In-line power meter for use during laser angioplasty

摘要

Recanalization of occluded limb arteries can be accomplished using a pulsed dye laser. Either ball-tipped 600 $mu@m fused quartz optical fibers or over-the-wire multifiber catheters are used to deliver laser energy. The alignment of the device is adjusted to achieve maximal transmitted power. To monitor power output during surgery the authors have developed an in- line powermeter (ILP). On leaving the laser the ball-tipped optical fiber is magnetically clamped in a V-groove. Radial light emission is converted to an electrical signal which is integrated to give an analogue output proportional to power. The reading is adjusted to be concordant with that from the bolometer. Over the range 20 to 200 mJ per pulse the linearity was better than 2.5% of full scale. The coefficient of variation of the ILP output following repeated placement of the same aligned fiber in the V-groove was less than 7%. Flexing the fiber through 90$DGR 10 cm from the V-groove caused the registered power to fall by up to 7%. In the case of the multifiber catheter a modified clamping arrangement was used. Linearity for a 7 Fr catheter comprising 15 fibers 200 $mu@m in diameter was better than 5% of full scale; the coefficient of variation for repeated alignment of a catheter was 14%. The catheters do not have a circular section, which accounts for this large variation. Flexing the catheters had no consistent effect on registered power, but changes of up to $POM 10% could be obtained by extreme bending of the catheter. The output of the ILP does not appear to be affected by the nature of the target. Changes in output power and/or delivery device alignment can be detected and corrected during laser angioplasty. Accurate control of power delivered without exposing the tip of the fiber reduces the risk of injury from inadvertent laser discharge and aids optimal ablation of atheroma. The ILP ensures that effective power is maintained throughout the procedure.