Investig Magn Reson Imaging.  2018 Mar;22(1):1-9. 10.13104/imri.2018.22.1.1.

Optimization of the Flip Angle and Scan Timing in Hepatobiliary Phase Imaging Using T1-Weighted, CAIPIRINHA GRE Imaging

• Kim J
• Kim BS
• Lee JS
• Woo ST
• Choi GM
• Kim SH
• Lee HK
• Lee MS
• Lee KR
• Park JH

• KMID: 2408812
• DOI: http://doi.org/10.13104/imri.2018.22.1.1

Abstract

PURPOSE
This study was designed to optimize the flip angle (FA) and scan timing of the hepatobiliary phase (HBP) using the 3D T1-weighted, gradient-echo (GRE) imaging with controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA) technique on gadoxetic acid-enhanced 3T liver MR imaging.
MATERIALS AND METHODS
Sixty-two patients who underwent gadoxetic acid-enhanced 3T liver MR imaging were included in this study. Four 3D T1-weighted GRE imaging studies using the CAIPIRINHA technique and FAs of 9° and 13° were acquired during HBP at 15 and 20 min after intravenous injection of gadoxetic acid. Two abdominal radiologists, who were blinded to the FA and the timing of image acquisition, assessed the sharpness of liver edge, hepatic vessel clarity, lesion conspicuity, artifact severity, and overall image quality using a five-point scale. Quantitative analysis was performed by another radiologist to estimate the relative liver enhancement (RLE) and the signal-to-noise ratio (SNR). Statistical analyses were performed using the Wilcoxon signed rank test and one-way analysis of variance.
RESULTS
The scores of the HBP with an FA of 13° during the same delayed time were significantly higher than those of the HBP with an FA of 9° in all the assessment items (P < 0.01). In terms of the delay time, images at the same FA obtained with a 20-min-HBP showed better quality than those obtained with a 15-min-HBP. There was no significant difference in qualitative scores between the 20-min-HBP and the 15-min-HBP images in the non-liver cirrhosis (LC) group except for the hepatic vessel clarity score with 9° FA. In the quantitative analysis, a statistically significant difference was found in the degree of RLE in the four HBP images (P = 0.012). However, in the subgroup analysis, no significant difference in RLE was found in the four HBP images in either the LC or the non-LC groups. The SNR did not differ significantly in the four HBP images. In the subgroup analysis, 20-min-HBP imaging with a 13° FA showed the highest SNR value in the LC-group, whereas 15-min-HBP imaging with a 13° FA showed the best value of SNR in the non-LC group.
CONCLUSION
The use of a moderately high FA improves the image quality and lesion conspicuity on 3D, T1-weighted GRE imaging using the CAIPIRINHA technique on gadoxetic acid, 3T liver MR imaging. In patients with normal liver function, the 15-min-HBP with a 13° FA represents a feasible option without a significant decrease in image quality.

Keyword

Magnetic resonance imaging/methods; Contrast media; Gadolinium DTPA; Breath holding; Imaging; Three-dimensional/method

MeSH Terms

Acceleration
Artifacts
Breath Holding
Contrast Media
Fibrosis
Gadolinium DTPA
Humans
Injections, Intravenous
Liver
Magnetic Resonance Imaging
Signal-To-Noise Ratio
Contrast Media
Gadolinium DTPA

Figure

• 

  Fig. 1. Graphs (signal intensity and contrast-to-noise ratio [CNR] to flip angle) of water, fat, and gadoxetic acid obtained from an in-vitro phantom. Changing the flip angle affects the signal intensity of water, fat, and gadoxetic acid (a, b). The shape of a water curve shows a specific flip angle at 6 degrees, which produces maximum signal intensity (a). The signal intensity of water converges with fat at 14 degrees (a, b). The CNR between gadoxetic acid and water is increased by raising the flip angle 12.4% per degree (b).

• 

  Fig. 2. MR images of a 44-year-old woman with a history of breast cancer and normal liver function. Four hepatobiliary phase (HBP), gadoxetic acid-enhanced 3D-gradient echo (GRE) images using the CAIPIRINHA technique obtained at 20 min (a) and 15 min (b) after contrast injection with a 13° flip angle (FA) and at 20 min (c) and 15 min (d) after contrast injection with 9° FA. Moderately high flip angle HBP images (a, b) showed the best delineation of intrahepatic vessels, compared with standard flip angle HBP images (c, d). At moderately high flip angle HBP images (a, b), intrahepatic vessels (arrow) were well defined with low signal intensity. The background liver showed high signal intensity due to enhanced, normal parenchyma, resulting in excellent conspicuity. The relative liver enhancement was highest with transverse, T1-weighted 3D-GRE images obtained 15 min after contrast injection with a 13° FA (b), followed by T1-weighted, 3D-GRE images obtained 20 min after contrast injection with a 13° FA (a), T1-weighted, 3D-GRE images obtained 20 min after contrast injection with a 9° FA (c), and T1-weighted, 3D-GRE images obtained 15 min after contrast injection with a 9° FA (d).

• 

  Fig. 3. MR images of a 70-year-old man with liver cirrhosis (Child-Pugh class: A) show hepatocellular carcinoma (arrow). Four hepatobiliary phase (HBP), gadoxetic acid-enhanced, 3D-gradient echo (GRE) images using the CAIPIRINHA technique obtained at 20 min (a) and 15 min (b) after contrast injection with 13° flip angle (FA) and at 20 min (c) and 15 min (d) after contrast injection with 9° FA. Moderately high flip angle HBP images (a, b) demonstrate clearly defined hepatocellular carcinoma. The fine intrahepatic vasculatures (short arrow) are well defined in moderately high flip angle HBP images (a, b).

Reference

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