R. M. Verdaasdonk

Imaging techniques for research and education of thermal and mechanical interactions of lasers with biological and model tissues.

A setup based on color Schlieren techniques has been developed to study the interaction of energy sources, such as lasers, with biological tissues. This imaging technique enables real-time visualization of dynamic temperature gradients with high spatial and temporal resolution within a transparent tissue model. High-speed imaging techniques were combined in the setup to capture mechanical phenomena such as explosive vapor, cavitation bubbles, and shock waves. The imaging technique is especially used for qualitative studies because it is complex to obtain quantitative data by relating the colors in the images to temperatures. By positioning thermocouples in the field of view, temperature figures can be added in the image for correlation to colored areas induced by the temperature gradients. The color Schlieren setup was successfully used for various studies to obtain a better understanding of interaction of various laser, rf, and ultrasound devices used in medicine. The results contributed to the safety and the optimal settings of various medical treatments. Although the interaction of energy sources is simulated in model tissue, the video clips have proven to be of great value for educating researchers, surgeons, nurses, and students to obtain a better understanding of the mechanism of action during patient treatment.

Side-firing devices for laser prostatectomy

SummaryTransurethral laser coagulation of the prostate has become an accepted treatment for benign prostatic hyperplasia (BPH). The most common method is the use of a sideward-firing fiber that, once inserted in the prostatic area, irradiates the abundant prostatic tissue with Nd: YAG laser light. In this study, eight different side-firing fibers that are commercially available were evaluated. The devices can be characterized by the way laser light is deflected sideward and by their thermal behavior. Most of the eight devices differ with regard to the angle at which the laser beam is deflected, the spot size on the irradiated tissue surface, and the heating of the device itself. Implementation of the optical and thermal characteristics of each device in the treatment protocol will contribute to the optimal use of laser energy for prostatectomy.

Bladder cancer diagnosis during cystoscopy using Raman spectroscopy

Raman spectroscopy is an optical technique that can be used to obtain specific molecular information of biological tissues. It has been used successfully to differentiate normal and pre-malignant tissue in many organs. The goal of this study is to determine the possibility to distinguish normal tissue from bladder cancer using this system. The endoscopic Raman system consists of a 6 Fr endoscopic probe connected to a 785nm diode laser and a spectral recording system. A total of 107 tissue samples were obtained from 54 patients with known bladder cancer during transurethral tumor resection. Immediately after surgical removal the samples were placed under the Raman probe and spectra were collected and stored for further analysis. The collected spectra were analyzed using multivariate statistical methods. In total 2949 Raman spectra were recorded ex vivo from cold cup biopsy samples with 2 seconds integration time. A multivariate algorithm allowed differentiation of normal and malignant tissue with a sensitivity and specificity of 78,5% and 78,9% respectively. The results show the possibility of discerning normal from malignant bladder tissue by means of Raman spectroscopy using a small fiber based system. Despite the low number of samples the results indicate that it might be possible to use this technique to grade identified bladder wall lesions during endoscopy.

Laser prostatectomy for patients with benign prostatic hyperplasia: a prospective randomized study comparing two different techniques using the Prolase-II fiber

SummaryLaser prostatectomy for patients with complaints due to benign prostatic hyperplasia is a relatively new treatment option. The most effective procedure for coagulation and vaporization of the prostate is not yet known. In a prospective randomized study of 30 patients, 2 techniques for the delivery of laser energy were compared at 40 W for 90 s. The complications were minimal and antegrade ejaculation was preserved in 15 of 18 potent men. In 24 patients urodynamics evaluation was possible. In both groups a significant reduction in the symptom score was observed. The decrease in detrusor pressure at maximal flow and the increase in flow rate were, however, disappointing. No significant difference in the results was found between the two groups. The power setting needs to be changed in further studies.

Correlation of thermal and mechanical effects of the holmium laser for various clinical applications

The Holmium laser has become established in orthopedic surgery and urology due to its unique combination of mechanical and thermal properties induced by explosive vapor bubbles. In a specialized setup, real-time high-speed and thermal images of dynamic vapor bubbles and thermal relaxation at a water tissue interface were obtained simultaneously. The thermal effects in the tissue model were correlated to the characteristics of the bubbles dependent on pulse energy (0.2 - 4 J), pulse repetition frequency (5 - 40 Hz), distance and angle of fiber delivery system (diameter 365 micrometer) to the tissue surface. Up to a fiber-to-tissue distance of 50% of the radius of the bubble, only a superficial tissue layer was heated. During bubble implosion, the tissue surface was attracted to the fiber, ripping of irregularities, and was effectively cooled by turbulence. In case of hard tissues, the bubble detached from the fiber imploding towards the hard surface. At closer distances (less than 50% of bubble radius), the tissue itself was vaporized resulting in mechanical damage and thermal relaxation into the tissue, especially above repetition rates of 5 Hz. There is a strong correlation between the path length of the free beam within the bubble and the degree of mechanical and thermal damage in the tissue directly irradiated by this beam. During clinical applications the surgeon should be aware of the size of the vapor bubble in relation to the distance and angle with the tissue for safe optimal use of the mechanical and thermal properties of the Holmium laser.

Development and clinical trial of a practical vessel imaging system for vessel punctures in children

Venipunctures to draw blood for diagnostics can be cumbersome. Multiple puncture attempts are distressing, painful and traumatic, especially for small children. Drawing blood from babies, in particular, is a problem, due to the cutaneous baby fat, tiny veins and, worst case, a pigmented skin. We developed a practical vein viewing system based on IR translumination that, contrary to commercial systems available, has the advantage of: a) low cost, b) easily implemented in routine practice, c) normal and IR image simultaneously available, d) small add-on, e) child friendly IR illuminator and f) efficient IR light coupling. Before introducing the vessel viewer for clinical application in the childrens department, parameters were measured in 194 patients (age 0-17 yrs): time to draw blood, number of attempts, skin characteristics, discomfort of patient, and experience of nurse. In this control group, time to draw blood increases significantly with decreasing age of the children. The instant feedback from the nurses has been valuable for the improvements of especially the illumination sources. A clinical trial has been performed in 125 patients (age 0-6 yrs) to prove effectivity of the system in the blood withdrawal procedure. There was a significant decrease from 13% to 2% in failure rate. Also time needed to search for a vein was significantly decreased. A practical and accessible vein viewing system has been developed and is being introduced for clinical application. Although the concept of patient friendliness is already accepted, measurements need to show the effectiveness for particular groups of patients.

The effect of argon gas flow during electrosurgery

Electrosurgery has been used for over fifty years. Recently a new modality has been introduced: gas-enhanced electrosurgery. A flow of argon gas is blown along the active electrode. For clinical application the temperature distribution in the tissue is of interest. The effect of argon was investigated using two methods. (1) Visualizing the temperature distribution in phantom tissue using Schlieren techniques. (2) Tissue experiments with macroscopic evaluation of the lesions. The electrodes were moved over the tissue surface with different parameter settings for speed (1-4 mm/s), gas now (0, 5 or 9 l/min.), gas-outlet positioning (6, 13 and 21 mm above the tissue) and depth of the electrode in the tissue (0-4 mm). The extent of the coagulation zone seemed to be depend most on gas flow rate in combination with power and the distance of the gas-outlet. Argon gas-enhanced electrodes showed to be especially effective just touching the tissue to obtain a superficial coagulation of the surrounding tissue.