Radiation Dose Reduction of Chest CT with Iterative Reconstruction in Image Space - Part I: Studies on Image Quality Using Dual Source CT

Objective

To determine whether the image quality (IQ) is improved with iterative reconstruction in image space (IRIS), and whether IRIS can be used for radiation reduction in chest CT.

Materials and Methods

Standard dose chest CT (SDCT) in 50 patients and low dose chest CT (LDCT) in another 50 patients were performed, using a dual-source CT, with 120 kVp and same reference mAs (50 mAs for SDCT and 25 mAs for LDCT) employed to both tubes by modifying a dual-energy scan mode. Full-dose data were obtained by combining the data from both tubes and half-dose data were separated from a single tube. These were reconstructed by using a filtered back projection (FBP) and IRIS: full-dose FBP (F-FBP); full-dose IRIS (F-IRIS); half-dose FBP (H-FBP) and half-dose IRIS (H-IRIS). Objective noise was measured. The subjective IQ was evaluated by radiologists for the followings: noise, contrast and sharpness of mediastinum and lung.

Results

Objective noise was significantly lower in H-IRIS than in F-FBP (p < 0.01). In both SDCT and LDCT, the IQ scores were highest in F-IRIS, followed by F-FBP, H-IRIS and H-FBP, except those for sharpness of mediastinum, which tended to be higher in FBP. When comparing CT images between the same dose and different reconstruction (F-IRIS/F-FBP and H-IRIS/H-FBP) algorithms, scores tended to be higher in IRIS than in FBP, being more distinct in half-dose images. However, despite the use of IRIS, the scores were lower in H-IRIS than in F-FBP.

Conclusion

IRIS generally helps improve the IQ, being more distinct at the reduced radiation. However, reduced radiation by half results in IQ decrease even when using IRIS in chest CT.     

双源CT双能量扫描显示胃癌的图像质量及迭代重建算法降低图像噪声的能力

目的评价不同管电压条件下双源CT(DECT)双能量扫描显示胃癌的图像质量及迭代重建成像(IRIS)技术降低图像噪声的能力。方法采用双源CT双能模式对60例经胃镜活检证实的胃癌患者行上腹平扫及双期增强扫描,获取不同管电压下的图像及融合图像;分别以FBP算法和IRIS算法重建图像,对不同算法下的CT值的差值和SNR进行统计学分析。结果动脉期和静脉期FBP-80kVp与FBP-DE图像中,胃癌与正常胃壁CT值差异有统计学意义(Z=-2.02、-2.29,P=0.04、0.02)。动脉期和静脉期FBP-80kVp与IRIS-80kVp图像的胃癌噪声、肝脏噪声差异均有统计学意义(P均<0.01)。动脉期FBP融合图像(FBP-DE)与IRIS-80kVp图像中的肝脏SNR差异无统计学意义(Z=-0.33,P=0.75),而动脉期FBP-DE与IRIS-80kVp图像中的胃癌SNR和静脉期胃癌及肝脏SNR差异均有统计学意义(P均<0.01)。结论 80kVp图像显示胃癌与正常胃壁间的CT值差异较好,有利于显示病变;利用IRIS技术可降低图像噪声,低电压与IRIS重建相结合可提高图像SNR。     

Fluorine-18 deoxyglucose and false-positive results: a major problem in the diagnostics of oncological patients

