Fluoroscopy & Tomography. Rhodes

Transcription

1 Fluoroscopy & Tomography Rhodes

2 Historical Development Dynamic examination Active Diagnosis Domain of radiologist Fluoroscope Invented by Edison in

3 Fluoroscopic Imaging Chain Components Specialized x-ray tube Image receptor Fluoroscopic screen Mirrors Image intensification Video camera (or CCD) and monitor 3

4 Historical First Generation Fluoroscopes Copper activated zinc cadmium sulfide Emitted green light green screen Sheet of lead glass covered screen 4

5 Historical Dark adaptation red goggles minutes prior to exam Screen very dim 5

6 RSNA Dr. W. Edward Chamberlain Piece of White Paper Light reflected from paper 30,000 x brighter than fluoro screen First to measure light intensity from screen 6

7 Vision Retina Rods Peripheral Night Scotopic Vision Cones Central Daylight Photopic Vision 7

8 Shoe Fitting Fluoroscopy Unit 8

9 Fluoroscopic Uses Functional studies GI tract studies Angiograms Myelograms, Arthrograms Roentgen Museum Fluoroscopy Equipment 9

10 NOT A FLUORO USE Fluoroscopic Positioning Previewing Radiographers are trained in positioning Unnecessary radiation exposure to patient is unethical Fluoroscopic equipment should not be used to preview patient s position 10

11 Types of Equipment C-arm Under table/over table units Siemens R & F room that stabilized the tube and screen together- Allowed some collimation- This unit was placed in a gynecological hospital 11

12 Types of Equipment Raise and lower image receptor for accuracy Can vary beam geometry and image resolution Full beam intercept 12

13 Image Intensification Introduced in 1948 Higher visual acuity Uses photopic vision (cones) Utilized II tube 13

14 Image Intensification Tube Input screen and photocathode Electrostatic lenses Magnification tubes Components 14

15 Image Intensification Tube Anode and output screen Total brightness gain Minification gain x flux gain Components 15

16 Input Screen and Photocathode Input screen mm layer of sodium activated CsI Converts intercepted x-ray beam to light Photocathode Emits electrons when struck by light emitted by input screen 16

17 Accelerate and focus electron pattern across tube to anode Primary source of brightness gain Electrostatic Lenses 17

18 Magnification Tubes Greater voltage to electrostatic lenses Increases acceleration of electrons Shifts focal point away from anode Dual focus 23/15 = measured in cm or ( 9 input/6 mag) Multifield 25/17/12 23/15/10 Magnification mode result in Better spatial resolution Better contrast resolution Higher patient dose 18

19 Magnification Tubes 19

20 Magnification Input screen diameter (25/17/12) Diameter used during exam Formula for calculating magnification Magnification = input screen diameter 25/12 =2.1 times as large diameter of input screen used during magnification Increased patient dose calculations Dose increase = Original II area used /12 2 =4.4 times the dose mag area of input phosphor used 2 20

21 Anode and Output Screen Anode Positively charged 25 kvp Hole in center allows electrons to pass through to output screen Output screen Glass fluorescent screen Zinc-cadmium sulfide Emits light when struck by electrons 21

22 Total Brightness Gain Brightness Gain = Minification gain x Flux gain Minification gain = Input screen diameter2 Output screen diameter2 Flux Gain is the measurement of conversion efficiency of output screen 1 electron strikes output screen 50 light photons are emitted Flux gain = 50 22

23 Flux Gain 23

24 Conversion Factor Conversion Factor = Output phosphor illumination (cd/m 2 ) Input exposure rate (mr/s) 24

25 Fluoroscopic Generators Same as those used for static radiography Maximum generators at 150 kw Designed to have high heating capabilities 25

26 Image Intensifier Quality 26

27 Image Intensifier - Brightness Automatic Brightness Control (ABC) Automatic Dose Control (ADC) Automatic Brightness Stabilization (ABS) Automatic Gain Control 27

