Adam Gribble

Rapid Detection of Necrosis in Breast Cancer with Desorption Electrospray Ionization Mass Spectrometry

Identification of necrosis in tumors is of prognostic value in treatment planning, as necrosis is associated with aggressive forms of cancer and unfavourable outcomes. To facilitate rapid detection of necrosis with Mass Spectrometry (MS), we report the lipid MS profile of necrotic breast cancer with Desorption Electrospray Ionization Mass Spectrometry (DESI-MS) imaging validated with statistical analysis and correlating pathology. This MS profile is characterized by (1) the presence of the ion of m/z 572.48 [Cer(d34:1) + Cl]− which is a ceramide absent from the viable cancer subregions; (2) the absence of the ion of m/z 391.25 which is present in small abundance only in viable cancer subregions; and (3) a slight increase in the relative intensity of known breast cancer biomarker ions of m/z 281.25 [FA(18:1)-H]− and 303.23 [FA(20:4)-H]−. Necrosis is accompanied by alterations in the tissue optical depolarization rate, allowing tissue polarimetry to guide DESI-MS analysis for rapid MS profiling or targeted MS imaging. This workflow, in combination with the MS profile of necrosis, may permit rapid characterization of necrotic tumors from tissue slices. Further, necrosis-specific biomarker ions are detected in seconds with single MS scans of necrotic tumor tissue smears, which further accelerates the identification workflow by avoiding tissue sectioning and slide preparation.

Rapid wide-field Mueller matrix polarimetry imaging based on four photoelastic modulators with no moving parts.

A new polarimetry method is demonstrated to image the entire Mueller matrix of a turbid sample using four photoelastic modulators (PEMs) and a charge coupled device (CCD) camera, with no moving parts. Accurate wide-field imaging is enabled with a field-programmable gate array (FPGA) optical gating technique and an evolutionary algorithm (EA) that optimizes imaging times. This technique accurately and rapidly measured the Mueller matrices of air, polarization elements, and turbid phantoms. The system should prove advantageous for Mueller matrix analysis of turbid samples (e.g., biological tissues) over large fields of view, in less than a second.

Assessment of local structural disorders of the bladder wall in partial bladder outlet obstruction using polarized light imaging

Partial bladder outlet obstruction causes prominent morphological changes in the bladder wall, which leads to bladder dysfunction. In this paper, we demonstrate that polarized light imaging can be used to identify the location of obstruction induced structural changes that other imaging modalities fail to detect. We induced 2-week and 6-week partial outlet obstruction in rats, harvested obstructed bladders, then measured their retardances while distended to high pressures and compared them to controls. Our results show that the retardance of the central part of the ventral side (above the ureters) closer to the urethra can be used as a potential metric of the distending bladder obstruction.

Experimental validation of optimum input polarization states for Mueller matrix determination with a dual photoelastic modulator polarimeter.

Dual photoelastic modulator polarimeters can measure light polarization, which is often described as a Stokes vector. By evaluating changes in polarization when light interacts with a sample, the sample Mueller matrix also can be derived, completely describing its interaction with polarized light. The choice of which and how many input Stokes vectors to use for sample investigation is under the experimenters control. Previous work has predicted that sets of input Stokes vectors forming the vertices of platonic solids on the Poincaré sphere allow for the most robust Mueller matrix determination. Further, when errors specific to the dual photoelastic modulator polarimeter are considered, simulations revealed that one specific shape and orientation of Stokes vectors (cube on the Poincaré sphere with vertices away from principal sphere axes) allows for the most robust Mueller matrix determination. Here we experimentally validate the optimum input Stokes vectors for dual photoelastic modulator Mueller polarimetry, toward developing a robust polarimetric platform of increasing relevance to biophotonics.

Flexible polarimetric probe for 3 × 3 Mueller matrix measurements of biological tissue

Polarimetry is a noninvasive method that uses polarised light to assess biophysical characteristics of tissues. A series of incident polarisation states illuminates a biological sample, and analysis of sample-altered polarisation states enables polarimetric tissue assessment. The resultant information can, for example, help quantitatively differentiate healthy from pathologic tissue. However, most bio-polarimetric assessments are performed using free-space optics with bulky optical components. Extension to flexible fibre-based systems is clinically desirable, but is challenging due to polarisation-altering properties of optical fibres. Here, we propose a flexible fibre-based polarimetric solution, and describe its design, fabrication, calibration, and initial feasibility demonstration in ex vivo tissue. The design is based on a flexible fibre bundle of six multimode optical fibres, each terminated with a distal polariser that ensures pre-determined output polarisation states. The resultant probe enables linear 3 × 3 Mueller matrix characterization of distal tissue. Potential in vivo Mueller matrix polarimetric tissue examinations in various directly-inaccessible body cavities are envisioned.

