Colorectal cancer is the second most common malignancy diagnosed globally. Critical need exists for imaging anddiagnosis of rectal tumors for both staging and therapeutic response evaluations. We have conducted a pilot study to imageand characterize colorectal masses using a real-time co-registered photoacoustic (PAT) and ultrasound (US) system. Atotal of 8 tissue samples including pre- and post-treatment colorectal cancer, polyps have studied. Four differentwavelengths (730, 780, 800, 830 nm) were used to illuminate the sample and a scanning stage was used to scan a largearea and obtain a sequence of B-scans. For the pre-treatment colorectal cancer, photoacoustic images have shownsignificantly higher vascular level than neighbor benign regions of the same sample. The pre-treatment colorectal cancerPAT signal level is also higher than polyps and post-treatment colorectal cancer. Additionally, the quantitative featuresextracted from PAT and US power spectrum such as spectral slope, mid-band fit and zero MHz intercept have shownstatistical significance between pre-treatment colorectal cancer and other 3 categories using t-test. Our initial results havedemonstrated that PAT/US has a great potential to reveal tumor angiogenesis development or residual tumors aftertreatment.
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