Pediatric Brain Tumor Consortium Multisite Assessment of Apparent Diffusion Coefficient z-Axis Variation Assessed with an Ice–Water Phantom

doi:10.1016/j.acra.2014.10.006

Academic Radiology

Volume 22, Issue 3, March 2015, Pages 363-369

https://doi.org/10.1016/j.acra.2014.10.006 Get rights and content

Rationale and Objectives

Magnetic resonance diffusion imaging can characterize physiologic characteristics of pediatric brain tumors used to assess therapy response. The purpose of this study was to assess the variability of the apparent diffusion coefficient (ADC) along z-axis of scanners in the multicenter Pediatric Brain Tumor Consortium (PBTC).

Materials and Methods

Ice–water diffusion phantoms for each PBTC site were distributed with a specific diffusion imaging protocol. The phantom was scanned four successive times to 1) confirm water in the tube reached thermal equilibrium and 2) allow for assessment of intra-examination ADC repeatability. ADC profiles across slice positions for each vendor and institution combination were characterized using linear regression modeling with a quadratic fit.

Results

Eleven sites collected data with a high degree of compliance to the diffusion protocol for each scanner. The mean ADC value at slice position zero for vendor A was 1.123 × 10⁻³ mm²/s, vendor B was 1.0964 × 10⁻³ mm²/s, and vendor C was 1.110 × 10⁻³ mm²/s. The percentage coefficient of variation across all sites was 0.309% (standard deviation = 0.322). The ADC values conformed well to a second-order polynomial along the z-axis, (ie, following a linear model pattern with quadratic fit) for vendor–institution combinations and across vendor–institution combinations as shown in the longitudinal model.

Conclusions

Assessment of the variability of diffusion metrics is essential for establishing the validity of using these quantitative metrics in multicenter trials. The low variability in ADC values across vendors and institutions and validates the use of ADC as a quantitative tumor marker in pediatric multicenter trials.

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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: 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.

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Original InvestigationPediatric Brain Tumor Consortium Multisite Assessment of Apparent Diffusion Coefficient z-Axis Variation Assessed with an Ice–Water Phantom

Rationale and Objectives

Materials and Methods

Results

Conclusions

Section snippets

Data Collection

Results

Discussion

Conclusions

Acknowledgment

Neuroimaging Clin N Am

Neoplasia

Acad Radiol

Magn Reson Imaging

CNS and miscellaneous intracranial and intraspinal neoplasms

Central Brain Tumor Registry of the United States in 2006–2010 (CBTRUS). Nov. 2013 Primary brain and central nervous system tumors diagnosed in the United States

The Neuroimaging Center of the Pediatric Brain Tumor Consortium-collaborative neuroimaging in pediatric brain tumor research: a work in progress

AJNR Am J Neuroradiol

Original Investigation
Pediatric Brain Tumor Consortium Multisite Assessment of Apparent Diffusion Coefficient z-Axis Variation Assessed with an Ice–Water Phantom