Nathaniel M. Fried

Noncontact stimulation of the cavernous nerves in the rat prostate using a tunable-wavelength thulium fiber laser.

BACKGROUND AND PURPOSE Laser nerve stimulation has recently been studied in neuroscience as an alternative to electrical stimulation. Its advantages include noncontact stimulation, better spatial selectivity, and elimination of electrical stimulation artifacts. This study explored laser stimulation of the rat cavernous nerves as a potential alternative to electrical nerve mapping during nerve-sparing radical prostatectomy. MATERIALS AND METHODS The cavernous nerves were surgically exposed in 10 male rats. A thulium fiber laser stimulated the nerves, with a wavelength of 1870 nm, pulse energy of 7.5 mJ, radiant exposure of 1 J/cm2, pulse duration of 2.5 msec, pulse rate of 10 Hz, and 1-mm laser spot diameter, for a stimulation time of 60 sec. RESULTS AND CONCLUSION A significant increase in the intracavernosal pressure was detected on laser stimulation, with pressure returning to baseline values after stimulation ceased. This study demonstrates the feasibility of noncontact stimulation of the cavernous nerves using near-infrared laser radiation.

Contact focusing multimodal microprobes for ultraprecise laser tissue surgery

Focusing of multimodal beams by chains of dielectric microspheres assembled directly inside the cores of hollow waveguides is studied by using numerical ray tracing. The device designs are optimized for laser surgery in contact mode with strongly absorbing tissue. By analyzing a broad range of parameters it is demonstrated that chains formed by three or five spheres with a refractive index of 1.65-1.75 provide a two-fold improvement in spatial resolution over single spheres at the cost of 0.2-0.4 attenuation in peak intensity of the central focused beam. Potential applications include ultra precise laser ablation or coagulation in the eye and brain, cellular surgery, and the coupling of light into photonic nanostructures.

Optical Coherence Tomography of Cavernous Nerves: A Step Toward Real-Time Intraoperative Imaging During Nerve-Sparing Radical Prostatectomy

OBJECTIVES To demonstrate the use of optical coherence tomography (OCT) for imaging of the cavernous nerve (CN) and periprostatic tissues. The rates of nerve preservation and postoperative potency after radical prostatectomy might improve with better identification of the CN using emerging intraoperative imaging modalities. OCT is an imaging modality that allows for real-time, high-resolution, cross-sectional imaging of tissues. METHODS Seven male Sprague-Dawley rats underwent surgery using a midline celiotomy to expose the bladder, prostate, and seminal vesicles. The CNs and major pelvic ganglion were identified. Visual identification of the CN was further confirmed by electrical stimulation with simultaneous intracorporeal pressure measurements. OCT images of the CN, major pelvic ganglion, bladder, prostate, and seminal vesicles were acquired and correlated directly with the histologic findings. Once a baseline technique for the scanning and interpretation of the acquired images was established using the rat model, OCT was used to image ex vivo human prostatectomy specimens. RESULTS OCT provided unique imaging characteristics, differentiating the CN from the bladder, prostate, seminal vesicles, and periprostatic fat. OCT images of the CN and prostate correlated well with the histologic findings. OCT of ex vivo human prostatectomy specimens revealed findings similar to those with the rat experiments, with, however, less dramatic architecture visualized in part because of the thicker capsule and more dense stroma of human prostates. CONCLUSIONS The results of our study have shown that OCT provides real-time, high-resolution imaging of the CN in the rat model with excellent correlation to the histologic findings. This study provides a basis for the intraoperative use of this emerging technology during nerve-sparing prostatectomy.

Thulium Fiber Laser Ablation of Urinary Stones Through Small-Core Optical Fibers

Complications during laser lithotripsy include optical fiber bending failure resulting in endoscope damage and low irrigation rates leading to poor visibility. Both problems are related to fiber diameter and limited by the holmium:YAG (Ho:YAG) laser (lambda = 2120 nm) multimode beam profile. This study exploits the thulium fiber laser (lambda = 1908 nm) beam profile for higher power transmission through smaller fibers. Thulium fiber laser radiation with 1 ms pulse duration, pulse rates of 10-30 Hz, and 70-mu m-diameter spot was coupled into silica fibers with 100, 150, and 200 mum core diameters. Fiber transmission, bending, and endoscope irrigation tests were performed. Damage thresholds for 100, 150, and 200 mum fibers averaged 40, 60, and > 80 W, respectively. Irrigation rates measured 35, 26, and 15 mL/min for no fiber, and 100 and 200 mum fibers. Thulium fiber laser energy of 70 mJ delivered at 20 Hz through a 100 mum fiber resulted in vaporization and fragmentation rates of 10 and 60 mg/min for uric acid stones. The thulium fiber laser beam profile provides higher laser power through smaller fibers than Ho:YAG laser, potentially reducing fiber failure and endoscope damage, and allowing greater irrigation rates for improved visibility.

Laser skin welding: In vivo tensile strength and wound healing results

Laser skin welding was investigated as a general model for laser tissue closure. Scanned delivery of near‐infrared laser radiation in combination with a dye can produce strong welds with limited thermal damage.

