Digital Radiography Fall 2012 1 filmless radiology departments

Digital Radiography Fall 2012 1

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 2

What Is Digital Imaging? Digital imaging is the acquisition of images to a computer rather than 3

New Technology n Has impacted everyone: 1. Practicing radiologic technologist 2. Educators 3. Administrators 4. Students in the radiologic sciences. 4

Computed Radiography Fundamentals of Computerized Radiography 5

Radiology 1895 Radiology 2001 6

CR SYSTEM COMPONENTS 1. CASSETTES (phosphor plates) 2. ID STATION 3. IMAGE PREVIEW (QC) STATION 4. DIGITIZER 5. VIEWING STATION 7

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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 9

Predictions n n n 1980 – Bell Labs believed that Unix would be the worlds dominant operating system 1982 – Bill Gates thought 640 K 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 10

History of CR n n n By 1998 – over 5, 000 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 – 1 st generation equipment 11

TERMINOLOGY 1. F/S - Film/Screen (currently used method) 2. CR - Computed Radiography 3. DR - Digital Radiography 4. DDR - Direct to Digital Radiography 12

IMAGE CREATION n n SAME RADIOGRAPHY EQUIPMENT USED THE DIFFERENCE IS HOW IT IS 1. 2. 3. 4. CAPTURED STORED VIEWED And POST -PROCESSED 13

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Conventional vs. Digital Imaging n Conventional X-ray imaging systems Produce an analog image (radiographs, & fluoroscopy). n Using x-ray tube with films & cassettes n 15

Conventional vs. Digital Imaging n n Digital radiography systems require that the electronic signal be converted to a digital signal – Using x-ray tube – n n CR cassettes with phosphor plate (PSP) DR systems with transistors (TFT) 16

COMPUTED RADIOGRAPHY & DIRECT RADIOGRAPHY & FILM SCREEN IMAGE CAPTURE FS - Film inside of cassette CR – Photostimuable Phosphor Plate (PSP) DR(DDR) - Thin Film Transitor (TFT) 17

Cassette with film CR with PSP 18

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Directed Digital Radiography (DDR) Directed digital radiography, a term used to describe total electronic imaging capturing. Eliminates the need for an image plate altogether. 20

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Amorphous Selenium detector technology for DR Direct Radiography 22

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IMAGE CAPTURE CR 1. n n PSP – photostimulable phosphor plate Replaces film in the cassette DR – No cassette- 2. n n Photons captured directly onto TFT Sent directly to a monitor 25

CR vs. FS FILM n Film in cassette n loaded in a darkroom n Processed in a processor CR n PSP in cassette n Digital image n Scanned & read- CR reader FILM n Hard copy image – stores the image n Viewboxes – view the images COMPUTER n Image stored on computer n Viewed on a Monitor n Hard copy (film) can be made with laser 26 printer

CR BASICS • Eliminates the need for film as a recording, storage & viewing medium. • PSP Plate – receiver • Archive Manager – storage • Monitor - Viewing 27

General Overview CR PSP cassette exposed by conventional X-ray equipment. n n Latent image generated as a matrix of trapped electrons in the plate. 28

CR – PSP plate 1. Photostimulable phosphor (PSP) plate 2. Captures photons 3. Stored in traps on plate (latent image) 4. PLATE scanned in CR READER 29

CR – PSP plate 1. 2. 3. 4. Stimulated by a RED LIGHT Energy is RELEASED in a form of BLUE light LIGHT captured by photomultiplier tube (PMT) Changed to a digital signal 30

How CR works 1. 2. 3. Blue 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 31

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CR “PROCESSORS” 35

Densities of the IMAGE 1. The light is proportional to amount of light received 2. 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 36

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ERASING PLATE 1. 2. 3. After image is recorded Plate is erased with high intensity white light Cassettes are reused 39

CR VS. DR (slide 41) n CR -Indirect capture where the image is first captured on plate and stored = then converted to digital signal n DDR -Direct capture where the image is acquired immediately as a matrix of pixels – sent to a monitor 40

Digital Radiography Direct Capture Direct-to-Digital Radiography (DDR) Indirect Capture Computed Radiography (CR) 41

DIRECT RADIOGRAPHY n Uses a transistor receiver (like bucky) n n n Captures and converts x-ray energy directly into digital signal Images seen immediately on monitor Sent to PACS/ printer/ other workstations FOR VIEWING 42

CR vs DR CR n Imaging plate n n n DR n Transistor receiver (like bucky) Processed in a Digital Reader n Signal sent to computer n Directly into digital signal Seen immediately on monitor Viewed on a monitor 43

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ADVANTAGE OF CR/DR n Can optimize image quality n Can manipulate digital data n Improves visualization of anatomy and pathology n AFTER EXPOSURE TO PATIENT 45

