Demonstration of nonlinearity bias in the measurement of the apparent diffusion coefficient in multicenter trials

Abstract

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 to 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 co-registration 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.

How reliable are ADC measurements? A phantom and clinical study of cervical lymph nodes

“…Specific phantom studies have shown that gradient-field error would be scanner-dependent [27] and not significant within 4 cm from the isocentre, explaining the good reproducibility of our ADC measurements and in other multicentric studies. On multiple scanners, measurements at 12 cm from the isocentre showed an average error of -20 % according to vertical shift and +7 % horizontally.…”

Phantom-based field maps for gradient nonlinearity correction in diffusion imaging

“…This confirms similar findings by others Malyarenko 2016, Bammer 2003, Newitt 2015 . These errors are large enough to cause important inaccuracies when measuring quantitative diffusion parameters.…”

“…One in particular is the error introduced by neglecting to account for the scanner-specific nonlinearity of the gradient fields, which leads to spatial variation in the amplitude and direction of the applied diffusion gradients. Empirically, this has been an important source of error in multi-site studies Malyarenko 2016 .…”

Variation in apparent diffusion coefficient measurements among women with locally advanced cervical cancer

“…Multi-center and inter-protocol ADC tends to range within 5% at isocenter and over the width of the slice package, consistent with our data [22], while off-center values can accrue considerable bias from gradient non-linearity [25].…”