Effect Of Cardiac Motion Research Articles

Letter to the Editor: re: Body physique and heart rate variability determine the occurrence of stair-step artefacts in 64-slice CT coronary angiography with prospective ECG-triggering

Sir, We read with great interest the article by Husmann and colleagues entitled “Body physique and heart rate variability determine the occurrence of stair-step artefacts in 64-slice CT coronary angiography with prospective ECG-triggering” [1]. The authors evaluated the presence and the determinants of stair-step artefacts in computed tomography coronary angiography (CTCA) with prospective ECG-triggering performed using 64slice multidetector CT (64-MDCT). In order to separate the effects of respiratory motion on the prevalence of stair-step artefacts, 13 patients were not included in the study “because they did not follow the breathing commands properly”. It is worth noting that “breathing commands were practised repetitively” before CT and that all patients were “carefully monitored during the examination in an effort to assure that breathing commands were adequately followed”. Therefore, we may assume that, despite careful coaching, 8.3% (13/156) of patients presented artefacts due to respiratory motion. Respiratory motion causes stair-step artefact both in the chest wall and in the coronary arteries [2]. This type of artefact frequently cannot be corrected by postprocessing techniques such as multisegment reconstruction or ECGediting [3], which are both common strategies used to overcome the effects of cardiac motion. Therefore, stair-step artefact due to respiratory motion may render a coronary segment unevaluable. The high incidence of thoracic wall stair-step artefacts (54%, 77/143) reported is concerning for a significant detrimental effect on vessel evaluability which was not assessed by the authors. The study by Husmann and colleagues brings to attention two important factors that may impair coronary segments evaluability through stair-step artefacts in prospective ECG-triggered CTCA: body physique and heart rate variability. However, the study indirectly reveals the high frequency of respiratory motion and encourages investigators to study this additional and overlooked source of image degradation in CT coronary angiography.

SU-FF-T-559: Effect of Cardiac Motion On the Cyberknife Synchrony Tracking System for Radiosurgical Cardiac Ablation

Purpose: To characterize the effect of cardiac motion on the CyberKnife Synchrony respiratory tracking system for radiosurgical cardiac ablation. Method and Materials: A high precision programmable haptic device (Force Dimensions Omega.6) was used to simulate cardiac and respiratory motion of a ball cube phantom. The CyberKnife Synchrony system was used to track the position of the 25 mm diameter target via spatial correlation of a fiducial within the phantom with the external LEDs placed on a second haptic device simulating chest wall motion. The targeting and tracking error were analyzed by comparing the actual target positions with the linac offset positions predicted from the Synchrony model. Film dosimetry was used to evaluate the effect of cardiac motion on target coverage. Results: Examination of log files revealed that the Synchrony modeling averaged out cardiac motion not present in the surrogate with some error. Superior‐inferior motion from both respiratory and cardiac motion contributed to the largest Synchrony modeling error. This modeling error led to misdirection of the beams from the time averaged target position. Additionally, untracked motion resulted in the target moving into and out of the radiation beams which manifested as softening of the dose gradient changes. Analysis of the films indicated that this was most severe in the superior inferior direction consistent with the extent of motion in that direction. Conclusion: A small additional margin would enable treatment of cardiac targets with the current CyberKnife if Synchrony tracking were used. For the motions and dose distributions tested, a 2 mm margin was sufficient to provide good target coverage in the presence of untracked cardiac motion. S. Dieterich consults for Cyberheart Inc.

Effect of Cardiac Motion on Solution of the Electrocardiography Inverse Problem

Previous studies of the ECG inverse problem often assumed that the heart was static during the cardiac cycle; consequently, a time-dependent geometrical error was thought to be unavoidably introduced. In this paper, cardiac motion is included in solutions to the electrocardiographic inverse problem. Cardiac dynamics are simulated based on a previously developed biventricular model that coupled the electrical and mechanical properties of the heart, and simulated the ventricular wall motion and deformation. In the forward computation, the heart surface source model method is employed to calculate the epicardial potentials from the action potentials, and then, the simulated epicardial potentials are used to calculate body surface potentials. With the inclusion of cardiac motion, the calculated body surface potentials are more reasonable than those in the case of static assumption. In the epicardial potential-based inverse studies, the Tikhonov regularization method is used to handle ill-posedness of the ECG inverse problem. The simulation results demonstrate that the solutions obtained from both the static ECG inverse problem and the dynamic ECG inverse problem approaches are approximately the same during the QRS complex period, due to the minimal deformation of the heart in this period. However, with the most obvious deformation occurring during the ST-T segment, the static assumption of heart always generates something akin to geometry noise in the ECG inverse problem causing the inverse solutions to have large errors. This study suggests that the inclusion of cardiac motion in solving the ECG inverse problem can lead to more accurate and acceptable inverse solutions.

