1. F. P. Castronovo and R. J. Callahan, J. Nucl. Med.,13, 823 (1972).
2. J. McRae, D. C. van Dyke, and J. Yano, US Patent No. 3,735,001 (1973).
3. A. J. Tofe and M. D. Marion, GFR Patent No. 2,424,496 (1974).
4. M. D. Francis, GFR Patent No. 1,813,659 (1969).
5. Chung Yu-Shang, US Patent No. 3,394,083 (1968).