Polarization image segmentation of radiofrequency ablated porcine myocardial tissue

Optical polarimetry has previously imaged the spatial extent of a typical radiofrequency ablated (RFA) lesion in myocardial tissue, exhibiting significantly lower total depolarization at the necrotic core compared to healthy tissue, and intermediate values at the RFA rim region. Here, total depolarization in ablated myocardium was used to segment the total depolarization image into three (core, rim and healthy) zones. A local fuzzy thresholding algorithm was used for this multi-region segmentation, and then compared with a ground truth segmentation obtained from manual demarcation of RFA core and rim regions on the histopathology image. Quantitative comparison of the algorithm segmentation results was performed with evaluation metrics such as dice similarity coefficient (DSC = 0.78 ± 0.02 and 0.80 ± 0.02), sensitivity (Sn = 0.83 ± 0.10 and 0.91 ± 0.08), specificity (Sp = 0.76 ± 0.17 and 0.72 ± 0.17) and accuracy (Acc = 0.81 ± 0.09 and 0.71 ± 0.10) for RFA core and rim regions, respectively. This automatic segmentation of parametric depolarization images suggests a novel application of optical polarimetry, namely its use in objective RFA image quantification.

Monte Carlo simulation of polarization-sensitive second-harmonic generation and propagation in biological tissue

Polarization-sensitive second harmonic generation (p-SHG) is a nonlinear optical microscopy technique that has shown great promise in biomedicine, such as in detecting changes in the collagen ultrastructure of the tumor microenvironment. However, the complex nature of light-tissue interactions and the heterogeneity of biological samples pose challenges in creating an analytical and experimental quantification platform for tissue characterization via p-SHG. We present a Monte Carlo (MC) p-SHG simulation model based on double Stokes-Mueller polarimetry for the investigation of nonlinear light-tissue interaction. The MC model predictions are compared with experimental measurements of second-order nonlinear susceptibility component ratio and degree of polarization (DOP) in rat-tail collagen. The observed trends in the behavior of these parameters as a function of tissue thickness, as well as the overall extent of agreement between MC and experimental results, are discussed. High sensitivities of the susceptibility ratio and DOP are observed for the varying tissue thickness on the incoming fundamental light propagation pathway.

Mueller matrix polarimetry imaging for breast cancer analysis (Conference Presentation)

Polarized light has many applications in biomedical imaging. The interaction of a biological sample with polarized light reveals information about its biological composition, both structural and functional. The most comprehensive type of polarimetry analysis is to measure the Mueller matrix, a polarization transfer function that completely describes how a sample interacts with polarized light. However, determination of the Mueller matrix requires tissue analysis under many different states of polarized light; a time consuming and measurement intensive process. Here we address this limitation with a new rapid polarimetry system, and use this polarimetry platform to investigate a variety of tissue changes associated with breast cancer. We have recently developed a rapid polarimetry imaging platform based on four photoelastic modulators (PEMs). The PEMs generate fast polarization modulations that allow the complete sample Mueller matrix to be imaged over a large field of view, with no moving parts. This polarimetry system is then demonstrated to be sensitive to a variety of tissue changes that are relevant to breast cancer. Specifically, we show that changes in depolarization can reveal tumor margins, and can differentiate between viable and necrotic breast cancer metastasized to the lymph nodes. Furthermore, the polarimetric property of linear retardance (related to birefringence) is dependent on collagen organization in the extracellular matrix. These findings indicate that our polarimetry platform may have future applications in fields such as breast cancer diagnosis, improving the speed and efficacy of intraoperative pathology, and providing prognostic information that may be beneficial for guiding treatment.

Rapid Mueller matrix polarimetry imaging based on four photoelastic modulators with no moving parts (Conference Presentation)

Polarized light has many applications in biomedical imaging. The interaction of a biological sample with polarized light reveals information about its composition, both structural and functional. For example, the polarimetry-derived metric of linear retardance (birefringence) is dependent on tissue structural organization (anisotropy) and can be used to diagnose myocardial infarct; circular birefringence (optical rotation) can measure glucose concentrations. The most comprehensive type of polarimetry analysis is to measure the Mueller matrix, a polarization transfer function that completely describes how a sample interacts with polarized light. To derive this 4x4 matrix it is necessary to observe how a tissue interacts with different polarizations. A well-suited approach for tissue polarimetry is to use photoelastic modulators (PEMs), which dynamically modulate the polarization of light. Previously, we have demonstrated a rapid time-gated Stokes imaging system that is capable of characterizing the state of polarized light (the Stokes vector) over a large field, after interacting with any turbid media. This was accomplished by synchronizing CCD camera acquisition times relative to two PEMs using a field-programmable gate array (FPGA). Here, we extend this technology to four PEMs, yielding a polarimetry system that is capable of rapidly measuring the complete sample Mueller matrix over a large field of view, with no moving parts and no beam steering. We describe the calibration procedure and evaluate the accuracy of the measurements. Results are shown for tissue-mimicking phantoms, as well as initial biological samples.