Chapter 1 Introduction to Digital Radiography and Picture Archiving System PDF

Chapter 1 Introduction to Digital Radiography and Picture Archiving and Communication System  Objectives Define digital imaging. Explain latent image formation for film/screen (F/S) radiography. Compare and contrast the latent image formation...

Chapter 1 Introduction to Digital Radiography and Picture Archiving and Communication System  Objectives Define digital imaging. Explain latent image formation for film/screen (F/S) radiography. Compare and contrast the latent image formation process for storage phosphor, flat panel with thin-film transistor (TFT), and charge-coupled device (CCD) digital imaging systems. Explain what a picture archiving and communication system (PACS) is and how it is used. Define digital imaging and communications in medicine (DICOM). 2  Key Terms Digital imaging Direct capture digital radiography Flat panel detector (FPD) Indirect capture digital radiography Photostimulable phosphor (PSP) image capture Teleradiology 3 Conventional Film/Screen Radiography Uses film and intensifying screens (F/S) in image production Film is placed on 1 or between 2 intensifying screens. Screens emit light when struck by x-rays. Light and x-rays expose the film. The film is processed chemically. Manifest image on the film is viewed on a lightbox. 4  Digital Imaging Defined as any image acquisition process that produces an electronic image The term was first used in the 1970s with the development of computed tomography (CT). Images can be viewed and manipulated on a computer. Images can be networked to various locations. 5  Digital Radiography Development Teleradiology Moving images via telephone lines to and from remote locations Concept began with Albert Jutras in Canada in the 1950s. Early PACS In the 1980s, U.S. government supported development of early PACS systems, specifically, for the U.S. military to send images between battlefields and established VA hospitals. 6 Digital Radiography Photostimulable Phosphor Flat Panel Detectors Comparison of Film/Screen to PSP and FPD Systems 7  Photostimulable Phosphor (PSP) Previously known as computed radiography (CR) PSP is more accurate and avoids confusion of “computed” and newer systems may not be cassette-based First introduced in the U.S. by Fuji Medical Systems of Japan in 1983 Slow acceptance by radiologists Installation increased in the early 1990s. A 1996 law that reduces Medicare reimbursements starting in 2018 will drive decrease in PSP use. 8  PSP Image Capture Equipment Existing radiographic equipment PSP storage plates PSP reader Technologist QC workstation Viewing station, a printer, or both Storage phosphor plates Similar to intensifying screens Store x-ray energy for an extended time 9 10  Flat Panel Detectors (FPDs) Uses an x-ray absorber material coupled to a TFT, CMOS, or CCD to form the image May retrofit existing room or a portable detector can be used in existing equipment. Two types of FPD Indirect capture Direct capture 11  Flat Panel Detectors (1 of 2) Indirect capture DR Device absorbs x-rays and converts them to light. Light is collected by an area-CCD, CMOS, or TFT and is converted into electric signals. Electronic signal sent to ADC Computer processes electric signals into images. Images are viewed on a monitor. 12  Flat Panel Detectors (2 of 2) Direct capture DR Photoconductor absorbs x-rays and converts them to electrical signals. TFT collects and sends the signal to the analog-to-digital converter (ADC). Computer turns digital data into an image. The digital image is processed and viewed on a monitor. 13 14 Comparisons of Conventional Film/Screen to Digital Imaging Equipment Image Characteristics Efficiency Scatter Sensitivity Latent Image Formation Noise Exposure Response 15  Comparison: Imaging Systems Equipment Conventional F/S and PSP use a traditional x-ray room with existing table and wall Bucky assemblies. FPD A detector replaces the table and wall Buckys. Or, portable detector is used in existing equipment. Efficiency ratings Conventional F/S and PSP are about the same. FPD is much more efficient, as images are available immediately. 16  Comparison: Latent Image Formation (1 of 4) Conventional F/S Film placed inside of a cassette containing an intensifying screen X-rays strike the intensifying screen, producing light. Light and x-ray photons interact with silver halide grains in the film emulsion. An electron is ejected from the halide. The ejected electron is attracted to the sensitivity speck. The speck now has a negative charge, and silver ions are attracted to equal out the charge. Process happens many times within the emulsion to form the latent image. After chemical processing, the sensitivity specks are processed into black metallic silver, and the manifest image is formed. 