Zhongjiang Chen

In vivo detection of hemoglobin oxygen saturation and carboxyhemoglobin saturation with multiwavelength photoacoustic microscopy.

A method for noninvasively detecting hemoglobin oxygen saturation (SO2) and carboxyhemoglobin saturation (SCO) in subcutaneous microvasculature with multiwavelength photoacoustic microscopy is presented. Blood samples mixed with different concentrations of carboxyhemoglobin were used to test the feasibility and accuracy of photoacoustic microscopy compared with the blood-gas analyzer. Moreover, fixed-point detection of SO2 and SCO in mouse ear was obtained, and the changes from normoxia to carbon monoxide hypoxia were dynamically monitored in vivo. Experimental results demonstrate that multiwavelength photoacoustic microscopy can detect SO2 and SCO, which has future potential clinical applications.

All-optically integrated photo-acoustic microscopy and optical coherence tomography based on a single Michelson detector

An all-optically noncontact dual-mode imaging system using a single Michelson detector that simultaneously achieved photo-acoustic microscopy (PAM) and optical coherence tomography (OCT) is presented. The pulse laser-induced photo-acoustic signals and the back-scattered photons were alternately detected by a single Michelson detector. The spatial resolution and imaging capability of the dual-mode imaging system were testified by scattering phantoms. Furthermore, in vivo images of the mouse ear demonstrated that the PAM-OCT can provide complementary anatomical and functional information for imaging of biological tissues, which could be the best co-imaging strategy of PAM and OCT in biomedicine.

Noncontact broadband all-optical photoacoustic microscopy based on a low-coherence interferometer

We developed and fabricated a noncontact broadband all-optical photoacoustic microscopy (BD-AO-PAM) with a microchip laser and an all-fiber low coherence interferometer. Currently, the available detection bandwidth of the BD-AO-PAM is 67 MHz, and the lateral resolution measured by carbon fibers reaches 11 μm. Furthermore, the imaging capability of the BD-AO-PAM was testified by imaging hairs embedded in scattering gel and in vivo blood vessels of a mouse ear. The experimental results demonstrate that the BD-AO-PAM can image the tissues with high spatial resolution in vivo, which can be used as portable noncontact PAM for biomedical applications.

Optically integrated trimodality imaging system: combined all-optical photoacoustic microscopy, optical coherence tomography, and fluorescence imaging.

We have developed a trimodality imaging system by optically integrating all-optical photoacoustic microscopy (AOPAM), optical coherence tomography (OCT), and fluorescence microscopy (FLM) to provide complementary information including optical absorption, optical back-scattering, and fluorescence contrast of biological tissue. By sharing the same low-coherence Michelson interferometer, AOPAM and OCT could be organically optically combined. Also, owing to using the same laser source and objective lens, intrinsically registered photoacoustic and fluorescence signals are obtained in a single pulse. Simultaneously photoacoustic angiography, tissue structure, and fluorescence molecular in vivo images of mouse ear were acquired to demonstrate the capabilities of the optically integrated trimodality imaging system, which can present more information to study tumor angiogenesis, vasculature, anatomical structure, and microenvironments in vivo.

Simultaneous imaging of atherosclerotic plaque composition and structure with dual-mode photoacoustic and optical coherence tomography

The composition of plaque is a major determinant of coronary-related clinical syndromes. By combining photoacoustic tomography (PAT) and optical coherence tomography (OCT), the optical absorption and scattering properties of vascular plaque can be revealed and subsequently used to distinguish the plaque composition and structure. The feasibility and capacity of the dual-mode PAT-OCT technique for resolving vascular plaque was first testified by plaque composition mimicking experiment. PAT obtained lipid information due to optical absorption differences, while owing to scattering differences, OCT achieved imaging of collagen. Furthermore, by combining PAT and OCT, the morphological characteristic and scattering difference of normal and lipid-rich plaque in the ex vivo rabbit aorta was distinguished simultaneously. The experiments demonstrated that the combined PAT and OCT technique is a potential feasible method for detecting the composition and structure of lipid core and fibrous cap in atherosclerosis.

