Digital Rad Ch.1
Introduction to Digital Radiography and Picture Archiving and Communication System
Objectives
Upon completion of this chapter, you should be able to:
Define the term digital imaging.
Explain latent image formation for conventional film/screen radiography.
Compare and contrast the latent image formation process for storage phosphor, flat panel, 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).
Outline
Conventional Film/Screen Radiography
Digital Imaging
Historical Development of Digital Imaging
Digital Radiography
Photostimulable Phosphor
Flat Panel Detectors
Comparison of Film/Screen to Photostimulable Phosphor and Flat Panel Detector Systems
Picture Archiving and Communication Systems
Picture Archiving and Communication System Uses
Transitioning From Film/Screen to Digital Imaging
The Imaging Chain
Film Versus Photostimulable Phosphor and Flat Panel Detector
Patient Demographics
Technologist Markers
Technical Choices
Speed
Single Versus Multiple Exposures
Preparing the Image for Reading
Getting the Image to the Radiologist
Summary
Key Terms
Digital imaging
Direct capture digital radiography
Flat panel detector (FPD)
Photostimulable phosphor (PSP)
Teleradiology
Introduction
This chapter provides an overview of digital imaging and PACS. Details will be elaborated in subsequent chapters. It is important to grasp basic definitions and concepts to understand more complex topics later in the text, which primarily focuses on entry-level radiography excluding advanced modalities like MRI and CT.
Conventional Film/Screen Radiography
Conventional radiography uses film and intensifying screens in the image formation process:
Film is placed on or between two intensifying screens that emit light when struck by X-rays.
The light exposes the film based on the amount and energy of the X-rays incident on the screen.
The film is chemically processed to reveal a manifest image.
For further details, consult a radiographic imaging textbook.
Digital Imaging
Digital imaging allows text, photos, drawings, animations, and videos to be visible on electronic devices.
It is any acquisition process that produces an electronic image viewable and manipulatable on a computer.
The first significant use in medicine was with the introduction of the CT scanner by Godfrey Hounsfield in the 1970s. Today, most medical imaging modalities are digital.
Historical Development of Digital Imaging
CT is considered a major milestone, bringing together computers and imaging devices. Early CT units took hours to acquire one slice and days to process the resulting image.
MRI was commercially introduced in the early 1980s, with pioneering efforts dating back to the mid-1970s.
Advances in fluoroscopy, enabled by computer technology in the 1970s, allowed images to be captured digitally via analog-to-digital converters (ADCs).
Digital Radiography
Teleradiology was conceptually introduced by Albert Jutras in the 1950s for remote image transmission.
PACS was developed by the US military in the 1980s for sharing images among VA hospitals and battlefield locations. Early analog radio-graphs were digitized for transmission.
Photostimulable Phosphor
Photostimulable phosphor (PSP) image capture, or computed radiography (CR), uses storage phosphor plates to produce images, similar to film/screen systems but requiring specific equipment like PSP plates, readers, and workstations.
PSP plates store incident X-ray energy in traps for later readout. The commercial introduction was by Fuji Medical Systems in 1983.
Adoption of PSP faced challenges initially due to reluctance from radiologists. However, by the early 1990s, installation rates increased due to technological advancements.
The Consolidated Appropriations Act of 2016 resulted in reductions of Medicare reimbursement for PSP systems, incentivizing transition to flat panel detector systems.
Flat Panel Detectors
Flat panel detectors utilize X-ray absorber materials coupled to thin-film transistors (TFT), CMOS, or CCD to form images.
They can be classified into:
Indirect capture systems: Absorb X-rays, convert to light, capture light as an electrical signal.
Direct capture systems: Convert incident X-ray energy directly to an electrical signal using a photoconductor.
Early applications of digital images were pioneered in digital subtraction angiography (DSA) in the early 1970s at the University of Arizona.
Comparison of Film/Screen to Photostimulable Phosphor and Flat Panel Detector Systems
Comparison Table:
Ease of use, latent image formation, and processing differ among systems.
Latent image formation in conventional radiography:
X-rays interact with an intensifying screen producing light, which exposes film resulting in a latent image processed chemically into a manifest image.
