Bone scan reveals estrogen effects. (Endocrinology).

There's little debate among scientists that the female hormone estrogen is integral to maintaining strong bones. Osteoporosis, in which the bones become brittle, most commonly strikes women after menopause cuts their natural estrogen supply.

Using a scanning technology called microcomputerized tomography, or micro-CT, scientists have a new way to look at the difference between bone exposed to estrogen and bone deprived of it. Researchers are already starting to use micro-CT scans to test the effects of new drugs designed to duplicate estrogen's bone-building power without its side effect of promoting cancer growth.

Applying micro-CT to a biopsy sample produces a three-dimensional image of a bone that is 100 times as detailed as that of a typical CT scan. Harry K. Genant of the University of California, San Francisco and his colleagues scanned the weblike matrix of crisscrossed fibers within bones of premenopausal and postmenopausal women. They found that in the former, the fibers form predominantly flat, rectangular structures, whereas in postmenopausal women lacking estrogen, most of these fibers have a rodlike appearance.

To directly test estrogen's effect on bone, the scientists then obtained pelvic-bone samples from 20 women with osteoporosis. After 2 years of estrogen therapy, the women underwent another bone biopsy.

The scans revealed that the ratio of plates to rods had increased on average by 14 percent after treatment, even though the bones themselves hadn't changed in volume, thickness, or density.

"It was principally [the] more platelike appearance of the bone that led to what should be a healthier and stronger skeleton," Genant says. "This helps to explain ... the reduction of spine and hip fractures in women who are placed on estrogen therapy."