Spatial-temporal Total Variation Regularization (STTVR) for 4D-CT Reconstruction

Four dimensional computed tomography (4D-CT) is very important for treatment planning in thorax or abdomen area, e.g. for guiding radiation therapy planning. The respiratory motion makes the reconstruction problem illposed. Recently, compressed sensing theory was introduced. It uses sparsity as a prior to solve the problem and improves image quality considerably. However, the images at each phase are reconstructed individually. The correlations between neighboring phases are not considered in the reconstruction process. In this paper, we propose the spatial-temporal total variation regularization (STTVR) method which not only employs the sparsity in the spatial domain but also in the temporal domain. The algorithm is validated with XCAT thorax phantom. The Euclidean norm of the reconstructed image and ground truth is calculated for evaluation. The results indicate that our method improves the reconstruction quality by more than 50 % compared to standard ART

Direct Percutaneous Left Ventricular Access and Port Closure Pre-Clinical Feasibility

ObjectivesThis study sought to evaluate feasibility of nonsurgical transthoracic catheter-based left ventricular (LV) access and closure.BackgroundImplanting large devices, such as mitral or aortic valve prostheses, into the heart requires surgical exposure and repair. Reliable percutaneous direct transthoracic LV access and closure would allow new nonsurgical therapeutic procedures.MethodsPercutaneous direct LV access was performed in 19 swine using real-time magnetic resonance imaging (MRI) and an “active” MRI needle antenna to deliver an 18-F introducer sheath. The LV access ports were closed percutaneously using a commercial ventricular septal defect occluder and an “active” MRI delivery cable for enhanced visibility. We used “permissive pericardial tamponade” (temporary fluid instillation to separate the 2 pericardial layers) to avoid pericardial entrapment by the epicardial disk. Techniques were developed in 8 animals, and 11 more were followed up to 3 months by MRI and histopathology.ResultsImaging guidance allowed 18-F sheath access and closure with appropriate positioning of the occluder inside the transmyocardial tunnel. Of the survival cohort, immediate hemostasis was achieved in 8 of 11 patients. Failure modes included pericardial entrapment by the epicardial occluder disk (n = 2) and a true-apex entry site that prevented hemostatic apposition of the endocardial disk (n = 1). Reactive pericardial effusion (192 ± 118 ml) accumulated 5 ± 1 days after the procedure, requiring 1-time drainage. At 3 months, LV function was preserved, and the device was endothelialized.ConclusionsDirect percutaneous LV access and closure is feasible using real-time MRI. A commercial occluder achieved hemostasis without evident deleterious effects on the LV. Having established the concept, further clinical development of this approach appears realistic

Local Tomography and the Motion Estimation Problem

In this paper we study local tomography (LT) in the motion contaminated case. It is shown that microlocally, away from some critical directions, LT is equivalent to a pseudodifferential operator of order one. LT also produces nonlocal artifacts that are of the same strength as useful singularities. If motion is not accurately known, singularities inside the object f being scanned spread in different directions. A single edge can become a double edge. In such a case the image of f looks cluttered. Based on this observation we propose an algorithm for motion estimation. We propose an empiric measure of image clutter, which we call edge entropy. By minimizing edge entropy we find the motion model. The algorithm is quite flexible and is also used for solving the misalignment correction problem. The results of numerical experiments on motion estimation and misalignment correction are very encouraging

Method for Estimating Scan Parameters from Tomographic Data

In this paper we study local tomography (LT) in the motion contaminated case. It is shown that microlocally, away from some critical directions, LT is equivalent to a pseudo-differential operator of order one. LT also produces non-local artifacts that are of the same strength as useful singularities. If motion is not accurately known, singularities inside the object f being scanned spread in different directions. A single edge can become a double edge. In such a case the image of f looks cluttered. Based on this observation we propose an algorithm for motion estimation. We propose an empiric measure of image clutter, which we call edge entropy. By minimizing edge entropy we find the motion model. The algorithm is quite flexible and is used also for solving the misalignment correction problem. The results of numerical experiments on motion estimation and misalignment correction are very encouraging

An Algorithm for Motion Estimation from the Tomographic Data

In this paper we study local tomography (LT) in the motion contaminated case. It is shown that microlocally, away from some critical directions, LT is equivalent to a pseudo-differential operator of order one. LT also produces non-local artifacts that are of the same strength as useful singularities. If motion is not accurately known, singularities inside the object f being scanned spread in different directions. A single edge can become a double edge. In such a case the image of f looks cluttered. Based on this observation we propose an algorithm for motion estimation. We propose an empiric measure of image clutter, which we call edge entropy. By minimizing edge entropy we find the motion model. The algorithm is quite flexible and is used also for solving the misalignment correction problem. The results of numerical experiments on motion estimation and misalignment correction are very encouraging

Deep motion tracking from multiview angiographic image sequences for synchronization of cardiac phases

