The editorial in the Archives (139:143, 1979) on leg scanning does not sufficiently emphasize recent scanning alternatives that have been developed to solve this clinical problem.
The low (18%) sensitivity in detecting deep vein thrombosis from Hunter's canal to the inguinal ligament reported in the Archives (139:148-153, 1979) may be explained in part by the physical characteristics of the isotope used. The photons from fibrinogen I 125 are a 35.5-keV υray and a 27-keV x-ray. These relatively soft photons are easily attenuated by the body tissues surrounding the deep veins. Since muscle mass in the thighs is greater than in the calves, detection efficiency (and hence the sensitivity of the test) drops in the proximal portions of the lower extremities. The signal-to-noise ratio also is worse in the pelvis than in the legs due to problems of blood pooling. The solution to this problem is to use an isotope with