Myocardial perfusion reserve assessed by T2-prepared steady-state free precession blood oxygen level-dependent magnetic resonance imaging in comparison to fractional flow reserve.

BACKGROUND: Blood oxygen level-dependent (BOLD) cardiac magnetic resonance imaging (CMR) has been shown to be able to detect myocardial perfusion differences. However, validation of BOLD CMR against fractional flow reserve (FFR) is lacking. The aim of our study was to analyze the potential diagnostic accuracy of BOLD CMR in comparison to invasively measured FFR, which served as gold standard for a hemodynamic significant coronary lesion. METHODS AND RESULTS: BOLD image was performed at rest and during adenosine infusion in a 1.5-T CMR scanner. Thirty-six patients were analyzed for relative BOLD signal intensity increase according to the 16-segment model. Invasive FFR measurements were performed in the 3 major coronary arteries during adenosine infusion in all patients. An FFR≤0.8 was regarded to indicate a significant coronary lesion. Relative BOLD signal intensity increase was significantly lower in myocardial segments supplied by coronary arteries with an FFR≤0.8 compared with segments with an FFR>0.8 (1.1±0.2 versus 1.5±0.2; P<0.0001). Sensitivity and specificity yielded 88.2% and 89.5%, respectively. CONCLUSIONS: CMR BOLD imaging reliably detects hemodynamic significant coronary artery disease and is, thus, an alternative to contrast-enhanced perfusion studies.

Absence of left ventricular apical rocking and atrial-ventricular dyssynchrony predicts non-response to cardiac resynchronization therapy.

AIMS: Current imaging techniques attempt to identify responders to cardiac resynchronization therapy (CRT). However, because CRT response may depend upon several factors, it may be clinically more useful to identify patients for whom CRT would not be beneficial even under optimal conditions. We aimed to determine the negative predictive value of a composite echocardiographic index evaluating atrial-ventricular dyssynchrony (AV-DYS) and intraventricular dyssynchrony. METHODS AND RESULTS: Subjects with standard indications for CRT underwent echo before and during the month following device implantation. AV-DYS was defined as a percentage of left ventricular (LV) filling time over the cardiac cycle. AV-DYS, which produces a characteristic rocking of the LV apex, was quantified as the percentage of the cardiac cycle over which tissue Doppler-derived displacement curves of the septal and lateral walls showed discordance. CRT responder status was determined based on the early haemodynamic response to CRT (intra-individual improvement >25% in the Doppler-derived LV dP/dt). Among 40 patients, optimal cut-points predicting CRT response were 31% for LV apical rocking and 39% for AV-DYS. The presence of either apical rocking >31% or AV-DYS ≤ 39% had a sensitivity of 95%, specificity of 80%, positive predictive value of 83%, and a negative predictive value of 94% for CRT response. CONCLUSION: After pre-selection of candidates for CRT by QRS duration, application of a simple composite echocardiographic index may exclude patients who would be non-responders to CRT and thus improve the global rate of therapy success.

Acceleration of tissue phase mapping with sensitivity encoding at 3T.

BACKGROUND: The objective of this study was to investigate the impact of sensitivity encoding on the quantitative assessment of cardiac motion in black blood cine tissue phase mapping (TPM) sequences. Up to now whole volume coverage of the heart is still limited by the long acquisition times. Therefore, a significant increase in imaging speed without deterioration of quantitative motion information is indispensable. METHODS: 20 volunteers were enrolled in this study. Each volunteer underwent myocardial short-axis TPM scans with different SENSE acceleration factors. The influence of SENSE acceleration on the measured motion curves was investigated. RESULTS: It is demonstrated that all TPM sequences with SENSE acceleration have only minimum influence on the motion curves. Even with a SENSE factor of four, the decrease in the amplitude of the motion curve was less than 3%. No significant difference was observed for the global correlation coefficient and deviation between the motion curves obtained by the reproducibility and the SENSE accelerated measurements. CONCLUSIONS: It is feasible to accelerate myocardial TPM measurements with SENSE factors up to 4 without losing substantial information of the motion pattern.

SAR reduced black-blood cine TPM for increased temporal resolution at 3T.

