DIGITAL RADIOGRAPHY

College of Dentistry516 MDS

Asma’a Al-Ekrish

A REVIEW

HISTORY

Image Plate Systems

1947- Berg and Kaiser

1975- optical scanner and digitizer

1981- publicly presented in

1994- the first dental PSP (Digora-Sordex)

Solid State Systems

1960's- development of CCD and CMOS

1970’s- CCD (Bell Laboratories)

1988- CMOS (Scotland)

1980’s- first intraoral digital system -Francis Mouyen (Radiovisiography system RVG, Trophy, France

TYPES OF DENTAL IMAGES

Analogue:• Gray shades are continuous and show a

gradual change

Digital:• Gray shades

have discrete values and are assigned to individual picture elements.

• Smooth transitions changed into a checker pattern, by the pixels

IMAGE RECEPTORS Sensors

When X-rays hit sensor, an electronic charge is produced on the surface of the sensor.

Electronic signal is sent to the computer (either directly or indirectly) as an analogue signal and there is digitized ( by a frame-grabber or A-D converter)

Measurements of the photon intensity are transmitted to the computer where they are recorded numerically

THE DIGITAL IMAGE

C) Numerical representation of pixel values.

A) X-rayshadow.

B) Image as detected by the digital sensor; each square is apixel.

D) Digital image on the computer screen.

(van der Stelt 2000; van der Stelt 2005)

THE DIGITAL IMAGE

C) Numerical representation of pixel values.

A) X-rayshadow.

B) Image as detected by the digital sensor; each square is apixel.

D) Digital image on the computer screen.

THE DIGITAL IMAGE

THE DIGITAL IMAGE

binary numerals

0 (zero) 1(one)

01101001 28 = 256 possible combinations

0011100011010101 216 = 64,000

possible combinations

DIRECT AND INDIRECT DIGITAL IMAGING

A. Direct Digital Radiography:Real Time Systems (CCD or CMOS)

B. Semi-direct Digital RadiographySPS Image Plates

C. Indirect Digital RadiographyConverting a pre-existing analogue image to a digital one

REQUIREMENTS OF DIGITAL SYSTEM

1. X-ray generator

2. Sensor

3. Computer

4. Software

5. Monitor

6. Printer

REQUIREMENTS OF DIGITAL SYSTEM

COMPONENTS OF THE SYSTEM MUST

BE DICOM COMPATIBLE

( Digital Imaging Communication in Medicine )

REAL TIME SYSTEMS

A- Charged Couple Device (CCD)

Sensors

B- Complementary Metal Oxide

Semiconductors(CMOS) sensors

REAL TIME SYSTEMS

CCD

CCD

fibreoptics

Intensifying screen

SILICON CHIP WITH ELECTRONIC CIRCUIT EMBEDDED INTO IT.

REAL TIME SYSTEMS

CCDProduction of the image

X-rays

electronic signal

To A-D converter

light from scintillating layer

REAL TIME SYSTEMS

CCDProduction of the image

A-D Converter

1- Sampling

2- Quantization

White and Pharoah (2004)

REAL TIME SYSTEMS

CCD

Advantages

and

Disadvantages

REAL TIME SYSTEMS

CMOS

RAM

Micro-controller

unit

REAL TIME SYSTEMS

CMOS

Advantages

and

Disadvantages

REAL TIME SYSTEMS CCD vs. CMOS

  CCD CMOS

When invented 1967 1967

Power consumption 400mW 40mW

Sensitivity to light Excellent Excellent

Sensitivity to x-rays High Unknown

Cost High Low

Manufacturing Expensive Expensive

Fixed pattern noise Low High

Quantum efficiency Excellent Fair

Adapted from Langlais, R.P., and Miles D.A. Digital radiographic imaging: Technology for the next millennium. www. Learndigital.net

REAL TIME SYSTEMS

ADVANTAGES

1. Image immediately displayed

2. Higher spatial resolution than semi-direct systems

(PSP)

REAL TIME SYSTEMS

DISADVANTAGES

1. Cost

2. Bulky

3. Electrical

4. cords

5. Rigid

6. Active- area limitations

Photostimulable Phosphor Plates (PSP)

IMAGE PLATE SYSTEMS

backing

barium flourohalide

Protective coating

IMAGE PLATE SYSTEMS

Production of the Image

Decay of the Image

IMAGE PLATE SYSTEMS

ADVANTAGES

1.Thin

2.Flexible

3.Cordless

4.Size comparable to standard size films

5.Reusable

6.Broad exposure latitudes

7.May be used with existing x-ray generators

IMAGE PLATE SYSTEMS

DISADVANTAGES

1. Extra step- scanning procedure

2. Dose reduction not as much as with solid-state detectors

EXTRA-ORAL RADIOGRAPHY

CCD or PSP may be used

Tomography only with PSP

QUALITY FACTORS

Resolution: how well closely spaced objects can be distinguished

Sharpness: distinctiveness of feature boundaries

Contrast: distinctiveness of light and dark areas.

