A virtual imaging platform for multi-modality medical image simulation.

This paper presents the Virtual Imaging Platform (VIP), a platform accessible at http://vip.creatis.insa-lyon.fr to facilitate the sharing of object models and medical image simulators, and to provide access to distributed computing and storage resources. A complete overview is presented, describing the ontologies designed to share models in a common repository, the workflow template used to integrate simulators, and the tools and strategies used to exploit computing and storage resources. Simulation results obtained in four image modalities and with different models show that VIP is versatile and robust enough to support large simulations. The platform currently has 200 registered users who consumed 33 years of CPU time in 2011.

Measurement of two-dimensional movement parameters of the carotid artery wall for early detection of arteriosclerosis: a preliminary clinical study.

The aim of this study was to clinically investigate the association between the risk factors of early-stage atherosclerosis and the two-dimensional (2-D) movement of the artery wall. To meet this objective, a speckle tracking approach for the estimation of the 2-D trajectory of the vessel wall was proposed and applied to B-mode ultrasound (US) sequences of the left common carotid artery (CCA). A deformable skeleton model was also introduced in the block matching scheme. Finally, the 2-D movements of both proximal and distal walls were investigated in three different local regions, with 1.5 × 0.3 mm(2) kernel blocks. A clinical study was conducted in which two different populations (26 young healthy volunteers and 26 older diabetic patients) were studied. The results show that the mean amplitude value of the diameter change ΔD, of the longitudinal displacement of the proximal wall ΔX(p) and of the longitudinal displacement of the distal wall ΔX(d) were 0.65 ± 0.17 vs. 0.41 ± 0.12 mm (p < 0.001), 0.48 ± 0.21 vs. 0.26 ± 0.18 mm (p < 0.001) and 0.48 ± 0.20 vs. 0.35 ± 0.23 mm (p = 0.006) for the young healthy volunteers and the older diabetic patients, respectively. The results of the three dynamic parameters ΔD, ΔX(p) and ΔX(d) were systematically and significantly lower for the diabetic subjects, respectively 37%, 46% and 27%. The method introduced in this feasibility study might constitute a pertinent approach to assess the presence of early-stage arteriosclerosis by the noninvasive estimation of the 2-D motion of the intima-media complex in the CCA.

A quantitative study to design an experimental setup for photoacoustic imaging.

During the last decade, a new modality called photoacoustic imaging has emerged. The increasing interest for this new modality is due to the fact that it combines advantages of ultrasound and optical imaging, i.e. the high contrast due to optical absorption and the low acoustic attenuation in biological tissues. It is thus possible to study vascularization because blood has high optical absorption coefficient. Papers in the literature often focus on applications and rarely discuss quantitative parameters. The goal of this paper is to provide quantitative elements to design an acquisition setup. By defining the targeted resolution and penetration depth, it is then possible to evaluate which kind of excitation and reception systems have to be used. First, we recall theoretical background related to photoacoustic effect before to describe the experiments based on a nanosecond laser at 1064 nm and 2.25-5 MHz transducers. Second, we present results about the relation linking fluence laser to signal amplitude and axial and lateral resolutions of our acquisition setup. We verify the linear relation between fluence and amplitude before to estimate axial resolution at 550 µm for a 2.25 MHz ultrasonic transducer. Concerning lateral resolution, we show that a reconstruction technique based on curvilinear acquisition of 30 lines improves it by a factor of 3 compared to a lateral displacement. Future works will include improvement of lateral resolution using probes, like in ultrasound imaging, instead of single-element transducers.

Blood flow evaluation in high-frequency, 40 MHz imaging: a comparative study of four vector velocity estimation methods.

Ultrasonic imaging is often used to estimate blood flow velocity. Currently, estimates are carried out using Doppler-based techniques. However, there are a number of shortcomings such as the limited spatial resolution and the inability to estimate longitudinal flows. Thus, alternative methods have been proposed to overcome them. Difficulties are notably encountered with high-frequency imaging systems that use swept-scan techniques. In this article, we propose to compare four vector velocity estimation methods that are complementary to Doppler, focusing on 40 MHz, high-frequency imaging. The goal of this study is to evaluate which method could circumvent the limitations of Doppler methods for evaluation of microcirculation, in the vessels having diameter on the order of 1 mm. We used two region-based approaches, one decorrelation-based approach and one spatiotemporal approach. Each method has been applied to seven flow sequences with various orientations and mean velocities. Four sequences were simulated with a system approach based on a 3D set of moving scatterers. Three experimental sequences were carried out by injecting blood-mimicking fluid within a gelatin phantom and then acquiring images with Visualsonics, Vevo 660 system. From velocity estimates, several performance criteria such as the normalized mean error or the normalized mean standard deviation were defined to compare the performance of the four estimators. The results show that region-based methods are the most accurate exhibiting mean errors less than 10% and mean standard deviation less than 13%. However, region-based approaches are those that require the highest calculative cost compared to the decorrelation-based method, which is the fastest. Finally, the spatiotemporal approach appeared to be a trade-off in terms of computational complexity and accuracy of estimates. It provides estimates with errors less than 10% for mean velocity and the CPU time is approximately 17s for a ROI of size 40*80 pixels.

Toward a real-time simulation of ultrasound image sequences based on a 3-D set of moving scatterers.

Data simulation is an important research tool to evaluate algorithms. Two types of methods are currently used to simulate medical ultrasound data: those based on acoustic models and those based on convolution models. The simulation of ultrasound data sequences is very time-consuming. In addition, many applications require accounting for the out-of-plane motion induced by the 3-D displacement of scatterers. The purpose of this paper is to propose a model adapted to a fast simulation of ultrasonic data sequences with 3-D moving scatterers. Our approach is based on the convolution model. The scatterers are moved in a 3-D continuous medium between each pair of images and then projected onto the imaging plane before being convolved. This paper discusses the practical implementation of the convolution that can be performed directly or after a grid approximation. The grid approximation convolution is obviously faster than the direct convolution but generates errors resulting from the approximation to the grid's nodes. We provide the analytical expression of these errors and then define 2 intensity-based criteria to quantify them as a function of the spatial sampling. The simulation of an image requires less than 2 s with oversampling, thus reducing these errors. The simulation model is validated with first- and second-order statistics. The positions of the scatterers at each imaging time can be provided by a displacement model. An example applied to flow imaging is proposed. Several cases are used to show that this displacement model provides realistic data. It is validated with speckle tracking, a well-known motion estimator in ultrasound imaging.