28 Fluoroscopic X-Ray Tubes ma range: ma 15 minimum SOD in fixed fluoroscopic equipment 12 minimum SOD in mobile fluoroscopic equipment Foot switch deadman Hand switch on fluoro tower 28

29 Image Intensification-Contrast Controlled by increasing the amplitude of the video signal Affected by scattered radiation and light scatter on input /output screens. Measured with ratio of light at output phosphor without blocker to light at output phosphor with blocker Contrast ratios range from 10:1 20:1or higher 29

30 Lag Persistence of luminescence after x-ray stimulation has been terminated. Lag times are about 1 ms. 30

31 Distortion Size Distortion - OID gives magnification Shape Distortion Geometric problems in the tube Most visible on the edges Pincushion is the non-linear magnification across the image 31

32 Vignetting Fall-off in brightness at the periphery of an image Causes the center of image to have: Better Resolution Increased Brightness Less Distortion 32

33 Resolution Determined by the equipment in the imaging chain such as the II tube Monitors Recording devices Magnification Modes 33

34 Spatial Resolution FOV inches 1023 LP/mm 525 LP/mm Bushberg 34

35 Quantum Mottle Blotchy or grainy appearance due to insufficient radiation Related to the amount of time necessary for the eye to acquire enough light photons to create an image.2 sec Controlled by the ma Many contributing factors 35

36 Detected Quantum Efficiency -DQE Quality of the output signal to the statistical quality of the incident x-rays DQE of 100% = perfect Additional noise lowers the number DQEs are 50 80% High DQEs mean that there is less noise at the same dose rate 36

37 Modulation Transfer Function - MTF Concept formulated to provide an objective measurement of the combined effects of sharpness and resolution. Measures the amount of information that was transferred from patient to Image receptor MTF = information recorded information available Cannot be greater than 1 Christensen 37

38 Flat Panel Image Receptor - FPIR No pincushion distortion No age degrading Spatial and Contrast resolution is uniform Square or rectangle versus circular High DQE at all dose levels Unaffected by external Magnetic fields 38

39 Viewing Systems 39

40 Previously used Direct viewing Discontinued Fiber optics Single location Beam Splitting Mirror Multiple locations 40

41 Video Viewing System Closed circuit television Video camera coupled to output screen and monitor Video cameras Vidicon or Plumbicon tube Being replaced in digital fluoroscopy with CCD 41

42 Video Camera Tubes Plumbicon and Vidicon tubes similar 42

43 Video Camera Tube Components Cathode Control grid Electromagnetic focusing coils Electrostatic deflecting coils 43

44 Video Camera Tube Components Anode Face plate Signal plate Positively charged thin film of graphite Target Changes light pattern to electronic signal sent to video system Thin insulating mica Matrix of globules of photoconductive material 44

45 Video Camera Cathode Heating assembly Electron gun thermionic emission Control grid Shapes electron beam 45

46 Raster Pattern Electron beam is accelerated across TV camera tube to anode Slowed at anode by wire mesh in front of target 46

47 Conventional versus Digital Imaging Chain 47

48 Analog and Digital Computers Analog Continuous data Digital Finite data On or off Ex: analog vs. digital watch 48

49 Analog to Digital Conversion Medical imaging uses digital computers Analog info is digitized Analog to Digital Conversion System locates raw data Samples Quantitize Determine average value 49

50 Sampling Frequency Hamamatsu Learning Center: Introduction to Digital Imaging in Microscopy 50

51 Charged Coupling Device - CCD Replacing Vidicon camera tubes 51

52 Video Camera Charged Coupled Devices (CCD) Semiconducting crystalline silicone device Emits electrons in proportion to amount of light striking photoelectric cathode Fast discharge eliminates lag, flat surface eliminates pin cushion distortion Operate at lower voltages than video tubes More durable, faster and long lasting than video tubes Molecular Expressions Microscopy Primer: Digital Imaging in Optical Microscopy - Concepts in Digital Imaging - Proximity-Focused Image Intensifiers 52

53 Charge-Coupled Device Layer of crystalline silicon Pixel size still an issue Reduction in Pincushion distortion artifacts High Detective quantum efficiency (DQE) Higher signal to noise ratios No image lag Linear response for contrast 53

