Objective assessment of image quality (OAIQ) in fluorescence-enhanced optical imaging

摘要

The statistical evaluation of molecular imaging approaches for detecting, diagnosing,and monitoring molecular response to treatment are required prior to their adoption. Theassessment of fluorescence-enhanced optical imaging is particularly challenging sinceneither instrument nor agent has been established. Small animal imaging does notaddress the depth of penetration issues adequately and the risk of administeringmolecular optical imaging agents into patients remains unknown. Herein, we focusupon the development of a framework for OAIQ which includes a lumpy-object modelto simulate natural anatomical tissue structure as well as the non-specific distribution offluorescent contrast agents. This work is required for adoption of fluorescence-enhancedoptical imaging in the clinic.Herein, the imaging system is simulated by the diffusion approximation of thetime-dependent radiative transfer equation, which describes near infra-red lightpropagation through clinically relevant volumes. We predict the time-dependent lightpropagation within a 200 cc breast interrogated with 25 points of excitation illuminationand 128 points of fluorescent light collection. We simulate the fluorescence generationfrom Cardio-Green at tissue target concentrations of 1, 0.5, and 0.25 ?M with backgrounds containing 0.01 ?M. The fluorescence boundary measurements for 1 ccspherical targets simulated within lumpy backgrounds of (i) endogenous opticalproperties (absorption and scattering), as well as (ii) exogenous fluorophore crosssectionare generated with lump strength varying up to 100% of the average background.The imaging data are then used to validate a PMBF/CONTN tomographic reconstructionalgorithm. Our results show that the image recovery is sensitive to the heterogeneousbackground structures. Further analysis on the imaging data by a Hotelling observeraffirms that the detection capability of the imaging system is adversely affected by thepresence of heterogeneous background structures. The above issue is also addressedusing the human-observer studies wherein multiple cases of randomly located targetssuperimposed on random heterogeneous backgrounds are used in a ?double-blind?situation. The results of this study show consistency with the outcome of abovementioned analyses. Finally, the Hotelling observer?s analysis is used to demonstrate (i)the inverse correlation between detectability and target depth, and (ii) the plateauing ofdetectability with improved excitation light rejection.