超短脉冲微波高效激发的高分辨率热声成像

微波热声成像综合了微波成像和超声成像的优点,具有很好的穿透深度及较高的图像分辨率。热声成像的激发源通常为基于脉冲调制的亚微秒级脉冲微波,激发能量密度约为几mJ/cm2,激发出的热声信号主频通常为2 MHz,成像分辨率约为500μm。随着热声成像向着临床应用方向发展,能否有效的减小辐射剂量并提高成像分辨率,是热声成像系统设计成败的一个关键因素。为了有效改善微波热声成像中热损伤及分辨率,设计开发了超短脉冲微波热声成像系统,实验结果表明该系统提高了热声转化效率约两个数量级,成像分辨率达到105μm,为热声成像的临床应用铺平了道路。     

快速微波热声层析成像在生物医学中的潜在应用

介绍了一种快速热声层析成像方法和装置,成功实现了生物组织的二维热声层析成像及异物检测.实验中采用频率为1.2 GHz的脉冲微波作为激发源,中心频率为3.5 MHz的320振元线性阵列探测器接收热声信号,然后用有限场滤波反投影方法重建得到热声层析图像.与原有方法相比,勿需全方位扫描采集数据,能大量节省时间,重建图像的对比度和抗噪声能力有极大提高.该方法和系统有望应用于乳腺癌早期检测、体内异物检测、微波热疗效果监测等方面.     

微波热声成像技术用于人体甲状腺检测

本文首次通过人体实验验证了微波热声成像技术用于人体甲状腺检测的可行性.文章首先讨论了该技术用于人体甲状腺检测的可行性;然后对3名志愿者的健康甲状腺进行了微波热声成像实验.结果表明:微波热声成像能够对人体健康甲状腺进行清晰成像,能够真实反映皮肤、甲状腺和气管等不同组织的结构特征;并且一次完整的检测过程时间约5 s,系统操作简单成像快速.综上所述,微波热声成像技术有望为甲状腺疾病的基础研究和临床诊断提供一种新的影像学参考.     

热声、光声双模态早期乳腺肿瘤成像系统

本文提出一种热声、光声双模态乳腺肿瘤检测成像系统。本装置中,脉冲微波和脉冲激光分别为热声、光声激发源,产生的热声、光声信号被同一个超声探测器、同一套数据采集装置接收,用同一种成像算法重建出图像。该系统可同时获取多种互补的诊断参数,提高检测早期乳腺肿瘤的准确率。     

用于光声内窥的中空声透镜聚焦PVDF换能器的研究

针对目前光声内窥成像中常用的基于压电陶瓷的中空聚焦超声换能器制作工艺复杂、定制费用高的问题,本文利用PVDF压电薄膜声阻抗低、频响宽、易于加工等优点,以及环氧树脂介于PVDF和生物组织的声阻抗特性,制作了一款基于110μm PVDF压电薄膜的中空声透镜聚焦超声换能器。声场测试实验表明,该换能器纵向分辨率为0.22 mm,焦点处横向分辨率约为0.65 mm,和理论设计值相符。随后又利用多模光纤和宽带介质膜反射镜,通过仿体实验对其内窥成像效果进行了初步验证。相比于基于压电陶瓷的聚焦超声换能器,本方案极大的降低了内窥光声成像中所需的中空聚焦超声换能器的设计和制作成本,方便了实验室条件下内窥光声系统的开发。     

三维微波热声成像系统及早期乳腺肿瘤检测研究

本文讨论了正常乳房组织与肿瘤组织的微波吸收差异,从理论上证明了利用微波热声成像技术检测乳腺肿瘤的可能性;建立了一套三维热声扫描系统,并利用此系统对模拟肿瘤和真实离体肿瘤进行成像实验。实验结果表明,三维微波热声成像系统能对乳腺肿瘤高分辨率高对比度成像,有希望应用于早期乳腺肿瘤检测。     

