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Picture Archiving And Communication System Pacs
I. Introduction
Timely management of medical imaging information is one of the greatest challenges facing medicine today. Patients with complex medical problems may require a large number of radiologic studies, which may be performed at physically separate locations; as a result, preexisting studies may be inadvertently duplicated. Simultaneous access to radiologic images may be needed for accurate interpretation. In addition, multiple physicians caning for a patient may want to review the images. As medical centers increase in size, illnesses increase in complexity, and the demand for rapid transfer of information increases accordingly, the capacity of film-based radiologic systems to meet these demands decreases. Films are often unavailable or lost, and film storage costs are relatively high. Systems designed to store images in computers and display them on high-resolution monitors have been developed over the past 10-12 years. These picture archiving and communication systems (PACS) attempt to overcome the limitations of film-based systems by providing economical storage, rapid retrieval of individual images, access to images acquired with multiple modalities, and simultaneous access to the same image at multiple sites. However, acceptance of this new technology has been limited by high capital costs, limited spatial resolution of the display monitors, limited spatial resolution of digitization modalities for projection radiography, slow image display (compared with that in film-based systems), and the need for system redundancy to provide backup in case of component failure. Most PACS in current use are prototypes intended for research, although recently some have been incorporated into segments of larger radiology department
PACS are computers or networks dedicated to the storage, retrieval, distribution and presentation of images. The medical images are stored in an independent format. The most common format for image storage is DICOM (Digital Imaging and Communications in Medicine). Most PACSs handle images from various medical imaging instruments, including ultrasound (US), magnetic resonance (MR), positron emission tomography (PET), computed tomography (CT), endoscopy (ENDO), mammograms (MAMMO), digital radiography (DR), computed radiography (CR) etc.
II. Picture archiving and communication system
The principles of PACS were first discussed at meetings of radiologists in 1982. Various people are credited with the coinage of the term PACS. Cardiovascular radiologist Dr Andre Duerinckx reported in 1983 that he had first used the term in 1981. Dr Samuel Dwyer, though, credits Dr Judith M. Prewitt for introducing the term. Dr Harold Glass, a medical physicist working in London in the early 1990s secured UK Government funding and managed the project over many years which transformed Hammersmith Hospital in London as the first filmless hospital in the United Kingdom. Dr Glass died a few months after the project came live but is credited with being one of the pioneers of PACS Organizational techniques that enable small departments to function efficiently often fail as departments become larger. With the recent growth in imaging technology, the capacity of film-based systems to meet the increasing needs of radiology departments has decreased. Electronic PACS have been developed in an attempt to provide economical storage, rapid retrieval of images, access to images acquired with multiple modalities, and simultaneous access at multiplies sites. Input to a PACS may come from digital or analog sources (when the latter have been digitized). A PACS consists primarily of an image acquisition device (an electronic gateway to the system), data management system (a specialized computer system that controls the flow of information on the network), image storage devices (both short- and long-term archives), transmission network (which serves local on wide areas), display stations (which include a computer, text monitor, image monitors, and a user interface), and devices to produce hard-copy images (currently, a multiformat or laser camera). The goals of PACS are to improve operational efficiency while maintaining or improving diagnostic ability. A. Image Acquisition Modules
An image acquisition device is an electronic gateway to the PACS and may be an analog-to-digital converter or device that passes along digital information from a digital imaging device. The number of acquisition modules necessary for a PACS to function varies with the system and is based on its size and the mix of analog and digital input devices.
B. Data Management System
The data management system is a specialized computer that controls the
network, image storage devices, and image acquisition devices in order to maintain orderly traffic flow in the system. This computer manages patient information and images as well as the associated reports. The data management system must provide short- and long-term archiving capabilities. Usually, the short-term archive employs magnetic media, and the long-term archive employs optical media. The short-term anchive has low capacity but is frequently used (ie, high utilization), whereas the long-term archive has high capacity and low utilization.
C. Transmission Network
Data for images, text, and system commands are transmitted over networks serving local or wide areas. The network medium could be a twisted-pain wire, coaxial cable, on fibenoptic cable. A variety of network topologies (eg, star) are available, each with its own advantages and disadvantages. In addition, several
communication protocols (eg, transmission control protocol/internet protocol [TCP/IP]) exist for managing the information on the network. These protocols provide instructions on how data will be moved on the network.
D. Image Display Stations
Image display stations are the principal area of physician interface with a PACS. A display station includes a computer with local stunage, a text monitor, a variable number of image monitors, and a user interface. A display station that can duplicate the full range of tasks, speed of display, and spatial resolution available with film systems has not yet been constructed. In fact, the cost of creating such
a station would be formidable. To help minimize the potential costs, studies have been undertaken to determine the minimal spatial and contrast resolution necessary to perform a variety of imaging tasks. This information may then be used to create a series of workstations with different levels of sophistication so that appropriate equipment may be selected for the task at hand.
