2006 National Primary Oral Health Care Conference Robert A. Cederberg, MA, DDS December 10 14, 2006 Scottsdale, Arizona

Transcription

1 Digital Radiography 2006 National Primary Oral Health Care Conference Robert A. Cederberg, MA, DDS December 10 14, 2006 Scottsdale, Arizona

2 Development of Dental Digital Radiography Background, history and development of dental digital radiography Evolution of the technology & systems Conversion from film to digital and options for the office or clinic Advantages and disadvantages Applications and functions Adjunctive techniques

3 Background The development of computed axial tomography (CAT) in 1972 and subsequent advances in digital sensors allowed for dental applications.

4 History of Digital in Dentistry Trophy Radiologie introduced the RVG in 1982 Sensor - CCD (charged-coupled device) with phosphor screen, active area 17mm x 26mm

5 Design and Development First sensors where designed with CCD chip layered with a phosphor screen, latter sensors were developed which were direct exposure.

6 Digital System Components Digital imaging requires a sensor (detector), analog to digital converter (A/D converter), computer or CPU, monitor, printer. Additionally, modem or other (cable, T1, DSL) connection for Teleradiograhpy is important.

7 Steps in Digital Acquisition Electromagnetic energy in the form of x-ray photons strike the detector (CCD electrical charge stored in pixels), (PSP latent image formation) A/D converter converts the electrical charge into a digital format (PSP visible light intensities converted to digital format) A number is assigned to each voltage output ranging from 0 to 256 (2 8 ) or 256 shades of gray in the image Once image is acquired and stored post processing, i.e. image manipulation

8 Enhancements Direct exposure CCDs Early 90 s Photostimuable Phosphor (PSP) technology Early 90 s Complementary Metal Oxide Semiconductor (CMOS) Flat Panel Detectors CBCT (Cone Beam Computed Tomography) Late 90 s software improvements, monitor fidelity improvements.

9 Evolution of Dental X-ray Image Receptors Discovery of x rays in 1895, first image receptors were glass plates celluloid film 1919 single emulsion dental film packets 1924 double emulsion dental film 1940 Ultraspeed film D speed 1980 Ektaspeed film E speed 1982 first intraoral digital sensor

10 Direct Digital Radiography

11 Basic Digital System X-ray source Components Sensor or detector (CCD, CMOS and storage phosphor) Computer or CPU Modem Printer

12 Sensors CCD (Charged Couple Device): silicon chip with an embedded electronic circuit. PSP (Photostimuable Storage Phosphor): plastic plate coated with a photostimuable phosphor layer. CMOS-APS (Complementary Metal Oxide Semiconductor - Active Pixel Sensor): silicon chip with an ADC for each column of pixels.

13 Digital Sensors Optime PSP plates Sizes 0, 1and 2 Trophy Sensor Size 2 Schick Sensors Sizes 0, 1 and 2

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15 The Physics of CCD Sensors

16 Available Sensors

17 CMOS Sensor

18 The Physics of PSP Sensors

19 Conversion from Film to Digital Probably easiest to slowly transition into digital. Probably best to consider utilizing more than one digital system since no one system will satisfy all of the imaging needs within one office or clinic, i.e. for intraoral imaging, both a PSP and CCD combination.

20 Conversion from Film to Work flow study Digital

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24 Conversion from Film to Digital Main advantage no darkroom needed Elimination of the mess of darkroom chemistry, cost and maintenance of film processors Many cities and local municipalities now regulate waste water discharge and require silver collectors to be installed on processors which adds additional mess as well as expense

25 Techniques and Systems Techniques vary only by the type of detector used: either CCD or Storage Phosphor All systems offer the ability to manipulate the image: i.e. image enhancement, colorization, etc.

26 Intraoral CCD Based Systems Product Name CDR CygnusRay MPS Dexis Dixi 2 Dixsy FI iox megapixel MPDx Company Schick Cygnus Technologies ProVision Dental Systems Planmeca Group Villa Sistemi Medicali Fimet Remedent N.V.