基于动态聚焦的声聚焦光声内窥成像算法研究

目的 声聚焦光声内窥成像具有成像深度大的优点,是一种非常有前景的功能成像技术,该技术被广泛应用于直肠、食道等内窥成像中。声聚焦光声内窥成像通常采用基于单个聚焦超声传感器的侧向扫描方式,同时采用传统的B扫描方法进行重建,会大大降低图像质量。为了获得高质量的图像,本文提出了几种动态聚焦的声聚焦光声内窥成像算法。方法 本文使用几种动态聚焦算法进行了数值仿真,并搭建系统进行了仿体实验验证,从横向分辨率和信噪比等多方面比较了各算法在动态聚焦中的成像效果。结果 相比B扫描方法,动态聚焦后的图像在离焦区域的横向分辨率与信噪比方面都有提升,仿真模拟中最高可将离焦区域的成像目标分辨率提升约26倍,其信噪比经动态聚焦后最高可提高2.3倍左右,实验中的远距离点目标经动态聚焦重建后分辨率提升3～6倍。结论 整体而言,基于时空响应的算法和合成孔径聚焦重建算法是在实验条件下更为适用的算法。本工作对后续的声聚焦光声内窥成像的设计具有指导意义。     

生物组织电导率图像的热声重建

本文以微波热声效应为基础,报道了一种重建生物组织电导率相对分布图像的方法。和传统的微波热声像相比,重建得到的组织电导率图像消除了由于微波场能量密度分布不均匀带来的影响,能够准确的反映组织的介电特性差异,实现对肿瘤的早期发现。本文首先从理论上详细推导了获得生物组织电导率分布图像的原理,然后在实验中通过结合已有的脉冲微波成像系统,重建得到了一块肌肉组织的电导率分布图像。实验结果表明利用热声成像技术,组织的电导率分布图像能够被清晰的重建,本研究为推进热声成像技术的实用性打下了理论和实验基础。     

基于样品及点源光声信号逆卷积的光声成像方法

光声成像是一种新的生物组织成像方法,在目前的光声成像中,都是通过样品光声信号和超声探测器的脉冲响应来计算样品光吸收的投影,但是由于无法获得超声探测器较准确的脉冲响应,影响重建图像质量。提出一种新的计算样品光吸收投影的方法,从理论上给出了样品光吸收投影和样品及点源光声信号的关系,由样品及点源光声信号的逆卷积可直接计算样品光吸收的投影,点源光声信号通过聚焦入射激光直接测得。试验结果显示,重建图像和样品的相对位置、形状及尺寸完全吻合,成像系统空间分辨率达到0．3mm,证明这是一种有效的光声成像方法。     

基于阵列式换能器的光声成像系统的实现

目的:本文设计了一套光声成像(photoacoustic imaging,PAI)系统,由脉冲激光、阵列换能器、临床超声(ultrasound,US)主机、软件平台以及成像样品组成。系统的图像质量、最大成像深度等重要参数需通过实验进行确定。方法:使用本系统对黑色头发丝横截面进行成像,比较、分析光声(photoacoustic,PA)信号幅值的半极大处全宽度以量化图像分辨率。此外,使用系统对特定的光吸收体和鸡胸肉组织进行成像,确定系统的成像深度。结果:实验结果证明了PAI系统的实现,其PA图像的平均轴向和横向分辨率分别约为0.18 mm和1.44mm,系统的最大成像深度达到4.6 cm。结论:本PAI系统PA图像分辨率优于US主机获得的US图像分辨率,系统最大成像深度与其他国际研究组的系统成像深度的数量级一致。通过进一步优化与活体组织实验的开展,本PAI系统将有望实现临床成像诊断。     

