Robust femur condyle disambiguation on biplanar X-rays

Three-dimensional (3D) reconstruction of the skeleton from biplanar X-rays relies on scarce information digitalised by an operator on both frontal and lateral radiographs. In clinical routine, difficulties occur for non-skilled operators to discriminate the medial from the lateral femur condyle on the lateral view. Our study proposes an algorithm able to detect automatically a possible inversion of the two condyles by the operator at an early stage of the reconstruction process. It relies on the computation of two 3D femur surfaces, one directly from the operator digitalisation and the other from the same digitalisation with medial and lateral condyles automatically swapped. Pairs of virtual biplanar X-rays are computed for both reconstructions and the closest pair to the original X-rays is selected on the basis of similarity measures, pointing the correct 3D surface. The algorithm shows a success rate higher than 85% for both asymptomatic and pathological femurs whatever the initial condyle digitalisation of the operator, bringing automatically non-skilled operators acting in clinical routine to the level of skilled operators. This study validates moreover the proof-of-concept of automatic shape adjustments of a 3D surface on the basis of similarity measures in the process of 3D reconstruction from biplanar X-rays.     

3D reconstruction of the spine from biplanar X-rays using parametric models based on transversal and longitudinal inferences

Reconstruction methods from biplanar X-rays provide 3D analysis of spinal deformities for patients in standing position with a low radiation dose. However, such methods require an important reconstruction time and there is a clinical need for fast and accurate techniques. This study proposes and evaluates a novel reconstruction method of the spine from biplanar X-rays. The approach uses parametric models based on longitudinal and transversal inferences.A first reconstruction level, dedicated to routine clinical use, allows to get a fast estimate (reconstruction time: 2 min 30 s) of the 3D reconstruction and accurate clinical measurements. The clinical measurements precision (evaluated on asymptomatic subjects, moderate and severe scolioses) was between 1.2° and 5.6°.For a more accurate 3D reconstruction (complex pathologies or research purposes), a second reconstruction level can be obtained within a reduced reconstruction time (10 min) with a fine adjustment of the 3D models. The mean shape accuracy in comparison with CT-scan was 1.0 mm. The 3D reconstruction method precision was 1.8 mm for the vertebrae position and between 2.3° and 3.9° for the orientation.With a reduced reconstruction time, an improved accuracy and precision and a method proposing two reconstruction levels, this approach is efficient for both clinical routine uses and research purposes.     

双侧股骨近端对称性及解剖形态的三维重建研究

目的建立正常成人双侧股骨近端的三维模型,分析双侧股骨近端形态并测量解剖形态的相关参数,研究双侧股骨近端的对称性及解剖形态。方法选取50例正常成人双侧股骨近端CT扫描数据,其中男性27例,女性23例;年龄20～65岁,平均年龄44.52岁。扫描参数:扫描层厚0.625 mm,扫描电压120 kV,扫描电流100 mA。扫描范围:自双侧股骨头上10 mm至小转子中点平面下50 mm。将双侧股骨近端CT薄层扫描数据利用Mimics 10.01软件进行三维重建,将左侧股骨与右侧股骨镜像模型相配准,对配准后模型进行三维测量,并测量左右股骨近端的形态参数,使用SPSS 16.0软件对测量结果进行统计分析。结果股骨近端形态和髓腔内部结构有明显的个体差异性,双侧股骨近端形态及内部结构具有高度对称性。股骨头直径为(45.71±4.08)mm,股骨头高度为(53.61±5.43)mm,偏心距为(39.91±5.07)mm,股骨颈中央直径为(36.71±3.75)mm,颈干角为(127.88±6.28)°,股骨颈长度(46.61±4.74)mm,小粗隆中点所在平面的髓腔内径为(26.21±4.59)mm,其中偏心距、颈干角与白种人形态参数相比,差异有显著统计学意义(P<0.01);提供了一种验证双侧股骨对称性的新方法。结论正常成人双侧股骨内外部形态存在一定的对称性,变异较小,为股骨形态的测量提供理论依据;三维重建更利于对股骨近端形态参数的测量;新配准方法的提出对于临床中股骨近端骨折的诊治具有重大意义。     

Three-dimensional reconstruction of the lower limb from biplanar calibrated radiographs