OBJECT: The objective was to improve the temporal resolution in black-blood CINE tissue phase mapping sequences at high field MR systems. The temporal resolution is limited due to SAR constraints causing idle times into the sequence. The aim was to avoid these idle times and therefore providing an increased number of heart phases. MATERIALS AND METHODS: Thirteen volunteers were enrolled in this study. Each volunteer underwent different myocardial short-axis scans comprising scans with application of both presaturation pulses, with alternating application of presaturation pulses and with an attenuation of the excitation angle. The last two approaches enable a SAR reduction or increased temporal resolution. The contrast to noise ratio (CNR) between myocardium and blood and the influence on the measured tissue motion were investigated. RESULTS: High CNR between myocardium and blood could be obtained with the application of alternating presaturation-pulses. Reduction of the flip angle of the presaturation-pulses provided reduced CNR relative to both the original and the alternated presaturation-pulses approach. More details of the myocardial motion were observed with increased temporal resolution. CONCLUSION: It is feasible to increase the temporal resolution at high field strength by reducing the SAR with either alternating presaturation-pulses or decreased flip angle of these pulses.

Acceleration of tissue phase mapping by k-t BLAST: a detailed analysis of the influence of k-t-BLAST for the quantification of myocardial motion at 3T.

BACKGROUND: The assessment of myocardial motion with tissue phase mapping (TPM) provides high spatiotemporal resolution and quantitative motion information in three directions. Today, whole volume coverage of the heart by TPM encoding at high spatial and temporal resolution is limited by long data acquisition times. Therefore, a significant increase in imaging speed without deterioration of the quantitative motion information is required. For this purpose, the k-t BLAST acceleration technique was combined with TPM black-blood functional imaging of the heart. Different k-t factors were evaluated with respect to their impact on the quantitative assessment of cardiac motion. RESULTS: It is demonstrated that a k-t BLAST factor of two can be used with a marginal, but statistically significant deterioration of the quantitative motion data. Further increasing the k-t acceleration causes substantial alteration of the peak velocities and the motion pattern, but the temporal behavior of the contraction is well maintained up to an acceleration factor of six. CONCLUSIONS: The application of k-t BLAST for the acceleration of TPM appears feasible. A reduction of the acquisition time of almost 45% could be achieved without substantial loss of quantitative motion information.

Assessment of the coronary venous system in heart failure patients by blood pool agent enhanced whole-heart MRI.

OBJECTIVE: To investigate the feasibility of MRI for non-invasive assessment of the coronary sinus (CS) and the number and course of its major tributaries in heart failure patients. METHODS: Fourteen non-ischaemic heart failure patients scheduled for cardiac resynchronisation therapy (CRT) underwent additional whole-heart coronary venography. MRI was performed 1 day before device implantation. The visibility, location and dimensions of the CS and its major tributaries were assessed and the number of potential implantation sites identified. The MRI results were validated by X-ray venography conventionally acquired during the device implantation procedure. RESULTS: The right atrium (RA), CS and mid-cardiac vein (MCV) could be visualised in all patients. 36% of the identified candidate branches were located posterolaterally, 48% laterally and 16% anterolaterally. The average diameter of the CS was quantified as 9.8 mm, the posterior interventricular vein (PIV) 4.6 mm, posterolateral segments 3.3 mm, lateral 2.9 mm and anterolateral 2.9 mm. Concordance with X-ray in terms of number and location of candidate branches was given in most cases. CONCLUSION: Contrast-enhanced MRI venography appears feasible for non-invasive pre-interventional assessment of the course of the CS and its major tributaries.

Blood oxygen level-dependent magnetic resonance imaging using T2-prepared steady-state free-precession imaging in comparison to contrast-enhanced myocardial perfusion imaging.

BACKGROUND: Diagnosis of inducible myocardial ischemia is important for deciding further diagnosis and therapy in coronary artery disease (CAD). Blood oxygen level-dependent (BOLD) cardiac magnetic resonance imaging (CMR) is a potential method to evaluate myocardial perfusion reserve alternatively to first-pass perfusion using contrast agents. METHODS AND RESULTS: We imaged 46 patients with suspected CAD on a 1.5 T whole-body CMR scanner using a T2-prepared steady-state free-precession (SSFP) BOLD-sensitive sequence and a SSFP-based first-pass sequence. All patients were scanned during rest and after 3 min of adenosine infusion (140 µg/kg/min). For myocardial first-pass visualization 0.1 mmol/kg Gadolinium-based contrast agent was used. In 90 myocardial segments a first-pass perfusion deficit could be seen. Relative BOLD signal increase was significantly lower in patients with perfusion deficits compared to patients without perfusion deficits (p < 0.0001). Patients with non-transmural and with transmural first-pass perfusion deficit also differed significantly for BOLD signal increase (p < 0.0001). ROC analysis showed an area under the curve of 0.83 for the T2-prepared SSFP sequence regarding detection of inducible perfusion deficit. CONCLUSIONS: T2-prepared BOLD imaging allows for visualization of myocardial perfusion reserve in a clinical setting without additional use of contrast agents.