ADVANTAGE OF CR/DR n n Changes made to image after the exposure Can eliminate the need to repeat the exposure 46

ADVANTAGE OF CR/DR vs FS 1. Rapid storage 2. Retrieval of images NO LOST FILMS! 3. PAC (storage management) 4. 5. Teleradiology - long distance transmission of image information Economic advantage - at least in the long run? 47

CR/DR VS FILM/SCREEN 1. 2. 3. FILM- these can not be modified once processed If copied – lose quality DR/CR – print from file – no loss of quality 48

“No fault” TECHNIQUES F/S: RT must choose technical factors (m. As & 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 n HOW THE IMAGE LOOKS CAN BE ALTERED BY THE COMPUTER – EVEN WHEN “BAD” TECHNIQUES ARE SET 49

DR 1. Initial expense high 2. Very low dose to pt – 3. 4. Image quality of 100 s using a 400 s technique Therefore ¼ the dose needed to make the image 50

Storage /Archiving FILM/SCREEN 1. 2. 3. 4. CR & DR Films: bulky 1. Deteriorates over time 2. Requires large storage & expense Environmental concerns 3. 4. 8000 images stored on CD-R Jukebox CD storage No deterioration of images Easy access 51

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Transmission of Images 1. 2. 3. PACS - Picture Archiving & Communications System DICOM - Digital Images & Communication in Medicine TELERADIOGRAPHY -Remote Transmission of Images 53

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Benefits of Computer (web)-based Viewing Systems 1. 2. 3. 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 55

“Film-less” components 1. 2. 3. 4. CR or DR CD-ROM or similar output Email capability Digitizing capability or service 56

PACS Digital Images Archive Database and Workflow Engine Remote Facilities Internet VPN Workstations Remote Workstations 57

Histogram Analysis 1. 2. 3. A histogram is a plot of gray scale value vs. the frequency of occurrence (# pixels) of the gray value in the image 58

n n 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 59

Adapted from AAPM TG 10 60

Statistical plots of the frequency of occurrence of each pixel's value 61

Basics of Digital Images n Digital images are a (matrix) of pixel (picture element) values 62

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n The algorithm attempts to distinguish among the parts of the histogram which represent the range of densities from bone to soft tissue 65

n n n Histograms set for specific exams (body parts) Should produce digital images that are consistent (regardless of k. Vp or m. As used) Correct Algorithm (body part) must be selected prior to processing imaging plate 66

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Methods to Digitize an Image 1. Film Digitizer - Teleradiography system (PACS, DICOM) 2. Video Camera (vidicon or plumbicon) 3. Computed Radiography 4. Direct Radiography 68

FILM DIGITIZER 69

Analog vs Digital (slide 73) 1. Analog - one value blends into another 1. 2. like a thermometer Digital - distinct separation 1. 2. 98. 6 exact 70

ANALOG TO DIGITAL IMAGE 1. 2. 3. Conversion of conventional analog films To digital format for PACs and teleradiology applications With scanning laser digitizers 71

CONTRAST & DENSITY Most digital systems are capable of 1024 shades of gray – 1. n 2. 3. 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 72

High displayed contrast – narrow window width 73

Low displayed contrast (stretched) – wide window width 74

Basics of Digital Images 1. 2. 3. 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 75

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80 KVP 5 5 100 30 15 200 500 78

n n n Then the COMPUTER corrects any exposure errors Therefore almost ANY technique can be used on the patient – The computer will fix it 79

DOSE IMPLICATIONS 1. 2. 3. 4. More exposure to the patient Techniques established Higher k. Vp = Less m. As Less patient dose 80

80 kvp 200 mas 10 mas 80 kvp Note Quantum Mottle 81

Dose Implications 1. 2. Images nearly always look better at higher exposures. Huge dynamic range means nearly impossible to overexpose. 82

POST PROCESSING 83

TECHNIQUE CONISDERATIONS 1. 2. 3. KVP Dependant Now COMPUTER controls CONTRAST Higher k. Vp to stimulate electron traps 84

standard image edge sharpening 85

REPROCESSED NO GRID HAND ALGO 86

QC – Reader (replaces Darkroom & Processor & Chemicals Diagnostic Viewer (replaces film, storage & viewboxes) 87

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REPEAT IMAGES 89

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EMERGING PROBLEMS 1. 2. Better – not necessarily faster Learning curve for technologists and physicians 3. Student applications and issues 4. Pitfalls of CR 91

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COLLIMATION CRITICAL 1. 2. 3. 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 93

1. 2. Digital imaging is not the end all, cure all for imaging problems It is still technologist dependent 94

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, Ma. S Patient Positioning 95

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• Towel that was used to help in positioning a child NEW IMAGE • CR is MORE sensitive to • ARTIFACTS 98

CR image – n NEW IMAGE Line caused from dirt collected in a CR Reader 99

High resolution with digital imaging 100