17  Comparison: Latent Image Formation (2 of 4) PSP Most are made of a barium fluorohalide with europium activator. Housed inside a cassette, some light is emitted when x-rays strike the PSP. Some of the photon energy is deposited within the phosphor particles, creating the latent image. Plate is then fed through the PSP reader. A focused laser scans the plate, causing the electrons to return to their original state, emitting light in the process. This light is picked up by a photomultiplier tube and converted into an electrical signal. The electrical signal is then sent through an ADC to produce a digital image that can then be sent to the technologist review station. 18 19  Comparison: Latent Image Formation (3 of 4) FPD No cassettes are required. The image acquisition device is built into the table or wall stand or is enclosed in a portable device. 3-5 second processing time Two image acquisition methods: indirect capture and direct capture. Indirect capture is like PSP in that the x-ray energy stimulates a scintillator, which gives off light that is detected and turned into an electrical signal. Direct capture - x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal. 20  Comparison: Latent Image Formation (4 of 4) Conventional film/screen radiography Image is determined by the shape of the film’s response curve and the processing chemicals. PSP and FPD Image processing takes place in a computer. For PSP, the computer is located near the readers. For FPD, the computer is located next to x-ray console, or it may be integrated within the console, and the image is processed before moving on to the next exposure. 21  Comparison: Exposure Response and Image Characteristics Conventional film/screen radiography Radiographic contrast is primarily controlled by kVp. Optical density on film is primarily controlled by mAs Exposure latitude narrow. PSP and FPD Exposure latitude replaced with dynamic range and is now is wide. Every detector is sensitive to a wide range of exposures. Subject contrast is influenced by kVp. Image noise is influenced by mAs. Look-up table (LUT), an image processing algorithm, controls quality of image display. 22 Comparison: Scatter Sensitivity and Noise Scatter All three image capture systems are sensitive to scatter. PSP and FPD can be more sensitive to scatter than screen/film. Noise Quantum mottle resulting from low mAs values is seen on all three image capture systems. 23  Medical Image Management and Processing Systems (MIMPS) Formerly PACS(Picture Archival and Communication System) Can accept any image that is in DICOM format FDA changed name to take storage and archiving out due to its ability to be manipulated for interpretation by physicians allowing it fall into category of medical device (2021) 24  Medical Storage device Physical hardware that provides electronic storage and retrieval Provides image access to multiple users at the same time, on-demand images Medical Image communications Device electronic transfer of medical images between devices and uses simple image manipulation tools - window/level, pan/zoom, measurements 25 26  MIMPS Uses Image manipulation tools Radiologist Reading stations Complex image processing enhancements reconstruction modern implementation of digital image viewing and processing 27  Transitioning from Film/Screen to Digital Imaging Patient demographics Patient identification is more important with digital imaging because incorrect or incomplete data may make retrieval impossible. The right image must be placed in the correct data file just as hard copy film must go into the correct patient folder. Technologist markers and postprocessing Every effort should be made to mark the side appropriately before exposure. Side marker errors can have catastrophic results for the patient. Postprocessing labels should annotate patient position and timing. After the images have been viewed and processed, they are sent via the network to the MIMPS for interpretation. 28  Summary (1 of 2) Digital imaging—any imaging acquisition process resulting in an electronic image that can be viewed and manipulated on a computer PSP systems—digital acquisition modality that uses photostimulable phosphor plates to produce digital images FPD—divided into two categories: indirect capture and direct capture Indirect capture—detector receives x-rays, converts it to light; then the light is captured and converted to an electrical signal 29  Summary (2 of 2) Direct capture—captures x-ray energy and converts it directly to an electrical signal PACS—networked group of computers, servers, and archives used to manage digital images DICOM—“language” standard that allows imaging modalities and PACSs to communicate MIMPS—comprised of many parts, such as the reading stations, physician review stations, web access, technologist QC stations, administrative stations, archive systems, and many interfaces to various hospital and radiology systems. 30