Due to the excellent contrast between blood and tissue, bSSFP is the current clinical standard for cardiac magnetic resonance imaging (CMR). Recently, several studies^1,2 have noted that changes in tissue structure such as edema and fibrosis can change steady state characteristics of myocardial signal intensity. It has also been shown that bSSFP is capable of quantifying myocardian edema³, though this has only been examined using 2D acquisitions. However, through-plane motion during the cardiac cycle can influence the signal evolution in steady state approaches. In this study, we examined the impact of through-plane motion on preservation of steady state magnetization in standard 2D balanced steady state free precession (bSSFP) compared to 3D volume (slab) cine bSSFP. In this study, nine healthy adult males between 20-30 years of age completed CMR on a 1.5T Seimens Aera scanner (Erlangen, Germany). Prospectively gated cine bSSFP images were acquired with excitation flip angle of 50° in five slabs, each consisting of six slices, and acquired from left ventricular base to apex. [TR/TE= 54.24/1.46 ms, FOV= 260x260 mm2, slice thickness 8mm, Matrix= 256x256, phases set to fill the cardiac interval]. 2D images were taken at the same location as the center two images in each slab, while maintaining all parameters except TR/TE= 35.64/1.36 ms. The percent change from the initial signal ΔS was calculated as ΔS = S/S₀, where S₀ is the average signal intensity at the first cardiac phase in each slice. This ratio was plotted against position in the cardiac cycle for each slice (see fig 2). The regions of interest were defined using a custom program used for feature tracking, and were manually adjusted for precision as described by Jing⁴. A MATLAB (Mathworks, Nattick, MA) script was used to analyze the signal intensity in these contoured images and calculate changes in the average signal. The averaged peak systolic ΔS was significantly higher in 2D bSSFP compared to the corresponding peak value in an identical slice acquired at the center of a 3D bSSFP slab. Data analyzed at mid-ventricular locations (center slices of the center slab) shows the maximum change in signal from S₀ in 2D is 40 ±21% and 16 ±7% (p<0.01) for 3D. The percent of phases in which the signal was within 10% of the S0 value is 48 ±11% for 2D and 83 ±16% (p<0.001) for 3D images at the same location (see fig 3). The peak ΔS of outer slice pairs 2,5 and 1,6 are greater than the center slices, though less than the 2D images. Previously, studies had compared 2D and 3D imaging, but only to demonstrate agreement in calculated cardiac function⁵ and diagnostic capabilities⁶. The authors concluded that the loss in spatial resolution did not significantly impact diagnoses, and that they had the clinical benefit of taking less take time and fewer breath holds to complete. However, with an emerging understanding of how changes in tissue structure alter steady state magnetization in bSSFP acquisitions, it is important to understand the mechanisms altering steady state conditions. Our results indicate that while steady state magnetization is only transiently maintained in 2D cine bSSFP, the final 30% of the cardiac cycle shows a return to initial magnetization values, and becomes similar to 3D acquisitions. In addition to having a much lower maximum change in signal, the variability of 3D images is much lower than those of 2D. Further analysis of 3D bSSFP revealed a position dependent steady state behavior, with steady state maintained only at the center of the 3D slab. The next step for this study is to look at motion and function through the cardiac cycle. 4-chamber images will be analyzed in the same custom program to determine strain and strain rate in the same time axis as signal intensity. Since the ΔS curves seem to reach local maxima around systole and the post-systolic kick, this change in signal could be indicative of certain cardiac functions. A more consistent signal can be measured in bSSFP by looking at the center images of a volumetric excitation as opposed to the standard 2D bSSFP. For studies that extract data via quantification of signal throughout the cardiac cycle, it is necessary to understand how the signal changes due to through-plane motion.