Fluoroscopic Sequences Research Articles

Auto-tracking system for human lumbar motion analysis

Previous lumbar motion analyses suggest the usefulness of quantitatively characterizing spine motion. However, the application of such measurements is still limited by the lack of user-friendly automatic spine motion analysis systems. This paper describes an automatic analysis system to measure lumbar spine disorders that consists of a spine motion guidance device, an X-ray imaging modality to acquire digitized video fluoroscopy (DVF) sequences and an automated tracking module with a graphical user interface (GUI). DVF sequences of the lumbar spine are recorded during flexion-extension under a guidance device. The automatic tracking software utilizing a particle filter locates the vertebra-of-interest in every frame of the sequence, and the tracking result is displayed on the GUI. Kinematic parameters are also extracted from the tracking results for motion analysis. We observed that, in a bone model test, the maximum fiducial error was 3.7%, and the maximum repeatability error in translation and rotation was 1.2% and 2.6%, respectively. In our simulated DVF sequence study, the automatic tracking was not successful when the noise intensity was greater than 0.50. In a noisy situation, the maximal difference was 1.3 mm in translation and 1° in the rotation angle. The errors were calculated in translation (fiducial error: 2.4%, repeatability error: 0.5%) and in the rotation angle (fiducial error: 1.0%, repeatability error: 0.7%). However, the automatic tracking software could successfully track simulated sequences contaminated by noise at a density ≤ 0.5 with very high accuracy, providing good reliability and robustness. A clinical trial with 10 healthy subjects and 2 lumbar spondylolisthesis patients were enrolled in this study. The measurement with auto-tacking of DVF provided some information not seen in the conventional X-ray. The results proposed the potential use of the proposed system for clinical applications.

Correlative Analysis between Diaphragm Positions in Fluoroscopic Sequence and Indicator Values of a Respiration Monitoring Device Which Represents the Level of Chest and Abdominal Wall

Correlative Analysis between Diaphragm Positions in Fluoroscopic Sequence and Indicator Values of a Respiration Monitoring Device Which Represents the Level of Chest and Abdominal Wall

Carbon fibre and nitinol needles for MRI-guided interventions: First in vitro and in vivo application

Objective To assess the artefact properties of a MR-compatible carbon fibre needle with a nitinol mandrin in vitro and to report first clinical experiences. Materials and methods In vitro, the carbon fibre/nitinol needle was imaged at different angles against the main magnetic field (1.5 T open bore magnet). A gradient echo MR fluoroscopy sequence (GRE: TR 9.3 ms, TE 3.12 ms, bandwidth 200 Hz/pixel, flip-angle 12°) and a fast turbo spin echo sequence (FSE: TR 412 ms, TE 9.7 ms, bandwidth 200 Hz/pixel, flip-angle 150°) were used. Artefact width, needle intensity contrast and needle tip location errors were assessed. In vivo, lumbar periradicular corticosteroid injections and one sclerotherapy were performed with carbon fibre needles (10 procedures) and with titanium alloy needles (2 procedures). The artefact sizes and contrasts were measured. Results In vitro, artefact diameters of the carbon fibre needle ranged from 3.3 to 4.6 mm, contrasts from 0.11 to 0.52, with larger artefact contrasts and widths with the GRE sequence. Needle tip location errors of −2.1 to −2.8 mm were observed. Decreasing angles to the main field lead to smaller artefacts. In vivo, the carbon fibre/nitinol needle produced smaller artefacts (mean width FSE/GRE: 2.8 mm/4.6 mm) with lower contrast (0.30–0.42) than the titanium alloy needle (mean width FSE/GRE: 4.1 mm/7.5 mm, contrast 0.60–0.73). Conclusions The carbon fibre/nitinol needle is useful for performing MR-guided interventions at 1.5 T, producing more subtle artefacts than a titanium alloy needle, but with an incomplete depiction and thus inaccurate localization of the needle tip.

Guidewire tracking during endovascular neurosurgery

This paper presents a new method for guidewire tracking on fluoroscopic images from endovascular brain intervention. The combination of algorithms chosen can be implemented in real time, so that it can be used in an augmented reality 3D representation to assist physicians performing these interventions. A ribbon-like morphing process combined with a minimal path optimization algorithm is used to track lateral motion between successive frames. Forward motions are then tracked with an endpoint tracking algorithm, based on a circular window processed with the Radon transform. The proposed method was tested on 6 fluoroscopic sequences presenting high-speed motions, which were saved during endovascular brain interventions. The experiments showed above-average precision and robust guidewire tracking, without any permanent error requiring manual correction.

