Flat-panel conebeam CT in the clinic: history and current state

Research into conebeam CT concepts began as soon as the first clinical single-slice CT scanner was conceived. Early implementations of conebeam CT in the 1980s focused on high-contrast applications where concurrent high resolution ( < 200    μ m ), for visualization of small contrast-filled vessels, bones, or teeth, was an imaging requirement that could not be met by the contemporaneous CT scanners. However, the use of nonlinear imagers, e.g., x-ray image intensifiers, limited the clinical utility of the earliest diagnostic conebeam CT systems. The development of consumer-electronics large-area displays provided a technical foundation that was leveraged in the 1990s to first produce large-area digital x-ray detectors for use in radiography and then compact flat panels suitable for high-resolution and high-frame-rate conebeam CT. In this review, we show the concurrent evolution of digital flat panel (DFP) technology and clinical conebeam CT. We give a brief summary of conebeam CT reconstruction, followed by a brief review of the correction approaches for DFP-specific artifacts. The historical development and current status of flat-panel conebeam CT in four clinical areas-breast, fixed C-arm, image-guided radiation therapy, and extremity/head-is presented. Advances in DFP technology over the past two decades have led to improved visualization of high-contrast, high-resolution clinical tasks, and image quality now approaches the soft-tissue contrast resolution that is the standard in clinical CT. Future technical developments in DFPs will enable an even broader range of clinical applications; research in the arena of flat-panel CT shows no signs of slowing down.

Long-term left atrial remodeling after ablation of persistent atrial fibrillation: 7-year follow-up by cardiovascular magnetic resonance imaging

PURPOSE

Restoration of sinus rhythm in patients with persistent atrial fibrillation (ps. AF) induces reverse atrial remodeling and improvement of left ventricular function. We evaluated the effect of ablative treatment on cardiac remodeling after a long follow-up period of 7 years by cardiovascular magnetic resonance (CMR).

METHODS

Patients with symptomatic ps. AF underwent CMR within 7 days prior to the ablation procedure. Left atrial and ventricular volumes were measured. All patients underwent circumferential pulmonary vein isolation. At the end of follow-up (FU), a CMR and 7-day ECG registration were performed.

RESULTS

Forty-two patients (67 ± 9 years) were included. After a FU of 86 ± 13 months, 23 patients had a successful outcome. In these patients, LVEF improved from 56 ± 5 to 62 ± 4% (p = 0.02), but left atrial volume and ejection fraction (LAV, LAEF) remained unchanged (105 ± 25 to 98 ± 34, p = 0.44; 34 ± 10 to 36 ± 11, p = 0.6, respectively). In 14 patients with a BMI < 30 and no left ventricular hypertrophy (LVH), LAV decreased (104 ± 30 to 82 ± 26 ml, p = 0.01) and LAEF improved (33 ± 12 to 40 ± 11%, p = 0.03). In 9 patients with successful outcome and either BMI ≥ 30 or LVH, LAV increased (110 ± 26 to 125 ± 30 ml, p = 0.03) and LAEF deteriorated (35 ± 11 to 31 ± 10%, p = 0.04).

CONCLUSIONS

Successful ablative treatment of atrial fibrillation is associated with reverse left atrial remodeling and improvement of left atrial and ventricular function. In patients with a BMI ≥ 30 or left ventricular hypertrophy, further left atrial enlargement occurs despite successful outcome.

Rotational Angiography Based Three-Dimensional Left Atrial Reconstruction: A New Approach for Transseptal Puncture

AIM

Rotational angiography is a well-known method for the three-dimensional (3-D) reconstruction of left atrium and pulmonary veins during left-sided atrial arrhythmia ablation procedures. In our study, we aimed to review our experience in transseptal puncture (TSP) using 3-D rotational angiography.

METHODS

We included a total of 271 patients who underwent atrial fibrillation ablation using cryoballoon. Rotational angiography was performed to get the three-dimensional left atrial and pulmonary vein reconstructions using cardiac C-arm computed tomography. The image reconstruction was made using the DynaCT Cardiac software (Siemens, Erlangen, Germany).