54 CCD Linear Response to Radiation Read more details from Bushong 54

55 Video Monitor- CRT 55

56 Monitor Resolution Vertical Resolution Dependent upon # of scan lines 525, 1025, Horizontal Resolution Bandwidth, bandpass, measured in frequency How fast the line is scanned 5 20 MHz 525 scan line II 9 mode has.8 lp/mm resolution 56

57 Monitor Improvements Progressive Mode scanning Flat Panel Monitors Liquid Crystal Display LCD Light Emitting Diodes - LED 57

58 Digital Fluoroscopy Image intensifier is either digital or analog II output screen coupled to TFTs TFT photodiodes are connected to each pixel element in digital II Electronic Signal assigned a pixel value 58

59 Direct Capture Radiography - DR Directly converts incoming photons to electronic digital signal Utilizes thin film transistors (TFT) in a matrix arrangement. Reusable flat panel image receptor attached to the equipment. Two methods to Capture latent image Both limited Spatial Resolution to about 5 lp/mm 59

60 Direct Exposure Imaging Systems Indirect silicon flat panel imaging plate systems Direct selenium flat panel imaging plate systems 60

61 Direct Selenium Flat Panel Imaging Plate Systems Amorphous selenium directly converts ionization from x-rays into electronic signal Electronic signal received by thin film transistors (TFTs) and sent to computer Prior to exposure high voltage charge applied to top surface of selenium 61

62 Direct Conversion amorphous selenium flat panel imaging plate

63 Indirect Silicon Flat Panel Imaging Plate Systems Amorphous silicon combined with scintillator Scintillator or intensifying screen converts x-rays to light Amorphous silicon acts as photodiode Converts light to electronic signal TFTs send signal to computer 63

64 Indirect Silicon Flat Panel Imaging Systems

65 Thin Film Transistors (TFTs) Array or matrix of pixel detectors 65

66 Digital Image Acquisition & Processing Requires detector for collection of input Monitor for display Resolution Field of view Matrix Pixel 66

67 Image Matrix Layout of rows and columns each linked to a location. The numerical value represents a color or shade of gray. Numerical value represents tissue characteristics Pixel Voxel 67

68 Matrix Size Matrix size affects spatial resolution 68

69 Inversely related to spatial resolution Sampling frequency Expressed as pixels/mm Dependent on: Matrix Image receptor size Pixel Size

70 Dynamic Range The range of values over which the system can respond The number of shades of gray that can be represented. 70

71 # = a gray scale or a color value 71

72 Pixel Depth Determines number of density values- Gray scale bit depth Affects density and contrast of system Controlled by ADC 10 bit (2 10 = 1024) 12 bit (2 12 = 4096) 16 bit (2 16 = 65,536) 72

73 Bit Depth and Gray Levels 73

74 Image File Size Affected by: Pixel size Matrix Bit depth 8, 10, 12, etc Range bytes of storage per pixel 2 12 = 12 bit gray scale depth-4096 shades of gray 74

75 Calculate Image file size XY ( B/8) X= x-axis pixel matrix size Y = y-axis pixel matrix size B = gray scale bit depth 2500 x 2500 (12/8) = = Mb 75

76 Digital Fluoroscopy Upgrades Required Use CCD to generate electronic signal Allows for post processing and electronic storage and distribution Need Server or PACS system Resolution limited in favor of radiation exposure Generator Upgrades High Frequency Generators Pulsing beam with grid controlled tube Interrogation and extinction times of less than 1 ms 1-10 exposures/sec Tube Upgrades Handle large amounts of heat Operates on 100 or more ma 76

77 DF equipment changes cont. Video system need 1000 scan lines minimum Signal to noise ratios of 1000:1 Progressive mode scanning Analog to digital converters 77

78 Digital Image Quality Data characteristics Frequency Contrast Noise Signal to Noise Ratios Bandwidth Display qualities Window level Window width Resolution Filtering 78

