Wendy J. Snyder

Time-resolved laser-induced fluorescence of arterial wall constituents: deconvolution algorithm and spectrotemporal characteristics

In this study, we had two objectives: (1) to develop an algorithm based on the Laguerre expansion of kernels technique for deconvoluting time-resolved fluorescence spectra; (2) to characterize the time-resolved emission of elastin and collagen, substances present in different amounts in healthy and diseased arterial wall. The transient fluorescence of purified samples excited with a Nitrogen laser pulse (3 ns) was measured at different wavelengths with an MCP-PMT and digitized at 2 Gsample/s. The deconvolution algorithm expressed the impulse response function as a weighted sum of Laguerre functions. We found that five Laguerre functions were sufficient to represent the fluorescence impulse response function for both substances. A fast-decay and a slow-decay components were identified in the impulse response function. The slow decay increased with the wavelength of emission ((lambda) ) for elastin (p < 0.05) whereas it decreased with (lambda) for collagen. The fast decay was independent of (lambda) for elastin and decreased with (lambda) for collagen. The fluorescence impulse response function can be retrieved even when the duration of the excitation pulse is in the range of the fluorescence lifetime. The dynamics of the temporal emission of collagen and elastin varies with the wavelength of emission suggesting that using temporally-resolved fluorescence spectra would improve optical analysis of the arterial wall.

Blood perfusion and pH monitoring in organs by laser-induced fluorescence spectroscopy

Sensitivity of laser-induced fluorescence spectroscopy (LIFS) in detecting a change in tissue pH, and blood perfusion was determined. Rabbits were anesthetized, paralyzed, and mechanically ventilated. The arterial and venous blood supplies of the kidney were isolated and ligated to alter the perfusion. The femoral artery was cannulated to extract samples for blood gas analysis. A 308-nm XeCl was used as an excitation source. A 600 micrometers core diameter fiber was used for fluorescence acquisition, and the spectra analyzed by an optical multichannel analyzer (EG & G, OMA III). the corresponding intensity ratio R equals INADH / ICOLL was used as an index for respiratory acidosis. Blood perfusion was assessed using the following algorithm: (IELAS minus ICOLL) divided by (INADH minus ICOLL). The intensity ratio linearly decreased with the reduction of blood perfusion. When we totally occluded the artery the ratio decreased tenfold when compared to the ratio of a fully perfused kidney. Results of monitoring blood acidosis by laser-induced fluorescence spectroscopy shows a significant trend between pH and intensity ratio. Since all the slopes were negative, there is an obvious significant correlation between the pH and NADH.COLLAGEN RATIO. Blue-light-induced fluorescence measurements and ratio fluorometry is a sensitive method for monitoring blood perfusion and acidity or alkalinity of an organ.

Effect of varying Nd:YAG laser fiber tips on porcine dermal tissue

We evaluated the effect of the 600 micrometers bare (flat tip) and 600/100 micrometers conical tip fibers on porcine skin. We compared their effect in both the continuous-wave (cw) and pulsed (P) modes (20 ms ON/OFF) at 20 W to that of the electrocautery at 100 W in the pure and blend 3 modes. On 11 farmer pigs, 6 cuts were made for each parameter combination. The samples were processed for histological evaluation. The cutting depth, cutting width, and total thermal damage (carbonization, coagulation and denaturation) were recorded for each parameter combination. The results show that the 600/100 micrometers conical fiber provides deeper resective capabilities than the 600 micrometers bare and electrocautery. In addition, the 600/100 micrometers conical tip fiber allows for narrower cuts with significantly less thermal necrosis when compared to the 600 micrometers bare and electrocautery. The results indicate that there is an advantage to using the sculptured tip fiber for creating incisions when compared to the bare fiber and electrocautery.

Laser effects in nonpigmented versus pigmented tissues using FiberTomeTM, Nd:YAG, and KTP

This study evaluated the effects of the FiberTomeTM (10, 20, 30 W), conventional Nd:YAG (10, 20, 30 W), and KTP (5, 10, 15 W) surgical laser systems, with respect to pigmented and nonpigmented tissues. The cutting width, cutting depth, and thermal damages were measured on the skin and liver of farmer pigs. The results show that there was no significant difference in the cutting width and depth, for nonpigmented versus pigmented tissues. KTP showed the most significant thermal damage reduction in pigmented tissue; 318 micrometers in nonpigmented vs 94 micrometers in pigmented tissue.

Tissue effects of Nd:YAG, KTP, and FiberTomeTM lasers with varying fiber tips and power settings

This study compared the laser tissue effect of the Dornier FiberTomeTM system, the conventional Nd:YAG and the KTP laser on the stomach and liver. The cutting capabilities, thermal effects of the laser systems, as well as their dependence on power output and tissue type, were evaluated. A motorized fiber holder to maintain constant conditions (cutting speed fiber angle, and pressure) was developed. The results show that the cutting depth and cutting width are inversely proportional to the output level. The thermal damage remained constant as the output increased. Use of the FiberTomeTM system appears to be more advantageous than the conventional Nd:YAG laser in pigmented tissues, in the range of the parameters tested.

