Laryngeal temperature simulations during carbon dioxide laser irradiation delivered by a scanning micromanipulator.

We use scatter-limited phototherapy techniques to calculate the time-dependent temperature profiles of incisions made with a commercial carbon dioxide laser being used to make a 1-mm incision under computer control using the Digital Acublade™ and with incisions made with the same laser under manual control. The goal is to understand the differences in the amount of lateral thermal damage that is likely from the computer-controlled incisions versus the manually controlled incisions. The temperature profiles are calculated from the absorption and scatter of light in a homogeneous material. The resulting temperature profiles are presented as videos showing how the tissue heats up and cools down with the incident laser pulses. The time-dependent thermal distributions indicate that the computer-controlled laser incision could show as little as 210 µm of lateral thermal damage, whereas the manually controlled laser incisions could show as much as 375 µm of lateral thermal damage. The computer-controlled laser incision is able to control laser pulses fast enough that subsequent pulses can ablate away tissue with a significant amount of residual heat from the previous laser pulse. Using the scatter-limited phototherapy techniques, we can see how a computer-controlled laser can make incisions with less thermal damage by ablating away tissue holding a significant amount of heat from the previous pulse before it has time to diffuse through the tissue. This method of heat removal from laser incisions has not been previously described or demonstrated.

Selective photoantisepsis.

BACKGROUND AND OBJECTIVE: Selective killing of pathogens by laser is possible due to the difference in absorption of photon energy by pathogens and host tissues. The optical properties of pathogenic microorganisms are used along with the known optical properties of soft tissues in calculations of the laser-induced thermal response of pathogen colonies embedded in a tissue model. The objective is to define the laser parameters that optimize pathogen destruction and depth of the bactericidal effect. MATERIALS AND METHODS: The virtual periodontium is a computational model of the optical and time-dependent thermal properties of infected periodontal tissues. The model simulates the periodontal procedure: Laser Sulcular Debridement.1 Virtual pathogen colonies are placed at different depths in the virtual periodontium to determine the depth for effective bactericidal effects given various laser parameters (wavelength, peak power, pulse duration, scan rate, fluence rate) and differences in pathogen sensitivities. RESULTS: Accumulated background heat from multiple passes increases the depth of the bactericidal effect. In visible and near-IR wavelengths the large difference in absorption between normal soft tissue and Porphyromonas gingivalis (Pg) and Prevotella intermedia (Pi) results in selective destruction. Diode laser (810 nm) efficacy and depth of the bactericidal effect are variable and dependent on hemin availability. Both pulsed-Nd:YAG and the 810 nm diode lasers achieve a 2-3 mm deep damage zone for pigmented Pg and Pi in soft tissue without surface damage (selective photoantisepsis). The model predicts no selectivity for the Er:YAG laser (2,940 nm). Depth of the bactericidal effect is highly dependent on pathogen absorption coefficient. Highly sensitive pathogens may be destroyed as deep as 5-6 mm in soft tissue. Short pulse durations enable confinement of the thermal event to the target. Temporal selectivity is achieved by adjusting pulse duration based on target size. CONCLUSION: The scatter-limited phototherapy model of the infected periodontium is applied to develop a proper dosimetry for selective photoantisepsis. Dosimetry planning is essential to the development of a new treatment modality. Lasers Surg. Med. 48:763-773, 2016. © 2016 Wiley Periodicals, Inc.

A simplified laser treatment planning system: proof of concept.

INTRODUCTION: The physician using a laser in medicine should have treatment planning software available that will help him or her to better understand the full effects of the laser radiation on the patient, similar to that of a radiation oncologist. Combining this software with imaging scans from the patient, treatments can be optimized for individual patients. METHODS: Using off-the-shelf computers and software, we put together a simple system that is able to calculate thermal profiles from laser irradiation using an algorithm that runs in real time on a laptop computer with commercial software. The tissues used in these studies are simulated. We use realistic parameters and add some random blood vessels to the simulated tissue. RESULTS: We demonstrate in the simulations the temperature profile in tissue after laser irradiation. We can see build up of temperature in tissue irradiated with multiple pulses at 2 Hz repetition rate. The simulations show how the volume of the tissue is important in calculating thermal relaxation times. We also show how temperature relaxes away from small volumes in a short time and longer durations are needed for larger volumes of tissue. DISCUSSION: The importance of understanding how a laser interacts fully with the tissue will allow the surgeon to better determine when a laser is appropriate and which laser is optimal for a patient. The results show how these calculations can be made in a simplified fashion. Ultimately, it would be convenient to combine such software with imaging systems for careful laser treatment planning.

