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Three-dimensional reconstruction of coronary arteries can be performed during x-ray-guided interventions by gated reconstruction from a rotational coronary angiography sequence. Due to imperfect gating and cardiac or breathing motion, the heart's motion state might not be the same in all projections used for the reconstruction of one cardiac phase. The motion state inconsistency causes motion artefacts and degrades the reconstruction quality. These effects can be reduced by a projection-based 2D motion compensation method. Using maximum-intensity forward projections of an initial uncompensated reconstruction as reference, the projection data are transformed elastically to improve the consistency with respect to the heart's motion state. A fast iterative closest-point algorithm working on vessel centrelines is employed for estimating the optimum transformation. Motion compensation is carried out prior to and independently from a final reconstruction. The motion compensation improves the accuracy of reconstructed vessel radii and the image contrast in a software phantom study. Reconstructions of human clinical cases are presented, in which the motion compensation substantially reduces motion blur and improves contrast and visibility of the coronary arteries.

The motion of the heart is a major challenge for cardiac imaging using CT. A novel approach to decrease motion blur and to improve the signal to noise ratio is motion compensated reconstruction which takes motion vector fields into account in order to correct motion. The presented work deals with the determination of local motion vector fields from high contrast objects and their utilization within motion compensated filtered back projection reconstruction. Image registration is applied during the quiescent cardiac phases. Temporal interpolation in parameter space is used in order to estimate motion during strong motion phases. The resulting motion vector fields are during image reconstruction. The method is assessed using a software phantom and several clinical cases for calcium scoring. As a criterion for reconstruction quality, calcium volume scores were derived from both, gated cardiac reconstruction and motion compensated reconstruction throughout the cardiac phases using low pitch helical cone beam CT acquisitions. The presented technique is a robust method to determine and utilize local motion vector fields. Motion compensated reconstruction using the derived motion vector fields leads to superior image quality compared to gated reconstruction. As a result, the gating window can be enlarged significantly, resulting in increased SNR, while reliable Hounsfield units are achieved due to the reduced level of motion artefacts. The enlargement of the gating window can be translated into reduced dose requirements.

A new method is introduce for the three-dimensional (3D) reconstruction of the coronary stents in-vivo utilizing two-dimensional projection images acquired during rotational angiography (RA). The method is based on the application of motion compensated techniques to the acquired angiograms resulting in a temporal snapshot of the stent within the cardiac cycle. For the first time results of 3D reconstructed coronary stents in vivo, with high spatial resolution are presented. The proposed method allows for a comprehensive and unique quantitative 3D assessment of stent expansion that rivals current x-ray and intravascular ultrasound techniques.

Three-dimensional (3D) reconstruction of the coronary arteries offers great advantages in the diagnosis and treatment of cardiovascular diseases, compared to two-dimensional X-ray angiograms. Besides improved roadmapping, quantitative analysis of vessel lesions is possible. To perform 3D reconstruction, rotational projection data of the selectively contrast agent enhanced coronary arteries are acquired with simultaneous ECG recording. For the reconstruction of one cardiac phase, the corresponding projections are selected from the rotational sequence by nearest-neighbor ECG gating. This typically provides only 5-10 projections per cardiac phase. The severe angular undersampling leads to an ill-posed reconstruction problem. In this contribution, an iterative reconstruction method is presented which employs regularizations especially suited for the given reconstruction problem. The coronary arteries cover only a small fraction of the reconstruction volume. Therefore, we formulate the reconstruction problem as a minimization of the L 1 -norm of the reconstructed image, which results in a spatially sparse object. Two additional regularization terms are introduced: a 3D vesselness prior, which is reconstructed from vesselness-filtered projection data, and a Gibbs smoothing prior. The regularizations favor the reconstruction of the desired object, while taking care not to over-constrain the reconstruction by too detailed a-priori assumptions. Simulated projection data of a coronary artery software phantom are used to evaluate the performance of the method. Human data of clinical cases are presented to show the method's potential for clinical application.

