Copyright 2006 by Thomson Delmar Learning ALL RIGHTS

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Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Unit III Creating the Image Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS

Unit III Creating the Image Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Chapter 25 Digital Radiography Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Chapter 25 Digital Radiography Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Objectives • Describe various digital radiography image receptor and detector systems • Explain critical

Objectives • Describe various digital radiography image receptor and detector systems • Explain critical elements used in the different digital radiography systems • Discuss limitations inherent in currently available digital radiography systems Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 4

Objectives • Describe how the digital radiography histogram is acquired • Describe how the

Objectives • Describe how the digital radiography histogram is acquired • Describe how the display algorithm is applied to collected data Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 5

Objectives • Explain why digital radiography systems have greater latitude than conventional film-screen radiography

Objectives • Explain why digital radiography systems have greater latitude than conventional film-screen radiography systems • Analyze elements of digital radiography systems Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 6

Objectives • Discuss what makes them prone to violation of ALARA radiation protection concepts

Objectives • Discuss what makes them prone to violation of ALARA radiation protection concepts • Explain the causes of sever digital radiography artifact problems Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 7

Historical Development • Fuji Systems – 1980 s • Today’s Systems – Several manufacturers

Historical Development • Fuji Systems – 1980 s • Today’s Systems – Several manufacturers Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 8

Indirect Photostimulable Phosphor Imaging Plate Systems • • Photostimulable imaging plates Latent image production

Indirect Photostimulable Phosphor Imaging Plate Systems • • Photostimulable imaging plates Latent image production Image acquisition Reading digital radiography data Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 9

Photostimulable Imaging Plates • Photostimulable phosphor – PSP • Imaging plate – IP Copyright

Photostimulable Imaging Plates • Photostimulable phosphor – PSP • Imaging plate – IP Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 10

Common Phosphors • Europium activated barium fluorohalides – Chemical formulas • Ba. FBr: Eu

Common Phosphors • Europium activated barium fluorohalides – Chemical formulas • Ba. FBr: Eu • Ba. FI: Eu Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 11

K-edge attenuation • Best between 35 – 50 ke. V – 35 ke. V:

K-edge attenuation • Best between 35 – 50 ke. V – 35 ke. V: average energy of 80 k. Vp beam • More exposure needed if applied k. Vp is outside of this range Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 12

Scatter Radiation • PSPs absorb more low energy radiation than radiographic film – More

Scatter Radiation • PSPs absorb more low energy radiation than radiographic film – More sensitive to scatter both before and after exposure than radiographic film Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 13

Latent Image Production • Electron pattern is stored in active layer of exposed IP

Latent Image Production • Electron pattern is stored in active layer of exposed IP • Fluorohalides absorb beam through photoelectric interactions – Energy transferred to photoelectrons – Several photoelectrons liberated – More electrons freed by photoelectrons Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 14

Latent Image Production • Liberated electrons have extra energy • Fluoresce - or- get

Latent Image Production • Liberated electrons have extra energy • Fluoresce - or- get trapped by fluorohalide to create holes Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 15

Hole Formation • Fluorohalide crystals trap half of the liberated electrons • Europium sites

Hole Formation • Fluorohalide crystals trap half of the liberated electrons • Europium sites contain electron holes – This is the actual latent image Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 16

Important Note! • The latent image will lose about 25 percent of its energy

Important Note! • The latent image will lose about 25 percent of its energy in 8 hours, so it is important to process the cassette shortly after exposure Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 17

Image Acquisition • IP cassettes – Also know as filmless cassettes – Can be

Image Acquisition • IP cassettes – Also know as filmless cassettes – Can be used tabletop or with a grid • Rules of positioning remain the same • Wider latitude when compared to film/screen radiography Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 18

Radiographic Technical Factor Selection “It is the responsibility of the radiographer to select proper

Radiographic Technical Factor Selection “It is the responsibility of the radiographer to select proper technique; chronic overexposure should be avoided. ” • Ethical principles • ALARA concept Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 19

Reading Digital Radiography Data • Trapped electrons are freed – IP is scanned by

Reading Digital Radiography Data • Trapped electrons are freed – IP is scanned by finely focused neonhelium laser beam in a raster pattern • Electrons return to lower energy state – Emit blue-purple light • Light captured by Photomultiplier (PM) tubes Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 20

Reading Digital Radiography Data • PM tubes convert light to analog electronic signal •

Reading Digital Radiography Data • PM tubes convert light to analog electronic signal • Analog electronic signal sent to analog to digital converter (ADC) • ADC sends digital data to computer for additional processing • IP erased via exposure to intense light Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 21

Reading Digital Radiography Data Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Reading Digital Radiography Data Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 22

Reading Digital Radiography Data • Two types of IP processing – Point by point

Reading Digital Radiography Data • Two types of IP processing – Point by point readout – Line by line readout Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 23

Reading Digital Radiography Data • Plate throughput – 30 – 200 plates per hour

Reading Digital Radiography Data • Plate throughput – 30 – 200 plates per hour • Throughput and spatial resolution can be improved by using dual-sided PSP • Self contained units – House plates and reader within upright bucky or table Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 24

