Abstract
The authors studied the effect of a pulse modulated Ho:YAG laser (Lumenis Moses platform) to fragment stone phantoms in an in vitro model. They are to be congratulated for this outstanding set of experiments. I interpret the following most relevant take-home points: Ho:YAG lithotripsy is most efficient in contact mode versus any separation distance between the fiber and the stone surface. Although the Moses platform allows pulse modulation modes that could bridge the gap and “part the waters like Moses” to permit fragmentation to occur in noncontact mode, the data conclusively show greatest fragmentation efficiency in contact regardless of pulse modulation mode selected. This finding is not surprising as mid-infrared energy is well absorbed by water.
1
The most efficient Ho:YAG lithotripsy occurs when the full quantity of photons is delivered to the stone and not wasted into creating a vapor channel where only a portion of photons reaches the stone.
2
The recent trend toward use of popcorn technique for Ho:YAG lithotripsy has potentially created the (false) belief you can simply break the stone without having to contact the stone. Popcorn lithotripsy works by imparting momentum from bubble expansion and collapse that causes the stone to displace. Fragmentation occurs when the displaced stone happens to “fly by” the fiber tip when the laser is emitted.
3
It is conceivable, however, that use of Moses mode (contact or distance) might create a longer “fly by strike distance” for popcorn lithotripsy. But I would still recommend urologists work in contact mode wherever technically possible as it is most efficient. Moses distance mode yielded 28% greater fragmentation in contact compared with other pulse modes in contact. This finding is striking. In contact mode, the relevance of getting liquid water out of the path of the photons is a moot point. In contact mode, all photons are being delivered to the stone regardless of mode. To date, the thinking has been a photon is a photon is a photon. There is an overall correlation with the number of photons delivered into the stone yields an equivalent amount of fragmentation.
4,5
However, we now have evidence that 1 J of energy delivered in pulse modulated manner yields significantly more fragmentation than the same total energy without the pulse modulation. This finding begs the question how pulse modulation seems to yield enhanced fragmentation with the same total amount of energy—the laser equivalent of a free lunch! It raises the possibility of further developments to define more efficient laser lithotripsy.