Motion Compensation Scheme Research Articles

Simple motion correction strategy reduces respiratory-induced motion artifacts for k-t accelerated and compressed-sensing cardiovascular magnetic resonance perfusion imaging

BackgroundCardiovascular magnetic resonance (CMR) stress perfusion imaging provides important diagnostic and prognostic information in coronary artery disease (CAD). Current clinical sequences have limited temporal and/or spatial resolution, and incomplete heart coverage. Techniques such as k-t principal component analysis (PCA) or k-t sparcity and low rank structure (SLR), which rely on the high degree of spatiotemporal correlation in first-pass perfusion data, can significantly accelerate image acquisition mitigating these problems. However, in the presence of respiratory motion, these techniques can suffer from significant degradation of image quality. A number of techniques based on non-rigid registration have been developed. However, to first approximation, breathing motion predominantly results in rigid motion of the heart. To this end, a simple robust motion correction strategy is proposed for k-t accelerated and compressed sensing (CS) perfusion imaging.MethodsA simple respiratory motion compensation (MC) strategy for k-t accelerated and compressed-sensing CMR perfusion imaging to selectively correct respiratory motion of the heart was implemented based on linear k-space phase shifts derived from rigid motion registration of a region-of-interest (ROI) encompassing the heart. A variable density Poisson disk acquisition strategy was used to minimize coherent aliasing in the presence of respiratory motion, and images were reconstructed using k-t PCA and k-t SLR with or without motion correction. The strategy was evaluated in a CMR-extended cardiac torso digital (XCAT) phantom and in prospectively acquired first-pass perfusion studies in 12 subjects undergoing clinically ordered CMR studies. Phantom studies were assessed using the Structural Similarity Index (SSIM) and Root Mean Square Error (RMSE). In patient studies, image quality was scored in a blinded fashion by two experienced cardiologists.ResultsIn the phantom experiments, images reconstructed with the MC strategy had higher SSIM (p < 0.01) and lower RMSE (p < 0.01) in the presence of respiratory motion. For patient studies, the MC strategy improved k-t PCA and k-t SLR reconstruction image quality (p < 0.01). The performance of k-t SLR without motion correction demonstrated improved image quality as compared to k-t PCA in the setting of respiratory motion (p < 0.01), while with motion correction there is a trend of better performance in k-t SLR as compared with motion corrected k-t PCA.ConclusionsOur simple and robust rigid motion compensation strategy greatly reduces motion artifacts and improves image quality for standard k-t PCA and k-t SLR techniques in setting of respiratory motion due to imperfect breath-holding.

Motion compensation with skin contact control for high intensity focused ultrasound surgery in moving organs

High intensity focused ultrasound (HIFU) is an emerging therapeutic solution that enables non-invasive treatment of several pathologies, mainly in oncology. On the other hand, accurate targeting of moving abdominal organs (e.g. liver, kidney, pancreas) is still an open challenge. This paper proposes a novel method to compensate the physiological respiratory motion of organs during HIFU procedures, by exploiting a robotic platform for ultrasound-guided HIFU surgery provided with a therapeutic annular phased array transducer. The proposed method enables us to keep the same contact point between the transducer and the patient’s skin during the whole procedure, thus minimizing the modification of the acoustic window during the breathing phases. The motion of the target point is compensated through the rotation of the transducer around a virtual pivot point, while the focal depth is continuously adjusted thanks to the axial electronically steering capabilities of the HIFU transducer.The feasibility of the angular motion compensation strategy has been demonstrated in a simulated respiratory-induced organ motion environment. Based on the experimental results, the proposed method appears to be significantly accurate (i.e. the maximum compensation error is always under 1 mm), thus paving the way for the potential use of this technique for in vivo treatment of moving organs, and therefore enabling a wide use of HIFU in clinics.

Nonrigid motion compensation in compressed sensing reconstruction of cardiac cine MRI

In this work, a robust nonrigid motion compensation approach, is applied to the compressed sensing reconstruction of dynamic cardiac cine MRI sequences. Respiratory and cardiac motion separation coupled with a registration algorithm is used to provide accurate reconstruction of dynamic cardiac images. The proposed scheme employs a variable splitting based optimization strategy to enable joint motion estimation along with reconstruction. We define the recovery as an energy minimization scheme utilizing an objective function that combines data consistency, spatial smoothness, and motion penalties. The validation of the proposed algorithm using numerical phantom and in-vivo cine MRI data demonstrates reconstruction of cardiac MRI data with less spatio-temporal blurring and motion artifacts from extensively under-sampled data. The proposed method is observed to provide improved reconstructions over state-of-the-art motion compensation schemes.

