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Biomedical subjects

F Canestri

Publications and source records attributed to F Canestri.

9 recordsLinked to original sources
PubMed2000

Thermal lesions produced by CO2 laser beams: new findings to improve the quality of minimally invasive and transmyocardial laser revascularization protocols.

OBJECTIVE: The objective of this study was to investigate the possible existence of a set of critical combinations among medical CO2 laser device set-ups and to compare the resigns of diameter and depth of irradiated tissue. These data are useful to the surgeon to identify a general operative protocol that allows both to forecast the beam behavior on a large variety of operative conditions accurately and to identify the related safety margins. Two methods have been addressed: the more traditional free-air beam delivery to the tissue and the more modern requirements of the minimally invasive surgery concepts, which use fiberoptic-based delivery systems for the CO2 laser beam. BACKGROUND DATA: In the past many articles have been written about the interaction between laser beams and biological media. However, the CO2 laser beam at 10.6 microm has always challenged research institutions and manufacturers to find the ideal combinations between a suitable fiberoptic-based delivery system concept and the injury threshold conditions recommended for minimally invasive surgery (MIS) and transmyocardial laser revascularization (TMLR) applications. One of the main challenges is to deliver the radiation at 10.6 microm without serious damage to the fiberoptic-based scalpel and the irradiated tissue by the burn of the fiber in use. METHODS: Five rabbits weighing 3 to 3.5 kg were sacrificed and 60 samples of trachea, myocardium, aorta, and esophagus were immediately excised, trimmed free of the adherent connective tissue, and irradiated in the intima portion of the wall. A commercial TEM medical CO2 laser was coupled to a silver halide fiber (0.9 mm in diameter) and subsequently to regular focusing heads (2.5-inch and 5-inch focal length) for pulsed laser beam delivery. The parameters chosen were: 33, 50, 65, and 100 mJ per pulse, 10 and 20 ms pulse width, delivered in two sets of experiments, one with all the pulsed beam frequencies below 5 Hz, the other between 15 Hz and 20 Hz. The same tests were conducted on 10 blocks of 3 different plastic types to simulate in one single procedure the laser radiation in responses to both hard, low-water content tissues such as bone and of common plastic compounds (such as polymethylmethacrylates [PMMA]) routinely used in orthopedic surgery. An optical microscope was used to measure all the lesions (diameter and depth in millimeters) in all the samples and to identify the smallest and the largest one against which similar thermal injuries found on the other media were compared. RESULTS: This study demonstrates that for power densities between about 520 and 790 W/cm2 per pulse achieved with the silver halide fiber generated a minimal lesion on the myocardium and aortic tissues. This can be used as reference threshold for MIS and TMLR. The minimal injury threshold on PMMA has been reached at 393 W/cm2 per pulse at 1 Hz. This approached the conditions of a pulsed beam delivered in air on the same medium via a focal spot of an 8.7 inch focal. Surprisingly, all the treated media show lesions that follow similar patterns within a well-defined and limited range of both diameter and depth. This effect was obtained by using power densities ranging from 393 to 6310 W/cm2 per pulse regardless of all the other parameters, including power delivery method, the type of irradiated tissue and the frequency between 0 and 20 Hz. Only the combination power density-type of tissue appears to be decisive. The geometrical convergence of the diameter shows a much smoother pattern than the one of the depth, due to two different irradiation modalities. CONCLUSIONS: The selection of the CO2 laser beam parameters and the irradiated media reported in this article have allowed identification of a critical set of ablative conditions to be further used in the operating room.

Animals↗
PubMed1999

The fluidodynamics of potentially neoplastic plumes produced by medical lasers: first quantitative non-tissue-specific measurements using PMMA samples (phase I).

