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High spatial and temporal resolution retrospective cine cardiovascular magnetic resonance from shortened free breathing real-time acquisitions.

Xue H, Kellman P, Larocca G, Arai AE, Hansen MS - J Cardiovasc Magn Reson (2013)

Bottom Line: Volumetric measurements of cardiac function were also compared by manually tracing the myocardium for segmented and retrospective cines.No significant differences were seen in end-diastolic volume (P = 0.460/0.268) but there was a trend towards a small overestimation of end-systolic volume of 2.0/2.5 ml, which did not reach statistical significance (P = 0.052/0.083).Further speedup of image reconstruction is still needed.

View Article: PubMed Central - HTML - PubMed

Affiliation: National Heart, Lung and Blood Institute, National Institutes of Health, 10 Center Drive, Bethesda, MD 20814, USA. hui.xue@nih.gov.

ABSTRACT

Background: Cine cardiovascular magnetic resonance (CMR) is challenging in patients who cannot perform repeated breath holds. Real-time, free-breathing acquisition is an alternative, but image quality is typically inferior. There is a clinical need for techniques that achieve similar image quality to the segmented cine using a free breathing acquisition. Previously, high quality retrospectively gated cine images have been reconstructed from real-time acquisitions using parallel imaging and motion correction. These methods had limited clinical applicability due to lengthy acquisitions and volumetric measurements obtained with such methods have not previously been evaluated systematically.

Methods: This study introduces a new retrospective reconstruction scheme for real-time cine imaging which aims to shorten the required acquisition. A real-time acquisition of 16-20s per acquired slice was inputted into a retrospective cine reconstruction algorithm, which employed non-rigid registration to remove respiratory motion and SPIRiT non-linear reconstruction with temporal regularization to fill in missing data. The algorithm was used to reconstruct cine loops with high spatial (1.3-1.8 × 1.8-2.1 mm²) and temporal resolution (retrospectively gated, 30 cardiac phases, temporal resolution 34.3 ± 9.1 ms). Validation was performed in 15 healthy volunteers using two different acquisition resolutions (256 × 144/192 × 128 matrix sizes). For each subject, 9 to 12 short axis and 3 long axis slices were imaged with both segmented and real-time acquisitions. The retrospectively reconstructed real-time cine images were compared to a traditional segmented breath-held acquisition in terms of image quality scores. Image quality scoring was performed by two experts using a scale between 1 and 5 (poor to good). For every subject, LAX and three SAX slices were selected and reviewed in the random order. The reviewers were blinded to the reconstruction approach and acquisition protocols and scores were given to segmented and retrospective cine series. Volumetric measurements of cardiac function were also compared by manually tracing the myocardium for segmented and retrospective cines.

Results: Mean image quality scores were similar for short axis and long axis views for both tested resolutions. Short axis scores were 4.52/4.31 (high/low matrix sizes) for breath-hold vs. 4.54/4.56 for real-time (paired t-test, P = 0.756/0.011). Long axis scores were 4.09/4.37 vs. 3.99/4.29 (P = 0.475/0.463). Mean ejection fraction was 60.8/61.4 for breath-held acquisitions vs. 60.3/60.3 for real-time acquisitions (P = 0.439/0.093). No significant differences were seen in end-diastolic volume (P = 0.460/0.268) but there was a trend towards a small overestimation of end-systolic volume of 2.0/2.5 ml, which did not reach statistical significance (P = 0.052/0.083).

Conclusions: Real-time free breathing CMR can be used to obtain high quality retrospectively gated cine images in 16-20s per slice. Volumetric measurements and image quality scores were similar in images from breath-held segmented and free breathing, real-time acquisitions. Further speedup of image reconstruction is still needed.