Gadolinium concentration analysis in brain phantom by X-ray fluorescence.

We have measured the X-ray fluorescence from gadolinium as a function of concentration and position in tumors of different sizes and shapes in a head phantom. The gadolinium fluorescence was excited with a 36 GBq Am-241 source. The fluorescence signal was detected with a CdTe detector and a multi-channel analyzer. The fluorescence peak was clearly separated from the scattered X-rays. Concentrations of 5.62-78.63 mg/ml of Gd ion were used in 1, 2, and 3 cm diameter spherical tumors and a 2x4 cm oblate spheroid tumor. The data show trends approaching saturation for the highest concentrations, probably due to reabsorption in the tumor. A comparison of X-ray photographic imaging and densitometer measurements to determine concentration is also presented.

Principal component analysis of fluorescence changes upon growth conditions and washing of Pseudomonas aeruginosa.

We have measured the autofluorescence from suspensions of Pseudomonas aeruginosa in the growth medium and after one, two, and three washes. The bacterium was grown in two different media, nutrient broth and King's B broth. The bacterium was harvested after 12, 24, and 48 h of growth. The fluorescence was measured with excitation every 10 nm from 200 nm to 600 nm. The fluorescence profiles were analyzed using principal component analysis. We found that most of the information is in the first three principal components. Stark differences in the value of the first principal component were noted between the samples in broth and those with one, two, or three washings. The second and third principal components noted differences between the samples washed once and those washed two or three times. There was no significant difference between samples washed two and three times. There are small differences noted between the samples grown in the two different broths, and no differences were noted among the samples harvested at different times.

Controlling thermal damage of incisions using diamond, copper, and sapphire heat-conducting templates with and without cooling.

INTRODUCTION: We investigated the reduction of thermal damage to the surrounding tissue when laser incisions were made with and without using thermal conducting templates at room temperature and cooled to 5 degrees C. STUDY DESIGN/MATERIALS AND METHODS: We used the Vanderbilt free-electron laser (FEL) at 5.4, 6.1, 6.45, and 7.7 microns. We also used a conventional continuous wave (CW) carbon dioxide laser at 10.6 microns. Incisions were made on 5x10 mm pieces of human breast skin (in vitro) and analyzed with histology. Computer morphometrics were used to measure the amount of thermal damage. RESULTS: All templates produced a statistically significant reduction in the thermal damage. Additionally, we showed that cooling the templates made a statistically significant greater reduction in the thermal damage. The cooled diamond template reduced the thermal damage from the FEL to 28% of the damage observed without a template. The same cooled template reduced the thermal damage from the CO(2) laser to 56% of the damage observed without a template. Lesser reductions were observed with the copper template and even less with the sapphire template. The sapphire template reduced the thermal damage to 39 and 67% of the damage observed without a template for the FEL and the CO(2) laser, respectively. CONCLUSION: These results indicate that unwanted lateral thermal damage from laser incisions can be reduced with cooled thermally conductive templates with the best results obtained with the diamond template, which is also the best thermal conductor.

Effect of washing on identification of Bacillus spores by principal-component analysis of fluorescence data.

The fluorescence spectra of Bacillus spores are measured at excitation wavelengths of 280, 310, 340, 370, and 400 nm. When cluster analysis is used with the principal-component analysis, the Bacillus globigii spores can be distinguished from the other species of Bacillus spores (B. cereus, B. popilliae, and B. thuringiensis). To test how robust the identification process is with the fluorescence spectra, the B. globigii is obtained from three separate preparations in different laboratories. Furthermore the fluorescence is measured before and after washing and redrying the B. globigii spores. Using the cluster analysis of the first two or three principal components of the fluorescence spectra, one is able to distinguish B. globigii spores from the other species, independent of preparing or washing the spores.

