Clinical evaluation of CAIPIRINHA: Comparison against a GRAPPA standard

Abstract

Purpose To evaluate image quality when using a CAIPIRINHA sampling pattern in comparison to a standard GRAPPA sampling pattern in patients undergoing a routine 3D breath-held liver exam. CAIPIRINHA uses an optimized phase encoding sampling strategy to alter aliasing artifacts in 3D acquisitions to improve parallel imaging reconstruction. Methods Twenty patient volunteers were scanned using a 3D VIBE acquisition with an acceleration factor of four using a CAIPIRINHA and standard GRAPPA sampling pattern. CAIPIRINHA and GRAPPA images were evaluated by three radiologists in a two alternative forced choice test, and the Wilcoxon signed rank test was performed. Results The CAIPIRINHA sampling pattern was preferred in an average of 68% of the comparisons, and the Wilcoxon signed rank test showed a significant improvement in CAIPIRINHA images (p=0.014). This analysis indicates that in the given sample set, CAIPIRINHA preference over the GRAPPA standard was statistically significant. Conclusion This work shows that for an acceleration factor of four, a CAIPIRINHA accelerated VIBE acquisition provides significantly improved image quality in comparison to the current GRAPPA standard. This allows a further reduction in imaging time for similar spatial resolutions, which can reduce long breath-hold requirements in abdominal imaging, and may be particularly helpful in patients who cannot provide requisite breath-holds with current protocols.

Comparison of Three, Motion-Resistant MR Sequences on Hepatobiliary Phase for Gadoxetic Acid (Gd-EOB-DTPA)-Enhanced MR Imaging of the Liver

“…For parallel imaging, SNR is proportional to 1/√R (R is the acceleration factor) (19). The application of 3D GRE with CAIPIRINHA using an acceleration factor of 4 results in a two-fold reduction in the SNR (7,9,16). In our study, the CNR of malignant tumors differ, particularly, between the free-breathing, 3D radial GRE sequence and 3D GRE with CAIPIRINHA in uncooperative patients.…”

“…The acquired k-space samplings are offset from the normal grid-like sampling by shifting the sampling positions of alternate rows with respect to the partition-encoding direction (7,9,10). This technique can save the acquisition time and the breathholding time more effectively than the generalized auto calibrating partially parallel acquisition (GRAPPA) technique (8)(9)(10)13).…”

“…The newly developed, parallel acceleration technique (3D gradient recalled echo [GRE], with controlled aliasing in parallel imaging, resulting in higher acceleration [CAIPIRINHA]), can save image acquisition time, by modifying the phase encoding sampling manner, which leads to reduced aliasing artifacts and provides better image quality, although patients cannot hold their breath long enough (7)(8)(9)(10). Therefore, this rapid imaging technique that reduces respiration artifacts, may propel patients with short breathing capacity, into routine clinical MR practice.…”

Shortened breath-hold contrast-enhanced MRI of the liver using a new parallel imaging technique, CAIPIRINHA (controlled aliasing in parallel imaging results in higher acceleration): a comparison with conventional GRAPPA technique

“…The principle of the parallel imaging technique is to reconstruct the image from the reduced number of sampled k-space data, using the inherent spatial information of different coil elements of multiple independent radiofrequency receiver coils [2]. The well-known limitations of parallel imaging reconstructions are a decrease in signal-to-noise ratio (SNR) and residual aliasing artifacts at a high acceleration factor (AF) compared with a fully sampled k-space data, which lead to a loss of image quality [3,[8][9][10]. They depend heavily on the geometry of the coil array used and various vendor-specific parallel imaging reconstruction algorithms, and the generalized autocalibrating partially parallel acquisition (GRAPPA) technique is now standard [2,4,8].…”

“…The well-known limitations of parallel imaging reconstructions are a decrease in signal-to-noise ratio (SNR) and residual aliasing artifacts at a high acceleration factor (AF) compared with a fully sampled k-space data, which lead to a loss of image quality [3,[8][9][10]. They depend heavily on the geometry of the coil array used and various vendor-specific parallel imaging reconstruction algorithms, and the generalized autocalibrating partially parallel acquisition (GRAPPA) technique is now standard [2,4,8]. In addition, an AF of 2 is preferred clinically at 1.5 T with an acquisition time of longer than 20 s [2,4].…”