C-arm Orientation Research Articles

Influence of radiation dose reduction gloves on exposure parameters, entrance dose rates and eye doses of interventionalists during mobile C-arm fluoroscopic procedures: A phantom study

IntroductionDuring fluoroscopic examinations, radiation dose reduction gloves (RRGs) protect the hands of the interventionalist against ionising scattered radiation from the patient. Some fluoroscopic procedures may require the hands of the interventionalist in the path of the primary X-ray beam. This study investigates the influence of RRGs in the field of view (FOV) on exposure parameters, entrance dose rates and eye doses of interventionalists during mobile C-arm fluoroscopic procedures. MethodPolymethylmethacrylate (PMMA) slabs were stacked on each other to simulate patient thicknesses. The abdomen protocol of the unit was selected for the study. The entrance dose rates to the surface of the PMMA slabs and the scattered radiation were measured for an undercouch configuration with and without RRGs in the FOV. The exposure parameters were noted. The scattered radiation for an overcouch configuration was measured. ResultsThe entrance dose rate increases as the FOV decreases for a fixed thickness of PMMA. The presence of RRGs in the FOV increases the exposure parameters, entrance dose rates and the scattered radiation to the eyes of the interventionalist. For the first level of RRG coverage, percentage increases in entrance dose rates and eye doses for the 23 cm FOV for all thicknesses of PMMA slabs ranged from 1.0% to 17.0% and 20.0%–30.0%, respectively; for the second level of RRG coverage, the entrance dose rates ranged from 17.0% to 45.0% and the eye doses from 50.0% to 60.0%. Percentage increases depend on the FOV, the patient's thickness, and the size and orientation of the RRGs in the FOV. Scattered radiation to the eyes of the interventionalist increases with an overcouch configuration compared to an undercouch configuration. ConclusionSterile RRGs protects the hands of the interventionalist against scattered radiation. But in the FOV, they increase the scattered radiation to the personnel and the patient entrance dose rate. Implications for practiceFor best practice in C-arm fluoroscopy-guided procedures, appropriate FOV and C-arm orientation should be selected, whilst RRGs should not be in the path of the primary beam unless necessary.

Technical and clinical study of x-ray-based surface echo probe tracking using an attached fiducial apparatus.

Several types of structural heart intervention (SHI) use information from multiple imaging modalities to complete an interventional task. For example, in transcatheter aortic valve replacement (TAVR), placement and deployment of a bioprosthetic aortic valve in the aorta is primarily guided by x-ray fluoroscopy (XRF), and echocardiography provides visualization of cardiac anatomy and blood flow. However, simultaneous interpretation of independent x-ray and echo displays remains a challenge for the interventionalist. The purpose of this work was to develop a novel echo/x-ray co-registration solution in which volumetric transthoracic echo (TTE) is transformed to the x-ray coordinate system by tracking the three-dimensional (3D) pose of a probe fiducial attachment from its appearance in two-dimensional (2D) x-ray images. A fiducial attachment for a commercial TTE probe consisting of rings of high-contrast ball bearings was designed and fabricated. The 3D pose (position and orientation) of the fiducial attachment is estimated from a 2D x-ray image using an algorithm in which a virtual point cloud model of the attachment is iteratively rotated, translated, and forward-projected onto the image until the average sum-of-squares of grayscale values at the projected points is minimized. Fiducial registration error (FRE) and target registration error (TRE) of this approach were evaluated in phantom studies using TAVR-relevant gantry orientations and four standard acoustic windows for the TTE probe. A patient study was conducted to assess the clinical suitability of the fiducial attachment prototype during TTE imaging of patients undergoing SHI. TTE image quality for the task of guiding a transcatheter procedure was evaluated in a reviewer study. The 3D FRE ranged from 0.32±0.03mm (mean±SD) to 1.31±0.05mm, depending on C-arm orientation and probe acoustic window. The 3D TRE ranged from 1.06±0.03mm to 2.42±0.06mm. Fiducial pose estimation was stable when >75% of the fiducial markers were visible in the x-ray image. A panel of reviewers graded the presentation of heart valves in TTE images from 48 SHI patients. While valve presentation did not differ significantly between acoustic windows (P>0.05), the mitral valve did achieve a significantly higher image quality compared to the aortic and tricuspid valves (P<0.001). Overall, reviewers perceived sufficient image quality in 76.5% of images of the mitral valve, 54.9% of images of the aortic valve, and 48.6% of images of the tricuspid valve. Fiducial-based tracking of a commercial TTE probe is compatible with clinical SHI workflows and yields 3D target registration error of less than 2.5mm for a variety of x-ray gantry geometries and echo probe acoustic windows. Although TTE image quality with respect to target valve anatomy was sufficient for the majority of cases examined, prescreening of patients for sufficient TTE quality would be helpful.