In the diagnosis and interventional treatment of coronary artery disease, the 3D+time reconstruction of the coronary artery on the basis of x-ray angiographic image sequences can provide dynamic structural information. The synchronization of cardiac phases in the sequences is essential for minimizing the influence of cardiorespiratory motion and realizing precise 3D+time reconstruction. Key points are initially extracted from the first image of a sequence. Matching grid points between consecutive images in the sequence are extracted by a multi-layer matching strategy. Then deep motion tracking (DMT) of key points is achieved by local deformation based on the neighboring grid points of key points. The local deformation is optimized by the Random sample consensus (RANSAC) algorithm. Then, a simple harmonic motion (SHM) model is utilized to distinguish cardiac motion from other motion sources (e.g. respiratory, patient movement, etc). Next, the signal which is composed of cardiac motions is filtered by a band-pass filter to reconstruct the cardiac phases. Finally, the synchronization of cardiac phases from different imaging angles is realized by a piece-wise linear transformation. The proposed method was evaluated using clinical x-ray angiographic image sequences from 13 patients. 85% matching points can be accurately computed by the DMT method. The mean peak temporal distance (MPTD) between the reconstructed cardiac phases and the electrocardiograph signal is 0.027 s. The correlation between the cardiac phases of the same patient is over 89%. Compared with three other state-of-the-art methods, the proposed method accurately reconstructs and synchronizes the cardiac phases from different sequences of the same patient. The proposed DMT method is robust and highly effective in synchronizing cardiac phases of angiographic image sequences captured from different imaging angles

Development of a Surgical Assistance System for Guiding Transcatheter Aortic Valve Implantation

Development of image-guided interventional systems is growing up rapidly in the recent years. These new systems become an essential part of the modern minimally invasive surgical procedures, especially for the cardiac surgery. Transcatheter aortic valve implantation (TAVI) is a recently developed surgical technique to treat severe aortic valve stenosis in elderly and high-risk patients. The placement of stented aortic valve prosthesis is crucial and typically performed under live 2D fluoroscopy guidance. To assist the placement of the prosthesis during the surgical procedure, a new fluoroscopy-based TAVI assistance system has been developed. The developed assistance system integrates a 3D geometrical aortic mesh model and anatomical valve landmarks with live 2D fluoroscopic images. The 3D aortic mesh model and landmarks are reconstructed from interventional angiographic and fluoroscopic C-arm CT system, and a target area of valve implantation is automatically estimated using these aortic mesh models. Based on template-based tracking approach, the overlay of visualized 3D aortic mesh model, landmarks and target area of implantation onto fluoroscopic images is updated by approximating the aortic root motion from a pigtail catheter motion without contrast agent. A rigid intensity-based registration method is also used to track continuously the aortic root motion in the presence of contrast agent. Moreover, the aortic valve prosthesis is tracked in fluoroscopic images to guide the surgeon to perform the appropriate placement of prosthesis into the estimated target area of implantation. An interactive graphical user interface for the surgeon is developed to initialize the system algorithms, control the visualization view of the guidance results, and correct manually overlay errors if needed. Retrospective experiments were carried out on several patient datasets from the clinical routine of the TAVI in a hybrid operating room. The maximum displacement errors were small for both the dynamic overlay of aortic mesh models and tracking the prosthesis, and within the clinically accepted ranges. High success rates of the developed assistance system were obtained for all tested patient datasets. The results show that the developed surgical assistance system provides a helpful tool for the surgeon by automatically defining the desired placement position of the prosthesis during the surgical procedure of the TAVI.Die Entwicklung bildgeführter interventioneller Systeme wächst rasant in den letzten Jahren. Diese neuen Systeme werden zunehmend ein wesentlicher Bestandteil der technischen Ausstattung bei modernen minimal-invasiven chirurgischen Eingriffen. Diese Entwicklung gilt besonders für die Herzchirurgie. Transkatheter Aortenklappen-Implantation (TAKI) ist eine neue entwickelte Operationstechnik zur Behandlung der schweren Aortenklappen-Stenose bei alten und Hochrisiko-Patienten. Die Platzierung der Aortenklappenprothese ist entscheidend und wird in der Regel unter live-2D-fluoroskopischen Bildgebung durchgeführt. Zur Unterstützung der Platzierung der Prothese während des chirurgischen Eingriffs wurde in dieser Arbeit ein neues Fluoroskopie-basiertes TAKI Assistenzsystem entwickelt. Das entwickelte Assistenzsystem überlagert eine 3D-Geometrie des Aorten-Netzmodells und anatomischen Landmarken auf live-2D-fluoroskopische Bilder. Das 3D-Aorten-Netzmodell und die Landmarken werden auf Basis der interventionellen Angiographie und Fluoroskopie mittels eines C-Arm-CT-Systems rekonstruiert. Unter Verwendung dieser Aorten-Netzmodelle wird das Zielgebiet der Klappen-Implantation automatisch geschätzt. Mit Hilfe eines auf Template Matching basierenden Tracking-Ansatzes wird die Überlagerung des visualisierten 3D-Aorten-Netzmodells, der berechneten Landmarken und der Zielbereich der Implantation auf fluoroskopischen Bildern korrekt überlagert. Eine kompensation der Aortenwurzelbewegung erfolgt durch Bewegungsverfolgung eines Pigtail-Katheters in Bildsequenzen ohne Kontrastmittel. Eine starrere Intensitätsbasierte Registrierungsmethode wurde verwendet, um kontinuierlich die Aortenwurzelbewegung in Bildsequenzen mit Kontrastmittelgabe zu detektieren. Die Aortenklappenprothese wird in die fluoroskopischen Bilder eingeblendet und dient dem Chirurg als Leitfaden für die richtige Platzierung der realen Prothese. Eine interaktive Benutzerschnittstelle für den Chirurg wurde zur Initialisierung der Systemsalgorithmen, zur Steuerung der Visualisierung und für manuelle Korrektur eventueller Überlagerungsfehler entwickelt. Retrospektive Experimente wurden an mehreren Patienten-Datensätze aus der klinischen Routine der TAKI in einem Hybrid-OP durchgeführt. Hohe Erfolgsraten des entwickelten Assistenzsystems wurden für alle getesteten Patienten-Datensätze erzielt. Die Ergebnisse zeigen, dass das entwickelte chirurgische Assistenzsystem ein hilfreiches Werkzeug für den Chirurg bei der Platzierung Position der Prothese während des chirurgischen Eingriffs der TAKI bietet

