Abstract
Recent progress regarding shortwave-infrared (SWIR) molecular imaging technology has inspired another modality of noninvasive diagnosis for early breast cancer detection in which previous mammography or sonography would be compensated. Although a SWIR fluorescence image of a small breast cancer of several millimeters was obtained from experiments with small animals, detailed numerical analyses before clinical application were required, since various parameters such as size as well as body hair differed between humans and small experimental animals. In this study, the feasibility of SWIR was compared against visible (VIS) and near-infrared (NIR) region, using the Monte Carlo simulation in voxelized media. In this model, due to the implementation of the excitation gradient, fluorescence is based on rational mechanisms, whereas fluorescence within breast cancer is spatially proportional to excitation intensity. The fluence map of SWIR simulation with excitation gradient indicated signals near the upper surface of the cancer, and stronger than those of the NIR. Furthermore, there was a dependency on the fluence signal distribution on the contour of the breast tissue, as well as the internal structure, due to the implementation of digital anatomical data for the Visible Human Project. The fluorescence signal was observed to become weaker in all regions including the VIS, the NIR, and the SWIR region, when fluorescence-labeled cancer either became smaller or was embedded in a deeper area. However, fluorescence in SWIR alone from a cancer of 4 mm diameter was judged to be detectable at a depth of 1.4 cm.
Highlights
Ductal carcinoma is the most common type of breast cancer and tends to progress to invasive cancer
The results show that SWIR fluorescence molecular imaging can be expected to detect breast cancer results show that SWIR fluorescence molecular imaging can be expected to detect breast cancer (4 (4 mm), which is smaller than the cancer size (6 mm) detectable by MRI and sonography so far mm), which is smaller than the cancer size (6 mm) detectable by MRI and sonography so far reported
In the Monte Carlo model where optical parameters were set faithfully to the internal structure of the breast tissue, photon migration in association with excitation and emission was examined in detail based on the rational mechanisms for fluorescence
Summary
Ductal carcinoma is the most common type of breast cancer and tends to progress to invasive cancer. As radiation exposure due to SWIR is much less than that from X-rays in mammography and gamma-rays in PET, SWIR fluorescence imaging can be used repetitively, which suggests its suitability in the case of young subjects. It would have a higher spatial resolution than the sentinel lymph-node biopsy with VIS (Patent blue) or NIR fluorescence (Indocyanine green, ICG) because of the lower scattering property [6,7,8,9]. A fluorescent image of a small breast cancer of several millimeters was obtained from small animal experiments [10]
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