Medical Imaging Storage

by admin on June 04, 2020
In medical imaging PACS systems, storage is a significant consideration. In fact, the "A" of "PACS" stands for "Archive" ("PACS" is an acronym for "Picture Archive Communication System"). Medical archives are comprised of newly acquired exams, prior studies (for comparison) and some type of disaster recovery. Newly acquired exams and prior studies from the past three to seven years are usually kept in an online archive, which provides retrieval of exams in a matter of seconds. Disaster recovery, in simple terms, ensures that all data has duplicate copies archived, often on a different format and/or in a separate location to eliminate threats from Acts-of-God, viruses, hackers and media failures in impacting the stored studies. Storage used to largely be on spinning disc servers, stratified in a hierarchical design, which organized and separated studies by age (some PACS providers permit this to be configured per a facility's preference). Online studies may include current to six months old; nearline exams could be comprised of six months to two years old; farline studies would be made of exams from two years to seven years and beyond. What drove this breakdown was the performance difference dictated by cost of hardware components (online servers were faster and more costly). As hardware costs have become more affordable, while simultaneously improving their performance, these server classifications have tended to disappear into simply, "online" and "long term archive". Historic media included tape (DAT, AIT, LTO formats), optical discs (DVD), spinning disc (SCSI, SATA, SAS) and, presently, SSD. State-of-the-art systems demand RAID-6 arrays and redundancy of components, with farline studies often still migrating to tape media. Rules of how long particular studies must be maintained in an archive vary by state; the general rule of thumb is seven years, except for mammography and pediatric studies, which are typically longer.


Disaster recovery can consist of simple replication of the images associated with a study, to a much more thorough duplication of all aspects of a system, including images, database, annotation, print pages, key images, user preferences and work environments. In a system with thorough, complete disaster recovery, entire PACS systems can be recreated from the disaster recovery layer should the main system suffer any corruption. Though spinning disc servers provide fast retrieval, they may be vulnerable to attacks on data stored, including viruses, hackers and ransomware. By opting to create a disaster recovery layer on a separate format, like tape, many of these risks are eliminated. Though most PACS providers strive to deliver .99999 uptime of their imaging system, some emergent care facilities seek to insulate themselves from any potential interruption to workflow. Further protection can be had via high-availability servers, where failover is instantaneous to a parallel server, or clustered servers, where multiple systems also offer load-balancing, increased processing power and scalability, or outright parallel systems, where both PACS applications and medical archives are mirrored in their entirety.


There are various ways of taking advantage of available archive capacity. Some PACS vendors store studies in an uncompressed state, which delivers the fastest performance in retrieval (there's no time required for decompression before a study can be displayed). However, compression of an exam allows much more data to be stored on a server with fixed capacity, so the trade-off between speed and capacity needs to be considered by a facility in designing its archive. Some vendors have a means of keeping the database quick and agile, no matter how large the archive grows. When exams are online, the images and the database information (patient, exam, series and image information stored in tables for every image) are kept together. When an exam is moved from an online state, vendors with sophisticated archives can archive (remove) the database information, leaving a pointer to where the exam is located on the storage disc, while simultaneously compressing the image data. This allows the database to remain lightweight and agile, rather than slowing down, as hundreds of thousands or millions of exams are added to the system. The industry standard in medical storage adheres to DICOM (Digital Imaging and Communications in Medicine), which ensures that technology from various vendors will be interoperable if they are DICOM compliant. In the past, PACS providers stored all of their data within their own system. With the advent of VNAs (Vendor Neutral Archives), additional options are available for medical data storage. However, some PACS providers have archives that are VNAs, but also offer sophisticated functionality in addition. In this instance, they deliver integrated servers, where archive software is installed on server hardware. In this way, when the PACS viewer is used in conjunction with the archive software, faster performance and additional functionality are the result. Examples of these types of benefits over mere DICOM storage include:
  • fast, 2-3 second retrieval
  • updating to patient demographics
  • automatic pre-fetch of prior exams when a new exam is scheduled
  • maintaining workflow flags into the archive
  • preserving annotation made on images
  • storing reports with exams
  • storing key image summaries
  • storing print pages
  • maintaining work environments
  • maintaining user preferences
  • system auto-diagnostics.
In addition, some PACS providers permit documents and other data of virtually any format to be stored with exams. This means not only PACS information and reports, but insurance information, prescriptions, audio recordings and many other types of related information is made available to the users of the PACS, via the archive, without having to launch other applications.


