Binders would cut pieces of parchment — sometimes full pages, sometimes just thin strips — and glue them on places like a book’s spine. The book would then be covered, and most of those binding fragments would be hidden from view.

“There’s actually a whole library within a library in the form of these fragments,” said Joris Dik, a materials scientist who studies binding fragments at Delft University of Technology in the Netherlands and was not involved in the new study.

In recent decades, researchers have begun peering beneath book covers using noninvasive techniques to to find medieval binding fragments and read what’s written on them. But many of those techniques have limitations, which prompted Dr. Ensley and his colleagues to try CT scanning, the same kind available in a hospital. The technique’s three-dimensional view solves the focus problems that plagued other methods, and a scan can be completed in seconds rather than the hours previously required.

The team scanned a three-book set of “Historia animalium,” an encyclopedia of animals printed in the 16th century. One book would serve as a control, the researchers decided, because its cover was damaged and could be peeled back to reveal medieval binding fragments — featuring red and black ink — on the spine. The other two books were intact. However, the researchers hypothesized that their spines might also contain fragments because the books appeared to have been bound in the same workshop, said Katherine H. Tachau, a historian at the University of Iowa and a member of the research team.