Maria Panayiotou

A statistical method for retrospective cardiac and respiratory motion gating of interventional cardiac x-ray images

PURPOSE Image-guided cardiac interventions involve the use of fluoroscopic images to guide the insertion and movement of interventional devices. Cardiorespiratory gating can be useful for 3D reconstruction from multiple x-ray views and for reducing misalignments between 3D anatomical models overlaid onto fluoroscopy. METHODS The authors propose a novel and potentially clinically useful retrospective cardiorespiratory gating technique. The principal component analysis (PCA) statistical method is used in combination with other image processing operations to make our proposed masked-PCA technique suitable for cardiorespiratory gating. Unlike many previously proposed techniques, our technique is robust to varying image-content, thus it does not require specific catheters or any other optically opaque structures to be visible. Therefore, it works without any knowledge of catheter geometry. The authors demonstrate the application of our technique for the purposes of retrospective cardiorespiratory gating of normal and very low dose x-ray fluoroscopy images. RESULTS For normal dose x-ray images, the algorithm was validated using 28 clinical electrophysiology x-ray fluoroscopy sequences (2168 frames), from patients who underwent radiofrequency ablation (RFA) procedures for the treatment of atrial fibrillation and cardiac resynchronization therapy procedures for heart failure. The authors established end-systole, end-expiration, and end-inspiration success rates of 97.0%, 97.9%, and 97.0%, respectively. For very low dose applications, the technique was tested on ten x-ray sequences from the RFA procedures with added noise at signal to noise ratio (SNR) values of √50, √10, √8, √6, √5, √2 and √1 to simulate the image quality of increasingly lower dose x-ray images. Even at the low SNR value of √2, representing a dose reduction of more than 25 times, gating success rates of 89.1%, 88.8%, and 86.8% were established. CONCLUSIONS The proposed technique can therefore extract useful information from interventional x-ray images while minimizing exposure to ionizing radiation.

Interactive visualization for scar transmurality in cardiac resynchronization therapy

Heart failure is a serious disease affecting about 23 million people worldwide. Cardiac resynchronization therapy is used to treat patients suffering from symptomatic heart failure. However, 30% to 50% of patients have limited clinical benefit. One of the main causes is suboptimal placement of the left ventricular lead. Pacing in areas of myocardial scar correlates with poor clinical outcomes. Therefore precise knowledge of the individual patient’s scar characteristics is critical for delivering tailored treatments capable of improving response rates. Current research methods for scar assessment either map information to an alternative non-anatomical coordinate system or they use the image coordinate system but lose critical information about scar extent and scar distribution. This paper proposes two interactive methods for visualizing relevant scar information. A 2-D slice based approach with a scar mask overlaid on a 16 segment heart model and a 3-D layered mesh visualization which allows physicians to scroll through layers of scar from endocardium to epicardium. These complementary methods enable physicians to evaluate scar location and transmurality during planning and guidance. Six physicians evaluated the proposed system by identifying target regions for lead placement. With the proposed method more target regions could be identified.

Extraction of Cardiac and Respiratory Motion Information from Cardiac X-Ray Fluoroscopy Images Using Hierarchical Manifold Learning

We present a novel and clinically useful method to automatically determine the regions that carry cardiac and respiratory motion information directly from standard mono-plane X-ray fluoroscopy images. We demonstrate the application of our method for the purposes of retrospective cardiac and respiratory gating of X-ray images. Validation is performed on five mono-plane imaging sequences comprising a total of 284 frames from five patients undergoing radiofrequency ablation for the treatment of atrial fibrillation. We established end-inspiration, end-expiration and systolic gating with success rates of 100%, 100% and 95.3%, respectively. This technique is useful for retrospective gating of X-ray images and, unlike many previously proposed techniques, does not require specific catheters to be visible and works without any knowledge of catheter geometry.

Image-based view-angle independent cardiorespiratory motion gating and coronary sinus catheter tracking for x-ray-guided cardiac electrophysiology procedures

Determination of the cardiorespiratory phase of the heart has numerous applications during cardiac imaging. In this article we propose a novel view-angle independent near-real time cardiorespiratory motion gating and coronary sinus (CS) catheter tracking technique for x-ray fluoroscopy images that are used to guide cardiac electrophysiology procedures. The method is based on learning CS catheter motion using principal component analysis and then applying the derived motion model to unseen images taken at arbitrary projections, using the epipolar constraint. This method is also able to track the CS catheter throughout the x-ray images in any arbitrary subsequent view. We also demonstrate the clinical application of our model on rotational angiography sequences. We validated our technique in normal and very low dose phantom and clinical datasets. For the normal dose clinical images we established average systole, end-expiration and end-inspiration gating success rates of 100%, 85.7%, and 92.3%, respectively. For very low dose applications, the technique was able to track the CS catheter with median errors not exceeding 1 mm for all tracked electrodes. Average gating success rates of 80.3%, 71.4%, and 69.2% were established for the application of the technique on clinical datasets, even with a dose reduction of more than 10 times. In rotational sequences at normal dose, CS tracking median errors were within 1.2 mm for all electrodes, and the gating success rate was 100%, for view angles from RAO 90° to LAO 90°. This view-angle independent technique can extract clinically useful cardiorespiratory motion information using x-ray doses significantly lower than those currently used in clinical practice.

