This PDF file contains the front matter associated with SPIE Proceedings Volume 11958 including the Title Page, Copyright information, and Table of Contents.

Picosecond laser treatment effect for pigmented skin lesions is triggered by selective absorption of melanin particles packaged in cutaneous melanosomes. The treatment effect has been evaluated based on linear absorption of laser fluence in light distribution calculation. However, nonlinear absorption usually occurs when melanin particles are irradiated with a picosecond laser pulse with a high-power density. This paper proposes a two-level model that simulates absorption and nonradiative decay of melanin particles in picosecond skin laser treatment. The proposed two-level model supposes that the picosecond laser pulse width is comparable to the nonradiative relaxation time of melanin particles, and essentially all the absorbed energy in visible and near-infrared wavelengths is released nonradiatively. The numerical simulation result shows that nonlinear absorption occurred at pulse widths ranging from picoseconds to nanoseconds. The amounts of energy deposition within a single melanosome were reduced by 57% and 21% at pulse widths of 100 ps and 1 ns, respectively, compared with linear absorption, for a laser fluence of 0.05 J/cm² . The numerical results indicate that picosecond laser pulses are less absorbed by pigmented skin lesions than nanosecond laser pulses.

Accurate values of the optical properties of skin and subcutaneous tissues are critical for a variety of applications, such as optical imaging techniques and computational modeling of possible hazardous laser exposure. Several studies are available in the published literature that report skin optical properties, but the method of tissue preparation and storage in these experiments can be variable, ranging from measurement immediately after excision, to undergoing some form of cold storage, such as refrigeration or freezing. The degree to which cold storage affects the optical properties of skin tissues is unknown. We measured the absorption and reduced scattering coefficients of skin and subcutaneous tissues that underwent refrigeration and slow freezing, and compared them to freshly excised samples. Tissues were collected from several subjects in order to capture biological variability. We employed a goniometric spectrophotometer setup and a Monte Carlo light propagation method to determine optical properties. The results of this investigation will help contextualize existing studies on tissue optical properties and enable informed procedural design for future measurements.

Modern mobile phone imaging sensors wide availability and high quality have enabled development of low-cost imaging and sensing approaches that utilize the camera, including those which detect diffuse optical interactions and produce quantitative transcutaneous measures analogous to clinical techniques for bilirubin and oxygenation sensing. Concurrently, recent clinical studies report overestimation bias from dark skinned patients in transcutaneous bilirubinometery (TcB) and pulse oximetry. Here, Monte Carlo simulations of TcB and oximetery were used to investigate the source of possible racial biases in clinical measurements. Simulations of device calibration studies with dark, mixed, and light skinned cohorts were tested against groups with similar and different racial distributions. Results implicate a combination of tissue optics and biased enrollment in calibration studies for systematic overestimation in both TcB and oximetry. Next, identical Monte Carlo simulations were performed with a 2D image sensor capable of detecting spatially resolved diffuse reflectance. Quantification models were developed from simulated calibration studies where reflectance was extracted from 1 to 5 unique sensor regions of interest (ROI), followed by evaluation against test cohorts with different racial distributions. The results indicated overestimation bias in darkly pigmented subjects could be reduced through incorporation of an increasing number of sensor ROI’s. Models for quantification of bilirubin were then developed using clinical data from our mobile phone based TcB study, and increasing number of sensor ROI’s improved model performance (r²) . These results suggest promise for the development of mobile image-sensor based spatially resolved diffuse reflectance for improving accuracy and reducing racial bias in transcutaneous measurements.

In this work, we study the self-healing properties of the space-time (ST) light sheet upon interaction with a partially transparent object, namely a microtissue array of biological samples. In particular, we study the response of the ST light sheet upon encountering biological tissues that have been graded as normal (benign), malignant, and malignant tumor stage III. We find a differential response that can be leveraged for characterization of the tissue specimens. Specifically, the ST light sheet is observed to more completely reconstruct upon traversing the normal tissue compared to the malignant specimens. We believe that this is the first report exploring the potential of self-healing as a metric for tissue characterization.

