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First-pass perfusion CMR with reduced dark-rim artifact and instantaneous image reconstruction using optimized cartesian sampling and apodization
Journal of Cardiovascular Magnetic Resonance volume 17, Article number: P1 (2015)
Subendocardial dark-rim artifact (DRA) continues to be a major issue that limits the diagnostic performance of first pass perfusion (FPP) CMR. Non-Cartesian approaches such as radial or spiral acquisition have been proposed to minimize DRAs. Among these approaches, those that can operate without the need for breath-holding typically require a time-consuming offline image reconstruction procedure, which limits their clinical accessibility. We propose a free-breathing DRA-reduced FPP scheme with instant image reconstruction on the scanner.
Healthy subjects (n=10) were studied on a 3T Siemens scanner using the standard 12-channel coil. Two free-breathing FPP scans (3 slice coverage) were performed at rest, first using the proposed method followed by a conventional method (15 minute gap).
Apodization of k-space data is known to reduce Gibbs ringing effects, a major underlying cause of the DRA. It also enhances signal-to-noise (SNR) but comes at the cost of lower resolution. In the proposed method, a high parallel imaging factor (4 fold) with Cartesian sampling is used to acquire a high-resolution FPP scan (in-plane: 1.7 x 1.7 mm2). Following parallel imaging reconstruction, an optimized apodizer is applied, which both reduces Gibbs ringing and improves SNR. The apodization level was adjusted so that the apodized images had the same resolution as the conventional FPP scan (in-plane: 2.7 x 2.2 mm2).
Apodization was implemented as an additional post-filtering step and it was integrated to the inline image reconstruction routine of the scanner. Images were scored by 2 expert readers blinded to the protocol (consensus artifact scoring; scale: 0 = No DRA, 4 = Severe DRA). In addition, dogs with myocardial infarction (n=2) and a control dog were studied using a similar setting.
Fig. 1(a,b) shows representative images and the histograms of DRA scores are presented in Fig. 1(c,d). The mean DRA score for the proposed method is lower than the conventional method (p<0.01). More importantly, the number of slices with severe DRA (scores 3 or 4) is significantly lower for the proposed method. Image quality scores were also assigned by the readers (0-4 scale; 0: poor; 4: excellent). The difference of image quality between the two methods was not significant (3.5 for the proposed method and 3.9 for conventional; p=0.2).
Fig. 2 provides results from the canine studies, demonstrating that FPP images acquired with proposed method can detect small subendocardial defects corresponding to infarct territories (LGE images).
We developed an optimized Cartesian sampling and apodization scheme for free-breathing perfusion CMR. Compared to the conventional FPP imaging method, the severity and prevalence of subendocardial DRAs were significantly reduced. A key feature of the proposed method is that it uses the widely-available parallel imaging reconstruction software to achieve near-instant reconstruction on the scanner, potentially enhancing its accessibility in clinical studies.
Grant sponsors: NIH National Heart, Lung and Blood Institute grant nos. K99 HL124323-01, R01 HL038698-18, R01 HL091989-05, R01 HL090957-01; and the Barbra Streisand Women's Cardiovascular Research & Education Program, CSMC.
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Zhou, Z., Bi, X., Yang, HJ. et al. First-pass perfusion CMR with reduced dark-rim artifact and instantaneous image reconstruction using optimized cartesian sampling and apodization. J Cardiovasc Magn Reson 17, P1 (2015). https://doi.org/10.1186/1532-429X-17-S1-P1
- Image Quality Score
- First Pass Perfusion
- First Pass Perfusion Image
- Parallel Imaging Factor
- Gibbs Ringing