DICOM or Nothing:The Case for Informatics Standards in Quantitative Imaging

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As radiology enters the era of quantitative imaging, it is well advised to carry with it an old friend, the DICOM standard, according to David A. Clunie, PhD, CTO of CoreLab Partners. He lays out his case in “(Informatics) Standards for Quantitative Imaging,” which he presented on November 28, 2012, at the annual meeting of the RSNA in Chicago, Illinois. Clunie is hardly a disinterested observer. His informatics credentials include serving as editor of the DICOM standard, as cochair of the Integrating the Healthcare Enterprise Radiology Technical Committee, and as a member of the RSNA’s Quantitative Imaging Biomarkers Alliance. Although he works primarily in research, his message has serious implications for clinical practice and commercial product development: Standardization is no less important in quantitative imaging than in image acquisition, and it will play a pivotal role in the transition from traditional narrative reporting to quantitative reporting. The DICOM standard initially focused on standardizing the images that come from imaging modalities, but it has migrated into clinical applications that yield results for cerebral blood flow, regions of interest (to get the size of Hounsfield units), PET standardized-uptake values, and measurements—usually distance, but increasingly, area and volume. “In other words, quantitative imaging is nothing new; it’s just that it is growing in importance and expanding in scope in terms of its range of clinical uses,” Clunie says. “In a way, quantitative imaging (as we think of it now) has a different emphasis than traditional narrative reporting. What is different is a focus on greater rigor in deployment, with respect to quantitative imaging.” In narrative reporting, you see an image on the screen and compare it with a previous time point visually, after which you dictate your opinion. Quantitative reporting goes beyond mere description; it proceeds to the analysis, measurement, and coding of information that can be reused in downstream systems. “We can use the same standards; we just have a greater need for numbers and codes within the standards and a greater amount of structure in the output,” Clunie says. Traditionally, he notes, the radiologist looked at an MRI exam of the brain, saw something, and said that there was a hairy mass present. There might have been some context to indicate that it was a glioblastoma, but today, there is more to it: The radiologist uses an automated or semiautomated tool to attempt to find the lesion boundaries and then, the tool reports the volume, which is critical for looking at progression of the lesion over time. Quantitative imaging depends upon the precision of both the numerical and the categorical information, Clunie emphasizes. In addition to the lesion measurements, the following coded information is desirable: characteristics of the finding, anatomical location of the finding, coded indication of why the study was performed, time of exam, and a code representing the finding itself. The goal, Clunie explains, is not just a piece of plain text, but a searchable, repeatable, and consistent account of the exam results, using a standard lexicon or lexica that can be reviewed retrospectively by the physician (or prospectively, in the case of a randomized clinical trial). Using the example of plotting the change in a lesion’s volume over time, either for an individual patient or a group of patients, Clunie emphasizes the importance of being able to extract key data from a patient’s record. “In order to be able to do this downstream analysis, your report must not be a dead end,” he explains. “The information we are producing should be more than just cutting and pasting or transcribing.” Acknowledging that dictation continues to be the dominant form of reporting, Clunie adds, “There is no reason that dictation cannot be assisted by the quantitative information that has been extracted upstream—perhaps by the modality; perhaps by an analytic tool that has been run before the images got to you; or perhaps by a tool that you use interactively as you dictate, using prepopulated merge fields.” Beware the Pretty Pictures Screenshots and DICOM–encapsulated PDFs have gained popularity as more modalities have gone quantitative, Clunie notes, and these can, indeed, save attractive tables and graphics, either from the modality or from the reporting application. The problem with these pretty pictures is that they are the proverbial dead end to