Retinal pigment epithelial (RPE) cells undergo damage from laser exposure in the visible spectrum in a pigment-dependent manner. Achieving photothermal damage with short laser exposures require irradiances that generate significant temperature rise, even for wavelengths having photon energies sufficiently great enough to generate photochemical damage. To force photochemical damage, one typically exposes for long durations using relatively low irradiance. What mechanisms are responsible for damage caused by exposure durations between the short and long durations producing photothermal and photochemical damage, respectively? To address this question, we used microthermography in real-time with laser exposure in our artificially pigmented in vitro retinal model. We compared threshold peak temperatures for damage at exposure durations between 0.1 – 165 s at 447 nm, with those from 647 nm. The threshold temperature rises at 647 nm provided an example of purely photothermal damage processes. Because photons at 447 nm have sufficient energy to generate photochemical damage, the threshold temperature rises for this wavelength provided a measure of the photothermal component of what appears to be mixed damage mechanisms in the intermediate exposure durations. Differences between threshold temperatures at 647 nm and 447 nm help to define the degree to which the blue light contributes to the overall damage by way of the photochemical damage processes.

Recently, pulsed lasers with ultrashort pulse durations have become ubiquitous in a variety of applications, including medical procedures such as laser eye surgery. These sources are capable of generating extremely high peak powers that can cause laser-induced tissue breakdown upon exposure. However, current laser safety standards do not provide exposure limits for wavelengths longer than 1400 nm and pulse durations shorter than 1 ns due to a lack of biological data. Instead, the recommendation is to limit the peak irradiance to the maximum permissible exposure (MPE) limits applicable to 1 ns pulse durations. We applied femtosecond laser pulses of varying energies at 1540 nm and 2000 nm to corneas of anesthetized rabbits. We used slit lamp biomicroscopy and optical coherence tomography to examine the exposure sites and determine the presence or absence of visible lesions 1 h and 24 h post-exposure. The dose-response data correlating the presence or absence of any alteration of the corneal surface to the pulse energy 1 h post-exposure was evaluated using probit analysis to extract the median effective dose (ED₅₀) corresponding to the cornea damage threshold. We compared our results to the MPE limits applicable to 1 ns pulse durations and determined that the current safety standard procedures are not adequate to evaluate small diameter single pulse femtosecond exposures at 1540 nm and 2000 nm. The results of this study contribute to the knowledge base used for setting laser safety standards in the near infrared range for ocular exposure to ultrashort pulses.

Computer simulations (CS) are applied for instrument design, feasibility tests and education in low-resource settings. These applications have been targeted by research biophotonics CS. However, software enabling these CS were not designed for education, as they require programming experience from users as well as specialized training to use it. In this study, we have developed and tested a diffuse-optics web application to teach tissue optics to undergraduate students with diverse learning styles and backgrounds. Students’ feedback showed that CS session using our web app received 84.6% “Very good” and ““Good” responses for overall learning, 76.9% for quality of the user manual instructions, 92.3% for quality of teaching, 100.0% for quality of subject matter among the participant respondents. Also, 92.3% of participants considered CS important for their learning process.

Photodynamic therapy and radiotherapy have traditionally relied on fixed wavelength sources (typically 1064 nm Nd:YAG laser), due to their ready availability. But with advances in development of wide wavelength spanning Raman fiber lasers, a greater flexibility in choice of the light source is provided. In a previous work by our group, we demonstrated the first use of a widely tunable Raman fiber laser (from 1-1.5 um) in achieving varying degrees of cytotoxicity with wavelength at fixed power and exposure for an epithelial breast cancer cell line. However, the reasons for this variation in cytotoxicity was unknown. In this work, we analyse the causes of this variation of cytotoxicity with wavelength for the same epithelial breast cancer cells irradiated in-vitro. Cell-viability is performed through a Propidium-Iodide based assay analysed through a flow cytometer. Thereafter, with the implementation of a novel-image processing algorithm on the same cytometer plots, we obtain a surprising insight into the reasons for cell death for certain wavelengths of irradiation. Specifically, we hypothesise that the effect of these wavelengths is twofold: to desiccate the water content of the cells, leading to reduction in cell size; and to lead to increased granularity or denaturation in the intra-cellular components. We make a surprising observation that cell size reduction is not as correlated with cytotoxicity as increased granularity. This paves the way for a better and insightful deployment of tunable wavelength Raman lasers in photodynamic therapy with the choice of an optimum wavelength to achieve the greatest tumoricidal effect.

