Noninvasive imaging of the distribution in oxygen in tissue in vivo using near-infrared phosphors

Abstract

A newly developed water-soluble phosphor suitable for measuring oxygen pressure in the blood (Green 2W) was used for noninvasive, in vivo imaging of oxygen distribution in the vascular systems of mice. Oxygen quenches the phosphorescence of Green 2W, measured in the presence of 2% albumin, according to the Stern-volmer relationship. This oxygen-dependent quenching of phosphorescence has been used to obtain digital maps of the oxygen distribution in the tissue vasculature. EMT-6 mammary carcinoma tumors were grown by injecting 1 x 10(6) cells in 0.1-ml carrier into the subcutaneous space over the muscle on the hindquarter. When the tumors were approximately 8 mm in diameter, 300 micrograms of phosphorescence probe (Green 2W; absorption maximum 636 nm) was injected into the tail vein. The mice were immobilized with intraperotoneal Ketamine (133 mg/kg) and Xylazine (10 mg/kg) and illuminated with flashes (< 4-microseconds t1/2) of light of 630 +/- 12 nm. The emitted phosphorescence (790-nm maximum) was imaged an intensified CCD camera. Images were collected beginning at 30, 50, 80, 120, 180, 240, 420, and 2500 microseconds after the flash and used to calculate digital maps of the phosphorescence lifetimes and oxygen pressure. Both the illumination light and the phosphorescence were in the near-infrared region of the spectrum, where tissue has greatly decreased absorbance. The light therefore readily passed through the skin and centimeter thicknesses of tissue. The oxygen maps could be obtained by illuminating from the side of the mouse opposite the camera (and tumor). The tumors were readily observed as regions with oxygen pressures substantially below those of the surrounding tissue. Thus, phosphorescence measurements can noninvasively detect volumes of tissue with below-normal oxygen pressure in the presence of much larger volumes of tissue with normal oxygen pressures. In addition, tissue oxygen pressures can be monitored in real time, even through centimeter thicknesses of tissue.

Quantification of longitudinal tissue pO2 gradients in window chamber tumours: impact on tumour hypoxia

“…The rationale for using both wavelengths is that the penetration depth for blue light (approximately 50 µm) will be less than that for green light (>200 µm) because of differences in absorption by light absorbing chromophores, such as cytochromes haemoglobin and myoglobin. Details of these methods have been published previously (Wilson et al, 1992;Vinogradov et al, 1996;Cerniglia et al, 1997).…”

Tomographic imaging of oxygen by phosphorescence lifetime

“…11 Recently, an array of long-lived NIR metalloporphyrin-based probes has been developed. 12 The quenching constants (k q ) of these probes can be tuned by dendritic encapsulation and their properties made insensitive to biological macromolecules by modifying the dendrimer periphery.…”

Potential Usage of Liposome-Encapsulated Phosphor for in Vivo Imaging of Tissue Oxygenation

“…Understanding that oxygen is an essential metabolite and whose disturbance is underlying to various pathophysiological states, a functional tissue imaging methodology based on oxygen-dependent quenching of phosphorescence has been continuously developed and validated as an effective method to noninvasively measure the oxygen concentration in biological systems [1][2]. It can provide rapid and accurate measurements of tissue oxygen levels or two dimensional imaging of oxygen map through thickness of tissue [3][4]. The recent development of this method has been advanced to non-invasively assess the in vivo oxygen distribution in tissue by using a multifrequency system to perform the time-resolved phosphorescence analysis [5].…”

“…Vinogradov and Wilson [19][20] have reported synthesis of a group of oxygen sensitive phosphors (tetrabenzoporphyrins) with absorption maxima near 636 nm and phosphorescence maxima near 800 nm. The experiments in which a water soluble derivative of Pd-tetrabenzoporphyrin was used to determine the oxygen distribution in the vascularure of tumor bearing mice [4,11] and in the surface and deep areas of the kidney of rats [18] have established that, by using near infra-red phosphors, it is possible to image tissue oxygen distribution through centimeter thicknesses of tissue (such as through the abdomen of an adult mouse). Thus, phosphorescence quenching can now be used both to detect the presence of small regions of hypoxia (such as subcutaneous EMT-6 tumors) present in much larger volumes of normal…”