4.3. Clonogenic Microcolony Assay

To compare the dose-dependent radiation damage of X-rays, the mice were exposed to 0 (no irradiation), 9, 12, and 15 Gy of X-ray irradiation and sacrificed after 84 h (3.5 days) [19]. Regenerative crypts referred to the atrophic or withering crypts with nuclear atypia. The number of surviving crypts per circumference of the transverse sectioned intestine was enumerated from hematoxylin and eosin (H&E)-stained sections. To assess location-dependent radiation damage from X-rays, the mice were exposed to 15 Gy of X-ray irradiation, and the samples were harvested from the proximal half of the small intestine (proximal small intestine), the distal half of the small intestine (distal small intestine), and the colon after 84 h [19]. Fractional crypt survival was defined as the percentage of the number of surviving crypts in the circumference of the intestine in irradiated mice to the number of crypts per cross-section from the same region of the intestine in unirradiated mice of the same strain and age [10].