Burst-mode ultrafast laser treatments in biological tissues or in materials-processing use high-repetition-rate (⪆MHz) delivery of femtosecond laser pulses. This takes advantage of characteristically tiny residual heat left in a substrate through individual femtosecond-laser-matter interaction. At the same time, the approach opens the door to manipulating the accumulation of that same tiny heat during rapid pulse-repetition. This mode of fluence-delivery may, for instance, be able to denature the protein in the walls of a laser-cut wound and possibly improve infection rates in ultrashort-pulse laser surgery in certain contexts. Isolated intense sub-picosecond laser pulses typically do not rely on intrinsic chromophores for absorption, instead they first create a limited plasma via nonlinear ionization, then increase that plasma through collisional ionization. Used in burst-mode, plasma-mediated ablation can exploit some residual ionization which persists for a few nanoseconds, meaning that subsequent pulses need not re-initiate dielectric breakdown. In effect, the plasma is ‘simmered’ continuously throughout a burst, controlling the mode and amount of absorption and opening the door to particularly gentle laser cutting of tissues and dielectric materials. We describe pulse-by-pulse studies of the persistence of the plasma state within a burst of approximately 60 pulses, each of 300 fs duration, arriving with an intra-burst repetition rate of 200 MHz (5 ns separation). We also present the impact of these burst-mode treatments on cellular necrosis in a phantom of rat-glioma cells suspended in hydrogels and in porcine cartilage samples.
Nonlinear response of complex chiral structures depends on the fibers configuration in the focal volume. The impact of various configuration on nonlinear parameters extracted using a polarimetric second harmonic generation (SHG) microscope has been elucidated.
Intraoperative visualization of molecular processes delineated by fluorescence contrast agents offers the potential for increased surgical precision and better patient outcomes. To exploit fully the clinical potential for targeted fluorescence guidance, there is a growing need to develop high-resolution, quantitative imaging systems suitable for surgical use. Diffuse optical fluorescence tomography (DOFT) systems in pre-clinical and diagnostic imaging applications have demonstrated improvements in fluorescence quantification with the addition of a priori data from structural imaging modalities (e.g., MR, CT). Here, we investigate the use of a cone-beam CT (CBCT) surgical guidance system to generate spatial priors for intraoperative DOFT. Imaging and localization data is incorporated directly into a finite element method DOFT implementation (NIRFAST) at multiple stages. First, CBCT data from an intraoperative flat-panel C-arm is used to generate tetrahedral meshes. Second, optical tracking of laser and camera devices enables an adaptable non-contact DOFT approach to accommodate various anatomical sites and acquisition geometries. Finally, anatomical segmentations from CBCT are included in the optical reconstruction process using Laplacian-type regularization (“soft spatial priors”). Calibration results showed that light rays between the tissue surface and navigated optical devices were mapped with sub-millimeter accuracy. Liquid phantom experiments determined the improvements in quantification of fluorescence yield, with errors of 85% and <20% for no priors and spatial priors, respectively. CBCT-DOFT fusion in a VX2-tumor rabbit model delineated contrast enhancement using a dual CT/optical liposomal nanoparticle. These developments motivate future translation and evaluation in an ongoing CBCT-guided head and neck surgery patient study.
Linear polarization-in, polarization-out second-harmonic generation microscopy was used to
study the effect of Photodynamic therapy treatment on enhancing the healing of femur fracture by
investigating the ultrastructure of collagen as a major component of bone matrix.
We have developed an automated, wide-field optical coherence tomography (OCT)-based imaging device (OTISTM Perimeter Medical Imaging) for peri-operative, ex-vivo tissue imaging. This device features automated image acquisition, enabling rapid capture of high-resolution (15 μm) OCT images from samples up to 10 cm in diameter. We report on the iterative progression of device development from phantom and pre-clinical (tumor xenograft) models through to initial clinical results. We discuss the challenges associated with proving a novel imaging technology against the clinical “gold standard” of conventional post-operative pathology.
Albert Yee, Shane Burch, Margarete Akens, Emily Won, Victor Lo, Lisa Wise-Milestone, Stuart Bisland, Aimee Theriault, Carolyn Niu, Brian Wilson, Cari Whyne
Metastatic cancer causes the majority of tumors in bone, most frequently detected in the spinal column. Skeletal complications cause pain and neurologic impairment. Photodynamic therapy (PDT) has been used to treat a variety of cancers. Minimally invasive surgical (MIS) strategies may allow targeted light application essential for PDT within bone structures. The purpose of this manuscript is to provide an update on pre-clinical status as well as early clinical experience of a Phase I clinical trial on vertebral PDT.
A pre-clinical (rnu/rnu rat) vertebral metastasis model of osteolytic (MT-1 breast cancer) was optimized and used to evaluate the effect of vertebral PDT. PDT alone and in combination with other standard local (radiation therapy, RT) and systemic (bisphosphonates, BP) therapies was evaluated through bioluminescence imaging, micro-CT based stereology, histology, and biomechanical testing. Single PDT treatment (photosensitizer BPD-MA, 690nm light) ablated tumor tissue in targeted vertebrae. PDT led to significant increases in bone structural properties, with greatest benefits observed from combined BP+PDT therapy: 76% and 19% increases in bone volume fraction in treated tumor-bearing and healthy untreated controls, respectively. Similar synergistic improvements (but of lesser magnitude) were found in combined PDT+RT treatments.
