Not all protons behave the same way. The protons in a water molecule wobble slightly different from the protons in a fat molecule. These slight differences can be detected by the MRI and, with the help of a computer, be used to construct a visual image representing the types and locations of these different molecules.

We would need to do three types of scans on each subject. The localizer, which lasts only a few seconds, gives a snapshot of the location and orientation of the head in the magnet. The localizer scan of the lamb’s head came out well. We could clearly make out the brain. The human settings for the localizer seemed to work. Next up was the structural image. For humans, we like as much anatomical detail as possible, but this has to be weighed against the time it takes to get high-resolution images. Images clear enough to resolve features as small as one millimeter take six minutes to complete. Humans have no problem holding still for that long, but there was no way our dogs would. I told Lei that we needed to come up with a structural sequence that would take no more than thirty seconds. I figured that would be the limit for most dogs.

This turned out to be somewhat difficult. The normal structural scans couldn’t be completed that quickly, so we had to switch to a different type of scan. This one didn’t show as much detail, but we were able to find a combination of parameters that produced a usable image in under thirty seconds.

We spent an awful lot of time figuring out the best orientation of the brain. If you think of the MRI as being a digital bread slicer, we had to decide which way to cut the slices: left to right, top to bottom, or front to back. Since the human head is pretty close to a sphere, it doesn’t make a whole lot of difference which way you slice it. But a dog’s head, like the lamb’s, is elongated front to back and generally pretty flat from top to bottom.

As the images of the lamb’s head came up on the screen, we saw how little of the head was actually occupied by brain. Most of it was nose and muscle. Those air pockets in the nose can wreak havoc with the MRI images too. Abrupt transitions in tissue density, such as going from air to skull, cause distortions in the magnetic field, which result in warped images. By carefully selecting the orientation of the slices, you can minimize this effect. Slicing from front to back seemed to give us the best results.

Anatomical images of the lamb’s head. The slices go from front to back. The eyeballs are visible in the top row, while the brain appears prominently in the middle and lower rows. The large black cavities are nasal sinuses.

(Gregory Berns)

Finally, it was time to attempt some functional scans, which are two-second glimpses of the brain in action. By continuously acquiring these functional scans while the subject does something, we can measure changes in brain activity. Think of the functional scans as the individual frames of a movie. Even though each one takes only two seconds, the subject might be in the scanner for half an hour during functional scanning. During such a session, we would acquire nine hundred functional images, at a rate of thirty scans a minute for thirty minutes.

Of course, the lamb was dead, so we didn’t expect to see much “activation.” But we only needed to figure out how many slices it took to cover the brain and how to orient the brain for the most efficient coverage. Once we worked that out, Andrew and I recorded the sounds of the scanner running this sequence.

We could now introduce Callie and McKenzie to the actual noise they would experience in the scanner and gradually let them get used to it.

11

The Carrot or the Stick?

THE CHALLENGE OF ENTERING the head coil and placing her chin on the boogie board chin rest had long been overcome. As soon as Callie heard the rustling of the plastic baggie containing bits of chopped-up hot dog, she knew. She would bound into the kitchen, wagging her whole rear end, and look at me with excitement and anticipation.

“Wanna do some training?” I would ask in a high-pitched voice.

Our training regimen had outgrown the basement. The only room in the house big enough to contain what was now a full-blown MRI simulator was the living room. Kat eyed the monstrosity in her living room, a space formerly occupied by an elegant sofa set and coffee table now pushed off to the side.

“There isn’t any other place for this?” she asked.

“It’s too heavy to move down in the basement,” I replied. “And I don’t think it will fit through the door.”

“You mean you constructed this in the living room without a way to get it out?”

“No, no,” I reassured her. “It comes apart.”

I had dusted off a PA system left over from my guitar-swinging days in a garage band. As I set the speakers on a stand facing the tube, Helen came into the living room.

“What’s that for?”

“To simulate the noise of the scanner,” I explained. “It’s the only thing we have that’s loud enough.”

She nodded, and together we snaked cables from the speakers to the amplifier. We aimed one speaker at the side of the tube to simulate the vibrations that course through the MRI. The other speaker went at the end of the tube to achieve the full decibel level inside.

“Daddy?”

“Yes?”

“Can I come with you when you scan Callie?”

This question took me by surprise. I wondered what had motivated it.

“Why do you want to see the experiment?” I asked. “It might not even work.”

“I know, but I want to see it,” she said.

“Is it because you want to skip school?”

She turned away and mumbled, “Maybe.” But quickly recovering, she continued. “That’s not the main reason. I really want to see the experiment. Don’t you always say that real science is exciting? Wouldn’t I learn more there than I would at school?”

In that, her logic was flawless.

“I’ll have to think about it.”

I had no doubt that Helen would learn more about science watching this experiment than she would in an entire week of science class at the middle school.

This was Helen’s first year of middle school, and the transition from elementary school had been a shock for all of us. Her workload was so much larger than what she was used to, she still hadn’t quite figured out how to balance homework and fun. In addition to the usual math, English, and social studies, her school required Latin for all sixth graders. In a classic case of confusing correlation with causation, the curriculum committee cited studies showing that kids who learned Latin did better on the SAT and reasoned that if all kids took Latin, their test scores would improve. Unfortunately, just because kids who take Latin have higher SAT scores doesn’t mean that Latin is the cause. These kids might already have a larger vocabulary and an interest in learning another language.

Latin wasn’t the problem, though. Much to my dismay, it was science.

Early in the year, I had tried to explain to Helen that science is always changing.

To which she asked, “You mean that this stuff is wrong?”

“Some of it.”

“Then why am I learning it?”

Because the state says you have to, I thought. But what I said was “Science is a way of answering questions about the world around us. What you are learning is our current understanding of the universe. As we learn more, our understanding changes.”