Three-dimensional (3D) reconstruction of lower limbs is essential for surgical planning and clinical outcome evaluation. 3D reconstruction from biplanar calibrated radiographs may be an alternative to irradiation issues of CT-scan. A previous study proposed a two-step reconstruction method based on parametric models and statistical inferences leading to a fast Initial Solution (IS) followed by manual adjustments. This study aims to improve the IS using a new 3D database, a novel parametric model of the tibia and a different regression approach. The IS was evaluated in terms of shape accuracy on 9 lower limbs and reproducibility of clinical measurements on 22 lower limbs. Reconstruction time was also evaluated. Comparison to the previous method showed an improvement of the IS in terms of shape accuracy (1.3 vs. 1.6 and 2 mm respectively for both femur and tibia) and reproducibility of clinical measurements (i.e. 3.1° vs. 8.3° for neck-shaft-angle; 4.2° and 5° vs. 5° and 6° for tibial and femoral torsion respectively). The proposed approach constitutes a considerable step towards an automatic 3D reconstruction of lower limb.     

The prenatal development of the human femur

The study reported here is the result of a detailed investigation of the changes in shape of the femur with growth and torsion, the type, rate and character of ossification, and the onset, subsequent course, and general features of remodeling. Forty pairs of femurs, from a series of embryos and fetuses ranging from 26 to 342 mm in crown-rump length, were measured, radiographed, and sectioned for microscopic study. A primary bony collar was present before the end of the embryonic period, and in a 27 mm embryo it extended for about one-fifth of the length of the femur. Erosion of the collar was evident at 34 mm. and invasion and destruction of calcified cartilage were occurring by 37 mm. Cartilage canals first appeared in the proximal epiphysis at 57 mm and in the distal epiphysis at 61 mm. Along with the progression of endochondral ossification proximally and distally and the establishment of growth zones, periosteal bone formation also proceeded in both directions, and, until 275 mm, extended about 1 mm beyond the zones of cartilage destruction. After 275 mm, the extents of periosteal and endochondral ossification were the same and at term occupied almost four-fifths of the length of the femur. Trabeculation of the bony collar was first noted at 37 mm. Fusion of endochondral trabeculae with the inner aspect of the periosteal shell began by 61 mm. A central marrow cavity free of trabeculae was present at 86 mm and thereafter. Evidence of reconstruction appeared in both proximal and distal ends by 92 mm, and was consistently present in both ends in all specimens of 111 mm and larger.     

Assessment of accuracy and precision of 3D reconstruction of unicompartmental knee arthroplasty in upright position using biplanar radiography

This study aimed to evaluate the precision and accuracy of 3D reconstruction of UKA component position, contact location and lower limb alignment in standing position using biplanar radiograph. Two human specimens with 4 medial UKAs were implanted with beads for radiostereometric analysis (RSA). The specimens were frozen in standing position and CT-scanned to obtain relative positions between the beads, bones and UKA components. The specimens were then imaged using biplanar radiograph (EOS). The positions of the femur, tibia, UKA components and UKA contact locations were obtained using RSA- and EOS-based techniques. Intraclass correlation coefficient (ICC) was calculated for inter-observer reliability of the EOS technique. The average (standard deviation) of the differences between two techniques in translations and rotations were less than 0.18 (0.29) mm and 0.39° (0.66°) for UKA components. The root-mean-square-errors (RMSE) of contact location along the anterior/posterior and medial/lateral directions were 0.84 mm and 0.30 mm. The RMSEs of the knee rotations were less than 1.70°. The ICCs for the EOS-based segmental orientations between two raters were larger than 0.98. The results suggest the EOS-based 3D reconstruction technique can precisely determine component position, contact location and lower limb alignment for UKA patients in weight-bearing standing position.     

Estimation of 3D location and orientation of human vertebral facet joints from standing digital radiographs

This study provides a biplanar radiographic reconstruction method of volumes of interest to evaluate the location, dimensions and orientation of human facet joints. Visibility of facet anatomical landmarks and areas of interest was evaluated on digital radiographs of 20 idiopathic scoliotic adolescents. Areas of interest have provided the most reliable evaluation of facet joints on postero-anterior and lateral digital radiographs. Volumes of interest of a thoracic and lumbar spinal segment (T1 to L3) were computed using the proposed biplanar 3D reconstruction method and compared with serial tomographic reconstructed models. Differences of 1.5±0.7 mm in 3D location and 1.8±1.2° in sagittal orientation of volumes of interest were observed between both representations. This in vivo geometric information on human vertebral facet joints will help us to understand their role in spinal disorders and will provide important data for personalised biomechanical simulations.     

