Determining the Anatomic Position and Histological Effects in Murine Tumors of Gloxy an Oxygen-Sensitive Paramagnetic Material

High Spatial Resolution Multi-Site EPR Oximetry

“…Then the "best fit value" for the width of the Lorentzian broadening function derived from the fit B 1/2; FIT is related to the "natural" (or undistorted) linewidth B 1/2 of an oxygen probe by a modified Eq. [7] B 1/2;FIT = r 1/2 (gradB) 1…”

“…[3] could be applied to derive the width of the EPR spectrum and no correction by Eq. [7] is necessary. However, in a typical in vivo EPR oximetry experiment, the projection function p(r ) cannot be determined separately (e.g., the shape of the LiPc crystal is irregular and its orientation after implantation is unknown or there is an uncertainty whether the crystal has broken apart during the implantation).…”

“…Because the signal-to-noise ratio limits the maximum gradient, the more general Eqs. [6] and [7] can be used instead. In the latter case a convolution integral is constructed from the experimental spectrum J 2 (r) rescaled according to spatial coordinate r = B/(gradB) 2 and a Lorentzian function f (r, r 1/2 ) which is generated digitally.…”

“…Equation [6] shows that when expressed in spatial coordinates, the EPR spectrum J 1 (r ) taken at a smaller gradient can be presented as a convolution of a spectrum J 2 (r ) taken with a larger gradient (gradB) 2 and a Lorentzian function f (r, r 1/2 ) with a linewidth r 1/2 that depends on the undistorted linewidth B 1/2 and the magnitudes of the two gradients as given by Eq. [7]. When the second gradient is much larger than the ratio of the EPR linewidth to the size of the solid probe that gives rise to the EPR signal, the projection function p(r ) is well approximated by J 2 (r ) and Eq.…”

“…Several oxygen probes including LiPc, coals, and some carbohydrate chars do satisfy all these requirements (2,4,6,7). LiPc is a particularly attractive probe for EPR oximetry because its CW EPR spectrum is very narrow (with a peak-to-peak ∼30-mG linewidth in the absence of oxygen), the spectrum is modeled well by a Lorentzian function, and the response to oxygen is a linear function of pO 2 (3).…”