Download 心脏mri检查中自由呼吸单次激发ss fiesta序列应用

Application of single shot free-breathing FIESTA sequence
in cardiac MRI
Objective To investigate the imaging quality of single shot (SS) fast imaging
employing steady state (FIESTA) sequence in contrast-enhanced cardiac magnetic
resonance (MR) examination, in comparison with the IR FGRE sequence. Materials
and Methods Fifty-two cases with suspected or known heart disease were enrolled
in this study, including 24 patients who had enhanced myocardium in myocardial
delayed enhancement (MDE). We analyzed the imaging quality of the sequences by
measuring the myocardium and blood pool signal-to-noise ratios (SNR) and the
contrast-to-noise ratios (CNR) of blood pool relative to normal myocardium and of
enhanced myocardium relative to normal myocardium and compared the new
sequences with traditional sequence.
Results The scanning time of SS FIESTA was significantly shortened as
compared to IR FGRE. The differences in the image quality scores, enhanced
myocardium (EM) mass and percentages, SNR(bp), SNR(myo), CNR(myo/bp) and
CNR(l/bg) were not statistically significant between SS FIESTA and IR FGRE (P＞
0.05). However the difference in CNR(em/myo) was statistically significant between
SS FIESTA and IR FGRE (P＜0.0001), with CNR(em/myo) of IR FGRE higher than
SS FIESTA.
Conclusion SS FIESTA speeded up the acquisition time, halving it to (27.6±1.8
sec) instead of 146+13.8 sec (IR FGRE), it had higher SNR and CNR, and its image
quality did not differ significantly from IR FGRE. The SS FIESTA is more suitable
for patients with severely heart diseases or those unable to hold breath. 3D IR FGRE
sequence had higher SNR(myo) than the others and it is suitable for displaying the
subendocardial scar. However it has more artifacts and poor imaging quality than IR
FGRE.
Key Words contrast-enhanced cardiac magnetic resonance (CMR); single-shot
inversion recovery FIESTA (SS-FIESTA); segmented inversion
recovery 2D fast gradient echo (IR FGRE)； segmented inversion
recovery 3D fast gradient echo (3D IR FGRE)
Introduction
Cardiac magnetic resonance imaging (MRI) can reveal cardiac anatomical
structure, function and many types pathological scars and can diagnose a variety of
heart diseases [1-2]. Myocardial delayed enhancement (MDE) MRI for myocardial
infarction lesions was first reported in 1993 [3]. With the development of MRI
technologies, more research reports have confirmed that as a visual observation
method for myocardial infarction, delayed enhancement has important clinical value
[4]
. In recent years, because of the improvement in high performance gradient echo
sequence, MDE has become the diagnostic criterion for myocardial infarction, and
can be used for the rapid detection of myocardial lesions. MDE can not only be used
to diagnose myocardial infarction, but also be used to observe many other heart
diseases, such as myocarditis, infection, cardiomyopathy, cardiac tumors, and
congenital or secondary heart disease [5].
However, the biggest bottleneck of cardiac MRI is the lengthy scanning time.
Patients who have severe heart diseases or patients who can not hold breath well (such
as patients with acute myocardial infarction, dilated cardiomyopathy, and other
cardiopulmonary dysfunction) can not tolerate long time of scanning, resulting motion
artifacts in MRI images and thereby reducing diagnostic confidence. Therefore,
investigating sequences with shorter scanning time and better image quality has
become a hot research topic in the field of cardiac MRI both in China and abroad.
Single shot (SS) fast imaging employing steady state (FIESTA) (single-shot
inversion recovery 2D FIESTA) sequence is a type of fast scan sequence. Due to its
high contrast-to-noise ratio (CNR), especially cardiac blood pool CNR [6], it can
clearly show the myocardial edge, and in clinical practice, it is often used in delayed
enhancement sequence to directly display myocardial lesions. In 2006 it was reported
that the average scan time for this sequence was 10 minutes 13 ± 45 sec [7], and in
2010 Lene Rosendah [8] reported a scan time of 4.4 ± 1.6 min. Our studies used partial
sample collection along the X- and Y-axes, and collected more than 90 sequences
within 190 ms, with 3~4 ms for each sequence. Our scan time was fast, and one
collection can be completed every two heartbeats. We also investigated whether we
could obtain clear cardiac images on top of significantly shortened scan time,
therefore enabling patients unable to hold breath to benefit from this examination
technique.
