Optical, flow, and thermal analysis of a phototherapy extracorporeal membrane oxygenator for treating carbon monoxide poisoning.

BACKGROUND: Extracorporeal membrane oxygenators (ECMO) are currently utilized to mechanically ventilate blood when lung or lung and heart function are impaired, like in cases of acute respiratory distress syndrome (ARDS). ARDS can be caused by severe cases of carbon monoxide (CO) inhalation, which is the leading cause of poison-related deaths in the United States. ECMOs can be further optimized for severe CO inhalation using visible light to photo-dissociate CO from hemoglobin (Hb). In previous studies, we combined phototherapy with an ECMO to design a photo-ECMO device, which significantly increased CO elimination and improved survival in CO-poisoned animal models using light at 460, 523, and 620 nm wavelengths. Light at 620 nm was the most effective in removing CO. OBJECTIVE: The aim of this study is to analyze the light propagation at 460, 523, and 620 nm wavelengths and the 3D blood flow and heating distribution within the photo-ECMO device that increased CO elimination in CO-poisoned animal models. METHODS: Light propagation, blood flow dynamics, and heat diffusion were modeled using the Monte Carlo method and the laminar Navier-Stokes and heat diffusion equations, respectively. RESULTS: Light at 620 nm propagated through the device blood compartment (4 mm), while light at 460 and 523 nm only penetrated 48% to 50% (~2 mm). The blood flow velocity in the blood compartment varied with regions of high (5 mm/s) and low (1 mm/s) velocity, including stagnant flow. The blood temperatures at the device outlet for 460, 523, and 620 nm wavelengths were approximately 26.7°C, 27.4°C, and 20°C, respectively. However, the maximum temperatures within the blood treatment compartment rose to approximately 71°C, 77°C, and 21°C, respectively. CONCLUSIONS: As the extent of light propagation correlates with efficiency in photodissociation, the light at 620 nm is the optimal wavelength for removing CO from Hb while maintaining blood temperatures below thermal damage. Measuring the inlet and outlet blood temperatures is not enough to avoid unintentional thermal damage by light irradiation. Computational models can help eliminate risks of excessive heating and improve device development by analyzing design modifications that improve blood flow, like suppressing stagnant flow, further increasing the rate of CO elimination.

Reflectance confocal microscopy-guided carbon dioxide laser ablation of low-risk basal cell carcinomas: A prospective study.

BACKGROUND: Basal cell carcinoma (BCC) treatment modalities can be stratified by tumor subtype and recurrence risk. The main limitation of nonsurgical treatment modalities is the lack of histopathologic confirmation. Reflectance confocal microscopy (RCM) is a noninvasive imaging device that provides quasihistologic images. OBJECTIVE: To evaluate the feasibility and efficacy of RCM-guided carbon dioxide (CO2) laser ablation of low-risk BCCs. METHODS: Prospective study with biopsy specimen-proven low-risk BCCs imaged with RCM. RCM was performed on these sites before and after ablation. If residual tumor was found, a new series of laser passes were performed. The patients were then monitored for recurrence clinically and with RCM. RESULTS: Twenty-two tumor sites in 9 patients (5 men, 4 women) were imaged and treated. Median age was 59 ± 12.9 years (range, 30-74 years). Mean tumor size was 7.7 mm (range, 5-10 mm). Residual tumor was identified in 5 of 22 cases (22.7%) under RCM on immediate first-pass postablation sites, prompting additional laser passes. Median follow-up was 28.5 months (range, 22-32 months) with no recurrences found. CONCLUSIONS: Addition of RCM to laser ablation workflow can detect subclinical persistent tumor after initial ablation and may serve as an aid to increase the efficacy of laser ablation.

Reflectance confocal microscopy-guided laser ablation of basal cell carcinomas: initial clinical experience.

Laser ablation offers a procedure for precise, fast, and minimally invasive removal of superficial and early nodular basal cell carcinomas (BCCs). However, the lack of histopathological confirmation has been a limitation toward widespread use in the clinic. A reflectance confocal microscopy (RCM) imaging-guided approach offers cellular-level histopathology-like feedback directly on the patient, which may then guide and help improve the efficacy of the ablation procedure. Following an ex vivo benchtop study (reported in our earlier papers), we performed an initial study on 44 BCCs on 21 patients in vivo, using a pulsed erbium:ytterbium aluminum garnet laser and a contrast agent (aluminum chloride). In 10 lesions on six patients, the RCM imaging-guided detection of either presence of residual tumor or complete clearance was immediately confirmed with histopathology. Additionally, 34 BCCs on 15 patients were treated with RCM imaging-guided laser ablation, with immediate confirmation for clearance of tumor (no histopathology), followed by longer-term monitoring, currently in progress, with follow-up imaging (again, no histopathology) at 3, 6, and 18 months. Thus far, the imaging resolution appears to be sufficient and consistent for monitoring efficacy of ablation in the wound, both immediately postablation and subsequently during recovery. The efficacy results appear to be promising, with observed clearance in 19 cases of 22 cases with follow-ups ranging from 6 to 21 months. An additional 12 cases with 1 to 3 months of follow-ups has shown clearance of tumor but a longer follow-up time is required to establish conclusive results. Further instrumentation development will be necessary to cover larger areas with a more automatically controlled instrument for more uniform, faster, and deeper imaging of margins.

