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。     

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.     

生物组织光声粘弹显微成像

提出一种反演生物组织粘弹信息的新型无损光声粘弹显微成像方法,它是以强度调制激光作为激发源,通过检测光声（Photoacoustic,PA）信号的相位重建组织粘弹特性分布的成像方法.实验利用不同浓度的琼脂样品来验证光声粘弹显微测量中相位随浓度变化的依赖关系.利用埋有头发丝的琼脂样品来测试这种显微方法的成像分辨率.利用具有不同粘弹性的离体生物组织来验证系统的成像能力.实验结果表明,这种新方法能够高分辨率和高对比度地重建出具有不同粘弹性的生物组织的光声粘弹显微图像,有望实现组织结晶类病变水平的显微在体检测.     

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。     

一种提高乳腺扩散光学层析成像分辨率的方式

目的 扩散光学层析成像（diffuse optical tomography,DOT）在女性大尺寸乳腺检测时因信噪比低,导致其成像分辨率较低。本文基于计算机断层扫描激光乳腺成像系统（computed tomography laser mammography,CTLM）,提出一种提高乳腺扩散光学层析成像分辨率的方式。方法 本文首先通过仿体实验探讨仿体直径和目标深度对扩散光学层析成像分辨率的影响;其次,本文使用高透性的光敏树脂通过3D打印制作外壳定位件,在验证其对扩散光学层析成像分辨率无显著影响后,利用外壳定位件对被测物进行约束压缩,以减小被测物直径来提高信噪比,优化扩散光学层析成像分辨率。结果 本文通过仿体实验验证了仿体直径的增加和目标深度的变化均会在一定程度上影响成像分辨率,随着仿体直径的增加,其感兴趣区（region of interests,ROIs）宽轴和长轴半高宽基本属于上升趋势;随着目标深度的增加,也会对ROIs宽轴和长轴半高宽产生影响。同时发现仿体直径对ROIs长轴半高宽有显著影响,目标深度对ROIs宽轴半高宽有显著影响。另外通过仿体实验结果验证了外壳定位件对扩散光学层析成像分辨率无显著影响,利用外壳定位件约束压缩后ROIs长轴半高宽降幅明显,降幅达到30%以上,远大于宽轴半高宽的降幅,达到了提高成像分辨率的作用。结论 本文所提出的方式能够达到提高乳腺扩散光学层析成像分辨率的作用,且所使用的材料和方法简单,具有较强的可实施性,为提高乳腺扩散光层析成像分辨率提供了新思路。     

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。     

多波长光声层析成像技术用于人体气管探测

目的 通过多波长光声层析成像技术对气管结构进行重建成像.方法 基于阵列换能器的光声成像技术对7名志愿者的气管进行了多波长光声层析成像实验,研究光声层析成像技术对气管不同呼吸相、不同层面的高分辨率(高达150 μm)图像特征,并对该技术的成像优劣性进行评价.结果 光声层析成像技术能对人体气管进行清晰成像,能够真实反映气管...     

基于环形阵列探测器的快速光声成像

构建一套基于环形阵探测器的快速光声成像系统用于生物组织的结构成像。该系统以环形阵探测器探测光声信号,采用八通道的采集系统采集光声信号,再利用有限场滤波反投影算法重建光声图像。利用埋有铅笔芯的琼脂样品来测试该系统的分辨率,利用离体猪眼和在体老鼠头部血管成像来验证系统的成像能力。实验结果表明,该系统能方便快速地实现生物组织的结构成像,有望实现早期乳腺癌的临床检测应用。     

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。     

Enhancement of soft-tissue contrast in cone-beam CT using an anti-scatter grid with a sparse sampling approach

