Beth Goddu

Recurrence of Atrial Fibrillation Correlates With the Extent of Post-Procedural Late Gadolinium Enhancement : A Pilot Study

OBJECTIVES We sought to evaluate radiofrequency (RF) ablation lesions in atrial fibrillation (AF) patients using cardiac magnetic resonance (CMR), and to correlate the ablation patterns with treatment success. BACKGROUND RF ablation procedures for treatment of AF result in localized scar that is detected by late gadolinium enhancement (LGE) CMR. We hypothesized that the extent of scar in the left atrium and pulmonary veins (PV) would correlate with moderate-term procedural success. METHODS Thirty-five patients with AF, undergoing their first RF ablation procedure, were studied. The RF ablation procedure was performed to achieve bidirectional conduction block around each PV ostium. AF recurrence was documented using a 7-day event monitor at multiple intervals during the first year. High spatial resolution 3-dimensional LGE CMR was performed 46 +/- 28 days after RF ablation. The extent of scarring around the ostia of each PV was quantitatively (volume of scar) and qualitatively (1: minimal, 3: extensive and circumferential) assessed. RESULTS Thirteen (37%) patients had recurrent AF during the 6.7 +/- 3.6-month observation period. Paroxysmal AF was a strong predictor of nonrecurrent AF (15% with recurrence vs. 68% without, p = 0.002). Qualitatively, patients without recurrence had more completely circumferentially scarred veins (55% vs. 35% of veins, p = NS). Patients without recurrence more frequently had scar in the inferior portion of the right inferior pulmonary vein (RIPV) (82% vs. 31%, p = 0.025, Bonferroni corrected). The volume of scar in the RIPV was quantitatively greater in patients without AF recurrence (p < or = 0.05) and was a univariate predictor of recurrence using Cox regression (p = 0.049, Bonferroni corrected). CONCLUSIONS Among patients undergoing PV isolation, AF recurrence during the first year is associated with a lesser degree of PV and left atrial scarring on 3-dimensional LGE CMR. This finding was significant for RIPV scar and may have implications for the procedural technique used in PV isolation.

Cardiovascular magnetic resonance characterization of mitral valve prolapse.

OBJECTIVES This study sought to develop cardiovascular magnetic resonance (CMR) diagnostic criteria for mitral valve prolapse (MVP) using echocardiography as the gold standard and to characterize MVP using cine CMR and late gadolinium enhancement (LGE)-CMR. BACKGROUND Mitral valve prolapse is a common valvular heart disease with significant complications. Cardiovascular magnetic resonance is a valuable imaging tool for assessing ventricular function, quantifying regurgitant lesions, and identifying fibrosis, but its potential role in evaluating MVP has not been defined. METHODS To develop CMR diagnostic criteria for MVP, characterize mitral valve morphology, we analyzed transthoracic echocardiography and cine CMR images from 25 MVP patients and 25 control subjects. Leaflet thickness, length, mitral annular diameters, and prolapsed distance were measured. Two- and three-dimensional LGE-CMR images were obtained in 16 MVP and 10 control patients to identify myocardial regions of fibrosis in MVP. RESULTS We found that a 2-mm threshold for leaflet excursion into the left atrium in the left ventricular outflow tract long-axis view yielded 100% sensitivity and 100% specificity for CMR using transthoracic echocardiography as the clinical gold standard. Compared with control subjects, CMR identified MVP patients as having thicker (3.2 +/- 0.1 mm vs. 2.3 +/- 0.1 mm) and longer (10.5 +/- 0.5 mm/m(2) vs. 7.1 +/- 0.3 mm/m(2)) indexed posterior leaflets and larger indexed mitral annular diameters (27.8 +/- 0.7 mm/m(2) vs. 21.5 +/- 0.5 mm/m(2) for long axis and 22.9 +/-0.7 mm/m(2) vs. 17.8 +/- 0.6 mm/m(2) for short axis). In addition, we identified focal regions of LGE in the papillary muscles suggestive of fibrosis in 10 (63%) of 16 MVP patients and in 0 of 10 control subjects. Papillary muscle LGE was associated with the presence of complex ventricular arrhythmias in MVP patients. CONCLUSIONS Cardiovascular magnetic resonance image can identify MVP by the same echocardiographic criteria and can identify myocardial fibrosis involving the papillary muscle in MVP patients. Hyperenhancement of papillary muscles on LGE is often present in a subgroup of patients with complex ventricular arrhythmias.