79 Frequency Raw data Fourier transformed Measure of image contrast High contrast/high frequency Low contrast/low frequency 79

80 Contrast Measure of differences between data values Direct relationship Subject contrast acquired data contrast 80

81 Noise Random background information Detected but does not contribute to quality Similar in appearance to quantum mottle Static on stereo systems Snow on TV Signal to noise ratio S/N 81

82 Noise Most fluoroscopic noise Electronic sources Digital systems TV camera Commercial systems S/N 200 High resolution systems S/N

83 Noise and Image Quality Inversely related to contrast Increased contrast obscures noise Not related to density As long as there is adequate contrast Computer can compensate for lack of density 83

84 Each pixel assigned a numerical value Density and contrast controlled by varying this value Human visual range 32 shade of gray or less Digital detectors Capable of producing Display Qualities

85 Windowing Computer Brings density differences into visual range Compresses or expands image densities or gray scale

86 Window Level Changes pixel value Addition and subtraction Controls image density Direct relationship 86

87 Window Width Changes in pixel value through Multiplication and division Controls image contrast Inverse relationship Controls visibility of detail com/medical/en/ whitepapers/imag e90.gif

88 Resolution Matrix Bandwidth Progressive scanning Slow scanning 88

89 Filtering Mathematical alterations of image frequency Masking indicates what frequencies are altered Low Pass Filtering Alters or deletes all but low frequencies Smoothing Band-Pass Filtering Amplifies or deletes a specific range of frequencies High Pass Filtering Alters or deletes all but high frequencies Sharpening or edge enhancement 89

90 90

91 Grid Use Digital systems are more sensitive to scatter radiation Grids should be used more often Radiography of the chest > cm should use grid 91

92 Recording the Fluoroscopic Image Dynamic systems Cine film systems Videotape recording PACS electronic storage Static spot filming systems Cassettes 105 mm chip film Digital fluoroscopy 92

93 Dynamic Systems Cine film Videotape - VHS Magnetic tape Disc 93

94 105 mm Chip Film-Historic 12 frames per second Beam splitting mirror 94

95 Radiation Protection During Fluoroscopy The patient The radiographer and radiologist Others 95

96 Patient Protection Tabletop exposure rate Maximum 10 R/min normal mode 20 R/min in high level control modes Typically 1 3 R/min 2.1 Rad for each ma per minute at 80 kvp 96

97 Patient Protection Minimum source-toskin distance 12 (30 cm) for mobile equipment 15 (38 cm) for stationary systems Audible alarm at 5 mins. Same rules for collimation 97

98 Patient Protection Typical exposure rates Cinefluorography 7.2 R/min Cassettes 30 mr/exposure 105 mm film 10 mr/exposure 98

99 Protection of Radiographer and Radiologist Lead apron 0.25 mm Pb/eq Gloves & Equipment Highest energy scatter 90 o angle to the incident beam Same level as radiographer /radiologist s gonads 99

100 Protection of Radiographer and Radiologist Single step away from the table decreases exposure exponentially Bucky slot cover.25 mm Pb/Eq Lead Drape.25 mm Pb/Eq Radiologist as shielding 100

101 Protection of Others Radiographer s responsibility to inform others in the room to wear lead apron Do not initiate fluoroscopy until all persons have complied 101

102 Cardinal Principles Time Reduce the amount of time spent in areas of Radiation Leakage Radiation may not exceed 100 mr/hr at 1 meter distance Distance Distance Inverse Square Law Shielding

103 Fluoroscopy Greatest time thus greatest dose More use today with interventional procedures Majority of Dose in the primary Beam Table top dose for Fluoroscopy may not exceed: 2.1 Rad/min for each ma of operation at 80 kv About 10 Rad/min High level controls 20 Rad/min

104 Where to stand Radiographer/Physician should not be in the primary beam 1/1000 intensity of the primary beam in the form of scatter at 1 meter Distance Scatters most at 90% angles to the patient Iso Exposure Curves

