In Vivo Quantification of the Deformations of the Femoropopliteal Segment: Percutaneous Transluminal Angioplasty vs Nitinol Stent Placement.

PURPOSE: To quantify the deformations of the femoropopliteal (FP) segment in patients undergoing endovascular revascularization and to compare the posttreatment deformations caused by primary nitinol stent implantation to those produced by percutaneous transluminal angioplasty (PTA). METHODS: Thirty-five patients (mean age 69±10 years; 20 men) scheduled for endovascular therapy were recruited for the study. During endovascular interventions, angiographic images were acquired with the legs straight and with a hip/knee flexion of 20°/70°. Image acquisition was performed before PTA for all patients, after PTA in 17 patients receiving this treatment only, and after primary stent implantation in the remaining 18 patients. A semiautomatic approach was used to reconstruct the 3-dimensional patient-specific artery models from 2-dimensional radiographs. Axial shortening and curvature changes in the arteries in vivo were calculated for the calcified, dilated, and stented regions, as well as the regions that were distal and proximal to the diseased and treated segments. RESULTS: Leg flexion resulted in shortening of the artery in all investigated FP segments. The dilated arteries exhibited greater shortening compared with their stented counterparts (post-PTA 7.6%±4.9%, poststent 3.2%±2.9%; p=0.004). Leg flexion also led to an increase in the curvatures of all the sections of the FP segment. While stented arteries had significantly higher curvature values than PTA within the regions proximal to the treated sections, the choice of the treatment method did not affect the curvature of the other segments. Despite this, 40% of the stented arteries exhibited kinking during leg flexion. CONCLUSION: The choice of the treatment method affects the postinterventional axial deformations of the FP segment but does not influence the curvature behavior. While PTA results in a more flexible artery, stents restrict the arteries' shortening capabilities. Depending on the anatomical position of the stents, this axial stiffening of the arteries may lead to chronic kinking, which may cause occlusions and, consequently, affect the long-term success of the procedure.

A software program to measure the three-dimensional length of the spine from radiographic images: Validation and reliability assessment for adolescent idiopathic scoliosis.

BACKGROUND AND OBJECTIVE: The aim of this study was to validate a new program which aims at measuring the three-dimensional length of the spine's midline based on two calibrated orthogonal radiographic images. The traditional uniplanar T1-S1 measurement method is not reflecting the actual three dimensional curvature of a scoliotic spine and is therefore not accurate. The Spinal Measurement Software (SMS) is an alternative to conveniently measure the true spine's length. METHODS: The validity, inter- and intra-observer variability and usability of the program were evaluated. The usability was quantified based on a subjective questionnaire filled by eight participants using the program for the first time. The validity and variability were assessed by comparing the length of five phantom spines measured based on CT-scan data and on radiographic images with the SMS. The lengths were measured independently by each participant using both techniques. RESULTS: The SMS is easy and intuitive to use, even for non-clinicians. The SMS measured spinal length with an error below 2 millimeters compared to length obtained using CT scan datasets. The inter- and intra-observer variability of the SMS measurements was below 5 millimeters. CONCLUSIONS: The SMS provides accurate measurement of the spinal length based on orthogonal radiographic images. The software is easy to use and could easily integrate the clinical workflow and replace current approximations of the spinal length based on a single radiographic image such as the traditional T1-S1 measurement.

Effect of Stent Implantation on the Deformations of the Superficial Femoral Artery and Popliteal Artery: In Vivo Three-Dimensional Deformational Analysis from Two-Dimensional Radiographs.

The objective of this work was to develop a system for three-dimensional (3D) reconstruction of the femoropopliteal artery from two angiographic views and to quantify the in vivo 3D deformations in 18 patients before balloon angioplasty and after primary stent implantation. The procedure had an insignificant effect on the bending behavior of the artery, as the average mean curvature change within the lesion remained constant before (0.04 cm-1 ± 0.03) and after stent implantation (0.03 cm-1 ± 0.04). A significant effect of stent implantation was measured in terms of a decrease in arterial shortening during leg flexion.