In this contribution, the results of a phantom study for in-stent restenosis imaging with ECG gated continuous circular acquisition and reconstruction are summarized. Different rotation speeds and angular ranges are used to enable high resolution 3D and 4D reconstruction of objects covered by the cone at a high temporal resolution. Though the detector coverage of today's CT scanners is not large enough to irradiate the complete human heart, the coverage is sufficient to image smaller objects like conventional stents. We applied the proposed method to the visualization of an in-stent re-stenoses phantom covered by a clinical stent, attached to a dynamic heart phantom. The method delivers images of stents in vitro at an excellent visibility and is able to rule out in-stent occlusions.

A method is proposed that allows for a fully automated computation of a series of high-resolution volumetric reconstructions of a patient's coronary arteries based on a single rotational acquisition. During the 7.2 second acquisition the coronary arteries are injected with contrast material while the imaging system rotates around the patient to obtain a series of X-ray projection images over an angular range of 180 degrees. Based on the simultaneously recorded ECG-signal the projection images corresponding to the same cardiac cycle can be utilized to reconstruct three-dimensional (3D) high-spatial-resolution angiograms of the coronary arteries in multiple (3D+t) cardiac phases within the cardiac cycle. The proposed acquisition protocol has been applied to 22 patients and the tomograpic reconstructions depicted the main arteries as well as the main bifurcations in multiple cardiac phases in all enrolled patients. For the first time, this feasibility study shows that a three-dimensional description of the coronary arteries can be obtained intraprocedurally in a conventional interventional suite by means of tomographic reconstruction from projection images without any user interaction.

Computer tomography (CT) scanners with an increasing number of detector rows offer the potential of shorter scanning times. Nevertheless, the reconstruction problem becomes more challenging, since cone beam artifacts are likely to enter. Here, we consider helical cardiac CT. We analyze how a relationship can be established between exact reconstruction algorithms and the demand to perform a cardiac gating. Utilizing the redundancies requires the consideration of all kinds of Radon planes. For the reconstruction algorithm proposed here, we separate the data into two parts. The first part contains contributions of Radon planes, which are measured with a large number of redundancies. The second part contains the remaining contributions. As it turns out, the second part contributes rather to the low-frequency contents of trans-axial slices. Therefore, we propose to perform a gated back-projection only for the first part, while the second part is back-projected in an ungated way. Data from the complete source trajectory are employed in the reconstruction process in contrary to conventional helical cardiac reconstruction methods. Moreover, all different types of Radon planes are taken into account in the reconstruction, though an ECG-dependent cardiac gating is applied. The reconstruction results, which we present for clinical and simulated data, demonstrate the high potential of CEnPiT for helical cardiac CT with large cone angle systems.

A calcium-scoring phantom with hydroxyapatite-filled cylindrical holes (0.5 to 4 mm) was used. High-resolution scans were performed for an accuracy baseline. The phantom was mounted to a moving heart phantom. Non-moving data with the implementation of an ECG-signal were acquired for different pitches (0.2/0.3), heart rates (60/80/95 bpm) and collimations (16 x 0.75/16 x 1.5 mm). Images were reconstructed with a cone-beam multi-cycle algorithm at a standard thickness/increment of 3 mm/1.5 mm and the thinnest possible thickness (0.8/0.4 and 2/1). Subsequently, ECG-gated moving calcium-scoring phantom data were acquired. The calcium volume and Agatston score were measured. The temporal resolution and reconstruction cycles were calculated. High-resolution scans determine the calcium volume with a high accuracy (mean overestimation, 0.8%). In the non-moving measurements, the volume underestimation ranged from about 6% (16 x 0.75 mm; 0.8/0.4 mm) to nearly 25% (16 x 1.5 mm; 3/1.5 mm). Moving scans showed increased measurement errors depending on the reconstructed RR interval, collimation, pitch, heart rate and gantry rotation time. Also, a correlation with the temporal resolution could be found. The reliability of calcium-scoring results can be improved with the use of a narrower collimation, a lower pitch and the reconstruction of thinner images, resulting in higher patient doses. The choice of the correct cardiac phase within the RR interval is essential to minimize measurement errors.