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Retrospective real-time cine with improved temporal resolution can enhance the visualization of valve. In this 3CH slice, the mitral valve is well captured in both real-time reconstruction (b) and segmented cine (c). The image quality of raw real-time cine (a) is much worse than the retrospective reconstruction. (d) shows the intensity profiles across time for the retrospective real-time and segmented cine. The intensity profile of raw real-time cine is generated by interpolating all images acquired in one cardiac cycle. The trigger time of raw real-time cine is 342 ms and for retro-gated reconstruction (b and c), it is the 7th cardiac phase out of 30 with the approximated trigger time of 395 ms.
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Figure 6: Retrospective real-time cine with improved temporal resolution can enhance the visualization of valve. In this 3CH slice, the mitral valve is well captured in both real-time reconstruction (b) and segmented cine (c). The image quality of raw real-time cine (a) is much worse than the retrospective reconstruction. (d) shows the intensity profiles across time for the retrospective real-time and segmented cine. The intensity profile of raw real-time cine is generated by interpolating all images acquired in one cardiac cycle. The trigger time of raw real-time cine is 342 ms and for retro-gated reconstruction (b and c), it is the 7th cardiac phase out of 30 with the approximated trigger time of 395 ms.

Mentions: The mean RR interval for breath-held acquisition was 1039.0 ± 155.6 ms, reconstructed temporal resolution 34.6 ± 5.2 ms. For free-breathing acquisition, mean RR interval was 1028.7 ± 271.9 ms, reconstructed temporal resolution 34.3 ± 9.1ms. The mean breath-hold times for segmented acquisition were 10.9 ± 1.6 s for 256 × 144 matrix and 9.9 ± 1.4 s for 192 × 128 matrix. Compared to the 90-120 ms temporal resolution of acquired raw real-time cine, the improved temporal resolution is vital for valve visualization. Figure 6 shows a 3-chamber view with the mitral valve clearly visible in the retrospective images, while visualization of the valve was suboptimal on the raw real-time images due to insufficient SNR and low temporal resolution (Additional file 7: Figure S6.avi). The intensity profiles vs. time through the myocardium demonstrate that the retrospective reconstruction from real-time images and the segmented acquisition have comparable temporal characteristics. On the other hand, raw real-time images consistently gave inferior SNR and lower temporal resolution, which made them less attractive for clinical usage and volumetric quantification. While the inline reconstruction used in this study outputted both raw real-time and retrospective cine reconstructions for direct side-by-side comparison, we did not perform systematic image quality scoring between them. It was the consensus of the cardiologists that the raw real-time images were of inferior quality.


High spatial and temporal resolution retrospective cine cardiovascular magnetic resonance from shortened free breathing real-time acquisitions.

Xue H, Kellman P, Larocca G, Arai AE, Hansen MS - J Cardiovasc Magn Reson (2013)

Retrospective real-time cine with improved temporal resolution can enhance the visualization of valve. In this 3CH slice, the mitral valve is well captured in both real-time reconstruction (b) and segmented cine (c). The image quality of raw real-time cine (a) is much worse than the retrospective reconstruction. (d) shows the intensity profiles across time for the retrospective real-time and segmented cine. The intensity profile of raw real-time cine is generated by interpolating all images acquired in one cardiac cycle. The trigger time of raw real-time cine is 342 ms and for retro-gated reconstruction (b and c), it is the 7th cardiac phase out of 30 with the approximated trigger time of 395 ms.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3842803&req=5

Figure 6: Retrospective real-time cine with improved temporal resolution can enhance the visualization of valve. In this 3CH slice, the mitral valve is well captured in both real-time reconstruction (b) and segmented cine (c). The image quality of raw real-time cine (a) is much worse than the retrospective reconstruction. (d) shows the intensity profiles across time for the retrospective real-time and segmented cine. The intensity profile of raw real-time cine is generated by interpolating all images acquired in one cardiac cycle. The trigger time of raw real-time cine is 342 ms and for retro-gated reconstruction (b and c), it is the 7th cardiac phase out of 30 with the approximated trigger time of 395 ms.
Mentions: The mean RR interval for breath-held acquisition was 1039.0 ± 155.6 ms, reconstructed temporal resolution 34.6 ± 5.2 ms. For free-breathing acquisition, mean RR interval was 1028.7 ± 271.9 ms, reconstructed temporal resolution 34.3 ± 9.1ms. The mean breath-hold times for segmented acquisition were 10.9 ± 1.6 s for 256 × 144 matrix and 9.9 ± 1.4 s for 192 × 128 matrix. Compared to the 90-120 ms temporal resolution of acquired raw real-time cine, the improved temporal resolution is vital for valve visualization. Figure 6 shows a 3-chamber view with the mitral valve clearly visible in the retrospective images, while visualization of the valve was suboptimal on the raw real-time images due to insufficient SNR and low temporal resolution (Additional file 7: Figure S6.avi). The intensity profiles vs. time through the myocardium demonstrate that the retrospective reconstruction from real-time images and the segmented acquisition have comparable temporal characteristics. On the other hand, raw real-time images consistently gave inferior SNR and lower temporal resolution, which made them less attractive for clinical usage and volumetric quantification. While the inline reconstruction used in this study outputted both raw real-time and retrospective cine reconstructions for direct side-by-side comparison, we did not perform systematic image quality scoring between them. It was the consensus of the cardiologists that the raw real-time images were of inferior quality.

