Storage Dilemmas in the MDCT World

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Be aware of clinical, customer-service, and medicolegal issues in devising an image-storage solution for MDCT studies—and know that the interpretation tools are in transition

In the world of PACS, multidetector CT (MDCT) is widely regarded as disruptive technology. Explosive growth in the number of slices per study has created challenges in virtually every aspect of PACS, including display, image distribution, and storage. At the same time, MDCT has been hailed as a major breakthrough by those whose goal is to improve the ability of CT scanning to diagnose disease.

In order to address the challenges created by CT scanners that can produce thousands of images during a single study, the scan-thin, read-thick concept has emerged. The idea behind this concept is that the clinical information in an MDCT scan can be extracted by rendering the thin axial dataset into thicker, multiplanar series, occasionally supplemented by advanced visualization such as 3D modeling and specialized analytic software. This volumetric approach to MDCT interpretation has been shown to improve diagnostic accuracy, confidence, and speed.

To address this need, PACS vendors have recently started to integrate 3D tools fully into their standard display protocols. Most radiologists, however, are still forced to divide their attention between their PACS workstations and specialized 3D software. This division has facilitated a natural separation between the temporary storage of thin axial data on a 3D workstation or render server and the long-term storage of thick rendered data and selected 3D images on PACS.

Is this the best model for data storage? As we near the end of the first decade of the 21st century, we need to reexamine this concept in light of steadily improving storage technology and an improved understanding of the utility of thin-section data.

Stratifying the Issues

In order to decide which storage schema best suits your practice, it is important to look beyond the terabytes and gigabits to the clinical factors that can influence your decision. First, while most 3D and PACS vendors (and many radiologists) view 3D software as a single entity, when considering the storage of thin data, it is best to separate advanced visualization into two separate categories: 3D clinical applications (3DCA) and the 3D tool set (3DT). 3D clinical applications are those specialized clinical programs that allow for the interpretation and analysis of specific types of studies, such as cardiac CT, virtual colonoscopy, and brain-perfusion studies. These represent a small (but growing) fraction of most practices’ workloads, are typically interpreted by a subset of radiologists, and are interpreted with software that is technologically immature (that is, the software is rapidly improving).

In contrast, 3DTs are the basic volumetric tools, such as maximum-intensity projections, multiplanar reconstructions, and curved planar reconstructions. A 3DT is used every day by technologists and radiologists to create the thick-slab datasets that are stored on PACS and used for the interpretation of MDCT studies. A 3DT is used, either directly or indirectly, by every radiologist who reads MDCT; it is a mature technology. Whether a 3DT is available on your radiologist’s desktop as client-server software or is integrated into your hanging protocols will be a principal driver of your storage decisions.

Second, in this decade, referring physicians have divided naturally into two groups: report-focused and image-focused clinicians. Report-focused clinicians rely, for their day-to-day practice, on our radiology report, supplemented by access to key images and thick-section data. Image-focused clinicians, while still using the radiologist’s report, frequently need access to the original thin data, along with the 3D software used to re-render the data. Examples include orthopedic surgeons and neurosurgeons, as well as cardiologists. Radiologists require 3DTs to perform interactive volumetric interpretation. Whether these tools only reside in separate 3D software or are available within your PACS hanging protocols, allowing for volumetric interpretation will be a principal driver of your storage decisions.

Third, we must recognize the medicolegal aspects of image storage. Developed in the era of hard-copy imaging and paper medical records, the concept of saving all the images used by the radiologist to interpret the study seems confusing, at best, in our emerging thin-section