Two-dimensional multiwavelength fluorescence spectra of dipicolinic acid and calcium dipicolinate.

Dipicolinic acid (DPA) and the Ca2+ complex of DPA (CaDPA) are major chemical components of bacterial spores. With fluorescence being considered for the detection and identification of spores, it is important to understand the optical properties of the major components of the spores. We report in some detail on the room-temperature fluorescence excitation and emission spectra of DPA and its calcium ion complex and provide a comparison of the excitation-emission spectrum in a dry, wet paste and aqueous form. DPA solutions have weak, if any, fluorescence, with increased fluorescence when the DPA is dry. After exposure to a broad source UV light of the DPA, wet or dry, we observe a large increase in fluorescence with a maximum intensity emission peak at around 440 nm for excitation light with a wavelength of around 360 nm. There is a slight blueshift in the absorption spectra of UV-exposed DPA from the unexposed DPA solution. CaDPA in solution shows a slight fluorescence with increased fluorescence in the dry form, and a substantial increase of fluorescence was observed after UV exposure with an emission peak of around 410 nm for excitation around 305 nm. The detailed excitation-emission spectra are necessary for better interpretation of the fluorescence spectra of bacterial spores where DPA is a major chemical component.

Fluorescence quantum efficiency of dry Bacillus globigii spores.

Fluorescence spectroscopy has been used to measure fluorescence quantum efficiency (QE) of dried Bacillus spores (washed and unwashed) fixed to a quartz substrate. Fluorescence spectra and QE of anthracene in ethanol was used as the standard. We measured the absorption and fluorescence signal of the spores as a function of the number of spores. The absorption was measured from 600 nm to 250 nm using the reflectance in an integrating sphere. The fluorescence spectra were measured using excitation wavelengths at 280, 360 and 400 nm at room temperature. The absorption cross sections for the unwashed spores were 1.3 x 10-8, 8 x 10-9, and 5 x 10-9 mm2/spore at 280, 360 and 400 nm, respectively. The fluorescence QE was 0.13 +/- 0.03, 0.33 +/- 0.12 and 0.43 +/- 0.26 at 280, 360, and 400 nm, respectively. The QE decreased by a factor of 2, 4 and 4 at these same wavelengths after washing and redrying the spores.

Changes in the luminescence between dried and wet bacillus spores.

Fluorescence has been suggested as a method with which to detect and identify bacterial spores. To better understand the nature of the fluorescence signal, we observed the intrinsic steady-state fluorescence and phosphorescence spectra of Bacillus globigii (BG) in both dried and aqueous forms. In vitro, dried, and suspension forms of BG were measured at room temperature in 300-600-nm excitation wavelengths. Also, the phosphorescence of dry BG spores was measured at room temperature at 300-600-nm excitation wavelengths. The wet BG spores exhibited a strong maximum in their fluorescence spectrum, with the peak excitation wavelength near 300 nm and emission wavelength near 400 nm. When the BG was dried, this peak shifted to an approximately 450-nm excitation maximum and an 500-nm emission maximum. The difference between the wet and the dry spore fluorescence spectra cannot be explained by the phosphorescence of the dry spores. Other changes must take place when the spores are wet to account for the large changes observed in the spectrum.

Wound healing of 6.45-microm free electron laser skin incisions with heat-conducting templates.