RESULTS

The mean age of the study population was 61 ± 10 years. The indications for left atrial arrhythmia ablation were paroxysmal AF in 140 patients (52%) and persistent AF patients in 131 (48%) patients. The success rate of TSP using only rotational guidance was (264/271 patients, 97.4%). In the remaining seven patients, transesophageal guidance was used after the initial attempt due to thick interatrial septum in five patients and difficult TSP due to abnormal anatomy and mild pericardial effusion in the remaining two patients. Mean fluoroscopy dosage of the rotational angiography was 4896.4 ± 825.3 μGym(2). The mean time beginning from femoral vein puncture to TSP was 12.3 ± 5.5 min.

CONCLUSION

TSP guided by rotational angiography is a safe and effective method. Our results indicate that integration of rotational angiographic images into the real-time fluoroscopy can guide the TSP during the procedure.

CT coronary angiography in atrial fibrillation: a comparison of radiation dose and diagnostic confidence with retrospective gating vs prospective gating with systolic acquisition

OBJECTIVE

To compare unmodulated, retrospective electrocardiographic (ECG) gating to prospective ECG gating with systolic acquisition for CT coronary angiography (CTCA) in patients with atrial fibrillation (AF), considering the radiation dose and the diagnostic confidence achieved with each technique.

METHODS

A retrospective service evaluation was conducted before and after prospective gating with systolic acquisition replaced retrospectively gated imaging for patients with AF undergoing CTCA at our institution. 25 consecutive patients were examined in each group. The scan parameters and radiation dose information had been collected in a prospective fashion. The image sets were read by blinded, expert readers who rated their diagnostic confidence using a 5-point Likert scale.

RESULTS

The radiation dose received by patients was significantly greater in the retrospectively gated group than those being scanned using prospective gating (21 vs 5.9 mSv, p < 0.01). The prospective gating technique was also associated with greater diagnostic confidence (mean, per-patient score 3.09 vs 3.78, p = 0.02).

CONCLUSION

Prospective gating with systolic acquisition appears to improve diagnostic confidence at a significantly reduced radiation dose compared with retrospective gating in patients with AF.

ADVANCES IN KNOWLEDGE

The use of prospective gating with systolic triggering significantly reduces the radiation exposure to patients in AF undergoing CTCA. The same protocol also appears to improve diagnostic confidence.

Multi-phase rotational angiography of the left ventricle to assist ablations: feasibility and accuracy of novel imaging

AIMS

Interventional left ventricular (LV) procedures integrating static 3D anatomy visualization are subject to mismatch with dynamic catheter movements due to prominent LV motion. We aimed to evaluate the accuracy of a recently developed acquisition and post-processing protocol for low radiation dose LV multi-phase rotational angiography (4DRA) in patients.

METHODS AND RESULTS

4DRA image acquisition of the LV was performed as investigational acquisition in patients undergoing left-sided ablation (11 men; BMI = 24.7 ± 2.5 kg/m²). Iodine contrast was injected in the LA, while pacing from the RA at a cycle length of 700 ms. 4DRA acquisition and reconstruction were possible in all 11 studies. Reconstructed images were post-processed using streak artefact reduction algorithms and an interphase registration-based filtering method, increasing contrast-to-noise ratio by a factor 8.2 ± 2.1. This enabled semi-automatic segmentation, yielding LV models of five equidistant phases per cardiac cycle. For evaluation, off-line 4DRA fluoroscopy registration was performed, and the 4DRA LV contours of the different phases were compared with the contours of five corresponding phases of biplane LV angiography, acquired in identical circumstances. Of the distances between these contours, 95% were <4 mm in both incidences. Effective radiation dose for 4DRA, calculated by patient-specific Monte-Carlo simulation, was 5.1 ± 1.1 mSv.

CONCLUSION

Creation of 4DRA LV models in man is feasible at near-physiological heart rate and with clinically acceptable radiation dose. They showed high accuracy with respect to LV angiography in RAO and LAO. The presented technology not only opens perspectives for full cardiac cycle dynamic anatomical guidance during interventional procedures, but also for 3DRA without need for very rapid pacing.

