Lan Ge

3D Radial Sampling and 3D Affine Transform-based Respiratory Motion Correction Technique for Free-breathing Whole-Heart Coronary MRA with 100% Imaging Efficiency

The navigator gating and slice tracking approach currently used for respiratory motion compensation during free‐breathing coronary magnetic resonance angiography (MRA) has low imaging efficiency (typically 30–50%), resulting in long imaging times. In this work, a novel respiratory motion correction technique with 100% scan efficiency was developed for free‐breathing whole‐heart coronary MRA. The navigator signal was used as a reference respiratory signal to segment the data into six bins. 3D projection reconstruction k‐space sampling was used for data acquisition and enabled reconstruction of low resolution images within each respiratory bin. The motion between bins was estimated by image registration with a 3D affine transform. The data from the different respiratory bins was retrospectively combined after motion correction to produce the final image. The proposed method was compared with a traditional navigator gating approach in nine healthy subjects. The proposed technique acquired whole‐heart coronary MRA with 1.0 mm3 isotropic spatial resolution in a scan time of 6.8 ± 0.9 min, compared with 16.2 ± 2.8 min for the navigator gating approach. The image quality scores, and length, diameter and sharpness of the right coronary artery (RCA), left anterior descending coronary artery (LAD), and left circumflex coronary artery (LCX) were similar for both approaches (P > 0.05 for all), but the proposed technique reduced scan time by a factor of 2.5. Magn Reson Med, 2011.

Myocardial perfusion MRI with sliding-window conjugate-gradient HYPR

First‐pass perfusion MRI is a promising technique for detecting ischemic heart disease. However, the diagnostic value of the method is limited by the low spatial coverage, resolution, signal‐to‐noise ratio (SNR), and cardiac motion‐related image artifacts. In this study we investigated the feasibility of using a method that combines sliding window and CG‐HYPR methods (SW‐CG‐HYPR) to reduce the acquisition window for each slice while maintaining the temporal resolution of one frame per heartbeat in myocardial perfusion MRI. This method allows an increased number of slices, reduced motion artifacts, and preserves the relatively high SNR and spatial resolution of the “composite images.” Results from eight volunteers demonstrate the feasibility of SW‐CG‐HYPR for accelerated myocardial perfusion imaging with accurate signal intensity changes of left ventricle blood pool and myocardium. Using this method the acquisition time per cardiac cycle was reduced by a factor of 4 and the number of slices was increased from 3 to 8 as compared to the conventional technique. The SNR of the myocardium at peak enhancement with SW‐CG‐HYPR (13.83 ± 2.60) was significantly higher (P < 0.05) than the conventional turbo‐FLASH protocol (8.40 ± 1.62). Also, the spatial resolution of the myocardial perfection images was significantly improved. SW‐CG‐HYPR is a promising technique for myocardial perfusion MRI. Magn Reson Med, 2009.

Myocardial Perfusion Magnetic Resonance Imaging Using Sliding-Window Conjugate-Gradient Highly Constrained Back-Projection Reconstruction for Detection of Coronary Artery Disease

Myocardial perfusion magnetic resonance imaging (MRI) with sliding-window conjugate-gradient highly constrained back-projection reconstruction (SW-CG-HYPR) allows whole left ventricular coverage, improved temporal and spatial resolution and signal/noise ratio, and reduced cardiac motion-related image artifacts. The accuracy of this technique for detecting coronary artery disease (CAD) has not been determined in a large number of patients. We prospectively evaluated the diagnostic performance of myocardial perfusion MRI with SW-CG-HYPR in patients with suspected CAD. A total of 50 consecutive patients who were scheduled for coronary angiography with suspected CAD underwent myocardial perfusion MRI with SW-CG-HYPR at 3.0 T. The perfusion defects were interpreted qualitatively by 2 blinded observers and were correlated with x-ray angiographic stenoses ≥50%. The prevalence of CAD was 56%. In the per-patient analysis, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of SW-CG-HYPR was 96% (95% confidence interval 82% to 100%), 82% (95% confidence interval 60% to 95%), 87% (95% confidence interval 70% to 96%), 95% (95% confidence interval 74% to100%), and 90% (95% confidence interval 82% to 98%), respectively. In the per-vessel analysis, the corresponding values were 98% (95% confidence interval 91% to 100%), 89% (95% confidence interval 80% to 94%), 86% (95% confidence interval 76% to 93%), 99% (95% confidence interval 93% to 100%), and 93% (95% confidence interval 89% to 97%), respectively. In conclusion, myocardial perfusion MRI using SW-CG-HYPR allows whole left ventricular coverage and high resolution and has high diagnostic accuracy in patients with suspected CAD.