The iterative reconstruction of a circular cone-beam short-scan (180/spl deg/ plus fan angle) measurement with algebraic reconstruction technique (ART) is investigated. Simulated projections of a transmission tomography scan of the Forbild head phantom are reconstructed. The reconstruction of the short-scan sinogram with ART is compared with the reconstruction of a Parker weighted iterative update, which compensates for the redundancy of the measured rays. The results show that a Parker weighting improves the image quality of the reconstruction with ART during the first few iterations compared with the standard ART, but that this difference vanishes with increasing number of iterations.

We analyze a trajectory consisting of a line and a circle for cardiac cone-beam CT with large area detectors. The patient's ECG is used to assemble one complete circle consisting of data from different revolutions but measured within the same heart phase. The linear part is needed to achieve a mathematically complete trajectory. Data measured within this part contribute un-gated to the image. The reconstruction algorithm used is mathematically exact and of the filtered backprojection type. Excellent image quality is shown in a simulation study for a 256 row scanner.

In this contribution, we introduce a retrospectively gated cardiac cone-beam reconstruction scheme for continuous circular acquisition with parallel ECG recording. The technique is capable of handling variable angular ranges and enables high resolution 3D and 4D reconstruction of objects covered by the cone at a high temporal resolution. Though the detector coverage of nowadays CT scanners is not large enough to cover the complete human heart, it is sufficient to image smaller objects like conventional stents. We applied the proposed reconstruction method to the visualization of an in-stent re-stenoses phantom covered by a clinical stent, attached to a dynamic heart phantom. The method delivers images of stents in vitro at an excellent visibility and is able to rule out in-stent occlusions.

Recently, three-dimensional cardiac cone beam reconstruction has been introduced for retrospectively gated volume CT imaging. In order to investigate the resulting image quality for large area detectors (LAD), a simulation study has been carried out: The FORBILD thorax phantom has been extended with a dynamic heart insert forming a 4D cardiac CT phantom. Cone beam projection data for 256. 128, 64 and 40-row systems at three different relative pitches (0.1, 0.2 and 0.3) have been simulated at a constant heart rate of 64 bpm. Images have been reconstructed employing the Extended Cardiac Reconstruction (ECR) algorithm. The temporal resolution has been calculated for 256, 128.64 and 40-row systems with different rotation times (0.33 s, 0.42 s, 0.50 s), relative pitches (0.05 up to 0.35) and heart rates (40 up to 120 bpm). With the increased volume coverage of LAD systems, scans with a low to intermediate relative pitch (0.1-0.2) become feasible without resulting in extensive scan times, inhibiting single breath hold acquisitions. With ECR, the image quality is excellent for systems with an increased cone-angle. Alternative reconstruction approaches such as iterative or exact schemes may further improve the image quality for detectors above 128 rows. The study shows that an intermediate relative pitch, e.g. 0.2, is feasible for cardiac data acquisition. It results in good temporal resolution at fast volume coverage.

This paper presents a framework of non-interactive algorithms for the mapping of blood flow information to vessels in 3D-RA images. With the presented method, mapping of flow information to 3D-RA images is done automatically without user interaction. So far, radiologists had to perform this task by extensive image comparisons and did not obtain visualizations of the results. In our approach, flow information is reconstructed by forward projection of vessel pieces in a 3D-RA image to a two-dimensional projection series capturing the propagation of a short additional contrast agent bolus. For accurate 2D-3D image registration, an efficient patient motion compensation technique is introduced. As an exemplary flow-related quantity, bolus arrival times are reconstructed for the vessel pieces by matching of intensity-time curves. A plausibility check framework was developed which handles projection ambiguities and corrects for noisy flow reconstruction results. It is based on a linear programming approach to model the feeding structure of the vessel. The flow reconstruction method was applied to 12 cases of cerebral stenoses, AVMs and aneurysms, and it proved to be feasible in the clinical environment. The propagation of the injected contrast agent was reconstructed and visualized in three-dimensional images. The flow reconstruction method was able to visualize different types of useful information. In cases of stenosis of the middle cerebral artery (MCA), flow reconstruction can reveal impeded blood flow depending on the severeness of the stenosis. With cases of AVMs, flow reconstruction can clarify the feeding structure. The presented methods handle the problems imposed by clinical demands such as non-interactive algorithms, patient motion compensation, short reconstruction times, and technical requirements such as correction of noisy bolus arrival times and handling of overlapping vessel pieces. Problems occurred mainly in the reconstruction and segmentation of 3D-RA images in cases of complex AVMs. The concentration of injected contrast agent was often not sufficient to provide highly contrasted vessels in 3D-RA images. Another segmentation-related problem is known as 'kissing vessels' [19]. Kissing vessel artifacts introduce artificial vessel junctions and thereby distort the feeding structure of the vessel. This may finally cause implausible flow reconstruction results and inverse flow directions in vessel segments. We are currently planning to validate our reconstruction results using particle imaging velocimetry (PIV). PIV experiments with phantoms, for which the true flow parameters are known, will allow for the assessment of the accuracy of our contrast agent based method. In the context of computational fluid dynamics techniques, the potential of the presented flow reconstruction method is high. Flow reconstruction results based on the presented method could be used both as boundary conditions for simulations and as a reference for the validation of simulation results. Computational fluid dynamics provide useful information such as arterial wall shear stress and complex flow patterns in aneurysms.

