Digital_Radiography 2.ppt

DIGITAL RADIOGRAPHY 2 PROF. W. K. ANTWI  filmless’ radiology departments Diagnostic radiographers have traded their film and chemistry for a computer mouse and monitor advance for Rad Sci Prof, 8/9/99  What Is Digital Imaging? Digita...

DIGITAL RADIOGRAPHY 2 PROF. W. K. ANTWI  filmless’ radiology departments Diagnostic radiographers have traded their film and chemistry for a computer mouse and monitor advance for Rad Sci Prof, 8/9/99  What Is Digital Imaging? Digital imaging is the acquisition of images to a computer rather than directly to film. 3  New Technology Has impacted practicing radiologic technologist educators Administrators students in the radiologic sciences. Many local hospitals and medical centers have this equipment now  Computed Radiography Fundamentals of Computerized Radiography  CR SYSTEM COMPONENTS CASSETTES (phosphor plates) ID STATION IMAGE PREVIEW (QC) STATION DIGITIZER VIEWING STATION  COMPUTED RADIOGRAPHY Medical Imaging is changing “FILMLESS” Radiology is the future And the Future is here! El Camino College First educational institution in California or across the country to offer this new technology on a college  History of CR INDUSTRY Theory of “filmless radiography” first introduced in 1970 1981 Fugi introduced special cassettes with PSP plates (replaces film) Technology could not support system First clinical use in Japan - 1983  Predictions 1980 – Bell Labs believed that Unix would be the worlds dominant operating system 1982 – Bill Gates thought 640K of main memory would suffice for workplace operating systems ( This presentation is 80,000 kb) 1984 – IBM predicted that personal computers would not amount to anything  History of CR By 1998 – over 5000 CR systems in use nationwide 1998 – Local area hospitals begin to incorporate CR systems in their departments (Riverside Co. Hosp builds new hospital in Moreno Valley) – completely CR system – 1st generation equipment  TERMINOLOGY F/S - Film/Screen (currently used method) CR - Computed Radiography DR - Digital Radiography DDR - Direct to Digital Radiography  IMAGE CREATION SAME RADIOGRAPHY EQUIPMENT USED THE DIFFERENCE IS HOW IT IS CAPTURED STORED VIEWED And POST -PROCESSED  CONVENTIAL vs DIGITAL IMAGING Currently, most x-ray imaging systems produce an analog image (radiographs, & fluoroscopy). Using x-ray tube – films in cassettes  CONVENTIAL vs DIGITAL IMAGING Digital radiography systems require that the electronic signal be converted to a digital signal – Using x-ray tube – cassettes with phosphor plate OR DR systems - transistors  COMPUTED RADIOGRAPHY & DIRECT RADIOGRAPHY & FILM SCREEN IMAGE CAPTURE FS - Film inside of cassette CR - PHOTOSTIMULABLE PHOSPHOR PLATE DR(DDR) - TFT (THIN FILM TRANSISTOR) Cassette w/ film CR w psp plate Directed Digital Radiography (DDR) Directed digital radiography, a term used to describe total electronic imaging capturing. Eliminates the need for an image plate altogether. Amorphous Selenium detector technology for DR Direct Radiography  IMAGE CAPTURE CR – PSP – photostimulable phosphor plate – REPLACES FILM IN THE CASSETTE DR – NO CASSETTE – PHOTONS – CAPTURED DIRECTLY – ONTO A TRANSISTOR – SENT DIRECTLY TO A MONITOR  CR vs FS FILM CR Film in cassette PSP in cassette loaded in a darkroom Digital image Processed in a Scanned & read- CR processor reader FILM COMPUTER Hard copy image – Image stored on stores the image computer Viewed on a Monitor Viewboxes – view the Hard copy (film) can images be made with laser printer  CASSETTES with Intensifying Screens The CASSETTE holds the film in a light tight container It consist of front and back intensifying screens  CR BASICS Eliminates the need for film as a recording, storage & viewing medium. PSP Plate – receiver Archive Manager – storage Monitor - Viewing  General Overview CR PSP cassette exposed by conventional X-ray equipment. Latent image generated as a matrix of trapped electrons in the plate.  