SU‐GG‐J‐12: On‐Line Fluoroscopic Image of a Slice of Interest Using the X‐Ray Images and a Priori Anatomical Information

Purpose: On‐line 4‐D imaging is required for managing intra‐treatment organ motion. A new method which enables fluoroscopic imaging of a slice of interest (SOI) is developed and tested. This new technique uses projection images from the on‐board imaging system and does not use breathing surrogates. Method and Materials: Tomographic image via background subtraction (TIBS) uses a priori anatomical information from a previous cone beam or fan beam CT scan to isolate a SOI from a planar kV image by factoring out the attenuations by tissues outside the SOI (background). This study extends TIBS to 1) allow an SOI be imaged at any beam angle rather than only from that perpendicular to the SOI and 2) generate a temporal sequence of the SOI. The background is generated by substracting the SOI which is orthogonal to the desired viewing angle rather than to the gantry anlgle. Therefore, projection images taken during a gantry rotation can be used to generate images of the SOI of the same viewing angle but at different times, forming a fluoroscopic sequence of the SOI. A 14cm diameter cylindrical water phantom containing objects subject to one‐dimensional cyclic motion is used to test the feasibility. Results: The fluoroscopic image of the SOI containing moving objects was acquired by combining the SOI images from different gantry angles acquired at different times. Contrast of the objects is improved. Breathing surrogate or sorting process is not needed. Like tomosynthesis, a slice of interest can be clearly imaged. Unlike tomosysthesis, TIBS maintains the independence of each of the projections thereby reveals temporal variations within the SOI. Conclusion: A new technique which directly generates the fluoroscopic images of a SOI with x‐ray projections from the different angles is developed and proven feasible. This technique can be used for on‐line imaging of moving targets.

SU‐GG‐J‐148: Evaluation of Performance of a Conceptual Time‐Resolved Proton Range Telescope for In‐Room Respiration Monitoring Using Monte Carlo Simulations and 4DCT Patient Data

Purpose: To demonstrate the feasibility to perform and optimize a time‐resolved proton range telescope (TRRT) in localization of moving lung tumors and quantification of proton range variations. Method: A TRRT is designed to detect transmission protons and provide a fluoroscopic image showing tumor location and range perturbations prior to or during treatment. MCNPX code with a particle‐tracking feature was used to simulate and evaluate the TRRT performance, especially in visualizing and quantifying the proton range variations during respiration. Monoenergetic protons, 235 MeV in a 15cm × 15cm field, were tracked one by one as they pass through position detectors, 4DCT phantom, and finally scintillators that measured position and residual energies. Mass density and elemental composition of tissues were defined from a set of 4DCT of a lung patient. Radiological pathlength in the patient was determined by an energy‐range algorithm. Effects of multiple Coulomb scattering on image quality were determined by comparison with a pure ray‐tracing algorithm in Aqualyzer. Results: Interesting water equivalent length (WEL) maps for 10 respiratory phases were obtained to form fluoroscopic sequences. Appropriate color‐map windowing was used to visualize and measure tumor trajectories. The tumor trajectory extracted from the proton fluoroscopic simulation agreed with ground‐truth established by 4DCT to about 1mm. WEL difference maps were reconstructed to quantify respiration‐induced range changes. The maximum proton range pullback for the tumor target was measured to be 2.29 cm. Rejection of wide angle scatter events was found to effectively sharpen the image. Clinical applications to track the tumor during proton therapy using the range telescope are discussed. Conclusion: The performance of a TRRT is systematically studied and demonstrated by Monte Carlo simulations. When parameters are optimized, localization of a 2cm tumor is possible with an accuracy of about 1mm. Technical requirements for an operational device are discussed, including GPU acceleration.