Radiographic reconstruction of lower-extremity bone fragments: a first trial.

PURPOSE: The correct rotational alignment of the proximal and the distal bone fragments is an essential step in a long-bone deformity correction process. In order to plan the deformity correction, plain radiographs are conventionally used. But as three-dimensional information of the complex situation is not available, the correct amount of rotation can only be approximated. Thus, the objective of this study was to develop a system to assess the rotational relationship between the proximal and distal fragments of a long bone (tibia or femur) based on a set of two calibrated X-ray radiographs. METHODS: In order to robustly determine the rotational relationship of proximal and distal bone fragments, a statistical shape model-based 2D/3D reconstruction approach was employed. The resulting fragment models were used to determine the angle between its anatomical axes and the rotation around its particular axes. Two different studies were performed to evaluate the accuracy of the proposed system. RESULTS: The accuracy of the complete system was evaluated in terms of major bone axis and in-plane rotational difference. The angle between the anatomical fragment axes could be measured with an average error of 0.33[Formula: see text] ± 0.27[Formula: see text], while an average in-plane rotational error of 2.27[Formula: see text] ± 1.76[Formula: see text]  and 2.67[Formula: see text]  ± 1.80[Formula: see text]  was found for the proximal and distal fragments, respectively. The overall mean surface reconstruction error was 0.81  ± 0.59 mm when the present technique was applied to the tibia and 1.12 ± 0.87 mm when it was applied to the femur. CONCLUSIONS: A new approach for estimating the rotational parameters of long-bone fragments has been proposed. This approach is based on two conventional radiographs and 2D/3D reconstruction technology. It is generally applicable to the alignment of any long-bone fragments and could provide an important means for achieving accurate rotational alignment.

Evaluation of Constant Thickness Cartilage Models vs. Patient Specific Cartilage Models for an Optimized Computer-Assisted Planning of Periacetabular Osteotomy.

Modern computerized planning tools for periacetabular osteotomy (PAO) use either morphology-based or biomechanics-based methods. The latter relies on estimation of peak contact pressures and contact areas using either patient specific or constant thickness cartilage models. We performed a finite element analysis investigating the optimal reorientation of the acetabulum in PAO surgery based on simulated joint contact pressures and contact areas using patient specific cartilage model. Furthermore we investigated the influences of using patient specific cartilage model or constant thickness cartilage model on the biomechanical simulation results. Ten specimens with hip dysplasia were used in this study. Image data were available from CT arthrography studies. Bone models were reconstructed. Mesh models for the patient specific cartilage were defined and subsequently loaded under previously reported boundary and loading conditions. Peak contact pressures and contact areas were estimated in the original position. Afterwards we used a validated preoperative planning software to change the acetabular inclination by an increment of 5° and measured the lateral center edge angle (LCE) at each reorientation position. The position with the largest contact area and the lowest peak contact pressure was defined as the optimal position. In order to investigate the influence of using patient specific cartilage model or constant thickness cartilage model on the biomechanical simulation results, the same procedure was repeated with the same bone models but with a cartilage mesh of constant thickness. Comparison of the peak contact pressures and the contact areas between these two different cartilage models showed that good correlation between these two cartilage models for peak contact pressures (r = 0.634 ∈ [0.6, 0.8], p < 0.001) and contact areas (r = 0.872 > 0.8, p < 0.001). For both cartilage models, the largest contact areas and the lowest peak pressures were found at the same position. Our study is the first study comparing peak contact pressures and contact areas between patient specific and constant thickness cartilage models during PAO planning. Good correlation for these two models was detected. Computer assisted planning with FE modeling using constant thickness cartilage models might be a promising PAO planning tool when a conventional CT is available.

A cost-effective surgical navigation solution for periacetabular osteotomy (PAO) surgery.