Modern multislice CT systems with a fast rotating gantry are particularly suitable for cardiac volume imaging. Due to the cone angle, true 3D back-projection algorithms deliver superior image quality compared with 2D techniques. We propose a true cone-beam reconstruction algorithm making use of the maximum amount of the measured data in combination with retrospective cardiac gating. Results are presented on a patient data set, which has been acquired using a 16-slice CT system.

To evaluate the effect of heart rate on the quality of coronary angiograms obtained with 16-detector row computed tomography (CT) by using temporally enhanced three-dimensional (3D) approaches.The local ethics committee approved the study, and informed consent was obtained from all patients. Fifty patients underwent coronary CT angiography (heart rate range, 45-103 beats per minute). Raw data from helical CT and electrocardiography (ECG) were saved in a combined data set. Retrospectively ECG-gated images were reconstructed at preselected phases (50% and 80%) of the cardiac cycle. A 3D voxel-based approach with cardiac phase weighting was used for reconstruction. Testing for correlation between heart rate, cardiac phase reconstruction window, and image quality was performed with Kruskal-Wallis analysis. Image quality (freedom from cardiac motion-related artifacts) was referenced against findings at conventional angiography in a secondary evaluation step. Regression analysis was performed to calculate heart rate thresholds for future beta-blocker application.A significant negative correlation was observed between heart rate and image quality (r = 0.80, P.001). Motion artifact-free images were available for 44 (88%) patients and were achieved consistently at a heart rate of 80 or fewer beats per minute (n = 39). Best image quality was achieved at 75 or fewer beats per minute. Segmental analysis revealed that 97% of arterial segments (diameteror = 1.5 mm according to conventional angiography) were assessable at 80 or fewer beats per minute. Premature ventricular contractions and rate-contained arrhythmia did not impede diagnostic assessment of the coronary arteries in 10 (83%) of the 12 patients affected.Motion-free coronary angiograms can be obtained consistently with 16-detector row CT scanners and adaptive multicyclic reconstruction algorithms in patients with heart rates of less than 80 beats per minute.

With the introduction of cone beam (CB) scanners, cardiac volumetric computed tomography (CT) imaging has the potential to become a noninvasive imaging tool in clinical routine for the diagnosis of various heart diseases. Heart rate adaptive reconstruction schemes enable the reconstruction of high-resolution volumetric data sets of the heart. Artifacts, caused by strong heart rate variations, high heart rates and obesity, decrease the image quality and the diagnostic value of the images. The image quality suffers from streak artifacts if suboptimal scan and reconstruction parameters are chosen, demanding improved gating techniques. In this paper, an artifact analysis is carried out which addresses the artifacts due to the gating when using a three-dimensional CB cardiac reconstruction technique. An automatic and patient specific cardiac weighting technique is presented in order to improve the image quality. Based on the properties of the reconstruction algorithm, several assessment techniques are introduced which enable the quantitative determination of the cycle-to-cycle transition smoothness and phase homogeneity of the image reconstruction. Projection data of four patients were acquired using a 16-slice CBCT system in low pitch helical mode with parallel electrocardiogram recording. For each patient, image results are presented and discussed in combination with the assessment criteria.