OBJECTIVE: This study has two goals: (1) to identify and discuss key factors that contribute to the spread of potentially dangerous plumes chaotically in the vicinity of patients following surgery with medical lasers and (2) to recommend safety procedures for surgical staff members based on the measurements, analysis of results, and conclusions. SUMMARY BACKGROUND DATA: In the past years, only a few studies have attempted to quantify the risks associated with routine exposure to plumes generated by medical lasers used to treat malignant tissue. The invasive thermodynamic sublimation processes following beam-tissue interaction generate plumes, which also contain particles of tumoral tissue not completely burned by the laser beam itself. These fumes can also be chemical by-products produced by normal tissue combustion. In both cases they retain a certain degree of malignancy (mainly depending on the type of tumor and by-product), which could result in spreading metastasis in the respiratory system of the surgical staff members and of the patient following inhalation. Only a few studies in the literature discuss this phenomenon, but all of them demonstrate clearly that current fume evacuator systems based on fixed air suctioning probes near the tip of the laser's focal head do not guarantee sufficient aspiration of the total dangerous gas volume (mixture of air and fumes) generated during complete surgical intervention. METHODS: The author has made several measurements of the size, shape, dimension, and speed of the plumes associated with crater development in polymethylmethacrylate (PMMA) blocks exposed to a pulsed CO2 laser beam. The laser device has been optimized for visualization via the thermocamera and each smoke burst was measured as follows: 2.5 and 5 inch focal lengths, peak energy of 33 mJ, TEM00 mode, 4 Hz, pulse width tp = 10 msec, and total exposure time te = 10 sec have been used to irradiate 3 x 2 x 3 cm3 PMMA blocks. From a pure thermochemical point of view, PMMA has been used as the gross first approximation medium for a large variety of biological tissues because the aim is to provide a global non-tissue-specific modeling rather than a very detailed investigation of the large variety of possible combinations of tissues exposed to the laser beam. This part of the study is necessary and it will be addressed in Phase II of this project. RESULTS: A quantitative description of the dynamic process present in the production of plumes with PMMA samples has been obtained along with the quantification of seven key parameters, such as ejection velocities and plume size, which accurately describe the process itself. CONCLUSIONS: Although this can be only a first approximation study, its results provide a very good idea about the orders of magnitude of the key parameters involved in the processes and dynamics of global plume production. The author suggests how these conclusions can be extrapolated for in vivo applications and can be used as recommendations to design new suctioning devices aimed at increasing safety in the operating room.

Biophysical Phenomena↗
PubMed1999

On-line computer system to minimize laser injuries during surgery: preliminary system layout and proposal of the key features.

The aim of this paper is to investigate some new user interface ideas and related application packages which aim to improve the degree of safety in an operating room during surgical operations in which an invasive laser beam is deployed. The overall value of the proposition is that a means is provided which ensures the successful completion of the surgical case while minimizing the risk of thermal and mechanical injuries to healthy tissues adjacent to the surgical field. According to surgeons operating with a variety of CO2 lasers available at both the National Cancer Institute in Milan, Italy, and the Sackler School of Medicine, Tel Aviv University, Israel, each laser device presents different cutting and coagulation properties. In order to identify which 'ideal' procedure might corroborate the subjective impression of each surgeon and also to provide one common tool to ensure procedures with a high level of safety, the author has worked for several months with surgeons and technicians of both Institutions to define the general design of a new on-line surgical operation planning and design system to be used during the pre-operative briefing activities and also as a consultation tool during operation. This software package will be developed and tested on both 'C' and FORTRAN compilers running on a commercially available PC which is driving a continuous wave (CW) CO2 laser device via its Instrument Bus interface. The present proposal describes the details of a software package called LCA (Laser-beam Controller and Adviser) which performs several controls in parallel on the key output parameters of a laser beam device during its utilization in delicate surgical operations. The required performances of this device needed during a given surgical operation are pre-simulated and compared against the well-known safety limits, which are stored in the computer's mass storage. If the surgeon's decision about the laser device set-up are considered to be too close to the required physiological safety limits, then the SW alerts the surgeon and proposes alternatives based on other combinations of both HW and SW configurations. An additional application of LCA uses this SW as a warning tool during the operation itself. If a wrong set-up of the laser device is accidentally used, an alarm will be generated and the laser beam automatically switched-off prior to an 'incident report' printout. The operation will continue only when the surgeon validates the choices that the SW suggests for implementation. If necessary, the surgeon can switch off the device and continue to operate it manually. In this case, the surveillance mode will be totally excluded.

Bone Cements↗
PubMed1997

Proposal of a computerized algorithm for continuous wave CO2 laser on-line control during orthopaedic surgery. Phase II: simplified algorithm version (LCA-s) and helmet-mounted data access device solution.

This paper is the continuation of the Phase I report published in 1992 by Canestri. It contains recent findings on how to speed-up the process of sublimated volume forecasting for a TEM11* CO2 laserbeam in CW mode following an original model proposed by the author--called LCA--here presented in a simplified version (LCA-s) on PMMA (polymethylmethacrilate) samples. Other interesting parameters, such as the time required to create the minimal injury vb along with its physical interpretations, are reported and explained. TEM11*, TEM01* and TEM00 beams profiles are also compared and discussed for LCA-s. The results of both Phase I and Phase II of this investigation can be integrated in one single solution package for the end-user, combining fast decisions making and operational features. The final part of this paper describes the 'helmet-mounted' data recall visor methodology which allows the surgeon to access to a data base for information retrieval during the course of an operation without interrupting the surgical case itself. This particularly interesting application allows the surgeon to consult a centrally-located data base which contains important information regarding similar clinical cases, choice of laserbeam profiles and focal lengths, simulation of beam behaviours, performances and other data. The on-line and direct access to the data base supports him in all those borderline situations in the O.R. in which the laser device type and configuration/calibration play a device role in the success of the operation. Also, the helmet-mounted display frees surgeon's hands in order to allow him to continue the operation while consulting the data base on-line, thus speeding up decision processes regarding changes of laser set-up, general calibration optimization and remote clinical consultancy.