PURPOSE: To evaluate a low-cost, inertial sensor-based surgical navigation solution for periacetabular osteotomy (PAO) surgery without the line-of-sight impediment. METHODS: Two commercial inertial measurement units (IMU, Xsens Technologies, The Netherlands), are attached to a patient's pelvis and to the acetabular fragment, respectively. Registration of the patient with a pre-operatively acquired computer model is done by recording the orientation of the patient's anterior pelvic plane (APP) using one IMU. A custom-designed device is used to record the orientation of the APP in the reference coordinate system of the IMU. After registration, the two sensors are mounted to the patient's pelvis and acetabular fragment, respectively. Once the initial position is recorded, the orientation is measured and displayed on a computer screen. A patient-specific computer model generated from a pre-operatively acquired computed tomography scan is used to visualize the updated orientation of the acetabular fragment. RESULTS: Experiments with plastic bones (eight hip joints) performed in an operating room comparing a previously developed optical navigation system with our inertial-based navigation system showed no statistically significant difference on the measurement of acetabular component reorientation. In all eight hip joints the mean absolute difference was below four degrees. CONCLUSION: Using two commercially available inertial measurement units we show that it is possible to accurately measure the orientation (inclination and anteversion) of the acetabular fragment during PAO surgery and therefore to successfully eliminate the line-of-sight impediment that optical navigation systems have.

Cup Implant Planning Based on 2-D/3-D Radiographic Pelvis Reconstruction-First Clinical Results.

GOAL: In the following, we will present a newly developed X-ray calibration phantom and its integration for 2-D/3-D pelvis reconstruction and subsequent automatic cup planning. Two different planning strategies were applied and evaluated with clinical data. METHODS: Two different cup planning methods were investigated: The first planning strategy is based on a combined pelvis and cup statistical atlas. Thereby, the pelvis part of the combined atlas is matched to the reconstructed pelvis model, resulting in an optimized cup planning. The second planning strategy analyzes the morphology of the reconstructed pelvis model to determine the best fitting cup implant. RESULTS: The first planning strategy was compared to 3-D CT-based planning. Digitally reconstructed radiographs of THA patients with differently severe pathologies were used to evaluate the accuracy of predicting the cup size and position. Within a discrepancy of one cup size, the size was correctly identified in 100% of the cases for Crowe type I datasets and in 77.8% of the cases for Crowe type II, III, and IV datasets. The second planning strategy was analyzed with respect to the eventually implanted cup size. In seven patients, the estimated cup diameter was correct within one cup size, while the estimation for the remaining five patients differed by two cup sizes. CONCLUSION: While both planning strategies showed the same prediction rate with a discrepancy of one cup size (87.5%), the prediction of the exact cup size was increased for the statistical atlas-based strategy (56%) in contrast to the anatomically driven approach (37.5%). SIGNIFICANCE: The proposed approach demonstrated the clinical validity of using 2-D/3-D reconstruction technique for cup planning.

Beyond standard model calculations with Sherpa.

We present a fully automated framework as part of the Sherpa event generator for the computation of tree-level cross sections in Beyond Standard Model scenarios, making use of model information given in the Universal FeynRules Output format. Elementary vertices are implemented into C++ code automatically and provided to the matrix-element generator Comix at runtime. Widths and branching ratios for unstable particles are computed from the same building blocks. The corresponding decays are simulated with spin correlations. Parton showers, QED radiation and hadronization are added by Sherpa, providing a full simulation of arbitrary BSM processes at the hadron level.

A complete-pelvis segmentation framework for image-free total hip arthroplasty (THA): methodology and clinical study.

BACKGROUND: Complete-pelvis segmentation in antero-posterior pelvic radiographs is required to create a patient-specific three-dimensional pelvis model for surgical planning and postoperative assessment in image-free navigation of total hip arthroplasty. METHODS: A fast and robust framework for accurately segmenting the complete pelvis is presented, consisting of two consecutive modules. In the first module, a three-stage method was developed to delineate the left hemi-pelvis based on statistical appearance and shape models. To handle complex pelvic structures, anatomy-specific information processing techniques were employed. As the input to the second module, the delineated left hemi-pelvis was then reflected about an estimated symmetry line of the radiograph to initialize the right hemi-pelvis segmentation. The right hemi-pelvis was segmented by the same three-stage method, RESULTS: Two experiments conducted on respectively 143 and 40 AP radiographs demonstrated a mean segmentation accuracy of 1.61±0.68 mm. A clinical study to investigate the postoperative assessment of acetabular cup orientations based on the proposed framework revealed an average accuracy of 1.2°±0.9° and 1.6°±1.4° for anteversion and inclination, respectively. Delineation of each radiograph costs less than one minute. CONCLUSIONS: Despite further validation needed, the preliminary results implied the underlying clinical applicability of the proposed framework for image-free THA.