High Resolution 3D Imaging of Ex-Vivo Biological Samples by Micro CT

Non-destructive volume visualization can be achieved only by tomographic techniques, of which the most efficient is the x-ray micro computerized tomography (μCT).High resolution μCT is a very versatile yet accurate (1-2 microns of resolution) technique for 3D examination of ex-vivo biological samples^{1, 2}. As opposed to electron tomography, the μCT allows the examination of up to 4 cm thick samples. This technique requires only few hours of measurement as compared to weeks in histology. In addition, μCT does not rely on 2D stereologic models, thus it may complement and in some cases can even replace histological methods^{3, 4}, which are both time consuming and destructive. Sample conditioning and positioning in μCT is straightforward and does not require high vacuum or low temperatures, which may adversely affect the structure. The sample is positioned and rotated 180° or 360°between a microfocused x-ray source and a detector, which includes a scintillator and an accurate CCD camera, For each angle a 2D image is taken, and then the entire volume is reconstructed using one of the different available algorithms^5-7. The 3D resolution increases with the decrease of the rotation step. The present video protocol shows the main steps in preparation, immobilization and positioning of the sample followed by imaging at high resolution.     

Integrated photoacoustic and diffuse optical tomography system for imaging of human finger joints in vivo

In this study, we developed a dual‐modality tomographic system that integrated photoacoustic imaging (PAI) and diffuse optical tomography (DOT) into a single platform for imaging human finger joints with fine structures and associated optical properties. In PAI, spherical focused transducers were utilized to collect acoustic signals, and the concept of virtual detector was applied in a conventional back‐projection algorithm to improve the image quality. A finite‐element based reconstruction algorithm was employed to quantitatively recover optical property distribution in the objects for DOT. The phantom results indicate that PAI has a maximum lateral resolution of 70 µm in resolving structures of targets. DOT was able to recover both optical absorption and reduced scattering coefficients of targets accurately. To validate the potential of this system in clinical diagnosis of joint diseases, the distal interphalangeal (DIP) joints of 4 healthy female volunteers were imaged. We successfully obtained high‐resolution images of the phalanx and the surrounding soft tissue via PAI, and recovered both optical absorption and reduced scattering coefficients of phalanx using DOT. The in vivo results suggest that this dual‐modality system has the potential for the early diagnosis of joint diseases such as osteoarthritis (OA) and rheumatoid arthritis (RA).

Integrated PAI/DOT imaging interface (top) and typical reconstruction of structures and associated optical properties of a female finger joint via PAI and DOT (bottom).     

Size and CT density of iodine-containing ethosomal vesicles obtained by membrane extrusion: Potential for use as CT contrast agents

Computed tomography (CT) is the primary non-invasive imaging technique used for most patients with suspected liver disease. In order to improve liver-specific imaging properties and prevent toxic effects in patients with compromised renal function, we investigated the encapsulation of iodine within ethosomal vesicles. As a first step in the development of novel contrast agents using ethosomes for CT imaging applications, iodine was entrapped within ethosomes and iodine-containing ethosomes of the desired size were obtained by extrusion using a polycarbonate membrane with a defined pore size. Ethosomes containing iodine showed a relatively high CT density, which decreased when they were extruded, due to the rupture and re-formation of the lipid bilayer of the ethosome. However, when a solution with a high iodine concentration was used as a dispersion media during the extrusion process, the decrease in CT density could be prevented. In addition, ethosomes containing iodine were taken up efficiently by macrophages, which are abundant in the liver, and these ethosomes exhibited no cellular toxicity. These results demonstrate that iodine could be entrapped within ethosomal vesicles, giving the ethosomes a relatively high CT density, and that the extrusion technique used in this study could conveniently and reproducibly produce ethosomal vesicles with a desired size. Therefore, ethosomes containing iodine, as prepared in this study, have potential as contrast agents with applications in CT imaging.     