Handheld reflectance confocal microscopy to aid in the management of complex facial lentigo maligna.

Diagnosis and management of lentigo maligna (LM) and LM melanoma (LMM) is challenging. Novel noninvasive imaging technologies such as reflectance confocal microscopy (RCM) have advanced the ability to better diagnose and monitor challenging lesions. In addition, the new handheld RCM (HRCM) together with the use of videomosaics has allowed an accurate evaluation of large lesions in concave/convex areas of the body (eg, the face). Herein, we review the impact of HRCM in the detection, treatment decision-making, and monitoring of 5 cases of complex facial LM/LMM. In the cases presented, HRCM enabled the detection of subclinical margins, presence of invasion, detection of persistence/recurrence, and monitoring of surgical and nonsurgical therapies. In this preliminary report, our results suggest that HRCM is a versatile ancillary tool in pretreatment decision-making, intraoperative surgical mapping, and posttreatment monitoring of complex facial LM/LMM.

Confocal imaging of carbon dioxide laser-ablated basal cell carcinomas: An ex-vivo study on the uptake of contrast agent and ablation parameters.

BACKGROUND AND OBJECTIVES: Laser ablation can be an effective treatment for the minimally invasive removal of superficial and early nodular basal cell carcinomas (BCCs). However, the lack of histological confirmation after ablation results in high variability of recurrence rates and has been a limitation. Reflectance confocal microscopy (RCM) imaging, combined with a contrast agent, may detect the presence (or absence) of residual BCC tumors directly on the patient and thus provide noninvasive histology-like feedback to guide ablation. The goal of this ex vivo bench-top study was to determine affective ablation parameters (fluence, number of passes) for a CO2 laser that will allow both removal of BCCs and control of the underlying thermal coagulation zone in post-ablated tissue to enable uptake of contrast agent and RCM imaging. MATERIALS AND METHODS: We used 72 discarded fresh normal skin specimens and frozen BCC tumor specimens to characterize the depth of ablation and to evaluate uptake of contrast agent and image quality. Acetic acid was used to enhance nuclear brightness ("acetowhitening") during imaging pre- and post-ablation. Histology sections of the post-ablated imaged surface were visually examined for the appearance of nuclear and dermal morphology and compared to the RCM images. RESULTS: Results for 1-3 passes of 5.5 J/cm(2), 6.5 and 7.5 J/cm(2), and 1-2 passes of 8.5 J/cm(2) showed the uptake of acetic acid for contrast and RCM imaging of the presence and absence of residual BCC tumors in post-ablated tissue. Morphologic details in the images were validated by the histology. CONCLUSION: The use of effective ablation parameters may enable RCM imaging to guide ablation.

Novel approaches to imaging basal cell carcinoma.

The gold standard of diagnosis for nonmelanoma and melanoma skin cancer has been skin biopsy with routine paraffin embedded hematoxylin and eosin histopathology. This practice is frequently carried out on suspicious lesions to rule out a malignant process. Therefore, as a result, many biopsies are done on benign lesions. Unlike other fields of medicine that rely on noninvasive imaging modalities, the use of imaging devices in dermatology has not been as robust. This has been mainly due to the limited resolution offered by imaging devices that is needed to detect malignant changes in the cutaneous layers. However, the demand for more efficient in vivo and ex vivo imaging tools to reduce the amount of biopsies have led to new areas of investigation using noninvasive modalities to augment the clinical diagnosis of skin cancer. The use of noninvasive imaging both in vivo and ex vivo has the potential to increase efficiency of diagnosis and management, decrease healthcare cost, improve clinical care and enhance patient satisfaction.

Confocal microscopy-guided laser ablation for superficial and early nodular Basal cell carcinoma: a promising surgical alternative for superficial skin cancers.