E. Hard-Copy Devices
Although the major mode of storage and display with a PACS is electronic, provision must also be made for creating a conventional im age on x-ray film. Multiformat cameras on laser cameras are currently the most common way of meeting this demand.
F. Interfaces to Other Systems
To function properly, the image management system must interface with other patient care management systems. These include but need not be limited to a radiology information system (IllS) and a hospital information system (HIS). The goals of interfacing the PACS to an RIS and an HIS are to maintain data integrity across the global system and to optimize the performance of each component system by using only the specific data needed fon each. The 1115 provides basic patient histories, reporting of results, and collection of data for department management. The HIS manages the demographic standards and distributes patient care information throughout the medical center.
III. A Radiologic Picture Archiving and Communication System for a Coronary Care Unit
I chose the radiologic picture archiving and communication system for a coronary care unit (CCU) at a 700-bed teaching hospital ,as an example in my project for PACS. The major components of this PACS module are located in the Radiology Department and are shared with the Pediatric Radiology PACS. An important design goal was to create a system in which acquisition, routing, and management of patients' image data are accomplished with minimal operator intervention. The automatic acquisition of images is achieved through linkage of a computed radiography (CR) unit, FCR-1 01 (Fuji Photo Film, Kanagawa, Japan) to an external host, VAX-i i /750 minicomputer (Digital Equipment Corporation, Maynard, MA.) These two components are integrated through an interface unit that was developed in-house. The host computer is used to manage the processing and flow of data from creation, storage, and archive to display.
Under normal conditions, the only manual operation required for data input and subsequent management of the data base is the entry of the patient's name, hospital identification (ID) number, and hospital section code at the CR console. This task is performed by the X-ray technologist at the time the imaging plate is processed. Once this is completed, the remainder of the process is fully automated. The software that is resident on the host computer detects the incoming imaging plate and initiates the data transfer from the CR unit. The hospital section code is used to route the image to an appropriate data base (in this case, the CCU data base). The raw image data acquired at 2048 x 2048 x 8 bit resolution are reformatted into the standard image file structure defined for the
PACS and then archived. Subsequently, the image file is subsampled to 51 2 x 51 2 x 8 bit resolution for display purposes and the patient directory is updated to include the new entry. Active patient images are stored on magnetic disk for rapid access. Forty-five megabytes of disk space have been allocated for the CCU data base, which provides a maximum of 180 images on-line. The images are also automatically archived to an optical disk library unit manufactured by Filenet Costa Mesa, CA) and Hitachi (Tokyo, Japan). When a patient is selected at the user terminal in the CCU, the image files are loaded on a Gould 1P8500 image processor (Fremont, CA), and the video output signals are transmitted in real-time to the CCU via a broadband network. Three channels are multiplexed with Blonder-Tongue video modulators (Oldbridge, NJ) operating with 8-MHz bandwidths. The viewing station in the CCU consists of three 13-in. (30-cm) diagonal, 5i 2-line display monitors (Panasonic Industrial Company, Secaucus, NJ) and a VT-i 00 terminal for user interface.
A. User Interface
The user interacts with the system through a VT-i 00 terminal keypad. A directory of patients and various image manipulation functions are provided in a menu format. In a typical viewing session, the clinician first selects a patient from the alphabetic active-patient directory. The terminal prompts the user to wait while the data base is searched. Images appear on the three monitors in reverse chronological order, starting with the most recent image (Fig. 2). The information appearing at the bottom portion of the image includes the patient's name and hospital identification number, as well as the date and time of image acquisition. At this point, the viewer may return to the directory, view more images of the current patient, or apply an image manipulation function. The image manipulation functions include zoom (by pixel replication), mean-and-window, grayscale inversion, left-right reversal, and image rotation.
B. Data Bases
The data bases use the indexed sequential access method (ISAM) files. The record for the patient data base contains information such as the patient's name, hospital identification number, number of images acquired to date, and the image code, which is issued automatically when the patient is entered into the data base for the first time. The image code also serves as the primary key for the image data-base record, which provides information associated with the individual image file, including the date of acquisition, procedure, current location of the image (magnetic disk, optical disk, or both), and the volume and physical address of the optical disk archive. The images are deleted from the magnetic disk according to a probability algorithm that determines which images are least likely to be reviewed.
For a returning patient, the most recent image is retrieved.
automatically from the optical disk library for comparison purposes.
