In vivo assessment of optimal b-value range for perfusion-insensitive apparent diffusion coefficient imaging.
OBJECTIVE
To assess the optimal b-values range for perfusion-insensitive apparent diffusion coefficient (ADC) imaging of abdominal organs using short-duration DW-MRI acquisitions with currently available ADC estimation methods.


METHODS
DW-MRI data of 15 subjects were acquired with eight b-values in the range of 5-800 s∕mm(2). The reference-standard, a perfusion insensitive, ADC value (ADC(IVIM)), was computed using an intravoxel incoherent motion (IVIM) model with all acquired diffusion-weighted images. Simulated DW-MRI data was generated using an IVIM model with b-values in the range of 0-1200 s∕mm(2). Monoexponential ADC estimates were calculated using: (1) Two-point estimator (ADC(2)); (2) least squares three-point (ADC(3)) estimator and; (3) Rician noise model estimator (ADC(R)). The authors found the optimal b-values for perfusion-insensitive ADC calculations by minimizing the relative root mean square error (RRMS) between the ADC(IVIM) and the monoexponential ADC values for each estimation method and organ.


RESULTS
Low b-value = 300 s∕mm(2) and high b-value = 1200 s∕mm(2) minimized the RRMS between the estimated ADC and the reference-standard ADC(IVIM) to less than 5% using the ADC(3) estimator. By considering only the in vivo DW-MRI data, the combination of low b-value = 270 s∕mm(2) and high b-value of 800 s∕mm(2) minimized the RRMS between the estimated ADC and the reference-standard ADC(IVIM) to <7% using the ADC(3) estimator. For all estimators, the RRMS between the estimated ADC and the reference standard ADC correlated strongly with the perfusion-fraction parameter of the IVIM model (r = [0.78-0.83], p ≤ 0.003).


CONCLUSIONS
The perfusion compartment in DW-MRI signal decay correlates strongly with the RRMS in ADC estimates from short-duration DW-MRI. The impact of the perfusion compartment on ADC estimations depends, however, on the choice of b-values and estimation method utilized. Likewise, perfusion-related errors can be reduced to <7% by carefully selecting the b-values used for ADC calculations and method of estimation.
Moti Freiman, Computational Radiology Laboratory, Department of Radiology, Boston Children's Hospital, Harvard Medical School, 300 Longwood Avenue, Boston Massachusetts 02115, USA. moti.freiman@childrens.harvard.edu
Moti
M
Freiman
Stephan D
SD
Voss
Robert V
RV
Mulkern
Jeannette M
JM
Perez-Rossello
Michael J
MJ
Callahan
Simon K
SK
Warfield
D000005:Abdomen / Q000473:pathology*; D000293:Adolescent; D000328:Adult; D000465:Algorithms; D002648:Child; D003198:Computer Simulation; D003952:Diagnostic Imaging / Q000379:methods; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016018:Least-Squares Analysis; D016013:Likelihood Functions; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D015233:Models, Statistical; D010477:Perfusion; D015203:Reproducibility of Results