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

Jeongjae Kim; Bong Soo Kim; Jeong Sub Lee; Seung Tae Woo; Guk Myung Choi; Seung Hyoung Kim; Ho Kyu Lee; Mu Sook Lee; Kyung Ryeol Lee; Joon Hyuk Park

doi:10.13104/imri.2018.22.1.1

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Kim, Kim, Lee, Woo, Choi, Kim, Lee, Lee, Lee, and Park: Optimization of the Flip Angle and Scan Timing in Hepatobiliary Phase Imaging Using T1-Weighted, CAIPIRINHA GRE Imaging

Original Article

iMRI 2018;22(1):1-9.

Published online: 12 January 2018

DOI: https://doi.org/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

Jeongjae Kim¹, Bong Soo Kim¹, Jeong Sub Lee¹, Seung Tae Woo², Guk Myung Choi¹, Seung Hyoung Kim¹, Ho Kyu Lee¹, Mu Sook Lee¹, Kyung Ryeol Lee¹, Joon Hyuk Park³

^¹Department of Radiology, Jeju National University Hospital, Jeju, Korea

^²Radiology Division, Bayer Healthcare, Seoul, Korea

^³Department of Psychiatry, Jeju National University Hospital, Jeju, Korea

Correspondence to: Bong Soo Kim, M.D. Department of Radiology, Juju National University Hospital, Jeju National University School of Medicine, 15, Aran 13-gil, Jeju-si, Jeju Special Self-governing Province 63241, Korea. Tel. +82-64-717-1373 Fax. +82-64-717-1372 E-mail: 671228kbs@naver.com

Received 28 August 2017 Revised 9 November 2017 Accepted 28 November 2017

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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.

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

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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).

Table 1.

Results of the Qualitative Analysis: Comparison of the Hepatobiliary Phases at Different Flip Angles and Delayed Times

Quality parameter	Flip angle and delayed time				P value
	Flip angle and delayed time				Same flip angle		Same delayed time		Different flip angle and delayed time
	20 min 13°	15 min 13°	20 min 9°	15 min 9°	20 min 13° vs. 15 min 13°	20 min 9° vs. 15 min 9°	20 min 13° vs. 20 min 9°	15 min 13° vs. 15 min 9°	15 min 13° vs. 20 min 9°	20 min 13° vs. 13 min 9°
Liver edge sharpness
Total	4.77	4.69	4.63	4.54	0.083	0.047*	0.001*	0.001*	0.288	0.000*
LC	4.76	4.64	4.55	4.47	0.021*	0.084	0.011*	0.001*	0.185	0.000*
Non-LC	4.78	4.76	4.76	4.64	0.854	0.236	0.034*	0.564	1.000	0.272
Hepatic vessel clarity
Total	4.50	4.33	4.07	3.88	0.001*	0.004*	0.000*	0.000*	0.001*	0.000*
LC	4.43	4.24	3.93	3.80	0.003*	0.04*	0.000*	0.000*	0.005*	0.000*
Non-LC	4.62	4.46	4.28	4.00	0.143	0.04*	0.000*	0.002*	0.103*	0.001*
Lesion conspicuity
Total	4.73	4.58	4.26	4.13	0.003*	0.008*	0.000*	0.000*	0.000*	0.000*
LC	4.64	4.42	4.08	3.96	0.005*	0.034*	0.000*	0.000*	0.003*	0.000*
Non-LC	4.92	4.89	4.62	4.46	0.317	0.102	0.009*	0.025*	0.02*	0.01*
Artifact severity
Total	4.48	4.40	4.33	4.25	0.223	0.194	0.005*	0.001*	0.119	0.002*
LC	4.42	4.32	4.22	4.21	0.257	0.655	0.06	0.004*	0.057	0.005*
Non-LC	4.56	4.48	4.50	4.32	0.518	0.244	0.023*	0.083	0.891	0.098
Overall image quality
Total	4.60	4.48	4.31	4.23	0.041*	0.073	0.000*	0.000*	0.001*	0.000*
LC	4.55	4.42	4.18	4.13	0.029*	0.157	0.000*	0.000*	0.001*	0.000*
Non-LC	4.66	4.58	4.50	4.38	0.51	0.236	0.004*	0.011	0.219	0.024*

* P < 0.05

LC = liver cirrhosis

Table 2.

Results of Quantitative Analysis: Comparison of the Hepatobiliary Phase at Different Flip Angles and Times

Parameter	Flip angle and delayed time				P value
Parameter	20 min 13°	15 min 13°	20 min 9°	15 min 9°	P value
Relative liver enhancement
Total	0.9141 ± 0.3751	0.8819 ± 0.3454	0.7683 ± 0.3006	0.7546 ± 0.2782	0.012*
LC	0.9123 ± 0.3577	0.8760 ± 0.3307	0.7639 ± 0.9258	0.7515 ± 0.2800	0.073
Non-LC	0.9168 ± 0.4070	0.8906 ± 0.3728	0.7748 ± 0.3140	0.7593 ± 0.2812	0.272
SNR of the liver parenchyma
Total	251.06 ± 78.62	245.51 ± 72.69	239.76 ± 28.28	239.72 ± 60.89	0.757
LC	245.84 ± 86.75	232.49 ± 73.48	232.41 ± 56.00	236.84 ± 67.71	0.836
Non-LC	258.79 ± 65.71	264.78 ± 68.42	250.62 ± 61.01	243.98 ± 50.15	0.652

* P < 0.05

LC = liver cirrhosis; SNR = signal-to-noise ratio

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