We have previously shown a reduction in lateral thermal damage with acute studies of skin incisions made in vitro using heat-conducting templates. Here we examined the wound-healing response to laser incisions with heat-conducting templates and explored the use of an optically transparent template with the free electron laser (FEL) at 6.45 microm. First we evaluated the effects of a sapphire heat-conducting template on the lateral thermal damage of FEL incisions using in vitro human skin samples. Next we compared wound tensile strength and histological scoring of the healing of incisions created on the dorsal pelts of live rats with the FEL utilizing metal and sapphire heat-conducting templates and scalpel incisions. The animals were euthanized and the wounds were analyzed at postoperative days 7, 14, and 21. The depth and lateral thermal damage of FEL incisions on in vitro human skin were significantly reduced with the sapphire heat-conducting template. Nonstatistically significant differences in wound tensile strengths and histological scoring of wound healing were noted at days 7 and 14. By day 21, all of the incisions appeared similar. When the data from days 7 and 14 were combined, statistically significant differences were found for each of the templates (except the histological evaluation with the aluminum template) and the scalpel compared with laser incisions made without using a template. The use of metal or sapphire heat-conducting templates reduced the wound-healing delay of laser incisions seen at postoperative days 7 and 14.

Reduction in lateral thermal damage using heat-conducting templates: a comparison of continuous wave and pulsed CO2 lasers.

BACKGROUND AND OBJECTIVES: The advantages of the continuous wave (c.w.) CO(2) laser are offset by the delay in laser wound healing secondary to thermal damage. We have developed novel heat-conducting templates to reduce laser thermal damage. Because shortened pulse durations also decrease thermal damage, we tested the effectiveness of heat-conducting templates with a c.w. CO(2) clinical laser and a short-pulsed CO(2) laser to determine the best method and mechanism to minimize thermal damage. STUDY DESIGN/MATERIALS AND METHODS: Comparison of 0.2-second shuttered c.w. and 5-microsecond pulsed CO(2) lasers were made by doing incisions on 150 tissue samples from reduction mammoplasties and abdominoplasties. Copper, aluminum, glass, and Plexiglass heat-conducting templates were tested against no template (air) with both lasers. Histological samples were evaluated using computerized morphometrics analysis. RESULTS: Statistically significant reductions in lateral thermal damage were seen with the copper (50%) and aluminum (39%) templates used with the c.w. CO(2) laser. Only the copper template (39%) significantly reduced thermal damage when used with the pulsed CO(2) laser. Less thermal damage was seen using the pulsed CO(2) laser compared to the c.w. CO(2) laser with each template. CONCLUSIONS: Heat-conducting templates significantly reduced the amount of lateral thermal damage when used with the c.w. CO(2) laser (copper and aluminum) and short-pulsed CO(2) laser (copper). The c.w. CO(2) laser with the copper template compared favorably to the short-pulsed CO(2) laser without a template. Therefore, both heat conductive templates and short-pulse structure provide successful methods for reducing lateral thermal damage, and a combination of the two appears to provide optimal results.

Analysis of epidermal protection using cold air versus chilled sapphire window with water or gel during 810 nm diode laser application.

BACKGROUND AND OBJECTIVES: Many cutaneous laser devices incorporate a temperature-based epidermal protection system to minimize surface damage while continuing to affect targeted tissue. The use of cold air is a new technique to aid in epidermal protection during the application of cutaneous lasers. This study investigates the efficacy of cold air versus chilled sapphire in regards to epidermal preservation when used with an 810 nm diode laser. STUDY DESIGN/MATERIAL AND METHODS: White-haired pink piglets and dark-haired pigmented piglets were treated using the 810 nm diode laser in conjunction with either (1) no cryogen protection; (2) cold air alone; (3) chilled sapphire window alone; (4) cold air with water/gel; or (5) chilled sapphire window with water/gel. Laser fluence was varied by adjusting laser duration time while maintaining the intensity at 60 W. Biopsies were obtained from the sacrificed animals, stained with Masson's trichrome, and analyzed for extent of epidermal damage. RESULTS: Among white-haired pink pigs, the cold air afforded the same degree of epidermal preservation as the chilled sapphire window. Epidermal protection was further enhanced with the addition of either gel or water. Among dark-haired pigmented pigs, the chilled sapphire window alone likewise provided significant epidermal protection, although the cold air alone did not. However, with the addition of water/gel, epidermal preservation was demonstrated in both. CONCLUSIONS: Cold air is an effective means in promoting epidermal preservation, though slightly inferior to the chilled sapphire window on darkly pigmented subjects. Combining either method with water or gel further enhances surface protection, enabling safe use of higher fluences.