PurposeAnti-scatter grids suppress the scatter substantially thus improving image contrast in radiography. However, its active use in cone-beam CT for the purpose of improving contrast-to-noise ratio (CNR) has not been successful mainly due to the increased noise related to Poisson statistics of photons. This paper proposes a sparse-view scanning approach to address the above issue.MethodCompared to the conventional cone-beam CT imaging framework, the proposed method reduces the number of projections and increases exposure in each projection to enhance image quality without an additional cost of radiation dose to patients. For image reconstruction from sparse-view data, an adaptive-steepest-descent projection-onto-convex-sets (ASD POCS) algorithm regularized by total-variation (TV) minimization was adopted. Contrast and CNR with various scattering conditions were evaluated in projection domain by a simulation study using GATE. Then we evaluated contrast, resolution, and image uniformity in CT image domain with Catphan phantom. A head phantom with soft-tissue structures was also employed for demonstrating a realistic application. A virtual grid-based estimation and reduction of scatter has also been implemented for comparison with the real anti-scatter grid.ResultsIn the projection domain evaluation, contrast and CNR enhancement was observed when using an anti-scatter grid compared to the virtual grid. In the CT image domain, the proposed method produced substantially higher contrast and CNR of the low-contrast structures with much improved image uniformity.ConclusionWe have shown that the proposed method can provide high-quality CBCT images particularly with an increased contrast of soft-tissue at a neutral dose for image-guidance.     

Multi-parametric fit method in reconstruction of brachytherapy needles

PurposeTo adapt the multi-parametric fit method to reconstruct brachytherapy needles inserted with free hand technique for treatment of surface malignancies.MethodsAn alternative reconstruction method for brachytherapy (BT) needles is presented. The method is based on the digitized tip and end coordinates on pairs of posterior-anterior and posterior-oblique reconstruction images obtained with a non-isocentric C-arm. The needles tip and end coordinates are computed with the multi-parametric fit method that also incorporates the determination of the magnification factors of the reconstruction images. We tested the reconstruction accuracy with radio-opaque markers inserted into known positions. The range of C-arm angles that resulted in an accurate reconstruction was also investigated. We applied the method in treatments of the vulvar cancer using 3 to 5 pieces of BT needles located in a distance of approximately 1 cm.ResultsThe phantom test showed largest difference between the reconstructed and expected distance between the simulated needles ±1.3 mm. In vulvar insertions, the reconstructed position of the BT needles obtained with different image pairs agreed within 3 mm.ConclusionThe reconstruction accuracy of the multi-parametric fit method in with proper imaging is suitable for the clinical use.     

An iterative deconvolution algorithm for image recovery in clinical CT: A phantom study

PurposeTo study the feasibility of using an iterative reconstruction algorithm to improve previously reconstructed CT images which are judged to be non-diagnostic on clinical review. A novel rapidly converging, iterative algorithm (RSEMD) to reduce noise as compared with standard filtered back-projection algorithm has been developed.Materials and methodsThe RSEMD method was tested on in-silico, Catphan^®500, and anthropomorphic 4D XCAT phantoms. The method was applied to noisy CT images previously reconstructed with FBP to determine improvements in SNR and CNR. To test the potential improvement in clinically relevant CT images, 4D XCAT phantom images were used to simulate a small, low contrast lesion placed in the liver.ResultsIn all of the phantom studies the images proved to have higher resolution and lower noise as compared with images reconstructed by conventional FBP. In general, the values of SNR and CNR reached a plateau at around 20 iterations with an improvement factor of about 1.5 for in noisy CT images. Improvements in lesion conspicuity after the application of RSEMD have also been demonstrated. The results obtained with the RSEMD method are in agreement with other iterative algorithms employed either in image space or with hybrid reconstruction algorithms.ConclusionsIn this proof of concept work, a rapidly converging, iterative deconvolution algorithm with a novel resolution subsets-based approach that operates on DICOM CT images has been demonstrated. The RSEMD method can be applied to sub-optimal routine-dose clinical CT images to improve image quality to potentially diagnostically acceptable levels.     

