Scott Ferguson

Conductive interstitial thermal therapy device for surgical margin ablation: In vivo verification of a theoretical model

Purpose: To demonstrate the efficacy and predictability of a new conductive interstitial thermal therapy (CITT) device to ablate surgical margins. Method: The temperature distributions during thermal ablation of CITT were calculated with finite element modelling in a geometrical representation of perfused tissue. The depth of ablation was derived using the Arrhenius and the Sapareto and Dewey (S&D) models for the temperature range of 90 to 150°C. The female pig animal model was used to test the validity of the mathematical model. Breast tissues were ablated to temperatures in the range of 79–170°C, in vivo. Triphenyltetrazolium chloride viability stain was used to delineate viable tissue from ablated regions and the ablation depths were measured using digital imaging. Results: The calculations suggest that the CITT can be used to ablate perfused tissues to a 10–15 mm width within 20 minutes. The measured and calculated depths of ablation were statistically equivalent (99% confidence intervals) within ± 1mm at 170°C. At lower temperatures the equivalence between the model and the observations was within ± 2 mm. Conclusion: The CITT device can reliably and uniformly ablate a 10–15 mm wide region of soft tissue. Thus, it can be used to secure negative margins following the resection of a primary tumor, which could impede local recurrences in the treatment of local diseases such as early staged, non-metastatic, breast cancer.

Conductive interstitial thermal therapy (CITT) device evaluation in VX2 rabbit model.

We have developed a conductive interstitial thermal therapy (CITT) device to precisely and reliably deliver controlled thermal doses to the surgical margins at the cavity site following tumor resection, intraoperatively. The temperature field created by CITT ablation of a perfused tissue was modeled with a finite element package Femlab™. The modeling suggested that a maximum probe temperature of 120°C and an ablation time of 20 minutes were required to ablate highly perfused tissue such as the VX2 carcinoma. Deployable pins enable faster and more reliable thermal ablation. The model predictions were tested by thermal ablation of VX2 carcinoma tumors implanted in adult New Zealand rabbits. The size of the ablated region was confirmed with a viability stain, triphenyltetrazolium chloride (TTC). Histopathological examination revealed 3 regions in the ablated area: a carbonized region (1–3 mm); a region that contained thermally fixed cells; and an area of coagulated necrosis cells. Cells in the thermally fixed region stained for PCNA (proliferating cell nuclear antigen) and were bounded by the carbonized layer at the cavity wall, and by necrotic cells that exhibit nuclear fragmentation and cell dissociation, 5 to 10 mm away from the CITT probe. Adjacent tissue outside the target region was spared with a clear demarcation between ablated and normal viable tissue. It is suggested that the CITT device can be used, clinically, to inhibit local recurrence by creating negative surgical margins following the resection of a primary tumor in non-metastatic early staged tumors.

Photoacoustic effects of carbon dioxide lasers in stapes surgery: quantification in a temporal bone model.

Hypothesis The use of the CO2 laser in stapes surgery creates sound waves that could damage hearing. Background The application of a laser to any medium has absorption, reflection, and thermal effects. To date, the majority of research on the safety of CO2 laser stapedotomy has focused on the thermal effects of the laser alone. Because of the properties of the CO2 laser, its absorption also presents some risk to the inner ear. This absorbed energy can be converted to photoacoustic or photochemical effects. The goal of this paper is to measure these photoacoustic effects (sounds) produced by the CO2 laser. Methods Using a variety of settings, a Sharplan 150 XJ Laser and a Contour model Erbium:YAG laser were applied to the oval window of human temporal bones. Perilymph was simulated by fixing the temporal bone in a normal saline bath. Photoacoustic waves were measured by a hydrophone 2 mm beneath the oval window. Measurements were made with and without a simulated tissue seal over the window. Results No detectable sounds were created below 4 watts (continuous mode) or 60 mJ (superpulse mode). Above those settings, intensities of 90 dB sound pressure level and higher were detected when the laser was applied directly to the perilymph. With the tissue seal in place, no detectable sounds were identified. The accuracy of this model was confirmed by comparing these results with previously published results using the Erbium:YAG laser. Conclusions Below 4 watts in continuous wave mode and below 60 mJ in superpulse mode, any sound generated by the laser is small. Above these thresholds, however, impact sounds are produced that could result in threshold shifts with repeated applications.

