In this study, a low-cost procedure using evaporated milk is followed to make a gelatin-based phantom with ultrasound and optical properties close to soft tissues. To find out the effect of concentrations of gelatin and evaporated milk on the ultrasound properties, we first made two sets of phantoms. The first set was made by mixing different amounts of gelatin with deionized water (no evaporated milk in this set), while in the second set, evaporated milk concentration was changed (constant gelatin concentration). We measured the ultrasound attenuation of these phantoms at low and high frequency ranges and show that when the gelatin concentration is kept at 5 %, the ultrasound attenuation can vary from 0.4 to 0.6 dB/MHz/cm as the evaporated milk concentration increases from 20 % to 50 %. After getting some idea about the proper concentrations of evaporated milk and gelatin on ultrasound properties, n-propanol alcohol, glass microspheres, and Germall plus preservative were added to our recipe. We then measured the optical properties of the resulted phantom. A diffuse optical tomography system (DOT) was employed for this purpose to measure the optical absorption and reduced scattering coefficients of our phantom at four different wavelengths.
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.
Adenocarcinoma is a type of cancers that forms in mucus-secreting glands throughout the body. For example, adenocarcinomas make up around 96% of colorectal cancers and some cervical cancers (10%). Depth of invasion for early adenocarcinoma is generally around 1-7 mm. In this report, we propose an optimal design, implementation, and evaluation of an optical fiber-based transvaginal photoacoustic/ultrasound prototype imaging probe for endo-cavity imaging of adenocarcinoma with ball-shaped fiber tips (refractive index = 1.517, radius 0.75 mm), to improve the light illumination homogeneity and increase the light delivery fluence on the central imaging area of the tissue surface. The light delivery system consists of light coupling optics, a custom-made transducer sheath, four 1-mm-core multimode optical fibers with the ball-shaped fiber tip arranged around the transducer. The probe design was optimized by simulating the light fluence distribution of the fibers with and without ball-shaped tips using a 3D model in Zemax for different design parameters such as fiber effective numerical aperture, fiber displacement from the probe base, sheath taper angle, ball-shaped fiber tips’ diameter and refractive index, etc. The laser fluence profiles were experimentally recorded through calibrated intralipid solution by camera at various imaging depths. The output power on the central imaged areas were experimentally measured by calculating the PAT signal strengths from the black threads buried inside chicken breast tissue at various depths and in-vivo photoacoustic imaging of one palmar vein proximal to the human wrist.
More than 80% of the ovarian cancers are diagnosed at late stages and the survival rate is less than 50%. Currently, there is no effective screening technique available and transvaginal US can only tell if the ovaries are enlarged or not. We have developed a new real-time co-registered US and photoacoustic system for in vivo imaging and characterization of ovaries. US is used to localize ovaries and photoacoustic imaging provides functional information about ovarian tissue angiogenesis and oxygenation saturation. The system consists of a tunable laser and a commercial US system from Alpinion Inc. The Alpinion system is cable of providing channel data for both US pulse-echo and photoacoustic imaging and can be programmed as a computer terminal for display US and photoacoustic images side by side or in coregistered mode. A transvaginal ultrasound probe of 6-MHz center frequency and bandwidth of 3-10 MHz is coupled with four optical fibers surrounded the US probe to deliver the light to tissue. The light from optical fibers is homogenized to ensure the power delivered to the tissue surface is below the FDA required limit. Physicians can easily navigate the probe and use US to look for ovaries and then turn on photoacoustic mode to provide real-time tumor vasculature and So2 saturation maps. With the optimized system, we have successfully imaged first group of 7 patients of malignant, abnormal and benign ovaries. The results have shown that both photoacoustic signal strength and spatial distribution are different between malignant and abnormal and benign ovaries.