Two University of Rochester researchers have invented a new "phantom" for quicker, more accurate testing and standardization of ultrasound scanners.
The new phantom, an industry term for the device used to test the accuracy of ultrasound machines, is a digitally encoded plastic transparency that the researchers believe is more accurate, works more quickly, and is less expensive to manufacture than today's phantoms, which are cumbersome hand-built blocks made of various tissue-mimicking materials. The phantom was created by graduate student Dan Phillips and Kevin Parker, professor of electrical engineering and radiology and director of the Rochester Center for Biomedical Ultrasound. Phillips presented the work last week at the annual meeting of the Optical Society of America in Rochester.
"Medical imaging equipment needs to have 20/20 vision -- people's lives depend on this technology," Parker says. "Eye charts would be meaningless if they were not standardized. It's no different with ultrasound machines: They must be calibrated to 'see' correctly."
Millions of ultrasound scans are performed in the United States alone each year to trace the progress of conditions like heart disease, fetal development, and cancer. Scanners work by sending sound waves into a material and then measuring the waves that are reflected by any solid objects found inside. Phillips and Parker discovered that even tiny blobs of toner particles just a few thousandths of a millimeter high -- a sliver of the width of a human hair -- can effectively reflect sound waves.
Realizing that they could take a super-accurate ultrasound scan of precisely positioned, digitally created patterns of dots and lines, Parker and Phillips used a computer and a common laser printer to create a digital halftone pattern on a piece of copier paper, which they then transferred to an ordinary transparency. Currently they're experimenting with digitally created patterns of the letter "E," like those on eye charts, to check the accuracy of ultrasound scanners.
In contrast to such sleek thin films, the phantoms now used by ultrasound technicians are generally brick-sized blocks of materials that simulate human tissue; embedded inside are tumor-like lumps. It can take technicians hours of exhaustive readings to standardize a machine using such phantoms, which often cost more than $1,000 since they must be painstakingly produced by hand. Even then, the match between the phantom and the image on the screen is a rough approximation, since today's phantoms simulate only relatively large objects, typically the size of a marble or larger. With digital technology, Phillips and Parker can create a much more sophisticated pattern, down to a level of detail barely detectable by the naked eye.
"With current phantoms, you use the diagram of embedded objects that comes with the device to check the machine," says Parker. "With our phantom, you know and can precisely control the exact size, shape, and even the density of the lines and dots, at a much greater resolution. It's a phantom for the digital age."
Parker and Phillips have filed for a patent on the new phantom, and they are working closely with Applied Image Inc., a Rochester company that specializes in thin-film and imaging calibration technology, to manufacture it. Phillips believes the phantoms will cost less than conventional phantoms and will also be much simpler to use.
The new phantom addresses a major problem in the emerging field of telemedicine, where doctors transmit images to distant colleagues for consultation. In telemedicine, the image produced by an ultrasound system must be electronically encoded, transmitted, and decoded, and then displayed on a completely different computer -- a chain of events that presents many opportunities for distortion of the original scan. But by comparing test scans of a phantom sent just before and after a telemedical consultation, doctors can determine if the images have been transmitted with minimal distortion. Without such a system, a doctor accustomed to reading ultrasound scans taken on-site is hard-pressed to accurately interpret an image taken remotely.
The Rochester team says the new phantom can also be used in the rapidly growing field of color Doppler imaging, which is frequently used to observe movement within the body, such as the flow of blood. Simply by vibrating the phantom, Rochester graduate student Stephen McAleavey has found ways to more accurately evaluate color Doppler images -- a procedure that now requires the use of a complex $7,000 artificial circulatory system.
The research is funded by the National Institutes of Health and by the Greater Regional Industrial Technology (GRIT) program, a federally funded program for university-industry collaboration.