Latent image formation in PSP systems:
X-rays create light and store energy in phosphors. The latent image is released using laser stimulation and digitized for processing.
Latent image formation in FPD systems:
Indirect systems convert light to electrical signals; direct systems respond directly to X-ray energy.
Picture Archiving and Communication Systems (PACS)
PACS is a computer network group managing digital images and can accept images in DICOM format.
Functions include:
Serving as a digital file room, reading room, duplicator, and courier.
Allowing simultaneous access, electronic annotations, and specialized processing of images.
Early developments in PACS began in the 1980s with differing standards, but DICOM has standardized communications between modalities and PACS.
The first extensive PACS was installed in the VA Medical Center in 1993.
Picture Archiving and Communication System Uses
Components include reading stations, physician review stations, web access, and archive systems.
Initially used primarily in radiology, now PACS can integrate images from various departments into a shared archive space.
PACS systems offer advanced features for image processing, aiding specialists in planning pre-operative procedures.
Transitioning From Film/Screen to Digital Imaging
The Imaging Chain: The patient is positioned between the X-ray source and image receptor; image capture methods differ between modalities.
Film vs. Digital: Film is a medium that captures and archives images with chemical processing. Digital captures convert X-ray to electronic signals without physical images, stored in PACS.
Patient Demographics: Importance of accurate identification and tracking of patient information is critical in both systems but more complex in digital formats.
Technologist Markers: Use anatomical markers is essential for clarity in digital systems, preventing errors in side identification due to the display process.
Technical Choices: Radiation factors and their impacts, including adjustments necessary for digital capture sensitivity and scatter output.
Speed and Efficiency: Differences in imaging speeds; PSP system initial challenges due to speed classes compared to film/screen systems.
Single vs. Multiple Exposures: In digital systems, multiple exposures typically require separate capture to preserve processing integrity.
Preparing the Image for Reading
With digital systems, all data relevant to the image must be attached digitally, including annotations and notes.
Getting the Image to the Radiologist
After preparation, images are sent to a workstation or PACS for radiologists to access and review. Technologies available can enable quick retrieval and processing of images.
Summary
Digital imaging produces electronic images manipulatable on a computer. PSP and FPD systems are key components of image capture with PACS designed to manage digital images effectively. DICOM ensures standard communication across platforms.
Review Questions
Which radiographic image capture method uses chemical development to produce the manifest image?
✅ c. Film/screen radiography
Film/screen systems require chemical processing to make the latent image visible.
Which company was the first to introduce photostimulable phosphor (PSP) imaging commercially in the United States?
✅ b. Fuji
Fuji Medical Systems introduced PSP imaging in the U.S. in 1983.
Which radiographic image capture method uses an X-ray absorber material coupled with a thin-film transistor (TFT), complementary metal oxide semiconductor (CMOS), or charge-coupled device (CCD) to form the digital image?
✅ d. FPD (Flat Panel Detector)
FPD systems use TFT, CMOS, or CCD technology for image capture.
When X-rays strike a photostimulable phosphor material, what is released?
✅ a. Light
PSP plates release light when stimulated by a laser during image reading.
The exposure latitude of digital projection radiography responds in a ______ manner.
✅ b. Linear
Digital systems have a linear response, unlike the nonlinear response of film.
The acronym PACS stands for which of the following terms?
✅ d. Picture archiving and communication system
PACS manages image storage, retrieval, distribution, and display.
In what format must images be in so that they can be sent throughout the image viewing system?
✅ b. DICOM
DICOM is the standardized format that allows images to move between systems.
Patient demographics are unimportant because the RIS will automatically identify all digital images.
✅ b. False
Accurate patient identification and demographics are critical to avoid errors.
Digitally placed anatomic markers can always be used to determine the correct anatomic side of the patient.
✅ b. False
Physical lead markers are required; digital markers can be misleading.
Digital systems are less sensitive to scatter radiation than film/screen systems.
✅ b. False
Digital systems are actually more sensitive to scatter radiation, which can degrade image quality.