Development of a 3D optical scanner for evaluating patient-specific dose distributions

PurposeThis paper describes the hardware and software characteristics of a 3D optical scanner (P3DS) developed in-house. The P3DS consists of an LED light source, diffuse screen, step motor, CCD camera, and scanner management software with 3D reconstructed software.Materials and methodWe performed optical simulation, 2D and 3D reconstruction image testing, and pre-clinical testing for the P3DS. We developed the optical scanner with three key characteristics in mind. First, we developed a continuous scanning method to expand possible clinical applications. Second, we manufactured a collimator to improve image quality by reducing scattering from the light source. Third, we developed an optical scanner with changeable camera positioning to enable acquisition of optimal images according to the size of the gel dosimeter.ResultsWe confirmed ray-tracing in P3DS with optic simulation and found that 2D projection and 3D reconstructed images were qualitatively similar to the phantom images. For pre-clinical tests, the dose distribution and profile showed good agreement among RTP, optical CT, and external beam radiotherapy film data for the axial and coronal views. The P3DS has shown that it can scan and reconstruct for evaluation of the gel dosimeter within 1 min. We confirmed that the P3DS system is a useful tool for the measurement of 3D dose distributions for 3D radiation therapy QA. Further experiments are needed to investigate quantitative analysis for 3D dose distribution.     

Reduction of Metal Artifact in Single Photon-Counting Computed Tomography by Spectral-Driven Iterative Reconstruction Technique

PurposeThe exciting prospect of Spectral CT (SCT) using photon-counting detectors (PCD) will lead to new techniques in computed tomography (CT) that take advantage of the additional spectral information provided. We introduce a method to reduce metal artifact in X-ray tomography by incorporating knowledge obtained from SCT into a statistical iterative reconstruction scheme. We call our method Spectral-driven Iterative Reconstruction (SPIR).MethodThe proposed algorithm consists of two main components: material decomposition and penalized maximum likelihood iterative reconstruction. In this study, the spectral data acquisitions with an energy-resolving PCD were simulated using a Monte-Carlo simulator based on EGSnrc C++ class library. A jaw phantom with a dental implant made of gold was used as an object in this study. A total of three dental implant shapes were simulated separately to test the influence of prior knowledge on the overall performance of the algorithm. The generated projection data was first decomposed into three basis functions: photoelectric absorption, Compton scattering and attenuation of gold. A pseudo-monochromatic sinogram was calculated and used as input in the reconstruction, while the spatial information of the gold implant was used as a prior. The results from the algorithm were assessed and benchmarked with state-of-the-art reconstruction methods.ResultsDecomposition results illustrate that gold implant of any shape can be distinguished from other components of the phantom. Additionally, the result from the penalized maximum likelihood iterative reconstruction shows that artifacts are significantly reduced in SPIR reconstructed slices in comparison to other known techniques, while at the same time details around the implant are preserved. Quantitatively, the SPIR algorithm best reflects the true attenuation value in comparison to other algorithms.ConclusionIt is demonstrated that the combination of the additional information from Spectral CT and statistical reconstruction can significantly improve image quality, especially streaking artifacts caused by the presence of materials with high atomic numbers.     

Quantifying near metal visibility using dual energy computed tomography and iterative metal artifact reduction in a fracture phantom

PurposeTo quantitatively assess CT image quality and fracture visibility using virtual monochromatic imaging and iterative metal artifact reduction (iMAR) in a femoral bone fracture phantom with different fixation implants.MethodsA custom made phantom was scanned at 120-kVp and 140-kVp single-energy and 100/150-kVp dual-energy. Three stainless steel and two titanium implants with different thicknesses were placed on the phantom containing simulated one and two mm fractures. Single-energy CT images were reconstructed with and without iMAR, while DECT images were reconstructed at monochromatic energies between 70 and 190 keV. Non-metal scans were used as a reference. A Fourier power spectrum method and fracture model were used to analyze several anatomical areas.ResultsCT-value deviations of titanium implants were much lower compared to stainless steel implants. These deviations decreased for both DECT and iMAR. Fracture visibility, measured with the fracture model, improved the most when DECT was used while artifact reduction benefitted more from iMAR. The optimal monochromatic energy for metal artifact reduction, based on CT-value deviation, varied for each metal between 130 and 150 keV. The fracture model provided a signal-to-noise ratio for the near metal fracture visibility, providing the optimal keV.ConclusioniMAR and high keV monochromatic images extracted from DECT both reduce metal artifacts caused by different metal fixation implants. Quantitative femoral phantom results show that DECT is superior to iMAR regarding fracture visualization adjacent to metal fixation implants. The introduction of new artifacts when using iMAR impedes its value in near metal fixation implant imaging.     