高分辨率CT与常规CT检查对肺小结节及早期肺癌诊断价值的对比研究

目的:对比高分辨率电子计算机断层扫描(CT)与常规CT检查对肺小结节及早期肺癌的诊断价值。方法:将2018年6月2020年1月我院收治的肺小结节及早期肺癌患者94例纳入研究。以随机数字表法将其分为观察组及对照组,每组各47例,对照组实施常规CT检查,观察组则实施高分辨率CT检查。比较两组CT肿瘤征象情况(主要包括毛刺征、分叶征、棘突征、钙化征、空泡征、支气管征、胸膜凹陷征、血管集束征),CT扫描图像质量,诊断肺小结节及早期肺癌的效能。结果:观察组各项CT肿瘤征象人数占比均高于对照组(P<0.05)。观察组CT扫描图像质量优良率为97.87%(46/47),高于对照组的72.34%(34/47)(P<0.05)。高分辨率CT诊断早期肺癌的灵敏度及准确度、特异度分别为96.67%(29/30)、95.74%(45/47)、94.12%(16/17),高于常规CT检查的74.19%(23/31)、74.47%(35/47)、75.00%(12/16)。结论:高分辨率CT检查对肺小结节及早期肺癌诊断价值显著高于常规CT检查,可作为临床肺小结节及早期肺癌诊断的有效影像学手段,值得临床应用。     

Effects of the murine skull in optoacoustic brain microscopy

Despite the great promise behind the recent introduction of optoacoustic technology into the arsenal of small‐animal neuroimaging methods, a variety of acoustic and light‐related effects introduced by adult murine skull severely compromise the performance of optoacoustics in transcranial imaging. As a result, high‐resolution noninvasive optoacoustic microscopy studies are still limited to a thin layer of pial microvasculature, which can be effectively resolved by tight focusing of the excitation light. We examined a range of distortions introduced by an adult murine skull in transcranial optoacoustic imaging under both acoustically‐ and optically‐determined resolution scenarios. It is shown that strong low‐pass filtering characteristics of the skull may significantly deteriorate the achievable spatial resolution in deep brain imaging where no light focusing is possible. While only brain vasculature with a diameter larger than 60 µm was effectively resolved via transcranial measurements with acoustic resolution, significant improvements are seen through cranial windows and thinned skull experiments.

(a) Experimental setup for hybrid acoustic and optical resolution optoacoustic microscopy. (b) Transcranial scan of an adult mouse brain using the optical resolution mode. Scale bar is 375 µm.     

1064 nm acoustic resolution photoacoustic microscopy

Photoacoustic imaging is a noninvasive imaging technique having the advantages of high‐optical contrast and good acoustic resolution at improved imaging depths. Light transport in biological tissues is mainly characterized by strong optical scattering and absorption. Photoacoustic microscopy is capable of achieving high‐resolution images at greater depth compared to conventional optical microscopy methods. In this work, we have developed a high‐resolution, acoustic resolution photoacoustic microscopy (AR‐PAM) system in the near infra‐red (NIR) window II (NIR‐II, eg, 1064 nm) for deep tissue imaging. Higher imaging depth is achieved as the tissue scattering at 1064 nm is lesser compared to visible or near infrared window‐I (NIR‐I). Our developed system can provide a lateral resolution of 130 μm, axial resolution of 57 μm, and image up to 11 mm deep in biological tissues. This 1064‐AR‐PAM system was used for imaging sentinel lymph node and the lymph vessel in rat. Urinary bladder of rat filled with black ink was also imaged to validate the feasibility of the developed system to study deeply seated organs.      

Principles and applications of dual source CT

This article describes the technical principles and clinical applications of dual source CT. A dual source CT (DSCT) is a CT system with two x-ray tubes and two detectors at an angle of approximately 90°. Both measurement systems acquire CT scan data simultaneously at the same anatomical level of the patient (same z-position). DSCT provides temporal resolution of approximately a quarter of the gantry rotation time for cardiac, cardio-thoracic and pediatric imaging. Successful imaging of the heart and the coronary arteries at high and variable heart rates has been demonstrated. DSCT systems can be operated at twice the spiral pitch of single source CT systems (up to pitch 3.2). The resulting high table speed is beneficial for pediatric applications and fast CT angiographic scans, e. g. of the aorta or the extremities. Operating both X-ray tubes at different tube potential (kV) enables the acquisition of dual energy data and the corresponding applications such as monoenergetic imaging and computation of material maps. Spectral separation can be improved by different filtration of the X-ray beams of both X-ray tubes. As a downside, DSCT systems have to cope with some challenges, among them the limited size of the second measurement system, and cross-scattered radiation.