Digital Imaging and Communications in Medicine (DICOM)

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202 Chapter 9 DICOM Associations If at least one of the proposed contexts was accepted by the called AE, we have every reason to expect to receive the A-Associate-AC message, meaning that our DICOM association has been successfully established, and we can proceed with the actual data transfer. DICOM overhead? It has become commonplace (especially on the part of PACS manufacturers) to blame DICOM for communication overhead. Every single time we exchange information with another DICOM AE, A-Associate messages must be exchanged and an association must be established. In fact, most PACS companies often prefer to use their own proprietary data exchange protocols, at least between their own devices, to escape DICOM association complexities. Indeed, on a slow network, with frequent delays and interruptions, DICOM association establishment can take a second or two. If you have to transmit tons of small images, each one using its own C-Store handshake, these delays accumulate. However, nothing flows fast on a slow network. Let’s not forget that the main part of any DICOM networking is image data transfer. Images (megabytes in size) are much larger than A-Associate messages (where every single byte counts). Even if you have to establish a new association for every image in a 1000-image study being transferred, 99% of the transfer time will be consumed by the image data. On the other hand, the DICOM association mechanism provides us with a universal and flexible data communication protocol, which is much more important than gaining a fraction of transfer time. Another (and in fact, more real) aspect of DICOM overhead has nothing to do with networking and occurs because of DICOM data encoding. Complex DICOM data objects have to be built and parsed to encapsulate information. This becomes particularly important when large image data are affected. For example, image compression techniques, meant to reduce data size on the network, will load the CPU, compressing and decompressing image bytes, thus contributing to perceived time delays. So, I would never rely on “DICOM vs. FTP” network comparison charts: these tests compare oranges to apples, and depend on many nonnetworking aspects. DICOM-to-proprietary data conversions, which are often performed inside many PACS, also contribute to processing delays. But, once again, this has little to do with DICOM per se.
9.8 Protocol Data Unit 203 9.8.3 A-Associate-RJ The A-Associate-RJ message is used to reject a proposed association request (A-Associate-RQ). As we have already mentioned, the reasons for rejections can be many: incompatible devices, unsupported transfer protocols, invalid format, and so on. Unlike the A-Associate-RQ and the A-Associate-AC, which we have considered in all their complexity, the A-Associate-RJ message is really quite simple (Fig. 65). The only parameters to be supplied here are: 1. Result. This field can be either 1 (rejected-permanent) or 2 (rejected-transient). Transient rejection can correspond to temporary problems (network congestion), but more common permanent rejection indicates mismatched association parameters, incompatible device profiles, and such. 2. Source. This can be 1, 2, or 3 depending on the current provider and protocol type. The most typical code is 3, corresponding to service provider rejection. 3. Reason. This can take a code value from 1 to 8. You can find them all in PS3.8, but the most typical reason code you will encounter in your practical experience will unfortunately be 1, standing for “no reason given”. Because the choice of result, source, and reason codes is left to the rejecting application, it really depends on how explicit it wants to be about the rejection cause. In other words, even if you set reason, source, and result codes in the A-Associate-RJ to whatever codes you like, this will not change the outcome because none of these fields is meant for further processing. Simply, the association will be rejected, all association-related processing will stop, and (if we have a good piece of software) some error message will be written in the participating AEs error logs. Fig. 65 A-Associate-RJ message structure, from PS3.8, and its most typical example
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Oleg S. Pianykh Digital Imaging and
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Oleg S. Pianykh, Ph.D. Department o
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Foreword VII Foreword Digital Imagi
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X Foreword so technically challengi
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Contents XIII Contents Part I: Intr
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Contents XV 7.2.4 The Verification
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Contents XVII 12.2 Testing, Testing
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abbreviations 3D Three-Dimensional
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Part I: IntroductIon to dIcoM
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4 Chapter 1 What is DICOM? Fig. 1 M
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Chapter 2 How Does DICOM Work? “E
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Establishment-DICOM handshake, when
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12 Chapter 3 Where Do You Get DICOM
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18 Chapter 4 A Brief History of DIC
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20 ACR-NEMA vs. DICOM Chapter 4 A B
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22 ACR-NEMA 2.0 Chapter 4 A Brief H
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5.1 IT Boot Camp 25 Chapter 5 Parle
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5.2 Text vs. Binary 27 consisting o
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5.3 DICOM Grammar: Value Representa
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5.4 DICOM Data Dictionary 43 Table
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5.4 DICOM Data Dictionary 45 5.4.2
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5.5 DICOM Objects 47 mation and com
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5.5 DICOM Objects 49 Table 5 Implic
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5.5 DICOM Objects 51 Table 9 Explic
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5.5 DICOM Objects 53 5.5.2 Encoding
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5.5 DICOM Objects 55 2. Modifying a
