Deep Learning Signal Discrimination for Improved Sensitivity at High Specificity for CMOS Intraoperative Probes

The challenge in delineating the boundary between cancerous and healthy tissue during cancer resection surgeries can be addressed with the use of intraoperative probes to detect cancer cells labelled with radiotracers to facilitate excision. In this study, deep learning algorithms for background gamma ray signal rejection were explored for an intraoperative probe utilising CMOS monolithic active pixel sensors optimised towards the detection of internal conversion electrons from 99mTc. Two methods utilising convolutional neural networks (CNNs) were explored for beta-gamma discrimination: 1) classification of event clusters isolated from the sensor array outputs (SAOs) from the probe and 2) semantic segmentation of event clusters within an acquisition frame of an SAO. The feasibility of the methods in this study was explored with several radionuclides including 14C, 57Co and 99mTc. Overall, the classification deep network is able to achieve an improved area under the curve (AUC) of the receiver operating characteristic (ROC), giving 0.93 for 14C beta and 99mTc gamma clusters, compared to 0.88 for a more conventional feature-based discriminator. Further optimisation of the lower left region of the ROC by using a customised AUC loss function during training led to an improvement of 33% in sensitivity at low false positive rates compared to the conventional method. The segmentation deep network is able to achieve a mean dice score of 0.93. Through the direct comparison of all methods, the classification method was found to have a better performance in terms of the AUC.