Comparative study of continuous wave and pulsed Nd:YAG laser using different fiber optic delivery systems on the lung

The purpose of this study was to evaluate the cutting abilities and thermal effects of different fiber optic delivery systems on the lung, after varying the power levels and system modes. The Nd:YAG (1.064 micrometers ) laser was tested using 600 micrometers bare, and sculptured (600/300 micrometers cone and 1000 micrometers chamfer) fiber tips in the continuous wave (cw) and pulsed (P) modes. A standard porcine model (n equals 18) was used for this study. We did not observe any ablation in the noncontact mode with the 1000 micrometers chamfer (P and cw) and the 600 micrometers bare fiber, in pulsed mode. We observed tissue ablation in the contact mode for all fibers. In contact mode, there was no significant difference in the cutting width between the 600/300 micrometers cone, and 1000 micrometers chamfer. In the range of the parameters tested we observed no carbonization. There is an advantage using Nd:YAG laser and flexible fibers in minimal invasive thoracic surgery.

Ho:YAG laser sclerostomy in a long-term animal model

The effects of the Ho:YAG (2.13 micrometers ) laser on rabbit scleral tissue ablation were determined. Over a period of 12 months the status of the drain hole was monitored. A 3 mm incision was made on 26 rabbits through the conjunctiva and the laser probe was advanced and applied under it. A fluence of 255 J/cm2 was used to perforate the sclera with a pulse duration of 300 microsecond(s) ec full width at half maximum. Results of this study show that this laser thermal sclerostomy procedure provided a patent hole in 6 of 8 (75%) eyes at 3 months, 11 of 15 (73%) eyes at 6 months, and 3 of 3 at 12 months. No postoperative inflammation, hypotony or subsequent scar formation was observed in any of the rabbits.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Effectiveness of benzoporphyrin derivative monoacid (BPD-MA) and fiberoptic sensor in detecting metastatic neoplasm in lymph nodes in rats

An intensity ration of the photosensitizing agent to the natural fluorescence was used to determine the condition of lymph nodes (normal, inflammatory, or with metastases). Eighty- one Lobund Wistar rats were inoculated with Pollard rat adenocarcinoma cells. After 40 days the rats were injected with 0.75 mg/kg BPD-MA. A helium-cadmium lasers (442 nm) was used for both light delivery ad fluorescence acquisition. Fluorescence spectra were acquired and analyzed by an optical multichannel analyzer 9 EG&G, OMA III). Unbalanced repeated measures analysis of variance (ANOVA) was done on the mean intensity ratio according to location. Several locations recorded for each rat were modeled as the repeated variable. The fluorescence signal obtained from lymph nodes with metastases indicated high drug amounts, greater than in the skin, tumors, and all other tissues. The lowest fluorescence intensity ratios were observed in the skin. This leads us to the conclusion that the amount of Photofrin porfimer sodium and BPD-MA which localized in the metastatic lymph nodes is higher than in tumor and all other healthy tissues. Among normal lymph nodes there were significant differences according to the site of the node, with the left iliac lymph nodes having higher IR values than either the mesenteric (MC I or MC II) nodes. The geometric means of IR are consistently higher in normal as compared to inflammatory nodes for each location. The optical biopsy needle with laser-induced fluorescence detection and exogenic fluorochrome is a sensitive, novel techniques to localize small boundaries of metastatic neoplasm in lymph nodes.

1064-nm Nd:YAG laser nucleotomy

The high incidence of patients with clinical and neurological symptoms of lumbar disc herniation has spurred the development of less invasive and more cost efficient methods to treat patients. In this study we evaluated pulsed and continuous wave (cw) 1064 nm Nd:YAG laser ablation and induced thermal damage in sheep intervertebral disc. We used the Heraeus LaserSonics Hercules 5040 (Nd:YAG) laser system and 400 micrometers bare and 600 micrometers ball-tipped fibers in cw and pulsed mode. For the laser parameters and fibers used in this study, ablation of the intervertebral disc was successful and thermal damage did not exceed 0.5 mm. Varying beam diameters and focusing abilities (i.e., bare and ball) did not produce any difference in the coagulation thermal effect.

Comparative study of pulsed Ho:YAG versus Tm:YAG: impulse-induced pressure in porcine aorta

The goal of this study is to measure the average impulse induced pressure in porcine aorta by one laser pulse for both a free running Tm:YAG (2.014 microns) laser and a free running Ho:YAG (2.1 microns) laser. The pulsed Tm:YAG and Ho:YAG lasers operated at a repetition rate of 2 Hz and a FWHM pulse width of 150 microseconds. The laser energy was delivered to the tissue via a 600 micron core diameter low-OH silica fiber. The impulse pressure induced in the aortic wall was evaluated using tissue samples (n equals 50) mounted on a pendulum to measure the transferred momentum from the laser pulse to the tissue. The impulse induced pressure was determined using a contact mode, where the fiber tip and tissue surface are within 0.5 mm of each other. The impulse induced pressure was studied over a fluence range of 35 - 350 J/cm2, fifteen measurements were taken at each fluence level. The results showed that the average impulse induced pressure of the Ho:YAG pulsed laser in the fiber contact mode was 2 - 6 times greater than in the non-contact mode, where the energy at the fiber tip was imaged onto the tissue surface. The results also showed that both the Ho:YAG and the Tm:YAG average impulse induced pressure, in the contact mode, increased linearly at lower fluences, reaching a peak at approximately 13 - 14 atm.