Picture Archiving and Communication System PACS
A picture archiving and communication system (PACS) is
a medical imaging technology which provides economical storage of, and
convenient access to, images from multiple modalities (source machine
types)
Electronic images and reports are transmitted digitally via PACS; this
eliminates the need to manually file, retrieve, or transport film jackets.
The universal format for PACS image storage and transfer is DICOM
(Digital Imaging and Communications in Medicine).
WHAT IS PACS:
 P:Picture, Image & Reports
 A:Archive, On Line, Near Line, Off Line
 C: Communication, Networking, Transfer
Protocols
 S: System, Components & Architecture
 PACS: For storage and distribution of images and
information when necessary
PACS
 Non-image data, such as scanned documents, may be incorporated using
consumer industry standard formats like PDF (Portable Document Format),
once encapsulated in DICOM.
 A PACS consists of four major components: The imaging modalities such as
 X-ray computed tomography (CT)
 magnetic resonance imaging (MRI)
 a secured network for the transmission of patient information
 workstations for interpreting and reviewing images, and archives for
the storage and retrieval of images and reports. Combined with available and
emerging web technology
PACS has the ability to deliver timely and efficient access to images,
interpretations, and related data.
PACS breaks down the physical and time barriers associated with
traditional film-based image retrieval, distribution, and display.
PACS – Types Of Images
 Most PACSs handle images from various medical imaging
instruments, including ultrasound (US), magnetic resonance
(MR), positron emission tomography (PET), computed
tomography (CT), endoscopy (ES), mammograms
(MG), Digital radiography (DR), computed radiography
(CR)ophthalmology, etc.
 Additional types of image formats are always being added.
Clinical areas beyond radiology; cardiology, oncology,
gastroenterology and even the laboratory are creating
medical images that can be incorporated into PACS.
PACS - Uses
PACS has four main uses:
 Hard copy replacement: PACS replaces hard-copy based means of
managing medical images, such as film archives. Digital copies are
referred to as Soft-copy.
 Remote access: It expands on the possibilities of conventional systems by
providing capabilities of off-site viewing and reporting (distance
education, telediagnosis). It enables practitioners in different physical
locations to access the same information simultaneously for teleradiology.
 Electronic image integration platform: PACS provides the electronic
platform for radiology images interfacing with other medical automation
systems such as Hospital Information System(HIS), Electronic Medical
Record (EMR), Practice Management Software, and Radiology
Information System (RIS).
 Radiology Workflow Management: PACS is used by radiology personnel
to manage the workflow of patient exams.
PACS Work Flow Diagram:
PACS workflow diagram
 The architecture is the physical implementation of required
functionality. Typically a PACS consists of a multitude of devices.
The first step in typical PACS systems is the modality.
 Modalities are typically computed tomography (CT), ultrasound,
nuclear medicine, positron emission tomography (PET), and
magnetic resonance imaging (MRI).
 Depending on the facility's workflow most modalities send to a
quality assurance (QA) workstation or sometimes called a PACS
gateway.
 The QA workstation is a checkpoint to make sure patient
demographics are correct as well as other important attributes of
a study.
PACS workflow diagram
 If the study information is correct the images are passed to the
archive for storage. The central storage device (archive) stores
images and in some cases reports, measurements and other
information that resides with the images.
 The next step in the PACS workflow is the reading workstations.
The reading workstation is where the radiologist reviews the
patient's study and formulates their diagnosis. Normally tied to the
reading workstation is a reporting package that assists the radiologist
with dictating the final report. Reporting software is optional and
there are various ways in which doctors prefer to dictate their
report.
PACS workflow diagram
 Ancillary to the workflow mentioned, there is normally CD/DVD
authoring software used to burn patient studies for distribution to
patients or referring physicians. The diagram above shows a typical
workflow in most imaging centers and hospitals.
 PACS include web-based interfaces to utilize the internet or aWide
Area Network as their means of communication, usually
via VPN (Virtual Private Network) or SSL (Secure Sockets Layer).
The client side software may use ActiveX, JavaScript and/or a Java
Applet.
 More robust PACS clients are full applications which can utilize the
full resources of the computer they are executing on and are
unaffected by the frequent unattended Web Browser and Java
updates.
PACS workflow diagram
 As the need for distribution of images and reports become more
widespread there is a push for PACS systems to support DICOM
part 18 of the DICOM standard. Web Access to DICOM Objects
(WADO) creates the necessary standard to expose images and
reports over the web through truly portable medium. Without
stepping outside the focus of the PACS architecture, WADO
becomes the solution to cross platform capability and can increase
the distribution of images and reports to referring physicians and
patients.
