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