The main objective of this study was to assess the feasibility of NIRS (PortaMon®, Artinis Medical Systems) as a noninvasive monitoring method for kidney transplant function. We hypothesized that changes in NIRS (near infra-red spectroscopy) parameters are associated with changes in graft function as estimated by Glomerular Filtration Rate (GFR) based on serum creatinine level. Two cohorts of participants were recruited: Immediate postoperative and those with at least 8 weeks post-transplant. Other inclusion criteria were BMI<25kg/m2 and AWD (abdominal wall depth) <2cm. We evaluated 4 patients immediately after the surgery in the operating room and continued the examination every day while they were in the hospital. We also monitored them for 12 weeks after surgery. The second group (16 patients) had their surgery in a median of 26 months prior to their recruitment. The procedure of NIRS monitoring was the same for both groups. We examined the surgical sites and opposite sides of the abdomen as our control for at least 3 minutes each time. The collected data were compared with clinical parameters (BP, e-GFR, and Resistive Index). We analyzed the collected data using linear regression model and we noted a positive significant correlation between the tissue saturation index of the surgical site (TOISS%) and e-GFR adjusted for BMI. We also examined the ∆TOI% (percentage of difference of oxygen saturation index between the surgical site and opposite site) to account for the abdominal muscle effects on collected signals.

Virtual pathology techniques have demonstrated the capability to overcome surgical pathology’s critical disadvantage, time inefficiency, by imaging surgical samples ex vivo. Removing extensive tissue preparation steps allows virtual pathology to provide same-day or even within-procedure diagnosis. Structured illumination microscopy (SIM) is a wide-field fluorescent optical-sectioning microscopy technique that allows higher speed imaging as compared to similar modalities, making it a good candidate for real-time diagnostics. Although SIM image acquisition is fast, the staining procedure must also be fast to meet real-time use, considering a maximum time allotment of 20-30 minutes for staining and imaging during surgery. Thus, we require our staining procedure to take no more than 4 minutes for nuclear and extracellular matrix (ECM) staining. In this work, we evaluated multiple candidates for imaging of large surgical resection specimens based on staining time and specificity, image quality, and cost per sample. Based on phantom studies using bovine muscle, we found that SYBR Gold provides the best results for nuclear staining (compared to TO-Pro3 and DRAQ5) on samples with large volume and surface area. Also, we found an optimal ratio between concentration and staining time for Eosin as an ECM stain. We then applied these protocols to imaging of radical prostatectomy specimens immediately after surgical removal, and present here for the first-time SYBR Gold and Eosin (Sg&E) virtual pathology for whole prostate imaging. In ten cases (2 with positive margin), we were able to identify healthy and pathological structures using SG&E virtual pathology that corresponds to hematoxylin and eosin pathology.