The accuracy and repeatability of an automatic 2D-3D fluoroscopic image-model registration technique for determining shoulder joint kinematics

Fluoroscopic imaging, using single plane or dual plane images, has grown in popularity to measure dynamic in vivo human shoulder joint kinematics. However, no study has quantified the difference in spatial positional accuracy between single and dual plane image-model registration applied to the shoulder joint. In this paper, an automatic 2D-3D image-model registration technique was validated for accuracy and repeatability with single and dual plane fluoroscopic images. Accuracy was assessed in a cadaver model, kinematics found using the automatic registration technique were compared to those found using radiostereometric analysis. The in vivo repeatability of the automatic registration technique was assessed during the dynamic abduction motion of four human subjects. The in vitro data indicated that the error in spatial positional accuracy of the humerus and the scapula was less than 0.30mm in translation and less than 0.58° in rotation using dual plane images. Single plane accuracy was satisfactory for in-plane motion variables, but out-of-plane motion variables on average were approximately 8 times less accurate. The in vivo test indicated that the repeatability of the automatic 2D-3D image-model registration was 0.50mm in translation and 1.04° in rotation using dual images. For a single plane technique, the repeatability was 3.31mm in translation and 2.46° in rotation for measuring shoulder joint kinematics. The data demonstrate that accurate and repeatable shoulder joint kinematics can be obtained using dual plane fluoroscopic images with an automatic 2D-3D image-model registration technique; and that out-of-plane motion variables are less accurate than in-plane motion variables using a single plane technique.     

Uncertainty assessment of imaging techniques for the 3D reconstruction of stent geometry

This paper presents a quantitative assessment of uncertainty for the 3D reconstruction of stents. This study investigates a CP stent (Numed, USA) used in congenital heart disease applications with a focus on the variance in measurements of stent geometry. The stent was mounted on a model of patient implantation site geometry, reconstructed from magnetic resonance images, and imaged using micro-computed tomography (CT), conventional CT, biplane fluoroscopy and optical stereo-photogrammetry. Image data were post-processed to retrieve the 3D stent geometry. Stent strut length, separation angle and cell asymmetry were derived and repeatability was assessed for each technique along with variation in relation to μCT data, assumed to represent the gold standard. The results demonstrate the performance of biplanar reconstruction methods is comparable with volumetric CT scans in evaluating 3D stent geometry. Uncertainty on the evaluation of strut length, separation angle and cell asymmetry using biplanar fluoroscopy is of the order ±0.2 mm, 3° and 0.03, respectively. These results support the use of biplanar fluoroscopy for in vivo measurement of 3D stent geometry and provide quantitative assessment of uncertainty in the measurement of geometric parameters.     

