The Frequency-Doubled Double-Pulse Nd:Yag) (FREDDY) laser (World of Medicine, Berlin Germany) is a short-pulsed, double-frequency solid-state laser with wavelengths of 532 and 1064 nm. This low-power, low-cost laser was developed for intracorporeal lithotripsy. We designed an experimental set-up to test its fragmentation efficiency at different energy and frequency settings.
Forty previously weighed plaster-of-Paris stone phantoms were divided into four groups in order to test fragmentation at 5 and 10 Hz for 2 and 4 minutes. A hands-off underwater laboratory set-up including a holder to keep the stone phantom in contact with the quartz laser fiber was utilized. The 280-microm laser fiber was cleaved and stripped between runs to ensure optimal energy delivery. After fragmentation was completed, all of the stone fragments remaining within the holder were allowed to desiccate for 48 hours and reweighed. Fragmentation was measured as the percentage weight loss.
Stone phantoms fragmented at 5 Hz for 2 minutes sustained a mean 24% loss of weight, whereas the 4-minute treatment at 5 Hz reduced stone weight by 54%. Treatment at 10 Hz for 2 minutes demonstrated results similar to those of stones treated for 4 minutes at 5 Hz, reducing stone weight by 51%. Fragmentation at 10 Hz for 4 minutes revealed a 64% loss of mass, less than expected for these power settings. Fiber deterioration observed at the higher energy settings may be the cause of the reduced stone-fragmentation efficiency.
Fragmentation with the FREDDY laser in the 5 Hz, 4 minutes and 10 Hz, 2 minutes protocols is comparable, suggesting that stone fragmentation correlates well with the total energy delivered to the stone. The slight drop in fragmentation efficiency at 10 Hz, 4 minutes is most likely explained by fiber damage occurring consistently at these higher energy settings. The safety profile and low investment and running costs of this laser are advantages that suggest the laser warrants further clinical trials.