Chapter 1 Introduction to Digital Radiography and PACS

Chapter 1 Introduction to Digital Radiography and PACS Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 1

Objectives Define the term digital imaging. Explain latent image formation for conventional radiography. Describe the latent image formation process for computed radiography. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 2

Objectives Compare and contrast the latent image formation process for indirect capture digital radiography and direct capture digital radiography. Explain what a PACS (picture archiving and communication system) is and how it is used. Define digital imaging and communications in medicine. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 3

Key Terms Computed radiography DICOM (digital imaging and communications in medicine) Digital imaging Digital radiography Direct capture DR Indirect capture DR PACS Teleradiology Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 4

Conventional Radiography Method is film-based. Method uses intensifying screens. Film is placed between two screens. Screens emit light when x-rays strike them. Film is processed chemically. Processed film is viewed on lightbox. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 5

Digital Imaging Digital imaging is a broad term. Term was first used medically in 1970 s in computed tomography (CT). Digital imaging is defined as any image acquisition process that produces an electronic image that can be viewed and manipulated on a computer. In radiology, images can be sent via computer networks to a variety of locations. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 6

Historical Development of Digital Imaging CT coupled imaging devices and the computer. Early CT scanners required hours to produce a single slice. Reconstruction images took several days to produce. First CT scanners imaged the head only. First scanner was developed by Siemens. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 7

Historical Development of Digital Imaging Magnetic resonance imaging (MRI) became available in the early 1980 s. Lauterbur paper in 1973 sparked companies to research MRI. Many scientists and researchers were involved. Advancements in fluoroscopy occurred in the 1970 s as well. Analog-to-digital converters allowed real-time images to be viewed on TV monitors. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 8

Historical Development of Digital Imaging Fluoroscopic images could also be stored on a computer. Ultrasound and nuclear medicine used screen capture to grab the image and convert it digitally. Eventually, mammography converted to digital format. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 9

Digital Radiography Development Concept began with Albert Jutras in Canada in the 1950 s. Early PACS systems were developed by the military to send images between Veterans Administration hospitals in the 1980 s. Development was encouraged and supported by the U. S. government. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 10

Digital Radiography Development Early process involved scanning radiographs into the computer and sending them from computer to computer. Images were then stored in PACS. Computed and digital radiography followed. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 11

Computed Radiography Uses storage phosphor plates Uses existing equipment Requires special cassettes Requires a special cassette reader Uses a computer workstation and viewing station and a printer Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 12

Computed Radiography Storage phosphor plates are similar to intensifying screens. Imaging plate stores x-ray energy for 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, and a laser printer. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 13

Computed Radiography Method was slow to be accepted by radiologists. Installation increased in the early 1990 s. More and more hospitals are replacing film/screen technology with digital systems. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 14

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 Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 15

Digital Radiography Two types of digital radiography Indirect capture DR • • Machine absorbs x-rays and 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. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 16

Digital Radiography Direct capture DR Photoconductor absorbs x-rays. • TFT collects signal. • Electrical signal is sent to computer for processing. • Image is viewed on computer screen. • Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 17

Digital Radiography First clinical application was in 1970 s in digital subtraction. University of Arizona scientists applied the technique. Several companies began developing large field detectors. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 18

Digital Radiography DR used CCD technology developed by the military and then used TFT arrays shortly after. CCD and TFT technology developed and continues to develop in parallel. No one technology has proved to be better than the other. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 19

Comparison of Film to CR and DR For conventional x-ray film and computed radiography (CR), a traditional x-ray room with a table and wall Bucky is required. For DR, a detector replaces the Bucky apparatus in the table and wall stand. Conventional and CR efficiency ratings are about the same. DR is much more efficient, and image is available immediately. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 20

Comparison of Film to CR and DR Latent image formation is different in CR and DR. Conventional film/screen Film is placed inside of a cassette that contains an intensifying screen. • X-rays strike the intensifying screen, and light is produced. • The light and x-ray photons interact with the silver halide grains in the film emulsion. • Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 21

Comparison of Film to CR and DR • • • An electron is ejected from the halide. Ejected electron is attracted to the sensitivity speck. Speck now has a negative charge, and silver ions will be attracted to equal out the charge. Process happens many times within the emulsion to form the latent image. After chemical processing, the sensitivity specks will be processed into black metallic silver and the manifest image is formed. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 22

Comparison of Film to CR and 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. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 23

Comparison of Film to CR and DR CR, continued Focused laser light is scanned over 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 analog-to-digital converter to produce a digital image that can then be sent to the technologist review station. • Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 24

Comparison of Film to CR and DR No cassettes are required. • The image acquisition device is built into the table and/or wall stand or is enclosed in a portable device. • Two distinct image acquisition methods are indirect capture and direct capture. • Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 25

Comparison of Film to CR and DR DR, continued Indirect capture is similar to CR in that the x-ray energy stimulates a scintillator, which gives off light that is detected and turned into an electrical signal. • With direct capture, the x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal. • Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 26

Image Processing Conventional radiography • Image is determined by the film itself and the chemicals. CR and DR Image processing takes place in a computer. • For CR, the computer is located near the readers. • For DR, 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. • Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 27

Exposure Latitude or Dynamic Range Conventional radiography Based on the characteristic response of the film, which is nonlinear. • Radiographic contrast is primarily controlled by kilovoltage peak. • Optical density on film is primarily controlled by milliamperesecond setting. • Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 28

Exposure Latitude or Dynamic Range CR and DR • • Contain a detector that can respond in a linear manner. Exposure latitude is wide, allowing the single detector to be sensitive to a wide range of exposures. Kilovoltage peak still influences subject contrast, but radiographic contrast is primarily controlled by an image processing look-up table. Milliampere-second setting has more control over image noise, whereas density is controlled by image-processing algorithms. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 29

Scatter Sensitivity It is important to minimize scattered radiation with all three acquisition systems. CR and DR can be more sensitive to scatter than screen/film. Materials used in the many CR and DR image acquisition devices are more sensitive to low-energy photons. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 30

Picture Archival and Communication Systems Networked group of computers, servers, and archives to store digital images Can accept any image that is in DICOM format Serves as the file room, reading room, duplicator, and courier Provides image access to multiple users at the same time, ondemand images, electronic annotations of images, and specialty image processing Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 31

Picture Archival and Communication Systems Custom designed for each facility Components/features can vary based on the following: • • Volume of patients Number of interpretation areas Viewing locations Funding Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 32

Picture Archival and Communication Systems Early systems did not have standardized image formats. Matching up systems was difficult. Vendors kept systems proprietary and did not share information. DICOM standards helped change this by allowing communication between vendors’ products. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 33

Picture Archival and Communication Systems First full-scale PACS Veterans Administration Medical Center in Baltimore used PACS in 1993. • PACS covered all modalities except mammography. • Shortly after, PACS was interfaced with radiology information systems, hospital information systems, and electronic medical records. • Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 34

PACS Uses Made up of different components • • Reading stations Physician review stations Web access Technologist quality control stations Administrative stations Archive systems Multiple interfaces to other hospital and radiology systems Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 35

PACS Uses Early PACS seen only in radiology and some cardiology departments. PACS now can be used in multiple departments. Archive space can be shared among departments. PACS reading stations may also have image processing capabilities. PACS allows radiologists to reconstruct and stitch images in their offices. Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 36

PACS Uses Orthopedic workstations are available for the following: Surgeons can plan joint replacement surgery. • Specialized software allows matching of best replacement for patient with patient anatomy. • System saves time and provides better fit. • Elsevier items and derived items © 2008 by Mosby, Inc. , an affiliate of Elsevier Inc. 37