Coil is a kind of wire which is used to fill the aneurysm and is usually made of platinum. This wire which can be considered as a major achievement of metallurgical engineering actually consists of two separate wire knitting on each other; during the production shape memory is imparted to these wires and it takes the pre-taught shape itself as soon as it is out of the catheter despite being flat within the catheter. Being produces with such high-tech, diameter of the wires vary between 0.25 - 0.45mm (0.010-0.018 inches).
Coils have various dimensions, characteristics and wrapping shapes.
Numerically-mentioned features, include the diameter of the ring that the wire forms and the length of the coil piece forming this ring. Length of the coils which form rings in diameters of ranging from 1.5 mm to 20 mm, may range between 1 cm – 40 cm. For example, the definition specified as 5 x 15, refers to the coin in total length of 15 cm forming rings in diameter of 5 mm from the time it is out of the catheter.
There are different definitions depending on the nature of the movement of the ring formed by coils .The most commonly used ones are:
1 Helical: is the model of coil which forms a shape like a properly wrapped garden hose as soon as it is out of the catheter tip.
2- 2-D helical model is the coil which forms a shape like a garden hose whose first rings are winded in smaller sizes.
3. 3-D: is the model which present tortuosity in order to form a sphere at spatial plan as soon as it comes out of the catheter.
4. Complex: Although the rings which are out of the catheter form sphere, these rings form the wall of the sphere. The ball made up by using this model compounds of onion shaped layers.
-Definitions used according to the hardness of the wires forming the coil:
1.Standart: While a particular conditioning technique is not used, considering that the platinum wire forming the coil is in diameter of 0:10 to 0:20 mm it is understandable that the coil is still soft.
2.soft: consists of soft wire comparing to standard hardness
3.Hypersoft / ultrasoft: Can be counted as the softest wire that today's technology reached. Can be considered to be even smoother than normal sewing thread.
-There can be coating on the wire forming the coil made of materials with different function.
1 Hydrogel coated: Although this type of coil which has not contacted blood or water is in the similar size with normal coils, may swell and expand 5 to 10 times larger than its volume after contact with blood or water approximately in 20 - 30 minutes. Thanks to this feature a larger volume can be filled using fewer than the normal coil.
2 Texture-improving agents: these substances deposited on the wire become liberalized in time and help disappearance of the clot formed in aneurysm and instead helps to improve scar tissue.
In order for wire helix named as catheter reach till aneurysm by advancing through the catheter and entirely be within aneurysm, it should be attached to a tip of another wire (in the same thickness). Considering that the length of the catheter being used by entering inside the vein through groin is longer than 1 meter, necessity of this wire is obvious. In order for the coil reaching till aneurysm to form proper helixes, providing the most ideal winding shape is required by moving it forward and backward. In some cases, coil sent up to the aneurysm may need to be removed back. To that end, a link that is safe but which can provide breakout in control is required between the coil and the wire carrying it on its tip. Robust and secure tangle can be formed by winding coils in variety of diameters and lengths within the aneurysm only in this way. For example, initially a coil in diameter of 5 mm is winded to an aneurysm of 5 mm, after it is pulled of and left within the aneurysm, pusher wire is removed from the catheter, then a coil in diameter of 4 mm is sent and winded, following to appropriate winding of this coil, it is pulled off and pusher wire is removed and the procedure is continued with coils in diameter of 3 to 2 mm. The link between the pusher wire and the coil are produced in different forms by different producers. The most commonly used models have properties of electrolysis, hydrolysis or mechanically pulled of.