PACS systems and their archives used to be limited to having hardware installed on-site at the facility at which they were located. In the recent past, some flexibility has been introduced by allowing storage in the cloud, at data centers. Cloud storage offers advantages, including taking the burden off the facility of maintaining a proper, climate-controlled environment for their storage servers and disaster recovery system. However, it does introduce the need for secure communication of the exams from the facility to the data center. For many vendors, this requires the installation and expense of a VPN (Virtual Private Network) between the facility and the cloud site. Some sophisticated PACS vendors have built-in, encrypted, secure upload capabilities, eliminating the need for the VPN. If a facility is multi-site, and high-volume, some PACS providers can make exam retrieval even more efficient if they have the capability of using a distributed architecture. This capability allows storage modules to be located on-site, while interacting with the cloud, delivering not only faster retrieval of exams and more efficient network communication, but also relieves the burden on scanners inflicted by potential internet disruption.


When an archive contains many years worth of exams, perhaps collected from disparate medical facilities, matching existing studies with newly acquired exams is wrought with the potential to miss a prior study that could be a useful reference. This is caused by exams from different facilities being identified with varying facility naming conventions (first name/last name versus first initial/last name, for example), or being tagged with unique medical record numbers per facility, or, through simple human error. These differences present a challenge in matching exams, which usually looks at medical record number. Some PACS vendors have the capability to overcome these demographic variances from disparate centers using a Master Patient Index (MPI), which permits searching by a variety of fields, including medical record number, last name, first name, date-of-birth, sex and RIS key.


Archive needs are impacted by two major factors. The first is increase in volume. The second is growth of exam size. Over the years, an average exam size across all modalities hovered about 50MB in size. Some modalities have seen significant growth over a short period of time. For example, for the mammography modality, moving from film (approximately 162MB) to digital marked the first step in size growth for this exam. But, that was dwarfed by the addition of breast tomosynthesis, impacting the size to exams that are regularly 1GB each! The storage needs for mammography are compounded by the fact that studies of this modality must be kept significantly longer that other modalities. This raises the consideration of cost. PACS and archive used to be a purchase of a system, which was a capital expense. As forecasted storage capacity was filled, additional storage would be added, equating to additional budget considerations. Many PACS vendors diversified into business models that were based on volume, known as "Per-Exam". In these models, rather than budgeting for a significant capital expense, systems were leased at a per-exam (or, in some instances, a per-click) rate. A dollar figure per study was established, and multiplied by the number of studies done on an annual basis. Many PACS providers vary the price of the exam according to the modality size; as the modality size increases, the associated cost goes up. Some PACS vendors are able to keep the cost-per-study consistent, eliminating concerns for the facility, and simplifying the auditing of the business relationship. The per-study business model has been applied to VNAs and cloud storage (even without PACS viewer access).


In the ImageQube Cloud data center, access to PACS storage and disaster recovery are available. The archive is configurable per a facility's preference, permitting modalities to be kept online for defined periods of time in RAID-6 arrays, while delivering an industry-leading level of disaster recovery, duplicating not only images, but the database, annotation, print pages and much more. By replicating this data on tape via fully-robotic libraries, it is protected against viruses, hackers, ransomware and other threats. Though this storage offers many benefits when used with the ImageQube PACS viewer, it is also a DICOM compliant, Vendor Neutral Archive (VNA), guaranteeing interoperability with any DICOM device. The ImageQube Cloud PACS storage offers ease-of-use, where documents and attachments of virtually any format can be stored with the exams using a simple drag 'n drop (with the security to make these attachments available only to internal users, or extended to clinical users in addition). Taking advantage of the ImageQube Cloud's secure DICOM upload functionality, a Virtual Private Network (VPN) isn't required to upload exams to the archive. This feature offers encryption and security from an application installed on a simple desktop PC at the client facility. The ImageQube Cloud PACS archive has a configurable means of matching prior exams with new studies using its Master Patient Index, permitting comparison of a variety of fields in the patient record, including first name, last name, date of birth, sex and RIS key, overcoming the challenges inherent in exams stemming from different facilities, human error and other variances. Feel the freedom offered by the ImageQube Cloud's PACS storage, where there's no minimum volume, no commitment and no up-front cost. You get a vendor-neutral archive with a disaster recovery layer, providing its own secure, encrypted communication where no VPN is required. All with a consistent, competitive per-exam price regardless of modality.