Infrared surgical lasers, e.g., CTH:YAG @ 2100 nm and TM:YAG @ 2000 nm, are wonderful tools for minimally invasive surgery such as laser vaporization of hyperplastic prostate tissue (BPH), but they are completely incompatible with right angle, off-axis delivery. Fiber optics find great utility for vaporization of prostate gland lobes about the urethra at less-challenging wavelengths, e.g., 532 nm, where water is transparent. The fundamental advantage of infrared lasers is strong absorption by water (within tissue), but this very absorption renders water-cooled side-firing fibers useless with these laser generators, i.e., MoXy® by Boston Scientific; where the surgical beam passes through the coaxial cooling jacket, the coolant boils and blocks further flow, overheating the device rapidly.
Uncooled side-firing fibers are used by some surgeons, but these devices also overheat if used at anything approaching the maximum laser output. And, even at half power, more than one fiber is typically required to complete a surgical case due to accumulated thermal damage. Worse, the performance of these inadequate fiber devices degrades rapidly during surgery. Specifically, a MoXy fiber is rated at 180 W (532 nm) for 650 KJ total energy delivered, minimum where uncooled side-fire fibers are limited to 100 W (2000–2100 nm) and typically fail at 100 KJ.
The Quartet™ H2O LDD (Patent 9,662,173) is designed with multiple coolant conduction channels formed within the active end of the fiber optic device similar to a heat exchanger coil (for more efficient heat transfer due to Dean’s vortices induced in the tight coil) without crossing the optical path, thereby avoiding interaction with the therapeutic laser energy. The lateral redirection mechanism is contained entirely within the distal cap assembly such that steering the fiber output to address each of the three prostate lobes is accomplished without torquing the optical fiber, allowing more precise control. This cap assembly also contains optics that provide control of the output spot diameter and a more uniform (top hat) radiant intensity such that a larger tissue area may be treated when more laser power is used, thereby avoiding tissue charring due to the overtreatment that is common with fixed output, semi-Gaussian output profiles.
Due to the strong absorption of saline irrigant within the surgical field, lateral delivery fibers are typically held in contact with tissue to avoid energy loss in boiling the saline. Under these conditions, active cooling can only do so much to forestall performance degradation and increase longevity. The commercialized device performance will be augmented with a silver metal jacket around the distal cap to conduct excess heat to a proximally located steel cannula that also serves as the coolant conduit. Control of the fiber output spot diameter is via altering the separation between the fiber optic axial output and the input of the beam-shaping optic via a selector in a control device that is located ex vivo on the optical fiber. This control device is also used for aiming the beam by transferring rotations through the steel cannula to the distal output capsule.