Scatter-limited phototherapy: a model for laser treatment of skin.

BACKGROUND AND OBJECTIVES: To effectively deliver laser light into the skin for non-ablative resurfacing, hair removal, and other applications, one must account for scatter, absorption, and thermal diffusion. A novel method to control the penetration of laser light into tissue is proposed. This method uses the incident beam diameter, the pulse duration, and the intrinsic light scattering of tissues such as skin to limit the laser light penetration and thermal damage. We term this innovative laser delivery concept 'scatter-limited phototherapy'. STUDY DESIGN/MATERIALS AND METHODS: This study demonstrates how the delivery mechanism simplifies the non-ablative treatment of sun-damaged skin. Calculations are based upon Gaussian scatter of light and isotropic thermal diffusion. Calculations of light distribution and profiles of temperature increase are created. RESULTS: Using an optical fiber delivery system with the appropriate diameter, coupled with skin surface protection, one can create thermal damage at a given depth with preservation of the epidermis. CONCLUSIONS: Scatter-limited phototherapy is a predictive model, allowing one to design better laser delivery systems. Scatter-limited phototherapy should also be applicable to other fields of dermatologic surgery, such as hair removal and the treatment of vascular lesions. Additionally, other medical specialties will be able to use the concept of scatter-limited phototherapy to predict and better understand laser-tissue interactions.

New-generation pulsed carbon dioxide laser: comparative effects on vocal fold wound healing.

We investigated wound healing of vocal fold mucosal excisions using a canine model, comparing cold steel, the continuous wave (CW) carbon dioxide (CO2) laser, and a new, microsecond-pulsed CO2 laser. The thermal injury to the surrounding normal tissues produced by the laser increases the risk for scar formation and poor functional voice outcome. This injury may be reduced with a pulsed CO2 laser. Acute, 2-week, and 6-week studies of 15 dogs were made with blinded observers and nonparametric statistical analyses. Histologic comparison showed less thermal injury and scar formation in the vocal folds treated with the pulsed CO2 laser than with the CW CO2 laser. Functional outcomes as studied with laryngeal videostroboscopy revealed better vibratory characteristics with the pulsed CO2 laser as compared with the CW CO2 laser. No differences were seen on these measures between the pulsed laser and cold techniques. Pulsed CO2 lasers may offer the ease of laser laryngology and the superior wound healing of cold steel.

Free-electron laser and heat-conducting templates: a study of reducing cutaneous lateral thermal damage.

BACKGROUND AND OBJECTIVES: We developed novel heat-conducting templates, and tested whether they could effectively remove damaging heat from the tissue during laser ablation. The reduction of lateral thermal damage during cutaneous incisional laser procedures should decrease the time in wound healing. In addition, we selected various infrared wavelengths to determine whether the template effects would be influenced by the laser penetration depth and the particular chromophore absorbing the laser light. STUDY DESIGN/MATERIALS AND METHODS: This study utilized the Free-Electron Laser at wavelengths of 3.0, 5.5, 6.45, 7.5, and 7.7 microm to produce 1.0 cm incisions on in vitro lightly pigmented human skin. At each of these wavelengths, copper, aluminum, glass, and Plexiglas heat conducting templates were tested. At wavelength 5.5 microm, the study was duplicated using in vitro darkly pigmented skin. Histological samples were evaluated using computerized morphometric analysis. RESULTS: The adjunct use of both the copper and aluminum templates provided a decrease in thermal damage at each wavelength. Using the copper template reduced lateral thermal damage an average of 67% with no apparent wavelength dependence. The aluminum template reduced thermal damage an average of 54% with no apparent wavelength dependence. The glass and Plexiglas templates did not reduce the lateral thermal damage. At 5.5 microm, no statistically significant difference in lateral thermal damage was observed between darkly and lightly pigmented tissues. CONCLUSIONS: Heat-conducting templates are an effective new method to reduce lateral thermal damage from thermal laser incisions.