A Planning and Guidance Platform for Cardiac Resynchronization Therapy

Patients with drug-refractory heart failure can greatly benefit from cardiac resynchronization therapy (CRT). A CRT device can resynchronize the contractions of the left ventricle (LV) leading to reduced mortality. Unfortunately, 30%–50% of patients do not respond to treatment when assessed by objective criteria such as cardiac remodeling. A significant contributing factor is the suboptimal placement of the LV lead. It has been shown that placing this lead away from scar and at the point of latest mechanical activation can improve response rates. This paper presents a comprehensive and highly automated system that uses scar and mechanical activation to plan and guide CRT procedures. Standard clinical preoperative magnetic resonance imaging is used to extract scar and mechanical activation information. The data are registered to a single 3-D coordinate system and visualized in novel 2-D and 3-D American Heart Association plots enabling the clinician to select target segments. During the procedure, the planning information is overlaid onto live fluoroscopic images to guide lead deployment. The proposed platform has been used during 14 CRT procedures and validated on synthetic, phantom, volunteer, and patient data.

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

The clinical applications and benefits of multi-modal image registration are wide-ranging and well established. Current image based approaches exploit cross-modality information, such as landmarks or anatomical structures, which is visible in both modalities. A lack of cross-modality information can prohibit accurate automatic registration. This paper proposes a novel approach for MR to X-ray image registration which uses prior knowledge of adjacent anatomical structures to enable registration without cross-modality image information. The registration of adjacent structures formulated as a partial surface registration problem which is solved using a globally optimal ICP method. The practical clinical application of the approach is demonstrated on an image guided cardiac resynchronization therapy procedure. The left ventricle (segmented from pre-operative MR) is registered to the coronary vessel tree (extracted from intra-operative fluoroscopic images). The proposed approach is validated on synthetic and phantom data, where the results show a good comparison with the ground truth registrations. The vertex-to-vertex MAE was \(3.28\pm 1.18\) mm for 10 X-ray image pairs of the phantom.

Automatic image-based retrospective gating of interventional cardiac X-ray images

Gating of X-ray fluoroscopy images is required for catheter reconstruction for registration of pre-procedural images with fluoroscopy for guidance and biophysical modelling. We propose a novel and clinically useful retrospective method for automatic image-based cardiac and respiratory motion gating. The technique is based on tracking and statistical analysis of the shape of the coronary sinus catheter. We applied our method on five mono-plane imaging sequences comprising a total of 322 frames from five different patients undergoing radiofrequency ablation for the treatment of atrial fibrillation. We established systole, end-inspiration and end-expiration gating with success rates of 100%, 89.47% and 81.25% respectively.

Image-Based View-Angle Independent Cardiorespiratory Motion Gating for X-ray-Guided Interventional Electrophysiology Procedures

Cardiorespiratory phase determination has numerous applications during cardiac imaging. We propose a novel view-angle independent prospective cardiorespiratory motion gating technique for X-ray fluoroscopy images that are used to guide cardiac electrophysiology procedures. The method is based on learning coronary sinus catheter motion using principal component analysis and then applying the derived motion model to unseen images taken at arbitrary projections. We validated our technique on 7 sequential biplane sequences in normal and very low dose scenarios and on 5 rotational sequences in normal dose. For the normal dose images we established average systole, end-inspiration and end-expiration gating success rates of 100 %, 97.4 % and 95.2 %, respectively. For very low dose applications, the method was tested on images with added noise. Average gating success rates were 93.4 %, 90 % and 93.4 % even at the low SNR value of \(\sqrt{5}\), representing a dose reduction of more than 10 times. This technique can extract clinically useful motion information whilst minimising exposure to ionising radiation.

3D/2D Registration with Superabundant Vessel Reconstruction for Cardiac Resynchronization Therapy

Highlights3D/2D registration using adjacent anatomical structures is proposed.Superabundant 3D vessel reconstruction is performed without point correspondences.A globally optimal registration method is extended with dynamic outlier rejection.Novel evaluation framework using previously implanted artificial valves is proposed. Graphical abstract Figure. No caption available. ABSTRACT A key component of image guided interventions is the registration of preoperative and intraoperative images. Classical registration approaches rely on cross‐modality information; however, in modalities such as MRI and X‐ray there may not be sufficient cross‐modality information. This paper proposes a fundamentally different registration approach which uses adjacent anatomical structures with superabundant vessel reconstruction and dynamic outlier rejection. In the targeted clinical scenario of cardiac resynchronization therapy (CRT) delivery, preoperative, non contrast‐enhanced, MRI is registered to intraoperative, contrasted X‐ray fluoroscopy. The adjacent anatomical structures are the left ventricle (LV) from MRI and the coronary veins reconstructed from two contrast‐enhanced X‐ray images. The novel concept of superabundant vessel reconstruction is introduced to bypass the standard reconstruction problem of establishing one‐to‐one correspondences. Furthermore, a new dynamic outlier rejection method is proposed, to enable globally optimal point set registration. The proposed approach has been qualitatively and quantitatively evaluated on phantom, clinical CT angiography with ground truth and clinical CRT data. A novel evaluation method is proposed for clinical CRT data based on previously implanted artificial aortic and mitral valves. The registration accuracy in 3D was 2.94 mm for the aortic and 3.86 mm for the mitral valve. The results are below the required accuracy identified by clinical partners to be the half‐segment size (16.35 mm) of a standard American Heart Association (AHA) 16 segment model of the LV.

Image Integration to Guide Wireless Endocardial LV Electrode Implantation for CRT

Suboptimal left ventricular (LV) lead placement in myocardial scar (fibrosis) is associated with cardiac resynchronization therapy (CRT) nonresponse [(1)][1]. Image guidance (echocardiography and cardiac magnetic resonance [CMR]) avoiding fibrosis and targeting late mechanical activation may improve