Korean J Radiol.  2018 Apr;19(2):247-255. 10.3348/kjr.2018.19.2.247.

Self-Gated Late Gadolinium Enhancement at 7T to Image Rats with Reperfused Acute Myocardial Infarction

• Wang L
• Chen Y
• Zhang B
• Chen W
• Wang C
• Song L
• Xu Z
• Zheng J
• Gao F

• KMID: 2404921
• DOI: http://doi.org/10.3348/kjr.2018.19.2.247

Abstract

OBJECTIVE
A failed electrocardiography (ECG)-trigger often leads to a long acquisition time (TA) and deterioration in image quality. The purpose of this study was to evaluate and optimize the technique of self-gated (SG) cardiovascular magnetic resonance (CMR) for cardiac late gadolinium enhancement (LGE) imaging of rats with myocardial infarction/reperfusion.
MATERIALS AND METHODS
Cardiovascular magnetic resonance images of 10 rats were obtained using SG-LGE or ECG with respiration double-gating (ECG-RESP-gating) method at 7T to compare differences in image interference and TA between the two methods. A variety of flip angles (FA: 10°-80°) and the number of repetitions (NR: 40, 80, 150, and 300) were investigated to determine optimal scan parameters of SG-LGE technique based on image quality score and contrast-to-noise ratio (CNR).
RESULTS
Self-gated late gadolinium enhancement allowed successful scan in 10 (100%) rats. However, only 4 (40%) rats were successfully scanned with the ECG-RESP-gating method. TAs with SG-LGE varied depending on NR used (TA: 41, 82, 154, and 307 seconds, corresponding to NR of 40, 80, 150, and 300, respectively). For the ECG-RESP-gating method, the average TA was 220 seconds. For SG-LGE images, CNR (42.5 ± 5.5, 43.5 ± 7.5, 54 ± 9, 59.5 ± 8.5, 56 ± 13, 54 ± 8, and 41 ± 9) and image quality score (1.85 ± 0.75, 2.20 ± 0.83, 2.85 ± 0.37, 3.85 ± 0.52, 2.8 ± 0.51, 2.45 ± 0.76, and 1.95 ± 0.60) were achieved with different FAs (10°, 15°, 20°, 25°, 30°, 35°, and 40°, respectively). Optimal FAs of 20°-30° and NR of 80 were recommended.
CONCLUSION
Self-gated technique can improve image quality of LGE without irregular ECG or respiration gating. Therefore, SG-LGE can be used an alternative method of ECG-RESP-gating.

Keyword

Self-gated; Myocardial infarction; Flip angle; MRI; Late gadolinium enhancement; Animal studies; 7T

MeSH Terms

Animals
Electrocardiography
Gadolinium*
Magnetic Resonance Imaging
Methods
Myocardial Infarction*
Rats*
Respiration
Gadolinium

Figure

• 

  Fig. 1 Schematic summary of MRI protocol.Series of SG images were obtained after gadolinium injection, each with various FA. Last series of images with FAs of 20°–30° were used to select optimal FA images to yield best scar contrast. This FA was then used to perform subsequent SG FLASH imaging between 5–20 minutes after contrast agent administration. FISP-cine-Gate was then obtained following SG-FLASH-cine. ECG = electrocardiography, FA = flip angle, FISP = fast imaging with steady-state precession, FLASH = fast low angle shot MRI, LGE = late gadolinium enhancement, SG = self-gated

• 

  Fig. 2 SG-cine-LGE images (top) and ECG-gated-LGE images (bottom) are shown from three different rats.(A) and (E) are superb images after contrast agent injection whose scores were 4. (B) and (F) show a few artifacts that would not affect analysis results whose scores were 4. (C) and (G) were samples that ECG-gated technique could not show good enough images whose score was 1 while good images from SG sequence whose score was 3. (H) was triphenyl tetrazolium chloride staining demonstrating that infarction zone (in white or light pink color) was in anterior-lateral, lateral, and posterior-lateral wall of myocardium in (H), in good agreement with SG-LGE in (D). Black arrows (G) indicate flow and susceptibility artifacts in ECG-gated image which disappeared in SG image (C).

• 

  Fig. 3 Varying FA on LGE images are shown for three different rats.In left column, images (A, D, G) had FA of 10°. In middle column, images (B, E, H) had FAs of 20°–30°. In right column, images (C, F, I) had high FA of 60°–80°.

• 

  Fig. 4 Likert scale of SG sequence according to FAsQualitative grade was higher when FA was 20° to 30°. Qualities were minimized with lower or greater FA.

• 

  Fig. 5 Image quality and scan time varied with NR.(A-D) had NR of 40, 80, 150, and 300, respectively, with FA of 25°. Scan time was increased with increasing NR. NR = number of repetitions, L = Likert scale score, TA = acquisition time

• 

  Fig. 6 CNR according to FA and delay time.Both delay time and FA were critical factors that affected CNRs of SG-LGE images. SG-LGE images were acquired within 2 minutes due to sequence preparation and TA for each SG scan. FA (bottom x-axis) was 10°, 15°, 20°, 25°, 30°, 35°, and 40°, corresponding to delay time (top x-axis) of 2, 4, 6, 8, 10, 12, and 14 minutes, respectively. CNR was increased rapidly to maximum values when FAs were 20° to 30° accompanied by delay time of 6 to 10 minutes. CNR = contrast-to-noise ratio

• 

  Fig. 7 Simulation of ΔT1 values under various FAs.Vertical axis ΔT1 values refer to deviations of T1 values between normal myocardium and infarction regions. They can be plotted as function of FA. Circle hollow plot: MI T1 = 100 msec; square hollow plot: MI T1 = 244 msec. MI = myocardial infarction

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