Measurements of spatial and temporal resolution for ECG-gated scanning of a stationary and moving heart phantom with a 16-row MDCT were performed. A resolution phantom with cylindrical holes from 0.4 to 3.0 mm diameter was mounted to a cardiac phantom, which simulates the motion of a beating heart. Data acquisition was performed with 16×0.75 mm at various heart rates (HR, 60–120 bpm), pitches (0.15–0.30) and scanner rotation times (RT, 0.42 and 0.50 s). Raw data were reconstructed using a multi-cycle real cone-beam reconstruction algorithm at multiple phases of the RR interval. Multi-planar reformations (MPR) were generated and analyzed. Temporal resolution and cardiac cycles used for image reconstruction were calculated. In 97.2% (243/250) of data obtained with the stationary phantom, the complete row of holes with 0.6 mm was visible. These results were independent of heart rate, pitch, scanner rotation time and phase point of reconstruction. For the dynamic phantom, spatial resolution was determined during phases of minimal motion (116/250). In 40.5% (47/116), the resolution was 0.6 mm and in 37.1% (43/116) 0.7 mm. Temporal resolution varied between 63 and 205 ms, using 1.5–4.37 cardiac cycles for image reconstruction.

In this work, three different reconstruction algorithms for short scan helical cone-beam CT are compared: Two approximate algorithms, PI-SLANT and WVEDGE-PI, with the recently published exact algorithm by Katsevich. It is shown that WEDGE-PI performs as well as the exact method for a 64 row scanner and almost as well for a 128 row scanner. PI-SLANT produces significantly more artifacts, in particular for the 128 row scanner.

Coherent scatter computed tomography (CSCT) is a promising method for medical applications allowing superior tissue characterization and diagnosis. This imaging technique combines X-ray scattering and CT reconstruction resulting in angular resolved images of the coherent scatter cross-section. In preceding work synchrotron radiation and/or pencil beam geometry were used for the image acquisition reducing the applications to academic studies. With the advent of multi-slice CT (MSCT) this technique becomes applicable in the medical field. We present Monte-Carlo simulations and experimental data of scattering from biological materials in geometries equivalent to medical MSCT-scanners. To account for the specific geometry of a scatter experiment in a conventional CT-scanner a specific reconstruction technique was developed. The application of this reconstruction technique is demonstrated and the diagnostic significance is discussed.

Cone beam computed tomography scanners in combination with heart rate adaptive reconstruction schemes have the potential to enable cardiac volumetric computed tomography (CT) imaging for a larger number of patients and applications. In this publication, an adaptive scheme for the automatic and patient-specific reconstruction optimization is introduced to improve the temporal resolution and image quality. The optimization method permits the automatic determination of the required amount of gated helical cone beam projection data for the reconstruction volume. It furthermore allows one to optimize subvolume reconstruction yielding an increased temporal resolution. In addition, methods for the assessment of the temporal resolution are given which enable a quantitative documentation of the reconstruction improvements. Results are presented for patient data sets acquired in low pitch helical mode using a 16-slice cone beam CT system with parallel ECG recording.

The entropy method for stacking a series of angiographic images is presented and compared with the maximum opacity method, which is already established. The entropy method comprises calculation of the entropy of the time course for each image pixel. This accentuates image areas where a contrast agent bolus is passing. Quantitative analysis of the contrast-to-noise ratio and qualitative analysis of 11 cases were performed, the latter by eight independent viewers. Results indicate that the entropy images show more vascular detail in small peripheral vessels and increased contrast-to-noise ratio by up to a factor of 1.97 compared with maximum opacity images. © RSNA, 2003

The reconstruction of the contrast agent bolus propagation adds a new dimension to 3D rotational angiography. In this contribution, a noninteractive method for flow reconstruction in three-dimensional vessel structures is presented. It is based on a standard 3D rotational angiography procedure followed by the acquisition of a high-speed projection series with fixed angulation. The bolus propagation information which is calculated from the second series is mapped to the reconstructed volume data set resulting from the 3DRA procedure. Thus, a 4D data set results. Volume rendered images of 4D data sets which have been obtained by applying the flow reconstruction method to several patient data sets are presented. In these images, in addition to the pure static 3D information the contrast agent propagation within the 3D vessel tree is clearly visible.

