Field strength and diffusion encoding technique affect the apparent diffusion coefficient measurements in diffusion-weighted imaging of the abdomen
Dale, B.M.; Braithwaite, A.C.; Boll, D.T.; Merkle, E.M.
Investigative Radiology 45(2): 104-108
The purpose of this study is to determine what effects a variety of diffusion encoding techniques at 1.5 T and 3 T have on measured abdominal apparent diffusion coefficient (ADC) values obtained in a healthy population. Sixteen healthy male volunteers were enrolled in this prospective Institutional Review Board-approved study following written informed consent. Imaging was performed on a 1.5 T and a 3 T magnetic resonance system (Siemens, Erlangen) with several abdominal axial diffusion weighted imaging (DWI) acquisitions: an orthogonal diffusion encoding with b-values of 0/400 seconds/mm, and a series of four 3-scan trace weighted acquisitions with b-values of 0/50, 0/400, 0/800, 0/50/400/800 seconds/mm, respectively. The mean ADC values were calculated for 3 regions of interest (ROI) in 5 locations (right hepatic lobe, spleen, pancreatic head, body, and tail). The ADC data were analyzed using a repeated-measures analysis of variance. There was a significant difference between measured ADC values at 1.5 T and 3 T for liver (P < 0.001), but not for pancreas (P = 0.427) or spleen (P = 0.167). There was no significant difference (P > 0.999) in the measured ADC values between the orthogonal encodings and the 3-scan trace weighted encoding with the same b-value. There were significant differences (P < 0.001) between all 4 weighting schemes for the 3-scan trace with the measured ADC decreasing with increasing b-value. Measured abdominal ADC values depend on the exact selection of b-value used for encoding for liver, pancreas, and spleen. In addition, the measured ADC values depend on the field strength of the scanner for liver.