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Biomedical subjects

Franco Canestri

Publications and source records attributed to Franco Canestri.

2 recordsLinked to original sources
PubMed2006

Optical absorption coefficient, time of thermal relaxation, time of surface threshold, and time of heat incubation for PMMA samples at the CO2 laser-beam wavelength of 10.6 microm.

OBJECTIVE: This paper discusses in detail the mathematical identification of the optical absorption alpha (cm(1)) of Beer's law, a crucial parameter to study the development of laser beam craters into dry poly(methyl methacrylate) (PMMA) samples exposed to steady CO(2) laser beams emitting radiation at lambda = 10.6 microm in continuous- wave (CW) mode. Three additional time-dependent coefficients have been determined as well. In clinical applications, these results are important in order to precisely quantify and forecast the ablation capabilities of the CO(2) laser beam, to optimize its usage in the operating room, and to address the safety issues related to surgical interventions on human tissue. BACKGROUND DATA: Currently, the data available in the literature do not allow the identification of the numerical value of alpha (cm(1)) for PMMA at lambda = 10.6 microm with enough, and therefore satisfactory, accuracy. Additionally, the correct identification of the optical absorption of PMMA would allow the isolation, with better accuracy, of other key time-dependent coefficients, such as relaxation time, surface threshold time, and heat incubation time, which are all described in the literature in a qualitative rather than quantitative fashion. Correct bone cement preparation depends on the value of alpha (cm(1)) of the PMMA in order to avoid unwanted complications in patients during cement removal via laser techniques. METHODS: The laser in use was configured in different combinations with the following parameters: transverse electromagnetic modes (TEMnm), output power (I0), exposure times (te), and focal lengths (fk). Several PMMA blocks (1 cm x 4 cm x 4 cm) were exposed to CW radiation of three commercially available CO(2) medical laser devices showing a TEM11 mode. Each block was exposed to the beam on a horizontal and well-polished surface of each sample. Four focal lengths (2.5", 5", 7.5", and 15.75" [400 mm]) were used to focus the beam on the well-polished and dry surface of the PMMA samples. The resulting dimensions of the craters were measured after each exposure, which has been kept at a 10-Watt CW beam. Exposure time ranged from 0.5 to 2 sec. RESULTS: The value of alpha = 502 (cm(1)) for PMMAat 10.6 microm was identified, matching other results reported in the literature for similar compact media in the absence of water content, such as PMMA. The time of thermal relaxation was 9.358 x 10(4) sec, the time of surface threshold was 9.365 x 10(4) sec, and the time of heat incubation was 3.6 x 10(7) sec (all three for PMMAat 10.6 microm for any exposure). Using the calculated value of alpha, one of the practical clinical recommendations would be, for instance, to reduce or to abolish the utilization of colorant dopants in the preparation of the bone cement mixture and therefore reduce the danger of bone damage possible during the removal of bone cement via laser techniques. Other examples refer to other clinical bone and dental treatments.

Bone Cements↗
PubMed2002

Sudden and unpredictable below-surface ablation pattern changes by CO2 laser beams: a qualitative description of five macroscopic cases observed in PMMA with high probability to occur during surgery in low-water-content tissues.

OBJECTIVE: This paper describes five cases of macroscopic irregular CO(2) laser-beam ablation patterns that can generate below-surface complications during surgery. These five cases are related to curved reflected beams, curved craters generation with abnormal superficial thermal damage, and craters that show irregular wall contours. Although these alterations have been observed during irradiation in PMMA samples (polymethilmethacrylate), it is possible that similar unpredictable changes also happen in low-water-content, hard and uniform biological tissues such as compact bone, enamel, and dentin. This fact can predict severe impacts on the quality of the final surgical outcome, especially there where precision surgery techniques are required. A qualitative description about the possible causes of these effects and how to avoid them during surgery have been suggested too. BACKGROUND DATA: In the past decades, daily surgery and research studies have provided useful information about the interaction between medical CO(2) laser beams and animal, human, and other biological tissues. Several mathematical models describe with acceptable accuracy all the ablative properties of the 10.6 microm laser beam. Very few studies describe the presence and address the consequences of the ablative aberrations, which can frequently and randomly happen during laser surgery. The probability that these changes happen in below-surface, therefore invisible, parts of the biologic media under treatment makes the whole matter crucial, even in cases of traditional surgery. Where gross mass removals are considered, the presence of unpredictable and sudden deviations from the expected traditional cone-shaped patterns raise several questions about safety. The continuous need for properly engineered medical laser-beam devices, online laser-beam monitoring, and real-time control becomes mandatory in modern surgery. MATERIALS AND METHODS: The equipment used in this study was provided by the National Cancer Institute of Milan, Milan, Italy, and by the Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel. A large TEM-mode laser-beam device (Valfivre, Italy) and TEM00 laser-beam device (Synrad, USA), both coupled to 2.5- and 5-inch focusing lenses, have been used to irradiate, at 10 Watts nominal output, on the focal spot, several PMMA blocks (3 x 2 x 4 x 2 x 2 cm) up to 10 sec CW. For one set of experiments, a metallic, well-polished mirror was placed against one surface of each sample to simulate possible internal beam reflections caused by generic metallic surgical instruments, such as conventional scalpels or clamps. RESULTS: The experimental evidence of five major and unpredicted changes in the shape of craters produced by CO(2 )laser beams in PMMA are shown in photos and discussed in a qualitative way. Several physical and thermodynamic phenomena are proposed to identify and therefore minimize or avoid the causes of these events. CONCLUSION: The results discussed in this paper show how important it is to constantly and carefully observe both the irradiated tissue's or media's structure and the beam's broadening under surface during the ablation process. Fume attenuation of the incoming laser beam, fume escape paths, internal beam interference phenomena, media's microstructural changes and, perhaps more importantly, their combination can offer good explanations of all the described phenomena. In summary, the presence of fumes in at least two out of the five reported cases plays a key role in aberrant crater generation processes. Therefore, the author recommends paying extra attention to them in order to provide a higher quality outcome in Surgery where CO(2) laser beams are deployed.

Adipose Tissue↗