The Growing Culture Of A Minimally Fluoroscopic Approach In Electrophysiology Lab

Most of interventional procedures in cardiology are carried out under fluoroscopic imaging guidance. Besides other peri-interventional risks, radiation exposure should be considered for its stochastic (inducing malignancy) and deterministic effects on health (tissue reactions like erythema, hair loss and cataracts). In this article we analized the radiation risk from cardiovascular imaging to both patients and medical staff and discusses how customize the X-ray system and how to implement shielding measures in the cath lab. Finally, we reviewed the most recent developments and the latest findings in catheter navigation and 3D electronatomical mapping systems that may help to reduce patient and operator exposure.

Prolonged ablation on critical segments of pulmonary vein ostia in paroxysmal atrial fibrillation: a prospective randomized controlled study

INTRODUCTION

Electrical reconnection of the pulmonary veins (PVs) plays a key role in the recurrence of atrial fibrillation (AF) after ablative treatment. This randomized controlled study tested the hypothesis that prolonged ablations, on areas that may be critical for left atrial (LA)-PV conduction, can significantly reduce the rate of acute PV reconnection and AF recurrence.

METHODS

Patients with paroxysmal AF were randomly assigned to either a control or an add-on group.Ostial PV isolation (PVI) was performed by point-to-point RF ablation (irrigated tip, 30 Watts, 30 seconds).An ostial segment was assumed to be critical for LA-PV connection if any of the following reactions occurred during RF application: (1) sudden delay of LA-PV conduction, (2) change of activation sequence,and (3) PVI. In this case, RF application was prolonged from 30 seconds to 90 seconds in the add-on group only.

RESULTS

A total of 131 patients (58 ± 11 years, 47 female) were assigned to a control (n = 64) and an add-on (n = 67) group. Ablation time was longer in the add-on (48 ± 16 minutes vs 37 ± 15 minutes, P = 0.03). Acute PV reconnection was observed in 20 of 64 controls and in eight of 66 add-on patients (31% vs 12%, P < 0.001). During a follow-up of 26 months, AF recurred in 33 of 64 controls and in 16 of 66 add-on patients (52% vs 24%, P = 0.001) after a single ablation procedure.

CONCLUSIONS

Prolonged radiofrequency application on critical segments of LA-PV connection is a safe and effective ablative strategy that significantly reduces acute PV reconnection and AF recurrence rates after a single ablation procedure for paroxysmal AF.

Practical ways to reduce radiation dose for patients and staff during device implantations and electrophysiological procedures

Despite the advent of non-fluoroscopic technology, fluoroscopy remains the cornerstone of imaging in most interventional electrophysiological procedures, from diagnostic studies over ablation interventions to device implantation. Moreover, many patients receive additional X-ray imaging, such as cardiac computed tomography and others. More and more complex procedures have the risk to increase the radiation exposure, both for the patients and the operators. The professional lifetime attributable excess cancer risk may be around 1 in 100 for the operators, the same as for a patient undergoing repetitive complex procedures. Moreover, recent reports have also hinted at an excess risk of brain tumours among interventional cardiologists. Apart from evaluating the need for and justifying the use of radiation to assist their procedures, physicians have to continuously explore ways to reduce the radiation exposure. After an introduction on how to quantify the radiation exposure and defining its current magnitude in electrophysiology compared with the other sources of radiation, this position paper wants to offer some very practical advice on how to reduce exposure to patients and staff. The text describes how customization of the X-ray system, workflow adaptations, and shielding measures can be implemented in the cath lab. The potential and the pitfalls of different non-fluoroscopic guiding technologies are discussed. Finally, we suggest further improvements that can be implemented by both the physicians and the industry in the future. We are confident that these suggestions are able to reduce patient and operator exposure by more than an order of magnitude, and therefore think that these recommendations are worth reading and implementing by any electrophysiological operator in the field.