Bottom Line: Volumetric measurements of cardiac function were also compared by manually tracing the myocardium for segmented and retrospective cines.No significant differences were seen in end-diastolic volume (P = 0.460/0.268) but there was a trend towards a small overestimation of end-systolic volume of 2.0/2.5 ml, which did not reach statistical significance (P = 0.052/0.083).Further speedup of image reconstruction is still needed.

View Article: PubMed Central - HTML - PubMed

Affiliation: National Heart, Lung and Blood Institute, National Institutes of Health, 10 Center Drive, Bethesda, MD 20814, USA. hui.xue@nih.gov.

ABSTRACT

Background: Cine cardiovascular magnetic resonance (CMR) is challenging in patients who cannot perform repeated breath holds. Real-time, free-breathing acquisition is an alternative, but image quality is typically inferior. There is a clinical need for techniques that achieve similar image quality to the segmented cine using a free breathing acquisition. Previously, high quality retrospectively gated cine images have been reconstructed from real-time acquisitions using parallel imaging and motion correction. These methods had limited clinical applicability due to lengthy acquisitions and volumetric measurements obtained with such methods have not previously been evaluated systematically.

Methods: This study introduces a new retrospective reconstruction scheme for real-time cine imaging which aims to shorten the required acquisition. A real-time acquisition of 16-20s per acquired slice was inputted into a retrospective cine reconstruction algorithm, which employed non-rigid registration to remove respiratory motion and SPIRiT non-linear reconstruction with temporal regularization to fill in missing data. The algorithm was used to reconstruct cine loops with high spatial (1.3-1.8 × 1.8-2.1 mm²) and temporal resolution (retrospectively gated, 30 cardiac phases, temporal resolution 34.3 ± 9.1 ms). Validation was performed in 15 healthy volunteers using two different acquisition resolutions (256 × 144/192 × 128 matrix sizes). For each subject, 9 to 12 short axis and 3 long axis slices were imaged with both segmented and real-time acquisitions. The retrospectively reconstructed real-time cine images were compared to a traditional segmented breath-held acquisition in terms of image quality scores. Image quality scoring was performed by two experts using a scale between 1 and 5 (poor to good). For every subject, LAX and three SAX slices were selected and reviewed in the random order. The reviewers were blinded to the reconstruction approach and acquisition protocols and scores were given to segmented and retrospective cine series. Volumetric measurements of cardiac function were also compared by manually tracing the myocardium for segmented and retrospective cines.

Results: Mean image quality scores were similar for short axis and long axis views for both tested resolutions. Short axis scores were 4.52/4.31 (high/low matrix sizes) for breath-hold vs. 4.54/4.56 for real-time (paired t-test, P = 0.756/0.011). Long axis scores were 4.09/4.37 vs. 3.99/4.29 (P = 0.475/0.463). Mean ejection fraction was 60.8/61.4 for breath-held acquisitions vs. 60.3/60.3 for real-time acquisitions (P = 0.439/0.093). No significant differences were seen in end-diastolic volume (P = 0.460/0.268) but there was a trend towards a small overestimation of end-systolic volume of 2.0/2.5 ml, which did not reach statistical significance (P = 0.052/0.083).

Conclusions: Real-time free breathing CMR can be used to obtain high quality retrospectively gated cine images in 16-20s per slice. Volumetric measurements and image quality scores were similar in images from breath-held segmented and free breathing, real-time acquisitions. Further speedup of image reconstruction is still needed.

Show MeSH