Motion compensation on baseline oscillations for distributed array SAR by combining interferograms and inertial measurement

Distributed array synthetic aperture radar (DASAR), in which multiple distributed antennas are mounted on a crosstrack, has applications that include multibaseline interferometry, multiple-input multiple-output SAR, and tomography. However, this flexible imaging geometry requires accurate measurement of the movements of each antenna. High-precision navigation systems are commonly used, but configuring a separate navigational system for each antenna is challenging and costly. In this study, the authors proposed a novel motion compensation scheme for DASAR that combines inteferograms and inertial measurement. The authors fabricated a rigid baseline (RB) and multiple flexible baseline (FB) configuration, fitted with a large and accurate position and orientation system and with multiple smaller, low-precision inertial navigation systems (INS) for motion measurement. The authors introduced a new robust algorithm based on a function relating RB and FB interferometry, and used this to estimate the relative movements. Finally, a Kalman filter was designed to integrate the results of databased estimation and inertial measurement. This combined the strengths of data estimation for slow movement and inertial measurement for fast movement. The results of both simulations and airborne experiments confirmed the success of this novel approach in allowing a small INS to be used for motion compensation in DASAR applications.

4-D Reconstruction With Respiratory Correction for Gated Myocardial Perfusion SPECT.

Cardiac single photon emission computed tomography (SPECT) images are known to suffer from both cardiac and respiratory motion blur. In this paper, we investigate a 4-D reconstruction approach to suppress the effect of respiratory motion in gated cardiac SPECT imaging. In this approach, the sequence of cardiac gated images is reconstructed with respect to a reference respiratory amplitude bin in the respiratory cycle. To combat the challenge of inherent high-imaging noise, we utilize the data counts acquired during the entire respiratory cycle by making use of a motion-compensated scheme, in which both cardiac motion and respiratory motion are taken into account. In the experiments, we first use Monte Carlo simulated imaging data, wherein the ground truth is known for quantitative comparison. We then demonstrate the proposed approach on eight sets of clinical acquisitions, in which the subjects exhibit different degrees of respiratory motion blur. The quantitative evaluation results show that the 4-D reconstruction with respiratory correction could effectively reduce the effect of motion blur and lead to a more accurate reconstruction of the myocardium. The mean-squared error of the myocardium is reduced by 22%, and the left ventricle (LV) resolution is improved by 21%. Such improvement is also demonstrated with the clinical acquisitions, where the motion blur is markedly improved in the reconstructed LV wall and blood pool. The proposed approach is also noted to be effective on correcting the spill-over effect in the myocardium from nearby bowel or liver activities.

SC03.01 Advances in Stereotactic Body Radiotherapy

SC03.01 Advances in Stereotactic Body Radiotherapy

An iterative projection-based motion estimation and compensation scheme for head x-ray CT.

Although current computed tomography (CT) systems can scan the head in a very short time, patient motion sometimes still induces artifacts. If motion occurs, one has to repeat the scan; to avoid motion, sedation or anesthesia is sometimes applied. The authors propose a method to iteratively estimate and compensate this motion during the reconstruction. In every iteration, the rigid motion was estimated view-by-view and then used to update the system matrix. A multiresolution scheme was used to speed up the convergence of this joint estimation of the image and the motion of the subject. A final iterative reconstruction was performed with the last motion estimate. The method was evaluated on simulations, patient scans, and a phantom study. The quality of the reconstructed images was improved substantially after the compensation. In simulation and phantom studies, root-mean-square error was reduced and mean structural similarity was increased. In the patient studies, most of the motion blurring in the reconstructed images disappeared after the compensation. The proposed method effectively eliminated motion-induced artifacts in head CT scans. Since only measured raw data are needed for the motion estimation and compensation, the proposed method can be applied retrospectively to clinical helical CT scans affected by motion.