Free‐breathing myocardial perfusion MRI using SW‐CG‐HYPR and motion correction

First‐pass perfusion MRI is a promising technique to detect ischemic heart disease. Sliding window (SW) conjugate‐gradient (CG) highly constrained back‐projection reconstruction (HYPR) (SW‐CG‐HYPR) has been proposed to increase spatial coverage, spatial resolution, and SNR. However, this method is sensitive to respiratory motion and thus requires breath‐hold. This work presents a non‐model‐based motion correction method combined with SW‐CG‐HYPR to perform free‐breathing myocardial MR imaging. Simulation studies were first performed to show the effectiveness of the proposed motion correction method and its independence from the pattern of the respiratory motion. After that, in vivo studies were performed in six healthy volunteers. From all of the volunteer studies, the image quality score of free breathing perfusion images with motion correction (3.11 ± 0.34) is improved compared with that of images without motion correction (2.27 ± 0.32), and is comparable with that of successful breath‐hold images (3.12 ± 0.38). This result was further validated by a quantitative sharpness analysis. The left ventricle and myocardium signal changes in motion corrected free‐breathing perfusion images were closely correlated to those observed in breath‐hold images. The correlation coefficient is 0.9764 for myocardial signals. Bland–Altman analysis confirmed the agreement between the free‐breathing SW‐CG‐HYPR method with motion correction and the breath‐hold SW‐CG‐HYPR. This technique may allow myocardial perfusion MRI during free breathing. Magn Reson Med, 2010.

Myocardial perfusion magnetic resonance imaging using sliding-window conjugate-gradient HYPR methods in canine with stenotic coronary arteries

Purpose: First-pass perfusion magnetic resonance imaging (MRI) is a promising technique for detecting ischemic heart disease. However, the diagnostic value of the method is limited by the low spatial coverage, resolution, signal-to-noise ratio (SNR), and cardiac motion-related image artifacts. A combination of sliding window and conjugate-gradient HighlY constrained back-PRojection reconstruction (SW-CG-HYPR) method has been proposed in healthy volunteer studies to reduce the acquisition window for each slice while maintaining the temporal resolution of 1 frame per heartbeat in myocardial perfusion MRI. This method allows for improved spatial coverage, resolution, and SNR. Methods: In this study, we use a controlled animal model to test whether the myocardial territory supplied by a stenotic coronary artery can be detected accurately by SW-CG-HYPR perfusion method under pharmacological stress. Results: Results from 6 mongrel dogs (15-25 kg) studies demonstrate the feasibility of SW-CG-HYPR to detect regional perfusion defects. Using this method, the acquisition time per cardiac cycle was reduced by a factor of 4, and the spatial coverage was increased from 2 to 3 slices to 6 slices as compared with the conventional techniques including both turbo-Fast Low Angle Short (FLASH) and echoplanar imaging (EPI). The SNR of the healthy myocardium at peak enhancement with SW-CG-HYPR (12.68 ± 2.46) is significantly higher (P < 0.01) than the turbo-FLASH (8.65 ± 1.93) and EPI (5.48 ± 1.24). The spatial resolution of SW-CG-HYPR images is 1.2 × 1.2 × 8.0 mm3, which is better than the turbo-FLASH (1.8 × 1.8 × 8.0 mm3) and EPI (2.0 × 1.8 × 8.0 mm3). Conclusions: Sliding-window CG-HYPR is a promising technique for myocardial perfusion MRI. This technique provides higher image quality with respect to significantly improved SNR and spatial resolution of the myocardial perfusion images, which might improve myocardial perfusion imaging in a clinical setting.

GW24-e0504 3D myocardial perfusion MRI using SW-CG-HYPR

Objectives Time-resolved data acquisition with sliding-window conjugate-gradient highly constrained back projection (SW-CG-HYPR) has been proposed to acquire 2D myocardial perfusion images. This method allows increased spatial coverage, better spatial resolution, and improved signal-to-noise ratio (SNR). To further increase the spatial coverage and contrast-to-noise ratio (CNR), we developed a 3D sequence combined with inversion recovery (IR) pre-pulse and SW-CG-HYPR. Methods Five healthy volunteers were scanned using a 1.5T system (Espree, Siemens, Erlangen, Germany). An ECG-triggered, 3D turbo-FLASH sequence with radial k-space sampling and inversion recovery preparation was used in this study. Within each cardiac cycle, 6 partitions were acquired after a trigger delay time and inversion recovery preparation. Each partition was acquired in a segmented interleaved fashion with 16 projections per heartbeat, and the “composite images” were reconstructed by a sliding window method using k-space data from 10 consecutive cardiac cycles. CG-HYPR method was used to reconstruct the time-resolved images. SW-CG-HYPR allows a 3D acquisition window of 250 ms in each heartbeat. To compare the image quality and verify the signal changes after contrast administration, a conventional IR Turbo-FLASH scan was performed with the same contrast injection scheme. Results Left ventricle and myocardium signal changes in SW-CG-HYPR images were closely related to those observed in images obtained using the conventional protocol. The mean correlation coefficients between 3D sliding CG-HYPR and 2D single-slice reference images are 0.97, 0.95 for blood and myocardial signals, respectively. With SW-CG-HYPR, 6 partitions were acquired in each cardiac cycle for IR prepared myocardial perfusion imaging, while the conventional protocol only allows 1 slice with IR and 3 slices with saturation recovery preparation. Within the interpolated 12 partitions, the 10 central partitions have no slice aliasing. Conclusions 3D imaging improves SNR and allows inversion recovery preparation, which improves image contrast over saturation recovery preparation required for multi-slice 2D imaging.

