AUTHOR=Bailey Colleen , Collins David J. , Tunariu Nina , Orton Matthew R. , Morgan Veronica A. , Feiweier Thorsten , Hawkes David J. , Leach Martin O. , Alexander Daniel C. , Panagiotaki Eleftheria 

TITLE=Microstructure Characterization of Bone Metastases from Prostate Cancer with Diffusion MRI: Preliminary Findings

JOURNAL=Frontiers in Oncology

VOLUME=8

YEAR=2018

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2018.00026

DOI=10.3389/fonc.2018.00026

ISSN=2234-943X

ABSTRACT=<sec id="ST1"><title>Purpose</title><p>To examine the usefulness of rich diffusion protocols with high <italic>b</italic>-values and varying diffusion time for probing microstructure in bone metastases. Analysis techniques including biophysical and mathematical models were compared with the clinical apparent diffusion coefficient (ADC).</p></sec><sec id="ST2"><title>Methods</title><p>Four patients were scanned using 13 <italic>b</italic>-values up to 3,000 s/mm<sup>2</sup> and diffusion times ranging 18–52 ms. Data were fitted to mono-exponential ADC, intravoxel incoherent motion (IVIM), Kurtosis and Vascular, extracellular, and restricted diffusion for cytometry in tumors (VERDICT) models. Parameters from the models were compared using correlation plots.</p></sec><sec id="ST3"><title>Results</title><p>ADC and IVIM did not fit the data well, failing to capture the signal at high <italic>b</italic>-values. The Kurtosis model best explained the data in many voxels, but in voxels exhibiting a more time-dependent signal, the VERDICT model explained the data best. The ADC correlated significantly (<italic>p</italic> &lt; 0.004) with the intracellular diffusion coefficient (<italic>r</italic> = 0.48), intracellular volume fraction (<italic>r</italic> = −0.21), and perfusion fraction (<italic>r</italic> = 0.46) parameters from VERDICT, suggesting that these factors all contribute to ADC contrast. The mean kurtosis correlated with the intracellular volume fraction parameter (<italic>r</italic> = 0.26) from VERDICT, consistent with the hypothesis that kurtosis relates to cellularity, but also correlated weakly with the intracellular diffusion coefficient (<italic>r</italic> = 0.18) and cell radius (<italic>r</italic> = 0.16) parameters, suggesting that it may be difficult to attribute physical meaning to kurtosis.</p></sec><sec id="ST4"><title>Conclusion</title><p>Both Kurtosis and VERDICT explained the diffusion signal better than ADC and IVIM, primarily due to poor fitting at high <italic>b</italic>-values in the latter two models. The Kurtosis and VERDICT models captured information at high <italic>b</italic> using parameters (Kurtosis or intracellular volume fraction and radius) that do not have a simple relationship with ADC and that may provide additional microstructural information in bone metastases.</p></sec>