This study enrolled 52 cases of clinically diagnosed or suspected heart diseases.
The patients were examined by MDE MRI using the SS FIESTA sequence, 3D IR
FGRE (segmented inversion recovery 3D fast gradient echo) sequence and IR FGRE
(segmented inversion recovery 2D fast gradient echo) sequence that acted as the
conventional sequence. By measuring and analyzing the myocardial signal-to-noise
ratio (SNR) and CNR of 52 cases (including the comparison of CNR between
enhanced myocardium and normal myocardium in 24 myocardial lesion cases), we
observed and compared the SS FIESTA and 3D IR GRE sequences with the
conventional IR FGRE sequence, and examined whether the images showed
significant difference in image quality and contained rich imaging information on the
basis of significantly shortened scan time to correctly diagnose heart disease.
Materials and Methods
Subjects
We enrolled a total of 52 cases of suspected or confirmed heart disease, including
39 males and 14 females. The patients aged between 16 and 76 years, with a mean of
54 years. And there were 22 cases of ischemic heart diseases (including 14 cases
undergone reexamination 3 months after coronary artery bypass and bone marrow
stem cell transplantation), 5 cases of hypertrophic cardiomyopathy, 4 cases of dilated
cardiomyopathy, 1 case of cardiac amyloidosis (confirmed by pathological
examination) and 2 cases of myocardial fibrosis. This study was approved by the
ethics committee of our hospital, and all patients signed the consent form.
MR image collection
We used a 1.5 T scanner (Signa Excite HD Twinspeed, GE Healthcare,
Milwaukee, Wisconsin, USA) with a gradient of 40 mT/m and a slew rate of 150
mT/m-1/ms-1. All patients were in the supine position with foot entering first. The
antecubital vein was placed with an indwelling intravenous catheter. An 8-channel
phased array coil dedicated for cardiac MRI was used, the electrocardiogram (ECG)
leads were placed in the precordium for vectorcardiogram gating (or a peripheral
pulse gating device was placed around the fingers), and the respiratory gating device
was placed on the abdomen.
According to the myocardial segments defined by the American Heart Association
(AHA), cardiac MRI mostly uses long axis, three-chamber, four-chamber or short axis
views [9]. Delayed scanning often scans the entire left ventricular short axis, generally
with 8-10 layers.
For delayed enhancement scan, each subject was injected with 30 ml of contrast
agent and 20 ml of normal saline at 2 ml/s through the antecubital vein using
high-pressure syringes (binoculars pressure syringe, U.S. Gomal Medical Products
Co., Ltd.). The contrast agent that we used was gadopentetate dimeglumine with a
dose of 0.1 mmolkg-1 and a maximum dose of 30 ml (Schering, Germany). After 8
minutes of delay, we examined whether the left ventricular myocardium was black. If
the left ventricular myocardium was confirmed to be black, it indicated that the
contrast agent had entered fully into the myocardium, and the delayed enhancement
scan could be initiated. The scanning order of the three kinds of delayed enhancement
sequences, SS FIESTA, 3D IR FGRE and IR FGRE, was random. The parameters of
the three scan sequences were listed in Table 1. The scan was ECG-gated and
respiratory-triggered. The IR FGRE sequence had about 12 heartbeats for each breath
hold, and the ECG-based triggering was 25% of the R-wave phase on the ECG [10-11].
The SS FIESTA sequence had 2 heartbeats for each breath hold.
Analysis of MR images
Quality evaluation
According to the contrast of myocardium and cardiac chambers to the
background on cardiac MRI images, it was possible to freely adjust the window width
and position, in order to achieve the best visual effects of the images. Myocardial
hypo- or hyper-signal was determined according to the myocardial segmentation
defined by AHA, and the image quality was divided into five grades of scores. MDE
image quality was determined according to the following four conditions: (i) whether
there were breathing artifacts, (ii) evaluation of cardiac artifacts, (iii) whether the
myocardium was sufficiently suppressed, without enhanced myocardial signal
intensity (black), (iv) whether the endocardium adjacent to the left ventricular
endocardial cavity was sharp. All image quality was divided into grades 1-5 (1 is very
poor, 2 is poor, 3 is acceptable, 4 is good, and 5 is excellent) [12]. Image quality was
rated by two experienced cardiovascular MRI physicians. Disagreement was solved
by discussion, and the consensus was used as the final result.
