Since early last month, scientists at the Marshall Space Flight Center have been shooting X-rays through the skull of the Tyrannosaurus rex fossil known as Samson.

Tony Tye, Post-Gazette Amy Henrici, a preparator, and Chris Beard, curator for vertebrate paleontology, look over Samson last spring at the Carnegie Museum of Natural History. Click photo for larger image.

The result thus far has been more than 200 CT images showing the inner structure of the 65 million-year-old skull, one of the most complete and pristine T. rex skulls ever found.

"It hasn't told us too much yet," said Matt Lamanna, the Carnegie Museum of Natural History's dinosaur paleontologist. The real payoff is expected when the scanning is complete late next month.

Researchers will then take the 650 4-millimeter-thick vertical slices and meld them to produce a three-dimensional computer model of Samson's skull.

That 3-D visualization, in turn, could reveal much about Samson and about T. rex in general -- the shape and size of its brain, the sharpness of the giant meat-eater's senses and hints about the function of air-filled spaces within its bones. The model might even contribute to the debate over whether the animals we know as T. rex represent just a single species.

"To understand what's going on with these things, we really have to look inside," said Lawrence Witmer, an anatomy professor at Ohio University and an expert on the scanning and modeling of dinosaur bones.

Samson was found on a South Dakota ranch by a private fossil hunter in 1992 and was sold four years ago to Graham Ferguson Lacey, a British millionaire. Lacey last year hired the Carnegie to prepare the rock-encrusted skull for a planned European traveling exhibit and to study it.

Since May, the museum's preparators have been chipping away extraneous rock from the skull under the gaze of museum visitors. But in November the 1,500-pound specimen was crated up and shipped to Huntsville, Ala., so it could be examined using a large, industrial CT scanner at NASA's National Center for Advanced Manufacturing.

"CT scanning is becoming standard practice for dinosaur skulls of Samson's quality," Lamanna said. The X-rays reveal structures that simply can't be seen from the exterior, even after all of the rock has been cleared away.

For instance, the endocranial cavity, or brain case, is a fairly accurate cast of the brain's exterior, but isn't ordinarily visible. The 3-D model built from the CT scans thus will tell scientists about the brain's size and shape. That, in turn, may provide hints about the animal's sensory capabilities.

An earlier such study of the brain case of Sue -- another, more complete T. rex skeleton from South Dakota, now on display at the Field Museum in Chicago -- showed that the brain had a sizable olfactory lobe, suggesting the creature "had a decent sense of smell," Lamanna said.

Similarly, Witmer said, an analysis of Samson's brain case may provide information about T. rex's senses of smell, hearing and sight.

Witmer, who was busy performing CT scans on pieces of T. rex skulls last week at his lab in Athens, Ohio, has been involved in the scanning and modeling of numerous dinosaurs, including Sue. The 3-D visualization of Samson, he predicted, "will be in greater detail than was possible with Sue. The technology has advanced so much further."

Prior to CT scanning, paleontologists would have to study broken specimens to learn about these otherwise hidden structures. "There was a time when people would actually run these things through a bandsaw" to see inside, Witmer added.

In addition to the shape of the brain, the 3-D visualization will allow greater study of the large air sinuses found in the T. rex skull and perhaps provide more clues about their function.

The CT scanner at Marshall, built for examining rocket motor assemblies and turbine blades, is about 10 times more powerful than a medical CT scanner, said Ron Beshears, who is heading the project at Marshall.

The skull, still in its shipping crate, has been placed on a turntable that can accommodate items up to 50 inches in diameter and 75 inches high. To create each image slice, the skull is rotated in front of the X-ray source and detector. The process for each 4-millimeter slice takes about 30 minutes; the X-ray detector is then repositioned a few millimeters up or down and the process repeated.

Beshears said the Marshall scanner was used to scan a portion of Sue's tail 10 years ago, as part of a feasibility study, but the Samson project is otherwise its first use for paleontology.

Samson will return to the Carnegie for additional preparation and study. The museum is to be finished with its work by May 2006.

Much is being learned about T. rex, both because of technologies like CT scanning and 3-D visualization and because of the sheer number of specimens being discovered, Witmer said. About 30 skulls have been unearthed, depending on how they are counted, and many in just the last 20 years.

The numbers are allowing paleontologists to get a better idea of the variation within the species, and even to ask questions about whether enough exists to suggest separate species of Tyrannosaurus.

Specimens of T. rex are plentiful, in part because the Tyrannosaurus lived relatively recently. In age, T. rex is closer to modern humans than it is to early dinosaurs, such as stegosaurus, Witmer said.

And the sheer size of T. rex offers some advantages to fossil hunters.

"If you're looking in the right spot," he explained, "you're likely to find it."