MPEG offers solution to ultrasound and cardiac imaging transmission

Network bottlenecking caused by huge digital image files has a new remedy. MPEG (moving pictures experts group) is a lossy compression method commonly used to transmit movies over the Internet. In medical practice, MPEG is used to transmit ultrasound and echocardiographic images.

Its cost has slowed industry adoption.

"MPEG has been incorporated in diagnostic cardiac imaging very slowly," said Dr. Mario J. Garcia, director of the echocardiographic laboratory at the Cleveland Clinic.

The major limitation is the high cost of hardware necessary for MPEG compression at the front end, Garcia said. Equipment manufacturers seem reluctant to incorporate a technology that will result in cost increases that few consumers are so far willing to pay.

MPEG nevertheless offers distinct advantages.

"This method of image compression is superior in principle for studies that are larger in temporal domain (prolonged acquisition time), where temporal compression is most needed," Garcia said.

He cited specific situations when longer acquisition time is needed:

• evaluation of patients with congenital heart disease

• contrast perfusion and monitoring during procedures such as radio-frequency ablation, balloon mitral valvuloplasty, or atrial septal defect closure

"These studies can only be recorded on videotape or by intermittently acquired short digital clips, unless MPEG compression is available," Garcia said.

Sound Choices of Houston, a regional provider of ultrasound services, began the unique use of MPEG to augment routine diagnostic imaging.

When indicated, Sound Choices posts MPEG video of ultrasound exams (using an Internet file-sharing package from Mangosoft) to provide near-real-time evaluation for remote radiologists.

MPEG video enables near-real-time feedback to the scanning technologist requesting additional views, according to Dr. Randall A. Stoenoien, Sound Choices medical director. It also improves diagnostic capabilities when characterizing abnormalities such as fetal cardiac anomalies.

"Using MPEG to transmit US images is something I've devised as an adjunct to routine imaging, although we don't use it for a diagnostic tool," Stoenoien said. "We normally get high-quality images, but what we're missing is video."

Ultrasound images are commonly transported on VHS tape by courier, which is neither efficient nor cost-effective. Now, if there's a problem case, the technician makes an MPEG movie which can be transmitted instantly to the radiologist.

MPEG has only become practical in the past eight to 12 months due to the requirement for powerful computers and high bandwidth networks to transmit the 5 to 10 Mb ultrasound files, Stoenoien said. So far, the video capture system directly transfers ultrasound images to obstetricians' PCs. MPEG compresses ultrasound files that would otherwise be 200 Mb or more.

"MPEG as a compression modality is superior," he said. "It's the only thing that brings these files into a manageable size."

Other viewpoints:

Counterpoint: DICOM panel does not support MPEG

The ultrasound working group of the DICOM standard has decided not to proceed with adding MPEG compression to the DICOM standard.

Our studies found that MPEG compression only offered significant advantages over M-JPEG at very high compression ratios. Working group members could thus not find a clear need to support MPEG compression in their own systems, given that diagnostic clips are currently captured at lower compression ratios than those where MPEG has a clear advantage.

Also, working group members are concerned over the proliferation of possible lossy compression transfer syntaxes, given that JPEG 2000 compression will be added to the DICOM standard. Ultrasound vendors are already having difficulties due to lack of support for JPEG lossy compression by many archives and workstations.

Without a clear market need for MPEG compression, it was decided by the working group to not add MPEG to the DICOM standard.

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