Abstract:Small animal positron emission tomography (PET) is a well-established imaging modality in preclinical biomedical research. But depth encoding detectors are required to simultaneously achieve high spatial resolution and high sensitivity for a small animal PET scanner. In this work, we evaluated several dual-ended readout detector modules using lutetium oxyorthosilicate (LSO) arrays with crystal sizes ranging from 0.70 mm to 0.44 mm, read out by either position-sensitive avalanche photodiodes (PSAPDs) or position-sensitive silicon photomultipliers (PS-SiPMs). A new type of PS-SiPM was developed recently and was evaluated for the first time in this work. First, the signal-to-noise ratio (SNR) of both PSAPDs and PS-SiPMs was measured, and then the flood histograms, energy resolution and depth of interaction (DOI) resolution of dual-ended readout detector modules by using both PSAPDs and PS-SiPMs were measured. The PSAPD has much better SNR as compared with PS-SiPM. For the detectors using PSAPDs, crystals as small as 0.44 mm can be resolved and a DOI resolution as good as 1.4 mm was obtained. For the detectors using PS-SiPMs, 0.7 mm crystals can be resolved and a DOI resolution of 2.9 mm was obtained. Based on the results of the flood histograms, energy resolution and DOI resolution the detector modules using PSAPD are better than those using PS-SiPMs. The SNR of the PS-SiPM would need to be improved to resolve even smaller crystals and the number of SiPM cells also need to be increased to reduce the saturation effect to improve the DOI resolution. The performance of the three dimensional depth encoding PET detectors using PSAPDs is much better because the SNR of PSAPD is much higher than PS-SiPM. In the future, high resolution depth encoding PET detectors will be developed by using both new PS-SiPMs and SiPM arrays.

Abstract:Efficient investigation of models is important for promoting work efficiency in applications. As a result, view selection techniques play an important role, and have made substantial progresses in recent years. In this paper, we systematically survey the techniques for view selection, emphasizing on introduction of view evaluation techniques and their development states, and discussing the progress of view sampling strategies and the application of view selection in some areas. At last, the trends of view selection techniques and future applications were discussed.

Abstract:Fast brain T1 mapping is a quantitative technique of magnetic resonance imaging, and can provide important reference for the diagnosis of several brain diseases, such as Parkinson, epilepsy and hepatic encephalopathy. Fast T1 mapping techniques proposed previously had sped up acquisition to several seconds per slice. However, most of these techniques suffered seriously from the field inhomogeneity of main field, transmit field and susceptibility artifacts, which decreased the imaging accuracy and limited the clinic applications. To overcome the above mentioned shortcomings, we proposed a fast brain T1 mapping technique based on TurboFLASH and evaluated it on computer simulation, phantom experiment, and human brain T1 mapping. Results showed that T1 values from the proposed method were very close to the gold standard and literature (differences being less than 3%). Besides, the proposed technique can increase the acquisition speed to 3s per slice (with a slice resolution of 1.1 mm×1.1 mm) and 2 min for the whole brain (with a 4 mm slice distance).

Abstract:Compared with conventional hot-cathode X-ray source, carbon nanotube X-ray source has multiple advantages, such as compact structure, high time-resolution and programmable emission. Therefore, the electronic scanning strategy can be used to replace traditional scanning method for improving the time resolution of image acquisition, and reducing motion artifacts and radiation dose. This paper aims at designing the software and hardware platforms for this new-type stationary scanning system with X-ray source. Among them, the hardware platform integrates multi-beam X-ray source and its corresponding drive circuit, a high voltage generator, a compound vacuum gauge and digital flat-panel detector; the lower computer software implements the generation of multi-channel pulse and trigger signal using Quartus II development platform and Verilog hardware description language; the upper computer software platform implements the integrated control of multiple instruments and completes the stationary scanning, high voltage control, vacuum degree monitoring and image acquisition of multi-beam X-ray source adopting LabVIEW graphical programming tools. The design of this system was verified by our experiments, which reveals that it can realize the imaging of pulse-type stationary scanning of multi-beam carbon nanotube X-ray source, and thereby provide the experimental and testing platforms for the development of carbon nanotube stationary CT.

Abstract:Hydrogen gas (H2) is a novel, simple and safe antioxidant. However, its poor solubility in water, the difficulties to track by imaging and to be released in a controllable manner limit its bio-medicine application. Microbubbles (MBs) are ideal ultrasound contrast agents and can be used as the ultrasound-activated drug carriers. In this work, hydrogen-loaded microbubbles (H2-MBs) were prepared and their performance in ultrasound imaging in vitro and in vivo were examined. Experiment results showed that H2-MBs have excellent ultrasound imaging capability both in phosphate buffered saline and in the rat left ventricular and liver. The study provided a novel H2 formulation and laid the foundation for further H2 therapy application.