Computer assisted planning and navigation of periacetabular osteotomy with range of motion optimization.

Femoroacetabular impingement (FAI) before or after Periacetabular Osteotomy (PAO) is surprisingly frequent and surgeons need to be aware of the risk preoperatively and be able to avoid it intraoperatively. In this paper we present a novel computer assisted planning and navigation system for PAO with impingement analysis and range of motion (ROM) optimization. Our system starts with a fully automatic detection of the acetabular rim, which allows for quantifying the acetabular morphology with parameters such as acetabular version, inclination and femoral head coverage ratio for a computer assisted diagnosis and planning. The planned situation was optimized with impingement simulation by balancing acetabuar coverage with ROM. Intra-operatively navigation was conducted until the optimized planning situation was achieved. Our experimental results demonstrated: 1) The fully automated acetabular rim detection was validated with accuracy 1.1 ± 0.7mm; 2) The optimized PAO planning improved ROM significantly compared to that without ROM optimization; 3) By comparing the pre-operatively planned situation and the intra-operatively achieved situation, sub-degree accuracy was achieved for all directions.

Axial suspension test to assess pre-operative spinal flexibility in patients with adolescent idiopathic scoliosis.

INTRODUCTION: An accurate description of the biomechanical behavior of the spine is crucial for the planning of scoliotic surgical correction as well as for the understanding of degenerative spine disorders. The current clinical assessments of spinal mechanics such as side-bending or fulcrum-bending tests rely on the displacement of the spine observed during motion of the patient. Since these tests focused solely on the spinal kinematics without considering mechanical loads, no quantification of the mechanical flexibility of the spine can be provided. METHODS: A spinal suspension test (SST) has been developed to simultaneously monitor the force applied on the spine and the induced vertebral displacements. The system relies on cervical elevation of the patient and orthogonal radiographic images are used to measure the position of the vertebras. The system has been used to quantify the spinal flexibility on five AIS patients. RESULTS: Based on the SST, the overall spinal flexibility varied between 0.3 °/Nm for the patient with the stiffer curve and 2 °/Nm for the less rigid curve. A linear correlation was observed between the overall spinal flexibility and the change in Cobb angle. In addition, the segmental flexibility calculated for five segments around the apex was 0.13 ± 0.07 °/Nm, which is similar to intra-operative stiffness measurements previously published. CONCLUSIONS: In summary, the SST seems suitable to provide pre-operative information on the complex functional behavior and stiffness of spinal segments under physiological loading conditions. Such tools will become increasingly important in the future due to the ever-increasing complexity of the surgical instrumentation and procedures.

X-ray image calibration and its application to clinical orthopedics.

X-ray imaging is one of the most commonly used medical imaging modality. Albeit X-ray radiographs provide important clinical information for diagnosis, planning and post-operative follow-up, the challenging interpretation due to its 2D projection characteristics and the unknown magnification factor constrain the full benefit of X-ray imaging. In order to overcome these drawbacks, we proposed here an easy-to-use X-ray calibration object and developed an optimization method to robustly find correspondences between the 3D fiducials of the calibration object and their 2D projections. In this work we present all the details of this outlined concept. Moreover, we demonstrate the potential of using such a method to precisely extract information from calibrated X-ray radiographs for two different orthopedic applications: post-operative acetabular cup implant orientation measurement and 3D vertebral body displacement measurement during preoperative traction tests. In the first application, we have achieved a clinically acceptable accuracy of below 1° for both anteversion and inclination angles, where in the second application an average displacement of 8.06±3.71 mm was measured. The results of both applications indicate the importance of using X-ray calibration in the clinical routine.

