Determination of the optical properties of the human uterus using frequency-domain photon migration and steady-state techniques

Liquid crystal elastomer based dynamic device for urethral support: Potential treatment for stress urinary incontinence

Stress urinary incontinence (SUI) is characterized by the involuntary loss of urine due to increased intra-abdominal pressure during coughing, sneezing, or exercising. SUI affects 20-40% of the female population and is exacerbated by aging. Severe SUI is commonly treated with surgical implantation of an autologous or a synthetic sling underneath the urethra for support. These slings, however, are static, and their tension cannot be non-invasively adjusted, if needed, after implantation. This study reports the fabrication of a novel device based on liquid crystal elastomers (LCEs) capable of changing shape in response to temperature increase induced by transcutaneous IR light. The shape change of the LCE-based device was characterized in a scar tissue phantom model. An in vitro urinary tract model was designed to study the efficacy of the LCE-based device to support continence and adjust sling tension with IR illumination. Finally, the device was acutely implanted and tested for induced tension changes in female multiparous New Zealand white rabbits. The LCE device achieved 5.6% ± 1.1% actuation when embedded in an agar gel with an elastic modulus of 100 kPa. The corresponding device temperature was 44.9 °C ± 0.4 °C, and the surrounding agar temperature stayed at 42.1 °C ± 0.4 °C. Leaking time in the in vitro urinary tract model significantly decreased (p < 0.0001) when an LCE-based cuff was sutured around the model urethra from 5.2min ± 1min to 2min ±0.5min when the cuff was illuminated with IR light. Normalized leak point force (LPF) increased significantly (p = 0.01) with the implantation of an LCE-CB cuff around the bladder neck of multiparous rabbits. It decreased significantly (p = 0.023) when the device was actuated via IR light illumination. These results demonstrate that LCE material could be used to fabricate a dynamic device for treating SUI in women.

The Rationale for Photobiomodulation Therapy of Vaginal Tissue for Treatment of Genitourinary Syndrome of Menopause: An Analysis of Its Mechanism of Action, and Current Clinical Outcomes

Objective: Light, particularly in the visible to far-infrared spectrum, has been applied to the female genital tract with lasers and other devices for nearly 50 years. These have included procedures on both normal and neoplastic tissues, management of condylomata, endometriosis, and menometrorrhagia, and, more recently, a number of fractional laser devices have been applied for the management of genitourinary syndrome of menopause (GSM) and stress urinary incontinence (SUI), and to achieve so-called vaginal rejuvenation. Photobiomodulation therapy (PBMT) has been proposed as an alternative for use in managing GSM and SUI.

Methods: This article reviews the biological basis, symptoms, and management of GSM, and investigates the current status and rationale for the use of PBMT.

Results and conclusions: Based on the preliminary evidence available, PBMT is safe and appears to be efficacious in treating GSM.

Fabrication of a turbid optofluidic phantom device with tunable μa and μ's to simulate cutaneous vascular perfusion

Microfluidic devices are oftenly used to calibrate the imaging reconstruction, because they simulate the morphology of microvasculature. However, for lack of optical properties in microfluidics, the functional recovery of oximetry information cannot be verified. In this work, we describe the fabrication of a novel turbid optofluidic tissue phantom. It is designed to mimic the vascular perfusion and the turbid nature of cutaneous tissue. This phantom contains an interior hollow microfluidic structure with a diameter of ϕave = 50 μm. The microfluidic structure includes the geometry of an inlet, a river-like assay and an outlet. This structure can be perfused by hemoglobin solution to mimic the cutaneous micro-circulation. The multiple-layered phantom matrices exhibit the representative optical parameters of human skin cutis, namely the absorption coefficient μa and the reduced scattering coefficient . The geometry of the generated microfluidic structure is investigated by using Spectral-Domain Optical Coherence Tomography. This optofluidic phantom bridges the gap between tissue equivalent phantoms and Lab-On-Chip devices. Perspectively, this device can be used to calibrate a variety of optical angiographic imaging approaches.