Preoperative Planning for EndoAnchor Use During Thoracic Endovascular Aortic Repair in the Distal Aortic Arch

Purpose: To describe steps related to intraoperative C-arm orientations that can be taken during preoperative planning of thoracic stent-graft repair to facilitate the deployment of EndoAnchors in the distal aortic arch. Technique: Previous experience from transcatheter aortic valve implantation (TAVI) may be helpful in addressing issues with C-arm orientation. In TAVI, preoperative computed tomography (CT) images are routinely obtained to generate a patient-specific curve that represents a virtually complete rotation of the C-arm perpendicular to the annulus. The curve clearly demonstrates that each adjustment in cranial or caudal view needs parallax correction in the left or right anterior oblique direction to remain perpendicular, and vice versa. This experience can be translated to the preoperative planning of EndoAnchor use in the aortic arch. By placing markers along the circumference of the proximal landing zone of the preoperative CT scan, the required C-arm orientations can be determined for each marker. Conclusion: Determining the optimal C-arm orientation during preoperative planning will facilitate successful EndoAnchor deployment and may contribute to improved durability of endovascular repair in hostile necks in the aortic arch.

MP42-01 SCATTER RADIATION EXPOSURE TO THE SURGICAL TEAM DURING SUPINE AND PRONE PERCUTANEOUS NEPHROLITHOTRIPSY

You have accessJournal of UrologyImaging/Radiology: Uroradiology II (MP42)1 Apr 2020MP42-01 SCATTER RADIATION EXPOSURE TO THE SURGICAL TEAM DURING SUPINE AND PRONE PERCUTANEOUS NEPHROLITHOTRIPSY David Chapman*, Shubha De, and Devin Demitor David Chapman*David Chapman* More articles by this author , Shubha DeShubha De More articles by this author , and Devin DemitorDevin Demitor More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000000891.01AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Radiation is central to diagnostic and therapeutic procedures in Urology. Intraoperative exposure to patients and the care team continues to be a concern. Many strategies help reduce radiation exposure during percutaneous nephrolithotomy (PCNL), however, little has been studied in the contribution of patient positioning and C-arm orientation. The aim of this study was to compare the radiation exposure to the surgical team during supine and prone positions with common C-arm configurations. METHODS: A benchtop experiment was conducted using a Siemens C-arm, anthropomorphic model (80kg human torso) and a 180cc ionization chamber (RadCal Accu Gold Touch) to directly measure radiation scatter (mR/min) to the healthcare team during different configurations of the C-arm (AP, 150 oblique, lateral) for prone and supine (Bart’s free flank 150 decubitus) PCNL. Exposure was measured using regular and high dose fluoroscopy settings, for all personnel [radiation technologist (XRT), scrub nurse (SN), urologist (URO), and anesthesiologist (ANS)] for six c-arm orientations at eye and gonad level. RESULTS: Standard radiation dose was defined as detected scatter with the patient in traditional proned position, and c-arm in AP (eyes: URO 0.59, ANS 0.00, SN 0.00, XRT 0.00 mR/min; gonads URO 1.3, ANS 0.00, SN 0.22, XRT 0.00 mR/min). With the c-arm in lateral orientation and patient in supine, the average dose increased by 6.49 to 21.13 times compared to the oblique and AP configuration, respectively (see figure 1). When dose reduction methods were employed: positioning the surgical team opposite to the image intensifier, exposure was reduced by 3.14-3.58 times, whereas rotating the C-arm over the table (into lateral position) reduced exposure by 1.49-1.46 times (as compared to standard ‘under the table’ lateral positioning). CONCLUSIONS: Radiation is of increasing concern and current guidelines do not recommend physical strategies of dose reduction. This study highlights the ability for a surgical team to drastically alter radiation exposure by considering positioning as part of the contributing factors. Knowing relative exposure increases may empower surgeons to choose alternative orientations to accomplish tasks while minimizing scatter. Source of Funding: None © 2020 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 203Issue Supplement 4April 2020Page: e603-e603 Advertisement Copyright & Permissions© 2020 by American Urological Association Education and Research, Inc.MetricsAuthor Information David Chapman* More articles by this author Shubha De More articles by this author Devin Demitor More articles by this author Expand All Advertisement PDF downloadLoading ...

