Towards MRI Differentiation of Recurring Tumor from Delayed Radiation Necrosis
Carlos J Perez-Torres, John A Engelbach, Jeremy Cates, Dinesh K Thotala, Robert E Drzymala, Joseph JH Ackerman, and Joel R Garbow Department of Radiology, Washington University in Saint Louis, Saint Louis, Missouri, United States, Department of Radiation Oncology, Washington University in Saint Louis, Saint Louis, Missouri, United States, Department of Chemistry, Washington University in Saint Louis, Saint Louis, Missouri, United States
Assessment of MRI parameters as imaging biomarkers for radiation necrosis in the rat brain.
PURPOSE
Radiation necrosis is a major complication of radiation therapy. We explore the features of radiation-induced brain necrosis in the rat, using multiple MRI approaches, including T(1), T(2), apparent diffusion constant (ADC), cerebral blood flow (CBF), magnetization transfer ratio (MTR), and amide proton transfer (APT) of endogenous mobile proteins and peptides.


METHODS AND MATERIALS
Adult rats (Fischer 344; n = 15) were irradiated with a single, well-collimated X-ray beam (40 Gy; 10 × 10 mm(2)) in the left brain hemisphere. MRI was acquired on a 4.7-T animal scanner at ~25 weeks' postradiation. The MRI signals of necrotic cores and perinecrotic regions were assessed with a one-way analysis of variance. Histological evaluation was accomplished with hematoxylin and eosin staining.


RESULTS
ADC and CBF MRI could separate perinecrotic and contralateral normal brain tissue (p < 0.01 and < 0.05, respectively), whereas T(1), T(2), MTR, and APT could not. MRI signal intensities were significantly lower in the necrotic core than in normal brain for CBF (p < 0.001) and APT (p < 0.01) and insignificantly higher or lower for T(1), T(2), MTR, and ADC. Histological results demonstrated coagulative necrosis within the necrotic core and reactive astrogliosis and vascular damage within the perinecrotic region.


CONCLUSION
ADC and CBF are promising imaging biomarkers for identifying perinecrotic regions, whereas CBF and APT are promising for identifying necrotic cores.
Characterizing ASTM Carbon Black Reference Materials Using a Disc Centrifuge Photosedimentometer
ABSTRACT Cumulative and differential particle size distributions using disc centrifugation are presented for ASTM carbon black reference materials A4 through F4. The distributions for A4 through C4 form a group of relatively small-size particles. The distributions for D4 through F4 form a group of relatively large-size particles. The distributions for A4 and C4 are very nearly the same as are the distributions for F4 and E4. The results suggest that proper sample preparation can maintain size distribution stability for at least a year; only mild agitation is required to re-suspend the particles.