Original InvestigationPediatric Brain Tumor Consortium Multisite Assessment of Apparent Diffusion Coefficient z-Axis Variation Assessed with an Ice–Water Phantom
Section snippets
Data Collection
Eleven sites with a total of 15 scanners from three major vendors (vendors A, B, and C not necessarily in alphabetical order) participated in the study. An ice–water diffusion phantom (Fig 1) consisting of a sealed 29-mm diameter tube of distilled water within a larger plastic jug to contain ice cubes and tap water was distributed to each site along with instructions for its use and recommendations for a specific diffusion imaging protocol. Also included were instructions for preparing the
Results
Diffusion phantom data were obtained from 15 institution–vendor combinations where six institutions used vendor A (denoted A1–A6), five institutions used vendor B (denoted B1–B5), and four institutions used vendor C (denoted C1–C4). To magnify the model estimates in quadratic linear regression models, we multiplied the diffusion phantom ADC values by 100. Representative plots of ADC versus slice position are shown in Figure 2.
Of the 15 scanners, 13 were 3-Tesla (T) scanners and two from vendor
Discussion
A primary goal of the PBTC is to gauge response to therapy using quantitative neuroimaging methods. MRI is well suited to this task, and a number of quantitative parameters are available for tissue characterization, including the relaxation times T1, T2, and T2*, as well as diffusion-associated parameters, the most prominent being the trace ADC as acquired with single-shot echo-planar imaging sequences now common to most scanners. Understanding and accounting for instrumental sources of error
Conclusions
To conclude, it is rather remarkable that variations of ADC along the z-axis for approximately 200 mm show such small variations (Fig 2) and that ADC measures at each location are highly reproducible (Fig 5). Furthermore, the z-variations may be accounted for with a relatively simple polynomial equation from which corrections for this effect may be made. In addition, this study shows low variability in ADC values across vendors and institutions and validates the use of ADC as a quantitative
Acknowledgment
The authors acknowledge the Pediatric Brain Tumor Consortium Magnetic Resonance technologists and radiologists who scanned the diffusion phantom at each site. The authors also acknowledge Mrs. Cynthia Dubé for article preparation.
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2021, Magnetic Resonance ImagingCitation Excerpt :Even though our preliminary results show good reproducibility, other solutions like ice-water [6–9,11] and PVP [9,10] are probably even more robust against changing MRI sequence and hardware and environmental temperature fluctuations [6,7]. An ice-water phantom furnished with temperature control [6] showed a variation of measured ADC within 5% with excellent agreement across different systems, and PVP-based phantoms [10] remained below 4% across 13 scanners for a range of diffusivities from 0.4 to 1.1 × 10−6 mm2/s. Phantoms with stabilized temperature are more reliable in multicenter trials, but room temperature alternatives are best suited for everyday purposes like quality control and performance assessment. In our study, we ascribe the subtle differences in ADC observed across scanners to temperature variations that are not stabilized in this version of the phantom during the measurement session.
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2018, NeuroImageCitation Excerpt :Potential drawbacks of water are its low viscosity, making it prone to vibrational artifacts, its intrinsic long T1-and T2-values on the order of 1 s or more, depending on the dissolved oxygen, and its relative high diffusion coefficient (2 μm2/ms, cf. Fig. 1) at room temperature compared to those values in brain, e.g., at 3T for WM T1 ∼ 700–800 ms, T2 ∼ 80–110 ms (Oros-Peusquens et al., 2008; Wansapura et al., 1999), and mean diffusivity ranging 0.3–1 μm2/ms (Tofts, 2004). At 0 °C, ice-water has a D of 1.1 μm2/ms (Easteal et al., 1989), and when surrounding it by an insulating bath filled with ice and water, it has been shown useful as a temperature-controlled fluid in ADC phantoms in multi-center studies (Chenevert et al., 2011; Grech-Sollars et al., 2015; Malyarenko et al., 2016; Mulkern et al., 2015). Furthermore, (distilled) water is also by far the most commonly used fluid inside microstructural phantoms, where the long intrinsic T1-and T2-values are typically helping to have a reasonable SNR, as the proton density in such phantoms is typically much lower, and surface relaxation and local susceptibility differences cause additional T2(*) relaxation.
Funding Sources: This work was supported in part by National Institutes of Health (NIH) grant U01 CA81457 for the Pediatric Brain Tumor Consortium, The Pediatric Brain Tumor Consortium Foundation, The Pediatric Brain Tumor Foundation of the United States, and American Lebanese Syrian Associated Charities and NIH Quantitative Imaging Network grant U01-CA166104.