New 3-D Breast Scanner Lowers Radiation Dose, Improves Image
DURHAM, N.C. -- Scientists at Duke University Medical Center have created a new breast scanner that will dramatically improve their ability to visualize small tumors while also reducing radiation exposure to one-tenth that of normal mammograms. Moreover, the new device does not compress the breast, as do traditional mammograms.
The new scanner uses computed tomography (CT) – a sophisticated form of X-ray imaging -- with a unique variation: it provides a three-dimensional image of the breast. Moreover, the new scanner rotates around the breast to obtain a complete image, from the nipple to the chest wall. Traditional mammograms, on the other hand, provide only a two-dimensional image and they compress the breast, thereby distorting the image and causing discomfort for many women.
The Duke scientists have successfully demonstrated their new CT scanner can detect lesions as small as 5 mm in artificial breast models and in cadavers. Mammograms are considered able to detect about a 1 cm diameter soft tissue lesion – about the size of a marble – although they can detect far smaller micro-calcifications, which could be indicators of disease.
The Duke team plans to begin testing in women within two years and is in the process of developing a start-up company to commercialize the device, said Martin Tornai, Ph.D., associate professor of radiology and biomedical engineering at Duke and developer of the scanner.
Results of the tests with their new scanner will be presented Sunday, Feb. 12, 2006, at the annual Society of Photo-Optical Instrumentation Engineers (SPIE) medical imaging meeting in San Diego.
"Our goal in developing the camera was to develop a really efficient, patient-friendly, low-dose X-ray system that improved our ability to detect tumors in soft tissue," said Tornai. "The earlier we can detect breast cancer, the better chance there is of treating the disease."
Tornai said traditional mammography fails to detect some tumors because it is two-dimensional and thus projects a flattened image of the breast. The compression and two-dimensional image cause overlapped tissues to obscure some tumors. With 3-D imaging, the breast is fully depicted and the contrast between normal and cancerous tissues is more apparent, he said.
Tornai likens mammography to viewing the hand from the side, where only the thumb and first finger are obvious while the remaining fingers are obscured behind the first finger. If a ring is placed on one finger, it may be undetected or only a fraction of it may be visible.
The new CT scanner, in contrast, would depict the entire hand so that each finger can be visualized separately. A ringer on one finger would be immediately obvious, just as a tumor in a breast would stand out, he said.
Tornai's team tested the new scanner by implanting varied sizes of artificial tumors made of oil-filled spheres and plastic rods into a breast replica. Because they knew exactly where the tumor was situated in the breast replica, they could analyze the image and determine if they could correctly identify and locate the tumor.
In addition, the team dramatically enhanced the "dose efficiency" -- the amount of radiation needed to generate a clear image – by constructing a filter through which the radiation beam travels. The resulting beam, called a quasi-monochromatic x-ray beam, dramatically lowers the radiation dose while retaining the image quality that would typically be lost by traditional, broader beams.
"We raised the energy so the x-rays are more penetrating but created a narrower distribution of energies using a heavy K-edge filter," said Tornai. "Our data using the quasi-monochromatic beam show that the image quality does not change, even when we dramatically drop the radiation dose."
Their new CT technology is built into an innovative camera device, created by Tornai, Randolph McKinley and others at Duke, which actually orbits the breast itself. As the patient lies on her stomach, the camera swings up and down (north to south) as it encircles the breast in order to fully capture the entire volume. The new scanner takes many more projections at various angles than does a mammogram, so the resulting image reflects minute slices – like miniature slices in a loaf of bread - of the entire breast and not just a single projection, said Tornai.
Three-dimensional images are then produced at half-millimeter slices throughout the entire breast, and then all the images can be combined into a composite picture of the breast.
"Obtaining images every half-millimeter should ensure that we don't miss a tumor somewhere in the breast," said Tornai, "And, we're trying to improve the resolution even further."
The image depicted by the CT scanner is structural, meaning it shows the anatomical elements of the breast – similar to that of a magnetic resonance image (MRI). However, the new CT scanner is far smaller and less cumbersome than an MRI. Moreover, it should be far cheaper to employ on a large scale than MRI, which is costly – about $1,000 per image for breast scans.
Tornai and his team are now in the process of combining the CT breast scanner together with a "SPECT" scanner that uses nuclear medicine to detect chemical changes in breast cells that signal the cells are becoming malignant. The SPECT scanner is already constructed and being tested as a stand-alone camera.
The benefit of combining the two technologies, said Tornai, is that the dual images will depict both structural and chemical changes. Technicians can lay one image over the other to obtain a complete picture of breast changes, from actual tumor masses to subtle changes in the behavior of breast cells as they become malignant.
"Once you start seeing structural changes using X-ray imaging, that indicates the molecular process has been going on for some time," said Tornai. "Using the SPECT camera, we can detect subtle changes in cells before a tumor has developed, enhancing our ability to treat the abnormal cells in their earliest stages of malignancy."
Referring back to the hand analogy, Tornai explains that an X-ray will exquisitely depict the bones in his hand. Nuclear imaging will show the ring on his finger but not the bone upon which it rests. The hybrid camera would show the bones and the ring, enabling scientists to home in precisely to the location of a tumor or mass within the breast.
Tornai said the dual CT/SPECT scanner will not necessarily replace standard mammography but could supplement the breast imaging procedures in mammography clinics. He said the CT scanner, if proven beneficial in human studies, could potentially replace standard mammography.