Conductive interstitial thermal therapy (CITT) inhibits recurrence and metastasis in rabbit VX2 carcinoma model

Purpose: To investigate the potential of conductive interstitial thermal therapy (CITT) to inhibit recurrence and metastasis in a partially resected tumour model. Method: Fifteen New Zealand white rabbits were implanted with VX2 tumour intramuscularly in the rear thigh. Once the tumour size reached 20–25 mm in diameter, three animals were randomly selected to serve as controls, while the remaining animals were designated as the study group and treated with CITT. In the CITT group, the partially resected tumour and margins were thermally ablated. In the control group the tumour was partially resected to simulate positive margins. The animals were monitored for up to 12 weeks. At the endpoint, the animals were sacrificed, and whole-body diagnostic necropsy was conducted immediately. Results: Recurrences and metastatic lesions were observed in iliac and popliteal lymph nodes and abdomens of all control animals. In contrast, the observed rate of recurrence and metastatic lesion was 0% among CITT-treated animals, significantly less than the ≥50% null-hypothesis rate expected upon treatment failure (exact binomial P = 0.0002). Complete histopathological healing was obtained in 2 of 12 rabbits, and residual inflammation remained at the ablation site up to 12 weeks post-ablation in 10 of 12 rabbits. This pattern of necrosis and inflammatory response was not observed in any of the control rabbits. Conclusions: The CITT device effectively ablated partially resected VX2 carcinoma in a rabbit model, and inhibited recurrence and metastasis in this model. CITT evoked an inflammatory response that may be linked to the mechanism involved in reduced metastatic spread.

Confocal photothermal flow cytometry in vivo

The new experimental design of an integrated flow cytometry (FC) is presented, combining high-resolution transmission digital microscopy (TDM) with photothermal (PT), photoacoustic (PA), and fluorescence techniques. We used phantom in vitro to verify this concept with moving living cells, and micro- and nanoparticles. The transistion in vivo study was realized by using unique rat mesentery model for real-time detection of circulating red and white blood cells. The adaptation of confocal schematics to PT microscopy to provide 3-D measurement is discussed. We demonstrated that simulataneous transmission, PT and fluorescent imaging provide the basis for nanodiagnostics and nanotherpeutics in vivo with gold nanoparticles as PT probes and sensitizers as well as identification cells with specific absorbing endogenous and exogenous structures. First attempt to use in parallel PA methods with detection PA signals from single live cells are presented. Potential applications of integrated FC are discussed, including identification of selected cells with different natural absorptive properties, characterization of bioflow (e.g., velocity profile), and PT nanotherapeutics and nanodiagnostics of metastatic cells with gold nanoparticles.

Immunotargeted photodynamic therapy for cholesteatoma: in vitro results with anti-EGFR-coated indocyanine green nanocapsules.

Hypothesis The objective was to test the hypothesis that immunotargeted photodynamic therapy (IT-PDT) using anti–epithelial growth factor receptor (EGFR)–coated indocyanine green (ICG) nanocapsules would selectively kill cholesteatoma-derived keratinocytes while sparing middle ear–derived mucosa cells in vitro. Background Rates of residual cholesteatoma caused by incomplete microsurgical removal are unacceptably high; thus, development of an adjuvant therapy to safely destroy undetected residual cholesteatoma cells would be desirable. IT-PDT is a possible means to achieve this end. Methods ICG nanocapsules coated with anti-EGFR were synthesized and applied to cholesteatoma-derived keratinocytes and middle ear mucosa cells in vitro. Selective binding to keratinocytes was evaluated by fluorescence microscopy. Activation of ICG was undertaken by applying near-infrared light (810 nm) at an applied energy dose of 1,080 J/cm2. Cell death was evaluated 2 hours after treatment with trypan blue staining. Results Selective and robust nanocapsule binding to keratinocytes, but not mucosa cells, was confirmed by preapplication and postapplication fluorescence measurements. A keratinocyte cell death rate of 70.12% ± 2.50% was achieved, whereas negligible mucosa cell death was observed. Negligible cell death was also observed for both cell types with application of the nanocapsules alone or with application of near-infrared light alone. Conclusion Anti-EGFR ICG nanocapsules applied topically and activated as part of an IT-PDT scheme results in a high rate of cholesteatoma-derived keratinocyte cell death while negligibly affecting middle ear mucosal cells in vitro. These preliminary findings suggest that this is a feasible concept and that further investigation is warranted.

Addition of a telestrator for teaching during video-based procedures

Alow-cost telestrator, or video illustrator, has been developed to annotate live video feeds of surgical procedures (endoscopic or microscopic) performed in operating rooms equipped with a video tower. This device has been integrated into existing operating room video towers to be cost-effective. Similar technology is present in the operating room on the da Vinci Robotic Surgery platform (Intuitive Surgical, Sunnyvale, CA) and occasionally may be part of state of the art auditoria that can receive live surgical video feed. This concept of overwriting video feed has existed for over a decade, as made famous by John Madden, a color commentator for coverage of National Football League games. The telestrator consists of a laptop computer (Model VGNTXN15P; Sony Corporation, New York, NY) equipped with a PCMCIA TV tuner card (Model AverTV Card bus MCE [E502]; AVerMedia USA, Milpitas, CA, www.avermedia-usa.com// AVerTV/Product/ProductDetail.aspx?Id 458), annotation software (Slide Mate 2008, version 4.12; YPG Soft, Köln, Germany, slidemate.ypgsoft.com), and a wireless mouse (Model Air Mouse Go; Movea, Inc., Milpitas, CA, www. gyration.com/index.php/us/products/in-air-micekeyboards/ go-air-mouse.html) (Fig 1). These items are the minimum necessary equipment used in our prototype. Equipment from alternative manufacturers may be considered for substitution according to cost and availability. The video signal from the surgical camera unit (Model 1188HD SDC Ultra; Stryker, San Jose, CA) is fed to the tuner card via the S-video output. The live video is displayed on the laptop monitor by the software provided with the video card listed previously. The annotation software runs simultaneously with the live video and allows the user to apply annotation over the live video display. Conventionally, the commentator (or in our case the surgery attending) has a slate and a “pencil” that allow the commentator’s comments or illustrations to be projected onto a display layered over the video feed. An innovation we have added is a wireless mouse, which reduces the need for bulky equipment for the commentator and is more easily placed into the sterile field or used off field. The Gyration mouse features motion-sensing technology that eliminates not only wires but also the need for the mouse pad. The

