Seen above and below are MRI scans of sushi. Uhei Naruse scanned the rolls at a hospital in a personal research project to tease out the secret of good sushi. Trevor Corson, author of "The Story of Sushi," has the details of this experiment on his Sushi Concierge blog. From Sushi Concierge:
Pictured (at left) are three sushi nigiri–hand squeezed rectangles of rice topped with a slice of fish. The first was made by the veteran chef. It was small and light, weighing in at only 12 grams, and the MRI scan revealed a lot of empty space inside it, between the grains of rice. It also revealed another secret of a veteran chef's skill–the grains of rice were mostly aligned lengthwise, which helps the nigiri hold together without being too dense, by creating adhesion along the edges of the aligned grains."Want to See the Inner Secrets of Perfect Sushi?" (Sushi Concierge)
The second nigiri was made by the apprentice. It was denser–about the same size, but weighing 15 grams. And the rice grains were less uniform in their orientation.
The third nigiri was made by the robot, which couldn't come close to matching human skill. The grains of rice were hopelessly jumbled and the sushi was thick and heavy, clocking in at 20 grams. Naruse ate some of it and described it as "sticky." This is closer to the typical sushi that, sadly, we're content to eat in the States.
"The Story of Sushi: An Unlikely Saga of Raw Fish and Rice" (Amazon)