EFFECTS OF SPATIAL-DISTRIBUTION ON PROTON RELAXATION ENHANCEMENT BY PARTICULATE IRON-OXIDE

The proton relaxation effect of superparamagnetic iron oxide (SPIO) pa rticles under varying conditions of spatial distribution was investiga ted with use of phantoms. Agar phantoms containing various concentrati ons of SPIO or gadopentetate dimeglumine, with and without Sephadex be ads, were studied. Phantoms with Sephadex had a heterogeneous spatial distribution of iron oxide, comparable to liver tissue in vivo. Relaxo metry at 0.47 T showed decreased T2 relaxivity of SPIO in Sephadex pha ntoms compared with that in agar phantoms without Sephadex. On T2-weig hted images obtained at 1.5 T, the signal intensity of Sephadex phanto ms showed less SPIO relaxation effect than that of plain agar phantoms . Unlike SPIO, gadopentetate dimeglumine showed the same relaxivities and signal intensity in plain agar and Sephadex phantoms. The results show that the T2 relaxation effect of iron oxide depends on its spatia l distribution. A heterogeneous spatial distribution, as in intact liv er tissue, diminishes the T2 relaxivity of iron oxide particles.