Laser vibrometer measurements and middle ear prostheses

One of us has developed an improved partial ossicular replacement prosthesis that is easier to implant and, based on pilot clinical measurements, results in better high-frequency hearing as compared to patients receiving one of the alternative prostheses. It is hypothesized that the primary reason for this is because of the relatively light weight (about 25 mg) and low compliance of the prosthesis, which could conceivably result in better high frequency vibrational characteristics. The purpose of our initial work was to develop an instrument suitable for objectively testing the vibrational characteristics of prostheses. We have developed a laser based device suitable for measuring the vibrational characteristics of the oval window or other structures of the middle ear. We have tested this device using a piezoelectric transducer excited at audio frequencies, as well as on the oval window in human temporal bones harvested from cadavers. The results illustrate that it is possible to non-invasively monitor the vibrational characteristics of anatomic structures with a very inexpensive photonic device.

Photoacoustic-induced vascular tissue dissection resulting from irradition with a Q-switched frequency-doubled Nd:YAG laser

A Q-switched frequency-doubled Nd:YAG dye laser, tuned to 577 nm, was used to study the effect of nanosecond pulsed light on vascular tissue. Different reactions such as vasospasm, vessel expansion and vessel rupture were observed in living rats and were seen to be correlated with increasing fluence up to 3 J/cm2. When it occurred, localized vessel rupture was seen on the irradiated side of the blood vessel, as well as on the opposite side. It was hypothesized that the damage on the backside of the blood vessel is the result of intense acoustic waves produced by strong absorption of the laser radiant energy in the first 30 micrometers of blood. Experiments were performed in vitro using cuvettes filled with diluted hemoglobin on which the 532 nm radiant energy produced by a Q-switched frequency-doubled Nd:YAG laser impinged. High-speed imaging of the irradiated air-blood interface using a time-delayed pulsed nitrogen-dye laser did not show evidence of cavitation micro-bubbles but did show the formation of a large, slowly expanding vapor bubble. Measurements of the acoustic waves produced with 12 mJ pulse in a spot size estimated to be 0.25 mm gave pressures up to 74 bars. Measurements at different positions with respect to the irradiation spot showed differences in acoustic amplitude that could not be explained by absorption attenuation. It is hypothesized that these differences are a result of differential diffraction of the frequency components of the acoustic wave, components of which extend up to a maximum of about 4 MHz. It is the highly directional high frequency acoustic energy that could be causing the damage on the side of the blood vessel opposite the point of irradiation.

Tissue fluorescence changes and protein coagulation after Nd:YAG interstitial laser photocoagulation

In attempting to identify a tissue response suitable for monitoring interstitial laser photocoagulation (ILP) during treatment, we observed that the lesions produced in tissue by interstitial irradiation with the 1064 nm radiant energy produced by an Nd:YAG laser fluoresce when exposed to the long-wave ultraviolet light produced by a handheld UV fluorescent lamp. The visual extent of the fluorescence was correlated to the irradiation time and energy fluence rate. Fluorescence spectra of four tissue chromophores, serum albumin, Type 1 collagen, nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) exhibited similar spectra to the fluorescence of solubilized tissue. No significant changes in the fluorescent spectra were observed upon heating to 70°C for 5 minutes the chromophores or tissue sample prior to solubilization. In another experiment, the tissue was thermally damaged by immersion in phosphate buffered saline from 60-100°C for 30-90 seconds. The reflectance from 400-800 nm of the intact tissue was noted to increase with increasing thermal damage up to 80°C, and the decrease at 90°C and 100°C. Activation energies calculated from this data was suggestive of thermal damage to blood and other tissue constituents. In order to see if changes in electrophoretic mobility occurred upon heating, nondenaturing polyacrylamide gel electrophoresis (native PAGE) was done on heated that were solubilized by ultrasonication. The gels showed a quantitative loss of tissue proteins with increasing thermal damage, and the irreversible formation of heavy protein coagulums.