Digital Imaging in Radiography

Digital Imaging

• Digital imaging is an image acquisition process that produces an electronic image that can be manipulated by a computer and displayed as a matrix of intensities.
• Benefits include high image quality and resolution, image post-processing analysis, electronic storage, fast and high-quality image distribution, and image efficiency and throughput.

Types of Digital Radiography

• Computed Radiography (CR)
• Digital Radiography (DR) with indirect capture
• Digital Radiography (DR) with direct capture

Computed Radiography (CR)

• Uses a photostimulable phosphor (PSP) plate that stores latent images upon x-ray exposure.
• The PSP plate is housed in a protective cassette.
• Process involves getting the image, processing it at a CR image reader, and looking at it on a display.

Stages of PSP Image Formation

• Expose: energy transfer from x-ray photons to the PSP atom.
• Excitation: electrons in the PSP move to a higher energy level.
• Trapped: electrons stay trapped at the higher energy level for a period of time.
• Latent image: trapped electrons result in a latent image.

CR Reader

• The machine beautifies the image using mathematical algorithms.
• It puts in patient information and anatomy scanned.
• The CR reader takes out the PSP plate to process the latent image.

Steps of CR Image Formation

• Stimulate: the PSP plate is scanned with a low-energy laser beam to return metastable electrons to their lower energy level.
• Read: the latent image is read and converted into an electrical signal.
• Erase: the phosphor is flooded with white light to erase the latent image.

Image Fading

• PSP sensitivity to additional exposures causes stored energy to be lost immediately after exposure.
• 25% of stored energy is lost in 8 hours, reducing quality.
• 24 hours after exposure, ghosting will be evident, and the plate must be erased.

Direct and Indirect DR

• Direct capture: uses a flat-panel detector array without a scintillator.
• Indirect capture: uses a thin flat-panel detector with a scintillator.

Components and Terminology of Digital Imaging

• Digital images are a numeric representation of the x-ray beam energies transmitted through the patient to the IR.
• Digital radiography requires analog to digital conversion, binary numbers representing transmitted photon energies, and a raw data image matrix.

Digital Image Processing Operations

• Point processing: changes the input values of pixels to improve diagnostic quality.
• Local processing: manipulates image data to enhance specific areas.
• Geometric processing: involves flipping, rotating, magnifying, and annotating images.

Exposure Range and Dynamic Attitude

• Digital imaging systems have a wide dynamic range, producing a digital image across a large range of exposure values.
• Exposure latitudes for each x-ray system are important to have defined.

Exposure Indicators

• Provide a standard index for radiographers to determine the adequacy of exposure for specific x-ray systems.
• Displayed on the digital image as a numerical value, which must fall within an acceptable range.

PACs

• Storage system for images, with patient files, medical imaging request forms, and radiology reports.
• Advantages include remote access, transfer to other hospitals and clinics, and conversion to film/DVD if required.

Radiology Information System (RIS)

• Database to store and record patient information, with workflow management, patient registration, and scheduling capabilities.
• Also includes list and tracking capabilities, request and document scanning, reporting, and image storage.