Scanning photoacoustic imaging of submucosal gastric tumor based on a long focused transducer in phantom and in vitro experiments

Photoacoustic imaging,which can provide the maximum intensity contrast in tissue depth imaging without ionizing radiation,will be a promising imaging trend for tumor detection.In this paper,a column diffusionfiber was employed to carry a pulsed laser for irradiating stomach directly through esophagus based on the characteristics of gastric tissue structure.A long focused ultrasonic transducer was placed outside the body to detect photoacoustic signals of gastric tissue.Phantom and in vitro experiments of submucosal gastric tumors were carried out to check the sensitivity of scanning photoacoustic tomography system,including the lateral and longitudinal resolution of the system,sensitivity of different absorption coefficient in imaging,capability of transversal detection,and probability of longitudinal detection.The results demonstrate that our innovative technique can improve the parameters of imaging.The lateral resolution reaches 2.09 mm.Then a depth of 5.5mm with a longitudinal accuracy of 0.36mm below gastric mucosa of early gastric cancer(EGC)has been achieved.In addition,the optimal absorption coefficient differences among absorbers of system are 3.3-3.9 times.Results indicate that our photoacoustic imaging(PAI)system,is based on a long focusing transducer,can provide a potential application for detecting submucosal EGC without obvious symptoms.

Temperature rise induced by an annular focused transducer with a wide aperture angle in multi-layer tissue

In order to improve the operability and accuracy of high-intensity focused ultrasound （HIFU）, an annular focused transducer, whereby a B-ultrasound probe is placed in its center, is used to realize the real time monitoring and control of the treatment. In this paper, the spheroidal beam equation （SBE） was used to calculate the sound lield by an annular focused transducer with a wide aperture angle to first derive the heat deposition and the Pennes equation was used to calculate the temperature field in multi-layer tissue. We studied the effect of different parameters on the temperature of the tissues. The result shows that the focal length has a significant influence on both maximum liver temperature rise and skin temperature rise, and both increase with the increase in the focal length. When the frequency increases, the temperature rise first undergoes a rapid increase before gradually reaching a maximum, and then finally decreasing. The temperature rise increases while the inner radius decreases or the sound pressure increases. By choosing suitable parameters, the proper temperature rise both on the target tissue and skin via an annular tbcused transducer with a wide aperture angle can be obtained.

The experimental study of the calibration of the focus ultrasonic transducer on its picture

The shape and size of the energy transducer’s focus decide the constitution of the cure project using HIFU (High intensity focused ultrasound). The parameter of the focus will be different when the structure of the transducer is different, so we must calibrate each of them. This paper represents calibration principle and method of focal territory in a high-power ultrasonic focus transducer. The experiment is performed on our designed multiple wafer concave focus probe and HIFU apparatus, using 1010 nylon and pork as the target range. It can be seen that the geometric center and focal territory acoustic field center cannot match together. When using nylon as the target, the distributed curves and theoretical curves are a better match. Therefore, the method and principle of calibration here is constructive for the calibration on pictures of other types of HIFU apparatus.

NEW FOCUSED ULTRASOUND TRANSDUCER FOR FAT CELL DISRUPTION

Being an emerging body-shaping technology of fat cell disruption,high-intensity focused ultrasound has been investigated intensively in recent years for its favorable natures such as painlessness,safety and noninvasion.One of the major problems for the technology,however,is the overheating of transducers.In this study,we modified the transducer design in order to solve the overheating problem.We simulated the performance of the modified design by finite element analysis and fabricated the newly designed transducer.By measuring the actual performance data,we proved that the new design can effectively reduce temperature rise while keeping the acoustic intensity field unaffected.

Reflection-mode photoacoustic microscopy using a hollow focused ultrasound transducer for in vivo imaging of blood vessels

A reflection-mode photoacoustic microscope using a hollow focused ultrasound transducer is developed for highresolution in vivo imaging.A confocal structure of the laser and the ultrasound is used to improve the system resolution.The axial and lateral resolutions of the system are measured to be ～ 32 μm and ～ 58 μm,respectively.Ex vivo and in vivo modes are tested to validate the imaging capability of the photoacoustic microscope.The adjacent vein and artery can be seen clearly from the reconstructed photoacoustic images.The results demonstrate that the reflectionmode photoacoustic microscope can be used for high-resolution imaging of micro-blood vessels,which would be of great benefit for monitoring the neovascularization in tumor angiogenesis.

Photoacoustic microscopy by scanning mirror-based synthetic aperture focusing technique

Photoacoustic imaging with a synthetic aperture focusing technique（SAFT） is an effective method to improve the lateral resolution for out-of-focus regions in scanning microscopy systems, which commonly require a decent motorized scanning stage for a lateral scan of a transducer to obtain a cross-sectional image. In this study, we propose and test a photoacoustic imaging system with a scanning mirror-based SAFT（SM-SAFT） for simple and fast data acquisition, without the need for a physical scan of the transducer. Photoacoustic images of hair phantoms acquired by SM-SAFT are demonstrated, serving as a proof-of-concept experiment to show the feasibility and potential of the proposed approach.