DIGITAL EQUIPMENT MAY 2008 TERMINOLOGY REVIEW ARRT CONTENT SPECS 2008 ARRT SPECS
Haapala, Dan, News Director/On-Air Personality has reference to this Academic Journal, PHwiki organized this Journal DIGITAL EQUIPMENT MAY 2008 TERMINOLOGY REVIEW ARRT CONTENT SPECS 2008 ARRT SPECS – DIGITAL Image Receptors digital image characteristics spatial resolution sampling frequency DEL (detector element size) receptor size in addition to matrix size image signal (exposure related) quantum mottle SNR (signal to noise ratio) or CNR (contrast to noise ratio) Digital Systems electronic collimation grayscale rendition or look-up table (LUT) edge enhancement/ noise suppression contrast enhancement system malfunctions (e.g., ghost image, b in addition to ing, erasure, dead pixels, readout problems, printer distortion)
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ARRT SPECS – DIGITAL Image Display viewing conditions (i.e., luminance,ambient lighting spatial resolution contrast resolution/dynamic range DICOM gray scale function window level in addition to width function Image Acquisition in addition to Readout PSP (photo-stimulable phosphor) flat panel detectors (direct in addition to indirect) Noise Acceptable Range of Exposure Exposure Indicator Determination Gross Exposure Error Image Degradation (mottle, light or dark, low contrast) ARRT SPECS – DIGITAL Recognition of Malfunctions Digital Image Receptor Systems Digital artifacts (grid lines, Moiré effect or aliasing) maintenance (e.g., detector fog) ( non-uni as long as mity, erasure) ARRT SPECS – DIGITAL PACS HIS (hospital in as long as mation system) – work list RIS (radiology in as long as mation system) DICOM Workflow (inappropriate documentation, lost images, mismatched images, corrupt data) windowing in addition to leveling
Review of Digital Radiography in addition to PACS Key Terms Computed radiography DICOM (digital imaging in addition to communications in medicine) Digital imaging Digital radiography Direct capture DR Indirect capture DR PACS Teleradiology
Digital Radiography Direct Capture Indirect Capture Direct-to-Digital Radiography (DDR)-Selenium Computed Radiography (CR) – PSL Laser Scanning Digitizers Direct-to-Digital Radiography Silicon Scint. Image Acquisition in addition to Readout PSP (photo-stimulable phosphor) flat panel detectors (direct in addition to indirect) Computed Radiography Uses storage phosphor plates Uses existing equipment Requires special cassettes Requires a special cassette reader Uses a computer workstation in addition to viewing station in addition to a printer
Computed Radiography Storage phosphor plates are similar to intensifying screens. Imaging plate stores x-ray energy as long as an extended time. Process was first introduced in the United States by Fuji Medical Systems of Japan in 1983. First system used a phosphor storage plate, a reader, in addition to a laser printer. Imaging Plate Construction Image recorded on a thin sheet of plastic known as the imaging plate Consists of several layers: Cassette in addition to Imaging Plate Cassette contains a window with a barcode label or barcode sticker on the cassette. Label enables technologist to match the image in as long as mation with the patient-identifying barcode on the exam request.
Using the Laser to Read the Imaging Plate The light collection optics direct the released phosphor energy to an optical filter in addition to then to the photodetector. Although there will be variances between manufacturers, the typical throughput is 50 cassettes per hour. Some manufacturers claim up to 150 cassettes per hour, but based on average hospital department workflow, 50 cassettes per hour is much more realistic. Process up to 101 cassettes an hour. H in addition to le 16 cassettes at one time: up to 8 queued as long as processing, in addition to 8 erased in addition to ready as long as new imaging studies. Cassette is ready to reuse in 40 seconds. Review an image in 34 seconds at a Kodak DirectView remote operations panel. Drop- in addition to go workflow virtually Based on proven DirectView CR 850 system design ·Process up to 62 35 x 43 cm plates an hour ·Small footprint size of 25 x 29 inch (63.5 x 73.6 cm
Digital Radiography Cassetteless system Uses a flat panel detector or charge-coupled device (CCD) hard-wired to computer Requires new installation of room or retrofit Digital Radiography DR is hard-wired. DR is cassetteless. Detectors are permanently enclosed inside a rigid protective housing. Thin-film transistor (TFT) detector arrays may be used in direct- in addition to indirect-conversion detectors. Digital Radiography Two types of digital radiography Indirect capture DR Machine absorbs x-rays in addition to converts them to light. CCD or thin-film transistor (TFT) converts light to electric signals. Computer processes electric signals. Images are viewed on computer monitor.
Digital Radiography Direct capture DR Photoconductor absorbs x-rays. TFT collects signal. Electrical signal is sent to computer as long as processing. Image is viewed on computer screen. Digital Radiography DR used CCD technology developed by the military in addition to then used TFT arrays shortly after. CCD in addition to TFT technology developed in addition to continues to develop in parallel. No one technology has proved to be better than the other. Flat-Panel Detectors Consist of a photoconductor Amorphous selenium Holds a charge on its surface that can then be read out by a TFT
Direct Conversion X-ray photons are absorbed by the coating material. Photons are immediately converted into an electrical signal. The DR plate has a radiation-conversion material or scintillator. Direct Conversion DR Scintillator Typically made of amorphous selenium Absorbs x-rays in addition to converts them to visible photons Converts photons to electrical charges Charges stored in the TFT detectors Indirect Conversion Similar to direct detectors in that the TFT technology is also used Two-step process: X-ray photons are converted to light. Light photons are converted to an electrical signal. A scintillator converts x-rays into visible light. Light is then converted into an electrical charge by photodetectors such as amorphous silicon photodiode arrays or charge-coupled devices, or CCDs.
Indirect Conversion More than a million pixels can be read in addition to converted to a composite digital image in under a second. Comparison of Film to CR in addition to DR For conventional x-ray film in addition to computed radiography (CR), a traditional x-ray room with a table in addition to wall Bucky is required. For DR, a detector replaces the Bucky apparatus in the table in addition to wall st in addition to . Conventional in addition to CR efficiency ratings are about the same. DR is much more efficient, in addition to image is available immediately. Comparison of Film to CR in addition to DR CR A storage phosphor plate is placed inside of CR cassette. Most storage phosphor plates are made of a barium fluorohalide. When x-rays strike the photosensitive phosphor, some light is given off. Some of the photon energy is deposited within the phosphor particles to create the latent image. The phosphor plate is then fed through the CR reader.
Operator Errors Insufficient collimation results in unattenuated radiation striking the imaging plate. The resulting histogram is changed so that it is outside the normal exposure indicator range as long as the body part selected. Using the smallest imaging plate possible in addition to proper collimation, especially on small or thin patients, eliminates this error. Operator Errors If the cassette is exposed with the back of a cassette toward the source, the result is an image with a white grid-type pattern in addition to white areas that correspond to the hinges. Care should be taken to expose only the tube side of the cassette.
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