CR – PSP plate photostimulable phosphor (PSP) plate Captures photons Stored in traps on plate (latent image) PLATE scanned in CR READER  CR Phosphor Plates ABSORPTION EMISSION LASER STIMULATION ELECTRON ELECTRON TRAP TRAP X-RAY LIGHT  CR – PSP plate Stimulated by a RED LIGHT Energy is RELEASED in a form of BLUE light LIGHT captured by PMT – changed to a digiial signal  How CR works Released light is captured by a PMT (photo multiplier tube) This light is sent as a digital signal to the computer The intensity (brightness) of the light – correlates to the density on the image  Densities of the IMAGE The light is proportional to amount of light received digital values are then equivalent (not exactly the same) to a value of optical density (OD) from a film, at that location of the image  ERASING PLATE After image is recorded Plate is erased with high intensity white light and re-used  CR VS DR – CR -Indirect capture where the image is first captured on plate and stored = then converted to digital signal – DDR -Direct capture where the image is acquired immediately as a matrix of pixels – sent to a monitor  DIRECT RADIOGRAPHY uses a transistor receiver (like bucky) that captures and converts x-ray energy directly into digital signal seen immediately on monitor then sent to PACS/ printer/ other workstations FOR VIEWING  CR vs DR CR DR imaging plate transistor receiver (like bucky) processed in a Digital Reader directly into digital signal Signal sent to computer Viewed on a monitor seen immediately on monitor –  ADVANTAGE OF CR/DR Can optimize image quality by manipulating digital data to improve visualization of anatomy and pathology AFTER EXPOSURE TO PATIENT  ADVANTAGE OF CR/DR CHANGES MADE TO IMAGE AFTER THE EXPOSURE CAN ELIMINATE THE NEED TO REPEAT THE EXPOSURE  ADVANTAGE OF CR/DR vs FS Rapid storage retrieval of images NO LOST FILMS! PAC (storage management) Teleradiology - long distance transmission of image information Economic advantage - at least in the long run?  CR/DR VS FILM/SCREEN FILMS can not be modified once processed If copied – lose quality DR/CR – print from file – no loss of quality  “no fault” TECHNIQUES F/S: RT must choose technical factors (mAs & kvp) to optimally visualize anatomic detail CR: the selection of processing algorithms and anatomical regions controls how the acquired latent image is presented for display HOW THE IMAGE LOOKS CAN BE ALTERED BY THE COMPUTER – EVEN WHEN “BAD” TECHNIQUES ARE SET  DR Initial expense high very low dose to pt – image quality of 100s using a 400s technique Therfore ¼ the dose needed to make the image  Storage /Archiving FILM/SCREEN CR & DR films: bulky 8000 images stored deteriorates over time on CD-R requires large storage Jukebox CD storage & expense no deterioration of environmental images concerns easy access  Transmission of Images PACS - Picture Archiving & Communications System DICOM - Digital Images & Communication in Medicine TELERADIOGRAPHY -Remote Transmission of Images  Benefits of Computer (web)-based Viewing Systems Hardcopy studies are no longer misplaced or lost- eliminates films Multiple physicians may access same patient films Patients do not have to wait in Radiology for films once study is completed  “Film-less” components CR or DR CD-ROM or similar output Email capability Digitizing capability or service  Histogram Analysis A histogram is a plot of gray scale value vs. the frequency of occurrence (# pixels) of the gray value in the image  HISTOGRAM – a bar graph depicting the density