© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

8.3.4 Vascular Bifurcation Detection

The ~5 billion navicytes circulating in the 5400 cm³ blood volume can be used to form a dynamic transluminal geometric "virtual lattice" (with constantly changing membership) that remains positionally stationary near the bifurcation of each blood vessel whose diameter exceeds X_row ~ 100 microns. A spatial progression of such rows allows the bifurcation break point to be registered at most ~100 microns past the junction and in at most ~20 millisec after leaving the larger-diameter vessel, for nanorobots drifting with the blood flow in arterioles. In the high velocity aorta (Table 8.2), minimum bifurcation detection range increases to ~630 microns in a detection time of ~1 millisec. Transmission of local navicyte coordinates allows traveling nanorobots to determine which branch of the bifurcation they are about to enter, or have already entered. (Major organs, lymphatic topology, and other important landmarks can be accurately located by similar methods.)

Bifurcations involving capillaries and other vessels with diameters less than X_row may be readily detected by direct acoustic reflection echolocation from vessel walls (Section 4.8.2). Echoes from red blood cells are relatively weak (though still measurable)³⁰⁴⁴ in comparison with those from the solid tissues within the body because the characteristic impedance of red blood cells is very similar to that of the plasma in which the cells are suspended.⁵⁷⁰

Last updated on 19 February 2003