Titanium clip placement to allow accurate tumour bed localisation following breast conserving surgery – audit on behalf of the IMPORT Trial Management Group

To assess the feasibility of radiation therapy treatment planning 4-dimensional computed tomography (4DCT) and deep-inspiration breath-hold (DIBH) CT to accurately contour the left anterior descending artery (LAD), a primary indicator of radiation-induced cardiac toxicity for patients undergoing radiation therapy.Ten subjects were prospectively imaged with a cardiac-gated MRI protocol to determine cardiac motion effects, including the displacement of a region of interest comprising the LAD. A series of planar views were obtained and resampled to create a 3-dimensional (3D) volume. A 3D optical flow deformable image registration algorithm determined tissue displacement during the cardiac cycle. The measured motion was then used as a spatial boundary to characterize motion blurring of the radiologist-delineated LAD structure for a cohort of 10 consecutive patients enrolled prospectively on a breast study including 4DCT and DIBH scans. Coronary motion–induced blurring artifacts were quantified by applying an unsharp filter to accentuate the LAD structure despite the presence of motion blurring. The 4DCT maximum inhalation and exhalation respiratory phases were coregistered to determine the LAD displacement during tidal respiration, as visualized in 4DCT.The average 90th percentile heart motion for the region of interest was 0.7 ± 0.1 mm (left–right [LR]), 1.3 ± 0.6 mm (superior–inferior [SI]), and 0.6 ± 0.2 mm (anterior–posterior [AP]) in the cardiac-gated MRI cohort. The average relative increase in the number of voxels comprising the LAD contour was 69.4% ± 4.5% for the DIBH. The LAD volume overestimation had the dosimetric impact of decreasing the reported mean LAD dose by 23% ± 9% on average in the DIBH. During tidal respiration the average relative LAD contour increase was 69.3% ± 5.9% and 67.9% ± 4.6% for inhalation and exhalation respiratory phases, respectively. The average 90th percentile LAD motion was 4.8 ± 1.1 mm (LR), 0.9 ± 0.4 mm (SI), and 1.9 ± 0.6 mm (AP) for the 4DCT cohort, in the absence of cardiac gating.An anisotropic margin of 2.7 mm (LR), 4.1 mm (SI), and 2.4 mm (AP) was quantitatively determined to account for motion blurring and patient setup error while placing minimum constraint on the plan optimization.

Effect of cardiac motion on body surface electrocardiographic potentials: an MRI-based simulation study

This paper describes an electrical model of cardiac ventricles incorporating real geometry and motion. The heart anatomy and its motion through the cardiac cycle are obtained from segmentations of multiple-slice MRI time sequences; the special conduction system is constructed using an automated mapping procedure from an existing static heart model. The heart model is mounted in an anatomically realistic voxel model of the human body. The cardiac electrical source and surface potentials are determined numerically using both a finite-difference scheme and a boundary-element method with the incorporation of the motion of the heart. The electrocardiograms (ECG) and body surface potential maps are calculated and compared to the static simulation in the resting heart. The simulations demonstrate that introducing motion into the cardiac model modifies the ECG signals, with the most obvious change occurring during the T-wave at peak contraction of the ventricles. Body surface potential maps differ in some local positions during the T-wave, which may be of importance to a number of cardiac models, including those incorporating inverse methods.

Effect of cardiac motion on haemodynamics in the superior mesenteric artery (SMA)

Effect of cardiac motion on haemodynamics in the superior mesenteric artery (SMA)

Definition of a moving gross target volume for stereotactic radiation therapy of stented coronary arteries

Purpose : To measure the effect of cardiac motion on coronary artery stent position during the cardiac cycle as a first step toward exploring the feasibility of stereotactic external beam radiation therapy targeted at restenotic stented coronary arteries. Methods and Materials : The three-dimensional (3D) position of eight coronary artery stents in 8 patients immobilized in a stereotactic body frame was studied noninvasively by single-breathhold ECG-gated multislice spiral computed tomography (MSCT) during 10 retrospectively selected phases, equally distributed throughout the R-R interval of consecutive cardiac cycles. The volume encompassing all measured 3D positions of the stent was measured. Results : Stent volumes measured by MSCT closely agreed with measurements by quantitative coronary angiography ( r > 0.99). The mean of the maximum 3D stent center of mass displacement between any two phases during the cardiac cycle for all eight coronary arteries was 7.5 mm (range 3.3–20.5 mm) in the lateral direction, 8.6 mm (range 2.7–21.6 mm) in the ventrodorsal direction, and 8.2 mm (range 2.5–19.7 mm) in the craniocaudal direction. As was anticipated, the volume encompassing all measured 3D positions of the stent represented only a fraction of the whole heart volume in all patients, i.e., less than 0.6%. Conclusions : ECG-gated MSCT allowed the measurement of the volume encompassing multiphase 3D positions of coronary artery stents during the cardiac cycle. This volume, a measure of the cardiac motion effect on coronary artery stent position during the cardiac cycle, represents a moving gross target for stereotactic external beam radiation therapy.