Tumor motion prediction with the diaphragm as a surrogate: a feasibility study

We have previously assessed the use of the diaphragm as a surrogate for predicting real-time tumor position with linear models built with training data extracted from the same treatment fraction (Cerviño et al 2009 Phys. Med. Biol. 54 3529–41). However, practical use in the clinical setting requires the capability of predicting tumor position throughout the treatment course using a model built at the beginning of the course. We evaluate the inter-fraction applicability of linear models to predict superior–inferior tumor position based on diaphragm position using 21 fluoroscopic sequences from five lung cancer patients. Tumor position is predicted with models built during the first fluoroscopic sequence of each patient. Other fluoroscopic sets are registered to the first set with five different methods. The mean localization prediction error and maximum error at a 95% confidence level averaged over all patients are found to be 1.2 mm and 2.9 mm, respectively, for bony registration and 1.2 mm and 2.8 mm, respectively, for registration based on the mean position of the tumor in the first two breathing cycles. Other registration methods produce larger prediction errors. In the clinical setting, this prediction error could be added as a margin to the target volume. We therefore conclude that it is feasible to predict lung tumor motion with diaphragm with sufficient accuracy in the clinical setting.

MR-guided liver tumor ablation employing open high-field 1.0T MRI for image-guided brachytherapy

To determine the feasibility and safety of image-guided brachytherapy employing a modified open high-field MR system. This is a follow-up study of a development project enabling technologies for interventional use of 1.0T open MRI. Modifications included coils and in-bore visualization, fluoroscopic sequences and user interfaces. We recruited 104 patients with 224 liver malignancies to receive MR-guided brachytherapy. Interventions were performed >20 min after Gd-EOB-DTPA. We recorded interventional parameters including the intervention time (from acquisition of the first scout until the final sequence for brachytherapy treatment planning). Two reviewers assessed MR-fluoroscopic images in comparison to plain CT as used in CT intervention, applying a rating scale of 1-10. Statistical analysis included Friedman and Kendall's W tests. We employed freehand puncture with interactive dynamic imaging for navigation. Technical success rate was 218 complete ablations in 224 tumours (97%). The median intervention time was 61 min. We recorded no adverse events related to the use of MRI. No major complications occurred. The rate of minor complications was 4%. Local control at 3 months was 96%. Superiority of MR-fluoroscopic, Gd-EOB-DTPA-enhanced images over plain CT was highly significant (P < 0.001). MR-guided brachytherapy employing open high-field MRI is feasible and safe.

Image-guided spinal injection procedures in open high-field MRI with vertical field orientation: feasibility and technical features

We prospectively evaluated the feasibility and technical features of MR-guided lumbosacral injection procedures in open high-field MRI at 1.0 T. In a CuSO(4).5H(2)O phantom and five human cadaveric spines, fluoroscopy sequences (proton-density-weighted turbo spin-echo (PDw TSE), T1w TSE, T2w TSE; balanced steady-state free precession (bSSFP), T1w gradient echo (GE), T2w GE) were evaluated using two MRI-compatible 20-G Chiba-type needles. Artefacts were analysed by varying needle orientation to B(0), frequency-encoding direction and slice orientation. Image quality was described using the contrast-to-noise ratio (CNR). Subsequently, a total of 183 MR-guided nerve root (107), facet (53) and sacroiliac joint (23) injections were performed in 53 patients. In vitro, PDw TSE sequence yielded the best needle-tissue contrasts (CNR = 45, 18, 15, 9, and 8 for needle vs. fat, muscle, root, bone and sclerosis, respectively) and optimal artefact sizes (width and tip shift less than 5 mm). In vivo, PDw TSE sequence was sufficient in all cases. The acquisition time of 2 s facilitated near-real-time MRI guidance. Drug delivery was technically successful in 100% (107/107), 87% (46/53) and 87% (20/23) of nerve root, facet and sacroiliac joint injections, respectively. No major complications occurred. The mean procedure time was 29 min (range 19-67 min). MR-guided spinal injections in open high-field MRI are feasible and accurate using fast TSE sequence designs.

SU‐FF‐J‐47: Assessment of Diaphragm as An Internal Surrogate for Lung Tumor Motion Prediction

