A multi-spectral, portable, hand-held LED based spatial frequency domain imaging system was used for ex vivo imaging pretreatment and post treatment human colon and rectal tissues. Freshly excised human colon and rectal tissue samples were imaged with the hand-held SFDI probe with 9 wavelengths extending from visible to NIR (660-950 nm). Important tumor biomarkers such as hemoglobin, scatter amplitude, scatter spectral slope, water and lipid content were quantitatively extracted from the SFDI absorption and scattering images. Significant differences were observed between the absorption as well as scattering distribution of normal, tumor and polyp tissue as well as between pretreated and post-treated tumors.
Surgery for rectal cancer is associated with significant side effects including wound infections, incontinence, sexual and bladder dysfunction, and long-term ostomies. Though studies have shown that patients who completely respond to preoperative treatment can safely avoid surgery, nonoperative options remain limited by the poor performance of MRI and endorectal ultrasound after initial therapy. Therefore, new imaging modalities are needed to improve posttreatment tumor assessment and enable the widespread adoption of nonoperative management in rectal cancer. An acoustic resolution photoacoustic microscope (AR-PAM) was constructed with high frequency ultrasonic transducer and near infrared laser. We performed initial phantom, and then imaged ex vivo human colorectal specimens to evaluate different AR-PAM characteristics in each tissue type (normal, untreated tumor, and treated tumor). Our data suggest that photoacoustic imaging can differentiate the distorted vasculature of rectal tumors from normal vascular patterns. However, the vascular distribution of rectal tissue in pathological complete responders showed similar distribution as the normal colorectal tissue; mucosa, submucosa and muscle layer are clearly presented in ultrasound images, while photoacoustic images have revealed that most vasculatures distribute in submucosa. Encouraged by these initial results, we are developed a high-speed scanning (1 second for 20mm B-scan) AR-PAM with laser pulse repetition rate of 1kHz for large field 3D imaging. Lateral resolution of 65μm, axial resolution of 45μm, and 8mm tissue imaging depth can be achieved.
Colorectal cancer is the second most common malignancy diagnosed globally. Critical need exists for imaging and diagnosis of rectal tumors for both staging and therapeutic response evaluations. We have conducted a pilot study to image and characterize colorectal masses using a real-time co-registered photoacoustic (PAT) and ultrasound (US) system. A total of 8 tissue samples including pre- and post-treatment colorectal cancer, polyps have studied. Four different wavelengths (730, 780, 800, 830 nm) were used to illuminate the sample and a scanning stage was used to scan a large area and obtain a sequence of B-scans. For the pre-treatment colorectal cancer, photoacoustic images have shown significantly higher vascular level than neighbor benign regions of the same sample. The pre-treatment colorectal cancer PAT signal level is also higher than polyps and post-treatment colorectal cancer. Additionally, the quantitative features extracted from PAT and US power spectrum such as spectral slope, mid-band fit and zero MHz intercept have shown statistical significance between pre-treatment colorectal cancer and other 3 categories using t-test. Our initial results have demonstrated that PAT/US has a great potential to reveal tumor angiogenesis development or residual tumors after treatment.