Density resolution of proton computed tomography

Conformal proton radiation therapy requires accurate prediction of the Bragg peak position. Protons may be more suitable than conventional x-rays for this task since the relative electron density distribution can be measured directly with proton computed tomography (CT). However, proton CT has its own limitations, which need to be carefully studied before this technique can be introduced into routine clinical practice. In this work, we have used analytical relationships as well as the Monte Carlo simulation tool GEANT4 to study the principal resolution limits of proton CT. The noise level observed in proton CT images of a cylindrical water phantom with embedded tissue-equivalent density inhomogeneities, which were generated based on GEANT4 simulations, compared well with predictions based on Tschalar's theory of energy loss straggling. The relationship between phantom thickness, initial energy, and the relative electron density resolution was systematically investigated to estimate the proton dose needed to obtain a given density resolution. We show that a reasonable density resolution can be achieved with a relatively small dose, which is comparable to or even lower than that of x-ray CT.     

基于旋转准直器的锥形束CT散射矫正方法

针对锥形束CT（CBCT）图像质量受散射影响比较严重的情况,提出一种基于旋转准直器的CBCT散射矫正方法。该方法在射线源和模体之间放置一个圆形的旋转准直器,并通过准直器的旋转使透过准直器的射线不断沿轴向来回扫描,以获取整个容积图像的投影图像信息,然后利用投影图像的遮挡区域估计整幅图像的散射信息并将其从投影图像中去除,最后利用改进FDK算法重建图像。结果表明,与CBCT图像相比,散射矫正后的重建图像CBCT值的均方根误差从16.00%下降为1.18%,杯状伪影从14.005%下降为0.660%,峰值信噪比从16.959 4提高到31.450 0。CBCT图像质量得到明显提高。     

Pneumocystis carinii pneumonia: role of high resolution computed tomography

Pneumocystis carinii (PC) is a common opportunistic infection in renal transplant recipients and requires an early diagnosis for its successful treatment. For its definitive diagnosis PC needs to be demonstrated in bronchoalveolar lavage (BAL) fluid. At times BAL may not be possible or get delayed. In such conditions typical appearances seen on high resolution CT of the chest help in early diagnosis of PC pneumonia (PCP). This easily performed procedure helped in early diagnosis of PCP in two patients.     

Imaging of cellular spread on a three-dimensional scaffold by means of a novel cell-labeling technique for high-resolution computed tomography

Computed tomography (CT) represents a truly three-dimensional (3D) imaging technique that can provide high-resolution images on the cellular level. Thus, one approach to detect single cells is X-ray absorption-based CT, where cells are labeled with a dense, opaque material providing the required contrast for CT imaging. Within the present work, a novel cell-labeling method has been developed showing the feasibility of labeling fixed cells with iron oxide (FeO) particles for subsequent CT imaging and quantitative morphometry. A biotin-streptavidin detection system was exploited to bind FeO particles to its target endothelial cells. The binding of the particles was predominantly close to the cell centers on 2D surfaces as shown by light microscopy, scanning electron microscopy, and CT. When cells were cultured on porous, 3D polyurethane surfaces, significantly more FeO particles were detected compared with surfaces without cells and FeO particle labeling using CT. Here, we report on the implementation and evaluation of a novel cell detection method based on high-resolution CT. This system has potential in cell tracking for 3D in vitro imaging in the future.     

Optimal noise control in and fast reconstruction of fan-beam computed tomography image.

We proposed a linear approach that exploits statistically complementary information inherent in the projection data of fan-beam computed tomography (CT) for achieving a bias-free image-variance reduction in fan-beam CT. This linear approach leads to the development of infinite classes of hybrid algorithms for image reconstruction in fan-beam CT. These hybrid algorithms are computationally more efficient and numerically less susceptible to data noise and to the effect of finite sampling than the conventional fan-beam filtered back-projection (FFBP) algorithm. We also developed infinite classes of generalized fan-beam filtered back-projection (GFFBP) algorithms, which include the conventional FFBP algorithm as a special member. We demonstrated theoretically and quantitatively that the hybrid and GFFBP algorithms are identical (or different) in the absence (or presence) of data noise and of the effect of finite sampling. More importantly, we identified the statistically optimal hybrid algorithm that may have potentially significant implication to image reconstruction in fan-beam CT. Extensive numerical results of computer-simulation studies validated our theoretical results.     