SNR and CNR
When measuring myocardial SNR and CNR, the regions of interest (ROIs) were
placed in the center of areas such as the left ventricular blood pool (bp), normal left
ventricular myocardium (myo), background (bg) (chest air), lung tissue (l), and
abnormally enhanced myocardium (em) to measure signal intensity (I) and standard
deviation (SD). ROI was placed in the corresponding position of each slice of short
axis images, with an area of about 3 ± 0.7 mm2. The measured data included: blood
pool SNR (SNR(bp) = Ib/SDbg), myocardial SNR (SN (myo) = Imyo/SDbg), lung
tissue minus background CNR (CNR(l/bg) = (Il-Ibg)/SDbg), blood pool minus
myocardium CNR (CNR(bp/myo) = (Ibp-Imyo)/SDbg) and abnormal myocardium
minus normal myocardium CNR (CNR(em/myo)) = (Iem-Imyo)/SDbg).
Statistics
We statistically analyzed the average elapsed time for the three kinds of
sequences, and evaluated the image quality of the three kinds of sequences. We
compared the images obtained using the two fast scanning sequences with the
traditional IR FGRE sequence, and measured the image SNR and CNR, including
SNR(myo), SNR(bg), SNR(bp) and SNR(l), CNR(bp/myo), MDE CNR(em/myo)
and CNR(l/bg). The SSPS17.0 software was used to analyze and compare whether
there were statistically significant differences in image SNR and CNR. According to
conventional standards, image quality was examined using the homogeneity of
variance test. In the presence of homogeneous variance, the chi-square test for two
independent samples was used. In the presence of heterogeneous variance, the rank
sum test for two independent samples of non-normal data was used. P <0.05
indicated statistically significant difference, and P> 0.05 indicated no significant
difference.
Results
1 Scanning time and image quality
1.1 Scan time: The SS FIESTA sequence required 2-3 times of breath hold, each
lasting 7 ± 1.3 seconds, 3-4 slices (each with an average of 1.7 ± 0.5 sec) were
obtained, and the total scan time was 27.6 ± 1.8 s (not including the intervals
between breath-hold). IR FGRE required one breath hold per slice of scanning, each
breath hold lasted 10 ± 2.3 seconds, and the total scan time was 146 ± 13.8 sec (not
including the intervals between breath-hold). 3D IR FGRE required only once breath
hold lasting 30.4 ± 4.0 seconds, and the images of segmentations 24-26 of the left
ventricle were obtained (table 2). Compared with IR FGRE, the scan time of 3D IR
FGRE sequence was reduced by 81%, and that of SS FIESTA sequence was reduced
by 79%. The comparisons between the two fast sequences and IR FGRE sequence
both had P <0.001. And 50 out of 52 patients had successful examinations, and the
success rate was about 96.2%.
1.2 Evaluation MDE image quality: we compared the image quality of the SS
FIESTA sequence and IR FGRE sequence at free-breathing state. SS FIESTA had an
average score of 1.8 ± 0.2, which was better than IR FGRE (0.7 ± 0.1), and statistical
analysis showed that there were significant differences between the two (P <0.05). In
contrast, the image quality of 3D IR FGRE had a score of only 0.2 ± 0.04, with the
worst image quality, and there were significant differences between 3D IR FGRE and
IR FGRE (table 2) (Figure A). In the breath-holding state, IR FGRE had a score of 3.9
± 0.8, SS FIESTA had a score of 3.8 ± 0.7, and 3 D IR FGRE had a score of 2.9 ± 0.9.
There was no significant difference between SS FIESTA and IR FGRE, while there
was significant difference between 3D IR FGRE and IR FGRE (P <0.0001) (table 2)
(Figure B).
2 Diagnostic performances
2.1 Delayed enhancement quality and percentage measurements
Among 52 cases successful undergone cardiac MRI examination, 24 cases had
myocardial delayed enhancement. The mass and percentage of enhanced left
ventricular myocardium were automatically calculated in the ADW4.3 workstation
using the MASS software. The results were as follows: SS FIESTA showed an
enhanced myocardial mass of 25.4 ± 17.3 g, accounting for 15.1 ± 9.2% of the left
ventricular mass; 3D IR FGRE showed an enhanced myocardial mass of 33.2 ± 19.1g,
accounting for 21.9 ± 11.1% of the left ventricular mass; and IR FGR showed an
enhanced myocardial mass 26.7 ± 17.2g, accounting for 15.4 ± 9.7% of the left
ventricular mass. Compared with IR FGRE, SS FIESTA did not show statistically
significant differences in terms of lesioned myocardial mass and percentage (P> 0.05),
while 3D IR FGRE showed statistically significant difference in lesioned myocardial
mass and no statistically significant difference in the percentage of lesioned
myocardium (table 3) (Figure C).