Automatic segmentation of rotational x-ray images for anatomic intra-procedural surface generation in atrial fibrillation ablation procedures.

Since the introduction of 3-D rotational X-ray imaging, protocols for 3-D rotational coronary artery imaging have become widely available in routine clinical practice. Intra-procedural cardiac imaging in a computed tomography (CT)-like fashion has been particularly compelling due to the reduction of clinical overhead and ability to characterize anatomy at the time of intervention. We previously introduced a clinically feasible approach for imaging the left atrium and pulmonary veins (LAPVs) with short contrast bolus injections and scan times of approximately 4 -10 s. The resulting data have sufficient image quality for intra-procedural use during electro-anatomic mapping (EAM) and interventional guidance in atrial fibrillation (AF) ablation procedures. In this paper, we present a novel technique to intra-procedural surface generation which integrates fully-automated segmentation of the LAPVs for guidance in AF ablation interventions. Contrast-enhanced rotational X-ray angiography (3-D RA) acquisitions in combination with filtered-back-projection-based reconstruction allows for volumetric interrogation of LAPV anatomy in near-real-time. An automatic model-based segmentation algorithm allows for fast and accurate LAPV mesh generation despite the challenges posed by image quality; relative to pre-procedural cardiac CT/MR, 3-D RA images suffer from more artifacts and reduced signal-to-noise. We validate our integrated method by comparing 1) automatic and manual segmentations of intra-procedural 3-D RA data, 2) automatic segmentations of intra-procedural 3-D RA and pre-procedural CT/MR data, and 3) intra-procedural EAM point cloud data with automatic segmentations of 3-D RA and CT/MR data. Our validation results for automatically segmented intra-procedural 3-D RA data show average segmentation errors of 1) approximately 1.3 mm compared with manual 3-D RA segmentations 2) approximately 2.3 mm compared with automatic segmentation of pre-procedural CT/MR data and 3) approximately 2.1 mm compared with registered intra-procedural EAM point clouds. The overall experiments indicate that LAPV surfaces can be automatically segmented intra-procedurally from 3-D RA data with comparable quality relative to meshes derived from pre-procedural CT/MR.

Automatic intra-operative generation of geometric left atrium/pulmonary vein models from rotational X-ray angiography.

Pre-procedural imaging with cardiac CT or MR has become popular for guiding complex electrophysiology procedures such as those used for atrial fibrillation ablation therapy. Electroanatomical mapping and ablation within the left atrium and pulmonary veins (LAPV) is facilitated using such data, however the pre-procedural anatomy can be quite different from that at the time of intervention. Recently, a method for intra-procedural LAPV imaging has been developed based on contrast-enhanced 3-D rotational X-ray angiography (3-D RA). These intraprocedural data now create a compelling need for rapid and automated extraction of the LAPV geometry for catheter guidance. We present a new approach to automatic intra-procedural generation of LAPV surfaces from 3-D RA volumes. Using model-based segmentation, our technique is robust to imaging noise and artifacts typical of 3-D RA imaging, strongly minimizes the user interaction time required for segmentation, and eliminates inter-subject variability. Our findings in 33 patients indicate that intra-procedural LAPV surface models accurately represent the anatomy at the time of intervention and are comparable to pre-procedural models derived from CTA or MRA.

Estimation of radial strain and rotation using a new algorithm based on speckle tracking.

