2 - Digital Radiographic Imaging

• Digital radiographic imaging includes electronically measuring x-ray transmission patterns through a patient, converting this data into a digital file, and viewing it on a computer.
• This process resembles taking a photo with a digital camera: both record patterns, transmit the data and can be viewed on a screen.
• It's not about photographing a radiographic film or scanning an analog radiograph.
• Analog x-ray machines are usually compatible with new digital imaging systems.
• Veterinary practices have largely shifted from analog to digital radiography.
• The cost of digital radiography systems has decreased, but substantial investment is still needed.
• Selecting the right system requires careful planning.
• Not all digital systems offer equal quality, and cheaper options might not fully deliver the benefits of digital radiography.
• Getting expert advice is helpful unless the purchaser has knowledge of digital technology.
• Radiation safety and patient positioning remain crucial in digital radiography, as in analog imaging.
• The transition to digital has enhanced the quality of veterinary radiographic studies.
• A comprehensive understanding of digital radiography is vital for those using or considering these systems.

Digital Image Files

• The basis of a digital image is a computer file holding information about a measured signal.
• In medical imaging, signals include x-ray emission patterns (radiography), x-ray attenuation (CT), sound waves (ultrasound), or radiofrequency emission (MRI).
• In medical imaging, the computer file is a DICOM format.
• DICOM files differ from .jpeg and .tiff files, and use .dcm extension.
• Besides image data, DICOM files contain ancillary information called metadata tags:
• Metadata tags detail:
• Device manufacturer.
• Image acquisition date and time.
• Patient demographics.
• Acquisition parameters.
• Identifiers for the referrer, practitioner, and operator.
• Other image parameters.
• The DICOM format mainly seeks to ensure consistency for imaging device interconnectivity.
• Without the DICOM standard, digital images from one vendor might only be viewable with that vendor's software.
• The DICOM standard enables images from any vendor to be viewed on various platforms.
• Compliance with DICOM formatting is voluntary.
• Most vendors acknowledge the benefits of DICOM compliance, and DICOM has emerged to be universal.
• Verifying DICOM adherence from a vendor is key before purchasing a system to maintain viewing and file transmission flexibility.
• The DICOM standard handles medical images with network protocols that run on top of the Internet protocol.
• DICOM images can also be transferred using browser-based technology for enhanced portability.

Components of a Digital Image

• When opened with dedicated software, a digital image has individual picture elements - pixels.
• Pixels form a row-by-column matrix.
• In radiographic, ultrasound, CT, and MRI scans, each pixel has a specific gray shade.
• More pixels yield a larger file size, and a greater array size.
• Uncompressed digital radiographic DICOM files are typically 4 to 12 MB per image.
• A file size of approximately 0.1 MB would be expected for a 30-page document.doc file.
• Pixel size determines spatial resolution, or the smallest detectable object.
• The vendor-supplied hardware dictates the pixel array size in a digital image.
• More pixels is generally better, but benefits plateau past a certain point.
• Pixel size (pixel pitch) may be measured in microns or line pairs per mm.
• Guidelines exist for minimum spatial resolution standards.
• Besides pixel size, other technical factors affect spatial resolution.
• Software optimization of the raw image file can be more important than pixel density.
• In medical digital images, pixels are assigned gray shades.
• The number of shades per pixel influences image contrast.
• Few gray shades result in high contrast with only black, white, and a few intermediate shades.
• Many gray shades allow for a longer contrast scale.
• Computer files apply binary notation to assign pixel shades with 0 as black and 1 as white.
• If "n" equals the quantity of zeroes or ones per pixel, then 2" is the number of possible gray shades.
• The number of possible gray shades are referred to as the bit depth of the image.
• Image file size and bit depth are directly correlated.
• Assigning varying gray shades to each pixel is necessary for diagnostic value.

Digital Radiography Acquisition Hardware

• Two primary types of digital radiography acquisition hardware are available including:
• Computed radiography (CR).
• Direct digital radiography (DDR).
• Though conventional x-ray tubes and tables are used for both CR and DDR, film cassettes are only used with the older analog imaging.
• In CR systems, digital recording is done with a cassette containing a flexible imaging plate.
• With DDR systems, the digital recording device is a rigid imaging plate or chip.
• Special DDR charge-coupled device (CCD) systems might require a new x-ray table purchase.
• This would become the case if hardware components were housed in the x-ray table, and the equipment cannot be retrofitted into an existing x-ray table.