OCCUPATIONAL EYE LENS DOSE ESTIMATED USING WHOLE-BODY DOSEMETER IN INTERVENTIONAL CARDIOLOGY AND RADIOLOGY: A MONTE CARLO STUDY.

Medical personnel performing interventional procedures in cardiology and radiology is considered to be a professional group exposed to high doses of ionizing radiation. Reduction of the eye lens dose limit made its assessment in the interventional procedures one of the most challenging topics. The objective of this work is to assess eye lens doses based on the whole-body doses using methods of computational dosimetry. Assessment included different C-arm orientations (PA, LAO and RAO), tube voltages (80 -110 kV) and efficiency of different combinations of protective equipment used in interventional procedures. Center position at the height of the thyroid gives best estimate of eye lens dose, with spreads of 11% (13%), 13% (17%) and 14% (13%) for the left (right) eye lens. The conversion factors of 1.03 (0.83), 1.28 (1.06) and 1.36 (1.06) to convert whole body to eye lens dose were derived for positions of first operator, nurse and radiographer, respectively. The eye lens dose reduction factors for different combinations of applied protective equipment are 178, 5 and 6, respectively.

Inverted C-Arm Orientation During Simulated Hip Arthroscopy Decreases Patient Radiation Exposure by Half

Hip arthroscopy is a commonly used surgical technique utilized for treatment of symptomatic FAI, with good to excellent early outcomes. Hip arthroscopy for FAI has shown to have high return to duty and low risk for further surgical treatment in the active duty population.

Inverted C-arm Orientation During Simulated Hip Arthroscopic Surgery.

Background:Fluoroscopic guidance is routinely utilized during hip arthroscopic surgery. Previous studies have shown that the C-arm orientation can significantly affect radiation exposure for both the surgeon and the patient during orthopaedic procedures. However, this has not been previously assessed for hip arthroscopic surgery.Hypothesis:Using an inverted C-arm during hip arthroscopic surgery will reduce radiation exposure to the patient and surgeon.Study Design:Descriptive laboratory study.Methods:A simulation study measured scatter radiation during hip arthroscopic surgery performed in the supine position under fluoroscopic guidance with an anthropomorphic pelvic phantom on a radiolucent operating table. Radiation exposure tested 2 different C-arm orientations: standard and inverted. Testing was performed at 6 locations corresponding to the patient, surgeon’s neck, surgeon’s waist, surgical technician, anesthesiologist, and radiology technician. Statistical analysis was performed using univariate and multivariate analyses assessing radiation exposure between the C-arm orientations. A risk calculation for carcinogenesis was performed based on reported radiation dosages.Results:Radiation exposure (in mGy/min) was more than 100-fold higher for the patient compared with the surgeon in both C-arm orientations. The inverted C-arm orientation resulted in a 2.48-fold decrease in patient radiation exposure when compared with the standard orientation (10.8 mGy/min vs 26.8 mGy/min, respectively). There was a small but significant increase in surgeon radiation exposure in the inverted orientation compared with the standard orientation (0.072 vs 0.067 mGy/min, respectively). The patient’s carcinogenesis risk was decreased 2.64-fold with the inverted orientation compared with the standard orientation (1.4 × 10–5 vs 3.7 × 10–5, respectively).Conclusion:The inverted C-arm orientation resulted in a 2.48-fold decrease in patient radiation exposure with a 2.64-fold decrease in the carcinogenesis risk compared with the standard orientation. Inadvertently, the inverted orientation provided a 9-cm increase in the surgeon’s working area. Our data supported the clinical utilization of the inverted C-arm orientation during hip arthroscopic surgery to minimize patient radiation exposure. Although there was a minimal but significant increase in surgeon radiation exposure with the inverted orientation, we believe that this is negligible when incorporated with standard leaded protective equipment as contrasted with the significant dose reduction for the patient as well as the decreased risk of carcinogenesis and hereditary disorders.Clinical Relevance:Patients undergoing hip arthroscopic surgery routinely acquire radiation exposure during the use of the C-arm. Measures to minimize radiation via the inverted C-arm orientation will decrease the unnecessary risk to the patient while continuing to allow for optimal treatment.