Purpose: We have previously assessed the use of diaphragm as a surrogate for predicting real‐time tumor position with linear models built with training data extracted from the same treatment fraction. In this study, we evaluate inter‐fraction variability of model parameters and the prediction error for different fractions from the model built on the first fraction. Method and Materials: 21 fluoroscopic sequences from 5 lung cancer patients were used for this study. Each patient has from 2 to 6 fluoroscopic sequences from at least 2 different treatment fractions. Each sequence consists of 352 to 690 frames at 15 frames per second. Superior‐inferior motions of the diaphragm and the tumor were identified in every frame. A model to predict tumor position was built for each sequence, and the parameters from different sequences were compared. Then, the model built from the first fluoroscopic sequence was used to predict tumor position in the subsequent fluoroscopic sets of each patient. Prediction error was calculated for three different ways of registering fluoroscopic sets: manual bony anatomy registration, mean tumor position registration, and mean diaphragm position registration. Results: Average variability of the correlation and slope of linear models built from different fluoroscopic sequences are 1.3% and 8.6% respectively. Prediction based on the model built with data from the first sequence leads to an average mean localization error and average error at a 95% confidence level of 1.2mm and 2.9mm respectively for bony registration, 1.5mm and 3.3mm for mean tumor position registration, and 2.5mm and 4.7mm for mean diaphragm position registration. Conclusion: For the patients studied, diaphragm has shown to be a good surrogate for tumor motion. Variability of model parameters and prediction error from one sequence to another are small. Bony registration seems the most accurate method for patient setup when using diaphragm as a surrogate.

Fluoroscopic tumor tracking for image-guided lung cancer radiotherapy

Accurate lung tumor tracking in real time is a keystone to image-guided radiotherapy of lung cancers. Existing lung tumor tracking approaches can be roughly grouped into three categories: (1) deriving tumor position from external surrogates; (2) tracking implanted fiducial markers fluoroscopically or electromagnetically; (3) fluoroscopically tracking lung tumor without implanted fiducial markers. The first approach suffers from insufficient accuracy, while the second may not be widely accepted due to the risk of pneumothorax. Previous studies in fluoroscopic markerless tracking are mainly based on template matching methods, which may fail when the tumor boundary is unclear in fluoroscopic images. In this paper we propose a novel markerless tumor tracking algorithm, which employs the correlation between the tumor position and surrogate anatomic features in the image. The positions of the surrogate features are not directly tracked; instead, we use principal component analysis of regions of interest containing them to obtain parametric representations of their motion patterns. Then, the tumor position can be predicted from the parametric representations of surrogates through regression. Four regression methods were tested in this study: linear and two-degree polynomial regression, artificial neural network (ANN) and support vector machine (SVM). The experimental results based on fluoroscopic sequences of ten lung cancer patients demonstrate a mean tracking error of 2.1 pixels and a maximum error at a 95% confidence level of 4.6 pixels (pixel size is about 0.5 mm) for the proposed tracking algorithm.

Parametric characterization of spinal motions in osteoporotic vertebral fracture at level T12 with fluoroscopy

Vertebral fractures due to osteoporosis are a common skeletal disorder affecting the mobility of the patients, although little is known about the relationship between spinal kinematics and osteoporotic fracture. The purpose of this study was to characterize the motions of the thoracolumbar spine affected by osteoporotic vertebral fracture at level T12 and compare the results with those of non-fracture osteoporosis subjects. We examined the continuous segmental kinematics of the vertebrae, and describe the segmental motion of the spine when a fracture at T12 is present. Fluoroscopy sequences of the thoracolumbar spines during sagittal and lateral flexion were collected from 16 subjects with osteoporosis of their spine (6 with vertebral fractures at T12, 10 without a fracture). Vertebrae T10–L2 in each frame of the sequences were landmarked. Kinematic parameters were calculated based on the landmarks and motion graphs were constructed. Compared to the control subjects who did not have a fracture, fracture subjects had a more asymmetric lateral range of motion (RoM) and required a longer time to complete certain phases of the motion cycle which are parameterized as lateral flexion ratio and percentage of motion cycle, respectively. Prolonged deflection was more frequently found from the fracture group. Characterizing the motions of the fractured vertebra together with its neighboring vertebrae with these kinematic parameters is useful in quantifying the dysfunction and may be a valuable aid to tracking progress of treatment.