Fluorine-18 deoxyglucose (FDG) is not a very tumour-specific substance, and its accumulation in benign lesions with increased glucose metabolism may give rise to false-positive results and hence cause FDG positron emission tomography (PET) to display relatively low specificity (frequently below 85%). Correct interpretation of FDG PET studies is predicated upon detailed knowledge of morphological abnormalities, and the importance of the correlation of functional and morphological information, as derived from computed tomography or magnetic resonance imaging, is discussed. It is emphasized that image fusion programs cannot substitute for understanding of functional and morphological methods. The reconstruction of PET cross-sections is considered, and it is concluded that an iterative image reconstruction method is to be favoured, given its advantages in reducing image artefacts and improving quantification of radioactivity concentrations. The differentiation of malignant and benign lesions when using FDG PET is then reviewed; false-positive findings may be obtained, for example, in patients with acute inflammatory lesions, chronic pancretitis, retroperitoneal fibrosis or salivary gland tumours. It is suggested that these problems may be alleviated by means of multitracer studies, e.g. using carbon-11 labelled aminoisobutyric acid for quantification of A-type amino acid transport. Finally, the effects of radiotherapy and chemotherapy on FDG uptake and the problems that accrue from these effects are reviewed. Both radiotherapy and chemotherapy can cause increased FDG uptake, complicating diagnosis and evaluation. Knowledge of the effects of different treatment procedures on regional FDG metabolism is therefore necessary for correct interpretation of the PET data.     

用计算机确定双通道蓄热室的设计参数

基于Ｈａｕｓｅｎ和Ｒｕｍｍｅｌ的换热器理论，采用试差的方法，以每一层格子砖高度作为计算步长，并考虑多种因素的影响，建立了双通道蓄热室的设计计算模型，根据计算实例，提出了取得良好传热效果时格孔内的烟气流速与两通道换热面积之比。     

Conformational and electrostatic properties of V-G-G-V-G,a typical sequence of the glycine-rich regions of elastin An ab initio quantum molecular study

The conformational analysis and electrostatic properties of the monomeric sequence V-G-G-V-G of the glycine-rich regions of elastin is presented with the aim of explaining NMR and CD experimental results. On the basis of the molecular model NH₃^?-V-G-G-V-G-COO^?, Gaussian 92 quantum-molecular computations were performed by using principally an ab initio method at the 3-21G level and AM1. The occurrence of local secondary structures and of βI, βII, βII′ and VIa turns is discussed. Our results clearly demonstrate that the transconformations βI → half turn (which was invoked to explain experimental results) and βI→βII′ are theoretically allowed. © Munksgaard 1996.     

Adiabatic layering: A new concept of hierarchical multi-scale optimization

Recurrent neural networks (RNNs) with linearized dynamics have shown great promise in solving continuous valued optimization problems subject to bound constraints. Building on this progress, a novel method of constrained hierarchical multi-scale optimization is developed that applies to a wide range of optimization problems and signal decomposition tasks. Central to the underlying concept is the definition of adiabatic layering. Analytic justification of this model can be regarded as a natural development of the mean-field theory. What emerges is an alternative hierarchical optimization method that promises to improve upon existing hierarchical schemes in combining the accuracy of global optimization with the compact representation of hierarchical optimization. Whereas conventional hierarchical optimization techniques typically tend to average over fine-scale detail when applied to bound-constrained problems, such behavior is avoided by the modified dynamics of the proposed method. Applied to the signal decomposition problem of RBF approximation, the behaviour of the adiabatic layering model is shown to be in close correspondence with the theoretical expectations.     

The Group Mean SEP of Normal Human Subjects

Abstract: The following conclusions were deduced from the SEPs of 100 normal human subjects, whose mean age was 21.80 ± 1.62. It was confirmed that the waveform of a Group Mean SEP and of a Group SD each converges to a waveform different from a flat horizontal line. The waveform of the Group Mean SEP consisted of 12 components, and was roughly tetraphasic within 500 msec in latency. Large discrepancies were found in the later components between the Group Mean SEP and the Group Schematic SEPs reported by others, although some coincidences were shown in the early components within 100 msec in latency.
The results derived from the Scaled SEPs, which were converted from the (unscaled) SEPs, indicated the possibility of a reduction of the data by the Amplitude Scaling.     

