Tatsuhiro Wada1, Chiaki Tokunaga1, Osamu Togao2, Yasuo Yamashita1, Kouji Kobayashi1, Masami Yoneyama3, and Toyoyuki Kato1
1Division of Radiology, Department of Medical Technology, Kyushu University Hospital, Fukuoka, Japan, 2Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan, 3Philips Japan, Fukuoka, Japan
Synopsis
Multi-spin
echo acquisition cine imaging (MUSACI) is based on the multi-spin echo
technique and used for detection of cerebrospinal fluid (CSF) movement. MUSACI
detects CSF movement as a signal loss due to proton phase dispersion and flow
void. To better detect the CSF loss caused by CSF movement and reduce the CSF
signal loss caused by T2 decay, we modified the refocusing flip angle
modulation using pseudo steady state sequence (PSS). The modulation of
refocusing flip angle in PSS improved the CSF dynamic imaging using MUSACI.
INTRODUCTION
Hydrocephalus is an abnormality of the cerebrospinal fluid (CSF)
circulation caused by aqueductal stenosis, tumors, etc. A novel magnetic
resonance (MR) imaging technique, multi-spin echo acquisition cine imaging
(MUSACI), has been used to describe the movement of the CSF.1 This
technique is based on the proton phase dispersion and flow void using 3D
multi-spin echo imaging. However, in the 3D turbo spin-echo (TSE) sequence, CSF
signal loss can also occur when the refocusing flip angle modulation is low.2
The purpose of this study was to investigate the effect of modifying the
refocusing flip angle on the CSF dynamic imaging using MUSACI.METHODS
The MUSACI images were acquired in 10
healthy volunteers (7 men and 3 women; age range 24–44 years; mean age 29.4 ± 6.2 years). All images were acquired
on a 3T MR scanner (Ingenia, Philips, Best, The Netherlands) using a 15-channel head coil. MUSACI images were acquired
in the sagittal plane using 3D VISTA with pulse gating. The parameters were
TR = 2RR msec, TE = 44.0 + echo number (80 msec steps) msec, TSE
factor = 70–110, echoes = 7–10, field of view = 240 × 240 mm2, slice thickness = 1.2 (recon to 0.6) mm,
number of slices = 25,
matrix size = 416 × 416, scan time = approx. 5 min,
refocusing flip angle = constant 30°, constant 50°, constant 80°, pseudo steady
state (PSS) 50°–70°–100° (PSS 50°), PSS 80°–100°–130° (PSS 80°) (Fig. 1). We
modified the TSE factor and echo numbers so that the TR was within one pulse
wave in each study.
In
this study, circular regions of interest were placed to measure the signal
intensity (SI) in the lateral ventricle, the foramen of Monro, the third
ventricle, the fourth ventricle and the pons in MUSACI. The Pearson’s correlation coefficients were calculated to evaluate the statistical
correlation between the CSF SI and TEeff in the lateral ventricle. Values
of p<0.05 were considered
significant.RESULTS
Figure 2 shows the influence of refocusing
flip angle modulation on the midsagittal MUSACI images in a 26-year-old female.
The antegrade and retrograde
directions of CSF movement were detected in all sequences. The CSF
signal loss caused by CSF movement was greater when the refocusing flip angle
was lower under both the constant and PSS sequences.
Figure 3
shows the influence of refocusing flip angle modulation on the foramen of Monro
MUSACI images in a 26-year-old female. The antegrade direction of CSF movement was
detected in all constant sequences. In the PSS sequences, on the other hand, it
was detected in PSS 50° but was not clearly detected in PSS 80°. The CSF signal
loss caused by CSF movement was more apparent than the CSF signal decay by the
lower refocusing flip angle under both the constant and PSS sequences.
Figure 4
shows the SI change with an increase in TEeff in each sequence. The
reductions of the CSF SI in the foramen of Monro, third ventricle and fourth
ventricle were steeper than that in the lateral ventricle. The CSF SI was
decreased when using the lower refocusing flip angle under both the sequence
constant and PSS sequence conditions, and those under the PSS sequence were
higher than those under the constant sequence conditions.
Figure
5 shows the change of
CSF SI in the lateral ventricle with an increase in TEeff using
MUSACI at all sequences. A severe reverse correlation between the CSF SI and TEeff
was observed at constant 30° (r=-0.960, p<0.0001), 50° (r=-0.971,
p<0.0001) and 80° (r=-0.875, p=0.0009), a weak positive
correlation between the CSF SI and TEeff was observed at PSS 50° (r=0.280,
p=0.4340), and a moderate reverse correlation between the CSF SI and TEeff
was observed at PSS 80° (r=-0.597, p=0.0683).DISCUSSION
The CSF signal loss caused by CSF movement
in MUSACI was more apparent when using a lower refocusing flip angle than a
higher refocusing flip angle. The sensitivity of the refocusing flip angle on
flow using fast-spin-echo sequence has been reported.3,4 The
magnetization at each echo in turbo-spin echo is no longer rephased completely
into the transverse plane when the refocusing flip angles are less than 180°.
The phase dispersion caused by moving protons was accelerated due to a detour
in the longitudinal signal pathways when using a low refocusing flip angle.
The
relationship between the CSF signal and TEeff exhibited a reverse
correlation in the constant 30°, 50°, 80° and PSS 80° sequences, but a positive
correlation was observed in the PSS 50° sequence. The PSS sequence yielded a
higher echo signal of CSF than the constant sequence due to the use of the
variable flip angle.5,6 In addition, a lower refocusing flip angle
could maintain the signal variation of CSF to
the level of the constant in the PSS sequence.CONCLUSION
The CSF dynamic imaging using MUSACI was improved by modifying the refocusing
flip angle. We selected PSS 50° sequence as the optimal parameter, because the
CSF signal loss due to CSF movement was changed by modulating the flip angles
of the initial refocusing RF pulses and the use of a variable refocusing flip angle
also reduced the CSF signal decrease caused by T2 decay.Acknowledgements
No acknowledgement found.References
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