股骨近端假体周围骨折锁定加压接骨板的设计

目的 探索适用于国人全髋关节置换术(THA)术后股骨近端假体周围骨折(PPFF)内固定的锁定加压接骨板(LCP)的设计。方法 (1)回顾性分析2012年9月—2013年12月南京中医药大学附属常州市中医医院骨科收治首次行THA治疗的90例患者的影像学资料。在90例患者术后髋关节侧位X线片上测量股骨假体近端1/2假体柄后边缘与股骨后方外皮质、远端1/2股骨假体柄前边缘与股骨前方外皮质的最小和最大垂直距离。(2)选取20具股骨标本,测量股骨标本长度和周径。将20具股骨标本植入股骨假体,建立股骨假体模型;对其中5具标本模型进行宝石能谱CT扫描和三维重建,测量股骨假体近端1/2假体柄后边缘与后方股骨外皮质、远端1/2假体柄前边缘与前方股骨外皮质间垂直距离,测量股骨假体近端1/2和远端1/2垂直距离＞6 mm的股骨长度,测量股骨中段侧方的弧度。(3)依据90例患者和5具股骨假体模型的测量数据设计并数字化定制LCP。采用定制LCP固定5具股骨假体模型,通过大体和影像学观察LCP近段锁定螺钉与假体的关系,调整可能与假体接触的锁定螺钉的角度;再采用调整后的LCP固定10具股骨假体模型,观察LCP近段锁定螺钉与假体的关系,确定LCP的设计方案。结果 (1)90例患者术后髋关节侧位X线片测量结果:股骨假体近端1/2假体柄后边缘与股骨后方外皮质的垂直距离,最小(11.26±3.58)mm,最大(17.97±6.94)mm;远端1/2假体柄前边缘与股骨前方外皮质之间的垂直距离,最小(9.18±2.32)mm,最大(14.22±3.10)mm。(2)20具股骨标本的股骨长度为(41.67±0.24)cm,周径为(9.19±0.74)cm。股骨假体模型CT测量结果:假体近端1/2假体柄后边缘与股骨后方外皮质的垂直距离为(12.36±3.24 )mm;假体远端1/2假体柄前边缘和股骨前方外皮质的垂直距离为(8.14±1.21)mm。假体近、远端1/2与股骨外皮质垂直距离＞6 mm的股骨长度分别为(69.20±4.53)mm 和(57.31±3.82)mm。(3)LCP设计方案:LCP与假体近端1/2对应的部分设计3枚向后内成一定角度的锁定螺钉,对应3个锁定孔,分布于LCP中轴线偏后,向后内方向;与假体远端1/2对应的部分设计3枚向前内成一定角度的锁定螺钉,对应的3个锁定孔,分布于LCP中轴线偏前,向前内方向。采用设计、定制LCP固定股骨假体模型,LCP与股骨侧方弧度一致,锁定螺钉在股骨假体的后方或前方均实现双层皮质固定,角度合适。结论 根据国人资料设计、定制LCP,在股骨假体模型上获得有效的固定空间,为THA后PPFF的处理提供可行方案,但临床应用效果有待进一步验证。     

Fast 3D reconstruction of the rib cage from biplanar radiographs

The stereoradiographic reconstruction method allows obtaining the three-dimensional (3D) rib cage geometry, which is essential for clinical evaluation or biomechanical studies. However, reconstruction time is still high (about 20 min considering operator time). The purpose of this study is to propose a 3D reconstruction of the rib cage from biplanar radiographs, based on the deformation of a prepersonalized object. Validation in comparison with computed tomography (CT-scan) acquisitions was performed. Local parameters (rib length, cord length, maximum width, area, and rib orientations) were computed from reconstructions. Parameters’ reproducibility was assessed with two observers and two measurements for 15 subjects. Regarding validation of the parameters, the mean difference with the CT-scan was between 6.3 and 1.3%. Observer variability was maximal for rib area (6.2%) and was lower than 4.2% for others parameters. The proposed reconstruction method reduced time (less than three minutes for operator time) to obtain a 3D reconstruction of the rib cage.     

正常维吾尔族成年人股骨上段的X线解剖及其临床意义

目的了解维吾尔族正常成年人股骨上段X线解剖特征.方法拍摄36例正常维吾尔族成年人双侧股骨上段标准正位片,对股骨头直径、股骨头颈长度、股骨头高、小转子上20 mm平面处髓腔宽度、小转子处髓腔宽度、小转子下20 mm平面处髓腔宽度、狭窄处位置、狭窄处髓腔左右宽度8项指标进行测量并进行统计学处理.结果股骨上段各项指标间无侧别差异（P〉0.05）;男、女性股骨头直径、股骨头高、小转子下20 mm平面处髓腔宽度等指标存在性别差异（P〈0.05）;与汉族相比股骨头直径、股骨头颈长度、狭窄处位置、狭窄处髓腔宽度等指标存在种族差异（P〈0.05）,与外国人相比股骨头直径、股骨头颈长度、小转子上20 mm平面处髓腔宽度、小转子处髓腔宽度、狭窄处髓腔左右宽度等指标存在种族差异（P〈0.05）.结论维吾尔族正常成年人骨股上段结构有其特点,可为临床应用提供依据.     

