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RAD 220 QUALITY ASSURANCE FOR RADIOGRAPHERS DIGITAL IMAGING SYSTEMS DIAGNOSTIC IMAGING: THREE MAJOR COMPONENTS • ACQUISITION (CAPTURE) • PROCESSING • DISPLAY FILM-SCREEN IMAGING Image capture, processing and display are handled by the same recording medium. 1 DIGITAL IMAGING Image capture, processing and display are handled separately. DIGITAL IMAGING: DATA CONVERSION • DIGITAL CAMERA • SCANNING DIGITIZER (LASER) • SCANNING DIGITIZER (CCD) COMPUTED RADIOGRAPHY: IMAGE CAPTURE • BaFBr:Eu (Barium Flurobromide) • BaFI:Eu (Barium Fluoroiodide) • CsBr:Eu (Cesium Bromide) 2 COMPUTED RADIOGRAPHY: IMAGE PROCESSING & DISPLAY • • • • • • • IRD (IMAGE READING DEVICE) LASER SCANNING LIGHT DETECTION ANALOG-TO-DIGITAL CONVERSION PROCESSING DIGITAL TO ANALOG CONVERSION IMAGE DISPLAY HISTOGRAM COMPUTED RADIOGRAPHY: ADVANTAGES OVER FILM-SCREEN • BETTER CONTRAST RESOLUTION • GREATER EXPOSURE LATITUDE • FEWER TECHNIQUE-RELATED REPEATS 3 CR VERSUS FILM: EXPOSURE LATITUDE COMPUTED RADIOGRAPHY: DISADVANTAGES OVER FILM-SCREEN • LOWER SPATIAL RESOLUTION • MORE SENSITIVE TO SCATTER RADIATION • POTENTIAL FOR CARELESS TECHNIQUE SELECTION & HIGHER PATIENT DOSE MONITORING RADIATION EXPOSURE (FUJI) FUJI S-VALUES: THE HIGHER THE S NUMBER, THE LOWER THE EXPOSURE RECEIVED BY THE IR. 0.1 mR: S VALUE = 2000 1.0 mR: S VALUE = 200 10.0 mR: S VALUE = 20 THE NORMAL RANGE IS 150 TO 250 4 MONITORING RADIATION EXPOSURE (KODAK) KODAK INDEX NUMBERS: THE HIGHER THE NUMBER, THE HIGHER THE EXPOSURE RECEIVED BY THE IR. 0.1 mR: INDEX = 1000 1.0 mR: INDEX = 2000 10.0 mR: INDEX = 3000 NORMAL RANGE IS 1800 TO 2200 MONITORING RADIATION EXPOSURE (AGFA) AGFA logM: Logarithmic expression of median exposure. An increase of 0.3 represents a doubling of exposure. The measured exposure is compared to a baseline established by the imaging department. DIGITAL RADIOGRAPHY Use of solid-state semiconductor arrays (called the active matrix) to capture and convert x-ray signals to electrical signals. The image receptor is incorporated into table or upright grid assembly. 5 DIGITAL RADIOGRAPHY • INDIRECT CONVERSION • DIRECT CONVERSION INDIRECT CONVERSION DR • FLUORESCENT CRYSTALS (CsI) • AMORPHOUS SILICON (a-Si) DETECTORS • THIN-FILM TRANSISTOR STORAGE ASSEMBLY • LOWER SPATIAL RESOLUTION (VS. DIRECT CONVERSION DR) • HIGHER QUANTUM DETECTIVE SENSITIVITY DIRECT CONVERSION DR • AMORPHOUS SELENIUM (a-Se) PHOTOCONDUCTIVE DETECTORS • THIN-FILM TRANSISTOR (TFT) STORAGE ASSEMBLY • BETTER SPATIAL RESOLUTION • LOWER QUANTUM DETECTIVE SENSITIVITY 6 WHICH IS BETTER, CR or DR? An objective comparison of image quality is based on a concept called DETECTIVE QUANTUM EFFICIENCY (DQE). DETECTIVE QUANTUM EFFICIENCY A measure of detector transfer efficiency and is defined as: 2 SNRout SNRin2 DETECTIVE QUANTUM EFFICIENCY DQE measures overall image quality as a function of object detail. This is similar to the concept of MODULATION TRANSFER FUNCTION. The higher the DQE, the better the system is at displaying small low-contrast objects. 7 BASED ON DQE… • DIRECT-COVERSION DR IS GENERALLY BETTER THAN INDIRECT CONVERSION DR • INDIRECT CONVERSION DR IS BETTER THAN CR • CR IS BETTER THAN FILM-SCREEN RADIOGRAPHY WHICH IS MORE PRACTICAL, CR or DR? Every imaging department must decide on the proper mix of equipment. CR seems offers more flexibility in terms of use (table vs. bucky) and portability. DR systems are incorporated into a table or upright grid assembly and tend not be very portable. WHAT ABOUT QUALITY CONTROL? • CR AND DR SYSTEMS LACK UNIFORM STANDARDS • RELIANCE ON MANUFACTURERSPECIFIC INSTRUCTIONS ON TESTING AND MAINTENANCE • STILL, ALL CR AND DR EQUIPMENT SHARE COMMON ISSUES 8 QUALITY CONTROL OF DIGITAL IMAGING EQUIPMENT • • • • • WHO IS RESPONSIBLE WHAT TO TEST HOW OFTEN TO TEST PREVENTIVE MAINTENANCE SPECIALIZED TESTING EQUIPMENT QUALITY CONTROL OF DIGITAL IMAGING EQUIPMENT • IMAGING PLATES • IMAGE READING DEVICE • IMAGE DISPLAY SCREENS (CRT VS. LED) • COMPUTER SYSTEM TESTS TERMS TO KNOW • • • • • CONTRAST RESOLUTION SPATIAL RESOLUTION TEMPORAL RESOLUTION MODULATION TRANSFER FUNCTION DETECTIVE QUANTUM EFFICIENCY 9
