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Demonstration of nonlinearity bias in the measurement of the apparent diffusion coefficient in multicenter trials
Dariya I Malyarenko1, David Newitt2, Lisa J Wilmes2
1Radiology, University of Michigan, Ann Arbor, Michigan, USA.
Purpose:
Characterize system-specific bias across common magnetic resonance imaging (MRI) platforms for quantitative diffusion measurements in multicenter trials.
Methods:
Diffusion weighted imaging (DWI) was performed on an ice-water phantom along the superior-inferior (SI) and right-left (RL) orientations spanning ± 150 mm. The same scanning protocol was implemented on 14 MRI systems at seven imaging centers. The bias was estimated as a deviation of measured from known apparent diffusion coefficient (ADC) along individual DWI directions. The relative contributions of gradient nonlinearity, shim errors, imaging gradients, and eddy currents were assessed independently. The observed bias errors were compared with numerical models.
Results:
The measured systematic ADC errors scaled quadratically with offset from isocenter, and ranged between -55% (SI) and 25% (RL). Nonlinearity bias was dependent on system design and diffusion gradient direction. Consistent with numerical models, minor ADC errors (± 5%) due to shim, imaging and eddy currents were mitigated by double echo DWI and image coregistration of individual gradient directions.
Conclusion:
The analysis confirms gradient nonlinearity as a major source of spatial DW bias and variability in off-center ADC measurements across MRI platforms, with minor contributions from shim, imaging gradients and eddy currents. The developed protocol enables empiric description of systematic bias in multicenter quantitative DWI studies.
Insights
Gradient nonlinearity causes significant spatial bias in apparent diffusion coefficient (ADC) measurements across MRI platforms. This bias, crucial for multicenter quantitative diffusion imaging, is largely independent of other error sources.
Area of Science:
- Medical Imaging
- Quantitative MRI
- Diffusion Weighted Imaging
Background:
- Quantitative diffusion MRI is vital for multicenter trials.
- System-specific biases can affect the accuracy of diffusion measurements.
- Standardized protocols are needed to ensure reliable data across different MRI platforms.
Purpose of the Study:
- To characterize system-specific bias in quantitative diffusion measurements using common MRI platforms.
- To assess bias across different magnetic resonance imaging (MRI) systems in multicenter settings.
- To identify the sources of bias in diffusion weighted imaging (DWI) data.
Main Methods:
- Diffusion weighted imaging (DWI) was performed on an ice-water phantom across 14 MRI systems at seven centers.
- Apparent diffusion coefficient (ADC) bias was estimated as deviation from known values along SI and RL directions.
- Independent assessment of gradient nonlinearity, shim errors, imaging gradients, and eddy currents was conducted.
Main Results:
- Systematic ADC errors scaled quadratically with offset from isocenter, ranging from -55% (SI) to 25% (RL).
- Nonlinearity bias varied with MRI system design and diffusion gradient direction.
- Minor ADC errors from shim, imaging, and eddy currents were mitigated by advanced DWI techniques.
Conclusions:
- Gradient nonlinearity is a primary source of spatial bias and variability in off-center ADC measurements across MRI platforms.
- Shim errors, imaging gradients, and eddy currents contribute minor biases.
- A protocol was developed for empirical description of systematic bias in multicenter quantitative DWI studies.