Feasibility, Safety and Accuracy of Echocardiography-Fluoroscopy Imaging Fusion During Percutaneous Atrial Septal Defect Closure in Children

Imaging fusion between echocardiography and fluoroscopy was recently developed. The aim of this study was to assess its feasibility and accuracy during pediatric cardiac catheterization. Thirty-one patients (median weight, 26kg; interquartile range [IQR], 21-37kg) who underwent percutaneous atrial septal defect closure were prospectively included. The feasibility and accuracy of various imaging fusion modalities (live two-dimensional, live color two-dimensional, live three-dimensional and markers) with EchoNavigator software were assessed. To assess the accuracy of spatial registration of the echocardiogram on the fluoroscopic image, the occluder screw, an object that appeared on each image, was used as a reference tool, and the distance between the two when fused was measured. A distance was measured on the fusion screen between a marker positioned on the screw from the echocardiography screen and from the fluoroscopy screen (distance 1). Another distance was measured on the fusion screen between the screw visualized by three-dimensional echocardiography and by fluoroscopy (distance 2). The two distances were measured on four C-arm orientations in end-systolic and end-diastolic frames. Fusion and marker positioning were feasible in real time in all cases. On the fusion screen, median systolic and diastolic distance 1 were 0.5mm (IQR, 0.3-1mm) and 2mm (IQR, 1.5-2.5mm; P<.0001), respectively. The marker positioned from the echocardiography screen was fixed on the fusion screen anddid not follow the movement of the screw. Median systolic and diastolic distance 2 were 0.5mm (IQR, 0-0.5mm) and 2mm (IQR, 1.5-2.5mm; P<.0001), respectively. Echocardiographic fluoroscopic imaging fusion is feasible, safe, and accurate in children weighting >20kg. This technique offers a new method of imaging guidance in the catheterization laboratory for complex procedures and training.

C-arm Positioning Using Virtual Fluoroscopy for Image-Guided Surgery.

Fluoroscopically guided procedures often involve repeated acquisitions for C-arm positioning at the cost of radiation exposure and time in the operating room. A virtual fluoroscopy system is reported with the potential of reducing dose and time spent in C-arm positioning, utilizing three key advances: robust 3D-2D registration to a preoperative CT; real-time forward projection on GPU; and a motorized mobile C-arm with encoder feedback on C-arm orientation. Geometric calibration of the C-arm was performed offline in two rotational directions (orbit α, orbit β). Patient registration was performed using image-based 3D-2D registration with an initially acquired radiograph of the patient. This approach for patient registration eliminated the requirement for external tracking devices inside the operating room, allowing virtual fluoroscopy using commonly available systems in fluoroscopically guided procedures within standard surgical workflow. Geometric accuracy was evaluated in terms of projection distance error (PDE) in anatomical fiducials. A pilot study was conducted to evaluate the utility of virtual fluoroscopy to aid C-arm positioning in image guided surgery, assessing potential improvements in time, dose, and agreement between the virtual and desired view. The overall geometric accuracy of DRRs in comparison to the actual radiographs at various C-arm positions was PDE (mean ± std) = 1.6 ± 1.1 mm. The conventional approach required on average 8.0 ± 4.5 radiographs spent "fluoro hunting" to obtain the desired view. Positioning accuracy improved from 2.6° ± 2.3° (in α) and 4.1° ± 5.1° (in β) in the conventional approach to 1.5° ± 1.3° and 1.8° ± 1.7°, respectively, with the virtual fluoroscopy approach. Virtual fluoroscopy could improve accuracy of C-arm positioning and save time and radiation dose in the operating room. Such a system could be valuable to training of fluoroscopy technicians as well as intraoperative use in fluoroscopically guided procedures.

