Tech Briefs

New device improves existing molecular imaging system.

Preliminary testing shows that a new device may enable existing breast cancer imagers to provide up to six times better contrast of breast tumors, while maintaining the same or better image quality and halving the radiation dose to patients. The advance is made possible by a new device developed for 3D imaging of the breast by researchers at the Department of Energy’s Thomas Jefferson National Accelerator Facility.

Fig.1 – Adding the variable angle slant hole (VASH) collimator to an existing breast molecular imaging system allows the system to get six times better contrast of cancer lesions in the breast, providing the same or better image quality while also potentially reducing the radiation dose to the patient by half. (Credit: Thomas Jefferson National Accelerator Facility, U.S. Dept. of Energy)

Although mammography is the gold standard in breast cancer screening, half of all women who follow standard screening protocol for 10 years will receive a false-positive result that will require additional tests, particularly women who have dense breast tissue. Imaging based on nuclear medicine, used in conjunction with mammography, is proving to be a successful secondary screening to reduce the number of false positive results in women with dense breasts and at higher risk for developing breast cancer.

Researchers are now hoping to improve this imaging technique, known as molecular breast imaging or breast-specific gamma imaging, with better image quality and more precise location (depth information) within the breast, while also reducing the amount of radiation dose to the patient for these procedures.

According to Drew Weisenberger, leader of the Jefferson Lab Radiation Detector and Imaging Group, a new device, called a variable angle slant hole collimator, provides all of these benefits and more. Early studies show that when used in a molecular breast imager, the device can capture 3D molecular breast images at higher resolution than current 2D scans in a format that may be used alongside 3D digital mammograms. “These results really focus on the breast. We hope to build on this to perhaps improve the imaging of other organs,” Weisenberger said.

How It Works

The new device works by replacing a component in existing molecular breast imagers. While a mammogram uses X-rays to show the structure of breast tissue, molecular breast imagers show tissue function. For example, cancer tumors are fast growing, so they gobble up certain compounds more rapidly that healthy tissue. A radiopharmaceutical made of such a compound will quickly accumulate in tumors. A radiotracer attached to the molecule gives off gamma rays, which can be picked up by the molecular breast imager. “You can image that accumulation external to the breast by using a gamma camera,” said Weisenberger.

Current molecular breast imaging systems use a traditional collimator, which is essentially a rectangular plate of dense metal with a grid of holes used to “filter” the gamma rays for the camera. The collimator allows the system to only pick up the gamma rays that come straight out of the breast, through the holes of collimator, and into the imager. This provides for a clear, well-defined image of any cancer tumors.

The newly developed variable angle slant hole (VASH) collimator is constructed from a stack of 49 tungsten sheets, each one a quarter of a millimeter thick and containing an identical array of square holes. (See Figure 1) The sheets are stacked like a deck of cards, with angled edges on two sides. The angle of the array of square holes in the stack can be easily slanted by two small motors that slide the individual sheets by their edges. The result is a systematic varying of the focusing angle of the collimator during the imaging procedure.

“Now, you can get a whole range of angles of projections of the breast without moving the breast or moving the imager. You’re able to come in real close, you’re able to compress the breast, and you can get a one-to-one comparison to a 3D mammogram,” Weisenbeger explained.

In a recent test, the researchers evaluated the spatial resolution and contrast-to-noise ratio in images of a “breast phantom,” a plastic mockup of a breast with four beads inside simulating cancer tumors of varying diameters that are marked with a radiotracer. They found that by using the VASH collimator with an existing breast molecular imaging system, they could get six times better contrast of tumors in the breast, which could potentially reduce the radiation dose to the patient by half from the current levels while maintaining or improving image quality. The test results match a published paper that predicted this performance via a Monte Carlo simulation.

The collimator was built at Jefferson Lab and the test results were analyzed at the University of Florida with funds provided by a Commonwealth Research Commercialization Fund grant from the Commonwealth of Virginia’s Center for Innovative Technology, and with matching support provided by Dilon Technologies.

For more information, visit www.jlab.org/news/releases/archive.