Statistical model-based segmentation of the proximal femur in digital antero-posterior (AP) pelvic radiographs.

PURPOSE: Segmentation of the proximal femur in digital antero-posterior (AP) pelvic radiographs is required to create a three-dimensional model of the hip joint for use in planning and treatment. However, manually extracting the femoral contour is tedious and prone to subjective bias, while automatic segmentation must accommodate poor image quality, anatomical structure overlap, and femur deformity. A new method was developed for femur segmentation in AP pelvic radiographs. METHODS: Using manual annotations on 100 AP pelvic radiographs, a statistical shape model (SSM) and a statistical appearance model (SAM) of the femur contour were constructed. The SSM and SAM were used to segment new AP pelvic radiographs with a three-stage approach. At initialization, the mean SSM model is coarsely registered to the femur in the AP radiograph through a scaled rigid registration. Mahalanobis distance defined on the SAM is employed as the search criteria for each annotated suggested landmark location. Dynamic programming was used to eliminate ambiguities. After all landmarks are assigned, a regularized non-rigid registration method deforms the current mean shape of SSM to produce a new segmentation of proximal femur. The second and third stages are iteratively executed to convergence. RESULTS: A set of 100 clinical AP pelvic radiographs (not used for training) were evaluated. The mean segmentation error was 0.96 mm ± 0.35 mm, requiring <5 s per case when implemented with Matlab. The influence of the initialization on segmentation results was tested by six clinicians, demonstrating no significance difference. CONCLUSIONS: A fast, robust and accurate method for femur segmentation in digital AP pelvic radiographs was developed by combining SSM and SAM with dynamic programming. This method can be extended to segmentation of other bony structures such as the pelvis.

An integrated system for 3D hip joint reconstruction from 2D X-rays: a preliminary validation study.

The acquisition of conventional X-ray radiographs remains the standard imaging procedure for the diagnosis of hip-related problems. However, recent studies demonstrated the benefit of using three-dimensional (3D) surface models in the clinical routine. 3D surface models of the hip joint are useful for assessing the dynamic range of motion in order to identify possible pathologies such as femoroacetabular impingement. In this paper, we present an integrated system which consists of X-ray radiograph calibration and subsequent 2D/3D hip joint reconstruction for diagnosis and planning of hip-related problems. A mobile phantom with two different sizes of fiducials was developed for X-ray radiograph calibration, which can be robustly detected within the images. On the basis of the calibrated X-ray images, a 3D reconstruction method of the acetabulum was developed and applied together with existing techniques to reconstruct a 3D surface model of the hip joint. X-ray radiographs of dry cadaveric hip bones and one cadaveric specimen with soft tissue were used to prove the robustness of the developed fiducial detection algorithm. Computed tomography scans of the cadaveric bones were used to validate the accuracy of the integrated system. The fiducial detection sensitivity was in the same range for both sizes of fiducials. While the detection sensitivity was 97.96% for the large fiducials, it was 97.62% for the small fiducials. The acetabulum and the proximal femur were reconstructed with a mean surface distance error of 1.06 and 1.01 mm, respectively. The results for fiducial detection sensitivity and 3D surface reconstruction demonstrated the capability of the integrated system for 3D hip joint reconstruction from 2D calibrated X-ray radiographs.

Comparison of partial least squares regression and principal component regression for pelvic shape prediction.

This paper studied two different regression techniques for pelvic shape prediction, i.e., the partial least square regression (PLSR) and the principal component regression (PCR). Three different predictors such as surface landmarks, morphological parameters, or surface models of neighboring structures were used in a cross-validation study to predict the pelvic shape. Results obtained from applying these two different regression techniques were compared to the population mean model. In almost all the prediction experiments, both regression techniques unanimously generated better results than the population mean model, while the difference on prediction accuracy between these two regression methods is not statistically significant (α=0.01).

