A potential risk of overestimating apparent diffusion coefficient in parotid glands.
OBJECTIVE
To investigate transient signal loss on diffusion weighted images (DWI) and overestimation of apparent diffusion coefficient (ADC) in parotid glands using single shot echoplanar DWI (EPDWI).


METHODS
This study enrolled 6 healthy subjects and 7 patients receiving radiotherapy. All participants received dynamic EPDWI with a total of 8 repetitions. Imaging quality of DWI was evaluated. Probability of severe overestimation of ADC (soADC), defined by an ADC ratio more than 1.2, was calculated. Error on T2WI, DWI, and ADC was computed. Statistical analysis included paired Student t testing and Mann-Whitney U test. A P value less than 0.05 was considered statistically significant.


RESULTS
Transient signal loss was visually detected on some excitations of DWI but not on T2WI or mean DWI. soADC occurred randomly among 8 excitations and 3 directions of diffusion encoding gradients. Probability of soADC was significantly higher in radiotherapy group (42.86%) than in healthy group (24.39%). The mean error percentage decreased as the number of excitations increased on all images, and, it was smallest on T2WI, followed by DWI and ADC in an increasing order.


CONCLUSIONS
Transient signal loss on DWI was successfully detected by dynamic EPDWI. The signal loss on DWI and overestimation of ADC could be partially remedied by increasing the number of excitations.
Department of Automatic Control Engineering, Feng Chia University, Taichung, Taiwan, Republic of China.
Yi-Jui
YJ
Liu
Ph.D. program in Electrical and Communication Engineering in Feng Chia University, Taichung, Taiwan, Republic of China; Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
Yi-Hsiung
YH
Lee
Brain Imaging and Analysis Center, Duke University Medical Center, Durham, North Carolina, United States of America; Applied Science Laboratory, GE Healthcare, Taipei, Taiwan.
Hing-Chiu
HC
Chang
Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan, Republic of China.
Teng-Yi
TY
Huang
Ph.D. program of Technology Management, Chung Hua University, Hsinchu, Taiwan, Republic of China.
Hui-Chu
HC
Chiu
Department of Radiology, National Defense Medical Center, Taipei, Taiwan, Republic of China; Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
Chih-Wei
CW
Wang
Department of Medicine, Taipei Medical University, Taipei, Taiwan, Republic of China.
Ta-Wei
TW
Chiou
Department of Dentistry, National Defense Medical Center, Taipei, Taiwan, Republic of China.
Kang
K
Hsu
Department of Radiology, National Defense Medical Center, Taipei, Taiwan, Republic of China; Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
Chun-Jung
CJ
Juan
Department of Radiology, National Defense Medical Center, Taipei, Taiwan, Republic of China; Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
Guo-Shu
GS
Huang
Department of Radiology, National Defense Medical Center, Taipei, Taiwan, Republic of China; Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
Hsian-He
HH
Hsu
D000328:Adult; D016022:Case-Control Studies; D038524:Diffusion Magnetic Resonance Imaging; D017352:Echo-Planar Imaging; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D010306:Parotid Gland / Q000000981:diagnostic imaging* / Q000473:pathology; D011859:Radiography; D012306:Risk