27 Intraoral CCD Based Systems Product Name SIDEXIS SIGMA SuniRay TM RVG VistaRay VisualiX USB Company Sirona PaloDex Group Suni Medical Imaging Trophy DÜrr Dental Gendex

28 Intraoral PSP Systems Product Name Company Panorama Xi Orex Combi-Xi Orex DenOptix Gendex - Dentsply Digora Optime PaloDex Group VistaScan DÜrr Dental VistaScan Intra DÜrr Dental

29 Panoramic CCD Based Systems Product Name Company CDRPan Schick Digipan Trophy Dimax2, Proline, Promax Planmeca Group DXIS Signet Orthopantomograph OP100D PaloDex Group Orthoceph OC100D PaloDex Group ORTHOPHOS DS Sirona

30 Panoramic CCD Based Systems Product Name Company Cranex Base X D Cranex Excel D Scanora D Orthoralix 9200 (DDE, DPI) Versaview (5D, SDCP) PaloDex Group PaloDex Group PaloDex Group Gendex - Dentsply Morita

31 Panoramic PSP Based Systems Product Name Combi-Xi DenOptix DenOptix Ceph DEXpan Digora PCT Paxorama Xi VistaScan Company Orex Gendex - Dentsply Gendex - Dentsply Pro Vision Dental PaloDex Group Orex DÜrr Dental

32 Digital X-ray Image? Physical Definition Digital Image Mathematical Definition

33 PIXEL The matrix element of a digital array which identifies a gray level at that point. It can be processed and manipulated, usually expressed in values. Gray Scale O 255 O = Black 255 = White

34 Digital Imaging: Advantages Image enhancement and analysis - may increase diagnostic validity of x-rays of non-optimal density. No-processing problems - darkroom, processor and processing chemistry not required (environmentally friendly). Less exposure errors - density and contrast enhancement. Allows for quantitative evaluation. Lower absorbed doses - 20 to 90% compared to D-speed film. Better patient communication and time saver.

35 Digital Imaging: Disadvantages High cost (Processor/sensor, CPU, monitor, printer) - CCD and CMOS sensors 5 to $7,000 Inflexible cassette for CCD and CMOS sensor - may not allow proper placement in all intraoral locations. Spatial Resolution not as good as film - film 16 to 20 lp/mm, digital 7-13 lp/mm. Printed copy not as good as screen - resolution is lost when image is printed. Not standardized - proprietary hardware and software. Learning curve for staff.

36 PaloDex Group Soredex: Optime

37 Taking The Radiograph Place onto positioning device Use your current x- ray equipment Take x-ray with reduced exposure

38 Digora Optime Hardware Imaging Plate Processing

39 Digital Imaging Software Features Zoom Contrast/Brightness Pseudocolor Rotation Annotation Filters 3D Analysis (Line, Angle) Manipulating implant Video Inversion

40 Negative Conversion

41 Pseudo-Colorization

42 3D Function

43 Measuring Distance and Angle

44 Applications Patient Education Quantifying the image Implant planning Teleradiography Other

45 Patient Education

46 Quantifying the Image All systems provide the ability to measure lengths and angles and to analyze the density gradients throughout the image.

47 Implant Planning Some systems provide for implant overlays which are helpful in assessing potential implant sites.

48 Teleradiography Transmission of digital images to remote sites is a major driving force in the evolution of digital radiography. Remote consultation, Insurance approval.

