Design And Evaluation Of A Compound Acoustic Lens For Photoacoustic Computed Tomography

With the development of science,medical imaging is increasingly crucial in diagnosis of disease.Benefiting from non-invasive and non-ionizing,photoacoustic imaging attracts more and more attention in medical imaging.Recently,PAI can be divided into photoacoustic microscopy(PAM)and photoacoustic computed tomography(PACT).In photoacoustic computed tomography,limited directivity of detectors may cause deformation of off-center targets and reduce signal to noise ratio and lead to low imaging quality.Small aperture angle of transducer has been a problem that need to be solved.Convex acoustic lens can increase aperture angle of transducer and improve imaging quality.Traditional convex acoustic lenses are mostly made of single material and partial solve the small aperture angle of transducer.However,a single material acoustic lens can only increase directivity of transducer one time.In the case where transducer is close to target,single material acoustic lens still causes deformation of off-center targets.In this study,we develop a new compound acoustic lens fabricated by integrating a concave polydimethylsiloxane lens and a convex epoxy lens.We explore the theory of acoustic lenses simultaneously.From the experiment results,compound acoustic lens shows better performance compared with other acoustic lenses.Without acoustic lens,transducer has a small directivity.But both transducers with compound lens,epoxy lens and PDMS lens respectively have a larger directivity..We conducted a traditional circular scanning photoacoustic computed tomography system.Pencils and human hairs are inserted into phantoms in our experiments.We also conducted an experimental system to test the directivity of acoustic lenses.Compared results of experiments,transducer with compound acoustic lens has a larger directivity and better imaging quality than other single lenses.The acceptance angles of a 6 mm piezoelectric acoustic transducer equipped with the compound lens,PDMS lens,epoxy lens and liquid lens were measured to be 84.5°,22°,42° and 38°,respectively.No deformation was observed in off-center targets by using compound lens.In all,compound acoustic lens has a great influence to large the directivity of transducer and a great value of clinical use.