Linear lesions in myocardium created by Nd:YAG laser using diffusing optical fibers: In vitro and in vivo results

Linear lesions may be necessary for successful catheter ablation of cardiac arrhythmias such as atrial fibrillation. This study uses laser energy delivered through diffusing optical fibers as an alternative to radiofrequency energy for the creation of linear lesions in cardiac tissue in a single application.

Comparison of holmium:YAG and thulium fiber laser lithotripsy: ablation thresholds, ablation rates, and retropulsion effects

The holmium:YAG (Ho:YAG) laser lithotriptor is capable of operating at high pulse energies, but efficient operation is limited to low pulse rates (∼10 Hz) during lithotripsy. On the contrary, the thulium fiber laser (TFL) is limited to low pulse energies, but can operate efficiently at high pulse rates (up to 1000 Hz). This study compares stone ablation threshold, ablation rate, and retropulsion for the two different Ho:YAG and TFL operation modes. The TFL (λ = 1908 nm) was operated with pulse energies of 5 to 35 mJ, 500-μs pulse duration, and pulse rates of 10 to 400 Hz. The Ho:YAG laser (λ = 2120 nm) was operated with pulse energies of 30 to 550 mJ, 350-μs pulse duration, and a pulse rate of 10 Hz. Laser energy was delivered through 200- and 270-μm-core optical fibers in contact mode with human calcium oxalate monohydrate (COM) stones for ablation studies and plaster-of-Paris stone phantoms for retropulsion studies. The COM stone ablation threshold for Ho:YAG and TFL measured 82.6 and 20.8 J∕cm(2), respectively. Stone retropulsion with the Ho:YAG laser linearly increased with pulse energy. Retropulsion with TFL was minimal at pulse rates less than 150 Hz, then rapidly increased at higher pulse rates. For minimal stone retropulsion, Ho:YAG operation at pulse energies less than 175 mJ at 10 Hz and TFL operation at 35 mJ at 100 Hz is recommended, with both lasers producing comparable ablation rates. Further development of a TFL operating with both high pulse energies of 100 to 200 mJ and high pulse rates of 100 to 150 Hz may also provide an alternative to the Ho:YAG laser for higher ablation rates, when retropulsion is not a primary concern.

Denoising during optical coherence tomography of the prostate nerves via wavelet shrinkage using dual-tree complex wavelet transform

The dual-tree complex wavelet transform (CDWT) is a relatively recent enhancement to the discrete wavelet transform (DWT), with important additional properties. It is nearly shift-invariant and directionally selective in two and higher dimensions. In this letter, a locally adaptive denoising algorithm is applied to reduce speckle noise in time-domain optical coherence tomography (OCT) images of the prostate. The algorithm is illustrated using DWT and CDWT. Applying the CDWT provides improved results for speckle noise reduction in OCT images. The cavernous nerve and prostate gland can be separated from discontinuities due to noise, and image quality metrics improvements with a signal-to-noise ratio increase of 14 dB are attained.

Characterization of novel microsphere chain fiber optic tips for potential use in ophthalmic laser surgery

Ophthalmic surgery may benefit from use of more precise fiber delivery systems during laser surgery. Some current ophthalmic surgical techniques rely on tedious mechanical dissection of tissue layers. In this study, chains of sapphire microspheres integrated into a hollow waveguide distal tip are used for erbium:YAG laser ablation studies in contact mode with ophthalmic tissues, ex vivo. The lasers short optical penetration depth combined with the small spot diameters achieved with this fiber probe may provide more precise tissue removal. One-, three-, and five-microsphere chain structures were characterized, resulting in FWHM diameters of 67, 32, and 30 μm in air, respectively, with beam profiles comparable to simulations. Single Er:YAG pulses of 0.1 mJ and 75-μs duration produced ablation craters with average diameters of 44, 30, and 17 μm and depths of 26, 10, and 8 μm, for one-, three-, and five-sphere structures, respectively. Microsphere chains produced spatial filtering of the multimode Er:YAG laser beam and fiber, providing spot diameters not otherwise available with conventional fiber systems. Because of the extremely shallow treatment depth, compact focused beam, and contact mode operation, this probe may have potential for use in dissecting epiretinal membranes and other ophthalmic tissues without damaging adjacent retinal tissue.

Identification and Imaging of the Nerves Responsible for Erectile Function in Rat Prostate, In Vivo , Using Optical Nerve Stimulation and Optical Coherence Tomography

The cavernous nerves on the prostate surface are responsible for erectile function. Optical diagnostic tools such as optical coherence tomography and laser nerve stimulation may assist in the identification, imaging, and preservation of these microscopic nerves during prostate cancer surgery, and thus, help preserve sexual function after surgery. The feasibility of noncontact laser stimulation of the cavernous nerves is demonstrated in an in vivo rat prostate model with comparison to conventional electrical nerve stimulation. High-resolution optical coherence tomographic images of the nerves are also obtained and compared with histology. These optical technologies may be suitable as surgical guidance tools during laparoscopic and robotic nerve-sparing prostate cancer surgery.