title: Statistical assessment of bi-exponential diffusion weighted imaging signal characteristics induced by intravoxel incoherent motion in malignant breast tumors.
abstract: BACKGROUND
  The purpose of this study is to statistically assess whether bi-exponential intravoxel incoherent motion (IVIM) model better characterizes diffusion weighted imaging (DWI) signal of malignant breast tumor than mono-exponential Gaussian diffusion model.
  
  
  METHODS
  3 T DWI data of 29 malignant breast tumors were retrospectively included. Linear least-square mono-exponential fitting and segmented least-square bi-exponential fitting were used for apparent diffusion coefficient (ADC) and IVIM parameter quantification, respectively. F-test and Akaike Information Criterion (AIC) were used to statistically assess the preference of mono-exponential and bi-exponential model using region-of-interests (ROI)-averaged and voxel-wise analysis.
  
  
  RESULTS
  For ROI-averaged analysis, 15 tumors were significantly better fitted by bi-exponential function and 14 tumors exhibited mono-exponential behavior. The calculatedADC,D(true diffusion coefficient) andf(pseudo-diffusion fraction) showed no significant differences between mono-exponential and bi-exponential preferable tumors. Voxel-wise analysis revealed that 27 tumors contained more voxels exhibiting mono-exponential DWI decay while only 2 tumors presented more bi-exponential decay voxels.ADCwas consistently and significantly larger thanDfor both ROI-averaged and voxel-wise analysis.
  
  
  CONCLUSIONS
  Although the presence of IVIM effect in malignant breast tumors could be suggested, statistical assessment shows that bi-exponential fitting does not necessarily better represent the DWI signal decay in breast cancer under clinically typical acquisition protocol and signal-to-noise ratio (SNR). Our study indicates the importance to statistically examine the breast cancer DWI signal characteristics in practice.
authors.affiliation: Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, Hong Kong, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Yuan
authors.affiliation: Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, Hong Kong, China.
authors.forename: Oi Lei
authors.initials: OL
authors.lastname: Wong
authors.affiliation: Department of Diagnostic and Interventional Radiology, Hong Kong Sanatorium & Hospital, Hong Kong, China.
authors.forename: Gladys G
authors.initials: GG
authors.lastname: Lo
authors.affiliation: Department of Diagnostic and Interventional Radiology, Hong Kong Sanatorium & Hospital, Hong Kong, China.
authors.forename: Helen H L
authors.initials: HH
authors.lastname: Chan
authors.affiliation: Breast Care Centre, Hong Kong Sanatorium & Hospital, Happy Valley, Hong Kong, China.
authors.forename: Ting Ting
authors.initials: TT
authors.lastname: Wong
authors.affiliation: Breast Care Centre, Hong Kong Sanatorium & Hospital, Happy Valley, Hong Kong, China.
authors.forename: Polly S Y
authors.initials: PS
authors.lastname: Cheung
keywords: Breast cancer; apparent diffusion coefficient (ADC); diffusion weighted imaging (DWI); intravoxel incoherent motion (IVIM); magnetic resonance imaging (MRI)