Virtual patient 3D dose reconstruction using in air EPID measurements and a back-projection algorithm for IMRT and VMAT treatments

PurposeAt our institute, a transit back-projection algorithm is used clinically to reconstruct in vivo patient and in phantom 3D dose distributions using EPID measurements behind a patient or a polystyrene slab phantom, respectively. In this study, an extension to this algorithm is presented whereby in air EPID measurements are used in combination with CT data to reconstruct ‘virtual’ 3D dose distributions. By combining virtual and in vivo patient verification data for the same treatment, patient-related errors can be separated from machine, planning and model errors.Methods and materialsThe virtual back-projection algorithm is described and verified against the transit algorithm with measurements made behind a slab phantom, against dose measurements made with an ionization chamber and with the OCTAVIUS 4D system, as well as against TPS patient data. Virtual and in vivo patient dose verification results are also compared.ResultsVirtual dose reconstructions agree within 1% with ionization chamber measurements. The average γ-pass rate values (3% global dose/3 mm) in the 3D dose comparison with the OCTAVIUS 4D system and the TPS patient data are 98.5 ± 1.9%(1SD) and 97.1 ± 2.9%(1SD), respectively. For virtual patient dose reconstructions, the differences with the TPS in median dose to the PTV remain within 4%.ConclusionsVirtual patient dose reconstruction makes pre-treatment verification based on deviations of DVH parameters feasible and eliminates the need for phantom positioning and re-planning. Virtual patient dose reconstructions have additional value in the inspection of in vivo deviations, particularly in situations where CBCT data is not available (or not conclusive).     

Few-view CT reconstruction via a novel non-local means algorithm

PurposeNon-local means (NLM) based reconstruction method is a promising algorithm for few-view computed tomography (CT) reconstruction, but often suffers from over-smoothed image edges. To address this problem, an adaptive NLM reconstruction method based on rotational invariance (ART-RIANLM) is proposed.MethodsThe method consists of four steps: 1) Initializing parameters; 2) ART reconstruction using raw data; 3) Positivity constraint of the reconstructed image; 4) Image updating by RIANLM filtering. In RIANLM, two kinds of rotational invariance measures which are average gradient (AG) and region homogeneity (RH) are proposed to calculate the distance between two patches and a novel NLM filter is developed to avoid over-smoothed image. Moreover, the parameter h in RIANLM which controls the decay of the weights is adaptive to avoid over-smoothness, while it is constant in NLM during the whole reconstruction process. The proposed method is validated on two digital phantoms and real projection data.ResultsIn our experiments, the searching neighborhood size is set as 15 × 15 and the similarity window is set as 3 × 3. For the simulated case of Shepp-Logan phantom, ART-RIANLM produces higher SNR (36.23 dB > 24.00 dB) and lower MAE (0.0006 < 0.0024) reconstructed images than ART-NLM. The visual inspection demonstrated that the proposed method could suppress artifacts or noises more effectively and recover image edges better. The result of real data case is also consistent with the simulation result.ConclusionsA RIANLM based reconstruction method for few-view CT is presented. Compared to the traditional ART-NLM method, SNR and MAE from ART-RIANLM increases 51% and decreases 75%, respectively.