Digital Radiography Seminar
-
Upload
abhishek-bose -
Category
Documents
-
view
133 -
download
2
Transcript of Digital Radiography Seminar
Patient
FSRFilm ScreenRadiography
Imaging PlateCR - 2 Step
Digital DetectorDR – 1 Step
Digital radiography is a form of x-ray imaging, where digital X-ray sensors are used instead of traditional photographic film.
Digital Radiography (DR) or (DX) is essentially filmless X-ray image capture. In place of X-ray film, a digital image capture device is used to record the X-ray image and make it available as a digital file that can be presented for interpretation and saved as part of the patient’s medical record.
Pixel: The pixel is the smallest addressable screen element; it is the smallest unit of picture that can be controlled.Has a varied set of tones in shades of white/ black/grey. Expressed in binary codes (bits).
Size of the pixel : Smaller the size , better resolution.
CR- 50 to 200 microns, DR- 100 to 200 microns. Gray Scale: Shades of Gray in between pure black
and pure white. Bit Depth: No of shades to define each
pixel ,measured as no of bits. Larger the depth, increased gray scale and large file size.
Spatial Resolution: The measure of how closely lines can be resolved in an image is called spatial resolution and depends on the no. of pixels and property of the material.
Contrast Resolution: Color or gray scale differentiation. Indicate the no of shades of grey that a detector can capture.
Scintillator: It is material which exhibits scintillation - the property of luminescence when excited by ionizing radiation.
Digital bucky
Incorporated into x-ray equipment
Receptor provides direct digital output
No processor / reader required◦ Images available in < 15 seconds◦ Much less work for technologist
TFT = THIN-FILM TRANSISTOR ARRAY
X-ray energy converted directly to electrical signal
X-rays interact with semiconductor material◦ Amorphous selenium◦ The amorphous
selenium (a-Se) layer provides high spatial resolution.
X-rays converted directly into electrical charge◦ No intermediate steps
◦ CCD Cameras
◦ CMOS Cameras
◦ Thin Film Transistor (TFT) Flat Panel Arrays
X-ray strike scintillator producing light Photodiode array converts light to
electrons
Light
Light spreads can limit spatial resolution Can be controlled by “channeling” Winning in the marketplace
Film Digitization
Computed Radiography
Potentially lower patient dose than CR
High latitude as for CR Digital bucky fragile
◦ First DR portables comingto market
Unprocessed image as read from receptor◦ CR
Intensity data from PMT’s as a result of scanning plate with laser
◦ DR Raw Data read directly from TFT array
Not a readable diagnostic image
Requires computer post-processing◦ Specific software algorithms must be
applied to image prior to presenting it as finished radiograph
1. Identify collimated image border
2. Separate raw radiation from anatomy
3. Apply appropriate tone-scale to image
◦ Done with look-up table (LUTLUT)
This process is specific to a
particular body part and
projection
*
Converts a raw data pixel value to a processed pixel value
“Original” raw data pixel value indicates amount of radiation falling on pixel
Computer must establish location of collimated border of image
• Computer then defines anatomic region
• Finished image produced by tone scalingRequires histogram analysis of
anatomic region
Graph showing how much of image is exposed at various levels
Body part & projection-specific algorithms determine average exposure◦ Must correctly identify anatomical region
LUT computed to display image with proper◦ Density◦ Contrast
LUT calculated by algorithm depends on◦ Body part◦ projection
User can also alter LUT manually
Monitors on CR reader or DR console compared to reading workstations have◦ lower resolution◦ poorer quality◦ Recommended that LUT
not be manually modified
Film use has little ambiguity about proper radiation exposure
Measure of radiation received by receptor below anatomy Not a direct measure of patient exposure If exposure index higher than recommended range, patient
overexposed. Each manufacturer provides feedback to technologist on
exposure to digital receptor Displayed on CR reader monitor Displayed on workstations
Technologist should strive to keep exposure index consistent
Kodak recommendation for exposure index◦ 1800 – 2200
George’s recommendation◦ “Maximum tolerable noise”◦ As low as possible while providing
tolerable noise◦ This is not a beauty contest!
DR type image receptor Conventional Image Intensifier with Video
Signal Digitized (“Frame Grabber”)
Image
Tube
X-RayInput
ImageTube TV
Amplfier
Analogto
DigitalConvert
er
DigitalMemory
(Computer)
Lens System
DR images displayed & stored in about 8 seconds. Immediate image preview and availability, a wider
dynamic range which makes it more forgiving for over- exposure.
Reduced costs associated with processing, managing and storing films.
Time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images.
DR has faster throughput◦ Up to 2-4 times faster than traditional screen-film-
darkroom technology
Expensive Equipment , hence not all medical facilities are able to afford.
Difficult to transport due to bulkiness and fragility.
Trained manpower and supervision required.