a low m. A (0. 5 to � Deadman type switch � 5 -minute timer � 5) Fluoroscopic images viewed on a monitor Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 101
Fluoroscopy/tomography � � Please review Power. Points from this semester. Any questions email me Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc. 102
- Slides: 102