Oxygen-dependent quenching of phosphorescence can provide a quantitative measurement with high temporal resolution of tissue oxygenation in vivo. It is a real-time optical means for prognosis of diseases where the oxygen concentration is essential. Phosphorescence quenching is a non-invasive methodology, otherwise no more than minimally invasive as the phosphor is necessarily introduced into vasculature prior to the measurement. Oxyphor R2, a dendritic phosphor with two-layer of glutamates, is a suitable phosphor for oxygen measurements owing to its high water solubility. We used a frequency-domain, phase modulation based instrument to calibrate Oxyphor R2. The acquired quenching constant (k<sub>Q</sub>) and lifetime at zero oxygen (τ°) were consistent with those calibrated from conventional time-domain instrument. Administered with Oxyphor R2, the rat hepatic oxygen distributions were imaged throughout the course of ischemia and reperfusion. After 5 min ischemia and subsequent 20 min reperfusion, distinct ischemic areas on the hepatic tissue were observed. In order to extend the application of in vivo oxygen imaging using phosphorescence quenching by minimizing the possible immunoresponse induced by phosphor, we are the first to co-synthesize the dipalmitoylphosphatidylglycerol (DPPG)-rich liposome with Oxyphor R2 to generate the liposome-encapsulated Oxyphor R2. Its calibration using the frequency domain measurement displayed higher quenching constant and shorter lifetime at zero oxygen (k<sub>Q</sub> = 1186 mmHg<sup>-1</sup> sec<sup>-1</sup>; τ° = 150 μsec) comparing to original Oxyphor R2 (k<sub>Q</sub> = 438 mmHg <sup>-1</sup> sec<sup>-1</sup>; τ° = 630 μsec). It implicated that the liposome-encapsulated Oxyphor R2 designed to neutralize the immunoresponse could be further applied to measure the tissue oxygenation in vivo, especially those with low oxygen concentration such as tumor.
Date:
2004-08
Relation:
Biomedical Engineering - Applications, Basis and Communications. 2004 Aug;16(4):224-232.