Range-Dependent Map-Drift Algorithm for Focusing UAV SAR Imagery

Synthetic aperture radar (SAR) systems mounted on unmanned aerial vehicles (UAVs) are usually sensitive to trajectory deviations that cause serious motion error in the recorded data. In this letter, a novel range-dependent map-drift algorithm (RDMDA) is developed to accommodate the range-variant characteristics of severe motion errors. Utilizing the algorithm as a core estimate, we come up with a robust motion compensation strategy for the UAV SAR imagery. RDMDA outperforms the conventional MDA in both accuracy and robustness while it keeps similar efficiency. Real data experiment shows that the proposed approach is appropriate for precise imaging of UAV SAR systems equipped with only a low-accuracy inertial navigation system.

The Analysis and Realization of Motion Compensation for Circular Synthetic Aperture Radar Data

Regarding the two-dimensional (2-D) imaging processing of circular synthetic aperture radar (CSAR), the motion compensation (MOCO) in the frequency domain is not fully developed. To perform the MOCO for CSAR data in the frequency domain, a novel three-step strategy is presented in this paper. The motion error model is established first, and it is found that a difficulty of MOCO for CSAR lies in the space variance of the motion errors. Specifically, according to the proposed MOCO strategy, this first step is space-invariant MOCO, the second step is space-variant MOCO in the range-compressed angular-wavenumber domain with respect to subaperture data, and the last step is the autofocus operation in the 2-D wavenumber domain after the polar format resampling. Eventually, the complete MOCO flowchart is obtained. Simulation and experimental tests verify that the proposed motion error model is valid and the three-step MOCO strategy can remove motion errors accurately and figure out well-focused CSAR images.

Evaluation of Rigid-Body Motion Compensation in Cardiac Perfusion SPECT Employing Polar-Map Quantification.

We have recently been successful in the development and testing of rigid-body motion tracking, estimation and compensation for cardiac perfusion SPECT based on a visual tracking system (VTS). The goal of this study was to evaluate in patients the effectiveness of our rigid-body motion compensation strategy. Sixty-four patient volunteers were asked to remain motionless or execute some predefined body motion during an additional second stress perfusion acquisition. Acquisitions were performed using the standard clinical protocol with 64 projections acquired through 180 degrees. All data were reconstructed with an ordered-subsets expectation-maximization (OSEM) algorithm using 4 projections per subset and 5 iterations. All physical degradation factors were addressed (attenuation, scatter, and distance dependent resolution), while a 3-dimensional Gaussian rotator was used during reconstruction to correct for six-degree-of-freedom (6-DOF) rigid-body motion estimated by the VTS. Polar map quantification was employed to evaluate compensation techniques. In 54.7% of the uncorrected second stress studies there was a statistically significant difference in the polar maps, and in 45.3% this made a difference in the interpretation of segmental perfusion. Motion correction reduced the impact of motion such that with it 32.8 % of the polar maps were statistically significantly different, and in 14.1% this difference changed the interpretation of segmental perfusion. The improvement shown in polar map quantitation translated to visually improved uniformity of the SPECT slices.

Clinical evaluation of 4D PET motion compensation strategies for treatment verification in ion beam therapy

A clinical trial named PROMETHEUS is currently ongoing for inoperable hepatocellular carcinoma (HCC) at the Heidelberg Ion Beam Therapy Center (HIT, Germany). In this framework, 4D PET-CT datasets are acquired shortly after the therapeutic treatment to compare the irradiation induced PET image with a Monte Carlo PET prediction resulting from the simulation of treatment delivery. The extremely low count statistics of this measured PET image represents a major limitation of this technique, especially in presence of target motion. The purpose of the study is to investigate two different 4D PET motion compensation strategies towards the recovery of the whole count statistics for improved image quality of the 4D PET-CT datasets for PET-based treatment verification. The well-known 4D-MLEM reconstruction algorithm, embedding the motion compensation in the reconstruction process of 4D PET sinograms, was compared to a recently proposed pre-reconstruction motion compensation strategy, which operates in sinogram domain by applying the motion compensation to the 4D PET sinograms. With reference to phantom and patient datasets, advantages and drawbacks of the two 4D PET motion compensation strategies were identified. The 4D-MLEM algorithm was strongly affected by inverse inconsistency of the motion model but demonstrated the capability to mitigate the noise-break-up effects. Conversely, the pre-reconstruction warping showed less sensitivity to inverse inconsistency but also more noise in the reconstructed images. The comparison was performed by relying on quantification of PET activity and ion range difference, typically yielding similar results. The study demonstrated that treatment verification of moving targets could be accomplished by relying on the whole count statistics image quality, as obtained from the application of 4D PET motion compensation strategies. In particular, the pre-reconstruction warping was shown to represent a promising choice when combined with intra-reconstruction smoothing.

