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World J Gastroenterol. Oct 14, 2008; 14(38): 5893-5899
Published online Oct 14, 2008. doi: 10.3748/wjg.14.5893
Effect of b value on monitoring therapeutic response by diffusion-weighted imaging
Zhao-Xia Jiang, Wei-Jun Peng, Wen-Tao Li, Feng Tang, Shi-Yuan Liu, Xu-Dong Qu, Jian-Hua Wang, Hong-Feng Lu
Zhao-Xia Jiang, Wei-Jun Peng, Wen-Tao Li, Feng Tang, Department of Radiology, Affiliated Cancer Hospital of Fudan University, Shanghai 200032, China
Zhao-Xia Jiang, Wei-Jun Peng, Wen-Tao Li, Feng Tang, Department of Oncology, Shanghai Medical College, Fudan University, Shanghai 200032, China
Shi-Yuan Liu, Department of Radiology, Affiliated Changzheng Hospital of the Second Military Medical University, Shanghai 200032, China
Xu-Dong Qu, Jian-Hua Wang, Department of Radiology, Affiliated Zhongshan Hospital of Fudan University, Shanghai 200032, China
Hong-Feng Lu, Department of Pathology, Affiliated Cancer Hospital of Fudan University, Shanghai 200032, China
Author contributions: Jiang ZX, Peng WJ designed the research; Jiang ZX, Li WT, Liu SY, Qu XD and Wang JH performed the research; Jiang ZX, Tang F and Lu HF analyzed data; Jiang ZX wrote the manuscript; Peng WJ revised the paper.
Supported by The National Natural Science Foundation of China, NO. 30470503; The Key Program of Shanghai Science and Technology Commission, NO. 04JC14074; The Foundation of Shanghai Educational commission, NO. 03J405037
Correspondence to: Wei-Jun Peng, Department of Radiology, Affiliated Cancer Hospital of Fudan University, 270 Dong’an Road, Shanghai 200032, China. weijunpeng@yahoo.com
Telephone: +86-21-64433384 Fax: +86-21-64433384
Received: July 7, 2008
Revised: August 26, 2008
Accepted: September 2, 2008
Published online: October 14, 2008
Abstract

AIM: To explore the diffusion gradient b-factor that optimizes both apparent diffusion coefficient (ADC) measurement and contrast-to-noise (CNR) for assessing tumor response to transarterial chemoembolization (TACE) in a rabbit model.

METHODS: Twelve New Zealand white rabbits bearing VX2 tumors in the liver were treated with TACE. Diffusion-weighted imaging (DWI) with various b values was performed using the same protocol before and 3 d after treatment with TACE. ADC values and CNR of each tumor pre- and post-treatment with different b factors were analyzed. Correlation between ADC values and extent of necrosis in histological specimens was analyzed by a Pearson’s correlation test.

RESULTS: The quality of diffusion-weighted images diminished as the b value increased. A substantial decrease in the mean lesion-to-liver CNR was observed on both pre- and post-treatment DW images, the largest difference in CNR pre- and post-treatment was manifested at a b value of 1000 s/mm2 (P = 0.036 ). The effect of therapy on diffusion early after treatment was shown by a significant increase in ADCs (P = 0.007), especially with large b factors (≥ 600 s/mm2). The mean percentage of necrotic cells present within the tumor was 76.3%-97.5%. A significant positive correlation was found between ADC values and the extent of necrosis with all b values except for b200, a higher relative coefficient between ADC values and percentage of necrosis was found on DWI with b1000 and b2000 (P = 0.002 and 0.006, respectively).

CONCLUSION: An increasing b value of up to 600 s/mm2 would increase ADC contrast pre- and post-treatment, but decrease image quality. Taking into account both CNR and ADC measurement, diffusion-weighted imaging obtained with a b value of 1000 s/mm2 is recommended for monitoring early hepatic tumor response to TACE.

Keywords: Hepatic carcinoma; Diffusion-weighted MR; Treatment response; Apparent diffusion coefficient