Calibration of led-photodiode optical tomography system and in-vitro experiments

Objective: This study aims to create tomographic images from measurement data obtained from breast phantoms with inclusions using a light-emitting diode (LED)-photodiode diffuse optical tomography (DOT) system. Additionally, the study aims to evaluate the LED-Photodiode DOT system's sensitivity to changes in the diameter and depth of the inclusions. Method: In this study, to ensure the calibration of the LED-Photodiode DOT system, the measurement values obtained by the system were made independent of the different LED light levels and the photodiode's light collection durations used. The hardware calibration of the system was completed by making corrections to the measurement values of detectors located in the same vicinity. In the prepared breast phantoms, the mixture ratios were set to achieve a reduced scattering coefficient (µs' = 10 cm⁻¹) and an absorption coefficient (µa = 0.04 cm⁻¹). Measurements were taken on breast phantoms containing tumor-like spherical inclusions using the LED-Photodiode DOT system. The measurement data was used to generate tomographic images, and the size and depth of the inclusions in these images were analyzed relative to their actual sizes and depths. Findings: To evaluate the continuous wave (CW) LED-Photodiode DOT system's accuracy in detecting the actual diameter of the prepared inclusions at various depths, two different in-vitro experimental setups were prepared. The images generated by the back-projection algorithm using the measurement data were evaluated. It was demonstrated that the CW LED-Photodiode DOT system accurately imaged the depths and diameters of inclusions with varying diameters. Conclusion: The CW LED-Photodiode DOT system accurately determined the depths and sizes of inclusions within clinical study limits in breast phantom experiments. The results suggest that the system is suitable for initiating in-vivo and real-time studies to evaluate treatment efficacy in neoadjuvant chemotherapy for breast cancer patients. Key words: diffuse optical tomography, tissue phantom, reconstruction algorithm, system calibration, breast cancer