Digital Radiography (DR) Quiz

Digital Radiography (DR)

• Advanced form of x-ray inspection that produces a digital radiographic image instantly on a computer
• Uses x-ray sensitive plates to capture data during object examination
• Incident x-ray radiation is converted into an equivalent electric charge and then to a digital image through a detector sensor

Flat Panel Detectors

• Provide high-quality digital images with better signal-to-noise ratio and improved dynamic range
• Work on two different approaches: indirect conversion and direct conversion

Indirect Conversion

• Flat panel detectors have a scintillator layer that converts x-ray photons to photons of visible light
• Utilize a photo diode matrix of amorphous silicon to convert light photons into an electrical charge
• Charge is proportional to the number and energy of x-ray photons interacting with the detector pixel and the amount and density of material that has absorbed the x-rays

Direct Conversion

• Silicon alone is not sensitive enough to the energy of x-ray quanta used in diagnostic radiology
• Therefore, the silicon layer is covered with a scintillator material, cesium iodide (CsI) known as intensifying screens
• CsI absorbs the X-ray quanta and transfers them to light, which is detected by the a-Si, converting light to electrical charge

The Process

• X-rays hit CsI or CdTe
• Light hits a-Si
• Electrons and holes are drawn toward the positive bias, and holes are stored in the charge storage wells beneath the electrodes
• When enough charge is stored, a voltage runs across the a-Si, and the electronics read this voltage

Fat Panel Detectors

• Use photo conductors like amorphous Si, CdSe, or Copper Telluride (CdTe) on a multi-micro electrode plate
• Providing the product charge, information on both types of detectors read for thin film transistors

The Direct Conversion Process

• When x-ray photons impact the photo conductor (amorphous Selenium), they are directly converted to electronic signals, which are amplified and digitized
• Thus, there is no scintillator lateral spread of light photons, ensuring a sharper image

Flat-panel: a-Se

• Uses selenium instead of silicon
• No need for Cesium Iodide (CsI) layer
• A more direct technology
• More efficient and electric bits are avoiding shadow minimum as electrons build in a field
• More expensive but has good spatial resolution and is more efficient than the a-Si detectors

Direct Digital Radiographic Receptor

• DR Image Converter
• Directly converts X-ray to an electrical signal
• X-rays hit the detector where pixels are arranged in a matrix
• These pixels each hold a charge that depends on the intensity of the X-ray
• This charge gets converted into an electrical signal
• An analog to digital converter converts the signal into information that the computer can process

Direct Radiography

• A type of digital radiography like CR, but is more digital in the sense that there is no cassette, removable imaging hardware or equipment that physically reads the imaging plates
• Has digital imaging sensors built into the x-ray table or equipment to the system, meaning that the images are captured directly onto the digital system, allowing for faster image processing and reduced costs

Test your knowledge of Digital Radiography, a digital x-ray inspection technique that produces instant digital images. Learn about x-ray sensitive plates, detector sensors and more.