CELLULAR CHANGES IN RESPONSE TO EMBEDDED METALS: SURVEILLANCE USING PET-CT

The purpose of this study was to determine the sensitivity and specificity of small animal Positron Emission Tomography-Computed Tomography (PET-CT) in identifying metabolic changes in muscle tissue surrounding simulated shrapnel injuries and compare this imaging to traditional x-ray images. The study was structured as an experimental design with repeated measures. Fischer 344 male rats randomly assigned to three groups, planted with weapons grade heavy metal tungsten alloy (HMTA) pellets, tantalum (Ta) pellets as the control metal or Sham control without pellet implantation. Rats from each metal category received a series of x-rays and ¹⁸F fluoro-2-deoxy-D-glucose (FDG) PET-CT scans over 16 weeks. Animals sacrificed at each of five time points over a 16 week period had tissue excised for histopathological examination.

Tracer uptake on PET-CT was quantified using standard unit value (SUV). Image data comparisons were accomplished using Kolmogorov-Smirnov Z, Friedman’s ANOVA and Wilcoxon signed-rank tests. Sensitivity and specificity were determined. Receiver Operating Characteristic (ROC) curve and the area under the curve (AUC) were calculated. Significance level was set at p < .05. Histopathology was assessed by a pathologist, blinded to treatment groups. The data indicate increased FDG uptake was associated with an aggressive malignancy in the HMTA implanted rats. There was a significant difference in tracer uptake between the Ta and HMTA animals and also in tracer uptake over the sixteen weeks for the HMTA animals. PET-CT imaging had a sensitivity of 86%, specificity of 100% and AUC .938.

HMTA induced an aggressive cancer that, using PET-CT imaging, was apparent as early as one week post-implantation. These results point to the applicability of PET-CT imaging as a surveillance tool for detecting early tissue changes around embedded fragments. Support: VA Embedded Metals Center, TSNRP HU0001-11-1-TS15, & VA B5044R.