Dosimetric effect of source centering and residual plaque for beta-emitting catheter based intravascular brachytherapy sources.

Catheter-based radiation delivery systems employing both beta-particle and gamma-ray emitters are currently being investigated for their efficacy in addressing restenosis following percutaneous coronary intervention (PCI). The dosimetric consequences of source centering within the arterial lumen and presence of residual plaque are potentially important issues for the uniform delivery of dose to the arterial tissue. In this study, we have examined the effect of source centering on the resulting dose to the arterial wall from clinical intravascular brachytherapy sources containing 32P and 90Sr/Y90. Monte Carlo simulations using the MCNP code were performed for these catheter-based sources with offsets of 0.5 mm and 1 mm from the center of the arterial lumen in homogenous water medium as well as in the presence of residual plaque. Three different positions were modeled and the resulting dose values were analyzed to assess their impact on the resulting dose distribution. The results indicate a variation ranging from -40% to +70% for 32P source and -30% to +50% for 90Sr/90Y at a radial distance of 2 mm from the center of the coronary artery, relative to the dose from a centered source, for a 0.5 mm offset. The variation for a 1 mm offset ranges from -65% to +182% for 32P source and to -50% to +140% for 90Sr/90Y. A concentric residual plaque layer was also modeled so as to assess the combined influence of offset and residual plaque on the dosimetry. Finally the effect of cardiac motion and its potential impact on catheter position and hence the dose distribution is also examined by considering two separate cases of catheter displacement. The results indicate that dose variations range between -28% to +91% when it is assumed that cardiac motion causes catheter movement during coronary lesion irradiation.

Correcting organ motion artifacts in x-ray CT systems based on tracking of motion phase by the spatial overlap correlator. II. Experimental study.

This paper presents the experimental part of an investigation on tracking and eliminating organ motion artifacts in x-ray CT cardiac applications with emphasis on imaging coronary calcification. The system methodology consists of a software implementation of the spatial overlap correlator (SSOC) concept in x-ray CT scanners to track the net amplitude and phase of organ motion during the CT data acquisition process. A coherent sinogram synthesis (CSS) method is then used to identify the repeated phases of a periodic organ motion from the information provided by the SSOC process and hence synthesize a new sinogram with no motion effects. Since the SSOC scheme is capable of tracking cardiac motion, it identifies also the projection points associated with minimum amplitude cardiac motion effects. These points are used to identify a 180 degrees plus the fan angle sinogram for image reconstruction. This leads to a retrospective gating (RG) scheme that is based on the output of the SSOC process. Performance comparison of the proposed methodology with the retrospective ECG gating using real data sets with phantoms and human patients provides a performance assessment of the merits of the proposed methods. Real results demonstrate that the new methodology eliminates the requirement for ECG gating. Moreover, the CSS and the new RG methods do not require breath holding and they can be implemented in x-ray CT scanners to image coronary calcification and the heart's ventricles.

Coronary MR angiography: selection of acquisition window of minimal cardiac motion with electrocardiography-triggered navigator cardiac motion prescanning--initial results.

The authors developed an electrocardiography-triggered M-mode navigator-echo technique to help monitor cardiac motion and identify the period of minimal cardiac motion in the cardiac cycle. Coronary magnetic resonance angiography was performed in eight healthy adult volunteers and one patient with heart disease. To minimize cardiac motion effects, trigger delays were estimated with the navigator-echo technique and two empirical formulas. The quality of images obtained with the different delay times was compared for clarity of depiction of the coronary arteries. Image quality was best with the delay calculated with the navigator-echo technique.

The effect of heart motion on kinetic parameter estimates for dynamic cardiac SPECT

Dynamic cardiac SPECT is used to estimate kinetic rate parameters that describe the washin and washout of tracer activity between the blood and the myocardial tissue. These kinetic parameters correlate to myocardial perfusion. There are, however, many physical aspects associated with dynamic SPECT which introduce bias and variance into the estimates. This paper describes a study which investigates the effect of heart motion on kinetic parameter estimates. Dynamic SPECT simulations are performed using a beating version of the MCAT phantom. The amount of blood and background activity in the myocardial tissue regions of interest is shown to vary over the cardiac cycle causing errors in the kinetic parameter estimates, particularly estimates of the washin rate constant. The effect of cardiac motion on kinetic parameter estimates is reduced by bias and variance introduced by photon noise and geometric collimator response. This suggests that techniques used to correct for motion must do so without further reducing photon statistics.

