Digital Radiography and Pacs

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Review for digital radiography

Digital Imaging

any acquisition process that produces an electronic image that can viewed and manipulated on a computer.

Compare latent Analog & Digital cassette image formation.

Analog: Film placed on one or between two intensifying screens; X-rays strike screen, light is emitted, and film is exposed to light. Digital: X-rays strike phosphor, energy is deposited in the phosphor plate; energy is released from phosphor into image when stimulated by a focused laser light in reader.

CR (Computed Radiography or cassette based DR)

Digital acquisition modality that uses photostimulable phosphor plates to produce digital projection images.

DR (Digital Radiography) two types

Direct capture and Indirected Capture

DR - Indirect capture

absorbs x-rays by Scintillator Screen and converts them into light. The light is then detected by an area-CCD or thin-film transistor (TFT) array and then converted into an electrical signal.

DR - Direct Capture

x-ray energy is detected by a photoconductor that converts it directly to a digital electrical signal.

How is the latent image formed when using cassette-less DR?

Formed two ways: 1. Indirect Capture:- Uses a detector that produces light when struck by x-rays, and then the light is captured by CCD or TFT array and converted to an electrical signal. 2. Direct Capture:- Uses a detector that captures the x-ray energy and converts it directly to an electrical image.


Picture Archival and Communication System: - Is a networked group of computers, servers and archives that can be used to manage digital images. DICOM is the universal format for PACS.


Digital Imaging and Communications in Medicine: The standard for handling, storing, printing, and transmitting information in medical imaging.

PACS are made up of many different parts such as

reading stations, physician review stations, web-access, technologist quality control stations, administrative stations, archive systems, and many interfaces to various hospital and radiology systems.

Comparison of Conventional, Computed, and Digital Radiography


A Computer is

A programmable electronic device that can store, retrieve, and process data.

Define Binary Code, Bit, and Byte.

Binary Code = Computer language of 1's and 0's
Bit = A single unit of data
Byte = 8 Bits

Computer Consist of input, output, and processing devices

Input= Keyboard, mouse, scanner, barcode reader and microphone.
Output = Monitor, printer, and speaker
Processing = motherboard, microprocessor, BIOS, bus, memory, ports and CMOS.

3 Major types of Monitors

CRT = More responsive than LCD, can provide multiple resolutions, can sustain rough handling, less expensive. Bulky, heavy unit, not easily adjustable for viewing.
LCD = Takes up less space than CRT, consumes less power and produces less heat, little or no glare. Costs more, less of viewing angle, not as bright as CRT, only capable of working with one physical resolution.
Plasma = Widescreen with a thin depth, brighter than LCD, can be viewed at varying angles, light weight. High Cost, low availability.

Measurements used to classify monitor Quality are

Resolution, dot Pitch, refresh rate, aspect ratio, and viewable area.

Different types of OS Software

OS is the software that controls the computer hardware and acts as a bridge between applications and hardware. 4 types of OS Software are: 1. Real time - used to control specific machinery, such as X-ray consoles on modern X-ray equipment. 2. Single-user single task - Designed so that a computer can effectively do on task for one person at a time, such as handheld organizer. 3. Single-user, multitask -performs multiple functions such as OS on a PC. 4. Multiuser -Designed to handle multiple users and multiple tasks at the same time, such as a UNIX running on a large server or mainframe computer.

How are Computers utilized in the Radiology department?

Found throughout the radiology department, and has been chosen to fulfill a specific purpose.

How are networks Classified?

Two Major categories are LAN and WAN, there are two typical classifications of networks based on the roles that various components play: peer-to-peer and server/client-based.

A Network is defined as

two or more objects sharing resources and information.

A server is a

computer that manages resources for other computers, servers, and network devices. A client is a device that is found on a network that requests services and resources from a server. A thick-client is a computer that can work independently of the network and can process and manage its own files.

Physical connection among these devices are used through

Coaxial cable, twisted-pair wire, or fiberoptic cable.

Information is transmitted via a

NIC through a communication medium onto the network and possibly through a Network hub: Hub receives data from a device usually used for house and small office, Network switch: similar to hub but send data only to those devices to which the data is directed, Network bridge: created so that larger networks can be segmented or broken up into smaller networks, which can bring two or more network together, or Network router: A more sophisticated device, it can read portions of messages and direct them to their intended target, even if device is on separate network and uses different protocol.

Data travels along a network using an agreed-on set of rules known as a


Network Topology is the

physical layout of the connected devices on a network. There are four common topologic configurations: bus, ring, star and mesh.