GW24-e0505 Direct comparison of SW-CG-HYPR and conventional SR-Turbo-FLASH myocardial perfusion MRI for detection of coronary artery disease

Objectives Sliding-window conjugate-gradient highly constrained back-projection reconstruction (SW-CG-HYPR) myocardial perfusion MRI allows increased spatial coverage, improved temporal and spatial resolution and signal-to-noise ratio compared with the conventional SR-Turbo-FLASH. The diagnostic accuracy of myocardial perfusion MRI with SW-CG-HYPR for detecting coronary artery disease (CAD) has not been directly compared to that with conventional SR-Turbo-FLASH. The purpose of the work was to prospectively compare the diagnostic value of SW-CG-HYPR and conventional SR-Turbo-FLASH for myocardial perfusion MRI in patients with suspected CAD. Methods Thirtyconsecutivepatients with suspected CAD who were scheduled for coronary angiography underwent myocardial perfusion MRI with both SW-CG-HYPR and SR-Turbo-FLASH in random order at 3.0 T. Perfusion defects were interpreted visually by 2 blinded observers and were correlated to x-ray angiographic stenoses ≥ 50%. Receiver-operating characteristic (ROC) curve analysis was used to compare the diagnostic performance of the two imaging techniques. Results In the per-patient analysis, SW-CG-HYPR provided a higher sensitivity (94% vs. 89%), specificity (83% vs. 75%) and diagnostic accuracy (90% vs. 83%) for detection of CAD than SR-Turbo-FLASH. In the per-vessel analysis, the diagnostic performance of SW-CG-HYPR was significantly greater than that of SR-Turbo-FLASH for the overall detection of CAD (area under ROC curve: 0.96 ± 0.02 vs. 0.90 ± 0.03, respectively; p < 0.05). Conclusions SW-CG-HYPR myocardial perfusion MRI has higher diagnostic accuracy than conventional SR-Turbo-FLASH for detection CAD.

Adenosine-induced stress myocardial perfusion MRI using SW-CG-HYPR with whole left ventricular coverage: comparison of results with X-ray angiography in patients with suspected CAD

Myocardial perfusion MRI with sliding-window conjugate-gradient HYPR (SW-CG-HYPR) allows increased spatial coverage (whole left ventricular coverage), resolution, signal-to-noise ratio and reduced motion artifacts. The accuracy of this technique for detecting coronary artery disease (CAD) has not been determined in a large number of patients.

Free breathing myocardial perfusion MRI with SW-CG-HYPR using motion correction

Introduction The diagnostic value of first-pass perfusion MRI is limited by the low spatial coverage, resolution, SNR, and motion artifacts. Sliding-Window Conjugate-Gradient HYPR [1] (SW-CG-HYPR) has been proposed to acquire perfusion images with increased spatial coverage, better spatial resolution, and improved SNR [2]. However, this method is sensitive to the respiratory motion and thus limited to the breath hold. Motion correction may be useful to reduce motion artifacts and allow for free-breathing first-pass perfusion.

3.0 T contrast-enhanced whole-heart coronary magnetic resonance angiography for the evaluation of the cardiac venous anatomy

Introduction In cardiac resynchronization therapy (CRT), left ventricular (LV) pacing is achieved by positioning the LV lead in one of the tributaries of the coronary sinus (CS). Pre-implantation knowledge of the venous anatomy may help to decide whether transvenous LV lead placement for CRT is feasible. A recent study using navigator-gated whole-heart steady-state free precession coronary artery imaging demonstrates that MR can depict the anatomy of the venous system at 1.5 T [1]. Contrast-enhanced whole-heart coronary magnetic resonance angiography (CMRA) has been used to evaluate coronary artery disease at 3.0 T [2]. The purpose of the work is to assess whether contrast-enhanced wholeheart CMRA can be used to evaluate the coronary venous anatomy as well.