2.2 SNR and CNR
Compared with IR FGRE sequence, SS FIESTA sequence did not show
statistically significant differences in SNRbp, SNRmyo, CNRbp/myo, and CNRl/bg
(P> 0.05), but SS FIESTA differed significantly from IR FGRE in CNRem/myo (P
<0.05), with IR FGRE higher than SS FIESTA (table 3). Compared with IR FGRE
sequence, 3D IR FGRE sequence showed statistically significant differences in
SNRbp, SNRmyo, CNRbp/myo, CNRl/bg and CNRem/myo, and all parameters
except CNRem/myo were higher than those of IR FGRE (Table 3). CNRem/myo of
IR FGRE was significantly higher than the other two sequences, and was statistically
different from that of SS FIESTA and 3D IR FGRE (Table 4).
3 SNR of intracardiac blood pool and various segments of myocardium
IR FGRE sequence showed that intracardiac blood pool had the highest SNR.
However, the SNR of each myocardial segment in 3D IR FGRE sequences was
superior to IR FGRE and SS FIESTA. The two fast sequences showed statistically
significant differences as compared with IR FGRE (P <0.001) (Table 5). These two
sequences also clearly revealed the myocardium, endocardium and epicardium, and
had unique advantages for subendocardial infarction (Figure D).
Table 1 Scan parameters for the three group of myocardial delayed enhancement MRI
Scan Parameters
2D IR FGRE
3D IR FGRE
2D SS FIESTA
TR/TE
FA
TI
Segment
per heartbeat
Matrix
FOV
Slice thickness/gap
Number of excitation
Acquisition
time(RR)
4.0/1.8
20
250
1/12 heartbeat
3.3/1.4
15
200-250
1/heartbeat
3.4/1.4
45
200-400
3/8 heartbeat
256×256
35
8/3mm
2
10-15 phases /R-R
256×256
35
5/-4mm
256×256
35
8/3mm
1
17-19 phases /R-R
15-20 phases /R-R
Table 2 Image quality scores and the mass and percentage of myocardium with delayed
enhancement for the three delayed enhancement cardiac MRI sequences
MDE image
SS FIESTA
3D IR FGRE
Free-breathing
image score
Breath-holding
image score
Scan time (s)
1.8±0.2
0.2±0.04
3.8±0.7
2.9±0.9
3.9±0.8
27.6±1.8
30.4±4.0
146+13.8
P value
IR GRE
0.7±0.1
0.000﹙＜0.0001﹚△
0.000﹙＜0.0001＝●
0.43﹙＞0.05﹚△
0.000﹙＜0.0001＝●
0.000﹙＜0.0001﹚△
0.000﹙＜0.0001﹚●
△ P value for the comparison of SS FIESTA and IR GRE sequences
● P value for the comparison of 3D IR FGRE and IR GRE sequences
Table 3 Comparison of the SS FIESTA and IR FGRE sequences and of the 3D IR FGRE and
IR FGRE sequences in the means, standard deviations and statistical significances of SNR
(bp), SNR (myo), CNR (bp /myo), CNR (l/bg), and CNR (em/myo)
Parameter
SNR(bp)
SNR(myo)
CNR
(bp/myo)
CN
R(l/bg)
CNR
(em/myo)
SS FIESTA
(SD)
30.2(14.1)
7.2(2.7)
23.1(12.9)
3D IR
FGRE (SD)
83.8(51)
48.5(48.7)
37 (14.8)
IR FGRE
(SD)
P value
25.4(11.7)
0.108 △
0.000 ●
7.6(2.5)
0.412 △
0.000 ●
17.9(10.4)
0.108 △
0.000 ●
1.5(1.7)
8.1(4.6)
1.7(2.8)
0.8 △
0.000 ●
21(13.7)
15.7(13.8)
36.7(24.6)
0.000 △
0.000 ●
0.306 △
0.02 ●
EM mass
(g)
25.4±17.3
33.2±19.1
26.7±17.2
EM (%)
15.1±9.2
21.9±11.1
15.4±9.7
0.59 △
0.07 ●
△ P value for the comparison of SS FIESTA and IR GRE sequences
● P value for the comparison of 3D IR FGRE and IR GRE sequences
Table 4 Comparison of the three sequences, SS FIESTA, 3D IR GFRE and IR FGRE, in
CNRem/myo between myocardium with delayed enhancement and normal myocardium, with
the former two showing significantly differences compared with the latter
Table 5 Compared with IR EGRE, the SS FIESTA and 3D IR FGRE sequences showed
statistically significant difference in SNR of all LV myocardial segments (P＜0.0001)
SS FIESTA
(SD)
3D IR