3D Imaging for Planning of Minimally Invasive Surgical Procedures

Novel minimally invasive surgeries are used for treating cardiovascular diseases and are performed under 2D fluoroscopic guidance with a C-arm system. 3D multidetector row computed tomography (MDCT) images are routinely used for preprocedural planning and postprocedural follow-up. For preprocedural planning, the ability to integrate the MDCT with fluoroscopic images for intraprocedural guidance is of clinical interest. Registration may be facilitated by rotating the C-arm to acquire 3D C-arm CT images. This dissertation describes the development of optimal scan and contrast parameters for C-arm CT in 6 swine. A 5-s ungated C-arm CT acquisition during rapid ventricular pacing with aortic root injection using minimal contrast (36 mL), producing high attenuation (1226), few artifacts (2.0), and measurements similar to those from MDCT (p\u3e0.05) was determined optimal. 3D MDCT and C-arm CT images were registered to overlay the aortic structures from MDCT onto fluoroscopic images for guidance in placing the prosthesis. This work also describes the development of a methodology to develop power equation (R2\u3e0.998) for estimating dose with C-arm CT based on applied tube voltage. Application in 10 patients yielded 5.48┬▒177 2.02 mGy indicating minimal radiation burden. For postprocedural follow-up, combinations of non-contrast, arterial, venous single energy CT (SECT) scans are used to monitor patients at multiple time intervals resulting in high cumulative radiation dose. Employing a single dual-energy CT (DECT) scan to replace two SECT scans can reduce dose. This work focuses on evaluating the feasibility of DECT imaging in the arterial phase. The replacement of non-contrast and arterial SECT acquisitions with one arterial DECT acquisition in 30 patients allowed generation of virtual non-contrast (VNC) images with 31 dose savings. Aortic luminal attenuation in VNC (32┬▒177 2 HU) was similar to true non-contrast images (35┬▒177 4 HU) indicating presence of unattenuated blood. To improve discrimination between c

3D Imaging for Planning of Minimally Invasive Surgical Procedures

Novel minimally invasive surgeries are used for treating cardiovascular diseases and are performed under 2D fluoroscopic guidance with a C-arm system. 3D multidetector row computed tomography (MDCT) images are routinely used for preprocedural planning and postprocedural follow-up. For preprocedural planning, the ability to integrate the MDCT with fluoroscopic images for intraprocedural guidance is of clinical interest. Registration may be facilitated by rotating the C-arm to acquire 3D C-arm CT images. This dissertation describes the development of optimal scan and contrast parameters for C-arm CT in 6 swine. A 5-s ungated C-arm CT acquisition during rapid ventricular pacing with aortic root injection using minimal contrast (36 mL), producing high attenuation (1226), few artifacts (2.0), and measurements similar to those from MDCT (p\u3e0.05) was determined optimal. 3D MDCT and C-arm CT images were registered to overlay the aortic structures from MDCT onto fluoroscopic images for guidance in placing the prosthesis. This work also describes the development of a methodology to develop power equation (R2\u3e0.998) for estimating dose with C-arm CT based on applied tube voltage. Application in 10 patients yielded 5.48┬▒177 2.02 mGy indicating minimal radiation burden. For postprocedural follow-up, combinations of non-contrast, arterial, venous single energy CT (SECT) scans are used to monitor patients at multiple time intervals resulting in high cumulative radiation dose. Employing a single dual-energy CT (DECT) scan to replace two SECT scans can reduce dose. This work focuses on evaluating the feasibility of DECT imaging in the arterial phase. The replacement of non-contrast and arterial SECT acquisitions with one arterial DECT acquisition in 30 patients allowed generation of virtual non-contrast (VNC) images with 31 dose savings. Aortic luminal attenuation in VNC (32┬▒177 2 HU) was similar to true non-contrast images (35┬▒177 4 HU) indicating presence of unattenuated blood. To improve discrimination between c