1356572 - View-Sharing and KWIC Filtering Improves Spatial Resolution of Highly-Accelerated Multi-TI, Single-shot Late Gadolinium Enhancement MRI with GRASP-PRO Reconstruction

Late gadolinium enhancement (LGE) is the gold standard for myocardial scar evaluation. Its limitations include a long scan time, poor breath holding in segmented LGE, and low spatial resolution in single-shot LGE. An inversion time (TI) scout is also required to identify an optimal TI to null the normal myocardium. We had previously developed a highly-accelerated multi-TI, single-shot LGE with radial k-space sampling and GRASP reconstruction [1]; the advantage with this sequence is that it is a single-shot and does not require a TI scout. The resulting images, however, produced blurry image quality due to high acceleration factor ( >20). The objective of this study was to incorporate view sharing (VS) and k-space weighted image contrast (KWIC) filtering [2] into GRASP-PRO [3] to minimize image blurring.

Methods:

Human subjects and pulse sequence:

We scanned 30 patients (mean age=61.0±16.5years; 21 males; 9 females) with both clinical standard single-shot LGE and multi-TI, single-shot LGE approximately 10-15 min following 0.15 mmol/kg gadobutrol at 1.5 Tesla (Siemens; Aera and Avanto). Relevant imaging parameters are summarized in Table 1.

Image reconstruction and quantitative analysis:

For the conventional GRASP-PRO method, we reconstructed multiple TI frames using 9 radial spokes per frame. For GRASP-PRO with VS+KWIC, we used 33 radial spokes per frame, where 12 radial spokes before and after the 9 native spokes were shared with adjacent frames. We then applied KWIC filter to zero out the central portion of shared k-space lines, which is necessary to minimize motion blurring and the contrast mixture of different TIs inherent to radial k-space sampling. For illustration of sampling schemes, see Figure 1. Following GRASP-PRO and GRASP-PRO with VS+KWIC, we also applied temporal low-rank block wise filter to remove residual noise.

For quantitative analysis, the blur metric (0=sharp; 1=blur)[4] was calculated for conventional GRASP-PRO LGE, GRASP-PRO LGE with VS+KWIC, and clinical LGE for basal, mid, and apex slices. The variable normality was tested using the Shapiro-Wilk test. The final results were compared using ANOVA with Bonferroni correction for pairwise comparison.

Results:

According to the Shapiro-Wilk test, the measured blur metrics were normally distributed. The blur metric was significantly (P< 0.05) lower for clinical LGE (0.31±0.04) and GRASP-PRO LGE with VS+KWIC  (0.29±0.05) than conventional GRASP-PRO LGE (0.40±0.05). Compared to clinical LGE (0.31±0.04), the blur metric was significantly lower (P< 0.05) for GRASP-PRO LGE with VS+KWIC (0.29±0.05). Figure 2 shows representative basal, mid, and apex slices of clinical, conventional GRASP-PRO, GRASP-PRO with VS+KWIC LGE images of one patient with myocardial scarring.

Conclusion:

This study suggests that incorporation of VS and KWIC filtering into the GRASP-PRO improves spatial resolution for multi-TI, single-shot LGE obtained with radial k-space sampling. Future studies include quantification of myocardial scar volume.