Coherent scatter computed tomography (CSCT) is a reconstructive x-ray imaging technique that yields the spatially resolved coherent-scatter form factor of the investigated object. Reconstruction from coherently scattered x-rays is commonly done using algebraic reconstruction techniques (ART). In this paper, we propose an alternative approach based on filtered back-projection. For the first time, a three-dimensional (3D) filtered back-projection technique using curved 3D back-projection lines is applied to two-dimensional coherent scatter projection data. The proposed algorithm is tested with simulated projection data as well as with projection data acquired with a demonstrator setup similar to a multi-line CT scanner geometry. While yielding comparable image quality as ART reconstruction, the modified 3D filtered back-projection algorithm is about two orders of magnitude faster. In contrast to iterative reconstruction schemes, it has the advantage that subfield-of-view reconstruction becomes feasible. This allows a selective reconstruction of the coherent-scatter form factor for a region of interest. The proposed modified 3D filtered back-projection algorithm is a powerful reconstruction technique to be implemented in a CSCT scanning system. This method gives coherent scatter CT the potential of becoming a competitive modality for medical imaging or nondestructive testing.

Fan-beam coherent scatter computed tomography (CSCT) is a novel X-ray based imaging method revealing structural information of tissue under investigation. The source of contrast is the angular-dependent coherent scatter cross-section, which is determined by the molecular structure. In this work a phantom consisting of water, tricalcium phosphate, collagen and fat was used to investigate the contrast resolution of these four tissue constituents. Scatter projections were measured in fan-beam 3rd generation CT-geometry using an experimental demonstrator set-up equipped with a 4.5 kW DC power X-ray tube and photon-counting detectors. Reconstruction was performed using two algorithms, one based on algebraic reconstruction technique (ART) and the other based on filtered back-projection (FBP). The reconstruction results of the two techniques are compared. Furthermore, scatter functions of the four components were extracted from the 3D data sets and compared to previous measurements. The applicability of this technique for medical diagnosis is discussed.

Sequential cone-beam tomography is a method that uses data of two or more parallel circular trajectories of a cone-beam scanner to reconstruct the object function. We propose a condition for the data acquisition that ensures that all object points between two successive circles are irradiated over an angular span of the x-ray source position of exactly 360 degrees in total as seen along the rotation axis. A fast and efficient approximative reconstruction method for the proposed acquisition is presented which uses data from exactly 360 degrees for every object point. It is based on the Tent-FDK method which was recently developed for single circular cone-beam CT. The measurement geometry does not provide sufficient data for exact reconstruction but it is shown that the proposed reconstruction method provides satisfying image quality for small cone angles.

Motorized high-end C-arm systems can be used for 3D imaging of high contrast objects such as bones [1]. Based on cone-beam data acquisition, careful calibration and conebeam reconstruction, volume data sets can be obtained that enable an improved insight into 3D structures of bones in order to analyse complex joint fractures or to position prostheses. New developments offer this functionality on hand-moved low-end C-arm systems too.

To investigate the feasibility of 3D-RCA for high-spatially resolved 3D reconstruction and visualization of the coronary arteries in the pig model. Two-dimensional projections of the coronary artery tree were acquired during rotation of the X-ray fluoroscopy system (INTEGRIS V3000, Philips Medical Sytems, Best, The Netherlands) around a pig. The pigs were anaesthetized and under mechanical respiratory support with heart rates between 75 and 102 bpm. Data acquisition was performed over an angular range of 180° during continuous injection of Iodine (300mg/ml) through a catheter introduced to the ostium of either the left or the right coronary artery tree. To ensure constant filling of the artery tree, the injection of contrast was started slightly before starting the scan. After the data acquisition, a gated reconstruction was performed. Volume reconstructions at isotropic spatial resolution down to 250μm were performed using a gating window of 20 or 40ms length. By moving the gating window over the cardiac a multi-phase reconstruction of the coronary arteries could be provided, yielding a temporally resolved impression of the coronary artery tree. Volumes reconstructed from data obtained during diastole provide a clear visualization of the coronary artery tree including proximal, medial and distal parts. The feasibility of 3D-RCA could be shown in the animal model. The excellent results imply that data acquired over a single rotational run can provide high quality morphological three-dimensional information of the coronary arteries in the catheter laboratory.

