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1110 Improved real-time cine with the use of a 32-channel cardiac array and Karhunen-Loeve Transform filter
© Ding et al; licensee BioMed Central Ltd. 2008
- Published: 22 October 2008
- Acceleration Rate
- Heart Region
- Noise Standard Deviation
- Temporal Subtraction
- Parallel Acquisition Technique
Real-time cine MRI can be accelerated with parallel acquisition techniques at the expense of signal-to-noise ratio (SNR). 32-channel coil arrays can reduce the SNR loss at high acceleration rates . The Karhunen-Loeve Transform (KLT) filter can enhance SNR in dynamic images without compromising image information . In this work, we investigate the combination of a 32-channel cardiac array with KLT filtering to maintain SNR at high parallel acceleration rates.
Our standard clinical real-time SSFP cine method  utilizes a 12-channel array and TSENSE parallel acceleration rate R3. The purpose of this study is to demonstrate that the combination of a 32-channel array and KLT filter permits higher acceleration rates while maintaining sufficient SNR. Higher acceleration can in turn be used to improve the temporal or spatial resolution of real-time cine.
The study was performed on a 1.5 T MRI system (Avanto, Siemens Medical Solutions, Inc). Five normal volunteers (age range from 25 to 54 with mean age 34) were imaged after giving written informed consent. Eight 256-frame real-time SSFP cines in the same mid-ventricular short axis view were acquired in each volunteer. Four cines with TSENSE rates R1, R3, R4 and R5 were acquired using a standard 12-channel array, and four additional cines with the same imaging parameters were acquired using a 32-channel coil (RAPID International, LLC). Other imaging parameters were: 192 × 144 matrix, 8.0 mm thick slice, flip angle 68 degrees, TE = 1.02 ms, TR = 1.62 ms, pixel bandwidth = 1370 Hz/pixel. The SNR was defined as the ratio of mean signal in the left ventricular blood pool to the noise standard deviation (SD) in the heart region. The noise in the heart region was evaluated using a modified temporal subtraction method . All images were KLT filtered and the SNR compared between filtered and unfiltered images, and between 12-channel and 32-channel acquisitions. The KLT filter cutoff was set at 40/256 eigenimages based on an evaluation of the autocorrelation of the eigenimages. No significant spatial structure was evident beyond the 40th eigenimage, so this cutoff was expected to have no significant impact on image information content while providing an expected reduction in image noise of 60%.
SNR comparison. The combination of a 32-channel cardiac array and Karhunen-Loeve image filter is utilized to maintain SNR in highly accelerated real-time cine imaging.
p value 2-channel vs. 32-channel unfiltered
p value 32-channel unfiltered vs. KLT filtered
97.8 ± 20.7
90.6 ± 26.3
TSENSE Rate 3
31.9 ± 2.4
28.6 ± 4.3
61.9 ± 10.3
TSENSE Rate 4
20.4 ± 3.7
22.2 ± 3.8
48.8 ± 6.5
TSENSE Rate 5
10.9 ± 3.3
15.2 ± 4.7
38.6 ± 9.3
Equivalent or better SNR is achieved at R5 with the combination of the 32-channel array and KLT filter compared to the standard coil without filter at R3. This results in a 67% improvement in imaging speed, which in this study was used to improve temporal resolution from 78 msec at R3, to 47 msec at R5. This gain in temporal resolution is important for the application of real-time cine in dobutamine and exercise stress CMR.
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This article is published under license to BioMed Central Ltd.