How the Optix System Works
Most in vivo optical molecular imaging systems measure all of the photons that propagate through tissue without any temporal discrimination. This method is limited to providing the attenuation, or the total loss of photons, in tissue.
In TD optical molecular imaging, short pulses of light are sent to illuminate the specimen under study. Individual photons are then detected, along with their arrival time. This constitutes a TD dataset. The figure below depicts this process in more detail. From the specimen’s surface, excitation light travels through the tissue and then reaches and excites the fluorophore. A secondary light pulse at the fluorophore’s emission wavelength is created and travels back to the surface of the tissue, where it is detected along with its time of arrival.
The TPSF
The histogram of the time delay between the laser pulse onset and the detection of each photon constitutes a temporal point-spread function, or TPSF. A typical TPSF, with a normalized peak, is shown below. The TPSF contains information relative to the depth, intensity, and lifetime of the embedded fluorophore. A tomographic algorithm may also be used to combine information from several TPSFs in order to produce a 3D map of the fluorophore’s concentration.
