1. A device for visualizing a structure located on the interior of a visually opaque substance relative to a region of interest in a body, the device comprising: a marker member, the marker member composed of a biologically stable material, the marker member configured to permit non-obstructive visualization, via positron emission tomography and single photon emission computed tomography, of at least one structure located relative to the region of interest, the marker member having an interior defining a lumen, a proximal end, and a distal end, the lumen being closed at the distal end, and the distal end of the marker member being removably insert able in the visually opaque substance in proximate relationship to a cavity of potential space defined therein; an external access member contiguously connected to the proximal end of the marker member, at least a portion of the external access member extending from the marker member to a location external to the visually opaque substance when the marker member is in removable insertable position in the visually opaque substance, the external access member including a gas metering device; an imaging material contained within the lumen via the closed distal end, such that the imaging material does not directly contact the visually opaque substance, wherein the imaging material produces a signal detectable external to the visually opaque substance, the imaging material containing at least one radiopharmaceutical material, the imaging material producing an image detectable by positron emission tomography and single photon emission computed tomography, the gas metering device configured to movably position the imaging material at a discrete location relative to a longitudinal plane of the marker member; and a pressure equalization member operatively connected to the lumen near or adjacent to the distal end.