SU‐GG‐J‐174: Study On the Correlation of Diaphragm Motion and Lung Tumor Motion

Purpose: To assess the correlation of diaphragm motion and lung tumor motion as seen in anterior‐to‐posterior (AP) fluoroscopic sequences. Method and Materials: Fluoroscopic sequences of 7 different lung cancer patients were used for this study. Each sequence consists of 500 to 700 frames at 15 frames per second. Diaphragm position was identified in every frame by an intensity gradient method and tumor positions were manually marked as the ground truth by an expert observer. A Principal Component Analysis model based on 225 (15sec) training frames was built for each patient for tumor tracking based on surrogates. Surrogates included the current diaphragm position alone or an optimal combination of the current diaphragm position plus the diaphragm position temporal history. This optimal set was obtained by the Sequential Forward Floating Search method for feature selection. The error of each model was computed by using the rest of each sequence as testing data. Results: Results show that, in most of the patients, the diaphragm position alone is a good surrogate of the tumor motion, with an average localization error ē of 1.6mm and average error at a 95% confidence level e95 of 3.9mm. The model is improved in most of the patients by adding new surrogates from the diaphragm position history (ē=1.3mm, e95=3.5mm). However, some patients, especially patients with irregular breathing, do not show a good correlation. Conclusion: Gated radiotherapy of the lung relies on the correlation of the tumor motion with respect to the diaphragm. It has been observed that although this correlation is in general good, and can be improved with more sophisticated correlation models, some patients do not show a good correlation regardless of how sophisticated the model is. In future work, new surrogates which better correlate with the tumor motion will be explored for use in gated treatment.

WE‐C‐330A‐01: Robust Tracking of Interventional Tools Under X‐Ray Fluoroscopy Using Particle Filters

Purpose: Motion estimation is an important problem. In diagnostic and therapeutic interventions, intraoperative motion estimation is needed to guide interventional tools with high precision. In radiation therapy, intrafraction motion estimation is essential to improve the precision with which therapeutic radiation is delivered. The purpose of this study is to estimate the pose (location and orientation) of interventional tools such as needles in an X‐ray fluoroscopic sequence using a particle filter. Method and Materials: Tracking Algorithm: The tools were tracked using a particle filter. Two models are of concern in such an implementation — (i) the observation model was defined on the output of an edge detector by taking transverse and longitudinal samples of the tool, and (ii) the dynamic model was assumed to be given by Brownian motion.Experimental Setup: The accuracy of the tracking algorithm was validated on an X‐ray fluoroscopy test bench. A modified anthropomorphic Rando™ phantom was placed in the field‐of‐view in order to emulate the background presented by a patient. Two sites on this phantom were used — the pelvis and the thorax. The pelvis presents a case of low signal while the thorax presents a cluttered background. The tool to be tracked was attached to a linear actuator and moved in known increments while capturing fluoroscopic images. The acquired image sequence was then sampled to generate new image sequences for testing the tracking algorithm. Results: The algorithm was robustly able to track the tool under a low signal in the abdomen, and under dense clutter presented by the ribs in the thorax. The rms error in each case was found to be as little as 0.7mm and 0.12mm, respectively. Conclusion: This study demonstrates the robustness of estimation under noise and clutter that can be achieved when tracking tools in a fluoroscopic sequence using a particle filtering approach.

TU‐FF‐A4‐02: Active Tool/Fiducial Segmentation and Tracking in Multiple Modalities

Purpose: To build a tracking framework that, given a description of a tool/fiducial, the geometry of the imaging system and a sequence of images, outputs estimates of selected kinematics of the tool/fiducial along with a measure of the uncertainty in these estimates. The output of the system may be used as feedback to actively modify the imaging system parameters in order to achieve the desired precision with which the object is tracked while minimizing other parameters (eg. dose delivered to the patient). Method and Materials: A two stage approach is employed where (i) the object is segmented using its invariant features, its model, and other prior information that may be available and (ii) a particle filter is applied to the results of the segmentation for robustly tracking the object. A particle filter is chosen because of its simplicity, its robustness to noise and occlusion, its ability to represent multimodal beliefs, and also because its performance approaches that of the optimal Kalman filter given enough samples. Results: This approach has been applied to a (physically) simulated brachytherapy procedure to track the position of a needle loaded with seeds in an X‐ray fluoroscopic sequence. The system outputs the 3D position and orientation of the needle along with a confidence measure along each dimension. This output is robust to noise and partial occlusion. Conclusion: This work provides a generic framework for segmentation and tracking across multiple modalities that also reports a confidence measure for each estimated parameter. Such a system has many online applications such as radiation therapy guidance, intra‐operative image‐guided laparoscopic surgery, brachytherapy and various biopsy procedures.