HRCT在肺单发性磨玻璃样病灶鉴别诊断中的价值分析

目的:探讨肺单发性磨玻璃样病灶(solitary pulmonary ground glass opacity,spGGO)的计算机断层扫描(computed tomography, CT)影像学表现与其良恶性的关系.方法:收集196例手术治疗的spGGO患的临床资料.回顾性分析病灶的CT影像学特征,包括肿瘤大小、内部结构(空泡征、支气管充气征)、毛刺征、病变分叶征、血管集束征、胸膜凹陷征.对照CT与病理结果,总结影像学特征与GGO性质的关系.结果:良恶性GGO患的CT空泡征、支气管充气征表现的差异无统计学意义(P>0.05).在肿瘤的大小、分叶征、毛刺征、胸膜凹陷征、血管集束征的表现方面,其差异具有统计学意义(P<0.05).结论:GGO的影像学特征上,直径越大其恶性可能性越大,病变的分叶、毛刺征、胸膜凹陷征和血管集束征可作为恶性GGO的特征.     

Accurate technique for complete geometric calibration of cone-beam computed tomography systems

Cone-beam computed tomography systems have been developed to provide in situ imaging for the purpose of guiding radiation therapy. Clinical systems have been constructed using this approach, a clinical linear accelerator (Elekta Synergy RP) and an iso-centric C-arm. Geometric calibration involves the estimation of a set of parameters that describes the geometry of such systems, and is essential for accurate image reconstruction. We have developed a general analytic algorithm and corresponding calibration phantom for estimating these geometric parameters in cone-beam computed tomography (CT) systems. The performance of the calibration algorithm is evaluated and its application is discussed. The algorithm makes use of a calibration phantom to estimate the geometric parameters of the system. The phantom consists of 24 steel ball bearings (BBs) in a known geometry. Twelve BBs are spaced evenly at 30 deg in two plane-parallel circles separated by a given distance along the tube axis. The detector (e.g., a flat panel detector) is assumed to have no spatial distortion. The method estimates geometric parameters including the position of the x-ray source, position, and rotation of the detector, and gantry angle, and can describe complex source-detector trajectories. The accuracy and sensitivity of the calibration algorithm was analyzed. The calibration algorithm estimates geometric parameters in a high level of accuracy such that the quality of CT reconstruction is not degraded by the error of estimation. Sensitivity analysis shows uncertainty of 0.01 degrees (around beam direction) to 0.3 degrees (normal to the beam direction) in rotation, and 0.2 mm (orthogonal to the beam direction) to 4.9 mm (beam direction) in position for the medical linear accelerator geometry. Experimental measurements using a laboratory bench Cone-beam CT system of known geometry demonstrate the sensitivity of the method in detecting small changes in the imaging geometry with an uncertainty of 0.1 mm in transverse and vertical (perpendicular to the beam direction) and 1.0 mm in the longitudinal (beam axis) directions. The calibration algorithm was compared to a previously reported method, which uses one ball bearing at the isocenter of the system, to investigate the impact of more precise calibration on the image quality of cone-beam CT reconstruction. A thin steel wire located inside the calibration phantom was imaged on the conebeam CT lab bench with and without perturbations in source and detector position during the scan. The described calibration method improved the quality of the image and the geometric accuracy of the object reconstructed, improving the full width at half maximum of the wire by 27.5% and increasing contrast of the wire by 52.8%. The proposed method is not limited to the geometric calibration of cone-beam CT systems but can be used for many other systems, which consist of one or more point sources and area detectors such as calibration of megavoltage (MV) treatment system (focal spot movement during the beam delivery, MV source trajectory versus gantry angle, the axis of collimator rotation, and couch motion), cross calibration between Kilovolt imaging and MV treatment system, and cross calibration between multiple imaging systems. Using the complete information of the system geometry, it was demonstrated that high image quality in CT reconstructions is possible even in systems with large geometric nonidealities.     

