Research On The Influence Factors And Key Technology Of Correlated Imaging For Endoscopic Applications

Correlated imaging is a kind of imaging technology based on intensity correlation.Different from traditional imaging technology,correlated imaging has the characteristics of non-local imaging and advantage of improving imaging resolution.In the correlated imaging experiment,the signal optical path contains an object to be imaged.The optical signal reacts with the object and is received by a detector with no resolution.The signal of the reference optical path travels freely over a certain distance and then reach a detector with high resolution.An object image or diffraction image with high resolution can be obtained by correlated calculation of the fluctuation information of light intensity detected by the two detectors.Therefore,correlated imaging h as potential applications in national defense,optical information encryption,remote sensing,biomedicine and other fields.In recent years,minimally invasive surgery has brought great convenience to doctors and patients because of its characteristics of small incision,quick recovery and less pain.Endoscope diagnosis and treatment technology is one of the means of minimally invasive surgery.However,in the closed endoscopic environment,uneven organizational structure is likely to cause multipath effec t.In addition,when the light is sent to the endoscopic environment through a small hole,the small hole may filter part of the light.These factors bring great interference to endoscopic detection.Considering that correlated imaging has the advantages o f strong anti-interference ability and super-resolution,it can be applied to endoscopic environment.At present,endoscope is mainly developing towards miniaturization and higher resolution.Based on these two points,this paper studies the correlated ima ging in endoscopic applications,and discusses the influencing factors of imaging quality in detail.The primary contents and innovations are as shown below:1.The model of correlated imaging system in endoscopic application is established.Based on the characteristics of correlat ed imaging,an active light source is introduced into the endoscopic environment through a small hole through an optical fiber,and the object light signal af ter multiple reflections is received by the barrel detector,so as to achieve the purpose of endoscopic detection.According to the model,the corresponding intensity fluctuation correlation function and point spread function are derived.The function expression can simply describe the influence of multipath effect on imaging resolution in endoscopic environment.The mismatch ratio and reflection ratio are defined to characterize the signal intensity change caused by multipath effect.Theoretical research s hows that the increase of mismatch ratio and reflection ratio will lead to poor imaging resolution.2.The influence of different fiber core diameter s on imaging quality is studied.Firstly,a grayscale object with four slits is selected as the target to s imulate the biological tissue.Secondly,the reconstructed images of different fiber core diameters are analyzed.It is found that when the fiber core diameter is less than twice the focal spot diameter of the lens,the background noise of the reconstructe d image is too large to recognize objects with low grayscale value.The coupling loss of optical fiber is too large,which makes the image seriously distorted.In this case,it is meaningless to discuss the range of anti-multipath interference.However,However,when the diameter of the fiber core is more than twice of the focal spot,the object with low grayscale values can be recognized.The coupling loss of optical fiber can be ignored and the distortion of reconstructed image is mainly caused by multipa th effect.In addition,by comparing the SNR of images corresponding to different core diameters,it can be found that the increase of the coupling loss lead to the decrease of the SNR of the reconstructed image.3.The influence of multipath effect on imaging quality in endoscopic environment is studied.The image obtained by correlating the reflected light with the reference light is called defocused image.Theoretical and experimental results show that with the increase of mismatch ratio and reflection r atio,the defocused image gradually shrink and its intensity becomes weaken,which affects the grayscale distribution of the reconstructed image.When the mismatch ratio is less than 0.3 and the reflection ratio is less than 0.2,the interference of multipath e ffect on correlated imaging can be ignored in endoscopic application.In addition,we also found that the increase of mismatch ratio and reflection ratio will lead to the deterioration of image resolution,and the effect of the mismatch ratio is greater th an that of the reflection ratio.The influence of multipath effect on imaging quality in endoscopic environment is studied.The image obtained by correlating the reflected light with the reference light is called defocused image.