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.