Personalized 3D reconstruction of the rib cage for clinical assessment of trunk deformities

Scoliosis is a 3D deformity of the spine and rib cage. Extensive validation of 3D reconstruction methods of the spine from biplanar radiography has already been published. In this article, we propose a novel method to reconstruct the rib cage, using the same biplanar views as for the 3D reconstruction of the spine, to allow clinical assessment of whole trunk deformities. This technique uses a semi-automatic segmentation of the ribs in the postero-anterior X-ray view and an interactive segmentation of partial rib edges in the lateral view. The rib midlines are automatically extracted in 2D and reconstructed in 3D using the epipolar geometry. For the ribs not visible in the lateral view, the method predicts their 3D shape. The accuracy of the proposed method has been assessed using data obtained from a synthetic bone model as a gold standard and has also been evaluated using data of real patients with scoliotic deformities. Results show that the reconstructed ribs enable a reliable evaluation of the rib axial rotation, which will allow a 3D clinical assessment of the spine and rib cage deformities.     

Morphometric evaluations of personalised 3D reconstructions and geometric models of the human spine

In the past, several techniques have been developed to study and analyse the 3D characteristics of the human spine: multi-view radiographic or biplanar 3D reconstructions, CT-scan 3D reconstructions and geometric models. Extensive evaluations of three of these techniques that are routinely used at Sainte-Justine Hospital (Montréal, Canada) are presented. The accuracy of these methods is assessed by comparing them with precise measurements made with a coordinate measuring machine on 17 thoracic and lumbar vertebrae (T1-L5) extracted from a normal cadaveric spine specimen. Multi-view radiographic 3D reconstructions are evaluated for different combinations of X-ray views: lateral (LAT), postero-anterior with normal incidence (PAO^o) and postero-anterior with 20^o angled down incidence (PA20^o). The following accuracies are found for these reconstructions obtained from different radiographic setups: 2.1±1.5 mm for the combination with PAO^o-LAT views, and 5.6±4.5 mm for the PAO^o-PA20^o stereopair. Higher errors are found in the postero-anterior direction, especially for the PAO^o-PA20^o view combination. Pedicles are found to be the most precise landmarks. Accuracy for CT-scan 3D reconstructions is about 1.1±0.8 mm. As for a geometric model built using a multiview radiographic reconstruction based on six landmarks per vertebra, accuracies of about 2.6±2.4 mm for landmarks and 2.3±2.0 mm for morphometric parameters are found. The geometric model and 3D reconstruction techniques give accurate information, at low X-ray dose. The accuracy assessment of the techniques used to study the 3D characteristics of the human spine is important, because it allows better and more efficient quantitative evaluations of spinal dysfunctions and their treatments, as well as biomechanical modelling of the spine.     

儿童股骨近端解剖钢板生物力学及三维有限元分析

背景：以往的三维有限元研究多集中在成人骨科生物力学方面。 目的：以三维有限元方法分析儿童股骨近端解剖钢板固定股骨转子下骨折的生物力学性能。 方法：从6具儿童尸体上取股骨12根,X射线排除骨病后分为2组,实验组采用儿童股骨近端解剖钢板固定,对照组采用重建钢板固定。分别进行生物力学实验,测试其轴向压缩、扭转刚度、弯曲刚度。选取1名健康男性儿童进行螺旋CT扫描技术,获得股骨近端图像数据,建立儿童股骨近端三维有限元模型,并进行三维有限元力学分析。 结果与结论：在轴向压缩刚度、扭转刚度上儿童股骨近端解剖钢板与重建钢板两者比较差异无显著性意义(P > 0.05);在抗弯曲刚度上,两者相比差异有显著性意义(P < 0.05)。结果显示儿童股骨近端解剖钢板的抗压能力、抗扭能力上与重建钢板相当,而在抗弯曲能力上强于重建钢板。生物力学三维有限元分析显示儿童股骨近端解剖型钢板的设计符合生物力学原理,具有较好的强度、刚度和稳定性,能够满足对儿童股骨近端骨折固定的需要。儿童股骨近端解剖型钢板对固定股骨转子下骨折具有良好的生物力学性能。     

基于体素互信息的多模式和多时相图像中股骨近端配准

在股骨近端骨质疏松进程以及股骨头坏死状况评估方法中,图像分析是常用的工具,通过不同时相以及不同模式的多组影像可以对病人病情进行更全面的综合评估。然而,在综合评估过程中,由于病人多次在不同系统中成像,体位的差异使不同图像组之间的解剖点位置无法一一对应,因此分析之前需要将多组图像对齐,才能观察同一感兴趣区在不同模式或不同时间骨组织状况的差异。针对这个问题,设计一种多模式、多时相图像配准的解决方案,通过图像的前处理、双阈值分类并结合贝叶斯分类的股骨分割得到股骨体素,然后通过基于归一化互信息的图像配准获得各组图像中股骨之间的三维空间刚性变换矩阵,其中CT与MR图像的配准误差在4 mm以下,CT与CT图像的配准误差在2 mm以下。利用矩阵传递关系,以CT-CT多时相的配准矩阵为基础,可获取任何两组图像间的变换矩阵。在此基础上,再进行任意两组图像的融合、点对点的分析以及骨质状况和血供状况的定量评估。通过该方案,可以对多时相、多模式图像分析中相同感兴趣的区域进行对比。     

