Takayuki Hirano

Pulsed liquid jet dissector using holmium:YAG laser--a novel neurosurgical device for brain incision without impairing vessels.

Summary¶Background. Neurosurgery has long required a method for dissecting brain tissue without damaging principal vessels and adjacent tissue, so as to prevent neurological complications after operation. In this study we constructed a prototype of such a device and used it in an attempt to resect beagle brain cortex. Method. The prototype device consisted of an optical fibre, a Y adaptor, and a nozzle whose internal exit diameter was 100 µm. Cold physiological saline (4 °C) was supplied to it at a rate of 40 ml/h. Pulsed liquid jets were ejected from the nozzle by a pulsed Holmium:YAG) (Ho:YAG) laser at an irradiation energy of 300 mJ/pulse. The profile of the liquid jet was observed with a high-speed camera while changing the distance between the optical fibre end and nozzle exit (equivalent to the standoff distance). With this device (3 Hz operation), brain dissection of anaesthetized beagles was attempted while measuring the local temperature of the target. A histological study of the incised parts was also performed. Findings. When the standoff distance was 24 mm, the liquid jet was emitted straight from the nozzle at a maximum initial velocity of 50 m/s. The brain parenchyma was cut with this device while preserving vessels larger than 200 µm in diameter and keeping the operative field clear. The local temperature rose to no more than 41 °C, below the functional heat damage threshold of brain tissue. Histological findings showed no signs of thermal tissue damage around the dissected margin. Interpretation. The Ho:YAG laser-induced liquid jet dissector can be applied to neurosurgery after incorporating some minor improvements.

A novel method of drug delivery for fibrinolysis with Ho:YAG laser-induced liquid jet

Two of the problems inherent in the treatment of cerebral emboli are the narrow therapeutic time window and the severe side effects of fibrinolytic drugs. Thus, it is necessary to develop a new method of removing a cerebral thrombus more rapidly and with smaller quantities of fibrinolytics. The behaviour of a bubble formed by holmium (Ho):YAG laser irradiation in a capillary tube filled with pure water was observed at various stand-off distances (L; distance between the end of optical fibre and the capillary exit). Subsequently, a liquid-jet generator was created by insertion of an optical fibre (core diameter: 0.6 mm) into a catheter (6 Fr) filled with pure water, and a pulsed Ho:YAG laser (pulse duration time=350 µs, laser energy=230 mJ/pulse) was used to irradiate the optical fibre. The maximum penetration depth, into a gelatin artificial thrombus, of a liquid jet generated with this device was measured for various stand-off distances. Additionally, the phenomenon and the pressure around the catheter exit were captured via shadowgraph and PVDF needle hydrophone, respectively. The laser-induced bubble in the capillary tube grew rapidly in the direction of propagation and generated a liquid jet. The maximum penetration depth of this liquid jet into an artificial thrombus increased in proportion to L and reached a maximum value (9 mm) when L was around 13 mm. A shock wave whose overpressure at a point 4 mm away from the catheter exit exceeded 12 MPa was captured by shadowgraph. It was concluded that Ho:YAG laser irradiation within a water-filled catheter caused liquid jet formation, which could penetrate straight into an artificial thrombus. Hence, this jet is expected to promote fibrinolysis by means of injecting fibrinolytics deeply into the thrombus. After resolving some problems, this system will be applied to an endovascular therapy for cerebral embolisms in the near future.

On the efficiency of Gore-Tex layer for brain protection from shock wave damage in cranioplasty

The effectiveness of a Gore-Tex layer for protecting soft tissue from damage in shock wave therapy is investigated analytically, numerically and experimentally. Analytical considerations based on the fundamentals of wave dynamics and two-dimensional numerical simulations based on the elastodynamic equations are carried out for underwater shock wave propagation and interaction with Gore-Tex membrane models of different complexity. The results clearly demonstrate that considerable attenuation of shock waves with Gore-Tex is due to the air trapped inside the membrane. The experimental results confirm that a Gore-Tex sheet placed in the liquid reduces the transmitted shock wave peak overpressure significantly, by up to two orders of magnitude. Another experimental series reveals what kind of damage in the rat brain tissue can be caused by shock waves of different intensity.

Metachronous neurohypophysial immature teratoma occurring 10 years after total resection of pineal mature teratoma

Abstract An 18-year-old boy presented with an immature neurohypophysial teratoma occurring 10 years after total resection of a mature pineal teratoma through an occipital transtentorial approach in 1989. Thorough histological examination had revealed a mature teratoma. He developed panhypopituitarism and diabetes insipidus in 1999. Magnetic resonance imaging revealed a suprasellar tumor occupying the third ventricle. This tumor was totally resected through a frontobasal approach. Histological examination revealed an immature teratoma. This tumor occurred in a different site from the initial tumor and was considered to be de novo and thus a so-called metachronous germ cell tumor. Patients with completely resected mature teratoma require extended follow-up, including periodic magnetic resonance imaging, because of the risk of such a metachronous germ cell tumor.