Digital Imaging and Communication in Medicine: A universal standard for exchanging medical images among networked medical devices.

How is DICOM used?

acts networks communcation defines specific information objects and the functions (service classes) that can be performed on them.


HL-7 Standard oversees most clinical and administrative data such as demographics, reports, claims and orders.

HL-7 is used by

The HIS : holding the patients full medical information, from hospital billing to the inpatient ordering system. The RIS: Holds all radiology-specific patient data, from the patient scheduling information to the radiologist's dictacted and transcribed report.

What are the parts of the digital imaging cassette, and what purpose do the serve?

Cassette made of lightweight plastic material, backed by a think sheet of aluminum that absorbs x-rays. Instead of Intensifying screens inside there is antistatic material (usually felt) that protects against static electricity. Protects imaging plate from light and handling.

How is the imaging plate constructed?

image is recorded on thin sheet of plastic known as imaging plate constructed of ;
Protective layer: which is a very thin clear plastic that protects the phosphor layer.
Phosphor layer: which is photostimulable which "traps" electrons during exposure. Usually made from Barium fluorohalide family of crystals.
Reflective layer: sends light in a forward direction when released in the cassette reader.
Conductive layer: Absorbs and reduces static electricity.
Color layer: absorbs the stimulating light but reflects emitted light.
Support Layer: Semirigid material that gives sheet strength
Backing layer: Soft polymer that protects the back of Cassette.

What is Photostimulation, and purpose in the imaging plate?

It is the Phosphor or active layer that "Traps" electrons during exposure. This is then used to help laser excite the electrons to attain digital reading.

How is imaging plate read?

Reader uses a laser to scan the imaging plate, releasing the energy stored in the conductive layer as blue light. A photomultiplier amplifies the light and sends it to a signal digitizer which assigns a numerical value to each pixel in a matrix according to the brightness of light and its position.

How is the imaging plate erased?

Imaging plates are erased by exposing them to bright light such as fluorescent light.


are used to identify the cassette or imaging plate and is linked to patient during examination and processing.

Color labels on cassette

green or blue stickers indicating the top and left side of the cassette and or back of cassette indicating top right side of cassette. These stickers serve to orient patient along with line computer algorithm.

What is meant by matching the body part to be imaged with the examination menu selection?

Image Recognition is accomplished through complex mathematical computer algorithms, and if the improper part and/or position is selected, the image will not display properly. Improper menu selections may lead to overexposure and/or repeats.

How are technical factors chosen for each examination?

Just like in conventional radiography, optimum technical factors should be chosen for each examination.
kVp selected for type and amount of contrast desired.
mAs selected for necessary photon penetration of body part (Body Mass consideration needed). Care must be taken to no overuse mAs to avoid Quantum Mottle.
Collimation reduces area irradiated which will reduce the amount of scatter reaching the grid thus better digital image.

Why is the size of the imaging plate important?

CR digital images are displayed in a matrix of pixels. The pixel size is an important factor in determining the resolution of the displayed image. Smallest imaging plate results in highest spatial resolution. Therefore selecting size of imaging plate should be proportional to the size of the body part being imaged.

What determines the choice of imaging plate size?

Size of the body part being imaged.

Why is collimation important?

Collimation reduces area irradiated which will reduce the amount of scatter reaching the grid thus better digital image and lessens patient dose.


A black background added post-exposure, eliminating distractive light transmitting borders.

Why is it important to properly mark the patient's right or left side with radiographic markers?

Marking the patient examination at the time of exposure not only identifies the patients's correct side but also identifies the tech performing the examination, which covers you for any legality issues.

How do Major equipment manufacturers determine exposure indicators?

The light given off by the imaging plate is a result of the radiation exposure the plate has received. The light is converted into a signal that is used to calculate the exposure indicator number. Phillip=S (Sensitivity Number) Carestream NY =EI (Exposure Index), Agfa system = lgM (Logarith of the median exposure). As the number goes up exposure goes down.

A histogram is a

graphic representation of the numerical tone values of an x-ray exposure. This is determined by collimation borders and edges.

Imaging Plate Artifacts

Plate Artifacts
Plate Reader Artifacts
Image Processing Artifacts
Printer Artifacts

How are indirect cassettes-less imaging systems Constructed?

absorbs x-rays by Scintillator Screen and converts them into light. The light is then detected by an area-CCD or thin-film transistor (TFT) array and then converted into an electrical signal.

What is the difference between indirect and direct imaging systems?

Direct sensors absorb x-ray photons and immediately convert them to an electrical signal. where as Indirect uses a second step such as a CCD or CMOS to convert light into an electrical charge.