distribution (in numerical values) of the imaging plate ALGORITHM – a set of mathematical values used to solve a problem or find an average  Histogram Low attenuation High attenuation (e.g., lungs) (e.g., mediastinum) 12,000 10,000 8,000 Frequency 6,000 4,000 2,000 0 0 200 400 600 800 1,000 Digital number Adapted from AAPM TG10  Statistical plots of the frequency of occurrence of each pixel's value  Basics of Digital Images digital images are a (matrix) of pixel (picture element) values  The algorithm attempts to distinguish among the parts of the histogram which represent the range of densities from bone to soft tissue  Histograms set for specific exams (body parts) should produce digital images that are consistant (regardless of kVp or mAs used Correct Algorithm (body part) must be selected prior to processing imaging plate  Methods to Digitize an Image 1. Film Digitizer - Teleradiography system (PACS, DICOM) 2. Video Camera (vidicon or plumbicon) 3. Computed Radiography 4. Direct Radiography FILM DIGITIZER  Analog vs Digital Analog - one value blends into another 100 (like a thermometer) 80 60 East Digital - distinct 40 West separation 20 North 98.6 0 exact 1st 3rd Qtr Qtr  ANALOG TO DIGITAL IMAGE Conversion of conventional analog films to digital format for PACs and teleradiology applications with scanning laser digitizers  CONTRAST & DENSITY Most digital systems are capable of 1024 shades of gray - but the human eye can see only about 30 shades of gray The Optical Density and Contrast can be adjusted after the exposure by the Radiographer. This is POST - PROCESSING High displayed contrast – narrow window width Low displayed contrast (stretched) – wide window width  Basics of Digital Images Pixel values can be any bit depth (values from 0 to 1023) Image contrast can be manipulated to stretched or contracted to alter the displayed contrast. Typically use “window width” and “window level” to alter displayed contrast  Then the COMPUTER corrects any exposure errors Therefore almost ANY technique can be used on the patient – The computer will fix it  DOSE IMPLICATIONS MORE EXPSOURE TO PATIENT TECHNIQUES ESTABLISHED HIGHER KVP = LESS MAS LESS PATIENT DOSE 80 kvp 200mas 10 mas 80 kvp Note Quantum Mottle  Dose Implications Images nearly always look better at higher exposures. Huge dynamic range means nearly impossible to overexpose. POST PROCESSING TECHNIQUE CONISDERATIONS KVP Dependant Now COMPUTER controls CONTRAST Higher kVp to stimulate electron traps standard image edge sharpening  DEVELOPER FIXER WASH DRY WATER - SOLVENT PROCESSOR PROBLEM – FIXER scratch Crimping /cresent mark REPEAT IMAGES  EMERGING PROBLEMS “BETTER” –NOT NECESSARILY FASTER “LEARNING CURVE” FOR TECHNOLOGIST & PHYSICIANS STUDENT APPLICATIONS & “ISSUES” “PITFALLS OF CR”  POSITIONING & PROPER COLLIMATION ARE CRITICAL TO GOOD IMAGING OUTCOMES Just like Phototiming, it can magnify your mistakes  COLLIMATION CRITICAL AS THE COMPUTER READS THE DENSITY VALUE OF EACH PIXEL – IT IS AVERAGED INTO THE TOTAL CLOSE COLLIMATION = BETTER CONTRAST BAD COLLIMATION = MORE GRAYS AND LESS DETAIL Digital imaging is not the end all, cure all for imaging problems. It is still technologist dependent.  To Produce Quality Images For Conventional Projection or CR Radiography: The same rules, theories, and laws still apply and can not be overlooked FFD/OFD (SID/SOD) Inverse Square Law Beam Alignment Tube-Part-Film Alignment Collimation Grids Exposure Factors: KVP, MaS Patient Positioning  towel that was used NEW IMAGE to help in positioning a child CR is MORE sensitive to ARTIFACTS CR image – NEW IMAGE Line caused from dirt collected in a CR Reader  Double exposure Child  ? Hands over upper abdomen High resolution with digital imaging