基于2D/3D配准技术测量颈椎间孔形态学的精度研究

目的　探讨基于2D/3D配准技术测量离体颈椎标本椎间孔形态学的精度。 方法　获取16具颈椎离体标本的螺旋CT影像,通过三维重建获得相应标本的三维模型。然后改变标本的体位,再次行CT扫描并分别拍摄各具离体标本正侧位X线平片,采用2D/3D图像配准技术还原拍摄平片时颈椎的三维位置。利用Rapidform XOR3软件测量配准前与配准后C2/3至C6/7双侧的椎间孔面积、前后径和上下径。 结果　共测得椎间孔的面积、前后径和上下径各158个,经配对样本t检验,配准后椎间孔的面积、前后径、上下径与配准前相比较,结果无显著性差异(P>0.05);椎间孔面积的准确度为96.77%、精确度为（1.27±1.16）mm2,前后径的准确度为94.35%、精确度为（0.30±0.27）mm,上下径的准确度为96.14%、精确度为（0.32±0.28）mm。 结论　应用2D/3D配准技术测量颈椎间孔的形态学参数具有较高的准确度和精确度。     

3D dynamic position assessment of the coronary sinus lead in cardiac resynchronization therapy

Although cardiac resynchronization therapy (CRT) is an effective treatment for chronic systolic heart failure with dyssynchrony, about one-third of patients do not respond favorably. The interaction between the pacing lead and the coronary sinus (CS) branches is of paramount importance for an effective resynchronization. Minor changes in lead position overtime could interfere with CRT mechanics, without affecting even biophysical parameters or ECG morphology. Although late post-implant CS lead dislodgement rate is consistent, lead movements have been little investigated and only with bi-dimensional methods. The aim of this study was (1) to develop a method for quantifying CS lead position in the 3D domain throughout the cardiac cycle and (2) to test it by comparing the CS lead position at implant and at follow-up, using chest fluoroscopy. Method performance, its accuracy and reproducibility were qualitatively and quantitatively assessed. Intra- and inter-observer percent discordance between trajectories were also computed. The accuracy of the procedure resulted in 0.3 ± 0.1 mm and its resolution was 0.5 mm. Intra- and inter-observer discordances were 2.2 ± 1.5 and 5.5 ± 3.6 mm, respectively. The proposed method for measuring the CS lead dynamic placement in 3D space seems accurate and reproducible. Investigating CS lead 3D dynamics could provide further insights into CRT mechanics.     

A Robust 3D Finite Element Simulation of Human Proximal Femur Progressive Fracture Under Stance Load with Experimental Validation

Clinical implementation of quantitative computed tomography-based finite element analysis (QCT/FEA) of proximal femur (hip) fractures requires (i) to develop a bone material behavior able to describe the progressive fracturing process until complete failure of the hip. And (ii) to validate the model with realistic test data that represent typical hip fractures. The objective of the current study was to develop and experimentally validate an accurate 3D finite element (FE) model coupled to a quasi-brittle damage law to simulate human proximal femur fracture considering the initiation and progressive propagation of multiple cracks phases under quasi-static load. The model is based on continuum damage mechanics that can predict hip fracture in more adequate physical terms than criteria-based fracture models. In order to validate the model, ten human proximal femurs were tested until complete fracture under one-legged stance quasi-static load. QCT/FE models were generated and FE simulations were performed on these femurs with the same applied loads and boundary conditions than in the stance experiments. The proposed FE model leads to excellent agreement (R ² = 0.9432) between predicted and measured results concerning the shape of the force–displacement curve (yielding and fracturing) and the profile of the fractured edge. The motivation of this work was to propose a FE model for possible clinical use with a good compromise between complexity and capability of the simulation.