Thomas Nelson

Professor, Radiology, UC San Diego

Dr. Nelson is Professor in the Department of Radiology at the University of California, San Diego. Dr. Nelson is a Fellow of the American Association of Physicists in Medicine and the American Institute of Ultrasound in Medicine. Dr. Nelson is a Diplomate of the American Board of Health Physics and the American Board of Radiology. His research interests include medical imaging including breast imaging and 3D ultrasound, computer modeling, and visualization. Dr. Nelson received his B.A. degree in Mathematics from San Diego State University in 1972, his M.S. in Radiological Physics from San Diego State University in 1974 and his Ph.D. degree in Medical Physics from the University of California, Los Angeles in 1977.

Breast cancer is a disease with high incidence that will affect the lives of one of every eight women in the United States. X-ray mammography is the principal screening tool for breast cancer, although an important weakness is in its application to women with extremely dense, glandular breasts – mammography is less sensitive in these women. For them, an imaging modality with better contrast resolution for breast cancer is needed. Computed tomography (CT) depends upon x-ray contrast mechanisms like mammography, but has about 10 times the contrast resolution.

As such, CT is very capable of identifying soft tissue lesions in the 3-5 mm range. Therefore, CT has great potential for much earlier detection — by as much as a year — of breast cancer than mammography for high-risk patients. The overall goals of our research are to assess the potential of breast CT for the earlier detection of breast cancer. Our initial work has shown radiation dose equivalence between conventional two-view mammography and an optimized breast CT scanner.

A collaborative NIH/NCI funded program between UC Davis and UC San Diego has built two dedicated breast CT scanners. Phase I and Phase II clinical trials evaluating normal volunteers and women with mammographically identified breast lesions are evaluating normal breast architecture and computerized cancer detection.

A complementary California Breast Cancer Research Program research project at UC San Diego has built a dedicated breast ultrasound scanner. Initial clinical trials in volunteers have demonstrated high quality tomographic images of the entire breast without compression or radiation. The potential for volumetric breast ultrasound to complement current breast imaging and enhance early detection of cancer is being investigated with further refinements exploring the role of elastography and perfusion imaging in addition to volume imaging.

If these volumetric breast imaging modalities achieve their potential, breast cancer could be detected as much as 1.5 years earlier than with conventional mammography, reducing the possibility and severity of metastasis and improving the treatment outcome.