Distortion: the difference between the apparent and true locations of points on an image.

QUALITY FACTORS Modulation Transfer Function (MTF):

Describes the ability of a system to record the spatial frequencies that are available to be recorded

Noise: unwanted fluctuations in image density

Detector Quantum Efficiency (DQE): combined effect of noise and contrast performance of an imaging system, expressed as a function of object detail.

QUALITY FACTORS

CONTRAST RESOLUTION

QUALITY FACTORS

SPATIAL RESOLUTION

QUALITY FACTORS

SPATIAL RESOLUTION

QUALITY FACTORS SPATIAL RESOLUTION

QUALITY FACTORS

SIGNAL TO NOISE RATIO (SNR):

Reproduced from Oakley (2003 )

QUALITY FACTORS

ARTIFACTS

Distortions are any unwanted elements in the image

Produced by either:• the image sensor (CCD/CMOS),

• optical system,

• internal image processing algorithms, or

• compression algorithm.

IMAGE DISPLAY- MONITORS

Cathode Ray Tubes (CRT)

Flat panel- Liquid Crystal Displays

(LCD)

Reproduced from Oakley (2003 )

IMAGE DISPLAY- MONITORS

QUALITY FACTORS OF MONITORS

1. dot pitch

2. resolution

3. luminance

4. brightness and contrast settings

IMAGE DISPLAY- MONITORS

QUALITY FACTORS OF MONITORS

5. refresh rate

6. color depth

7. footprint and weight

8. contrast layer

FACILITIES OFFERED BY DIGITAL RADIOGRAPHY

Dose reduction

( van der Stelt 2000; van der Stelt 2005 )

FACILITIES OFFERED BY DIGITAL RADIOGRAPHY

Dose reduction

Image processingImage Enhancement

Contrast enhancementFiltering

SubtractionColor

Image Restoration

System defectsGeometric

Transformation

Image Analysis

MeasurementSegmentation

Feature extractionObject classification

CADIA

Image Compression

LosslessLossy

Image Synthesis

TomosynthesisTACT

Localized CT

FACILITIES OFFERED BY DIGITAL RADIOGRAPHY

Miles, D. (2000). "The future of digital imaging in dentistry." Dental Clinics of North America 44: 427-438

Storage, archiving, retrieval

FACILITIES OFFERED BY DIGITAL RADIOGRAPHY

Electronic transmission

FACILITIES OFFERED BY DIGITAL RADIOGRAPHY

1. Dose reduction

2. Time- faster to acquire

3. No chemical processing- eliminating processing errors, saving space and money on the long term. Environmentally friendly

4. Long term savings on film processing

5. Better gray scale resolution

6. Image processing

7. Teleradiology

8. Less storage space

GENERAL ADVANTAGES

1. Initial setup cost

2. Less spatial resolution

3. Sensor size

4. Requires more space in the operatory- but no

dark room.

5. more time to process information

GENERAL DISADVANTAGES

Quality diagnostic images

Radiation dose less than film

Lossless archiving is allowed in an image file format DICOM compatible

ESSENTAIALS OF ANY SYSTEM

The paperless office

Computer aided diagnosis and detection of defects

3-D visualization of dental structures based on radiographic data at the level of single teeth

Wireless technology

FUTURE of DIGITAL RADIOGRAPHY

Continued reduction is storage media and size

Testing, maintenance, and upgrade of equipment and software online

Research towards a "smart card"- which could carry a patient's medical and dental notes along with their radiographic images

Global education and distanc learning

FUTURE of DIGITAL RADIOGRAPHY

 Analoui, M. and K. Buckwalter (2000). "Digital radiographic image archival, retreival, and management." Dental Clinics of North America 44(2): 339-358

Farman, A. and T. Farman (2005). "A comparison of 18 different x-ray detectors currently used in dentistry." Oral Surg Oral Med Oral Pathol Oral Radiol Endod 99: 485-9.

Miles, D. (2000). "The future of digital imaging in dentistry." Dental Clinics of North America 44: 427-438.

Oakley, J. (2003). Digital imaging. A primer for radiographers radiologists and health care professionals. London, Greenwich Medical Media Limited.

van der Stelt, P. F. (2000). "Principles of digital imaging." Dental Clinics of North America 44(2): 237-247.

van der Stelt, P. F. (2005). "Filmless imaging. The uses of digital radiography in dental practice." JADA 136: 1379-1387.

White, S. C. and M. J. Pharoah (2004). Oral radiology.Principles and interpretation. St. Louis, Mosby.

References:

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