We are adapting traditional ultrasound imaging with an emerging non-ionizing photoacoustic imaging (PAI) technique that essentially lets us “hear” light.
PAI strategies allow deeper tissue penetration than optics alone while preserving the spatial and temporal resolution advantages of ultrasound.
Therefore, tissues within a human body can be more clearly visualized at a depth that is clinically relevant. Because hemoglobin is one of the primary molecules present naturally that produce a photoacoustic signal, PAI is especially suitable for detecting blood vessels associated with tumors, as well as monitoring changes in blood vessel growth that can accompany tumor formation and growth.
At Stanford, we have engineered a new PAI device that is being tested for visualization of prostate cancer. We are adapting this device for use in ovarian cancer imaging.
After development and pre-clinical testing of the device, we will move into the clinical setting to test in patients. Our goal is to reliably visualize cancer even from several centimeters deep inside ovarian tissue. We propose the following specific aims:
1. Refine and validate a combined transvaginal ultrasound and photoacoustic-imaging device by imaging models of ovarian tissue and surgically removed human ovaries. In this aim, we will adapt the current transrectal ultrasound and PAI system shown in figure 1, to develop the probe for transvaginal imaging of ovaries.
Figure 1. Photograph of the transrectal ultrasound and photoacoustic-imaging instrument currently used for prostate cancer imaging. The capacitive micromachined ultrasound transducer (CMUT) array is flip-chip bonded to a custom-designed integrated circuit that comprises the front-end circuitry for the transducer elements. The CMUT and integrated circuit are flip-chip bonded and placed on a PCB (printed circuit board). The PCB is rested in between two parallel fiber optic light guides that focus light 0.5 inches above the CMUT surface.
2. Conduct a pilot test of the combined transvaginal ultrasound and PAI instrument in patients undergoing ovarian cancer excision surgery. Fully optimized dual-modality transvaginal ultrasound and PAI with well-defined image metrics have the potential to further enhance the sensitivity and specificity of standard transvaginal ultrasound imaging of ovaries prior to surgery. In this study, we will test the efficacy of the combined device for clinical ovarian imaging. We anticipate that the combined procedure should not be more uncomfortable than a traditional transvaginal ultrasound procedure, since both are done with a hand-held transvaginal device of similar dimensions. The combined transvaginal ultrasound-PAI can be done at the time of traditional ultrasound, and in preclinical studies adds less than five to 10 minutes to each procedure.
The primary objective of this specific aim is to assess the combined instrument performance in a clinical setting, to understand the limitations of this instrumentation, to help improve the next-generation instrument design, and to understand how to integrate the combined transvaginal ultrasound and photoacoustic imaging into the standard clinical ultrasound workflow.