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.