A copper crystal lens developed at the Advanced Photon Source represents a new and promising approach in nuclear medicine for imaging very small tumors in the human body with higher sensitivity and higher spatial resolution than the cameras now in use.
The lens is designed to focus gamma-ray energies of 100 to 200 keV, which makes it ideal for focusing the 140.6-keV gamma rays from Technetium-99m typically used in radioactive tracers. This new approach to medical imaging relies on crystal diffraction to focus incoming gamma rays in a manner similar to a simple convex lens focusing visible light. The lens would be part of an array of lenses that could be used as a complementary technique to gamma cameras for localized scans of questionable regions in the body. In addition, a 2-lens array can be used to scan a woman's breast in search of tumors with no discomfort to the patient. Experiments performed with a Technetium-99m and Cobalt-57 indicate that a 6-lens array should be capable of detecting sources with 1 µCi strength.
For almost half a century, gamma (or Anger) cameras have provided images of potential tumors in the body by detecting the radioactivity produced by a radiopharmaceutical that is given to a patient who is undergoing a full-body scan. Suspected tumor regions contain higher concentrations of the radiopharmaceutical, which produces a higher count rate and therefore greater contrast between the tumor region and its surroundings. Most of the radiopharmaceuticals that are given to patients for body imaging are gamma-ray emitters with energies between 100 to 250 keV and with relatively short half-lives. Although most gamma cameras are optimized for detecting gamma-ray energies of 100 to 250 keV, only 0.01% of the emitted gamma rays are detected by the gamma camera. This reduction in sensitivity, along with the short scanning time usually required, limits the spatial resolution of the camera to object sizes of no less than 7 mm on a side. Therefore, traces of tumors smaller than 7 mm may appear in an image, but with little information to precisely determine its location in the body.
The crystal diffraction 6-lens array should be able to detect tumors as small as 2 mm in diameter with a factor of 10 to 20 times higher sensitivity than gamma cameras. Moreover, it can provide sufficient information to locate a tumor accurately in three dimensions and eliminate false position determination. The data from each lens can be viewed independently or can be rendered as a 3-D image containing precise information on the size of the tumor and its location. It must be emphasized that the crystal diffraction lens array is a complementary imaging tool to be used following a full-body scan performed with a gamma camera; therefore, the patient would not require any additional radioactivity.
This work was featured in the February 4, 2002, issue of Radiology Today.
See also: D. E. Roa, R. K. Smither, "Copper Crystal Lens for Medical Imaging: First Results," Proc. SPIE: Physics of Medical Imaging, L.E. Antonuk and M.J. Yaffe, eds., Vol. 4320, SPIE, (2001) pp. 435-446; and R. K. Smither, D. E. Roa, "The Physics of Medical Imaging with Crystal Diffraction Lenses," Proc. SPIE:Physics of Medical Imaging, L.E. Antonuk and M.J. Yaffe, eds., Vol. 4320, SPIE, (2001) pp. 447-458.
Research funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract W-31-109-ENG-38.
For further information, send e-mail to: R. K. Smither, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439