In this paper, we developed a real-time dual-modality Photoacoustic (PA) /ultrasound (US) imaging system and performed initial clinical study, including both healthy and cancerous nodules. This dual-modality imaging system was based on a commercial US device (Resona7, Mindray Inc, China) modified to be capable to acquire PA signals without scarifying US functions. We also made special mechanical components to allow this handheld probe to perform 3D scanning dual-modality operation.
Optical excitation was provided by a tunable pulsed OPO (SpitLight 600 OPO, InnoLas Laser GmbH, Germany), which emits 7ns width pulses at 10Hz repetition rate. Light delivery was facilitated by a fiber bundle with bifurcated ends mounted on each axial side of a linear array transducer (L9-3U, Mindray Inc., China). The transducer consisted of 192 elements that were specially covered with a highly light scattering acoustic lens. Therefore, elements were mechanically focused 3cm beneath the surface of the lens in elevation direction and capable of detecting PA signals at frequencies of up to 7 MHz. The array was connected to the US machine to acquire and digitize all channel data in parallel. For optimal light coupling, a 7 mm-thick transparent soft gel pad was placed between the tissue surface and the probe. This pad provided a gap that allow light shining on the interested area just under the probe without sacrificing US imaging.
This dual-modal US machine can show both PA and US images (including B-scan and Doppler) simultaneously, as well as functional PA imaging. Our study demonstrated that PA imaging could provide important complementary information for traditional ultrasound examination, which has a great potential for clinical diagnosis of many diseases, including breast cancer and thyroid cancer.
Objective: To develop dual-modality Photoacoustic(PA)/Ultrasound(US) system based on clinical US machine and performed imaging study of in vivo human superficial lesions.
Methods: A dual-modality PA/US system was developed based on a high-end clinical US machine with a handheld probe for US/PA dual modality imaging, equipped with multi-wavelength laser source. Twenty-three patients were enrolled consecutively from the outpatients and inpatients of Peking Union Medical College Hospital (PUMCH) from Dec. 15th 2016 to Apr.15th 2017. All the patients underwent ultrasound examinations including both gray scale and color Doppler flow imaging ultrasound (CDFI) to evaluate the morphological and vascular information of the lesions. PA/US imaging was performed right after CDFI, the CDFI and the PA/US dual imaging information of each case were compared.
Results: The laser source for PAI generates multi-wavelength laser pulses at 10Hz. Therefore, deoxyhemoglobin and hematoglobulin in tumor vasculature, which serve as different optical absorbers at specific wavelengths, can be evaluated and compared through PAI. PA/US dual modality imaging was performed in 23 cases, including 10 thyroid lesions, 10 breast lesions, and 3 soft tissue endometriosis lesions. All of the lesions performed surgery with pathology confirmed diagnosis. Our PA/US dual modality imaging system showed high quality gray scale ultrasonic and dual-modality fusion images. According to the results, significant differences exist between PAI and CDFI. PAI could reveal some blood vessels that were not sensitive for Doppler ultrasound. PAI proved the ability of imaging both the peripheral and intra-nodular vessels of human superficial lesions, as well as detecting the difference of oxygen saturation between benign and malignant tumor.
Conclusion: Our study demonstrated that photoacoustic imaging could provide important complementary information for traditional ultrasound in superficial lesion examination, which has a great potential for clinical diagnosis.