BACKGROUND: The aim of this study was to test the ability of a new algorithm to accurately measure point-to-point Lagrangian strain (LS) and local rotation (ROT). Change in distance between 2 separate regions of interest (ROIs) can theoretically be computed with speckle tracking (SpT) and used to calculate LS in any tissue location with angle independence and high spatial resolution. Similarly, tracking an ROI relative to a fixed point should provide an estimate of ROT. METHODS: Two dynamic phantoms (60 beats/min) were scanned in short axis at frame rates of 30, 60, and 90 Hz. To estimate LS, 2 ROIs were positioned immediately beneath the inner and outer borders of the superior wall of the first phantom and tracked using SpT. LS derived from SpT (SpT-LS) was compared with LS measured by sonomicrometers placed on the inner and outer walls of the phantom (SN-LS). To estimate ROT, the rotational vectors around the centroid of a second phantom were calculated for 3 epicardial bead targets imaged with gated computed tomography (CT) and compared with measurements derived from SpT. RESULTS: There was a significant correlation between SpT-LS and SN-LS at 30 Hz (R(2) = 0.99; P < .0001), 60 Hz (R(2) = 0.98; P < .0001), and 90 Hz (R(2) = 0.99; P < .0001). There was also a significant correlation between ROT derived from SpT and ROT derived from CT: R(2) = 0.97 (P < .0001) at 30 Hz, R(2) = 0.95 (P < .0001) at 60 Hz, and R(2) = 0.98 (P < .0001) at 90 Hz. CONCLUSIONS: Point-to-point SpT permits the determination of LS between 2 distinct tissue regions as well as ROT measurement of specific tissue regions without the need for border detection.

Intraprocedural volume imaging of the left atrium and pulmonary veins with rotational X-ray angiography: implications for catheter ablation of atrial fibrillation.

INTRODUCTION: The use of preprocedural CT or MR imaging to generate patient-specific cardiac anatomy greatly facilitates catheter ablation of the left atrium and pulmonary veins (LA-PVs) to treat atrial fibrillation (AF). This report details the accuracy and utility of an intraprocedural means to generate 3-D volumetric renderings of the LA-PV anatomy: contrast-enhanced rotational X-ray angiography (3DRA). METHODS AND RESULTS: Preprocedural CT or MR imaging and intraprocedural rotational angiography was performed in 42 patients undergoing AF ablation procedures. Initially, pulmonary artery (PA) bolus-chase contrast injections were performed (20 mL, 20 mL/s) to establish pulmonary transit time and cardiac isocentering. Depending on cardiac size, either a single PA injection (80-100 mL, 20 mL/s) or two separate dedicated left/right PA branch injections were performed (60 mL each, 20 mL/s). For the latter, the two volumes of the left/right portions of the LA-PVs were registered and fused. LA-PV 3DRA images were assessed qualitatively and quantitatively in comparison with CT/MR images. The majority of the 3DRA acquisitions (71%) were deemed at least "useful" in delineating the LA-PV anatomy. The LA appendage was delineated in 57% of the cases. A blinded quantitative comparison of PV ostial diameters resulted in an absolute difference of only 2.7 +/- 2.3 mm, 2.2 +/- 1.8 mm, 2.4 +/- 2.2 mm, and 2.2 +/- 2.3 mm for the left-superior, left-inferior, right-superior, and right-inferior PVs, respectively. The feasibility for registering the 3DRA image with real-time electroanatomical mapping was also demonstrated. CONCLUSION: Intraprocedural contrast-enhanced rotational angiography provides volumetric 3-D images of the LA-PVs of comparable diagnostic value to dedicated preprocedural CT/MR imaging.

Usefulness of high-speed rotational coronary venous angiography during cardiac resynchronization therapy.