Study of optical parameters of polystyrene spheres in dense aqueous suspensions

We investigated the dependence of the scattering and absorption coefficients of particles in dense suspensions by the low-coherence fiber optic dynamic light scattering (FODLS) technique. The estimated particle size was used to calculate the scattering coefficient of particles suspended in dense suspensions. The path-length resolved intensity distributions of light backscattered from absorbing dense suspensions were investigated experimentally. The absorption coefficient can be obtained by applying the measured path-length resolved intensity distributions to the modified Lambert-Beer law. As a result, the low-coherence FODLS technique can simultaneously measure the scattering and absorption coefficients of particles in absorbing dense suspensions, and the scattering and absorption coefficients are independent of each other in dense suspensions in the low-scattering regime of 2l(d) < 10ℓ*.

Measurement of the penetration depths of red and near infrared light in human "ex vivo" tissues

The increasing application of light in new medical treatments has led to the need for optical characterization of tissues in order to obtain correct dosimetry. This study presents the results of measurements of the optical penetration depth of different human tissues based on the diffusion approximation of the transport theory of light.

Quantitative near-infrared spectroscopy of cervical dysplasia in vivo

The aims of this study were: (i) to quantify near-infrared optical properties of normal cervical tissues and high-grade squamous intra-epithelial lesions (H-SIL); (ii) to assess the feasibility of differentiating normal cervical tissues from H-SIL on the basis of these properties; and (iii) to determine how cervical tissue optical properties change following photodynamic therapy (PDT) of H-SIL in vivo. Using the frequency domain photon migration technique, non-invasive measurements of normal and dysplastic ecto-cervical tissue optical properties, i.e. absorption (mu(a)) and effective scattering coefficients, and physiological parameters, i.e. tissue water and haemoglobin concentration, percentage oxygen saturation (%SO(2)), were performed on 10 patients scheduled for PDT of histologically-proven H-SIL. Cervix absorption and effective scattering parameters were up to 15% lower in H-SIL sites compared with normal cervical tissue for all wavelengths studied (674, 811, 849, 956 nm). Following PDT, all mu(a) values increased significantly, due to elevated tissue blood and water content associated with PDT-induced hyperaemia and oedema. Tissue total haemoglobin concentration ([TotHb]) and arterio-venous oxygen saturation measured in H-SIL sites were lower than normal sites ([TotHb]: 88.6 +/- 35.8 micromol/l versus 124.7 +/- 22.6 micromol/l; %SO(2): 76.5 +/- 14.7% versus 84.9 +/- 3.4%).

Near-infrared optical properties of ex vivo human uterus determined by the Monte Carlo inversion technique

The optical properties, absorption (mua) and reduced scattering coefficient (mu's), of ex vivo human myometrium and leiomyoma (fibroid) have been determined by the Monte Carlo inversion technique over the wavelength range 600-1000 nm. This region is currently of interest for new, minimal-access, surgical laser procedures such as photodynamic therapy (PDT) for abnormalities of the uterus, and interstitial laser photocoagulation (ILP) for the thermal ablation of fibroids. In the region 630-675 nm (corresponding to PDT), the optical coefficients of myometrium are mua = 0.041+/-0.012 mm(-1) and mu's = 1.37+/-0.19 mm(-1). For the wavelength range 800-1000 nm (associated with infrared lasers for ILP), the optical coefficients of fibroid were found to be mua = 0.020+/-0.003 mm(-1) and mu's = 0.56+/-0.03 mm(-1). Overall, the optical properties of fibroid were found to be lower than myometrium, and this was attributed to the differences in both anatomy and vascularity. The results show that PDT for ablation of the uterine endometrium is most unlikely to affect any tissues beyond the myometrium, and that the region around 800 nm is the most effective for ablation of fibroids using ILP as the penetration depth of light is greatest at this wavelength.

Non-invasive measurements of breast tissue optical properties using frequency-domain photon migration

A multiwavelength, high bandwidth (1 GHz) frequency-domain photon migration (FDPM) instrument has been developed for quantitative, non-invasive measurements of tissue optical and physiological properties. The instrument produces 300 kHz to 1 GHz photon density waves (PDWs) in optically turbid media using a network analyser, an avalanche photodiode detector and four amplitude-modulated diode lasers (674 nm, 811 nm, 849 nm, and 956 nm). The frequency of PDW phase and amplitude is measured and compared to analytically derived model functions in order to calculate absorption, mu a, and reduced scattering, mu s, parameters. The wavelength-dependence of absorption is used to determine tissue haemoglobin concentration (total, oxy- and deoxy- forms), oxygen saturation and water concentration. We present preliminary results of non-invasive FDPM measurements obtained from normal and tumour-containing human breast tissue. Our data clearly demonstrate that physiological changes caused by the presence of small (about 1 cm diameter) palpable lesions can be detected using a handheld FDPM probe.

