André Fischer1,2, Michael N. Hoff3, Piero Ghedin1,2,4, and Anja C.S. Brau2
1GE Global Research, Garching bei München, Germany, 2Cardiac Center of Excellence, GE Healthcare, Garching bei München, Germany, 3Department of Radiology, University of Washington, Seattle, WA, United States, 4GE Healthcare, Waukesha, WI, United States
Synopsis
Banding artifacts in bSSFP
sequences pose a challenge in cardiac cine imaging, especially at 3.0T.
Recently, a “Geometric Solution” (GS) which is capable of completely removing
banding artifacts has been introduced and demonstrated in applications outside
the heart. This work investigates the feasibility of extending GS to cardiac
cine imaging at 3.0T and explores its potential to enable longer TRs than have
conventionally been feasible with bSSFP, permitting sub-millimeter resolution
cine imaging free of banding artifacts.Introduction
Balanced Steady-state free precession (bSSFP) sequences are the gold
standard in cardiac magnetic resonance (CMR) cine functional imaging due to the
inherently high SNR and contrast between the blood pool and myocardium.
However, when compared to spoiled gradient echo sequences, bSSFP is highly
sensitive to inhomogeneities caused by the main magnetic field or by tissue susceptibility
differences. These inhomogeneities lead to the well-known banding artifacts in
bSSFP images, which along with flow-related artifacts can limit diagnostic
information in CMR. Though banding can be minimized by using shorter TR and
optimized pre-scan calibrations, it remains a challenge for CMR, especially at
3.0T. Recently, a “Geometric Solution” (GS) based on a novel elliptical signal
model has been introduced and demonstrated in bSSFP applications outside the
heart [1]. GS is capable of completely removing banding from four different
phase- cycled bSSFP datasets, and mitigates
flow artifacts [2]. This work investigates the feasibility of extending GS to
CMR and explores its potential to enable longer TRs than have conventionally been
feasible with bSSFP, permitting sub-millimeter resolution cine imaging free of
banding artifacts.
Methods
Cine imaging is usually limited in terms of spatial resolution, due to
the requirement to keep TR short to limit banding artifacts in bSSFP. First, to
assess the benefit of the GS in a clinically relevant cardiac protocol, cine
bSSFP datasets with typical 1.9x1.9mm
2 spatial resolution were acquired. Second,
to explore the ultra-high resolution parameter space typically inaccessible
with bSSFP, sub-millimeter resolution datasets with high TR values were acquired.
In both cases, four different phase cycles, 0°, 90°, 180°, and 270°, were
collected, each in a separate breath-hold. Banding was then removed using the GS
as described in [1]. This was compared to a complex sum (ComSum) of the four
phase cycled datasets. Two short-axis cine
datasets were acquired on a 3.0T clinical scanner (MR750w, GE Healthcare,
Waukesha/WI, USA): one employed clinical parameters (TR/TE = 3.6/1.3ms, α = 50°,
FOV = 360x288mm
2, matrix = 188x152, slice thickness = 8mm, BW = ±111.11kHz,
resolution=1.9x1.9mm
2), and the other used sub-millimeter resolution
(TR/TE = 5.6/2.6ms, α = 65°, FOV = 360x252mm
2, matrix = 384x270,
slice thickness = 8mm, BW = ±125.00kHz, resolution=0.9x0.9mm
2). In
both cases, no parallel imaging was applied, and standard shimming procedures
were followed.
Results
Figures 1 and 2 show frames from the individual cine datasets. Several
phase cycles show either significant banding in the cardiac region (white arrows)
or flow related artifacts (blue arrows). The standard 180° phase-cycled images
suffer from banding artifacts in the myocardium despite proper local shimming.
The GS completely removes all banding from the FOV. Furthermore, the GS depicts
mitigated flow-related dephasing in both datasets, and more homogenous overall
image intensity relative to the phase-cycled data and the ComSum. However, in the
ComSum and GS, a slight blurring compared to the individual phase-cycled images
can be seen.
Discussion
This work represents the first known application of GS to cardiac bSSFP
imaging. Despite severe banding and flow artifacts in some phase-cycled images,
GS proved to be a promising tool for obtaining high-quality bSSFP cine datasets
without visible banding in CMR. The GS also demonstrates mitigated flow
artifacts relative to the ComSum [2], although the slight blurring observed in
GS and ComSum datasets compared to standard 180° phase-cycled bSSFP images indicates
that motion can still pose a challenge. Since four different phase cycles are
necessary, care must be given to avoid misregistration artifacts due to
respiratory motion. Future work will
focus on optimizing data acquisition strategies to lower the additional scan
time burden. Furthermore, motion compensation strategies similar to [3] may
remove blurring by compensating any misregistration between the individual
phase-cycled datasets. In summary, this initial feasibility study demonstrates
the potential of GS to improve the robustness of clinical bSSFP CMR at 3.0T as
well as to enable access to typically unavailable parameter spaces such as sub-millimeter
resolution with very high TRs. This may improve clinical CMR performance at
both 1.5T or 3.0T.
Acknowledgements
No acknowledgement found.References
[1] Q.-S. Xiang, M.N. Hoff; MRM V.71 pp.927-933 (2014)
[2] M.N. Hoff, J.B. Andre, Q.-S. Xiang; Proc ISMRM V.23 p.818 (2015)
[3] Bustin A, Menini A, Lui S, et al.; Proc ISMRM V.23 p.810 (2015)