Ruixin Jiang

Integrated diffuse optical tomography and photoacoustic tomography: phantom validations

We designed, fabricated and tested a novel imaging system that fuses diffuse optical tomography (DOT) and photoacoustic tomography (PAT) in a single platform. This platform takes advantages of both DOT and PAT, and can potentially provide dual-modality two dimensional functional and cellular images of the breast quantitatively. Here we describe this integrated platform along with initial tissue phantom validations.

Pre-seizure state identified by diffuse optical tomography

In epilepsy it has been challenging to detect early changes in brain activity that occurs prior to seizure onset and to map their origin and evolution for possible intervention. Here we demonstrate using a rat model of generalized epilepsy that diffuse optical tomography (DOT) provides a unique functional neuroimaging modality for noninvasively and continuously tracking such brain activities with high spatiotemporal resolution. We detected early hemodynamic responses with heterogeneous patterns, along with intracranial electroencephalogram gamma power changes, several minutes preceding the electroencephalographic seizure onset, supporting the presence of a “pre-seizure” state. We also observed the decoupling between local hemodynamic and neural activities. We found widespread hemodynamic changes evolving from local regions of the bilateral cortex and thalamus to the entire brain, indicating that the onset of generalized seizures may originate locally rather than diffusely. Together, these findings suggest DOT represents a powerful tool for mapping early seizure onset and propagation pathways.

Cortical neurovascular coupling driven by stimulation of channelrhodopsin-2.

While functional imaging is widely used in studies of the brain, how well the hemodynamic signal represents the underlying neural activity is still unclear. And there is a debate on whether hemodynamic signal is more tightly related to synaptic activity or action potentials. This study intends to address these questions by examining neurovascular coupling driven by pyramidal cells in the motor cortex of rats. Pyramidal cells in the motor cortex of rats were selectively transduced with the light sensitive cation channel channelrhodopsin-2 (ChR2). Electrophysiological recordings and optical intrinsic signal imaging were performed simultaneously and synchronously to capture the neural activity and hemodynamics induced by optical stimulation of ChR2-expressing pyramidal cells. Our results indicate that both synaptic activity (local field potential, LFP) and action potentials (multi-unit activity, MUA) are tightly related to hemodynamic signals. While LFPs in γ band are better in predicting hemodynamic signals elicited by short stimuli, MUA has better predictions to hemodynamic signals elicited by long stimuli. Our results also indicate that strong nonlinearity exists in neurovascular coupling.

Phase-contrast diffuse optical tomography for in vivo breast imaging: a two-step method

We present a two-step reconstruction method that can qualitatively and quantitatively improve the reconstruction of tissue refractive index (RI) distribution by phase-contrast diffuse optical tomography (PCDOT). In this two-step method, we first recover the distribution of tissue absorption and scattering coefficients by conventional diffuse optical tomography to obtain the geometrical information of lesions, allowing the incorporation of geometrical information as a priori in the PCDOT reconstruction using a locally refined mesh. The method is validated by a series of phantom experiments and evaluated using in vivo data from 42 human subjects. The results demonstrate clear contrast of RI between the lesion and the surroundings, making the image interpretation straightforward. The sensitivity and specificity from these 42 cases are both 81% when RI is used as an imaging parameter for distinguishing between malignant and benign lesions.

Imaging Blood Flow and Cellular Morphology in Epilepsy with Diffuse Optical Tomography

We present a method that is capable of imaging cerebral blood flow (CBF) and particle size/density in epilepsy using diffuse optical tomography. In vivo images during seizure onset are obtained using a multispectral DOT system.

Enhanced Phase-Contrast Diffuse Optical Tomography for in vivo Breast Imaging

We present a two-step reconstruction method that can qualitatively and quantitatively improve the reconstruction of tissue RI distribution by PCDOT. The method is validated by phantom experiments and data from 42 human subjects.

Multispectral phase-contrast diffuse optical tomography for breast cancer imaging

We present a multispectral phase-contrast diffuse optical tomography method that is able to simultaneously reconstruct tissue refractive index and functional parameters such as hemoglobin concentration and oxygen saturation. We validate the method using numerical simulations.

In vivo studies of 144 breast masses by phase contrast diffuse optical tomography

We report our continued study of phase-contrast diffuse optical tomography (PCCDOT) for evaluating its fidelity in distinguishing malignant breast lesions form benign ones. 144 breast masses were examined from 134 patients, aging from 22~82 with the mean age of 56. Tissue optical parameters including refractive index, and absorption and scattering coefficients, were obtained and compared with their corresponding biopsy/pathology reports. In consistent with our previous study, malignant masses tended to have a decreased refractive index relative to their surrounding normal tissue, which acts as the key character to differentiate them from benign masses. The results show that the specificity is improved significantly over the previous smaller scale study (85% vs. 70%) due to the addition of significantly more benign cases, while the sensitivity stays about the same (81% vs. 82%) due to the similar number of malignant cases used compared to the smaller scale study.