Algorithms↗
PubMed1992

Proposal of a computerized algorithm for continuous wave CO2 laser on-line control during orthopaedic surgery. Phase I: theoretical introduction and first in vitro trials.

New data obtained from treating polymethylmethacrylate (PMMA) with a non-moving cw- 10 watt-CO2 laser-beam focused at 2.5'', 5'', 7.5'' and 15.75'' are presented. . The final equations R(tc) and Z(tc) for each focal length are proposed. A very interesting correlation between the focal lengths in use and the integrated values of R and Z between 0 and 2 sec has been identified and discussed. This result has been used as basis to define a convenient operative protocol to follow during the planning phase of critical osteotomies or bone cement removal operations using a continuous-wave CO2 laser-beam set to any output power and focused by a set of most common, moving or non-moving focal lengths placed on the operating area. With a simple equation, it is possible to compare craters obtained with moving and non-moving laser-beams at different operative conditions between 0 and 2 sec, time interval which covers the majority of cases. A value of 2.3 +/- 0.1 between ablated volumes of PMMA and bone tissue has been identified. Several case studies regarding orthopaedic procedures from Literature are here reported and compared to the present LCA model. The computerized on-line flow of information for the laser-beam optimization and safety control is also described. Finally, a method for the simultaneous data collection from several operating rooms via a Local Area Network (LAN-Industry Standard IEEE) onto a central data base for later consultation is proposed in its general design.

Algorithms↗
PubMed1983

CO2 lasers: beam patterns in relation to surgical use.

According to surgeons operating with a variety of CO2 lasers available at the National Cancer Institute of Milan (Coherent, Sharplan, Valfivre), these lasers have different cutting and coagulation properties. To identify what physical parameters might corroborate the subjective impression of the surgeons, a comparative study of the crater forms in perspex samples was performed. Perspex was chosen for its thermal properties (in fact, its thermal conductivity and diffusivity are similar to those of organic tissue) and because it allowed good visualization and measurement of crater characteristics. Depth of penetration, crater diameter, and extension of thermal damage were measured against power, focal length, and exposure time for each CO2 laser model. These results can be used as an index of behaviour of different surgical lasers. It appears that for fully characterizing the interaction of surgical lasers with the sample, it is necessary to specify either power, focal length, exposure time, or beam mode.

Biophysical Phenomena↗
PubMedDate not supplied

A proposed clinical application of a model of CO2 laser radiation induced damage craters.

A method for a controlled generation of primary damage craters in methacrylate ester samples (Vedril C, Montedison) induced by continuous and long-term exposure to CO2 laser radiation is proposed. The results are compared with the experimental values obtained 'in vitro' with 10 W continuous output power of a CO2 laser beam and fg = 7.5 in focal length of the laser's focusing head, and this shows that the proposed model can explain the phenomenon related to the generation of the limiting crater in typical biological tissue. It may have applications in clinical procedures where long-term exposure of the tissue to a laser beam must be considered. Also, the method may possibly be used to create and update a computer library automatically collecting data regarding different thermodynamic characteristics and values of various biological media.

Computer Systems↗
PubMedDate not supplied

Effects of nonorthogonal CO2 laser-beam delivery on the geometry of the resulting crater: a qualitative description.

New experimental data obtained using previously described methodologies relating to types, power densities, and media of CO2 lasers are presented. This report considers a nonorthogonal beam direction to the sample's surface. The CO2 laser beam does not always produce clean cuts. This is a potential danger during routine operations but might be useful in special applications in which a curved crater or cut would be preferable to a traditional rectilinear one. In-vitro investigations have shown that the angle theta between the beam direction and the sample's surface determines both the degree of curvature and its direction with respect to the surface. The phenomenon can apparently be reproduced each time the direct beam hits a reflecting surface during propagation and continues to perforate the sample afterwards at the same incoming angle: only the second segment of the crater always appears curved. The curved crater lies totally on the geometric plane that is perpendicular to the reflecting surface and contains both the point of the beam-spot position and the point of reflection. From the point of view of surgical application, the probability of occurrence of this phenomenon is high because of the frequent and dramatic tissue density variations encountered over a very short period of time. Muscles, bones, tendons, fat, blood, skin, and vapors create favorable conditions to allow partial reflections along the direction of the cut. A possible explanation for the phenomenon could lie in the energy conservation process within the crater. The modified internal symmetry of the crater is thus a consequence of the reflection process combined with the power density reduction along the "reflected" section of the crater.

Laser Therapy↗