C. Clinical Operation
The CCU is one of the largest intensive care units in the hospital. It is located five floors above and 1000 ft. (300 m) away from the Radiology Department. This busy unit has an average daily occupancy of 25.9 patients, and the average duration of stay in the unit is 4.4 days. During their stay in the CCU, 72% of patients have at least one chest radiograph. On the average, 10 chest examinations are performed each day, about half of them with a mobile unit. Because use of the mobile unit is often indicative of the critical condition of the patient, a protocol has been established to make these images (about five examinations per day) immediately available to the CCU physicians through the digital viewing system. Traditionally, in order to view films, the physician would have to walk to the Radiology Department to check out the patient's film jacket, a procedure that can be quite time-consuming. After a month long preclinical trial, the system was released to the CCU physicians for their use. The system was available at all times, and physicians could choose between the film-based viewing system and the digital viewing system. The decision to release the system for clinical use without restriction was based on the premise that the functionality of a computer-based system ought to be defined and evaluated within the normal task environment. The usage and performance of the system were logged into a file to provide (1) the name and hospital identification number of the patient reviewed, (2) the date and time of viewing, (3) image manipulation function(s) used, (4) the identification of the image manipulated, and (5) the speed of various operations.
IV. DICOM Images
DICOM stands for Digital Imaging and Communications in Medicine. Its standard was created by the National Electrical Manufacturers Association (NEMA) to aid the distribution and viewing of medical images, such as CT scans, MRIs, and ultrasound. Part 10 of the standard describes a file format for the distribution of images. This format is an extension of the older NEMA standard. Most people refer to image files which are compliant with Part 10 of the DICOM standard as DICOM format files. A single DICOM file contains both a header (which stores information about the patient's name, the type of scan, image dimensions, etc), as well as all of the image data (which can contain information in three dimensions). This is different from the popular Analyze format, which stores the image data in one file (*.img) and the header data in another file (*.hdr). Another difference between DICOM and Analyze is that the DICOM image data can be compressed (encapsulated) to reduce the image size. Files can be compressed using lossy or lossless variants of the JPEG format, as well as a lossless Run-Length Encoding format (which is identical to the packed-bits compression found in some TIFF format images).
A. The DICOM header
The below Image shows a hypothetical DICOM image file. In this example, the first 794 bytes are used for a DICOM format header, which describes the image dimensions and retains other text information about the scan. The size of this header varies depending on how much header information is stored. Here, the header defines an image which has the dimensions 109x91x2 voxels, with a data resolution of 1 byte per voxel (so the total image size will be 19838). The image data follows the header information (the header and the image data are stored in the same file).Furthermore, the DICOM header is shown. The DICOM requires a 128-byte preamble (these 128 bytes are usually all set to zero), followed by the letters 'D', 'I', 'C', 'M'. This is followed by the header information, which is organized in 'groups'. For example, the group 0002hex is the file meta information group, and (in the example on the left) contains 3 elements: one defines the group length, one stores the file version and the third stores the transfer syntax.
The DICOM elements required depends on the image type. For example, this image modality is 'MR' (see group : element 0008:0060), so it should have elements to describe the MRI echo time. The absence of this information in this image is a violation of the DICOM standard. In practice, most DICOM format viewers (including MRIcro and ezDICOM) do not check for the presence of most of these elements, extracting only the header information which describes the image size.
The NEMA standard preceded DICOM, and the structure is very similar, with many of the same elements. The main difference is that the NEMA format does not have the 128-byte data offset buffer or the lead characters 'DICM'. In addition, NEMA did not explicitly define multi-frame(3D) images, so element 0028,0008 was not present.
Of particular importance is group : element 0002:0010. This defines the 'Transfer Syntax Unique Identification'. This value reports the structure of the image data, revealing whether the data has been compressed. Note that many DICOM viewers can only handle uncompressed raw data. DICOM images can be compressed both by the common lossy JPEG compression scheme (where some high frequency information is lost) as well as a lossless JPEG scheme that is rarely seen outside of medical imaging (this is the original and rare Huffman lossless JPEG, not the more recent and efficient JPEG-LS algorithm). Note that as well as reporting the compression technique (if any), the Transfer Syntax UID also reports the byte order for raw data. Different computers store integer values differently, so called 'big endian' and 'little endian' ordering. Consider a 16-bit integer with the value 257: the most significant byte stores the value 01 (=255), while the least significant byte stores the value 02. Some computers would save this value as 01:02, while others will store it as 02:01. Therefore, for data with more than 8-bits per sample, a DICOM viewer may need to swap the byte-order of the data to match the ordering used by your computer.