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5.5 DICOM Objects 57 change the pri
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5.5 DICOM Objects 59 Table 11 SQ en
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5.5 DICOM Objects 61 mark the end o
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5.5 DICOM Objects 63 5.5.6 Required
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5.5 DICOM Objects 65 5.5.8 Unique I
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5.6 DICOM Information Hierarchy 67
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5.7 Modules, IODs, and Information
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86 Chapter 6 Medical Images in DICO
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88 Fig. 20 Storing pixel sample bit
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94 CAD and lossy compression Chapte
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98 6.2.4 Choosing the Right Compres
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100 Chapter 6 Medical Images in DIC
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Part III: DICOM COMMunICatIOns
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116 Chapter 7 DICOM SOPs: Basic net
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118 Connecting the unconnectable Ch
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120 7.2 Services and Data Chapter 7
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122 Fig. 34 Building DICOM Message
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124 Table 21 C-Echo-Rsp: responding
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126 Table 22 C-Echo-Rq in a final D
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128 Table 23 C-Echo-Rsp in final DI
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130 7.2.3 Service-Object Pairs Chap
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132 Chapter 7 DICOM SOPs: Basic The
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134 Fig. 38 Storage SOP Chapter 7 D
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136 Table 26 C-Store-Rq Message fie
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138 Fig. 39 DICOM C-Store 7.4 Query
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140 7.4.1 A Few Words on Data Match
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142 7.4.2 C-Find IOD Chapter 7 DICO
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144 Table 29 (continued) Query para
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146 Table 30 C-Find-Rq Message fiel
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148 Chapter 7 DICOM SOPs: Basic 4.
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254 Chapter 11 DICOM Security senti
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256 11.3.2 Encryption Chapter 11 DI
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258 Chapter 11 DICOM Security from
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260 Fig. 82 Digital signature Chapt
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12.1 DICOM Conformance 263 Chapter
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12.2 Testing, Testing, and Yes, Mor
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12.4 DICOM from a Black Box 267 Thi
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12.6 Open-Source DICOM 269 on their
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12.6 Open-Source DICOM 271 processo
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13.1 Can I See the Image? 275 Chapt
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13.1 Can I See the Image? 277 confe
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13.2 You’ve Got Mail 279 bytes. I
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13.3 Teleradiology 281 Fig. 85 Exte
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13.3 Teleradiology 283 Stealth tele
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13.3 Teleradiology 285 not always r
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13.4 DICOM and the WWW 287 (see 5.5
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13.5 “DICOM Email” 289 4. XML i
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13.5 “DICOM Email” 291 Fig. 87
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13.6 From PACS to PDAs? 293 images
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13.7 Starting Your Teleradiology Pr
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13.7 Starting Your Teleradiology Pr
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13.8 Conclusion 299 C-Stores, and f
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302 14.1 HL7: HIS and RIS Chapter 1
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304 Chapter 14 Standards and System
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15.1 What it Takes to Kill a PACS 3
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15.1 What it Takes to Kill a PACS 3
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15.2 Extreme PACS 317 15.2.1 Diggin
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15.2 Extreme PACS 319 unstable netw
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15.2 Extreme PACS 321 cally configu
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323 Fig. 93 Modular, distributed PA
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326 Chapter 16 DICOM Software Devel
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332 Chapter 17 DICOM Implementation
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334 Real case: teleradiology or bac
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336 Chapter 17 DICOM Implementation
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18.1 Frequent Problems 339 Chapter
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18.1 Frequent Problems 341 18.1.5 I
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18.2 Naive Questions Physicians Lik
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A.1 DICOM Transfer Syntaxes 351 App
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A.2 DICOM SOPs 353 A.2 DICOM SOPs T
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A.2 DICOM SOPs 355 Table 53 (contin
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A.2 DICOM SOPs 357 Table 53 (contin
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A.3 C-Find Bytes 359 Table 53 (cont
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380 References Langer S (2005) Cont
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382 DICOM email 221, 289, 290, 292
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