Biological effect of shock waves on rat brain: pathological evaluation by compact Ho:YAG-laser-induced cavitational shock wave generator

To introduce shock wave as a new treatment modality for the lesions in the vicinity of brain and skull, pressure-dependent brain damages after exposure of shock wave were investigated. A novel compact Ho:YAG laser-induced cavitational shock wave generator (diameter: 15 mm, weight: 20g) was used intstead of clinical lithotriptors due to their wide distribution of shock waves. In the first part, we have developed and investigated characteristics of present generator by means of high-speed photography, shadowgraphy, and pressure measurement. Generation of localized shock wave without harmful effect of laser was observed after irradiation of Ho:YAG laser in the brass tube with internal water supply. Mechanical effect of accompanying laser-induced liquid jet was mitigated after placement of latex diaphragm with acrylic water reservoir. Maximum overpressure of generated shock wave was 15 MPa before placement of diaphragm, and 5 MPa after placement of diaphragm. In the second part, shock wave-induced brain damages were investigated in 5 male Sprague-Dawley rats. While subarachnoid hemorrhage could be observed between 1 and 5 MPa, intracerebral hemorrhage, and laceration of tissue were also observed above 5 MPa. We therefore conclude that overpressure of exposing shock wave over brain surface should be managed under 1 MPa.

Quasi-Real Time Bio - Tissues Monitoring using Dynamic Laser Speckle Photography

AbsractJoint development of a laser monitor for the real-time bio-tissue analysis is presented. The monitor is based on the digital dynamic laser speckle photography and deals with soft and hard bio-tissues. In soft tissues, the dynamic bio-speckles are formed in a scattered from a tissue laser light. An optically transparent model of hard bio-tissue was prepared and preliminary analysis of a stress field in the stressed model was performed using the dependence of the refractive index of transparent solids upon the state of stress and the double exposure speckle photography data. The refractive index of the stressed material was evaluated and the state of stress was reconstructed using the stress-optical law.

Short-range displacement detection from speckle interference using transparent thin-film photodiode

Speckle interference in space was monitored by using a newly developed transparent thin-film photodiode, which was fabricated by micromachining techniques. Since the sensitive region of the developed photodiode was thinner than one-half of the wavelength, an optical standing wave generated by the interference between two waves propagating in opposite directions was detected. This photodiode was used in a short-range displacement measurement in a speckle field. Using the sinusoidal phase modulation technique, object displacement was sensed with an accuracy of about 30 nm in a speckle granular structure.

A laser-induced liquid jet catheter system: a novel endovascular device for rapid and reliable fibrinolysis in acute cerebral embolism.

OBJECTIVE Mechanical removal of intravascular clots in addition to administration of tissue plasminogen activator are both desirable for improved outcome in acute embolic stroke. We have developed a novel endovascular catheter system for rapid and reliable mechanical recanalization of cerebral embolisms with little or no requirement for fibrinolytic agents. Here, we describe the evaluation of this device in vitro. MATERIALS Pulsed liquid jets were generated and ejected from the catheter exit by accelerating cold physiological saline (4 degrees C, 40 mL/h) using the energy of a pulsed holmium:yttrium-aluminum-garnet (YAG) laser (3 Hz, 1.2 W). Accessibility beyond the tortuous cavernous portion of the internal carotid artery to the M1 and A1 regions was confirmed using a transparent model of the human cerebral artery. Mechanical characteristics of the liquid jets were evaluated with a high-speed camera. Liquid jets of physiological saline or urokinase solution (1,200 IU/mL) were exposed to artificial thrombi made of human blood under temperature monitoring. Remnants of thrombi were collected and incubated at 37 degrees C for 10 min for estimation of fibrinolysis rates. RESULTS The jet velocity (maximum: 5 m/s) was controlled by changing the laser energy. The fibrinolysis rates (mean+/-SD) after exposure to jets of saline or urokinase solution for 45 s were 62.2+/-16.4 and 94.0+/-3.4%, respectively, and were significantly better than the rate of 8.1+/-2.0% with administration of urokinase alone. The local temperature rise was less than 8 degrees C. CONCLUSIONS The results show that the laser-induced liquid jet catheter system may be a powerful tool for mechanical destruction of emboli and augmentation of the effect of fibrinolytic agents beyond the tortuous part of the internal carotid artery.

Study of weak underwater shock waves generated by Ho:YAG pulse laser beam

For medical application of underwater shock waves as a less‐invasive approach, a reliable micro shock wave source is required. The present paper reports progress in production of underwater micro shock waves by direct irradiation of pulse laser beam. Energy source was a Q‐switched Ho:YAG laser (Nippon Infrared Industries Co. Ltd.) with 91 mJ/pulse energy measured at the end of a 0.60‐mm diameter glass optical fiber, pulse duration of 200 ns, and wavelength of 2.1 μm. The laser beam was focused and transmitted through the optical fiber. The generation and propagation of underwater shock waves from the roughened end of the fiber were quantitatively visualized by double‐exposure holographic interferometry. Sequential flow visualization revealed that plasma generated by the laser beam drove spherical shock waves. The diameter of plasma region increased, then reduced and detached from the fiber end. Heat‐induced flow in front of the fiber vanished after 100 ms. Peak overpressures were measured at various stand...

Experimental application of pulsed Ho:YAG laser-induced liquid jet for neuroendoscopic hematoma removal

To develop the novvel device for neuroendoscopic hematoma removal, we describe the Ho:YAG laser-induced liquiud jet system for hematoma fragmentation and liquefaction. Two types of nozzle were used (nozzle 1: internal diameter: 200 μm, nozzle 2: internal diameter: 1000 μ, each length: 5mm) and the pressure profiles of LILJ ejected from those nozzles were measured. And also the effectiveness of present system was evaluated by calculating liquefaction rate (measured as the percentage of the weight loss of the treated artificial hematoma) in vitro experiments.