In addition to the Transfer Syntax UID, the image is also specified by the Samples Per Pixel (0028:0002), Photometric Interpretation (0028:0004), the Bits Allocated (0028:0100). For most MRI and CT images, the photometric interpretation is a continuous monochrome (e.g. typically depicted with pixels in grayscale). In DICOM, these monochrome images are given a photometric interpretation of 'MONOCHROME1' (low values=bright, high values=dim) or 'MONOCHROME2' (low values=dark, high values=bright). However, many ultrasound images and medical photographs include color, and these are described by different photometric interpretations (e.g. Palette, RGB, CMYK, YBR, etc). Some color images (e.g. RGB) store 3-samples per pixel (one each for red, green and blue), while monochrome and paletted images typically store only one sample per image. Each images store 8-bits (256 levels) or 16-bits per sample (65,535 levels), though some scanners save data in 12-bit or 32-bit resolution. So a RGB image that stores 3 samples per pixel at 8-bits per can potentially describe 16 million colors' (256 cubed).
B. ezDICOM
The ezDICOM is a software that is easy to use, mature (stable, few if any bugs) and can view a wide range of medical images including proprietary formats as well as images in the DICOM standard. For example, In addition, most free DICOM viewers only read a small subset of the DICOM images available, while ezDICOM can view a broad range of images. In addition to DICOM images, the software will automatically recognize and display Analyze, GE (LX, Genesis), Interfile, Siemens (Magnetom, Somatom) and NEMA images. The greatest strength of ezDICOM is that it is free and open source. There are many variations of medical images 'in the wild' - many of these are poorly or incorrectly documented. By being free, ezDICOM has developed a wide user base, and this ensures the quality of the code. Thousands of people have used ezDICOM and sent in unusual and rare images, and the code is now mature and able to read virtually all the popular medical images.
Therefore, the users are the most important strength of this software. It is important to acknowledge the many people who shared their images with the developers. The advantage of being open source is that programmers can modify and improve the code if they want. The project was started by Wolfgang Krug and has been expanded and maintained by Chris Rorden. Development was particularly aided by Earl F. Glynn's general programming tutorials and David Clunie's medical imaging FAQ. This software is covered by the BSD open source license. You can distribute both compiled projects and the source code. However, you should also distribute the license (the compiled standalone program makes this easy: the license is built into the 'about' window). The license also notes that the software is provided 'as is', use it at your own risk. This software attempts to reproduce medical images accurately. However, it is not designed for clinical use: computer monitors can vary tremendously in image quality. All grayscale images are rendered in 256-levels of gray.
The standalone ezDICOM for windows program is a basic but useful tool for viewing medical images. This software will run on computers with Windows 95 or later and requires less than 300 Kb of disk space. To view an image, you simply drag and drop the image onto the program (or you can choose 'Open...' from the 'File' menu). Despite the ease of use, ezDICOM has a number of powerful features. For example, you can set the brightness and contrast of an image with great precision. You can also animate images that have multiple slices (e.g. see a heart beating over time or see different depths into the brain). The ezDICOM standalone application [version 1, release 19] is free software and is distributed as a compressed zip file - simply extract the files and double click on ezDICOM.exe. Delphi source code is also included, and a personal edition of this compiler is available for free.
D. DCM2JPG console application
DCM2JPG is a simple command-line Windows program. If you drop a file on the program it will create a JPEG version of the file (alternatively, if you name the program 'dcm2png.exe' or 'dcm2bmp.exe' it will create PNG or BMP format images). You can also call the program from the command line, to do special functions like change the image brightness or contrast (most grayscale DICOM images have much higher precision than can be saved to standard bitmap formats). Another nice feature is the ability to create nice zoomed versions of DICOM images - e.g. save a 128x128 pixel image as a 192x192 pixel bitmap (scaling is done using a bilinear-interpolation method to reduce any jaggy edges). Both a compiled program and the (ezDICOM-based) source code can be downloaded from the internet. The program has some command as follows:
b Brightness [window center]: a,h,-9999..9999 for auto, header, custom default: auto
c Contrast [window width]: a,h,0..9999 for auto, header, custom default: auto
-f Format of Output: b,p,j, txtfor bmp, png, jpg, txt default: jpg
-o Output Directory, e.g. 'C:TEMP' default: source directory
-s Silent [errors not reported]: y,n for yes or no default: no
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-z Zoom of Output, e.g. ''1.5'' for 150% zoom default: 1.0
V. Conclusion
This report gave brief description about Picture archiving and communication system PACs. It explains its setup components and how it works through an example of a Radiologic Picture Archiving and Communication System for a Coronary Care Unit. It show also the format of the file extension of the image of the PACs and how it can be shown in ezDICOM software. However, output format of the ezDICOM is can be converted easily to other format according to the requirements such as jpg by using simple software called DCM2JPG console application. It is really interesting in this life to see how science affected the life of the human being.
About the Author
- Senior Telecommunication Specialist in Arab National Bank (ANB).
- B.S Electrical Engineering in 1997 from King Fahd university of Petroleum and Minerals (KFUPM).
- KFUPM MBA in 2002.