As the innermost layer of the gastrointestinal (GI) tract, the mucosa layer has critical importance in carcinogenesis. Barrett’s esophagus is a pre-cancerous lesion characterized by intestinal metaplasia within the stratified squamous epithelium of esophageal mucosa. Mucosal lesions that are not adequately treated tend to enlarge and become cancerous tissue over the surface and deeper layers. Although various treatment strategies are available, uncontrolled depth of treatment to eliminate lesions is still challenging. Exceeding the treatment depth may cause adverse effects on the underlying healthy tissue layers, while insufficient treatment depth may cause the lesion to recur. Besides, the inhomogeneity of the distribution of the lesions on the esophageal surface makes it difficult to apply ablation therapy in a single session, requiring more sessions. However, a feasible approach is still needed to perform the desired results in photothermal ablation at a single therapy session. This study demonstrates an endoscopy capsule that provides well confined and angle-controlled photothermal mucosal ablation. The capsule consists of three parts: a base that holds a stepper motor and a GRIN lens; a cap that includes gold-coated right-angle prism mirrors; an optically transparent and perforated body for negative pressure unites the base and cap. The mucosa layer is confined to the recessed area of the capsule by negative pressure delivered through holes. The laser beam at 1505 nm is rotated with a constant speed and defined rotation angles for circumferential photothermal ablation.

The objectives of this retrospective study were first to evaluate the safety and early-stage efficacy and durability of targeted (focal/partial to whole-gland) TULSA as a treatment for prostate cancer (PCa). For those PCa patients simultaneously presenting with symptomatic and obstructive benign prostatic hyperplasia (BPH), TULSA was also evaluated as a combination therapy. Materials & Methods: The study included men diagnosed with MRI-guided biopsy-confirmed PCa who underwent TULSA as primary or salvage treatment, with Gleason Grade Groups from 1-5. Treatment planning and targeted ablation volume was dependent on individual PCa characteristics, concordant BPH and patient preferences. Treatment was performed under permanent MRI control and temperature mapping. Surgeon-assessed functional outcomes were reported. Early-stage oncological control was evaluated using multi-parametric MRI (mpMRI) and prostate specific antigen (PSA). The Clavien-Dindo classification of surgical complications was used to record adverse events. Repeat treatment was allowed. Results: Fifty-two consecutive patients with a median follow-up of 27 months were included, with a baseline median age of 67 years (63-76) and PSA of 8.0 ng/ml (5.2-13). Median PSA nadir after primary treatment was 1.1 ng/ml (0.51-2.2). In total, 9 patients underwent repeat TULSA. Early-stage treatment success was 73% after initial TULSA and 88% after repeat TULSA. Of the patients who received a combination treatment 83% experienced LUTS symptom improvement. Two Grade IIIa adverse events were observed, with no bowelrelated complications. For continence outcomes, one patient worsened to 1 pad per day. No changes from baseline regarding erectile dysfunction were reported. Treatment results confirmed durable in longer follow-up. Conclusions : Targeted TULSA appears to offer a good compromise between safety and early oncological efficacy, and is a feasible combination therapy for treating concordant BPH.

Lasers are commonly employed in surgery for hard and soft tissues due to their precise space-time energy delivery and compatibility with optical fibers for delivery into body cavities, including for treatment of urological diseases. Infrared laser ablation in tissues can result in non-specific heating and thermal injury. Methods that maximize ablation efficiency, or tissue volume removed per unit energy, while minimizing non-specific thermal injury can improve surgical workflows and outcomes. We report a novel approach for increased ablation efficiency by modifying the beam shape. Specifically, a Ho:YAG laser is shaped into a converging annular beam. Ablation efficiency was measured on a hard tissue phantom (BegoStone) and soft tissue (porcine kidney). An annular beam ~800 μm in diameter was used to ablate each sample at 10 different locations using a single 1 J pulse per location. The procedure was repeated using a circular beam with similar diameter by placing a 200 μm fiber 1 mm from the tissue surface. Each ablation crater was imaged with optical coherence tomography and the crater volumes calculated from recorded images. For hard tissue phantoms, ablation efficiency increased 183% for annular vs. circular beams (0.065±0.013 vs. 0.023 ± 0.003 mm³ /J). For soft tissue, ablation efficiency increased 69% for annular vs. circular beams (0.098±0.021 vs 0.058 ± 0.018 mm3 /J). Hard and soft tissue ablation with an annular beam is a promising technique for increasing the speed and safety of laser surgery.