Amorphous Silicon Detectors, what are the conversion steps?

A type of Flat panel sensor, uses thin films of silicon integrated with arrays of photodiodes. These photodiodes coated with a crystalline Cesium lode (CsI) Scintillator. When the scintillator is struck by x-rays, visible light is emitted. Light is then converted into and electrical charge.

How does a CCD work?

the charge-couple device converts the light given off by the amorphous silicon detector into an electrical charge. This charge is stored in a sequential pattern and released line by line and sent to an analog-digital converter.

What is Detector quantum efficiency?

is used to measure the quality of a digital image by looking at the combination of the effects of noise and contrast on an imaging system. Basically how efficiently a system converts the x-ray input signal in to a useful output image.

Detector Size

is critical. Detectors must be large enough to cover the entire area to be imaged and small enough to be practical. If different parameters are used the image acquired will be incorrect.

What Factors affect Spatial resolution?

excessive processing, in an effort to alter image sharpness, can lead to excessive noise. Therefore the spatial resolution for direct detectors is dependent on the detector element size.

What is an image Histogram?

is a graphical representation of exposure values collected from the imaging plate.

How is the image histogram formed?

After The plate is scanned and the image location is determined, a value is placed on each pixel, and the histogram is generated displaying the minimum and maximum diagnostic signal.

What is the purpose of automatic rescaling?

When exposure is greater or less than what is needed to produce an image, automatic rescaling in an effort to display the pixels for the area of interest. Rescaling is no substitute for appropriate technical factors.

How does image latitude in digital imaging compare with film/screen radiography?

Exposure latitude is greater with digital imaging than with film/screen imaging because of the wider range of exposures recorded with digital systems.

What is the Nyquist theorem? How does it affect digital image processing?

when sampling a signal (analog to digital), the sampling frequency must be greater than twice the bandwidth of the input signal. Therefore if too few pixels are sampled, the result will be a lack of resolution.

What happens if the incorrect algorithm is applied to an examination?

Occurs when wrong anatomy part is selected therefore when image plate is scanned over/under exposing creating a unnecessary repeat.

What does image manipulation mean? Choices and functions?

Utilization of certain digital tools to slightly enhance image.
Window and Level = Controls contrast & Density
Shuttering = blackens the veil glare from collimation
Image orientation = Orientation of anatomy on imaging plate.
Image Stitching = When anatomy areas too large, multiple images will be stitched together.
Image Annotation = annotations overplayed digitally on image.
Magnification = Zooms in on desired image.

What are the major factors in image management?

Patient Demographics
- Patient name
- health care facility
- Patient Id number
- Date of Birth
- examination date


Picture Archival and Communication System: - Is a networked group of computers, servers and archives that can be used to manage digital images. DICOM is the universal format for PACS.

Different Type of PACS workstations?

- Display Workstation, the most interactive part of PACS
- Radiologist Reading station, Primary diagnosis. Highest quality hardware.
- Physician Review Stations, step down to radiologist reading station.
- Technologist QC stations, used to review images after acquisition.
- File Room/Image Management Stations, used to look up examinations for a physician or print copies for outside needs.

Define Workflow?

How a process is done, step by step:
Transcribed report
order entry
Exam Performed
Image Processed
Image Interpreted

System Architecture

Hardware and Software infrastructure of a computer system. Three common PACS architectures are:
Client/Server-Based Systems : Images sent directly to the archive server and images requested from Archive.
Distributed Systems (Stand Alone): Have local reading stations and hard rives before sent to main server.
Web-Based Systems: Uses Active server to manage workflow.

Advantage and Disadvantage of the three system architecture models?

Client/Server-Based Systems : Available anywhere with out other intervention, Archive is single point of failure.
Distributed Systems (Stand Alone): Local reading and workstations not interrupted if archive server goes down. Reliance on distribution of images done correctly.
Web-Based Systems: Can be utilized for Tele-radiology. Archive is single point of failure.

Most common function found on a PACS workstation?

- Navigation Functions
- Image Manipulation / enhancement Functions
- Image management Functions
- Advance workstation Functions

Specialized PACS workstation may be found in a hospital, and how are they used?

Technologist QC station advanced Functions: Stitching, common application for a full spine examination.

Image Archive

Computer components where records are stored digitally and preserved.

Two Major categories of the Image archive

1. Image manager/controller - Contains the master database of everything that is in the archive.
2. Image storage/server - Physical storage device of archive system.