The ABC of a Simple Method for Pulmonary Vein Angiography

Catheter-directed intervention to treat atrial fibrillation (AF) is becoming widely accepted procedure in current clinical practice. For assessment of pulmonary vein (PV) anatomy, angiography of left atrium (LA) and/or PV is often performed. We present a new, simple angiographic method for PVs and LA opacification using SL1 sheath. Total of 100 patients in our clinic underwent this procedure. In all of the cases good angiographic results were achieved. No immediate or late complications related to this procedure were observed.

Preprocedural imaging for patients with atrial fibrillation and heart failure

Various electrophysiological procedures and device implantation has been shown to improve morbidity and mortality in patients with atrial fibrillation (AF) and patients with heart failure (HF). Noninvasive cardiac imaging is used extensively in the preprocedural patient selection and for procedural guidance. In this review, we will discuss the application of preprocedural cardiac imaging in patients with AF prior to pulmonary vein and left atrial ablation as well as insertion of left atrial occluder device. We also discuss the role of noninvasive cardiac imaging in the selection of appropriate HF patients for device therapy as well as their use in guiding implantation of biventricular pacemaker for cardiac resynchronization therapy by assessing left ventricular ejection fraction, coronary venous anatomy, mechanical dyssynchrony and myocardial scar. We describe new research associated with preprocedural imaging in these patient cohorts.

Rotational angiography for preinterventional imaging in transcatheter aortic valve implantation

OBJECTIVE

To evaluate the clinical value of 3D rotational angiography, as a tool for imaging and measuring 3D anatomy, coupled with transesophageal echocardiogram (TEE) as preinterventional imaging for transcatheter aortic valve implantation (TAVI) procedures.

BACKGROUND

TAVI is a growing field in cardiology. An understanding of the 3D anatomy of the aortic root is crucial for patient selection and for the optimal planning and guidance of such procedures. Current techniques include 3D imaging (with MSCT MRI and 3D TEE) combined with multiplane TEE. Nevertheless, a gold standard of 3D imaging is yet not defined. 3D rotational angiography provides 3D anatomy information in the cathlab. Initially designed for nonmoving anatomical structures, one can adapt the protocol to temporarily minimize the heart anatomy motion during rotational angiography.

METHODS

Ninety-nine consecutive patients (61 females, 38 males, age 80.9 ± 5.2 years) with symptomatic aortic stenosis underwent 3D rotational angiography to assess the anatomical suitability of potential TAVI candidates. 3D rotational angiography with a C-Arm (Innova 3100(IQ) , GE Healthcare, Chalfont St Giles, UK) was performed to create the 3D anatomy of the aortic root. Coronary angiography and pelvic vessel angiography were performed during the same examination. Measurements of the aortic annulus and the sinotubular junction were made on the 3D cross-sections and were compared to TEE. Radiation dose to the patient was also monitored.

RESULTS

In all 99 patients, 3D rotational angiography was performed successfully with good imaging of the aortic root and measurements of the aortic annulus. In patients scheduled for SAPIEN valve implantation, the distances from the annulus to the coronary ostia were also measured. Of 99 patients, 80 subsequently underwent successful implantation. There is a good correlation to the TEE in the measured aortic annulus (22.13 ± 2.09 mm in rotational angio, 21.58 ± 2.09 mm TEE, Spearman r = 0.88, 95% IC [0.83;0.92], P < 0.0001) and sinotubular junction (26.19 ± 2.71 mm in rotational angio, 26.22 ± 2.73 mm TEE, Spearman r = 0.83, 95% IC [0.75;0.88], P < 0.0001). The effective dose is a fraction of the X-ray dose required for multi-slice computed tomography.

CONCLUSION

Given that this technology is available in the cathlab at reasonable dose levels, 3D rotational angiography has proven to be a suitable preinterventional 3D imaging modality for TAVI procedures. Together, the raw angiographic data and the reconstructed 3D volume provide all the necessary anatomical information necessary for this procedure, including the measurements.

