Observations on the validity of using "NEN-TRAC" microspheres for measuring organ blood flow

"NEN-TRAC" brand of radioactive microsphere, 15 micron in diameter, have recently become available and therefore organ blood flow (Q) values obtained using these have been compared with values simultaneously obtained with the well-established "TRACER" brand of microspheres. For all major tissues of the body of two conscious sheep, there was excellent agreement between Q values obtained using NEN-TRAC Ce-141 and TRACER Sr-85 in one sheep, and between Q values obtained using NEN-TRAC Ce-141 and Sn-113 and TRACER Cr-51, Sr-85 and Nb-95 in a second sheep. It is concluded that NEN-TRAC microspheres satisfy the major validation tests to which TRACER microspheres have been previously subjected, and therefore it is valid to proceed with use of the new product.