Standard coronary venous angiography (SCVA) provides a static, fixed projection of the coronary venous (CV) tree. High-speed rotational coronary venous angiography (RCVA) is a novel method of mapping CV anatomy using dynamic, multiangle visualization. The purpose of this study was to assess the value of RCVA during cardiac resynchronization therapy. Digitally acquired rotational CV angiograms from 49 patients (mean age 69 +/- 11 years) who underwent left ventricular lead implantation were analyzed. RCVA, which uses rapid isocentric rotation over a 110 degrees arc, acquiring 120 frames/angiogram, was compared with SCVA, defined as 2 static orthogonal views: right anterior oblique 45 degrees and left anterior oblique 45 degrees . RCVA demonstrated that the posterior vein-to-coronary sinus (CS) angle and the left marginal vein-to-CS angle were misclassified in 5 and 11 patients, respectively, using SCVA. RCVA identified a greater number of second-order tributaries with diameters >1.5 mm than SCVA. The CV branch selected for lead placement was initially identified in 100% of patients using RCVA but in only 74% of patients using SCVA. RCVA showed that the best angiographic view for visualizing the CS and its tributaries differed significantly among different areas of the CV tree and among patients. The area of the CV tree that showed less variability was the CS ostium, which had a fairly constant relation with the spine in shallow right anterior oblique and left anterior oblique projections. In conclusion, RCVA provided a more precise map of CV anatomy and the spatial relation of venous branches. It allowed the identification of fluoroscopic views that could facilitate cannulation of the CS. The final x-ray view displaying the appropriate CV branch for left ventricular lead implantation was often different from the conventional left anterior oblique and right anterior oblique views. RCVA identified the target branch for lead implantation more often than SCVA.

Integrating functional and anatomical information to facilitate cardiac resynchronization therapy.

Multiple imaging modalities are required in patients receiving cardiac resynchronization therapy. We have developed a strategy to integrate echocardiographic and angiographic information to facilitate left ventricle (LV) lead position. Full three-dimensional LV-volumes (3DLVV) and dyssynchrony maps were acquired before and after resynchronization. At the time of device implantation, 3D-rotational coronary venous angiography was performed. 3D-models of the veins were then integrated with the pre- and post-3DLVV. In the case displayed, prior to implantation, the lateral wall was delayed compared to the septum. The LV lead was positioned into the vein over the most delayed region, resulting in improved LV synchrony.

Automatic determination of minimal cardiac motion phases for computed tomography imaging: initial experience.

Low motion phases for cardiac computed tomography reconstructions are currently detected manually in a user-dependent selection process which is often time consuming and suboptimal. The concept of motion maps was recently introduced to achieve automatic phase selection. This pilot study compared the accuracy of motion-map phase selection to that with manual iterative selection. The study included 20 patients, consisting of one group with low and one with high heart rate. The technique automatically derives a motion strength function between multiple low-resolution reconstructions through the cardiac cycle, with periods of lowest difference between neighboring phases indicating minimal cardiac motion. A high level of agreement was found for phase selection achieved with the motion map approach compared with the manual iterative selection process. The motion maps allowed automated quiescent phase detection of the cardiac cycle in 85% of cases, with best results at low heart rates and for the left coronary artery. They can also provide additional information such as the presence of breathing artifacts. Motion maps show promise as a rapid off-line tool to automatically detect quiescent cardiac phases in a variety of patients.

Intra-operative volume imaging of the left atrium and pulmonary veins with rotational X-ray angiography.

Complex electrophysiology (EP) procedures, such as catheter-based ablation in the left atrium and pulmonary veins (LAPV) for treatment of atrial fibrillation, require knowledge of heart chamber anatomy. Electroanatomical mapping (EAM) is typically used to define cardiac structures by combining electromagnetic spatial catheter localization with surface models which interpolate the anatomy between EAM point locations in 3D. Recently, the incorporation of pre-operative volumetric CT or MR data sets has allowed for more detailed maps of LAPV anatomy to be used intra-operatively. Preoperative data sets are however a rough guide since they can be acquired several days to weeks prior to EP intervention. Due to positional and physiological changes, the intra-operative cardiac anatomy can be different from that depicted in the pre-operative data. We present a novel application of contrast-enhanced rotational X-ray imaging for CT-like reconstruction of 3D LAPV anatomy during the intervention itself. We perform two selective contrast-enhanced rotational acquisitions and reconstruct CT-like volumes with 3D filtered back projection. Two volumes depicting the left and right portions of the LAPV are registered and fused. The combined data sets are then visualized and segmented intra-procedurally to provide anatomical data and surface models for intervention guidance. Our results from animal and human experiments indicate that the anatomical information from intra-operative CT-like reconstructions compares favorably with pre-acquired CT data and can be of sufficient quality for intra-operative guidance.

Noninvasive coronary angiography with 16-detector row CT: effect of heart rate.

PURPOSE: 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. MATERIALS AND METHODS: 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. RESULTS: 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 (diameter > or = 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. CONCLUSION: 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.

Artifact analysis and reconstruction improvement in helical cardiac cone beam CT.

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.