Deflection of Coil Tipped Catheter
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Published: Wed, 30 Aug 2017
It happens that most of it are remotely steerable catheters. In this paper, it becomes fit to the lines can be used for turning of the wall unto the pool of the inclination of the times, the rotation can be made, the counsel and the miniaturization capabilities.
The deflection of the coil-tipped catheter has been studied and verified by the following experimental derived equation .
The above equation majorly depends on the magnetic field strength, current applied, the number of turns of the solenoid coil and stiffness of the catheter. The torque generated by the excitation of the deflection coil that allows the catheter tip to deflect or move in the desired direction has been counter balance by reinstating torque created mechanically by the catheter . A linear relation has been observed between the number of turns of the solenoid coil and the mechanical angular bend of the tip, it has also been found that by increasing the magnetic field strength of the MRI Scanner like making it double from 1.5 Tesla to 3 Tesla effecting the deflection angle to be double over a broader spectrum of current values . For better understanding in the clinical application, the catheter tip could get the deflection of about 90 degrees for a standard catheter which has the tip length around 7mm having the 100 turns of solenoid coil that will be energized with current of 300 milliamps and the MRI gantry is at 1.5 Tesla . It is important to note that the decrease in the tip length will result a reduction in the number of turns and by increasing the coil current can get the same result.
It is worth noting that the catheter tip could be kept on hold for about a minute towards a defined target due to the magnetic force, this aspect is most useful for the application of Cardiac Ablation . Since the time required to deflect the catheter tip is rapidly that’s why charging the coil for few seconds could allow steering inside the vessels .
By using three different coils on the catheter tip arranged orthogonally, allows the tip movement in the 3D space means the tip can be navigated at any required direction . Design and manufacturing of these coils are done by laser Lithography technique which is been smartly arranged on the catheter tip. Further studies show the limitation to acquire smaller diameter deflection of the tip due to the arranging of one coil over another, therefore an alternative design can be suggested to eliminate this issue in which the coils should spread along the length of the tip rather than overlapping each other .
The design of the ferromagnetic sphere approach has the advantage of allowing independent motion in all directions irrespective of the main magnetic field of MRI by using forces of the magnetic gradient . As we have previously discussed in the design, that by using two ferromagnetic beads the deflection will increase twice as compared to the single bead configuration. Due to using two beads the bending occurred in catheter tip will make like S shape curve, where as its shape and amplitude will become more pronounced by increasing the beads distance.
According to the studies, when the two beads having the distance of 4.5mm and tip length of 32.7mm then we get the largest lateral deflection of about 20.3 mm . The deflection up to that extent will add up the weight of a second bead and casing dimensions at the catheter tip. Studies also reveals that with single bead or too closely spaced two beads, the catheter tip could deflect erratically in amplitude. Time required for the successful deflection depend on the time to energize the magnetic gradient .
The catheter tip containing material called as SMPs and SMAs allow a border spectrum of catheter navigation. Both materials having different properties of thermal conductivity and thermal expansion. Comparatively SMAs is more quick to regain its original shape from SMPs, numerically SMAs take only few milliseconds where as SMPs takes few seconds to restore their original shape .
To regain original shape by cooling in SMAs is very slow and the structure is so small that we cannot use forced cooling, SMAs show irregularity so its precision is quite doubtful . A very small amount of SMP or SMA is required to provoke the movement because the size of the catheter tip is so small.
The design of a catheter tip proposed with hydraulic or pneumatic approach would have an instantaneous response time to the pressure changes occurred due to gas or fluid . The material of catheter is responsible for the flexibility of pressurizing lumens to pull wire catheter. The major problem of pneumatic and hydraulic actuator is precision and force control, shows nonlinearity because of the kinetic molecular properties of fluids . Other parameter like temperature, shape, fatigue and friction is also changeable during procedure .
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