Assessment of coronary blood flow by transesophageal two-dimensional pulsed Doppler echocardiography

Recent advances in Doppler echocardiographic techniques enable us to estimate coronary flow dynamics in patients. 1–5 These methods, however, require invasive procedures, and repeated examinations in the same patient are undesirable. Although noninvasive detection of coronary flow with conventional Doppler technique from a transthoracic approach has been performed, 6,7 technical problems—effects of cardiac motion and difficulty in differentiating coronary blood flow from other intracardiac flow—remain. Transesophageal pulsed Doppler echocardiography, 8 originally reported to estimate mitral regurgitation, 9 may also be available in detecting coronary flow when combined with 2-dimensional echocardiography. In the present study, we attempted to detect coronary flow by the transesophageal Doppler technique.

DETERMINATION OF LEFT VENTRICULAR MASS BY COMPUTED TOMOGRAPHY

Abstract The capability of computed tomographic scanning to provide measurements of left ventricular mass in vivo was explored and compared with postmortem values. The study group comprised 22 dogs weighing between 9 and 28 kg and included 5 dogs with left ventricular hypertrophy. Serial nongated computed tomographic scans from the cardiac apex to base were obtained during steady state infusion of contrast medium. The total number of picture elements (pixels) representing the left ventricular myocardium on each 1 cm thick computed tomographic scan was determined in two ways: with a computer technique and with a manual tracing method. Left ventricular mass was calculated as the product of total myocardial volume (determined by pixels) and the specific gravity of canine myocardium. The results obtained with both computed tomographic methods correlated with the left ventricular mass measured at autopsy (computer method, correlation coefficient [r] = 0.95; standard error of the estimate [SEE] = 8.10 g and for the tracing method, r = 0.95; SEE = 8.38 g). These in vivo measurements were reproducible and appeared not to be significantly affected by left ventricular hypertrophy. The effect of cardiac motion on the measurements was assessed by rescanning eight animals at postmortem examination with the heart in situ. These results showed a modest (twofold) increase due to motion in the standard error of the estimate over the computed tomographic value at autopsy. Artifact due to adjacent lung tissue with low density is known to be a source of error in computed tomographic measurements. This was examined by scanning the excised hearts in a water phantom and was found not to significantly influence the results. This feasibility study represents a logical step in the application and validation of computed tomography in diagnosing heart disease. The extrapolation of these results to human subjects must be made cautiously, but there appear to be no major technical reasons why this use of computed tomography cannot be optimistically pursued.

Determination of left ventricular mass by computed tomography

The capability of computed tomographic scanning to provide measurements of left ventricular mass in vivo was explored and compared with postmortem values. The study group comprised 22 dogs weighing between 9 and 28 kg and included 5 dogs with left ventricular hypertrophy. Serial nongated computed tomographic scans from the cardiac apex to base were obtained during steady state infusion of contrast medium. The total number of picture elements (pixels) representing the left ventricular myocardium on each 1 cm thick computed tomographic scan was determined in two ways: with a computer technique and with a manual tracing method. Left ventricular mass was calculated as the product of total myocardial volume (determined by pixels) and the specific gravity of canine myocardium. The results obtained with both computed tomographic methods correlated with the left ventricular mass measured at autopsy (computer method, correlation coefficient [r] = 0.95; standard error of the estimate [SEE] = 8.10 g and for the tracing method, r = 0.95; SEE = 8.38 g). These in vivo measurements were reproducible and appeared not to be significantly affected by left ventricular hypertrophy. The effect of cardiac motion on the measurements was assessed by rescanning eight animals at postmortem examination with the heart in situ. These results showed a modest (twofold) increase due to motion in the standard error of the estimate over the computed tomographic value at autopsy. Artifact due to adjacent lung tissue with low density is known to be a source of error in computed tomographic measurements. This was examined by scanning the excised hearts in a water phantom and was found not to significantly influence the results. This feasibility study represents a logical step in the application and validation of computed tomography in diagnosing heart disease. The extrapolation of these results to human subjects must be made cautiously, but there appear to be no major technical reasons why this use of computed tomography cannot be optimistically pursued.

Synchronized pulsed cardiac planigraphy.

The authors describe sagittal and transverse axial planigraphy of the cardiac ventricles during angicardiography and selective coronary arteriography. The blurring effect of cardiac motion is eliminated by controlled intermittent x-ray exposures during the planigraphic sweep, the instant of exposure being predetermined and programmed to occur at an identical point in each cardiac cycle.