Conventional FMT (fluorescence molecular tomography) reconstruction using only emission data is not practical, because it is nearly impossible to accurately measure the source strength and the instrumentation response functions that impact the detected intensity of signals. The small errors accumulated by the system during this process produce a declining reconstruction quality. The use of nonlinear normalized Born ratio (nBorn) method greatly improves the image reconstruction. However, as the nonlinear nBorn method normalizes the acquired fluorescence signals with the excitation data nonlinearly, the relative distributions of the normalized measurement are different from those of the emission data. When compared with the reconstruction using only emission data, what the nonlinear nBorn method does is equivalent to introducing excitation noise to the emission data. The introduction of measurement noise also makes it difficult to quantify the signal-to-noise ratio of the resulting normalized measurements and to find the true fluorescence distribution. Finally, it can result in worse localization and quantitative performance of FMT.

To overcome this, Qingming Luo’s group from Britton Chance Center for Biomedical Photonics, Wuhan National Laboratory for Optoelectronics presented a linear nBorn method. Under this method, the emission data for each projection is normalized with the average excitation data of all detectors. It offers advantages of eliminating the experimental factors, the unknown source strength, and the coupling losses, which can also be achieved by using the nonlinear nBorn method. Moreover, the relative distributions of the normalized measurements are consistent with those of the emission data and the acquired excitation data are averaged which is effective in suppressing excitation noise. The phantom and in vivo results indicated that the linear nBorn method can effectively localize and quantify the fluorescent targets and has better localization and quantitative performance than the nonlinear nBorn method.

The research article “Enhancement of the localization and quantitative performance of fluorescence molecular tomography by using linear nBorn method” was published online in Optics Express on 6 Feb 2017 (Vol. 25, Issue 3, pp. 2063-2079). This work is supported by the Key Research and Development Program (2016YFA0201403), Science Fund for Creative Research Group (61421064), National Natural Science Fund (91442201), and Fundamental Research Funds for the Central Universities (2016YXMS035).

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Fig. 1. The localization and quantitative results of in vivo experiments. (a) The relative positions of the fluorescent targets T1, T2,and T3 in the lower abdominal cavity of the mouse. (b) The 3D reconstruction result of the fluorescent targets with the nonlinear nBorn method. (c) The 3D reconstruction result of the fluorescent targets with the linear nBorn method. [Coordinate system was defined by D (dorsal), V (ventral), Cr (cranial), Cd (caudal), L (left), and R (right). 3D renderings in (b)–(c) were implemented using AMIRA software.]