In vivo assessment of optimal b-value range for perfusion-insensitive apparent diffusion coefficient imaging
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Published on: April 7, 2015
Moti Freiman1, Stephan D Voss, Robert V Mulkern
1Moti 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
Purpose:
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.
Insights
Optimizing b-values in diffusion-weighted MRI (DW-MRI) is crucial for accurate apparent diffusion coefficient (ADC) imaging. Careful selection of b-values and estimation methods minimizes perfusion-related errors in abdominal organ ADC measurements.
Area of Science:
- Medical Imaging
- Radiology
- Biophysics
Background:
- Diffusion-weighted MRI (DW-MRI) is essential for assessing tissue microstructure.
- Apparent diffusion coefficient (ADC) quantification is sensitive to perfusion effects, especially in abdominal organs.
- Intravoxel Incoherent Motion (IVIM) modeling provides a reference standard for perfusion-insensitive ADC (ADC(IVIM)).
Purpose of the Study:
- To determine optimal b-value ranges for perfusion-insensitive ADC imaging in abdominal organs.
- To evaluate the performance of different ADC estimation methods with short DW-MRI acquisitions.
- To minimize relative root mean square error (RRMS) between estimated ADC and reference ADC(IVIM).
Main Methods:
- Acquired DW-MRI data from 15 subjects with b-values ranging from 5 to 800 s/mm².
- Computed reference ADC(IVIM) using a biexponential IVIM model.
- Generated simulated data and calculated monoexponential ADC estimates using two-point (ADC(2)), three-point (ADC(3)), and Rician noise model (ADC(R)) estimators.
- Minimized RRMS between ADC(IVIM) and monoexponential ADC estimates across various b-value combinations and organs.
Main Results:
- The ADC(3) estimator achieved <5% RRMS with simulated data using b-values of 300 and 1200 s/mm².
- For in vivo data, ADC(3) achieved <7% RRMS with b-values of 270 and 800 s/mm².
- All estimators showed a strong correlation between RRMS and the IVIM perfusion fraction (r = 0.78–0.83, p ≤ 0.003).
Conclusions:
- Perfusion significantly impacts ADC estimates in short-duration DW-MRI of abdominal organs.
- The choice of b-values and estimation method critically influences perfusion-related errors.
- Perfusion-induced errors in ADC can be reduced to below 7% through careful selection of b-values and estimation techniques.