Context region discovery for automatic motion compensation in fluoroscopy.

Image-based tracking for motion compensation is an important topic in image-guided interventions, as it enables physicians to operate in a less complex space. In this paper, we propose an automatic motion compensation scheme to boost image guidence power in transcatheter aortic valve implantation (TAVI). The proposed tracking algorithm automatically discovers reliable regions that correlate strongly with the target. These discovered regions can assist to estimate target motion under severe occlusion, even if target tracker fails. We evaluate the proposed method for pigtail tracking during TAVI. We obtain significant improvement (12%) over the baseline in a clinical dataset. Calcification regions are automatically discovered during tracking, which would aid TAVI processes. In this work, we open a new paradigm to provide dynamic real-time guidance for TAVI without user interventions, specially in case of severe occlusion where conventional tracking methods are challenged.

Shape-based motion correction in dynamic contrast-enhanced MRI for quantitative assessment of renal function.

To incorporate a newly developed shape-based motion estimation scheme into magnetic resonance urography (MRU) and verify its efficacy in facilitating quantitative functional analysis. The authors propose a motion compensation scheme in MRU that consists of three sequential modules: MRU image acquisition, motion compensation, and quantitative functional analysis. They designed two sets of complementary experiments to evaluate the performance of the proposed method. In the first experiment, dynamic contrast enhanced (DCE) MR images were acquired from three sedated subjects, from which clinically valid estimates were derived and served as the "ground truth." Physiologically sound motion was then simulated to synthesize image sequences influenced by respiratory motion. Quantitative assessment and comparison were performed on functional estimates of Patlak number, glomerular filtration rate, and Patlak differential renal function without and with motion compensation against the ground truth. In the second experiment, the authors acquired a temporal series of noncontrast MR images under free breathing from a healthy adult subject. The performance of the proposed method on compensating real motion was evaluated by comparing the standard deviation of the obtained temporal intensity curves before and after motion compensation. On DCE-MR images with simulated motion, the generated relative enhancement curves exhibited large perturbations and the Patlak numbers of the left and right kidney were significantly underestimated up to 35% and 34%, respectively, compared with the ground truth. After motion compensation, the relative enhancement curves exhibited much less perturbations and Patlak estimation errors reduced within 3% and 4% for the left and right kidneys, respectively. On clinical free-breathing MR images, the temporal intensity curves exhibited significantly reduced variations after motion compensation, with standard deviation decreased from 30.3 and 38.2 to 8.3 and 11.7 within two manually selected regions of interest, respectively. The developed motion compensation method has demonstrated its ability to facilitate quantitative MRU functional analysis, with improved accuracy of pharmacokinetic modeling and quantitative parameter estimations. Future work will consider performing more intensive clinical verifications with sophisticated pharmacokinetic models and generalizing the proposed method to other quantitative DCE analysis, such as on liver or prostate function.

Motion compensation for high-resolution automobile-SAR

This article concerns the analysis and compensation of track deviations in high-resolution automobile synthetic aperture radar (SAR). We establish the geometry in which the automobile-SAR raw data is acquired. Based on the derived model, the research investigates the impact of track deviations on the final focused image quality and we propose a motion compensation strategy which can be applied to obtain a well-focused SAR image. This article presents how to obtain the accurate positions of the antenna phase centre using the velocity and attitude angles measured by inertial navigation system/global positioning system, and proposes a new method to compensate for forward velocity errors which are decomposed into two components and compensated individually, that is, high-order and low-order phase compensation. Finally, the results from both simulated data and real data are presented to validate the whole analysis and the proposed procedure.