Advances in imaging for atrial fibrillation ablation

Over the last fifteen years, our understanding of the pathophysiology of atrial fibrillation (AF) has paved the way for ablation to be utilized as an effective treatment option. With the aim of gaining more detailed anatomical representation, advances have been made using various imaging modalities, both before and during the ablation procedure, in planning and execution. Options have flourished from procedural fluoroscopy, electroanatomic mapping systems, preprocedural computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, and combinations of these technologies. Exciting work is underway in an effort to allow the electrophysiologist to assess scar formation in real time. One advantage would be to lessen the learning curve for what are very complex procedures. The hope of these developments is to improve the likelihood of a successful ablation procedure and to allow more patients access to this treatment.

Rapid ventricular pacing: a fast, reliable, and safe technique for optimization of image acquisition during rotational angiography for catheter ablation of atrial fibrillation

Rotational angiography is a novel method for three-dimensional reconstruction of the left atrium and pulmonary veins during catheter ablation for atrial fibrillation, but is still hampered by suboptimal reconstructions in a considerable number of patients. We describe the results of rapid pacing of the right ventricle for optimization of image acquisition during rotational angiography.

[Cardiac electrophysiology and arrhythmias]

This article contains a review of some of the most important studies in the field of arrhythmias and cardiac electrophysiology that have been reported in publications during the last year. They were selected because of their clinical relevance and because they made a positive contribution to the continuing technological development of the invasive procedures used in cardiac electrophysiology.

Optimal fluoroscopic projections for angiographic imaging of the pulmonary vein ostia: lessons learned from the intraprocedural reconstruction of the left atrium and pulmonary veins

AIMS

Electrical isolation of the pulmonary veins (PVs) is the cornerstone of the ablative treatment of atrial fibrillation. Selective angiography of the PVs in standard fluoroscopic projections is often used for intraprocedural identification of PVs and their ostia. Variable spatial orientation and significant variability of PV anatomy are important limitations of this imaging approach.

METHODS AND RESULTS

Sixty patients undergoing a PV isolation procedure received intraprocedural rotational angiography and three-dimensional reconstruction of the left atrium (LA) and PVs. For each patient, 33 angiographic projections were independently evaluated [right anterior oblique (RAO) 80 degrees to left anterior oblique (LAO) 80 degrees, in steps of 5 degrees] by two physicians in order to identify the optimal projections of the PV ostia according to the following definition: Sagittal plane: (i) clear identification of both superior and inferior segments of the LA-PV junction and (ii) no overlapping between LA (and/or left atrial appendage) and PV ostium. Frontal plane: (i) clear identification of all four quadrants of the PV ostium and (ii) fluoroscopic angles at which the maximal horizontal ostial diameter is visualized. A successful reconstruction of the LA and all PVs was obtained in 58 (97%) patients. An optimal ostial projection in a sagittal plane was identified for all four PVs. The optimal ostial projection was RAO 5 degrees for the right superior PVs in 57 out of 58 patients (98%), RAO 55 degrees for the right inferior PVs in 54 out of 58 patients (93%), LAO 45 degrees for the left superior PVs in 46 out of 58 patients (80%), and LAO 60 degrees for the left inferior PVs in 48 out of 58 patients (83%). An optimal ostial projection in a frontal plane was identified only for the inferior PVs. The optimal ostial projection was LAO 40 degrees for the right inferior PVs in 55 out of 58 patients (95%) and RAO 45 degrees for the left inferior PVs in 51 out of 58 patients (88%).

CONCLUSION

If selective angiography is to be used to delineate anatomy and location of the PV ostia to guide PV isolation, different fluoroscopic projections are required for different PVs. The preselected RAO and LAO projections proposed in our study result in optimal angiographic projections of all PV ostia in at least one plane in the majority of patients.

Image integration of three-dimensional cone-beam computed tomography angiogram into electroanatomical mapping system to guide catheter ablation of atrial fibrillation

AIMS

To evaluate the feasibility of integrating three-dimensional images created by intra-procedural cone-beam computed tomography (CBCT) into three-dimensional electroanatomical maps (EAM) and compare its accuracy with that of pre-procedural multi-slice CT (MSCT).