Spectrum to space transformed fast terahertz imaging.

We present an imaging technique in which the broadband frequency information of terahertz (THz) pulses is transformed into spatial resolution. Efficient blazed diffractive gratings spread the individual frequency components over a wide and defined spatial range and f-theta optics are employed to focus the individual components onto a one-dimensional image-line. Measuring the time domain waveform of the THz waves allows therefore for a direct reconstruction of spatial sample characteristics as the spatial domain information is encoded in the terahertz spectrum. We will demonstrate terahertz imaging on selected samples with an improvement in acquisition speed up to two orders of magnitude.

Understanding jet scaling and jet vetos in Higgs searches.

Jet counting and jet vetos are crucial analysis tools for many LHC searches. We can understand their properties from the distribution of the exclusive number of jets. LHC processes tend to show either a distinct staircase scaling or a Poisson scaling, depending on kinematic cuts. We illustrate our approach in a detailed study of jets in weak boson fusion Higgs production.

Compensation of sound speed deviations in 3-D B-mode ultrasound for intraoperative determination of the anterior pelvic plane.

An accurate determination of the pelvic orientation is inevitable for the correct cup prosthesis placement of navigated total hip arthroplasties. Conventionally, this step is accomplished by percutaneous palpation of anatomic landmarks. Sterility issues and an increased landmark localization error for obese patients lead to the application of B-mode ultrasound imaging in the field of computer-assisted orthopedic surgery. Many approaches have been proposed in the literature to replace the percutaneous digitization by 3-D B-mode ultrasound imaging. However, the correct depth localization of the pelvic landmarks could be significantly affected by the acoustic properties of the penetrated tissues. Imprecise depth estimation could lead to a miscalculation of the pelvic orientation and subsequently to a misalignment of the acetabular cup implant. But so far, no solution has been presented, which compensates for acoustic property differences for correct depth estimation. In this paper, we present a novel approach to determine pelvic orientation from ultrasound images by applying a hierarchical registration scheme based on patch statistical shape models to compensate for differences in speed of sound. The method was validated based on plastic bones and a cadaveric specimen.

Determination of pelvic orientation from sparse ultrasound data for THA operated in the lateral position.

BACKGROUND: B-mode ultrasound imaging has the potential to replace conventional percutaneous digitization of bony landmarks in navigated total hip arthroplasties (THAs). For THAs operated in the lateral position, only one side of the pelvis is freely accessible. This paper presents a new ultrasound to statistical shape model (SSM) registration method for operating the pelvis in the lateral position, based on sparse ultrasound images, which does not interfere with the clinical routine in terms of redraping and repositioning the patient. METHODS: It is proposed to use the mid-sagittal plane of the pelvis to symmetrically reflect data derived from sparse B-mode ultrasound images of the ipsilateral patient side to the contralateral side. A SSM of the pelvis is registered to the bilaterally available data without additional information on the pubic tubercle region. RESULTS: The feasibility and robustness of the proposed method were evaluated by comprehensive in silico studies and laboratory experiments with plastic and dry cadaveric pelvises, showing a mean error of 3.48 ± 1.10° for anteversion angle and 1.26 ± 1.62° for inclination angle. CONCLUSION: Experimental results demonstrate that the symmetry property of the pelvis could be used for registration in the lateral position without accessing the error-prone pubic tubercle landmarks.

Terahertz Brewster lenses.

Typical lenses suffer from Fresnel reflections at their surfaces, reducing the transmitted power and leading to interference phenomena. While antireflection coatings can efficiently suppress these reflections for a small frequency window, broadband antireflection coatings remain challenging. In this paper, we report on the simulation and experimental investigation of Brewster lenses in the THz-range. These lenses can be operated under the Brewster angle, ensuring reflection-free transmission of p-polarized light in an extremely broad spectral range. Experimental proof of the excellent focusing capabilities of the Brewster lenses is given by frequency and spatially resolved focus plane measurements using a fiber-coupled THz-TDS system.