The reconstruction of three-dimensional (3D) objects from 2D X-ray cone-beam projections using a circular source path is most commonly done with an algorithm according to Feldkamp et al. [Feldkamp LA, Davis LC, Kress JW. Practical cone-beam algorithms. J Opt Soc Am A 1984;6:612-619]. An adaptation of this so-called Feldkamp method to cone-beam projections acquired with a C-arm system is presented here. In a phantom study, reconstruction results obtained along real source-detector trajectories of a C-arm system are compared to reconstruction results obtained from projections acquired from a full-circular trajectory and from one consisting of two full orthogonal circles, which fulfills Tuy's sufficiency condition. The straightforward application of Feldkamp's method adapted to projection data obtained with a C-arm system illustrates the 3D imaging potential of image intensifier based cone-beam computed tomography. Reconstruction results from projection data of different patients acquired with a motorized C-arm system such as vessel structures filled with contrast agent and bones are presented.

Purpose: Reconstruction of the beating heart in 3D + time in the catheter laboratory using only the available C-arm system would improve diagnosis, guidance, device sizing, and outcome control for intracardiac interventions, e.g., electrophysiology, valvular disease treatment, structural or congenital heart disease. To obtain such a reconstruction, the patient's electrocardiogram (ECG) must be recorded during the acquisition and used in the reconstruction. In this paper, the authors present a 4D reconstruction method aiming to reconstruct the heart from a single sweep 10 s acquisition. Methods: The authors introduce the 4D RecOnstructiOn using Spatial and TEmporal Regularization (short 4D ROOSTER) method, which reconstructs all cardiac phases at once, as a 3D + time volume. The algorithm alternates between a reconstruction step based on conjugate gradient and four regularization steps: enforcing positivity, averaging along time outside a motion mask that contains the heart and vessels, 3D spatial total variation minimization, and 1D temporal total variation minimization. Results: 4D ROOSTER recovers the different temporal representations of a moving Shepp and Logan phantom, and outperforms both ECG-gated simultaneous algebraic reconstruction technique and prior image constrained compressed sensing on a clinical case. It generates 3D + time reconstructions with sharp edges which can be used, for example, to estimate the patient's left ventricular ejection fraction. Conclusions: 4D ROOSTER can be applied for human cardiac C-arm CT, and potentially in other dynamic tomography areas. It can easily be adapted to other problems as regularization is decoupled from projection and back projection.

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Three-dimensional (3-D) reconstruction of the coronary arteries from a rotational X-ray angiography sequence can support diagnosis of coronary artery disease, treatment planning, and intervention guidance during catheter interventions. 3-D reconstruction enables quantitative vessel analysis, including vessel dynamics from a time-series of reconstructions. This contribution presents a method for reconstructing coronary arteries with high contrast and high level of detail. It employs an iterative reconstruction algorithm in combination with projection-based motion compensation. An efficient implementation using a graphics processing unit delivers reconstruction times close to clinically acceptable values. Reconstructions from clinical human cases, acquired on an interventional C-arm system, are presented. Excellent image quality is achieved.

The diagnostic value of medical images significantly depends on the signal-to-noise ratio (SNR). Especially in fluoroscopic tomography, the SNR is limited by the radiation dose (Computer Tomography), or by the suitable acquisition techniques (Magnetic Resonance Imaging). The purpose of this paper is to introduce a projection-based method for the motion-compensated SNR enhancement applied in Radon space. It is based on a projection-based motion estimation with subsequent motion-compensated, edge-preserving filtering of the measured projections. The effect of temporal filtering as well as spatial filtering will be presented. In contrast to the recently introduced image-based approach, this method allows a very efficient computational implementation, likely to be used in real time imaging. It will be shown that a significant increase of the SNR can be achieved without introducing additional motion artifacts or blurring in the reconstructed images. The proposed technique has the potential to be used for SNR enhancement in low-dose fluoroscopy applications in CT as well as for SNR improvements in MR fluoroscopy using projection reconstruction based techniques.