Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

Disadvantagesof PACS1. Initial and recurring equipment costs (e.g., replacing file cabinets with arraysof disk and tape drives, replacing lightboxes with workstations with high-performancevideo monitors, installing cables for networks)2. Massive data storage requirements of radiologic images (e.g., one pair of chestimages uncompressed '" 20 MB)3. Expensive technical personnel to support the system4. Loss of information when films are digitized or solid-state image receptors aresubstituted for film-screen combinations5. Loss of information when lossy image compression is used6. Lower dynamic range with video monitors than with film, when viewing animage over a similar gray-scale range, and lower spatial resolution when viewingan image without magnification7. Physician reluctance to interpret from video monitors8. Conversion of film to digital images9. Provision of hardware and software to permit transfer of images between equipmentfrom different manufacturers10. Maintaining access to previously archived images after converting to a newarchival technology11. Security and reliabilityThese two lists are not all-inclusive. Of course, the desirable strategy during aPACS implementation is to enhance the advantages and minimize the disadvantages.Benefits expand as experience with these systems increase. Furthermore, therapidly increasing capabilities and falling costs of the technology used in PACS continuesto increase their performance while reducing their cost.Security and ReliabilityTwo important issues regarding PACS are security and reliability. The main goals ofsecurity, as mentioned in Chapter 4 and earlier in this chapter, are to deny unauthorizedpersons access to confidential information (e.g., patient data) and to protectsoftware and data from accidental or deliberate modification or loss. Methodsfor protection against unauthorized access were described in earlier sections. Protectionagainst loss can be achieved by maintaining copies on more than one magneticdisk drive, tape cassette, or optical disk. The value of a study declines withtime after its acquisition, and so, therefore, does the degree of protection requiredagainst its loss. A very high degree of protection is necessary until a study has beeninterpreted.The goal of reliability is to ensure that acquired studies can be interpreted at alltimes. Reliability can be achieved by the use of reliable components and by faulttolerantdesign. A design that continues to function despite equipment failure issaid to be fault-tolerant. The design of a PACS must take into account the fact thatequipment will fail. Fault tolerance usually implies redundancy of critical components.Not all components are critical. For example, in a PACS with a centralarchive connected by a network to multiple workstations, the failure of single workstationwould have little adverse effect, but failure of the archive or network couldprevent the interpretationof studies.