FGRE (SD)
IR GRE (SD)
LV blood
pool
123 (67.7)
54.7(21.1)
178.2(55.7)
ISEP
45(38.1)
88.1(46.2)
24.3(12.2)
ASEP
56.2(48.8)
85.9(48.9)
26.7(12.9)
ANT
48.3(38.5)
72.7(56.1)
23.6(12.9)
ALAT
39(30.1)
77.3(33.6)
21(11.8)
ILAT
42.5(34.2)
81.1(37.9)
21.4(11.7)
INF
43 (35.1)
23.6(12.1)
94.3(43.8)
Mean
45.2(35.8)
84.1(36.9)
22.8(10.4)
P value
0.000﹙＜0.0001﹚△
0.000﹙＜0.0001﹚●
0.000﹙＜0.0001﹚△
0.000﹙＜0.0001﹚●
0.000﹙＜0.0001﹚△
0.000﹙＜0.0001﹚●
0.000﹙＜0.0001﹚△
0.000﹙＜0.0001﹚●
0.000﹙＜0.0001﹚△
0.000﹙＜0.0001﹚●
0.000﹙＜0.0001﹚△
0.000﹙＜0.0001﹚●
0.000﹙＜0.0001﹚△
0.000﹙＜0.0001＝●
0.000﹙＜0.0001﹚△
0.000﹙＜0.0001﹚●
△ P value for the comparison of SS FIESTA and IR GRE sequences
● P value for the comparison of 3D IR FGRE and IR GRE sequences
Figure A. Comparison of the image qualities of the three free breathing sequences, SS FIESTA, 3D IR FGRE and
IR GRE. The cardiac fine structures were unclear in 3D IR FGRE images with more artifacts, and the diaphragm
(narrow short arrow) and intrapulmonary large vessel (long arrow) had significant motion artifacts. The pulmonary
vessel was not revealed clearly in IR FGRE. Figure B. Under the breath hold condition, IR FGRE and SS FIESTA
clearly displayed the myocardium (white arrow) and the border of papillary muscle (black arrow), while 3D IR
FGRE had artifacts. Figure C. Comparison of the three sequences, IR FGRE, SS FIESTA and 3D IR FGRE, in the
volume and area of revealed myocardial infarction (long white arrow indicated the anterior interventricular septum,
and short black arrow indicated the left ventricular inferior wall and inner wall). Statistical analysis showed that
there were no statistically significant differences between IR FGRE sequence and other sequences. Figure D.
Compared with other sequences, 3D IR-FGRE displayed the subendocardial myocardial infarction (black
arrowhead) more clearly.
Discussion
Contrast-enhanced cardiac MR images can reveal acute or chronic myocardial
lesions well due to its high resolution [13]. Therefore, contrast-enhanced cardiac MRI
is often used in clinical practice as the gold standard for the diagnosis of myocardial
infarction. In particular, it can reveal micro-subendocardial myocardial infarction, and
can measure the infarct size and volume [14], predict the functional recovery of
lesioned myocardium [15], guide revascularization therapy and accurately determine
the disease progression of patients [16]. In this study, we compared the myocardium
with delayed enhancement in the re-examinations for 14 myocardial ischemia cases 3
months after the initial surgery of coronary artery bypass graft and bone marrow stem
cell transplantation and determined that the lesions showed varying degrees of
improvement as compared with those three months ago.
However, the bottleneck of cardiac MRI is the lengthy scan time, preventing it
being used widely in clinical applications, especially for those suffering from severe
heart disease and unable to cope with breath holding. Traditional IR FGRE is
two-dimensional inversion recovery fast gradient echo sequence. Its advantages
include high image spatial resolution and high CNRem/myo, facilitating the clear
visualization of lesion. Its disadvantage is that repeated scans are required to collect
multiple sets of data when scanning the entire left ventricle, the total scan time is too
long, and satisfactory image quality can not be obtained for patients having trouble to
hold breath [16].