Projective invariant biplanar registration of a compact modular orthopaedic robot

This paper presents a compact orthopedic robot designed with modular concept. The layout of the modular configuration is adaptive to various conditions such as surgical workspace and targeting path. A biplanar algorithm is adopted for the mapping from the fluoroscopic image to the robot, while the former affine based method is satisfactory only when the projection rays are basically perpendicular to the reference coordinate planes. This paper introduces the area cross-ratio as a projective invariant to improve the registration accuracy for non-orthogonal orientations, so that the robotic system could be applied to more orthopedic procedures under various C-Arm orientation conditions. The system configurations for femoral neck screw and sacroiliac screw fixation are presented. The accuracy of the robotic system and its efficacy for the two typical applications are validated by experiments.

C-arm angle measurement with accelerometer for brachytherapy: an accuracy study

X-ray fluoroscopy guidance is frequently used in medical interventions. Image-guided interventional procedures that employ localization for registration require accurate information about the C-arm's rotation angle that provides the data externally in real time. Optical, electromagnetic, and image-based pose tracking systems have limited convenience and accuracy. An alternative method to recover C-arm orientation was developed using an accelerometer as tilt sensor. The fluoroscopic C-arm's orientation was estimated using a tri-axial acceleration sensor mounted on the X-ray detector as a tilt sensor. When the C-arm is stationary, the measured acceleration direction corresponds to the gravitational force direction. The accelerometer was calibrated with respect to the C-arm's rotation along its two axes, using a high-accuracy optical tracker as a reference. The scaling and offset error of the sensor was compensated using polynomial fitting. The system was evaluated on a GE OEC 9800 C-arm. Results obtained by accelerometer, built-in sensor, and image-based tracking were compared, using optical tracking as ground truth data. The accelerometer-based orientation measurement error for primary angle rotation was -0.1 ± 0.0° and for secondary angle rotation it was 0.1 ± 0.0°. The built-in sensor orientation measurement error for primary angle rotation was -0.1 ± 0.2°, and for secondary angle rotation it was 0.1 ± 0.2°. The image-based orientation measurement error for primary angle rotation was -0.1 ± 1.3°, and for secondary angle rotation it was -1.3 ± 0.3°. The accelerometer provided better results than the built-in sensor and image-based tracking. The accelerometer sensor is small, inexpensive, covers the full rotation range of the C-arm, does not require line of sight, and can be easily installed to any mobile X-ray machine. Therefore, accelerometer tilt sensing is a very promising applicant for orientation angle tracking of C-arm fluoroscopes.

Precise X-ray and video overlay for augmented reality fluoroscopy

The camera-augmented mobile C-arm (CamC) augments any mobile C-arm by a video camera and mirror construction and provides a co-registration of X-ray with video images. The accurate overlay between these images is crucial to high-quality surgical outcomes. In this work, we propose a practical solution that improves the overlay accuracy for any C-arm orientation by: (i) improving the existing CamC calibration, (ii) removing distortion effects, and (iii) accounting for the mechanical sagging of the C-arm gantry due to gravity. A planar phantom is constructed and placed at different distances to the image intensifier in order to obtain the optimal homography that co-registers X-ray and video with a minimum error. To alleviate distortion, both X-ray calibration based on equidistant grid model and Zhang's camera calibration method are implemented for distortion correction. Lastly, the virtual detector plane (VDP) method is adapted and integrated to reduce errors due to the mechanical sagging of the C-arm gantry. The overlay errors are 0.38±0.06mm when not correcting for distortion, 0.27±0.06mm when applying Zhang's camera calibration, and 0.27±0.05mm when applying X-ray calibration. Lastly, when taking into account all angular and orbital rotations of the C-arm, as well as correcting for distortion, the overlay errors are 0.53±0.24mm using VDP and 1.67±1.25mm excluding VDP. The augmented reality fluoroscope achieves an accurate video and X-ray overlay when applying the optimal homography calculated from distortion correction using X-ray calibration together with the VDP.

