Relationship between Two Types of Coil Packing Densities Relative to Aneurysm Size

BACKGROUND AND PURPOSE: Coil packing density (PD) can be calculated via a formula (PD_F) or software (PD_S). Two types of PD can be different from each other for same aneurysm. This study aimed to evaluate the interobserver agreement and relationships between the 2 types of PD relative to aneurysm size. METHODS: Consecutive 420 saccular aneurysms were treated with coiling. PD (PD_F, [coil volume]/[volume calculated by formula] and PD_S, [coil volume]/[volume measured by software]) was calculated and prospectively recorded. Interobserver agreement was evaluated between PD_F and PD_S. Additionally, the relationships between PD_F and PD_S relative to aneurysm size were subsequently analyzed. RESULTS: Interobserver agreement for PD_F and PD_S was excellent (Intraclass correlation coefficient, PD_F; 0.967 and PD_S; 0.998). The ratio of PD_F and PD_S was greater for smaller aneurysms and converged toward 1.0 as the maximum dimension (D_M) of aneurysm increased. Compared with PD_S, PD_F was overestimated by a mean of 28% for D_M < 5 mm, by 17% for 5 mm ≤ D_M < 10 mm, and by 9% for D_M ≥ 10 mm (P < 0.01). CONCLUSIONS: Interobserver agreement for PD_F and PD_S was excellent. However, PD_F was overestimated in smaller aneurysms and converged to PD_S as aneurysm size increased.