Xingmin Guan1,2, Yinyin Chen1,3,4, Hsin-Jung Yang1, and Rohan Dharmakumar1
1Cedars-Sinai Medical Center, Los Angeles, CA, United States, 2University of California, Los Angeles, Los Angeles, CA, United States, 3Radiology, Zhongshan Hospital, Fudan University, Shanghai, China, 4Medical Imaging, Shanghai Medical School, Shanghai Institute of Medical Imaging, Shanghai, China
Synopsis
Double
inversion recovery preparation is often used in T2* cardiac MRI to
acquire dark-blood images. We investigated the impact of dark-blood preparation on imaging of
intramyocardial hemorrhage in patients with acute MI at 1.5T. SNR and CNR were compared between dark-blood and bright-blood T2* weighted images. Hemorrhage size, T2* were evaluated and compared between methods. Inter-observer reliability were reported as intraclass correlation coefficients. Our
findings here support the notion that when choosing between bright-blood and
dark-blood T2* cardiac MRI for the determination of intramyocardial hemorrhage
in patients at 1.5T, bright-blood T2* cardiac MRI is likely the preferred
approach.
Introduction
Double
inversion recovery (DIR) preparation is often used in T2* cardiac MRI to
acquire dark-blood (DB) images. This magnetization preparation approach, which
suppresses the blood signal through DIR preparation, has been proven to be
beneficial for evaluating iron overload in Thalassemia patients since
dark-blood images provide a clearer border definition between the blood pool
and the myocardium [1]. For similar reasons, DIR prepared dark-blood T2* cardiac
MRI has been utilized for imaging intramyocardial hemorrhage as well. However, previous
studies from our group using large animal models at 3T has showed that contrast-to-noise
ratio for identifying intramyocardial hemorrhage is significantly reduced in
dark-blood T2* images compared to bright-blood T2* images [2]. In this study,
we investigated whether the dark-blood preparation compromises the diagnostic
capacity to detect intramyocardial hemorrhage in patients with acute MI at 1.5T.Methods
Following
informed consent, patients (n=5) with first ST-elevated myocardial infarction
(STEMI) who underwent successful percutaneous coronary intervention (PCI) were
prospectively enrolled and studied within 10 days after PCI. ECG-triggered,
breath-held T2* weighted bright-blood (BB) mGRE images (TE = 2.01, 3.83, 5.65,
7.47, 9.29, 11.11, 12.93, 14.75 ms), as well as slice-position-matched double-inversion-recovery
(DIR) prepared dark-blood (DB) T2* weighted mGRE images (same TEs) and LGE
images were acquired. Size of hemorrhage was estimated on both BB and DB T2*
weighted images (TE=14.75 ms) using the mean-2SD criterion by two expert
readers using CVI42. T2* values were measured from T2* maps which were
generated by pixel-wise exponential fitting. Intraclass correlation coefficients
(ICC) were calculated in SPSS. Signal-to-noise ratio (SNR) and contrast-to-noise
ratio (CNR) were calculated as:
$$SNR = \frac{SI_{myo}}{σ_{air}}$$
$$CNR = \frac{SI_{myo} - SI_{hemo}}{σ_{air}}$$
where SImyo is the signal intensity of remote myocardium, SIhemois the signal intensity of hemorrhage and σair is SD of background noise. Paired t-test was
used to compare the two methods and the differences were considered significant if p<0.05.Results
Table 1 details
some of the key clinical features of patients with STEMI. Figure 1 shows a case
example of a patient with hemorrhagic MI. Corresponding CNR and SNR
measurements averaged across all patients is shown in Figure 2. Consistent with
our past studies in animals, compared to bright-blood T2*-weighted images,
dark-blood images T2*-weighted images provided lower CNR and SNR between
hemorrhage and remote myocardium (CNR (between zone of hemorrhage and remote
myocardium): 36.45 ± 18.05 (DB) vs 49.09 ± 15.83 (BB), p<0.05; SNR (remote
myocardium): 149.04 ± 47.50 (DB) vs. 178.61 ± 47.75 (BB), p<0.01)).
Mean size of
hemorrhage measured from BB and DB imaging slices are reported in figure 3(A). The
size and T2* of hemorrhage were lower on dark-blood images (1.64 ± 0.84 cm2
(size); 16.30 ± 2.66 ms (T2*) compared to that on bright-blood images (1.93 ± 0.69
cm2 (size); 17.69 ± 3.58 ms (T2*)). T2* of remote myocardium estimated
using both methods were not statistically different (36.65 ± 4.26 ms (DB) vs 34.68
± 4.49 ms (BB)). Intraclass correlation coefficients (ICC) with 95% confidence
interval are shown in Table 2. ICC for hemorrhage size on dark-blood images (0.790)
was markedly lower than that on bright-blood images (0.903), which suggests
that bright-blood T2* images has greater reliability for identifying area of acute
reperfusion hemorrhage.Discussion
Double-inversion-recovery
dark-blood preparation will reduce image contrast on T2* images when used for
intramyocardial hemorrhage assessment in patients with acute MI at 1.5T. Our
previous studies showed that that the source of CNR loss stems from the signal
loss from double inversion and insufficient recovery time [3]. The loss of CNR
and SNR can lead to underestimation of hemorrhage size on dark-blood T2* images
compared to that on bright-blood T2* images and reduce inter-observer
reliability of hemorrhage identification. Conclusion
Our early
findings here support the notion that when choosing between bright-blood T2* and
dark-blood T2* cardiac MRI for the determination of intramyocardial hemorrhage
in patients at 1.5T, bright-blood T2* cardiac MRI appears to be the most
desirable approach.Acknowledgements
No acknowledgement found.References
[1]
G C Smith, J P Carpenter, T He, et al. Value of black blood T2* cardiovascular
magnetic resonance. JCMR, 2011.
[2] X Guan, H Yang, G Wang, et al. T2* based detection of
localized iron deposits in hemorrhagic myocardial infarction: the impact of
dark-blood preparation on image contrast. SCMR abstract, 2019
[3]
X Guan, X Zhang, J Sykes, et al. Image Contrast Loss in Double Inversion
Recovery Dark-blood T2* CMR of Intramyocardial Hemorrhage. SCMR abstract, 2020.