IMPORTANCE: Laser ablation is a rapid and minimally invasive approach for the treatment of superficial skin cancers, but efficacy and reliability vary owing to lack of histologic margin control. High-resolution reflectance confocal microscopy (RCM) may offer a means for examining margins directly on the patient. OBSERVATIONS: We report successful elimination of superficial and early nodular basal cell carcinoma (BCC) in 2 cases using RCM imaging to guide Er:YAG laser ablation. Three-dimensional (3D) mapping is feasible with RCM to delineate the lateral border and thickness of the tumor. Thus, the surgeon may deliver laser fluence and passes with localized control-ie, by varying the ablation parameters in sublesional areas with specificity that is governed by the 3D topography of the BCC. We further demonstrate intraoperative detection of residual BCC after initial laser ablation and complete removal of remaining tumor by additional passes. Both RCM imaging and histologic sections confirm the final clearance of BCC. CONCLUSIONS AND RELEVANCE: Confocal microscopy may enhance the efficacy and reliability of laser tumor ablation. This report represents a new translational application for RCM imaging, which, when combined with an ablative laser, may one day provide an efficient and cost-effective treatment for BCC.

Confocal microscopy to guide erbium:yttrium aluminum garnet laser ablation of basal cell carcinoma: an ex vivo feasibility study.

For the removal of superficial and nodular basal cell carcinomas (BCCs), laser ablation provides certain advantages relative to other treatment modalities. However, efficacy and reliability tend to be variable because tissue is vaporized such that none is available for subsequent histopathological examination for residual BCC (and to confirm complete removal of tumor). Intra-operative reflectance confocal microscopy (RCM) may provide a means to detect residual tumor directly on the patient and guide ablation. However, optimization of ablation parameters will be necessary to control collateral thermal damage and preserve sufficient viability in the underlying layer of tissue, so as to subsequently allow labeling of nuclear morphology with a contrast agent and imaging of residual BCC. We report the results of a preliminary study of two key parameters (fluence, number of passes) vis-à-vis the feasibility of labeling and RCM imaging in human skin ex vivo, following ablation with an erbium:yttrium aluminum garnet laser.

Measurement of object structure from size-encoded images generated by optically-implemented Gabor filters.

We use optical Fourier processing based on two dimensional (2D) Gabor filters to obtain size-encoded images which depict with 20nm sensitivity to size while preserving a 0.36µm spatial resolution, the spatial distribution of structural features within transparent objects. The size of the object feature measured at each pixel in the encoded image is determined by the optimal Gabor filter period, S(max), that maximizes the scattering signal from that location in the object. We show that S(max) (in µm) depends linearly on feature size (also in µm) over a size range from 0.11µm to 2µm. This linear response remains largely unchanged when the refractive index ratio is varied and can be predicted from numerical simulations of Gabor-filtered light scattering. Pixel histograms of the size-encoded images of isolated spheres and diatoms were used to generate highly resolved size distributions ("size spectra") exhibiting sharp peaks characterizing the known major structural features within the studied objects. Dynamic signal associated with changes in selected feature sizes within living cells is also demonstrated. Taken together, our data suggest that a label-free, direct and objective measurement of sample structure is enabled by the size-encoded images and associated pixel histograms generated from a calibrated optical processing microscope based on Gabor filtering.

Acquiring 3-D information about thick objects from differential interference contrast images using texture extraction.

The extraction of 3-D morphological information about thick objects is explored in this work. We extract this information from 3-D differential interference contrast (DIC) images by applying a texture detection method. Texture extraction methods have been successfully used in different applications to study biological samples. A 3-D texture image is obtained by applying a local entropy-based texture extraction method. The use of this method to detect regions of blastocyst mouse embryos that are used in assisted reproduction techniques such as in vitro fertilization is presented as an example. Results demonstrate the potential of using texture detection methods to improve morphological analysis of thick samples, which is relevant to many biomedical and biological studies. Fluorescence and optical quadrature microscope phase images are used for validation.

Modeling phase microscopy of transparent three-dimensional objects: a product-of-convolutions approach.

We present a product-of-convolutions (POC) model for phase microscopy images. The model was designed to simulate phase images of thick heterogeneous transparent objects. The POC approach attempts to capture phase delays along the optical axis by modeling the imaged object as a stack of parallel slices. The product of two-dimensional convolutions between each slice and the appropriate slice of the point spread function is used to represent the object at the image plane. The total electric field at the image plane is calculated as the product of the object function and the incident field. Phase images from forward models based on the first Born and Rytov approximations are used for comparison. Computer simulations and measured images illustrate the ability of the POC model to represent phase images from thick heterogeneous objects accurately, cases where the first Born and Rytov models have well-known limitations. Finally, measured phase microscopy images of mouse embryos are compared to those produced by the Born, Rytov, and POC models. Our comparisons show that the POC model is capable of producing accurate representations of these more complex phase images.