Tumor blood vessels have been known as being heterogeneous because of their chaotic and abundant distribution. Thus, imaging techniques which reveal hemodynamic information of tumor vasculature play significant roles in tumor studies. Photoacoustic (PA) imaging could acquire hemodynamic information based on the intrinsic characteristics of hemoglobin, while ultrasound (US) imaging provides information of structure and blood flow. Therefore, an integrated system was developed for both US microvascular imaging and PA imaging of the tumor region. To further improve the imaging performance, a liquid filled dual-modality microdroplets was designed for both ultrasound flow and PA imaging. The microdroplets were manufactured using the microfluidics technique to produce consistent microbubble with diameters between 23 µm to 25 µm, determining the vascular size for imaging. Additionally, the microdroplets were filled with saline diluted organic nanoparticles as contrast agents for PA imaging, while commercial microbubbles are filled with inert gas. Both in vitro and in vivo studies have been conducted for evaluating the designed contrast agent and system. Results of in vitro experiments, which performed with microtubes submerged in a scattering medium, demonstrated different flow speeds and directions of the designed phantom. Subcutaneous tumor was next tested during in vivo studies. Based on the organic nanoparticle-doped droplet, we were able to obtain the information of total hemoglobin concentration, oxygen saturation and blood flow speed of the tumor angiogenesis region with a higher sensitivity. In the future, our microdroplets could be applied to more applications, such as slow drug release based on its specific structure.
Angiogenesis is a key factor for the growth and expansion of malignant tumors. Recently, non-invasive imaging techniques have been largely employed to observe the functional neovascular status of tumor progression. In this study, we present an integrated hybrid-resolution photoacoustic microscopy (PAM) capable of both optical-resolution (OR: a tightly focused beam for finer lateral resolution at shallower region) and acoustic-resolution (AR: a deeper imaging depth based on its ultrasound-dominated detection with relatively large illumination area) imaging for monitoring the progression of angiogenesis. The hybrid-resolution design is achieved by using a liquid lens to adjust the beam size for OR/AR mode selection. A multimode fiber with small core diameter is used to maintain the fine lateral resolution and deliver the laser light with higher energy for OR and AR illumination, respectively. The imaging resolutions of the proposed PAM are demonstrated by phantom experiments: the lateral resolution of OR mode is ~20 μm at a depth of 1 mm, while the resolution of AR mode is ~80 μm at depths of 2 to 3 mm. Additionally, in vivo experiments are conducted to show the capability of this PAM. Angiogenesis imaging of a subcutaneous tumor model in mice is presented using its intrinsic optical contrast (i.e., hemoglobin). Besides, information of oxygen saturation is also acquired using two wavelengths to indicate the hypoxic region of the tumor. In summary, the developed hybrid-resolution PAM is able to monitor the angiogenesis and provide hemodynamic information of tumor covering a broader depth range with high resolutions.
Cathodal-transcranial direct current stimulation induces therapeutic effects in animal ischemia models by preventing the expansion of ischemic injury during the hyperacute phase of ischemia. However, its efficacy is limited by an accompanying decrease in cerebral blood flow. On the other hand, peripheral sensory stimulation can increase blood flow to specific brain areas resulting in rescue of neurovascular functions from ischemic damage. Therefore, the two modalities appear to complement each other to form an integrated treatment modality. Our results showed that hemodynamics was improved in a photothrombotic ischemia model, as cerebral blood volume and hemoglobin oxygen saturation (SO2) recovered to 71% and 76% of the baseline values, respectively. Furthermore, neural activities, including somatosensory-evoked potentials (110% increase), the alpha-to-delta ratio (27% increase), and the (delta+theta)/(alpha+beta) ratio (27% decrease), were also restored. Infarct volume was reduced by 50% with a 2-fold preservation in the number of neurons and a 6-fold reduction in the number of active microglia in the infarct region compared with the untreated group. Grip strength was also better preserved (28% higher) compared with the untreated group. Overall, this nonpharmacological, nonintrusive approach could be prospectively developed into a clinical treatment modality.
Restoring perfusion to the penumbra during the hyperacute phase of ischemic stroke is a key goal of neuroprotection. Thrombolysis is currently the only approved treatment for ischemic stroke. However, its use is limited by the narrow therapeutic window and side effect of bleeding. Therefore, other interventions are desired that could potentially increase the perfusion of the penumbra. Here, we hypothesized that bilateral peripheral electrical stimulation will improve cerebral perfusion and restore cortical neurovascular response. We assess the outcomes of bilateral forepaw electrical stimulation at intensities of 2 and 4 mA, administered either unilaterally or bilaterally. We developed a combined electrocorticogram (ECoG)-functional photoacoustic microscopy (fPAM) system to evaluate the relative changes in cerebral hemodynamic function and electrophysiologic response to acute, focal stroke. The fPAM system is used for cerebral blood volume (CBV) and hemoglobin oxygen saturation (SO2) and the ECoG for neural activity, namely somatosensory-evoked potential (SSEP), interhemispheric coherence, and alpha-delta ratio (ADR) in response to forepaw stimulation. Our results confirmed the neuroprotective effect of bilateral forepaw stimulation at 2 mA as indicated by the 82% recovery of ADR and 95% improvement in perfusion into the region of penumbra. This experimental model can be used to study other potential interventions such as therapeutic hypertension and hypercarbia.
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