Radiography Technology Quiz

Chapter 1: Introduction to Digital Radiography and Picture Archiving and Communication System

• This chapter introduces digital radiography and Picture Archiving and Communication Systems (PACS)
• Digital imaging is an image acquisition method that produces electronic images.
• The term digital imaging was first used in the 1970s with the development of computed tomography (CT).
• Digital images can be viewed and manipulated on computers.
• Digital images can be networked to various locations.
• Teleradiology is the movement of images via telephone lines to remote locations.
• The concept of teleradiology began with Albert Jutras in Canada in the 1950s.
• Early PACS systems were developed in the 1980s with U.S. government support for the U.S. military to transfer images between battlefields and VA hospitals.

Objectives

• Define digital imaging.
• Explain latent image formation for film/screen (F/S) radiography.
• Compare and contrast latent image formation 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).

Key Terms

• Digital imaging
• Direct capture digital radiography
• Flat panel detector (FPD)
• Indirect capture digital radiography
• Photostimulable phosphor (PSP) image capture
• Teleradiology

Conventional Film/Screen Radiography

• Uses film and intensifying screens (F/S) in image production.
• Film is placed on one or between two intensifying screens.
• Screens emit light when struck by x-rays.
• Light and x-rays expose the film.
• The film is processed chemically.
• The manifest image on the film is viewed on a lightbox.

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.

Photostimulable Phosphor (PSP)

• Previously known as computed radiography (CR).
• More accurate than computed radiography and avoids confusion.
• 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.
• 2018 will drive a decrease in PSP use.

PSP Image Capture

• Equipment includes existing radiographic equipment, PSP storage plates, PSP reader, technologist QC workstation, viewing station (a printer, or both).
• Storage phosphor plates are similar to intensifying screens.
• Store x-ray energy for an extended time.

CR Detector

• Photostimulable Storage Phosphor (PSP)
• BaFBr compound, Eu activated
• Phosphor plate or imaging plate ("IP")

Flat Panel Detectors (FPDs)

• Uses an x-ray absorber material coupled to a TFT, CMOS, or CCD to form the image.
• May retrofit existing rooms or use portable detectors in existing equipment.
• Two types of FPD: indirect capture and direct capture.

Flat Panel Detectors (1 of 2): Indirect Capture

• Device absorbs x-rays and converts them to light.
• Light is collected by an area-CCD, CMOS, or TFT.
• Converted into electrical signals.
• Electronic signal is sent to ADC.
• Computer processes electrical signals to images.
• Images are viewed on a monitor.

Flat Panel Detectors (2 of 2): Direct Capture

• 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.

Comparison of Film/Screen to Digital Imaging

• Equipment efficiency ratings.
• Conventional F/S and PSP are about the same efficiency.
• FPD is much more efficient as images are available immediately.

Comparison: Latent Image Formation (Film/Screen)

• Film placed inside 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.
• Silver ions are attracted to equal out the charge.
• This process happens many times within the emulsion to form a latent image.
• After chemical processing, the sensitivity specks are processed into black metallic silver, and the manifest image is formed.

Comparison: Latent Image Formation (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 photon energy is deposited within the phosphor particles, creating a latent image.
• Plate is then fed through the PSP reader.
• A focused laser scans the plate.
• Electrons return to their original state, emitting light in the process.
• The light is picked up by a photomultiplier tube and converted into an electrical signal.
• The electrical signal is sent through an ADC to produce a digital image.

Comparison: Latent Image Formation (FPD)

• No cassettes are required.
• Image acquisition device is built into the table or wall stand or is enclosed in a portable device.
• Processing time is 3-5 seconds.
• Two image acquisition methods: indirect capture and direct capture.
• Indirect capture is like PSP in that x-ray energy stimulates a scintillator, which gives off light 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.

Comparison: Latent Image Formation (Film/Screen -continued)

• Image is determined by the shape of the film's response curve and processing chemicals.

Comparison: Latent Image Formation (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 integrated within the console, and image is processed before the next exposure.

Comparison: Exposure Response and Image Characteristics (Film/Screen)

• Radiographic contrast is primarily controlled by kVp.
• Optical density on film is primarily controlled by mAs.
• Exposure latitude is narrow.

Comparison: Exposure Response and Image Characteristics (PSP and FPD)

• Exposure latitude is replaced with dynamic range and is now 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.

Comparison: Scatter Sensitivity and Noise

• All three image capture systems are sensitive to scatter.
• PSP and FPD can be more sensitive to scatter than screen/film.
• Quantum mottle resulting from low mAs values is seen on all three image capture systems.

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 the name to take storage and archiving out.
• Ability to be manipulated for interpretation by physicians, allowing it to fall into the category of medical devices (2021).

Medical Storage Device

• Physical hardware 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.
• Uses simple image manipulation tools (window/level, pan/zoom, measurements).

MIMPS Uses

• Image manipulation tools.
• Radiologist reading stations.
• Complex image processing.
• Enhancements.
• Reconstruction.

Transitioning from Film/Screen to Digital Imaging

• Patient demographics are more important with digital imaging.
• Incorrect or incomplete data can make retrieval impossible.
• The correct image must be placed into the correct data file.
• Technologist markers and post-processing are important for correct image capture.
• Every effort should be made to appropriately mark the side of the patient.
• Post-processing labels should annotate patient position and timing.
• Images are sent to MIMPS for interpretation after viewing and processing.

Summary (1 of 2)

• Digital imaging is an image acquisition process that results in an electronic image viewable and manipulatable on a computer.
• PSP systems are a digital acquisition modality using photostimulable phosphor plates to produce digital images.
• FPDs are divided into indirect and direct capture.
• Indirect capture detectors receive x-rays that are converted to light, captured, and converted to an electrical signal.

Summary (2 of 2)

• Direct capture converts x-ray energy directly into an electrical signal.
• PACS are networked groups of computers, servers, and archives used to manage digital images.
• DICOM is a standard that allows imaging modalities and PACSs to communicate.
• MIMPS consists of many parts, such as radiologist reading stations, physician review stations, web access, technologists QC stations, administrative stations, archive systems, and various interfaces for hospitals and radiology systems.