Computed Radiography

• CR was the first digital radiographic system introduced.
• CR cassettes resemble film cassettes. CR cassettes have a flexible imaging plate coated with photostimulable phosphor (PSP) instead of x-ray film.
• With CR an attenuation distribution temporarily stores as what is known as a latent image:
• Latent images are a product of changes in electron energy band.
• The changes are produced by a patient’s x-rays striking the PSP
• Upon exposure, the CR is processed in a plate reader. Key steps when processing CR radiography includes:
• CR cassette removal from the x-ray table before reader insertion. Reader automatically removes the PSP plate from the CR cassette.
• PSP plate illumination via reader laser.
• Laser illumination causes PSP plate emission of visible light.
• Emitted visible light strikes a photomultiplier tube where it is converted into electronic signal.
• The electronic signal is digitized and stored as a digital file.
• The PSP plate is exposed to bright white light to make sure all electrons are at ground state in preparation for the next exposure.
• The PSP plate is automatically returned to the cassette in the reader.
• The cassette is ejected from the reader for use on the next patient. CR isn’t very popular in veterinary imaging.
• With CR, plates are handled like film cassettes, the plate takes 1- 2 minutes to be processed.
• Workflow does not improve via CR compared to analog imaging. CR is slower than film processing.
• CR readers are not mobile, while the cassettes themselves tend be portable CR cassettes must be returned to the veterinary practice for processing, preventing rapid evalutation of radiographs in the field.
• Damaged CR cassettes are inexpensive relative to the cost of replacing DDR plates but good-quality CR systems are adequate replacements.

Direct Digital Radiography

• Three types of DDR are identified, including:
• Indirect flat-panel detector system.
• Direct flat-panel detector system.
• CCD system.
• In DDR the plate is swapped out with the detector allowing digital radiographic images for quality-control evaluation.

Indirect Flat-Panel Detectors

• So named due to visible light production as a preliminary step in image making.
• X-ray intensifying screens are used to convert energy into visible light.
• May be composed of gadolinium oxysulfide or cesium iodide.
• Intrinsic capabilities for x-ray detection are had by Cesium Iodide, thinner flat-panel device, allowing lower radiation.
• The intensifying screen is placed on a photodiede panel which is a signal read-out from the TFT.
• 43 x 43 cm. imaging plates may have a photodiode matrix equaling to 2600 x 2600.
• Good resolution is determined by small detector size. Flat-panel detectors may have 6-7 million photodiodes.
• Electronics must spatially localize a signal at each photodiode-this increased expense is contrasted with film-screen cassette systems .
• Bit depth of indirect flat-panel detectors is capable of grayscale resolution of 16,384 shades per pixels.

Direct Flat-Panel Detectors

• Operate without a visible light mediator, as the x-rays strike the photoconductor which is typically amorphous selenium.
• Electrons liberated in the selenium layer by the oncoming x-ray beam are collected to form a charge.
• Charge is read out by the film transistor array the pixel matrix consists of 14 in bit depth.
• Differs from Indirect, whereby light is produced by intensifying effects.
• Diffusion can potentially lead to blurring due to light spread leading to direct and indirect disadvantages and engineering for crystal structures.
• Systems are frequently replacing CR as the preferred digital means of taking diagnostic images in veterinary medicine:
• Higher throughput.
• Recent decrease in price.
• Provide lower doses decreasing radiation for personnel; DDR has tethered and nonwireless attributes
• Batteries and portability help the equine practices to thrive.

Charged-Coupled Device

• Found in camcorders and digital cameras.
• This makes it less common than film / CR / flat-panel for radiography.
• Vendors often advertise the use of CCD chips.
• DDR doesn’t involve equipment between exposure / imaging; No cassette is required and CCD are smaller than flat panels only in area.
• They may contain pixel elements 43 x43 cm for a flat panel which are light sensitive. a light intermediary via intensifying screens standard.
• Collection efficiency and quality of the focusing lenses are key.
• Image quality and lenses help determine quality.
• The lens suffers loss of light and potential distortion, Humans must be reserved;
• If the part is small CCD and veterinary light is needed for parts the physical device and the constant vertical must be met the size is limited by horizontal.
• New and old have limited the scope of the current situation.

Image Processing and Viewing

• Electronic data, post-hardware choice, are processed by computers before displaying information, processing occurs during preprocessing.
• Refers to modifications being applied correctively to data for image distortion.
• Eliminates the need for functional or dead pixels. Processing turns corrected data to a visual in the controller. Aims to optimize aspects; A number of the process happens when a vendor makes presets custom; Data does gets overwritten the processing step occurs the the most effective means which in great vendor /product improvement algorithms limit noise and improve process this is usually not the case and can reduce dose as necessary.
• Algorithm and processing are techniques applied that can vary and should improve contrast resolution;
• Processing creates image files ready to be viewed Appropriate header information is attached through the local network
• Software licenses allow the file to be viewed.
• Functionally, viewing software Is a major asset in digital radiography; Post-processing means enhancement and controls are 100% on an end-user basis.
• A vast means of adjustment exists, over normal manipulation.
• Lighting and monitor impact image reviewing; light makes a huge difference so viewing in darkness won’t improve imagery.
• Quality improves accuracy; radiology is best improved with a dedicated monitor; better is brighter, better whites help users resolve more shades of Gray.

Explore the initial steps in digital radiographic imaging. Understand X-ray machine types, the shift from analog, and crucial imaging aspects. Learn about digital image components and system selection.