METHODS AND RESULTS

In 24 patients with drug-refractory atrial fibrillation (AF), atriography using CBCT with pulmonary arterial contrast injection was performed at the beginning of the AF ablation procedure. Intra-procedural CBCT images and pre-procedural MSCT images were individually imported into the EAM system and compared their integration accuracy (point-to-surface distance) of each image and EAM just before ablation. The CBCT images were assessed qualitatively and quantitatively in comparison with MSCT images. All CBCT images were graded as optimal or useful in delineating the left atrium-pulmonary vein anatomy and were successfully integrated with the EAM. Overall, integration accuracy was similar for CBCT and MSCT. However, in 11 patients, the MSCT was performed 5 or more days prior to EAM, resulting in significantly shorter surface-to-point distance in CBCT than that in MSCT (P = 0.047). Radiation exposure with CBCT was significantly reduced compared with MSCT (P < 0.001).

CONCLUSION

It is feasible to integrate CBCT image into EAM, and the integration is relatively accurate. Intra-procedural atriography by CBCT may replace pre-procedural MSCT as the imaging source for image integration.

Imaging and atrial fibrillation: the role of multimodality imaging in patient evaluation and management of atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia, and is associated with an increased risk of cardiac morbidity and mortality. In this review, the role of multimodality imaging in the evaluation and treatment of AF is discussed in two main parts. First, an overview of the initial assessment of an AF patient is provided, including the role of different imaging techniques. Conditions that are associated with AF (coronary artery disease, heart failure, valvular heart disease, and left ventricular hypertrophy), and the assessment with various imaging modalities, will be reviewed. Furthermore, left atrial size assessment and the screening for thrombus formation are addressed. Secondly, the role of imaging in the invasive treatment of AF with catheter ablation is reviewed. Issues that should be considered before the procedure including contra-indications and pulmonary vein and left atrial anatomy will be discussed. Furthermore, the integration of different imaging modalities during catheter ablation is explored. Finally, an overview of the role of imaging in the follow-up of patients treated with catheter ablation will be provided.

Adenosine-induced ventricular asystole or rapid ventricular pacing to enhance three-dimensional rotational imaging during cardiac ablation procedures

AIMS

Rotational angiography with digital three-dimensional reconstruction (3DRA) allows per-procedural 3D imaging to facilitate cardiac ablation procedures. We developed a new approach that allows per-procedural 3D imaging of the atria and ventricles with a single C-arm rotation, combining higher 3D image quality with a lower contrast and radiation dose.

METHODS AND RESULTS

Forty patients underwent 3DRA of the left atrium (LA, n = 26), right atrium (RA, n = 11), left ventricle (LV, n = 2), or right ventricle (RV, n = 1) during ablation procedures performed under general anaesthesia. Contrast agent (60 +/- 12 mL) was diluted and injected directly in the chamber of interest, during adenosine-induced ventricular asystole (n = 31) or rapid RV pacing (n = 9, atrial imaging only) to reduce cardiac motion artefacts and enhance contrast opacification during rotational imaging. Reconstructed 3D data sets were graded according to predefined quality criteria (n = 40) and quantitatively compared with cardiac computed tomography (CT) (LA, n = 14). Adenosine-induced ventricular asystole and rapid pacing both allowed a sustained and homogeneous contrast opacification of target cardiac chambers, resulting in useful 3D data sets in 39 of 40 (98%) patients. Moreover, it was possible to achieve 'good' or 'optimal' 3D image quality in the majority of patients (adenosine: 61%, pacing 78%, P = 0.69). When compared with rapid pacing, the total elimination of cardiac motion artefacts with adenosine more frequently resulted in 'optimal' 3D image quality (42% vs. 11%, P = 0.01) and added the possibility for single-rotation 3D imaging of the ventricles. Quantitative analysis showed an excellent agreement between pulmonary vein diameters measured on cardiac CT and 3DRA images. Integration of 3DRA-based LA surfaces with real-time fluoroscopy was easy and highly accurate.

CONCLUSION

Adenosine-induced ventricular asystole or rapid ventricular pacing allow acquisition of 3DRA with an excellent direct contrast opacification of any cardiac chamber and a reduction of cardiac motion artefacts, resulting in high-quality per-procedural 3D imaging with a single C-arm rotation.