Combined saturation/inversion recovery sequences for improved evaluation of scar and diffuse fibrosis in patients with arrhythmia or heart rate variability.

To develop arrhythmia‐insensitive inversion recovery sequences for improved visualization of myocardial scar and quantification of diffuse fibrosis.

Low-dimensional-structure self-learning and thresholding: regularization beyond compressed sensing for MRI reconstruction.

An improved image reconstruction method from undersampled k‐space data, low‐dimensional‐structure self‐learning and thresholding (LOST), which utilizes the structure from the underlying image is presented. A low‐resolution image from the fully sampled k‐space center is reconstructed to learn image patches of similar anatomical characteristics. These patches are arranged into “similarity clusters,” which are subsequently processed for dealiasing and artifact removal, using underlying low‐dimensional properties. The efficacy of the proposed method in scan time reduction was assessed in a pilot coronary MRI study. Initially, in a retrospective study on 10 healthy adult subjects, we evaluated retrospective undersampling and reconstruction using LOST, wavelet‐based l1‐norm minimization, and total variation compressed sensing. Quantitative measures of vessel sharpness and mean square error, and qualitative image scores were used to compare reconstruction for rates of 2, 3, and 4. Subsequently, in a prospective study, coronary MRI data were acquired using these rates, and LOST‐reconstructed images were compared with an accelerated data acquisition using uniform undersampling and sensitivity encoding reconstruction. Subjective image quality and sharpness data indicate that LOST outperforms the alternative techniques for all rates. The prospective LOST yields images with superior quality compared with sensitivity encoding or l1‐minimization compressed sensing. The proposed LOST technique greatly improves image reconstruction for accelerated coronary MRI acquisitions. Magn Reson Med, 2011.

Coronary magnetic resonance vein imaging: Imaging contrast, sequence, and timing

Recently, there has been increased interest in imaging the coronary vein anatomy to guide interventional cardiovascular procedures such as cardiac resynchronization therapy (CRT), a device therapy for congestive heart failure (CHF). With CRT the lateral wall of the left ventricle is electrically paced using a transvenous coronary sinus lead or surgically placed epicardial lead. Proper transvenous lead placement is facilitated by the knowledge of the coronary vein anatomy. Cardiovascular MR (CMR) has the potential to image the coronary veins. In this study we propose and test CMR techniques and protocols for imaging the coronary venous anatomy. Three aspects of design of imaging sequence were studied: magnetization preparation schemes (T2 preparation and magnetization transfer), imaging sequences (gradient‐echo (GRE) and steady‐state free precession (SSFP)), and imaging time during the cardiac cycle. Numerical and in vivo studies both in healthy and CHF subjects were performed to optimize and demonstrate the utility of CMR for coronary vein imaging. Magnetization transfer was superior to T2 preparation for contrast enhancement. Both GRE and SSFP were viable imaging sequences, although GRE provided more robust results with better contrast. Imaging during the end‐systolic quiescent period was preferable as it coincided with the maximum size of the coronary veins. Magn Reson Med, 2007.

Left ventricular Infarct Size, Peri-Infarct Zone and Papillary Scar Measurements: A Comparison of High Resolution 3D and Conventional 2D Late Gadolinium Enhancement Cardiac MR

To compare higher spatial resolution 3D late gadolinium enhancement (LGE) cardiovascular magnetic resonance (Cardiac MR) with 2D LGE in patients with prior myocardial infarction.

Respiratory bellows revisited for motion compensation: Preliminary experience for cardiovascular MR

For many cardiac MR applications, respiratory bellows gating is attractive because it is widely available and not disruptive to or dependent on imaging. However, its use is uncommon in cardiac MR, because its accuracy has not been fully studied. Here, in 10 healthy subjects, the bellows and respiratory navigator (NAV) with the displacement of the diaphragm and heart were simultaneously monitored, during single‐shot imaging. Furthermore, bellows‐gated and NAV‐gated coronary MRI were compared using a retrospective reconstruction at identical efficiency. There was a strong linear relationship for both the NAV and the abdominal bellows with the diaphragm (R = 0.90 ± 0.05 bellows, R = 0.98 ± 0.01 NAV, P < 0.001) and the heart (R = 0.89 ± 0.06 bellows, R = 0.96 ± 0.02 NAV, P = 0.004); thoracic bellows correlated less strongly. The image quality of bellows‐gated coronary MRI was similar to NAV‐gated and superior to no‐gating (P < 0.01). In conclusion, bellows provides a respiratory monitor which is highly correlated with the NAV and suitable for respiratory compensation in selected cardiac MR applications. Magn Reson Med, 2010.