Abstract:Tunable localized acoustic fields have potential applications in the development of novel acoustic devices such as new filters, sensors and acoustic manipulation micro-devices. In this paper, tunable localized acoustic fields on a defect phononic crystal plate (PCP) have been numerically investigated. The results showed localized acoustic fields on a defect PCP can be tuned by changing the resonance frequency. It is attributed to the inconsistency of the resonate frequency for the defect hole and the periodic holes in the defect PCP, which induce various coupled fields on the surface of the defect PCP. This designed defect PCP can be used as acoustic holder for the investigation of the interaction between the acoustic field and microparticles.

Abstract:Over the past twenty years, the morbidity and mortality of tumor in our country was increasing. If the the cancer could be detected at early stages, targeting therapy would be performed which contribute to improve the cure rate of cancer. With the development of nanotechnology, nanomaterials used in early diagnosis of cancer imaging and treatment have aroused wide concern. A kind of organic fluorescent nanoprobes based on aptamer for tumor-targeted imaging with rapid, simple synthetic process was developed in this research. The nanoprobes not only exhibit excellent targeting function but also have good biocompatibility and stability, and provide a powerful tool for further tumor diagnosis and treatment.

Abstract:Quantitatively assessing the tissue stiffness with the acoustic radiation force impulse imaging (ARFI) method has proved its effectiveness in clinical trials, such as the staging of liver cirrhosis and diagnosis of benign and malignant breast tumor. However, it has also been found that, the stability of its result is affected by many factors, such as measurement depth and tissue’s anisotropy. In this study, several modified methods for shear wave speed estimation were designed based on the existing Radon transformation (RT) method, and were compared using ultrasound radio-frequency data collected from a self-developed ARFI system. These RT based algorithms were classified to two types: (I) RT being performed on the displacement matrix with the axes of time and lateral location, and (II) RT being performed on the displacement matrix with the axes of time and depth. Type (I) algorithm attempts to find the best fitting trajectory of shear wave propagation in the lateral direction at a given depth, while Type (II) algorithm tries to directly find the exact time points when the shear wave front passes each lateral location in the whole measurement depth range. Experiments were performed on the soft tissue mimicking phantom and the ex vivo pork tissue sample. The reliability of repeated measurements and the computation time of these modified algorithms were compared. These results can help to find the most stable and time-saving algorithm of shear wave speed estimation, and improve the measurement reliability of ARFI in clinical trials.

Abstract:Magnetic resonance acoustic radiation force imaging (MR-ARFI), a new guided technique for high intensity focused ultrasound (HIFU) therapy, can detect micro-scale displacement in soft tissue and implement HIFU focal localization. In this work, readout segmented echo plane imaging (rs-EPI) is used as a new MRARFI sequence to accelerate MR-ARFI imaging techniques. Compared with single shot echo plane imaging (ss-EPI) and 2DSE ARFI, the proposed method is time-efficient and more robust to image distortion. The quantification results show that the tissue displacements obtained by our method have high reproducibility and consistency compared with the other two methods. The displacement maps acquired in plane parallel and perpendicular to the ultrasound propagation direction are also consistent around the focal point. The capability of providing good image quality in both directions of rs-EPI facilitates better volumetric displacement mapping around the HIFU focal point. In general, segmented EPI is a potentially useful HIFU focal localization method in clinical application.

Abstract:Magnetic resonance amide proton transfer imaging is a novel technical to detect the concentration and viability of protein in vivo. Currently, amide proton transfer (APT) imaging is commonly implemented by the echo planar imaging (EPI) sequence with a series of pre-saturation pulses. However, EPI images suffer from image distortion and signal decay in higher field MR (magnetic resonance) system. In this paper, we proposed to replace EPI with the fast gradient echo sequence for APT imaging. Specifically, the APT data were acquired by a series of pre-saturation pulses with different offset frequency following a fast gradient echo readout with small flip angle. The APT images were then obtained with field inhomogeneity correction. Experimental results show that the images are free of distortion and the quantitative analysis of APT ratio with the concentration of amide proton exhibits good consistency.

Abstract:To investigate the hemodynamics parameter of stress phase angle (SPA) in different stenosis states, the high-frequency ultrasonic imaging system was employed to obtain ultrasound contrast images of stenotic plaques, and the value of SPA was calculated through echo particle image velocimetry and cross-correlation algorithms. The experimental results showed that when the stenosis was 30%, 50% and 70%, the mean SPA was －162.88°, －201.99° and －222.89°, respectively. The study may suggest that the bigger stenosis, the more negative the SPA and the more asynchronous between the wall shear stress and circumferential stress.