Microwave fields driven domain wall motions in antiferromagnetic nanowires

In this work, we study the microwave field driven antiferromagnetic domain wall motion in an antiferromagnetic nanowire, using the numerical calculations based on a classical Heisenberg spin model. We show that a proper combination of a static magnetic field plus an oscillating field perpendicular to the nanowire axis is sufficient to drive the domain wall propagation along the nanowire with the axial magnetic anisotropy. More importantly, the drift velocity at the resonance frequency is comparable to that induced by temperature gradients, suggesting that microwave field can be a very promising tool to control domain wall motions in antiferromagnetic nanostructures. Furthermore, the dependences of resonance frequency and drift velocity on the static and oscillating fields, the axial anisotropy, and the damping constant are discussed in details. This work provides useful information for the spin dynamics in antiferromagnetic nanostructures for spintronics applications.

Optical biopsy approach to basal cell carcinoma and melanoma based on all-optically integrated photoacoustic and optical coherence tomography

Basal cell carcinoma (BCC) and melanoma (MM), with the highest morbidity and mortality, respectively, are considered as two skin cancers of concern in dermatology. Histological studies have demonstrated that vascular patterns and collagenous stroma serve as key parameters for BCC and MM classification. In this Letter, we sought to identify BCC and MM based on the dual parameters of vascular patterns and scattering structures provided by all-optically integrated photoacoustic and optical coherence tomography (AOPA/OCT). The imaging capability of the AOPA/OCT was verified by the mimic phantoms. Furthermore, in vivo characterization of vasculatures and tissue structures from BCC and MM mice were successfully achieved with high resolution. Results prove the feasibility of AOPA/OCT as a novel method to dedicate to the in vivo biopsy of skin cancers which shows new insights into the study of skin diseases in early stages.

Biomechanical and morphological multi-parameter photoacoustic endoscope for identification of early esophageal disease

The combination of phase-sensitive photoacoustic (PA) imaging of tissue viscoelasticity with the esophagus-adaptive PA endoscope (PAE) technique allows the characterization of the biomechanical and morphological changes in the early stage of esophageal disease with high accuracy. In this system, the tissue biomechanics and morphology are obtained by detecting the PA phase and PA amplitude information, respectively. The PAE has a transverse resolution of approximately 37 μm and an outer diameter of 1.2 mm, which is suitable for detecting rabbit esophagus. Here, an in-situ biomechanical and morphological study of normal and diseased rabbit esophagus (tumors of esophagus and reflux esophagitis) was performed. The in-situ findings were highly consistent with those observed by histology. In summary, we demonstrated the potential application of PAE for early clinical detection of esophageal diseases.

Staggered field driven domain walls motion in antiferromagnetic heterojunctions

In this work, we study the antiferromagnetic (AFM) spin dynamics in heterostructures which consist of two kinds of AFM layers. Our micromagnetic simulations demonstrate that the AFM domain-wall (DW) can be driven by the other one (driven by field-like Neel spin-orbit torque, Phys. Rev. Lett. 117, 017202 (2016)) through the interface couplings. Furthermore, the two DWs detach from each other when the torque increases above a critical value. The critical field and the highest possible velocity of the DW depending on several factors are revealed and discussed. Bases on the calculated results, we propose a method to modulate efficiently the multi DWs in antiferromagnet, which definitely provides useful information for future AFM spintronics device design.

All-optically integrated multimodality imaging system: combined photoacoustic microscopy, optical coherence tomography, and fluorescence imaging

We have developed a multimodality imaging system by optically integrating all-optical photoacoustic microscopy (AOPAM), optical coherence tomography (OCT) and fluorescence microscopy (FLM) to provide complementary information including optical absorption, optical back-scattering and fluorescence contrast of biological tissue. By sharing the same low-coherence Michelson interferometer, AOPAM and OCT could be organically optically combined to obtain the absorption and scattering information of the biological tissues. Also, owing to using the same laser source and objective lens, intrinsically registered photoacoustic and fluorescence signals are obtained to present the radiative and nonradiative transition process of absorption. Simultaneously photoacoustic angiography, tissue structure and fluorescence molecular in vivo images of mouse ear were acquired to demonstrate the capabilities of the optically integrated trimodality imaging system, which can present more information to study tumor angiogenesis, vasculature, anatomical structure and microenvironments in vivo.