105 Iso Exposure Curves

106 Shielding Thickness of Pb Weight in lb 50 kv 75 kv 100 kv.25 mm mm mm All values from Bushong 8 th ed. 2004

107 Radiation Protection Measures Pulsed Fluoroscopy ( PF) Grid Controlled Fluoroscopy (GCF) Preset collimation 2 sets of parallel shutters Last image hold Anatomy mapping ( 2 monitors needed) High Resolution Monitors 107

108 Occupational Monitoring Thermo luminescence Dosimetry TLD Lithium Fluoride Read with Heat Nearly Tissue Equivalent Optically Stimulated Luminescence OSL Aluminum Oxide Read with Laser Light

109 Early Radiation Injury

110 Early Radiation Injuries March 3, Reports of possible x-ray injuries to the eyes. T.A. Edison April 1896 Skin effects and Epilation noted July 1896 Reports of burns 1898 Pb Tube Housing and collimators 1904 First Death attributed to cumulative overexposure CM. Dally R/week shown to cause injury H.M. Parker

111 Dose Limits Year Recommendation Fogging of a photographic plate after 7 minutes of contact exposure It is entirely safe if an operator does not receive every thirty days a dose exceeding 1/100 of an erythema dose One Skin Erythema Dose (SED) per 90,000 working hours 1931 Limit exposure to.2 R per day Approx. Daily Dose Limit (mrem) 10,000 Rollins 200 Source Mutscheller 40 Dutch Board of Health R per day Rem/year 5(N-18) rem Accumulated 50 msv/year 10 x N msv cumulative msv/yr Advisory Comm. On X-ray and Radium Protection in the U.S. Advisory Comm. On X-ray and Radium Protection in the U.S. National Council on Radiation Protection and Measurement National Council on Radiation Protection and Measurement International Commission on Radiation Protection All data from Bushong 8 th ed. 2004

112 Dose Limits Occupational Exposure Annual is 50 msv or 5000 mrem Cumulative - Not to exceed 10 msv x age ( 1000 mrem x age) Hands& Skin 500 msv ( 50 rem) National Council on Radiation Protection and Measurement

113 Safe Medical Devices Act of 1990 (SMDA) Required hospitals to report deaths, serious illness and injuries associated with the use of medical devices. Click on the FDA web link to see their guidelines on reporting injuries

114 U.S Food and Drug Administration -Center for Devices of Radiologic Health puts out Public Health Advisory. Avoidance of Serious X-ray induced Skin Injuries to Patients During Fluoroscopically-Guided Procedures Received reports of occasional but at times severe, radiationinduced skin injuries to patients resulting from prolonged, fluoroscopically-guided, invasive procedures Follow-up to record procedures approaching a suggested 1 gray (100 Rads)

115 Reporting 1992/93 Center for Devices and Radiological Health of the FDA received a number of unverifiable reports of radiation injury to patients from the use of fluoroscopic x-ray systems. 26 reports from procedures for Cardiac, biliary stents, angioplasty, and other special procedures Summarized in a report called Radiation-Induced Skin Injuries from Fluoroscopy, Thomas B. Shope, Ph.D., Nov. 1995

116 Cases of Skin Injury From Fluoroscopy Patient Sex/Age Procedure Nature of Injury A M/40 Coronary angiography & PTC followed by 2 nd coronary angiography B F/? RF Cardiac Catheter Ablation C F/25 RF Cardiac Catheter Ablation D F/34 RF Cardiac Catheter Ablation E F/62 Balloon Dilatation of Bile Duct Skin necrosis requiring skin graft 7.5 cm x 12.5 cm second degree skin burn Skin breakdown 3 weeks post procedure Draining skin lesion on back 5 weeks post procedure Burn-like injury on back requiring skin graft F F/61 Renal Angioplasty Skin necrosis requiring skin graft Fluoroscopic Exposure Time Unknown estimated to have received 120 minutes Unknown Unknown Procedure time of 325 minutes Unknown Procedure time of 190 Minutes Unknown Unknown procedure time of 165 minutes Radiation-induced Skin Injuries from Fluoroscopy, Thomas B. Shope, Ph.D.