Introduction & Objectives: The objectives of this study were to evaluate the safety and efficacy of targeted customized (transitional zone plus focal/partial to wholegland peripheral zone) TULSA as a treatment for patients in urinary retention due to BPO and concordant prostate cancer (PCa). Materials & Methods: The study included men in chronic urinary retention due to BPO and diagnosed with MRI-guided biopsy-confirmed PCa. All men had either transurethral (n=13) or suprapubic (n=4) catheters or intermittant selfcatheterization (n=3). Patients underwent TULSA as primary treatment, with Gleason Grade Groups from 1-5. Treatment planning and targeted ablation volume was dependent on individual PCa characteristics, and included the total transitional zone. Treatment was performed under permanent MRI control and temperature mapping. Suprapubic catheters for intermittent drainage were administered in all patients and left in place until sufficient voiding was achieved. Adverse events and surgical complications were reported using the Clavien-Dindo classification. Functional outcomes were reported using IPSS (International Prostate Symptom Score). Short-term oncological control was evaluated using multi-parametric MRI (mpMRI) and prostate specific antigen (PSA). Results: Twenty consecutive patients with a follow-up of 12 months were included. The baseline median age was 76 years (66-87). All patients recovered from urinary retention after a median post-treatment catheterization time of 46 days. 12-months oncological control was achieved in 17 of 20 patients. During follow-up, grade IIIa adverse events were observed in n=5 patients (epidydymitis n=5), with no bowelrelated complications. Conclusions: Targeted TULSA appears to offer a good option for men in chronic urinary retention due to BPO with concordant prostate cancer.

Sound has been established to play an essential role in plant growth. Sound of a particular frequency has been proven to increase yield and immunity. In this study, we have considered the possibility of functional Optical Coherence Tomography (fOCT) in investigating the changes in the internal structures in response to sounds of different frequencies, 100 Hz and 10kHz. Results showed a clear dependence of the fOCT signal on the sound frequency, with 100 Hz showing an increase while 10kHz showing a decrease. Our results extend the possibility of the application of OCT to the field of plant photonics.

Hair cells of the auditory and vestibular systems are capable of detecting sounds that induce sub-nanometer vibrations. These specialized cells convert mechanical deflections due to sound waves into electrical signals that are relayed to the brain through afferent neurons. This transduction involves mechanically gated ion channels that open following the deflection of mechanoreceptive hair bundles that reside on top of these cells. Moreover, internal energy-consuming processes in the hair bundle can amplify deflections and even generate innate oscillations in the absence of input. The transduction process ultimately leads to emission of the neurotransmitter glutamate, which in turn evokes spike trains in the innervating afferents. We performed measurements on in vitro preparations of the sacculus from the American bullfrog (Rana catesbeiana). Mechanical force was imposed on the hair bundle with a stimulus probe controlled with a piezo actuator and electrical signals were sent through the nerve with a bipolar suction electrode. Under these conditions, we observed variations in the intensity of light emitted by the Ca²⁺ indicator Fluo-8. Spatial and temporal recordings of Ca²⁺ hotspots were performed on the area near the hair cell synapse, in order to elucidate the temporal dynamics of neuronal activity. Further development of this optical technique would enable the study of voltage spikes in the afferent nerve fibers, so as to correlate them to the hair bundle mechanical movement.

During the COVID-19 pandemic, social distancing restrictions required courses to be offered fully online, which impacted multidisciplinary courses/events worldwide. The quality of education especially in events relying on in-person activities to convey information quicker than online activities. We have developed a fully-online biophotonics workshop (BW) integrating webinars, at-home experiments, and computer simulations to meet needs of undergraduate students with diverse backgrounds and learning styles. >91.7%, >70%, and >90% of feedback responses were “Very good” and “Good” regarding overall learning, co-ordination and quality of subject matter of BW activities. Other biophotonics/biomedical optics courses may benefit from using similar resources and educational strategies.