Xianjin Dai

Wearable 3-D Photoacoustic Tomography for Functional Brain Imaging in Behaving Rats

Understanding the relationship between brain function and behavior remains a major challenge in neuroscience. Photoacoustic tomography (PAT) is an emerging technique that allows for noninvasive in vivo brain imaging at micrometer-millisecond spatiotemporal resolution. In this article, a novel, miniaturized 3D wearable PAT (3D-wPAT) technique is described for brain imaging in behaving rats. 3D-wPAT has three layers of fully functional acoustic transducer arrays. Phantom imaging experiments revealed that the in-plane X-Y spatial resolutions were ~200 μm for each acoustic detection layer. The functional imaging capacity of 3D-wPAT was demonstrated by mapping the cerebral oxygen saturation via multi-wavelength irradiation in behaving hyperoxic rats. In addition, we demonstrated that 3D-wPAT could be used for monitoring sensory stimulus-evoked responses in behaving rats by measuring hemodynamic responses in the primary visual cortex during visual stimulation. Together, these results show the potential of 3D-wPAT for brain study in behaving rodents.

Fast noninvasive functional diffuse optical tomography for brain imaging

Advances in epilepsy studies have shown that specific changes in hemodynamics precede and accompany seizure onset and propagation. However, it has been challenging to noninvasively detect these changes in real time and in humans, due to the lack of fast functional neuroimaging tools. In this study, we present a functional diffuse optical tomography (DOT) method with the guidance of an anatomical human head atlas for 3-dimensionally mapping the brain in real time. Central to our DOT system is a human head interface coupled with a technique that can incorporate topological information of the brain surface into the DOT image reconstruction. The performance of the DOT system was tested by imaging motor tasks-involved brain activities on N = 6 subjects (3 epilepsy patients and 3 healthy controls). We observed diffuse areas of activations from the reconstructed [HbT] images of patients, relative to more focal activations for healthy subjects. Moreover, significant pretask hemodynamic activations were also seen in the motor cortex of patients, which indicated abnormal activities persistent in the brain of an epilepsy patient. This work demonstrates that fast functional DOT is a valuable tool for noninvasive 3-dimensional mapping of brain hemodynamics.

Low-cost high-power light emitting diodes for photoacoustic imaging

We present a photoacoustic imaging system based on a low-cost high-power miniature light emitting diode (LED), which has the capability of in vivo mapping vasculature networks in biological tissue. Phantoms were used to demonstrate the feasibility of the system, while in vivo imaging the vasculature of mouse ear shows that LED-based photoacoustic imaging (LED-PAI) could have great potential for label-free biomedical imaging applications, overcoming the practical limitations of the use of bulky and expensive pulsed lasers.

Miniature multimodal endoscopic probe based on double-clad fiber

Optical coherence tomography (OCT) can obtain light scattering properties with a high resolution, while photoacoustic imaging (PAI) is ideal for mapping optical absorbers in biological tissues, and ultrasound (US) could penetrate deeply into tissues and provide elastically structural information. It is attractive and challenging to integrate these three imaging modalities into a miniature probe, through which, both optical absorption and scattering information of tissues as well as deep-tissue structure can be obtained. Here, we present a novel side-view probe integrating PAI, OCT and US imaging based on double-clad fiber which is used as a common optical path for PAI (light delivery) and OCT (light delivery/detection), and a 40 MHz unfocused ultrasound transducer for PAI (photoacoustic detection) and US (ultrasound transmission/receiving) with an overall diameter of 1.0 mm. Experiments were conducted to demonstrate the capabilities of the integrated multimodal imaging probe, which is suitable for endoscopic imaging and intravascular imaging.

A fast atlas-guided high density diffuse optical tomography system for brain imaging

Near infrared spectroscopy (NIRS) is an emerging functional brain imaging tool capable of assessing cerebral concentrations of oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (HbR) during brain activation noninvasively. As an extension of NIRS, diffuse optical tomography (DOT) not only shares the merits of providing continuous readings of cerebral oxygenation, but also has the ability to provide spatial resolution in the millimeter scale. Based on the scattering and absorption properties of nonionizing near-infrared light in biological tissue, DOT has been successfully applied in the imaging of breast tumors, osteoarthritis and cortex activations. Here, we present a state-of-art fast high density DOT system suitable for brain imaging. It can achieve up to a 21 Hz sampling rate for a full set of two-wavelength data for 3-D DOT brain image reconstruction. The system was validated using tissue-mimicking brain-model phantom. Then, experiments on healthy subjects were conducted to demonstrate the capability of the system.

Targeted Molecular Imaging of Pancreatic Cancer with a Miniature Endoscope

It is highly desirable to develop novel approaches to improve patient survival rate of pancreatic cancer through early detection. Here, we present such an approach based on photoacoustic and fluorescence molecular imaging of pancreatic tumor using a miniature multimodal endoscope in combination with targeted multifunctional iron oxide nanoparticles (IONPs). A novel fan-shaped scanning mechanism was developed to minimize the invasiveness for endoscopic imaging of pancreatic tumors. The results show that the enhancements in photoacoustic and fluorescence signals using amino-terminal fragment (ATF) targeted IONPs were ~four to six times higher compared to that using non-targeted IONPs. Our study indicates the potential of the combination of the multimodal photoacoustic-fluorescence endoscopy and targeted multifunctional nanoparticles as an efficient tool to provide improved specificity and sensitivity for pancreatic cancer detection.

3-D Photoacoustic Tomography Brain Imaging in Behaving Animal

A miniaturized 3D wearable PAT (3D-wPAT) technique is described for brain study in behaving animals. This 3D-wPAT technique has a considerable potential in neuroscience studies, such as behavior, cognition, and preclinical brain disease researches.