117 Radiation Injuries

118 Fluoroscopy Cases

119 Skin Break Down

120 Fluoroscopy cases

121 Skin Damage

122 Radiation Damage

123 Skin Graft

124 Acute Localized Radiation Effects Radiation Effect Transient Erythema Threshold to Produce Rads Amount of Fluroscopy to Produce at 5R/min hours Epilation hour Main Erythema hours Pericarditis hours Dermal Necrosis hours Data from FDA report & Latent Period 3 days to 3 weeks 3 weeks 10 days Greater than 10 weeks Greater than 10 weeks

125 FDA Radiological Health Program Plan Collect & publish national exposure data for different procedures from health care facilities Encourage medical facilities to assess & compare exposures to national data Harmonize U.S. requirements with international standards for manufactures Continued Research on dose reduction Update industry and professional groups with web pages June 10, 2005 Statement

126 Additional Studies U.S. Radiologic Technologists study 1989 follow up 1994 & ,304 Respondants 1355 cases of basal cell cancer, 270 case of squamous cell cancer Conclusion 1.42 x the risk for R.T. prior to 1960 for basal cell Chronic low level exposure does increase CA risks

127 Changing Imaging Profiles NCRP % of all x-ray exam for patients below age 45 Estimated Number of CT scans in the U.S. for 2003 was estimated 50.1 million (ASRT) Common CT (Head, spine, abdomen) 85% Cardiac Catheterization procedures in U.S. increased estimates vary with numbers greater than 1,700,000 in 1997 (Shope)

128 Skin Exposure Doses for Various Exams Examination Technique kvp/mas Entrance Skin Exposure Skull 76/ Chest 110/3 10 Cervical Spine 70/ Lumbar Spine 72/ Abdomen 74/ Pelvis 70/ Extremity 60/5 50 CT Head 125/ CT Pelvis 125/ Numerical Values From Bushong 8 th Ed. 2004

129 Skin Exposure Doses For CT Examination Entrance Skin Exposure CT heat 3 7 Rads CT Chest 2 5 Rads CT Abdomen 2 5 Rads CT Biopsy Rads Fluoro Numerical Values From Gofmann

130 Equipment Changes

131 Dose Wise Systems & IQX Intelligent R/F Exposure Control Smart Beam Less Radiation on Time More Awareness Designed for Fluoroscopy Modification of pulsed beam Grid Controlled Fluoroscopy (GCF) Eliminates the pre & post trail of the KV pulse Regulates the kv based on object density

132 DR Digital Diagnost System ALARA in Pediatric Dose Image Gently Utilize addition filters of 1 mm Al,.1 0r.2 copper Preset Collimation Ability to remove grids but still use AEC Exposure Indicators (EI) Grid controlled (pulsed) fluoro for peds reduced dose 50% In some case dose reduction of up to 75% overall dose with all features

133 Working with a C-arm

134 Summary Radiation Safety Continued Increase in Fluoroscopy imaging for interventional exams Continued growth with CT and CT partnered equipment such as PET More reporting Continual equipment safety measures to reduce dose

135 Tomography M. Rhodes

136 Tomo Greek term means to cut Pre- CT Uses motion to blur out layers above and below layer of interest Keeps focal plane visible 139

137 Tomography Terms Blurs out planes above and below the object plane Tube and IR move synchronously in opposite directions Fulcrum is the imaginary pivot point Tomo Angle determines slice thickness 140

138 Object Plane 141

139 Section Thickness 142

140 143

141 Excursion Patterns Linear Circular Oval/Elliptical Spiral Hypocycloidal 144

142 Panelipse 145

143 LEVEL OF INTEREST Centemeters/millimeters up from table Pb markers identifying each level Immobilize or mark centering location on patient Shield High Doses - Kidney doses as high as 1 Rad ESE/exposure 146

144 Multiple Images on IR Traditional Tomo units 1:1, 2:1, 3:1, 4:1, 6:1, 8:1, 9:1 Today, Linear 1:1 Limited Use due to CT 147