Evaluation of vascularization in rabbits hydroxyapatite orbital implant by MRI

Abstract

Objective To study the fibrovascular ingrowth progression of orbital hydroxyapatite implant in rabbits with MRI,and to identify its findings and characteristics.Methods Hydroxyapatite orbital implants were implanted into the right orbits of 12 New Zealand white rabbits with the same surgery procedure.All rabbits underwent pre-and postcontrast MRI at 2,3,4,5 and 6 weeks after Hydroxyapatite placement.The enhancement volumes of HA orbital implant were measured,and the V_E/V_(HA) ratios were analyzed statistically by using one-way analysis of variance.At 2 and 4 weeks,two implants were extracted and examined histopathologically.The left implants were treated in the same way at 6 weeks.Results The average V_E/V_(HA) ratios were 0.570±0.055,0.787±0.036,0.995±0.014,1.000±0.000,and 1.000± 0.000 at 2,3,4,5 and 6 weeks respectively.The average V_E/V_(HA) ratios of the HA orbital implants increased gradually during the first 4 weeks after HA placement,and it showed statistical significance(F= 233.094,P=0).However,the average V_E/V_(HA) ratios of week 5 and week 6 were not higher than that of the week 4(F=0.686,P=0.520).The fibrovascular tissue invaded the pores of the HA orbital implants after 2 weeks,while almost all implants were fully vascularized after 4 weeks and 6 weeks.Conclusion MRI is a sensitive modality for assessing the process of vascularization in ocular HA implants.