Lymph node uptake of interstitially delivered particulate contrast media before and after irradiation in dogs

Rationale and Objectives. The authors' purpose was to assess the effects of ionizing radiation on the uptake and distribution of interstitially delive red particulate contrast medium in normal lymph nodes in dogs. Materials and Methods. Two milliliters of an iodinated nanoparticle suspens ion (NC 67722 Sterile Suspension, 76 mg of iodine per milliliter) was injec ted subcutaneously Or submucosally into nine normal adult beagle dogs. Targ eted lymph node groups were evaluated with computed tomography (CT), Region -of-interest analysis was used to estimate volume, attenuation, and iodine concentration of the opacified nodes and nonopacified contralateral nodes o n CT images obtained before and 24 hours after the injection. All right-sid ed and some left-sided lymph nodes were irradiated with 50 Gy in 25 fractio ns of 2 Gy per day, beginning 28-35 days after the CT examination. Contrast medium administration and quantitative CT imaging were performed again 3 m onths after irradiation. Results. Contrast material uptake resulted in a twofold increase in node vo lume before irradiation (P < .0001). Mean attenuation of contrast-enhanced nodes increased to 230-330 HU from a precontrast enhancement value of After irradiation, opacified node volumes decreased to approximately 25%-50% of their preirradiation volumes (P < .02). Contrast material uptake decreased 10%-15% after irradiation but was not significantly less than preirradiatio n uptake. Qualitatively, no substantial difference in contrast material dis tribution existed between irradiated and nonirradiated nodes. Conclusion. An elective irradiation dose decreased lymph node size, but the imaging characteristics of opacification were not otherwise appreciably al tered 3 months after irradiation.