| Micro vascular imaging plays an important role in basic research on vascular diseases.Both optical coherence tomography(OCT)and photoacoustic imaging have microvascular imaging capabilities.OCT is to use the backscattered light in the sample and image through broadband interference.The adjacent image difference operation extracts the motion information and three-dimensional reconstruction can obtain the blood flow perfusion map.Photoacoustic imaging is based on absorption imaging,and ultrasound transducers receive ultrasound signals generated by the thermoelastic effect to achieve imaging.Photoacoustic imaging can image blood vessels due to the strong absorption of hemoglobin by light of a specific wavelength.The two techniques based on different information to achieve vascular imaging,there is a certain complementarity,the combination of the two-mode imaging is of great significance for the study of related diseases.In conventional photoacoustic imaging,ultrasonic signal pickup requires physical contact between the transducer and the sample,which blocks the detection light of the OCT,which leads to certain difficulties in combining the two.In this study,the long-coherence light interferometry method was used to detect the surface displacement of the sample caused by photoacoustic signals,and all-optical non-contact photoacoustic imaging was realized.The technology was effectively combined with spectral OCT to construct an OCT-photoacoustic non-contact dual-mode imaging system.At the detection end,photoacoustic excitation light,photoacoustic detection light and OCT detection light are coupled into a coaxial beam through a dichroic mirror,and an X-Y scanning galvanometer is shared,making rapid scanning possible.In dual-mode imaging,photoacoustic imaging based on long-phase dry-light homodyne interferometry requires triggering acquisition at zero-crossing to maximize system sensitivity,which reduces photoacoustic imaging speed and is difficult to match with OCT fast imaging.In this thesis,a photoacoustic signal acquisition method based on reference arm modulation combined with multiple excitations is proposed,and the sensitivity compensation of photoacoustic signal detection is realized by calculating the instantaneous phase.The method greatly improves the acquisition speed of non-contact photoacoustic imaging,the two-dimensional imaging acquisition time is reduced to 40 seconds,and the dual-mode imaging acquisition time is less than 1 minute.The system was used to perform OCT angiography and photoacoustic imaging on the auricles of normal and occluded mice.The experimental results show that dual-mode imaging can not only display the blood vessel distribution,but also mark the blood flow state(flow and static).It provides an effective means for the study of vascular diseases such as cerebral infarction. |