A practical global distortion correction method for an image intensifier based x‐ray fluoroscopy system

X-ray images acquired on systems with image intensifiers (II) exhibit characteristic distortion which is due to both external and internal factors. The distortion is dependent on the orientation of the II, a fact particularly relevant to II's mounted on C arms which have several degrees of freedom of motion. Previous descriptions of distortion correction strategies have relied on a dense sampling of the C-arm orientation space, and as such have been limited mostly to a single arc of the primary angle, alpha. We present a new method which smooths the trajectories of the segmented vertices of the grid phantom as a function of a prior to solving the two-dimensional warping problem. It also shows that the same residual errors of distortion correction could be achieved without fitting the trajectories of the grid vertices, but instead applying the previously described global method of distortion correction, followed by directly smoothing the values of the polynomial coefficients as functions of the C-arm orientation parameters. When this technique was applied to a series of test images at arbitrary alpha, the root-mean-square (RMS) residual error was 0.22 pixels. The new method was extended to three degrees of freedom of the C-arm motion: the primary angle, alpha; the secondary angle, beta; and the source-to-intensifier distance, lambda. Only 75 images were used to characterize the distortion for the following ranges: alpha, +/- 45 degrees (Deltaalpha = 22.5 degrees); beta, +/- 36 degrees (Deltabeta = 18 degrees); lambda, 98-118 cm (Deltalambda = 10 cm). When evaluated on a series of test images acquired at arbitrary (alpha, beta, lambda), the RMS residual error was 0.33 pixels. This method is targeted at applications such as guidance of catheter-based interventions and treatment planning for brachytherapy, which require distortion-corrected images over a large range of C-arm orientations.

Safety and Efficacy of C2 Pedicle Screws Placed With Anatomic and Lateral C-Arm Guidance

This is a retrospective review of 150 C2 pedicle screw placements. Candidates had their C2 pedicle morphology assessed through three-dimensional imaging, including preoperative image guidance. After surgery, the patients were serially CT scanned. Follow-up, with fusion assessment, ranged from 1 to 12 years. We will show that an open technique combined with lateral C-arm guidance provides rapid placement of C2 pedicle screws. C2 pedicle screws can be successful anchors for a variety of cervical problems. Standard intraoperative image guidance, biplane fluoroscopy, or free hand techniques all have their drawbacks. After adequate C2 exposure, the C2 pedicle is palpated. The dissector remains stationary to provide coronal orientation while a lateral C-arm radiograph is obtained for sagittal orientation. The drill trajectory is set, the C2 pedicle cannulated, and a cancellous screw placed. A total of 71 patients had bilateral screws placed and 8 patients had unilateral screws placed. The overall complication rate was 2.7%. In our series, we have found a consistent way to cannulate the C2 pedicle. C2 fixation serves as an integral part of cervical reconstruction. Preoperative planning, anatomic knowledge, and lateral C-arm orientation create a low morbidity method for C2 screw placement.

A system for real-time XMR guided cardiovascular intervention

The hybrid magnetic resonance (MR)/X-ray suite (XMR) is a recently introduced imaging solution that provides new possibilities for guidance of cardiovascular catheterization procedures. We have previously described and validated a technique based on optical tracking to register MR and X-ray images obtained from the sliding table XMR configuration. The aim of our recent work was to extend our technique by providing an improved calibration stage, real-time guidance during cardiovascular catheterization procedures, and further off-line analysis for mapping cardiac electrical data to patient anatomy. Specially designed optical trackers and a dedicated calibration object have resulted in a single calibration step that can be efficiently checked and updated before each procedure. An X-ray distortion model has been implemented that allows for distortion correction for arbitrary c-arm orientations. During procedures, the guidance system provides a real-time combined MR/X-ray image display consisting of live X-ray images with registered recently acquired MR derived anatomy. It is also possible to reconstruct the location of catheters seen during X-ray imaging in the MR derived patient anatomy. We have applied our registration technique to 13 cardiovascular catheterization procedures. Our system has been used for the real-time guidance of ten radiofrequency ablations and one aortic stent implantation. We demonstrate the real-time guidance using two exemplar cases. In a further two cases we show how off-line analysis of registered image data, acquired during electrophysiology study procedures, has been used to map cardiac electrical measurements to patient anatomy for two different types of mapping catheters. The cardiologists that have used the guidance system suggest that real-time XMR guidance could have substantial value in difficult interventional and electrophysiological procedures, potentially reducing procedure time and delivered radiation dose. Also, the ability to map measured electrical data to patient specific anatomy provides improved visualization and a path to investigation of cardiac electromechanical models.