Browsing by Author "Duong, Timothy Q."

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Investigation of the cerebral hemodynamic response function in single blood vessels by functional photoacoustic microscopy
(2012-06-01)
Liao, Lun-De
;
Lin, Chin-Teng
;
Shih, Yen-Yu I.
;
Lai, Hsin-Yi
;
Zhao, Wan-Ting
The specificity of the hemodynamic response function (HRF) is determined spatially by the vascular architecture and temporally by the evolution of hemodynamic changes. Here, we used functional photoacoustic microscopy (fPAM) to investigate single cerebral blood vessels of rats after left forepaw stimulation. In this system, we analyzed the spatiotemporal evolution of the HRFs of the total hemoglobin concentration (HbT), cerebral blood volume (CBV), and hemoglobin oxygen saturation (SO2). Changes in specific cerebral vessels corresponding to various electrical stimulation intensities and durations were bilaterally imaged with 36 x 65-mu m(2) spatial resolution. Stimulation intensities of 1, 2, 6, and 10 mA were applied for periods of 5 or 15 s. Our results show that the relative functional changes in HbT, CBV, and SO2 are highly dependent not only on the intensity of the stimulation, but also on its duration. Additionally, the duration of the stimulation has a strong influence on the spatiotemporal characteristics of the HRF as shorter stimuli elicit responses only in the local vasculature (smaller arterioles), whereas longer stimuli lead to greater vascular supply and drainage. This study suggests that the current fPAM system is reliable for studying relative cerebral hemodynamic changes, as well as for offering new insights into the dynamics of functional cerebral hemodynamic changes in small animals. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [ DOI: 10.1117/1.JBO.17.6.061210]
Transcranial imaging of functional cerebral hemodynamic changes in single blood vessels using in vivo photoacoustic microscopy
(2012-06-01)
Liao, Lun-De
;
Lin, Chin-Teng
;
Shih, Yen-Yu I.
;
Duong, Timothy Q.
;
Lai, Hsin-Yi
Optical imaging of changes in total hemoglobin concentration (HbT), cerebral blood volume (CBV), and hemoglobin oxygen saturation (SO2) provides a means to investigate brain hemodynamic regulation. However, high-resolution transcranial imaging remains challenging. In this study, we applied a novel functional photoacoustic microscopy technique to probe the responses of single cortical vessels to left forepaw electrical stimulation in mice with intact skulls. Functional changes in HbT, CBV, and SO2 in the superior sagittal sinus and different-sized arterioles from the anterior cerebral artery system were bilaterally imaged with unambiguous 36x65-mu m(2) spatial resolution. In addition, an early decrease of SO2 in single blood vessels during activation (i.e., 'the initial dip') was observed. Our results indicate that the initial dip occurred specifically in small arterioles of activated regions but not in large veins. This technique complements other existing imaging approaches for the investigation of the hemodynamic responses in single cerebral blood vessels. Journal of Cerebral Blood Flow & Metabolism (2012) 32, 938-951; doi:10.1038/jcbfm.2012.42; published online 4 April 2012