Evaluation of respiratory and cardiac motion correction schemes in dual gated PET/CT cardiac imaging.

Cardiac imaging suffers from both respiratory and cardiac motion. One of the proposed solutions involves double gated acquisitions. Although such an approach may lead to both respiratory and cardiac motion compensation there are issues associated with (a) the combination of data from cardiac and respiratory motion bins, and (b) poor statistical quality images as a result of using only part of the acquired data. The main objective of this work was to evaluate different schemes of combining binned data in order to identify the best strategy to reconstruct motion free cardiac images from dual gated positron emission tomography (PET) acquisitions. A digital phantom study as well as seven human studies were used in this evaluation. PET data were acquired in list mode (LM). A real-time position management system and an electrocardiogram device were used to provide the respiratory and cardiac motion triggers registered within the LM file. Acquired data were subsequently binned considering four and six cardiac gates, or the diastole only in combination with eight respiratory amplitude gates. PET images were corrected for attenuation, but no randoms nor scatter corrections were included. Reconstructed images from each of the bins considered above were subsequently used in combination with an affine or an elastic registration algorithm to derive transformation parameters allowing the combination of all acquired data in a particular position in the cardiac and respiratory cycles. Images were assessed in terms of signal-to-noise ratio (SNR), contrast, image profile, coefficient-of-variation (COV), and relative difference of the recovered activity concentration. Regardless of the considered motion compensation strategy, the nonrigid motion model performed better than the affine model, leading to higher SNR and contrast combined with a lower COV. Nevertheless, when compensating for respiration only, no statistically significant differences were observed in the performance of the two motion models considered. Superior image SNR and contrast were seen using the affine respiratory motion model in combination with the diastole cardiac bin in comparison to the use of the whole cardiac cycle. In contrast, when simultaneously correcting for cardiac beating and respiration, the elastic respiratory motion model outperformed the affine model. In this context, four cardiac bins associated with eight respiratory amplitude bins seemed to be adequate. Considering the compensation of respiratory motion effects only, both affine and elastic based approaches led to an accurate resizing and positioning of the myocardium. The use of the diastolic phase combined with an affine model based respiratory motion correction may therefore be a simple approach leading to significant quality improvements in cardiac PET imaging. However, the best performance was obtained with the combined correction for both cardiac and respiratory movements considering all the dual-gated bins independently through the use of an elastic model based motion compensation.

Spatiotemporal deinterlacing using a maximuma posterioriestimator based on multiple-field registration

This paper proposes an accurate deinterlacing algorithm using a maximum a posteriori (MAP) estimator. First, we produce accurate motion vector fields between the current field and adjacent fields by employing an advanced motion compensation scheme that is suitable for an interlaced format. Next, the progressive frame corresponding to the current field is found via the MAP estimator based on the derived motion vector fields. Here, in order to obtain a stable solution, well-known bilateral total variation–based regularization is applied. Then, at a specific mode decision step, it is decided whether the result from the aforementioned temporal deinterlacing is acceptable or not. Finally, if the temporal deinterlacing is determined to be inappropriate by the mode decision, a typical spatial deinterlacing is applied instead of the MAP estimator-based temporal deinterlacing. Experimental results show that the proposed algorithm provides at maximum 2 dB higher PSNR than a cutting-edge deinterlacing algorithm, while providing better visual quality than the latter.

Dosimetric feasibility of MRI-guided external beam radiotherapy of the kidney

At our institution a treatment for kidney tumours with an MRI-Linac is under development. In order to set inclusion criteria for this treatment the anatomical eligibility criteria and the influence of the motion compensation strategy on the delivered dose should be known. Twenty patients with a renal lesion underwent an MR-scan to image the kidney. Static treatment plans were made and the doses to the organs at risk were evaluated. Furthermore, to calculate the influence of remnant motion in a gated treatment, a convolution of the static dose plan with the residual motion in a gating window was done. For ten patients (50%) a static plan within the dose constraints could be obtained. For all patients where the kidney constraint was obeyed in the static plan, the dose to the gross tumour volume (GTV) and the ipsilateral kidney remained within limits for residual motion in a gating window up to and including 12 mm. For four patients (20%) no static plan without violation of the constraint to the ipsilateral kidney could be made. One of these patients had a tumour of 73 mm in the upper pole and the other patients had a tumour of at least 30 mm in the mid pole. In 6 patients (30%), where the bowels were within the planning target volume, the maximum dose to the bowels was above the limit used. Patient specific assessment might degrade this violation. For tumours smaller than 30 mm a clinically acceptable plan could be created. For other patients the feasibility depends on the geometry of the GTV and kidney. Neither the GTV coverage nor the ipsilateral kidney dose is compromised by breathing motion for gating with a gating window up to and including 12 mm.

