1 Digital Radiography Fall 2012

2 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

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

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

5 Computed Radiography Fundamentals of Computerized Radiography

6 Radiology 1895 Radiology 2001

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

8

9 History of CR INDUSTRY Theory of “filmless radiography” first introduced in Fugi introduced special cassettes with PSP plates (replaces film) Technology could not support system First clinical use in Japan

10 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

11 History of CR 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

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

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

14

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

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

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

18 Cassette with film CR with PSP

19

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

21

22 Amorphous Selenium detector technology for DR Direct Radiography

23

24

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

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

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

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

29 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

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

31 How CR works 1. Blue released light is captured by a PMT (photo multiplier tube) 2. This light is sent as a digital signal to the computer 3. The intensity (brightness) of the light – correlates to the density on the image

32

33

34

35 CR “PROCESSORS”

36 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

37

38

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

40 CR VS. DR (slide 41) 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

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

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

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

44

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

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

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

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

49 “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

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

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

52

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

54

55 Benefits of Computer (web)-based Viewing Systems 1. Hardcopy studies are no longer misplaced or lost- eliminates films 2. Multiple physicians may access same patient films 3. Patients do not have to wait in Radiology for films once study is completed

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

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

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

59 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

60 Adapted from AAPM TG10

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

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

63

64

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

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

67

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

69 FILM DIGITIZER

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

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

72 CONTRAST & DENSITY 1. Most digital systems are capable of 1024 shades of gray – but the human eye can see only about 30 shades of gray 2. The Optical Density and Contrast can be adjusted after the exposure by the Radiographer. 3. This is POST - PROCESSING

73 High displayed contrast – narrow window width

74 Low displayed contrast (stretched) – wide window width

75 Basics of Digital Images 1. Pixel values can be any bit depth (values from 0 to 1023) 2. Image contrast can be manipulated to stretched or contracted to alter the displayed contrast. 3. Typically use “window width” and “window level” to alter displayed contrast

76

77

KVP

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

80 DOSE IMPLICATIONS 1. More exposure to the patient 2. Techniques established 3. Higher kVp = Less mAs 4. Less patient dose

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

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

83 POST PROCESSING

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

85 standard image edge sharpening

86 NO GRID HAND ALGO REPROCESSED

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

88

89 REPEAT IMAGES

90

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

92

93 COLLIMATION CRITICAL 1. As the computer reads the density value of each pixel- it is averaged into the total 2. Close collimation= Better contrast 3. Bad collimation= more grays and less detail

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

95 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

96

97

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

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

100 High resolution with digital imaging