Single-shot FIESTA (GE company) is an ultra-fast pulse train and its signal
mainly consists of spin-echo signal weights. The imaging principle of this sequence is
similar to spin-echo without spin refocusing in the excitation process. This principle is
in contrast to that of the spoiled gradient echo sequence. In order to correct proton
dephasing caused by spatial encoding gradient field and phase drift caused by flow,
after the acquisition of each echo, FIESTA applies a corresponding gradient field with
the same gradient strength and time integration and the opposite direction at the slice
selection phase, the phase encoding phase and the frequency encoding phase. When
selecting a very short repetition time (TR) and large flip angle (FA), the lateral and
longitudinal magnetization vectors achieve true steady state [17]. The SS FIESTA
pulse sequence in this study used a very short TR (3.3 ms) and a single shot FA
(350-750), transformed the the original T2-weighted image into the T1-weighted, and
then inverted to null the myocardium. At this point, the normal myocardium signal is
black, while the myocardial lesions present high signal.
After FIESTA sequences were routinely used in movie sequences of cardiac
MRI examination [18], Kim [15] and Simonetti [19] improved the application of FIESTA
in T1-weighted enhanced sequences of infarcted myocardium, and obtained strong
T1-weighted images. Simonetti compared 10 pulse sequences and found that contrast
enhanced images of myocardial infarction from the FIESTA sequence had the
strongest signal strength, which differs from our results. Our results showed that 3D
IR FGRE sequence had the strongest signal strength of myocardial infarction. But in
the current literature, the FIESTA sequence is considered to be the fastest sequence
with the best image quality [41520-22]. It has been reported [7] that this sequence not only
can shorten the scan time (an average of 16 ± 3.2 seconds per slice, and the total scan
time of 10 minutes 13 ± 45 seconds), but also can accurately reflect the subacute and
acute myocardial infarct size. In this study, FIESTA sequence required 3-4 times of
breath hold per scan, each breath hold lasted for 7 ± 1.3 seconds, 3-4 slices of images
(an average of 1.7 ± 0.5 seconds per slice) were obtained, the total scan time was 27.6
± 1.8 seconds, and the delayed scan speed was significantly improved.
After comparing the SS FIESTA, 3D IR FGRE and IR FGRE sequences, this
study proved that the three sequences were all feasible to act as MDE methods to
reveal various myocardial segments. SS FIESTA, which is a fast sequence, has the
scan time only ¼ of the conventional sequence (IR FGRE sequence), without showing
statistically significant differences in the size and the percentage of infarcted
myocardium as compared with IR FGRE. This is consistent with the related reports
[23]
. Compared with IR FGRE sequence, SS FIESTA sequence could lead to images of
high quality in many aspects. However, the size and percentage of myocardium with
delayed enhancement were high, which may be due to the fact that SS FIESTA
sequence has higher SNR and CNR, thus displaying more clearly the border between
myocardium and lesion. High SNR can increase spatial resolution and shorten the
scan time. High CNR can better reveal the myocardial edge and fine structure of the
heart, and help to identify small lesions. Therefore, high SNR and CNR are very
important for cardiac MRI [7]. Our results showed that compared with the IR FGRE
sequence, SS FIESTA sequence did not show statistically significant differences in
SNRmyo, SNRbp, and CNRl/bg.
The most prominent feature of 3D IR FGRE sequence is its short total inspection
time, and one breath hold (with multiple cardiac cycles) is sufficient for data
collection on the entire left ventricle. Images are of thin slices (5 mm), with high
myocardial noise SNR, can more clearly show small lesions and also can be used for a
comprehensive understanding of myocardial scar. The study found that 3D IR FGRE
sequence had the highest SNR and CNR among the three sequences, and could clearly
reveal subendocardial myocardial infarction[24]. However, excessively long
breath-hold time and acquisition time often lead to failed scan and more artifacts in
the images, therefore limiting its clinical application. Our results also showed that this
sequence required a breath-hold time of 30 seconds, which is difficult even for people
with normal respiratory function, not to mention in patients with abnormal cardiac
function. It has been reported [25-26] that 3D IR FGRE sequences can shorten the
acquisition time without affecting the image quality and diagnostic accuracy by using
a variety of improved technologies and image reconstruction method.
For studies using delayed enhancement scan sequence, the selection of the best
inversion time (TI) is crucial for delayed scan [5]: the TI value for the scanning of this
group of cases was in general set to start from 200 ms, and increased by 50 ms after
scanning one sequence.
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