Querying (C-FIND) and Image Retrieval
(C-MOVE)
 The communication with the PACS server is done through dicom objects that are
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similar to dicom images, but with different attributes. A query typically looks as
follows:
The client establishes the network connection to the PACS server.
The client prepares a query object which is an empty dicom dataset object.
The client fills in the query object with the keys that should be matched. E.g. to
query for a patient ID, the patient ID attribute is filled with the patient's ID.
The client creates empty attributes (attributes with zero length string values) for
all the attributes it wishes to receive from the server. E.g. if the client wishes to
receive an ID that it can use to receive images (see image retrieval) it should
create the attribute SOPInstanceID with attribute tag (0008,0018) in the query
object with an empty value.
The query object is sent to the server.
The server sends back to the client a list of response dicom objects.
The client extracts the attributes that are of interest from the response dicom
objects.
Querying (C-FIND) and Image Retrieval
(C-MOVE)
 Images are retrieved from a PACS server through a C-MOVE
request, as defined by the DICOM network protocol.
 Typically a radiologist is looking for prior studies on a patient to
compare the progression of some pathology. In some cases prior
studies may be on an off-site archive or a long term storage device.
In the example being used, the radiologist or radiology technical
must query the off-site or long term archive for the prior exam(s).
The archive receives the C-FIND and if the C-FIND is successful the
archive invokes a C-MOVE on the study to the called AE Title, inturn sending the study from the archive to the device requesting the
study.
DICOM
(Digital Imaging and Communications in Medicine)
 DICOM is a standard for handling, storing, printing,
and transmitting information in medical imaging.
 It includes a file format definition and a network communications
protocol.
 The communication protocol is an application protocol that
uses TCP/IP to communicate between systems.
 It was developed by the DICOM Standards Committee, National
Electrical Manufacturers Association NEMA.
DICOM
Digital Imaging and Communications in Medicine
 DICOM enables the integration of scanners, servers,
workstations, printers, and network hardware from multiple
manufacturers into a picture archiving and communication
system (PACS).
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DICOM has been widely adopted by hospitals and is making
inroads in smaller applications like dentists' and doctors' offices.
 DICOM is the First version of a standard developed by American
College of Radiology (ACR) and National Electrical
Manufacturers Association(NEMA).
Derivations in DICOM standard
 DICONDE - Digital Imaging and Communication in
Nondestructive Evaluation, was established in 2004 as a way
for nondestructive testing manufacturers and users to share
image data.
 DICOS - Digital Imaging and Communication in Security was
established in 2009 to be used for image sharing in airport
security.[6]
DICOM Format
 DICOM differs from some, but not all, data formats in that it
groups information into data sets.
 That means that a file of a chest x-ray image, for example,
actually contains the patient ID within the file, so that the
image can never be separated from this information by
mistake.
 This is similar to the way that image formats such
as JPEG can also have embedded tags to identify and
otherwise describe the image.
DICOM Object
 A DICOM data object consists of a number of attributes, including
items such as name, ID, etc., and also one special attribute
containing the image pixel data .
 A single DICOM object can have only one attribute containing
pixel data. For many modalities, this corresponds to a single
image.
 3D- 4D data can be encapsulated in a single DICOM object. Pixel
data can be compressed using a variety of standards,
including JPEG, JPEG Lossless, JPEG 2000, and Run-length
encoding (RLE). LZW (zip) compression can be used for the
whole data set (not just the pixel data), but this has rarely been
implemented.
DICOM services
DICOM consists of many different services, most of which involve
transmission of data over a network.
Store
 The DICOM Store service is used to send images or other persistent
objects (structured reports, etc.) to a PACS or workstation.
Storage commitment
 The DICOM storage commitment service is used to confirm that an
image has been permanently stored by a device (either on redundant
disks or on backup media, e.g. burnt to a CD). The Service Class User
(SCU: similar to a client), a modality or workstation, etc., uses the
confirmation from the Service Class Provider (SCP: similar to a server),
an archive station for instance, to make sure that it is safe to delete the
images locally.
Query/Retrieve
 This enables a workstation to find lists of images or other such objects
and then retrieve them from a PACS.
DICOM services
Modality work list
 This enables a piece of imaging equipment (a modality) to obtain details
of patients and scheduled examinations electronically, avoiding the need
to type such information multiple times (and the mistakes caused by
retyping).
Modality performed procedure step(MPPS )
 A complementary service to Modality Work list, this enables the
modality to send a report about a performed examination including data
about the images acquired, beginning time, end time, and duration of a
study, dose delivered, etc. It helps give the radiology department a more
precise handle on resource (acquisition station) use.
 This service allows a modality to better coordinate with image storage
servers by giving the server a list of objects to send before or while
actually sending such objects.
Printing
 The DICOM Printing service is used to send images to a DICOM
Printer, normally to print an "X-Ray" film.