Ultrafast Handheld Optical Resolution Photoacoustic Microscopy

With the continuous development,medical imaging technology has been widely applied in health monitoring,diagnosis and treatment of diseases.Ultrasound,X-ray computed tomography(X-Ray CT)and Magnetic Resonance Imaging(MRI)are common tools;however,limitations still exist.Methods which enable rapid,non-invasive and high-resolution are in urgent need for the fundamental researches and clinical applications.Photoacoustic Imaging(PAI)has been evidenced to be a good candidate for such purpose.Combining both advantages of optical imaging and ultrasonic imaging,PAI can provide images with high contrast and high penetration depth;in addition,PAI enables the way to simultaneously picking up both the structural and functional information of biological tissues,which are of vital importance for the early diagnosis of cancer.PAI basically employs a pulsed laser to excite the biological tissue,which subsequently produces ultrasonic signals due to the thermal expansion effect.With processing steps as signal amplification,filtering,data acquisiiton and image reconstruction,the images of biological tissue can be obtained.As an important branch of PAI,optical resolution photoacoustic microscopy(ORPAM)is well known for characteristics as high resolution and high contrast.In ORPAM,a pulsed laser is basically employed to irradiate to the surface of biological tissue with a focused spot,that is close to the wavelength of the optical wave;Due to the small size of the focused spot,this technology can greatly improve the horizontal resolution of the image of biological tissue.Conventional ORPAM adopts twodimensional motorized positioning systems for the raster scanning;however,due to the bulky size and the inherent disadvantages of scanning mechanism,the imaging speed is typically low.As a result,it is difficult be implemented for dynamic and real-time monitoring which is desirable for various clinical applications.Besides,conventional ORPAM can not provide flexible arrangements for both imaging system and targets,which prohibites the further development and potential application.In order to address such issue,this paper proposes a superfast and hand-held ORPAM system,which utilizes a X-Y two-dimensional scanning galvanometer for modulating the pulsed laser,a line-focused ultrasound probe for capturing photoacoustic signal,and a two-phase stepper motor that cooperated with waterproof bearing,conductive slip ring that drives the probe super rapidly,for rotatory scanning and detection.By doing so,the scanning and imaging speeds of photoacoustic imaging can be increased greatly,which are beneficial for monitoring the dynamic change of certain diseases.The capability of ultrafast imaging is verified by experiments as performed to the ear,brain and tumors of mice in-vivo.Taking into account that fast speed and portability(small size and light weight)can be realized in the proposed ORPAM system,the suggested design is expected to be applied in clinical diagnostics.