pO<sub>2</sub>-weighted imaging in vivo by delayed fluorescence of intracellular Protoporphyrin IX
Marek Scholz, Xu Cao, Jason R. Gunn, Petr Brůža, Brian W. Pogue
Abstract
In this Letter, we report on the imaging of tissue oxygen by means of time-gated wide-field lifetime imaging of the microsecond-scale delayed fluorescence from Protoporphyrin IX (PpIX). PpIX is produced endogenously from a clinically used <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>δ</mml:mi> </mml:math> -aminolevulinic acid (5-ALA) by most cells. The lifetime of delayed fluorescence is lengthened by the absence of oxygen to quench its triplet state. Here, the images of the delayed emission from the human skin and the skin of nude mice were captured after topical application of 5-ALA, using a pulsed 635 nm excitation. Macroscopic lifetime-based images were found to be associated with the tissue oxygenation and obtained with a low light dose ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>10</mml:mn> </mml:mrow> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">m</mml:mi> <mml:mi mathvariant="normal">J</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> ) and “capture-times” of a few seconds.