A fine image motion compensation method for the panoramic TDI CCD camera in remote sensing applications

The image motion caused by camera housing rotation is the natural component in panoramic TDI CCD camera, and it cannot be eliminated thoroughly by traditional motion compensation schemes. After researching on the operation of a typical panoramic TDI CCD imaging system, we present a fine rolling rate independent motion compensation method. Employing the correction factor k, a TDI CCD line transfer synchronization signal is generated by the high resolution optical encoder as long as the ground scene moves one pixel with respect to the detector. Then, the effect of the motion compensation method is evaluated using the Monte Carlo method. The simulation results indicate that the magnitude of the modulation transfer function at the Nyquist frequency increases more than three times by increasing the subdivision steps from 100 to 500, and also of the imaging experimental results show that the image quality improvement can be achieved.

Couch-based motion compensation: modelling, simulation and real-time experiments

The paper presents a couch-based active motion compensation strategy evaluated in simulation and validated experimentally using both a research and a clinical Elekta Precise Table™. The control strategy combines a Kalman filter to predict the surrogate motion used as a reference by a linear model predictive controller with the control action calculation based on estimated position and velocity feedback provided by an observer as well as predicted couch position and velocity using a linearized state space model. An inversion technique is used to compensate for the dead-zone nonlinearity. New generic couch models are presented and applied to model the Elekta Precise Table™ dynamics and nonlinearities including dead zone. Couch deflection was measured for different manufacturers and found to be up to 25 mm. A feed-forward approach is proposed to compensate for such couch deflection. Simultaneous motion compensation for longitudinal, lateral and vertical motions was evaluated using arbitrary trajectories generated from sensors or loaded from files. Tracking errors were between 0.5 and 2 mm RMS. A dosimetric evaluation of the motion compensation was done using a sinusoidal waveform. No notable differences were observed between films obtained for a fixed- or motion-compensated target. Further dosimetric improvement could be made by combining gating, based on tracking error together with beam on/off time, and PSS compensation.

Sci-Thur PM: YIS - 03: Comparing 4D-VMAT, Gated-VMAT and 3D-VMAT in SBRT treatment of lung cancer.

To evaluate the treatment plan qualities of 4D-VMAT, gated-VMAT and 3D-VMAT in the treatment of non-small cell lung cancer (NSCLC) in stereotactic body radiation therapy (SBRT). 4D-VMAT is a motion compensation strategy that aims to exploit relative target and OAR motion to increase OAR sparing over 3D-VMAT without the long treatment times associated with gated-VMAT. The 4D-VMAT algorithm incorporates the entire patient respiratory cycle and 4D-CT in the optimization process. Resulting treatment plans synchronize the delivery of each MLC aperture to a specific phase of the target motion. Using software developed in Matlab™, SBRT treatment plans for 4D-VMAT, gated-VMAT and 3D-VMAT were generated on 3 patients with NSCLC. Tumour motion ranged from 1.4-3.4 cm. The fractionation scheme was 48Gy in 4 fractions with the GTV receiving 100% of the prescribed dose. For gated-VMAT, the treatment window constrained residual tumour motion to 3 mm or less corresponding to duty cycles of 40-60%. In 3D-VMAT, the ITV was generated by merging the GTV from all phases. A b-spline transformation model was used to register the 4D-CT images and DVHs were calculated from total dose accumulated on the max expiration phase. For the majority of OARs, gated-VMAT provided the greatest radiation sparing but significantly extended treatment times (25-35 gantry interruptions/arc). For 3D-VMAT, only 2 patients had clinically acceptable plans that met all the strict dose limits. OAR sparing in 4D-VMAT was comparable to gated-VMAT but with significantly improved delivery efficiency.