49 DenOptix QST

50 Digital X-ray Imaging 100% re-usable Same size as film Flexible Thin No wires like CCD sensor Use with existing x-ray equipment Plates

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52 Preparing the plates To prevent cross contamination, the plates are placed in a disposable plastic barrier

53 Preparing the plates Panometric and Cephalometric are placed in the cassette with screens

54 Taking an x-ray Tear the barriers and drop the imaging plate into the dark box Be careful of light exposure and contamination

55 The DenOptix Scanner Scans all image plate sizes Integrates with practice management software Simple to learn No patient discomfort

56 Scanning In a semi-darkened area Load the plate on the carousel (can hold up to 29 plates) Attach the pan/ceph plates

57 Scanning Place the loaded carousel into the scanner Close the lid Begin scanning 1 min 12 secs for up to 8 I/O 2 min 30 secs for a Pan 3 min 30 secs for a Ceph

58 Sensor - CCD or CMOS GX-S RFG CDR (Schick) Sidexis Dixi (Planmeca)

59 DC Intraoral Unit

60 Panoramic Unit

61 The source of x-rays, the tube Must have Smallest focal point AC - DC Range of Kv, ma adapted to dental x- rays (digital or not)

62 The detector Film, sensor, imaging plates Image quality parameters are: Quantum Mottle Noise (signal/noise ratio) Resolution Sensitivity or dynamic range All three are important!!

63 Signal/Noise Ratio Depends on the amount of photons that strike the image sensor Noise level: PSP < film < CCD Images with lots of noise are described as grainy

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65 Resolution X-ray photon detection takes place in layers vs on a surface Resolution is limited by the thickness of the layer, not pixel size Measured by line pairs resolved per mm (lp/mm) Limited by what the eye can detect Film = 20 lp/mm PSP = 7-14 lp/mm (I/O) Sensor = lp/mm (I/O) Diagnostic resolution is the key.

66 Resolution 600 dpi 300 dpi

67 A good image means Good x-ray source Small focal spot, collimator, x-ray beam quality Good positioning Good detector

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70 RINN Sensor Holder

71 Dexis Sensor

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82 Comparison of Image Receptor Characteristics Contrast resolution Spatial resolution Sensor/receptor latitude Sensor/receptor sensitivity MTF, SNR (NEQ and DQE) Contrast and spatial resolution of the human eye

83 Contrast Resolution The ability to distinguish different densities in the radiographic image. Factors affecting contrast resolution: 1. Attenuation characteristics of the tissues being imaged. 2. Sensor bit depth and noise level. 3. Monitor resolution, bit depth, dot pitch, luminance and display size. 4. Ambient lighting.

84 Contrast Resolution Digital imaging systems are capable of capturing up to 256 different densities, monitors/operating systems are only capable of displaying 242 different densities. The human eye can only distinguish 32 different densities.

85 Spatial Resolution The capacity of the image to display fine detail. *The theoretical limit of resolution is a function of the pixel size of the system.* Image receptor pixel sizes: film 8 microns, high res. CCD 20 microns, PSP 40 microns. Resolution: film = > 20 lp/mm, CCD = 25 lp/mm (theoretical with software enhancements), PSP = 12.5 lp/mm.

86 Sensor Latitude The ability of the sensor to capture a range of x-ray exposures. A desirable quality of a sensor/receptor is the ability to display a full range of densities. Dynamic range of film extends to 4 orders of magnitude (with hot lighting), CCD/CMOS sensors extend to 2 orders of magnitude and PSP sensors extend to 5 orders of magnitude of x-ray exposure.

87 Sensor Sensitivity Sensitivity of a sensor is its ability to respond to small amounts of radiation. Sensitivity of film is directly related to film speed. Sensitivity of digital sensors affected by pixel size and system noise. PSP systems allow dose reductions of about 50% compared to F-speed film. CCD/CMOS less dose reduction than PSP.

88 Modulation Transfer Function (MTF) MTF is a measure of the combined effects of sharpness and resolution. The MTF of E-speed film is superior to the MTF of PSP at high spatial frequencies. The 50% modulation level for PSP is reached at 2.5 lp/mm whereas E-speed film is not reached until 10 lp/mm.

89 Signal-to-Noise Ratio (SNR) NEQ and DQE The ratio of the signal amplitude to the standard deviation of the fluctuations in noise. NEQ noise equivalent quanta DQE detective quantum efficiency At low spatial frequencies PSP systems have superior NEQ to E-speed film across the exposure range. Data suggested that a PSP sensors are able to absorb more quanta (photons) per unit area as compared to film.