Structural and functional effects of endometrial photodynamic therapy in a rat model

OBJECTIVE

Our purpose was to determine the optical dose required for irreversible endometrial destruction and prevention of implantation by photodynamic therapy with topical 5-aminolevulinic acid.

STUDY DESIGN

Three hours after drug application 74 female Sprague-Dawley rats received varying doses of 630 nm of light delivered by an intrauterine cylindric diffusing fiber.

RESULTS

A 64 J/cm2 in situ optical dose resulted in long-term irreversible endometrial destruction; 43 J/cm2 damaged endometrial stroma and myometrium but not glandular epithelium 1 day after photodynamic therapy. At this lower light dose endometrium regenerated to full thickness within 3 weeks; however, implantation sacs were significantly reduced.

CONCLUSIONS

Photodynamic destruction of glandular epithelium accompanies irreversible endometrial ablation, whereas isolated stromal damage leads to reproductive impairment only. The optical dose required for endometrial ablation is approximately 1.5-fold higher than for reproductive impairment (functional damage) because of differential cell photosensitivity.

A mathematical model for light dosimetry in photodynamic destruction of human endometrium

We are involved in the development of photodynamic therapy (PDT) as a minimally invasive method for treating dysfunctional uterine bleeding, one of the primary clinical indications for hysterectomy. In this paper, we analyse light propagation through the uterus in order to specify the requirements for a light delivery system capable of effectively performing endometrial PDT. Our approach involves developing an analytical model based on diffusion theory to predict optical fluence rate distributions when cylindrical and spherical optical applicators are placed in the uterine cavity. We apply the results of our model calculations to estimate the thermal effects of optical irradiation and the effective photodynamic optical dose. Theoretical fluence rate calculations are compared to fluence rate measurements made in fresh, surgically removed human uteri. Our results show that a trifurcated cylindrical optical applicator inserted into the human uterus can provide a light dose that is sufficient to cause photodynamic destruction of the entire endometrium. When the optical power per unit length of each cylindrical applicator is 100 mW cm-1 (at 630 nm), a fluence rate of 40 mW cm-2 is delivered to the boundary layer between the endometrium and the myometrium (a depth of about 4-6 mm). The optical fluence delivered to the boundary layer after 20 min of exposure is 50 J cm-2, a level that is generally accepted to cause tissue damage throughout the endometrium in most patients.

The influence of glucose concentration upon the transport of light in tissue-simulating phantoms

The effect of glucose upon the transport of light in tissue-simulating phantoms is shown and its possible application for non-invasive glucose monitoring in diabetic patients is discussed. The aim of this paper is to investigate the physical background of this effect. The presence of glucose in an aqueous solution increases its refractive index and therefore has an influence upon the scattering properties of particles suspended in solution. Experimental data on the effect of glucose upon the scattering coefficient and the phase function of aqueous suspensions of spherical polystyrene particles are presented for near-infrared wavelengths and compared to values predicted by Mie theory. The subsequent effect upon light transport in multiple scattering, tissue-simulating phantoms is demonstrated experimentally in a slab geometry and theoretically by applying diffusion theory. It is furthermore shown that optional measurements in the frequency domain allow changes of absorption and scattering coefficient to be separately determined. The possible magnitude of this glucose effect in tissue in vivo is discussed.

Portable, high-bandwidth frequency-domain photon migration instrument for tissue spectroscopy

We describe a novel frequency-domain photon migration instrument employing direct diode laser modulation and avalanche photodiode detection, which is capable of noninvasively determinating the optical properties of biological tissues in near real time. An infinite medium diffusion model was used to extract absorption and transport scattering coefficients from 300-kHz to 800-MHz photon-density wave phase data. Optical properties measured in tissue-simulating solutions at 670 nm agreed to within 10% of those expected.