Two types of Image storage/server

Short-Term storage: RAID (Redundant array of independent disk. Composed of several magnetic disks or hard drives linked together in an array.
Long-Term storage: RAID also used for long term as well as optical disk, tape and magnetic disk. Tape provides the greatest scalability of Long-Term Archive options.

Most Common RAID for PACS is?

RAID 5 because it provides adequate redundancy and fault tolerance.


Redundant Array of Independent Disk:
RAID 0: 'Striped', Data broken down and placed among all disks.
RAID 1: All data mirrored on 2 disks
RAID 3: Just like RAID 0 but one disk is set aside for error correction.
RAID 5: Similar to RAID 3 but error correction written into all disks.


Company that provides outsourcing of archiving and management functions for a pay-per-use or pay-per-month charge.

How does a laser digitizer digitize a film? (Scanner)

uses helium neon laser beam to convert the analog film image into a digital image.

How does a CCD digitizer digitize a film? (Scanner)

uses fluorescent bulbs that shine through the film and a CCD array that detects the light and transforms the light into an electrical signal.

Common uses of a digitizer? (Scanner)

- Transfer Films from off-site clinics to the main department for primary reading
- Compare old films
- Film Duplication

Wet laser Imager (Printer)

use chemicals to process the film that has been exposed to the laser.

Dry laser Imager (Printer)

uses HEAT to process the latent image that is etched into the silver emulsion by the laser.

Common uses of Film Imagers

- Backup
- For locations without PACS
- Outside Physicians
- Legal cases
- Teaching Purposes

How are CD/DVD burners used in a radiology department?

A CD/DVD burner can burn images to be shared outside of the radiology department. Along with the images, a DICOM viewer is burned to the disk for ease of viewing.

Quality Assurance (QA)

Systematic observation and assessment of different aspects of a project, service or facility to make certain that QA is being met.

Quality Control (QC)

Comprehensive set of activities to monitor and maintain systems.

Continuous quality improvement (CQI)

tends to focus on the process rather than on the people or the service. The belief is If process is good, health care workers will follow.

Monitor QC

Daily QC: Retrieve a QC monitor test pattern, General image quality, geometric distortion, verify 16 luminance meter or photometer.
Monthly/Quarterly QC: Same as daily plus Test pattern Contrast Ratio Test TG18-CT, Depth Resolution TG18-MP, Luminance Uniformity TG18-UN10 and TG18-UN80.

Laser Imagers QC

Wet Laser Imager Daily/Weekly QC:
- Monitor Film Printed
- Print a test Pattern
- Measure steps on test pattern
- Monitor the processing mechanism
- Preventative maintenance schedule
Dry Laser Imager Daily/Weekly QC: Same as wet laser.

Speed and Data integrity QC

Processing speed of the workstation and the image retrieval/transfer rate. Monitor 1-2 weeks of procedure and utilize those stats to compare to future times.

QA activities used in digital radiology:

- Daily and Monthly/quartely monitor QC
- Printer image quality
- Speed assessment
- Data QC

Total quality management

Three areas define digital image quality:
- Contrast
- Resolution
- Noise
These must be monitored to avoid unnecessary repeat examinations and overexposure to patients and staff. Because review of images relys heavily on these hardware equipment, it is impairative that QC and correct calibration should be a stand in the workplace.

Technologist Daily QC duties

- Inspect and clean cassettes
- Inspect hing and latch
- Erase imaging Plates
- Verify digital interfaces and network transmission
- Inspect laser printer

Technologist Weekly QC duties

- Clean and Inspect receptors
- Clean air intakes of CR reader
- Clean CRT screen
- Clean computer keyboard and mouse

Technologist Monthly QC duties

Reject or Repeat analysis:
- Reason
- Positioning errors
- Marker errors
- Equipment malfunction errors

Clean Imaging plates
Artifact Identification
Problem reporting

Reason for QC

to avoid errors and equipement malfunction providing unnecessarry exposure to the patient.

Service Personnel Responsibilites

There are many services that should only be serviced by correct service engineer such as:
- X-ray generator, tube and reader
- Phosphor accuracy testing
- Image processing functions
- Image display testing
- Reader erasure functions
- Spacial frequency response testing

Radiation Physicist's Responsibilities

Semiannual/Annual QC:
- Maintain base-line vlaues
- Exposure trends
- Reject rate analysis
- QC record review
- Service history analysis

Important to know how Artifacts occur

Artifact Identification is important because it can produce a trend of occurances than can help pinpoint where the issue is arrising. eg. Several reports are recieved from a particular room that images are exessivley noisy or too light, the room may need to be inspected for system interference or AEC recalibration.

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