Accelerated aortic flow assessment with compressed sensing with and without use of the sparsity of the complex difference image

Phase contrast (PC) cardiac MR is widely used for the clinical assessment of blood flow in cardiovascular disease. One of the challenges of PC cardiac MR is the long scan time which limits both spatial and temporal resolution. Compressed sensing reconstruction with accelerated PC acquisitions is a promising technique to increase the scan efficiency. In this study, we sought to use the sparsity of the complex difference of the two flow‐encoded images as an additional constraint term to improve the compressed sensing reconstruction of the corresponding accelerated PC data acquisition. Using retrospectively under‐sampled data, the proposed reconstruction technique was optimized and validated in vivo on 15 healthy subjects. Then, prospectively under‐sampled data was acquired on 11 healthy subjects and reconstructed with the proposed technique. The results show that there is good agreement between the cardiac output measurements from the fully sampled data and the proposed compressed sensing reconstruction method using complex difference sparsity up to acceleration rate 5. In conclusion, we have developed and evaluated an improved reconstruction technique for accelerated PC cardiac MR that uses the sparsity of the complex difference of the two flow‐encoded images. Magn Reson Med 70:851–858, 2013.

Accelerated contrast-enhanced whole-heart coronary MRI using low-dimensional-structure self-learning and thresholding

We sought to evaluate the efficacy of prospective random undersampling and low‐dimensional‐structure self‐learning and thresholding reconstruction for highly accelerated contrast‐enhanced whole‐heart coronary MRI. A prospective random undersampling scheme was implemented using phase ordering to minimize artifacts due to gradient switching and was compared to a randomly undersampled acquisition with no profile ordering. This profile‐ordering technique was then used to acquire contrast‐enhanced whole‐heart coronary MRI in 10 healthy subjects with 4‐fold acceleration. Reconstructed images and the acquired zero‐filled images were compared for depicted vessel length, vessel sharpness, and subjective image quality on a scale of 1 (poor) to 4 (excellent). In a pilot study, contrast‐enhanced whole‐heart coronary MRI was also acquired in four patients with suspected coronary artery disease with 3‐fold acceleration. The undersampled images were reconstructed using low‐dimensional‐structure self‐learning and thresholding, which showed significant improvement over the zero‐filled images in both objective and subjective measures, with an overall score of 3.6 ± 0.5. Reconstructed images in patients were all diagnostic. Low‐dimensional‐structure self‐learning and thresholding reconstruction allows contrast‐enhanced whole‐heart coronary MRI with acceleration as high as 4‐fold using clinically available five‐channel phased‐array coil. Magn Reson Med, 2012.

Compressed-sensing motion compensation (CosMo): A joint prospective-retrospective respiratory navigator for coronary MRI

Prospective right hemidiaphragm navigator (NAV) is commonly used in free‐breathing coronary MRI. The NAV results in an increase in acquisition time to allow for resampling of the motion‐corrupted k‐space data. In this study, we are presenting a joint prospective–retrospective NAV motion compensation algorithm called compressed‐sensing motion compensation (CosMo). The inner k‐space region is acquired using a prospective NAV; for the outer k‐space, a NAV is only used to reject the motion‐corrupted data without reacquiring them. Subsequently, those unfilled k‐space lines are retrospectively estimated using compressed sensing reconstruction. We imaged right coronary artery in nine healthy adult subjects. An undersampling probability map and sidelobe‐to‐peak ratio were calculated to study the pattern of undersampling, generated by NAV. Right coronary artery images were then retrospectively reconstructed using compressed‐sensing motion compensation for gating windows between 3 and 10 mm and compared with the ones fully acquired within the gating windows. Qualitative imaging score and quantitative vessel sharpness were calculated for each reconstruction. The probability map and sidelobe‐to‐peak ratio show that the NAV generates a random undersampling k‐space pattern. There were no statistically significant differences between the vessel sharpness and subjective score of the two reconstructions. Compressed‐sensing motion compensation could be an alternative motion compensation technique for free‐breathing coronary MRI that can be used to reduce scan time. Magn Reson Med, 2011.