Temperature and concentration calibration of aqueous polyvinylpyrrolidone (PVP) solutions for isotropic diffusion MRI phantoms

<div><p>To use the “apparent diffusion coefficient” (<i>D</i>_app) as a quantitative imaging parameter, well-suited test fluids are essential. In this study, the previously proposed aqueous solutions of polyvinylpyrrolidone (PVP) were examined and temperature calibrations were obtained. For example, at a temperature of 20°C, <i>D</i>_app ranged from 1.594 (95% CI: 1.593, 1.595) μm²/ms to 0.3326 (95% CI: 0. 3304, 0.3348) μm²/ms for PVP-concentrations ranging from 10% (w/w) to 50% (w/w) using K30 polymer lengths. The temperature dependence of <i>D</i>_app was found to be so strong that a negligence seems not advisable. The temperature dependence is descriptively modelled by an exponential function exp(<i>c</i>₂ (<i>T</i> − 20°<i>C</i>)) and the determined <i>c</i>₂ values are reported, which can be used for temperature calibration. For example, we find the value 0.02952 K^-1 for 30% (w/w) PVP-concentration and K30 polymer length. In general, aqueous PVP solutions were found to be suitable to produce easily applicable and reliable <i>D</i>_app-phantoms.</p></div

(double column): Images of the used phantom.

<p>a,b,c) High resolution images. d,e,f) Low resolution images. a,d) Signal images without diffusion weighting, i.e. with <i>b</i> = 0 s/mm². b,e) Signal image with <i>b</i> = 700 s/mm². Signal images are min-max normalized. c,f) <i>D</i>_app-maps of the phantom in units of μm²/ms. Cross sections of the volumes of interest are marked in blue in a and d.</p

(single column): Temperature calibration coefficient <i>c</i>₂ in dependence of PVP concentration for K30 and K90.

<p>Error bars denote 95% confidence intervals. The straight lines represent linear fits with weights inversely proportional to the width of the 95% confidence interval.</p

(single column): Dependence of apparent diffusion coefficient <i>D</i>_app on temperature for K30 and K90.

<p>Markers represent measured values and lines represent fits according to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179276#pone.0179276.e002" target="_blank">Eq 2</a>.</p

Recommended temperature calibration coefficient <i>c</i>₂ in K^-1.

<p>Recommended temperature calibration coefficient <i>c</i>₂ in K^-1.</p

Fit parameters describing the dependency of <i>D</i>_app on the temperature (see Eq (2)) for K90.

<p>95% confidence intervals are stated in brackets.</p