AJDRAJNR - American Journal of Neuroradiology

Published ahead of print on April 16, 2008
doi: 10.3174/ajnr.A1067
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Coils in a Nutshell: A Review of Coil Physical Properties

J.B. Whitea, C.G.M. Kenc, H.J. Cloftb and D.F. Kallmesb

a Department of Neurological Surgery, Mayo Clinic, Rochester, Minn
b Department of Radiology, Mayo Clinic, Rochester, Minn
c independent coil engineer


Figure 1
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  		Fig 1. The relative hardness of the metals and their alloys commonly used to construct coils. The G of each metal and alloy is referenced and then normalized to a nitinol value of 1 gigapascal (GPa).


Figure 2
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  		Fig 2. A cartoon depicting a helical coil design with representations of the primary (1°) configuration with D1, the secondary (2°) configuration with D2, and the tertiary (3°) configuration with D3.


Figure 3
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  		Fig 3. The relative coil softness for numerous coil lines developed from the 5 companies that manufacture them. For each coil, a simplified spring-constant equation (D1/D2) was used to derive k. This simplified equation makes several assumptions, including an identical value for G and n. It also negates the contribution of various stretch-resistant and bioactive components. The y-axis shows the name of each coil line. The x-axis reveals the k for each coil. The smaller the value of k, the softer the coil.


Figure 4
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  		Fig 4. A graph that compares the softness (y-axis) of each coil as it relates to its filling volume (x-axis). Softness is determined as in Fig 3. The volume for each coil is shown as a function of D2, which assumes an identical length for all coils compared. Softer coils are lower on the y-axis. Coils with a greater filling volume fall farther along the x-axis. The graph is divided into 4 quadrants as the watermarks illustrate. Quadrant 4 encompasses coils that are the softest while maintaining greater filling volumes. Conversely, quadrant 1 contains the "stiffest" coils with the lowest filling volume. The numbered squares in quadrant 4 represent the 6 softest coils with the greatest filling volume. The total number of squares in this figure is smaller than the number of coils compared due to identical overlap of some coils. 1 = Cashmere 14 (2–4 mm); 2 = Complex 18 (5–7 mm); and 3 = Axium 3D and Helix (7–10 mm), Helipaq-18 (2–6 mm), Cashmere 14 (5–12 mm), GDC-18 Soft, Helical 18 (2–6 mm), Complex 18 (2–4 mm), and Compass 18 (4–5 mm).





Copyright © 2009 by the American Society of Neuroradiology. Print ISSN: 0195-6108 Online ISSN: 1936-959X