Neutron-stimulated emission computed tomography of a multi-element phantom

This paper describes the implementation of neutron-stimulated emission computed tomography (NSECT) for non-invasive imaging and reconstruction of a multi-element phantom. The experimental apparatus and process for acquisition of multi-spectral projection data are described along with the reconstruction algorithm and images of the two elements in the phantom. Independent tomographic reconstruction of each element of the multi-element phantom was performed successfully. This reconstruction result is the first of its kind and provides encouraging proof of concept for proposed subsequent spectroscopic tomography of biological samples using NSECT.     

Extreme preconditioning: cold adaptation through sea swimming as a means to improving surgical outcomes

The practice of sea bathing for its health benefits was popularised by Richard Russell in Regency Brighton during the 18th Century. Although the cures he claimed it could effect seem a little far-fetched today, as with many historical remedies, there is much to be gained from revisiting such theories in the light of modern medical research. In this paper I will draw parallels between the surgical stress response and the response to cold exposure and hypothesise how a programme of sea bathing may be used to enhance postoperative recovery and reduce preoperative complications.     

Comparative study of a low-Z cone-beam computed tomography system

Computed tomography images have been acquired using an experimental (low atomic number (Z) insert) megavoltage cone-beam imaging system. These images have been compared with standard megavoltage and kilovoltage imaging systems. The experimental system requires a simple modification to the 4 MeV electron beam from an Elekta Precise linac. Low-energy photons are produced in the standard medium-Z electron window and a low-Z carbon electron absorber located after the window. The carbon electron absorber produces photons as well as ensuring that all remaining electrons from the source are removed. A detector sensitive to diagnostic x-ray energies is also employed. Quantitative assessment of cone-beam computed tomography (CBCT) contrast shows that the low-Z imaging system is an order of magnitude or more superior to a standard 6 MV imaging system. CBCT data with the same contrast-to-noise ratio as a kilovoltage imaging system (0.15 cGy) can be obtained in doses of 11 and 244 cGy for the experimental and standard 6 MV systems, respectively. Whilst these doses are high for everyday imaging, qualitative images indicate that kilovoltage like images suitable for patient positioning can be acquired in radiation doses of 1-8 cGy with the experimental low-Z system.     

Clinical significance of pattern types in high resolution computed tomography images of patients with idiopathic pulmonary fibrosis

The aim of the study was to assess significance of two types of HRCT pattern in patients with idiopathic pulmonary fibrosis (IPF), corresponding to usual interstitial pneumonia. The study population consisted of 34 patients, 11 women and 23 men, mean age 64.5 +/- 10.5 years. The patients were divided into two groups according to HRCT appearance: Group A--reticular pattern with some ground-glass attenuation (30 patients); group B--reticular pattern only (4 patients). Age, level of dyspnea, pulmonary function tests were similar in both groups. Longer history of dyspnea and more frequent finger clubbing (all patients) were found in Group B. 30 patients were followed-up for at least 12 months. In this period 4 out of 27 patients died in Group A, and 2 out of 3 patients died in Group B (p < 0.05). CONCLUSION: HRCT showing reticular pattern only corresponds to late phase of IPF and is connected with very short survival.     