The safety and feasibility of MIS+PDT were evaluated in scale-up animal studies, refining surgical technique for clinical translation. Following appropriate institutional review board as well as Health Canada approval, 5 patients (light only control group) have undergone protocoled treatment to date. These patients have guided further refinement of human therapeutic application from a laser delivery and vertebral bone access perspective.
A hierarchical model of the organization of fibrillar collagen is developed and its implications on polarization-resolved
second harmonic generation (SHG) microscopy are investigated. A “ground-up” approach is employed to develop the
theory for understanding of the origin of SHG from fibrillar collagen. The effects of fibril ultrastructure and fibril
macroscopic organization on the second-order polarization properties of fibrillar collagen are presented in conjunction
with recent ab initio results performed on a collagen triple-helix model (-GLY-PRO-HYP-)n. Various tissues containing
fibrillar collagen are quantified using a polarization-resolved SHG technique, termed polarization-in, polarization-out
(PIPO) and interpreted in light of the aforementioned theory. The method involves varying the incident laser
polarization, while monitoring the SHG intensity through an analyzer. From the SHG polarization data the orientation of
the fibers, in biological tissue, can be deduced. Unique PIPO signatures are observed for different rat tissues and
interpreted in terms of the collagen composition, fibril ultrastructure, and macroscopic organization. Similarities and
discrepancies in the second-order polarization properties of different collagen types and ultrastructures will be presented.
PIPO SHG microscopy shows promise in its ability to quantify the organization of collagen in various tissues. The
ability to characterize the structure of collagen in various tissue microenvironments will aid in the study of numerous
collagen related biological process, including tissue diseases, wound repair, and tumor development and progression.
Photodynamic therapy (PDT) as a non-radiative treatment has been applied successfully in various cancers. PDT may be a useful adjunct in the treatment of vertebral metastases. PDT efficacy requires the administration of a photosensitiser drug followed by subsequent drug activation by wavelength specific light. The study purpose was to establish the pharmacokinetic profiles for 2 photosensitisers, BPD-MA and 5-ALA induced PpIX, to determine the optimal drug-light interval for vertebral PDT.
Two-photon (2-γ) photodynamic therapy (PDT) as opposed to "standard" one-photon (1-γ) PDT with Visudyne has recently been suggested as a targeted treatment alternative for wet-form age-related macular degeneration (AMD) and other neovascular diseases. AMD is a major cause of severe vision loss in the older population. It occurs due to growth of new leaky blood vessels (neovasculature) from the choriocapillaris, which results in destruction of photoreceptors in the fovea and loss of central vision. Damage outside the diseased region is always a concern, due to photosensitizer accumulation and its 1-γ excitation. Highly targeted 2-γ excitation, due to its non-linear intensity dependence, intrinsically avoids out-of-focus damage to healthy tissues and so could be valuable for wet-AMD. We have previously developed a quantitative approach for comparing the 2-γ efficacy of photosensitizers in vitro. In this study, we report further the development of ex vivo and in vivo techniques. A mouse mesenteric vessel has been investigated as the ex vivo model of neovasculature. For the in vivo studies, we have explored a mouse dorsal skin-fold window chamber model. Two-photon PDT is delivered using tightly focused ~300 fs laser pulses from a Ti:sapphire laser operating at 850 nm with 90 MHz pulse repetition rate. Confocal microscopy coupled to the laser was used to visualize the vessel's/cell's response before, during and after the treatment. We are able to demonstrate quantitative biological techniques to evaluate efficacy of 2-γ PDT photosensitizers in vivo.
This study investigates the efficacy of low level laser therapy (LLLT) in modulating inducible nitric oxide synthase (iNOS) expression as molecular marker of the inflammation signaling pathway. LLLT was mediated by different therapeutic wavelengths using transgenic animals with the luciferase gene under control of the iNOS gene expression. Inflammation in 30 transgenic mice (iNOS-luc mice, from FVB strain) was induced by intra-articular injection of Zymosan-A in both knee joints. Four experimental groups were treated with one of four different wavelengths (λ=635, 785, 808 and 905nm) and one not laser-irradiated control group. Laser treatment (25 mW cm-2, 5 J cm-2) was applied to the knees 15 minutes after inflammation induction. Measurements of iNOS expression were performed at multiple times (0, 3, 5, 7, 9 and 24h) post-LLLT by measuring the bioluminescence signal using a highly sensitive charge-coupled device (CCD) camera.
The responsivity of BLI was sufficient to demonstrate a significant increase in bioluminescence signals after laser irradiation of 635nm when compared to non-irradiated animals and the other LLLT treated groups, showing the wavelength-dependence of LLLT on iNOS expression during the acute inflammatory process.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.