90 Signal-to-Noise Ratio (SNR) NEQ and DQE Higher quantum absorption of PSP leads to a superior DQE as compared to E-speed film. Theoretically higher quantum absorption and higher DQE of PSP sensors could provide a more efficient absorption of photons and thereby an image with improved definition.

91 Contrast & Spatial Resolution of the Human Eye In terms of contrast, the displayed image provides up to 8 times the amount of information that the eye can actually see. The minimum contrast threshold (greatest perceptual sensitivity) corresponds to a spatial frequency of approximately 5 lp/cm or about a 1mm wide pixel size. Consequently, the sensor can display approximately 2.5 times the amount of information that the eye can actually perceive.

92 Lesion Recognition Research Studies have looked at both natural carious lesions and simulated lesions and tested the resolving power of film vs digital. Conclusion The ability to recognize incipient caries lesions is NOT dependent on image receptor (film or digital), the system used or the manner in which it is displayed.

93 References Brettle DS, Workman A, et al. The imaging performance of a storage phosphor system for dental radiography, Br. J. Radiol. 69, (1996). Cowen AR, Workman A, Price JS. Physical aspects of photostimuable phosphor computed radiography, Br. J. Radiol. 66, (1993). Wang J, Langer S. A brief review of human perception factors in digital displays for picture archiving and communications systems, J. Digit. Imaging. 10(4), (1997). Cederberg RA, Tidwell E, et al. Endodontic working length assessment comparison of storage phosphor digital imaging and radiographic film. OOOOE. 85, (1998). Cederberg RA, Frederiksen NL, et al. Influence of the digital image display monitor on observer performance. Dentomaxillofac Radiol. 28, (1999).

94 Image Examples From Planmeca s website

95 Planmeca Bite Wing Series left side

96 OpTime Bite Wing Series left side

97 Planmeca image OpTime image

98 Conclusion Storage phosphor technology provides film-like sensors which are easier to place for all intraoral imaging sites. More comfortable for the patient and placement especially for premolar bitewings allows operator to image the distal of the canines. Elapsed time for completion of image is actually less than for some hard-wired systems.

99 Conclusion Portable no need to be tied to a computer. Can be taken in any operatory with a tube head and even with a hand held unit. Widest dynamic range of any sensor allows for potential recovery of diagnostic information in an otherwise underexposed image. Improved DQE theoretically provides better image clarity & definition.

100 Conclusion Some common fallacies concerning the superiority of film and/or CCD/CMOS receptors over PSP receptors: One sensor type will be sufficient for all intraoral imaging applications. Probably only true for film and PSP. Depending on the type of hard-wired sensor there may difficulty obtaining certain images such as molar periapicals and premolar bitewings.

101 Conclusion Some common fallacies concerning the superiority of film and/or CCD/CMOS receptors over PSP receptors: CCD/CMOS systems claims of superior resolutions of 25 lp/mm or greater as compared to PSP. The human eye has the best acuity at pixel sizes approximating 1 mm, 2.5 times the resolving power of most PSP systems. Is it enough to detect decay? Yes! But, image clarity is more important.

102 Digital Subtraction Radiography

103 Cone Beam CT

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105 Flat Panel Detector Amorphous Silicon Flat Panel Detector

106 Effective Dose Comparison i-cat 20 sec scan 68 usv i-cat 10 sec scan 34 usv Daily background 8 usv Panoramic film usv Panoramic digital usv Full Mouth Series film 150 usv Hitachi MercuRay CBCT 485 usv Medical CT usv

107 Panoramic

108 X-Sectional Imaging

109 Localization

110 Orthodontics

111 Pathology

112 What Does the Future of Digital Radiography Look Like? Evolution and development of existing systems It s here to stay! Further integration of other technologies into existing systems. CBCT will become standard of care for all dental imaging needs. CBCT will become more widely used, price will come down. Perhaps, a CBCT scan and bitewings will someday be the dental exam standard.