Browsing by Author "Park, Han Sang"

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    Automated Detection of P. falciparum Using Machine Learning Algorithms with Quantitative Phase Images of Unstained Cells.
    (PloS one, 2016-01) Park, Han Sang; Rinehart, Matthew T; Walzer, Katelyn A; Chi, Jen-Tsan Ashley; Wax, Adam
    Malaria detection through microscopic examination of stained blood smears is a diagnostic challenge that heavily relies on the expertise of trained microscopists. This paper presents an automated analysis method for detection and staging of red blood cells infected by the malaria parasite Plasmodium falciparum at trophozoite or schizont stage. Unlike previous efforts in this area, this study uses quantitative phase images of unstained cells. Erythrocytes are automatically segmented using thresholds of optical phase and refocused to enable quantitative comparison of phase images. Refocused images are analyzed to extract 23 morphological descriptors based on the phase information. While all individual descriptors are highly statistically different between infected and uninfected cells, each descriptor does not enable separation of populations at a level satisfactory for clinical utility. To improve the diagnostic capacity, we applied various machine learning techniques, including linear discriminant classification (LDC), logistic regression (LR), and k-nearest neighbor classification (NNC), to formulate algorithms that combine all of the calculated physical parameters to distinguish cells more effectively. Results show that LDC provides the highest accuracy of up to 99.7% in detecting schizont stage infected cells compared to uninfected RBCs. NNC showed slightly better accuracy (99.5%) than either LDC (99.0%) or LR (99.1%) for discriminating late trophozoites from uninfected RBCs. However, for early trophozoites, LDC produced the best accuracy of 98%. Discrimination of infection stage was less accurate, producing high specificity (99.8%) but only 45.0%-66.8% sensitivity with early trophozoites most often mistaken for late trophozoite or schizont stage and late trophozoite and schizont stage most often confused for each other. Overall, this methodology points to a significant clinical potential of using quantitative phase imaging to detect and stage malaria infection without staining or expert analysis.
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    ItemOpen Access
    Development of Quantitative Phase Imaging as a Diagnostic Modality with High-Throughput Implementation
    (2020) Park, Han Sang

    Without exogenous contrast agents, imaging semitransparent samples such as biological cells can be difficult with light microscopy that measures modulation in the intensity of transmitted light. Quantitative phase microscopy (QPM) that measures the phase delays imparted by the objects is often used to examine the spatial and temporal dynamics of individual cells without chemical modification.

    In order to demonstrate its effectiveness as a diagnostic tool, quantitative phase microscope is used to image red blood cells (RBCs) specifically those infected with malaria parasites, Plasmodium falciparum. RBCs are a favorite target for QPM studies, in particular because they have little internal structure and thus can be represented by a homogenous refractive index. The ability to profile RBCs is an important capability of QPM since these cells are affected by different disease stages, and thus they are essential in human health diagnostics. Classifiers built using QPM are able to distinguish and classify uninfected red blood cells from those infected with P. falciparum using morphological features of the cells with high accuracy. The study shows that QPM can be a very useful diagnostic modality and that it can be more clinically relevant by developing into a high throughput holographic imaging system.

    In addition to the morphological measurement of erythrocytes, biophysical properties of RBCs under mechanical stress are measured by incorporating microfluidic chips into the QPM platform. Highly precise microfluidic chips are manufactured with specific dimensions that will stress the RBCs at designated positions as they flow through them. Using a high refractive index medium, QPM is used to measure the optical volume changes associated with efflux of water through the membrane of the cells under mechanical stress. The OV changes in response to mechanical force are compared for different storage periods to evaluate the changes in response to deformation throughout the ageing cells.

    Finally, a novel approach for high throughput screening is developed based on holographic imaging of the cells flowing through microfluidic chips. To enable high throughput imaging, we have implemented a new quantitative phase imaging modality, holographic cytometry. Holographic cytometry maintains the high sensitivity of QPM while imaging a large number of cells flowing through the microfluidic devices. As demonstrated in previous studies, morphological parameters are extracted from these images to assess their changes over the storage time and classify them according to the time in the blood units.

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    Quantitative phase imaging of erythrocytes under microfluidic constriction in a high refractive index medium reveals water content changes.
    (Microsystems & nanoengineering, 2019-01) Park, Han Sang; Eldridge, Will J; Yang, Wen-Hsuan; Crose, Michael; Ceballos, Silvia; Roback, John D; Chi, Jen-Tsan Ashley; Wax, Adam
    Changes in the deformability of red blood cells can reveal a range of pathologies. For example, cells which have been stored for transfusion are known to exhibit progressively impaired deformability. Thus, this aspect of red blood cells has been characterized previously using a range of techniques. In this paper, we show a novel approach for examining the biophysical response of the cells with quantitative phase imaging. Specifically, optical volume changes are observed as the cells transit restrictive channels of a microfluidic chip in a high refractive index medium. The optical volume changes indicate an increase of cell's internal density, ostensibly due to water displacement. Here, we characterize these changes over time for red blood cells from two subjects. By storage day 29, a significant decrease in the magnitude of optical volume change in response to mechanical stress was witnessed. The exchange of water with the environment due to mechanical stress is seen to modulate with storage time, suggesting a potential means for studying cell storage.