Tracking Technique of a Micro Guide Wire in Sequential Fluorograms

In this paper, we propose a tracking technique for a micro guide wire in a sequence of fluorograms. A technique in which the region-growing technique was embedded was developed. It gives the center line of a micro guide wire. A sequence of 1,024 x 1,024 x 16 bit fluorograms (111 frames) with a carotid phantom and head phantom was obtained with a CAS-8000V (Toshiba America Medical Systems, Inc., CA, USA) C-arm angiography system and a Hi-Torque Standard micro guide wire (Advanced Cardiovascular Systems, Inc., CA, USA). To evaluate the technique, we manually traced the guide wire in each sequence frame three times, and a "true" single-width micro guide wire was created from them. The number of pixels on the true guide wire and inside the two-pixel tolerance of the center line was counted in each fluorogram, and the percentage of that count based on the number of all pixels on the true guide wire was calculated as true positive (TP). In addition, the number of pixels on the center line and outside the two-pixel tolerance of the true guide wire was counted in each frame as false positive (FP). The tracking technique has a mean TP of 94.8% and a mean FP of 5.1 pixels/frame. Several frames have low TP and high FP, but the technique could continue to track the micro guide wire until the end of the sequence. We therefore concluded that we had developed an accurate automatic tracking technique for micro guide wires in fluoroscopic sequences.

Analysis and evaluation of periodic physiological organ motion in radiotherapy treatments

Background and purposeA system for the detection, measurement and analysis of the periodic physiological organ motion during radiotherapy treatment is proposed and clinically tested in this paper. Material and methodsThe procedure is based on the acquisition of fluoroscopic sequences, followed by an automatic detection of the movement using cross-correlations with matched filters. ResultsThe system generates a probability density function (PDF) of finding a mobile organ in a position at a certain time. The maximum path of the mobile structures can be determined to define the planning target volume (PTV) without ambiguities. ConclusionsPhysiological movements can be accurately included in the daily planning routine, which is not essentially modified, without needing previous patient training.

Magnetic Resonance Imaging Characteristics of Six Radiofrequency Electrodes in a Phantom Study

To evaluate and compare visibility and artifacts in magnetic resonance (MR) compatible radiofrequency (RF) electrodes for MR-guided RF ablation. Six different MR compatible electrodes for RF ablation including two internally cooled single needles, one internally cooled cluster needle, two expandable needles and one perfused needle were tested in a phantom study at 0.2 Tesla and at 1.5 Tesla field strength. Fluoroscopic, T1- and T2-weighted fast spin echo (FSE) and gradient echo (GE) sequences, which are usually used for MR-guided interventions, were evaluated. Qualitative and quantitative evaluations were performed. Length, width, noise, tip artifacts, global artifacts and global visualization of the RF electrodes that showed all sequences at different angles. Qualitative analysis showed that electrodes were well visualized at all angles and sequences and on both MR imagers. Quantitative analysis showed that artifact-induced widening of the shaft was increased in all electrodes by: a). use of fluoroscopic sequences, GE sequences, and fat saturation, b). increasing the angle between the needle and main magnetic field, and c). high field strength (1.5 T). Expandable needles produced fewer tip artifacts but broader signal voids along the shaft compared to nonexpandable needles. Cluster electrodes produced less widening than the other electrodes. Visibility and artifacts in all six MR compatible RF electrodes are satisfactory and these electrodes could be used for MR-guided radiofrequency ablation procedures.

1155-82 Reduced fluoroscopy time and cine sequences with digital flat panel technology

1155-82 Reduced fluoroscopy time and cine sequences with digital flat panel technology

Evaluation of complex joint motion with computer-based analysis of fluoroscopic sequences.

To develop a computer-assisted analysis of complex joint motion based on standard fluoroscopic sequences. Fluoroscopic sequences of 10 normal shoulders and 20 patients after total shoulder arthroplasty were recorded during abduction and adduction. The analysis of the shoulder motion was based on automated tracking of selected components (models) of the shoulder joint. After processing the digitized images with an edge-detection procedure, visible edges were defined as base models. These models were tracked frame by frame. Several automated postprocessing evaluation procedures were developed and tested. The amounts of rotation and translation of the glenohumeral joint can be quantified and related. The mean translation parallel to the glenoid in the normal shoulder joints was 2.8 mm and 1.9 mm in joints after shoulder arthroplasty. The mean translation perpendicular to the glenoid was 0.9 mm and 0.8 mm, respectively. In complex motion patterns (ie, combined glenohumeral and thoracoscapular motion), electronic stabilization of an object (ie, stabilization of scapula) and, thus, separate analysis of each component. Computer assisted analysis allows automated evaluation of complex joint motion based on standard fluoroscopic sequences.