Reading Digital Radiography Data • PM tubes output signal – Infinite range of values

Reading Digital Radiography Data • PM tubes output signal – Infinite range of values must be digitized • Converted to limited, discrete values – Automatically adjusted • Optimizes handling during digitization – Pixel depth Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 25

Pixel Depth • Determines number of density values – Affects density and contrast of

Pixel Depth • Determines number of density values – Affects density and contrast of system • Controlled by ADC – 10 bit (210 = 1024) – 12 bit (212 = 4096) – 16 bit (216 = 65, 536) Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 26

Pixel Size • Inversely related to spatial resolution • Sampling frequency – Expressed as

Pixel Size • Inversely related to spatial resolution • Sampling frequency – Expressed as pixels/mm • Dependent on: – Matrix – Image receptor size Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 27

Image File Size • Affected by: – Pixel size – Matrix – Bit depth

Image File Size • Affected by: – Pixel size – Matrix – Bit depth Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 28

Preprocessing • Communicates to the system: – What part – Orientation of the part

Preprocessing • Communicates to the system: – What part – Orientation of the part – Number of projections per plate Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 29

Analog to Digital Conversion • • System locates raw data Samples Quantitize Determine average

Analog to Digital Conversion • • System locates raw data Samples Quantitize Determine average value Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 30

Exposure Data Recognition (EDR) • Fuji systems’ method of locating the raw data –

Exposure Data Recognition (EDR) • Fuji systems’ method of locating the raw data – Automatic • Adjusts the latitude and sensitivity for the image – Semiautomatic • Adjusts the sensitivity, but not the latitude Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 31

Exposure Data Recognition (EDR) • Fuji systems’ method of locating the raw data –

Exposure Data Recognition (EDR) • Fuji systems’ method of locating the raw data – Fixed • Does not adjust sensitivity or latitude Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 32

Multiple Projections on One IP • Scanning projection pattern – “The beam and part

Multiple Projections on One IP • Scanning projection pattern – “The beam and part should be centered within each pattern, and collimation should be parallel and equidistant from the edges of the imaging plate. ” Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 33

Multiple Projections on One IP • Automatic mode – Used when collimation is parallel/equidistant

Multiple Projections on One IP • Automatic mode – Used when collimation is parallel/equidistant and the central ray and part are centered Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 34

Multiple Projections on One IP • Semiautomatic mode – Can be used when collimation

Multiple Projections on One IP • Semiautomatic mode – Can be used when collimation is not parallel/equidistant Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 35

Multiple Projections on One IP • Fixed mode – Requires use of proper technical

Multiple Projections on One IP • Fixed mode – Requires use of proper technical factors Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 36

Histogram • Graphic representation of pixels and signal intensities present in image Copyright ©

Histogram • Graphic representation of pixels and signal intensities present in image Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 37

Look Up Table Data • Contains standard contrast, speed and latitude for given exam

Look Up Table Data • Contains standard contrast, speed and latitude for given exam • Appropriate part and projection selected by radiographer prior to processing Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 38

Look Up Table Data • True patient image information is determined – Automatically rescaled

Look Up Table Data • True patient image information is determined – Automatically rescaled – Algorithms used for processing Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 39

Histogram Adjustment • Image processing in proper range of exposure – Yields consistent gray

Histogram Adjustment • Image processing in proper range of exposure – Yields consistent gray scale regardless of technique • Outside of appropriate range – System cannot compensate Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 40

Image Reprocessing • Raw data – Stored by CR system workstation Copyright © 2006

Image Reprocessing • Raw data – Stored by CR system workstation Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 41

Gradation Curves • Contrast requirements • Similar to Dlog. E curves of different types

Gradation Curves • Contrast requirements • Similar to Dlog. E curves of different types of radiographic film • Scale of contrast or the slope of the Dlog. E curve can be adjusted – Window width Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 42

Spatial Frequency Processing • Affects image sharpness – Edge enhancement • • Unsharp mask

Spatial Frequency Processing • Affects image sharpness – Edge enhancement • • Unsharp mask technique Low-pass filter High spatial frequency signal remains High spatial frequency signal is amplified and added back into the image Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 43

Spatial Frequency Processing • Affects image sharpness – Edge enhancement • Increases noise resulting

Spatial Frequency Processing • Affects image sharpness – Edge enhancement • Increases noise resulting in lower quality images • Lower contrast and higher base fog levels Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 44

Computed Radiography Image Quality– Fuji System • Each manufacturer has their own system •

Computed Radiography Image Quality– Fuji System • Each manufacturer has their own system • Basic concepts are similar Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 45

CR Image Quality—Fuji System • S number – Inversely related to the amount of

CR Image Quality—Fuji System • S number – Inversely related to the amount of exposure to the image receptor – Properly exposed IP should have S number of 150 -250 – S number 200 ~ 1 m. R exposure • Higher S number indicates overexposure Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 46

CR Image Quality—Fuji System • Increased latitude compared to film/screen radiography Copyright © 2006

CR Image Quality—Fuji System • Increased latitude compared to film/screen radiography Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 47