Automatic point correspondence using an artificial immune system optimization technique for medical image registration

In this paper, an automatic method for determining pairs of corresponding points between medical images is proposed. The method is based on the implementation of an artificial immune system (AIS). AIS is a relatively novel, population based category of algorithms, inspired by theoretical immunologic models. When used as function optimizers, AIS have the attractive property of locating the global optimum of a function as well as a large number of strong local optimum points. In this work, AIS has been applied both for the extraction of an optimal set of candidate points on the reference image and the definition of their corresponding ones on the second image. The performance of the proposed AIS algorithm is evaluated against the widely used Iterative Closest Point (ICP) algorithm in terms of the accuracy of the obtained correspondences and in terms of the accuracy of the point-based registration by the two correspondence algorithms and the Mutual Information criterion, as an intensity-based registration method. Qualitative and quantitative results involving 92 X-ray dental and 10 retinal image pairs subject to known and unknown transformations are presented. The results indicate a superior performance of the proposed AIS algorithm with respect to the ICP algorithm and the Mutual Information, in terms of both correct correspondence and registration accuracy.     

超重患者肺动脉CT血管成像70 kV/sn150 kV联合高级模拟迭代重建的图像质量评估

目的 定量评价超重（25 kg/m²≤BMI<30 kg/m²）患者低剂量双能量（70 kV/sn150 kV）肺动脉成像中70 kVp、非线性融合联合高级模拟迭代重建（ADMIRE）图像的质量。方法 2018年10月至2019年3月行双源CT双能量肺动脉成像的可疑肺栓塞患者共70例,70 kV/sn150 kV扫描模式的体质量指数正常者及超重者各35例,对比剂用量均为30 ml。患者扫描后均获得70 kVp、150 kVp、线性融合及非线性融合图像,评估体质量指数正常者70 kVp （组1）、体质指数正常者非线性融合（组2）、超重者70 kVp （组3）、超重者非线性融合（组4）图像质量指标,包括肺动脉CT值、图像噪声（SD）、信噪比（SNR）、对比噪声比（CNR）,辐射剂量参数包括CT容积剂量指数（CTDI_vol）、剂量长度乘积（DLP）、有效剂量（E）。结果 4组肺动脉CT值差异无统计学意义（P>0.05）。段动脉SD值组1高于组4（t=2.69,P<0.05）。肺动脉主干、亚段动脉SNR值组2高于组3（t=1.44、5.40,P<0.05）。左肺动脉干SNR值组2高于组3、组4（t=1.52、1.52,P<0.05）。肺动脉主干、亚段动脉CNR值组2高于组3（t=1.45、5.01,P<0.05）。左肺动脉干CNR值组2高于组3、组4（t=1.50、1.50,P<0.05）。正常体质量指数组、超重组有效剂量为（1.60±0.54）、（1.88±0.45） mSv。结论 对于超重患者,肺动脉CT血管成像70 kV/sn150 kV双能量模式联合ADMIRE迭代重建的图像质量满足临床诊断,且对比剂用量及辐射剂量较低,是一种可行的双能量肺动脉扫描模式。     

Finite difference iterative solvers for electroencephalography: serial and parallel performance analysis

Currently the resolution of the head models used in electroencephalography (EEG) studies is limited by the speed of the forward solver. Here, we present a parallel finite difference technique that can reduce the solution time of the governing Poisson equation for a head model. Multiple processors are used to work on the problem simultaneously in order to speed up the solution and provide the memory for solving large problems. The original computational domain is divided into multiple rectangular partitions. Each partition is then assigned to a processor, which is responsible for all the computations and inter-processor communication associated with the nodes in that particular partition. Since the forward solution time is mainly spent on solving the associated matrix equation, it is desirable to find the optimum matrix solver. A detailed comparison of various iterative solvers was performed for both isotropic and anisotropic realistic head models constructed from MRI images. The conjugate gradient (CG) method preconditioned with an advanced geometric multigrid technique was found to provide the best overall performance. For an anisotropic model with 256 x 128 x 256 cells, this technique provides a speedup of 508 on 32 processors over the serial CG solution, with a speedup of 20.1 and 25.3 through multigrid preconditioning and parallelization, respectively.