(4) Digital Imaging
Advantages/disadvantages of radiographs vs digital images
Film -no inherent measurements -film size similar to beam size -film covers larger area -EPA film disposal -EPA chemical/silver disposal/recovery -film placement is easy -easy to view multiple images (shuffling) Digital -software driven measurements -receptor size smaller than beam size -receptor covers smaller area -no film disposal -no chemicals -cable connection interferes with placement (CCD) -awkward to view multiple images (shuffling)
Advantages/disadvantages of film radiographs vs digital radiographs
Film -portable -familiar -can be viewed by all -initially inexpensive -must send by mail -one viewer or duplicate (duplitized) -bulky storage -awkward retrieval from archives -hard copy -improper processing = non archival quality Digital -not portable -new technology (constantly evolving) -must have hardware/software -inexpensive after initial investment -transmissible by wire -viewed simultaneously -easy storage -easy retrieval from archives -electronic glitch sensitive -archival quality -new technology = uncertainty
Smaller pixel size --> lower/higher spatial resolution
Higher
Intraoral vs extraoral digital systems- differences
No basic differences
Digital image- describe
Numeric format of image content and its discreteness -digital images are numeric and discrete (0 or 1) -large collection of individual pixels organized in matrix of rows, columns -each pixel has row, column coordinate that uniquely identifies its location in matrix
Fundamental element of digital image
PIXEL (picture element)
CCD/CMOS sensors - describe material - describe active area - pixel size
Solid-state silicone chip - Active area arranged into 2D picture elements (pixels) - Pixel size: 20 - 70um
Solid State Detectors- how does it work
X-ray photons cause ionization of pixel silicone --> ejected electrons trapped in pixel similar to charge in a battery (charges are proportional to amount of radiation cells received) --> computer reads charge in each pixel (converts charge into 256/+ shades of gray) --> charge pattern formed from individual pixels in matrix represents the latent image
For every square (pixel) 2 numbers are recorded - significance of 1st vs 2nd numbers
- 1st number assigns location - 2nd number assigns brightness
Smaller vs bigger pixels --> less/more detailed image
- Bigger pixels --> less detailed the image - Smaller pixels --> better detail
Components of digital images: - image receptor - image processing - viewing - storage
- image receptor: CCD / screen - image processing: CPU, software; laser, CPU, software - viewing: image on screen / print-out (avoid printout- lowers resolution) - storage: disk / paper hard copy
Solid State Detectors- components
-CCD/CMOS detector -analog to digital converter -fiber-optical cable / wireless computer
Photostimulable phosphor plates (PSP) - describe
-based on Fuji medical imaging plates -developed in 1981 -reusable hard imaging plates -linear exposure response (wide latitude) -thin (1-1.7mm) same as film -no cord from sensor -requires separate reader device
Photostimulable phosphor plates (PSP)- how does it work
-plastic plate coated w/ Europium dopped Barium flourohalide -PSP plates absorb, store energy from xrays -phosphor emits stored energy when stimulated w/ red laser light -emission read w/ blue photo-diode
Flat panel detectors - use - components - affordability
-used for medical imaging, extra-oral imaging, cone beam computed tomography -direct detector OR indirect director + intensifying screen -expensive
Analog to digital conversion (ADC)- how does it work
-values stored in computer; represent the image -computer organizes pixels in their proper locations --> displays shade of gray that corresponds to number that was assigned during quantization step
Solid state detectors - sensor sizes - components of CCD sensors
0, 1, 2 Components of CCD: - physical size - active area (portion of sensor actually producing image)
Types of digital image receptors + describe
1. Solid State Technology (direct sensors) - CCD, CMOS, Flat panel 2. Photostimulate phosphor (PSP) technology (Indirect- PSP + Film)
Extra-oral digital systems- types
1. digital pantomography 2. digital cepholometric radiography
Solid state detectors- sensor size vs active area
Active area of solid state sensors is less than physical size -film and PSP utilize 100% of area
Digital dental radiography advantages and disadvantages
Adv -immediate image display -no film and dark room processing -dynamic image -reduced radiation dose to patients (60-80% reduction) -image storing and communication are easier -cheaper in long run (material costs) -software manipulation can enhance diagnosis -potential administrative savings -easy physical storage -cleaner office Disadv -decreased image resolution (11-20 line pair/mm) -initial expensive -more retakes -discomfort -wire lead -hygiene -initial expense
PSP detectors- advantages and disadvantages
Adv -lower initial cost modality -easy to use (as thin as film, no cord attached) -easy to perform full mouth radiograph -PSP plates cheaper to replace -great latitude in radiographic exposures Disadv -PSP plates scratch easily -need to insert each plate into individual barrier packages for intraoral use (time factor) -requires erasing after each use -requires scanning of latent image -high cost of scanner -lower resolution than CCD/CMOS
Formation of digital image begins w/
Analog process -at each pixel of electronic detector, absorption of x-rays generates small voltage (more xrays generate higher voltage) -at each pixel, voltage can fluctuate b/t a min, max value :: is an analog signal
Production of digital image - requirement - steps
Analog to digital conversion (ADC) 2 steps 1. Sampling: grouping small range of voltage values --> single value 2. Quantization: sample signal is assigned value
What can film vs digital detect
Both: -caries detection -periodontal bone loss -periapical bone loss -bony lesions Film -poor for soft tissue lesions Digital -soft tissue lesions
CCD vs CMOS analog digital converter method
CCD -sensors move charge row by row, pixel by pixel --> then convert to voltage at output anode -"bucket brigade" transfer CMOS -sensors convert charge to voltage inside each pixel -electronic transfer
What is international standard / format for digital images
DICOM
DICOM standards - what does it stand for - what is it - advantages
Digital imaging & communications in medicine -international standards for communication of biomedical diagnostic, therapeutic information in disciplines that use digital images - Is both a standard AND format (JPG is just format) - High encryption - Stores a LOT of information - Prevents fraud (photoshopping JPG images)
Photostimulable phosphor plates (PSP)- poor/good contrast resolution
Extremely good contrast resolution due to high exposure latitude -means longer gray scale -pretty image even w/ lower resolution