CR Image Quality—Fuji System • Linear response – No Dmax – Computer can bring

CR Image Quality—Fuji System • Linear response – No Dmax – Computer can bring densities into visual range despite overexposure Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 48

Toleration of Overexposure • Radiographers professional and ethical responsibility – Minimize patient dose –

Toleration of Overexposure • Radiographers professional and ethical responsibility – Minimize patient dose – ALARA concept Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 49

Image Acquisition Elements • Sensitivity • Data clipping • Spatial frequency processing – Edge

Image Acquisition Elements • Sensitivity • Data clipping • Spatial frequency processing – Edge enhancement – Image blurring • Look up table adjustments Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 50

Image Acquisition Elements • • Histogram equalization Collimator edge identification Image stitching Grid use

Image Acquisition Elements • • Histogram equalization Collimator edge identification Image stitching Grid use Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 51

Data Clipping • Clinically irrelevant data is not included in image display – Dependent

Data Clipping • Clinically irrelevant data is not included in image display – Dependent upon the part and projection Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 52

Spatial Frequency Processing • Edge enhancement • Image blurring Copyright © 2006 by Thomson

Spatial Frequency Processing • Edge enhancement • Image blurring Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 53

Look-up Table Adjustments • Adjustment similar to changing Dlog. E curve of the image

Look-up Table Adjustments • Adjustment similar to changing Dlog. E curve of the image receptor Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 54

Histogram Equalization • Example – Normal chest x-ray – Bone enhanced histogram image –

Histogram Equalization • Example – Normal chest x-ray – Bone enhanced histogram image – Soft tissue histogram image • Possibilities endless – ACR standard procedure Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 55

Collimator Edge Identification • Algorithm that detects edges of exposure vs. nonexposure • Can

Collimator Edge Identification • Algorithm that detects edges of exposure vs. nonexposure • Can sometimes be triggered by prosthetics or implants Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 56

Image Stitching • Overlapping exposures • Verified registration marks • Combine several images into

Image Stitching • Overlapping exposures • Verified registration marks • Combine several images into one Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 57

Grid Use • Digital systems are more sensitive to scatter radiation • Grids should

Grid Use • Digital systems are more sensitive to scatter radiation • Grids should be used more often • Radiography of the chest – > 24 -26 cm should use grid Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 58

Overexposure • Overexposure > 2 X – Results in enough scatter to degrade image

Overexposure • Overexposure > 2 X – Results in enough scatter to degrade image Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 59

Underexposure • Quantum mottle/reticulation Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED.

Underexposure • Quantum mottle/reticulation Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 60

Direct Exposure Imaging Systems • Direct selenium flat panel imaging plate systems • Indirect

Direct Exposure Imaging Systems • Direct selenium flat panel imaging plate systems • Indirect silicon flat panel imaging plate systems Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 61

Direct Selenium Flat Panel Imaging Plate Systems • Amorphous selenium directly converts ionization from

Direct Selenium Flat Panel Imaging Plate Systems • Amorphous selenium directly converts ionization from x-rays into electronic signal • Electronic signal received by thin film transistors (TFTs) and sent to computer Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 62

Indirect Silicon Flat Panel Imaging Plate Systems • Amorphous silicon combined with scintillator •

Indirect Silicon Flat Panel Imaging Plate Systems • Amorphous silicon combined with scintillator • Scintillator or intensifying screen converts x-rays to light • Amorphous silicon acts as photodiode – Converts light to electronic signal – TFTs send signal to computer Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 63

Thin Film Transistors (TFTs) • Array or matrix of pixel detectors Copyright © 2006

Thin Film Transistors (TFTs) • Array or matrix of pixel detectors Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 64

Charged Coupled Devices (CCD) • Photodetector typically used with a screen scintillator • Requires

Charged Coupled Devices (CCD) • Photodetector typically used with a screen scintillator • Requires optical coupling by lenses or fiber optics • Electric signal from CCD sent to computer Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 65

DICOM Standard • System of computer software standards • Allows different digital imaging software

DICOM Standard • System of computer software standards • Allows different digital imaging software to understand each other Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 66

Computed Radiography Artifacts • Acquisition artifacts • Post acquisition artifacts • Display artifacts Copyright

Computed Radiography Artifacts • Acquisition artifacts • Post acquisition artifacts • Display artifacts Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 67

Acquisition Artifacts • • Phantom images Scratches Light spots Dropout Fogging Quantum mottle (reticulation)

Acquisition Artifacts • • Phantom images Scratches Light spots Dropout Fogging Quantum mottle (reticulation) Heat blur Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 68

Heat Blur Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 69

Heat Blur Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 69

Post Acquisition Artifacts • • • Algorithm artifacts Dropout artifacts Laser film transport artifacts

Post Acquisition Artifacts • • • Algorithm artifacts Dropout artifacts Laser film transport artifacts Histogram error Nonparallel collimation Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 70

Display Artifacts • Density/brightness window level adjustments • Contrast window width adjustments • Image

Display Artifacts • Density/brightness window level adjustments • Contrast window width adjustments • Image enhancement artifacts Copyright © 2006 by Thomson Delmar Learning. ALL RIGHTS RESERVED. 71