Monte Carlo simulation of a computed tomography x-ray tube

The dose delivered to patients during computed tomography (CT) exams has increased in the past decade. With the increasing complexity of CT examinations, measurement of the dose becomes more difficult and more important. In some cases, the standard methods, such as measurement of the computed tomography dose index (CTDI), are currently under question. One approach to determine the dose from CT exams is to use Monte Carlo (MC) methods. Since the patient geometry can be included in the model, Monte Carlo simulations are potentially the most accurate method of determining the dose delivered to patients. In this work, we developed a MC model of a CT x-ray tube. The model was validated with half-value layer (HVL) measurements and spectral measurements with a high resolution Schottky CdTe spectrometer. First and second HVL for beams without additional filtration calculated from the MC modelled spectra and determined from attenuation measurements differ by less than 2.5%. The differences between the first and second HVL for both filtered and non-filtered beams calculated from the MC modelled spectra and spectral measurements with the CdTe detector were less than 1.8%. The MC modelled spectra match the directly measured spectra. This works presents a first step towards an accurate MC model of a CT scanner.     

Nanoparticulate carrier containing water-insoluble iodinated oil as a multifunctional contrast agent for computed tomography imaging

Contrast-enhanced computed tomography (CT) imaging is a valuable and routine strategy for the clinical diagnosis of various diseases. However, all current CT contrast agents are liquids, so they flow through the blood vessels and disappear very quickly by extravasation. If it were possible to make a blood-compatible particulate contrast agent, we could highlight a particular tissue by either passive or active targeting. In this work, Pluronic F127 and a naturally iodinated compound, Lipiodol, were used to form radiopaque nanoreservoir structures. The resultant nanoparticles have a stable structure at high concentrations, sufficient X-ray absorption, a safety profile similar to or better than that of Iopromide, and a longer circulation time than commercial iodinated preparations. The utility of the resultant radiopaque nanoparticles as a contrast agent was tested using micro-SPECT/CT imaging in vivo. Together with the very good solubility of hydrophobic drugs (e.g., Taxol) in Lipiodol, these results suggest the possibility that these particulate structures and their bioconjugates could become functional CT contrast agents that could deliver therapeutic agents to a particular tissue.     

The effect of computed tomography noise and tissue heterogeneity on cerebral blood flow determination by xenon-enhanced computed tomography

The errors associated with derivation of cerebral blood flow values by the xenon-enhanced computed tomography (CT) method have been evaluated as a function of tissue heterogeneity and CT noise. The results of this study indicate that CT noise introduces large errors in the derived flow value when data for a single, unprocessed voxel are used for this purpose. CT noise increases the derived flow values in a systematic way. Tissue heterogeneity results in a systematic error which lowers the derived flow values. Errors due to both parameters are computed for typical and extreme conditions.     

Correction of hyperlipidemia in patients with cholelithiasis as a means of improving the results of extracorporeal lithotripsy

The results of treatment of patients with uncomplicated cholelithiasis by extracorporeal lithotripsy are analyzed. Clinical evidence confirming the relationship between hyperlipidemia and cholelithiasis is presented. The number of recurrences is foudn to decrease considerably after extracorporeal lithotripsy for judicious correction of hyperlipoproteinemia. Presented by V. S. Savel'ev, Member of the Russian Academy of Medical Sciences Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 118, N ^o 11, pp. 555–558, November, 1994     

一种提高直肠癌诊断精度的基于U型网络和残差块的电子计算机断层扫描图像分割算法EI北大核心CSCD

作为确定病灶与诊断的重要基础,医学图像分割已成为生物医学领域中极其重要的热门研究领域之一,其中基于全卷积神经网络和U型网络(U-net)等神经网络的医学图像分割算法得到越来越多研究人员的重视。目前,医学图像分割算法应用于直肠癌诊断的研究报道较少,且已有的研究对直肠癌的分割结果精度不高。本文提出了一种结合图像裁剪和预处理方法的编码—解码卷积网络模型。该模型在U型网络的基础上,借鉴残差网络思想,用残差块代替传统的卷积块,有效避免了梯度消失的问题。此外,本文还采用了图像增广的方法提高了所提模型的泛化能力,并在"泰迪杯"数据挖掘挑战赛所提供的数据集进行测试。测试结果表明,本文提出的基于残差块的改进U型网络模型结合图像裁剪预处理,可以大大提高直肠癌的分割精度,得到的戴斯系数在验证集上达到0.97。