Dynamic imaging advocates await new DICOM standard

Large digital files containing real-time imaging sequences and interactive 3D or 4D reconstructions can place a considerable burden on a hospital's PACS. The introduction of smarter DICOM-approved compression tools to facilitate fast transfer of these files is becoming increasingly important, according to Prof. Michel Claudon, president of the European Federation of Societies for Ultrasound in Medicine and Biology and professor of radiology at Brabois Hospital, Nancy, France.

Transmission of real-time ultrasound data, for instance, can improve communication between radiologists and their clinical colleagues, said Claudon, who made the case for integrating dynamic sequences into PACS at this year's Management in Radiology meeting in Basel, Switzerland. Doctors who might previously have struggled to appreciate a radiologist's interpretation of static ultrasound images are more likely to understand the pathology when viewing it on a real-time scan.

"Surgeons and clinicians know how to analyze CT or MR images because they have a fixed anatomical reference frame. They know that the orientation of images will be transverse, sagittal, or coronal," he said. "With ultrasound, you can take any oblique view, so the doctors often do not understand the exact location of slices. But when you show them a real-time clip and sweep across the organ, it is much easier to understand."

Files containing dynamic sequences must be compressed before transfer. A 10-second gray-scale ultrasound sequence acquired at 20 frames per second, for example, will generate a 100-MB file. Up to 10 different sequences may need to be recorded, stored, and transferred depending on the specific application.

The only DICOM-approved file compression tool, MJPEG, is relatively basic and compresses all images in a series equally, Claudon said. More sophisticated non-DICOM algorithms, such as MPEG, account for the similarity of images within a series when compressing files. One DICOM working group is currently investigating the suitability of MPEG-2 as a new DICOM standard.

"We have the DICOM world and the non-DICOM world. I would prefer to improve things within the DICOM world, which is the heart of the system, rather than use non-DICOM compression tools," Claudon said.

Use of MPEG-2 could be especially useful when transferring long sequences, such contrast-enhanced ultrasound or echocardiography exams, he said. The powerful compression algorithm has the potential to decrease file size by a factor of four or five without losing diagnostic information. Introduction of MPEG-2 as a DICOM standard is expected during 2004, Claudon said.

"We now need to push things to get approval by vendors," he said.