Candid Cancer: Medical imaging has come a long way

We cancer patients are routinely poked, prodded, knifed, examined, drugged — and photographed with "cameras" that take "pictures" ever so candidly of parts that some of us never knew we had, much less wanted to see. Indeed, medical imaging devices have come a long way since the first X-ray was taken in 1895.
Since then, generations of scientists have competed or cooperated to develop better techniques to visualize our interiors and to see the parts of us that are hidden by others — and not only in two dimensions but in three. In 1930, the Italian radiologist Alessandro Vallebona was the first to propose a way of capturing a single slice of the body on radiographic film. This method became known as tomography, which means imaging by sections.
In the years that followed, other scientists attempted to advance the technique, but it wasn't until 1971 that technology caught up to ideas. The following year, the first computer axial tomography (CAT) scanner, then known as an EMI-scanner, was installed at a hospital in Wimbledon, England and a patient's brain was the first to be scanned. In the U.S., the first machine was installed at Mayo Clinic where it resides, on display, today. Eventually, the word "axial" was dropped and we now have computer tomography, or CT.

As CT technology emerged, a few scientists, working independently of each other, were developing a different type of technology: magnetic resonance imaging, or MRI. There was great debate on who played what role — Nobel prizes were at stake — but in 1977, the first MRI was performed on a human being using a prototype nicknamed Indomitable, which is now housed in the Smithsonian. The first commercial MRI scanner was produced in 1980.
Both CTs and MRIs produce cross-sectional images of the body, but they use different techniques. CT scanners capture multiple images using X-ray beams and a computer then generates cross-sectional views. An MRI machine also creates multiple images, but rather than using X-ray beams, the machine creates a magnetic field and sends radio waves into the body. Tissues react to the radio waves by sending signals, and different tissues emit different signals, depending on the mixture of elements they contain. A computer translates the signals into images.
But a picture's worth a thousand words. Following are are two short videos that explain CT's and MRI's.

We can think of the entire series of CT and MRI images as a loaf of bread and each image as a slice. Any slice can be taken out of the loaf and turned sideways, over, up or around, so that it can be viewed from the front, the side, the back or any angle and depth desired. As slices are re-stacked into the loaf, a three-dimensional view emerges. (After CTs were explained this way to me, I've slid through every scan hoping my insides are as perfect as Zingerman's Cherry Chocolate bread — seriously yummy!)
As CTs and MRIs emerged, so too did PET, or positive emission tomography. PET evolved in the 1970s from the invention in 1958 of the gamma camera, which could view the distribution of radioactivity by injecting radioactive material, known as a tracer, into the patient.
PET imaging began to play a role in diagnosing cancer in 1999 when the FDA approved an imaging agent called FDG (F-fluorodeoxyglucose, derived from sugar and a small amount of radioactive fluorine) which is the tracer most frequently used to image cancer.
Unlike CT or MRI, which "sees" the anatomy, PET measures metabolism, meaning that it identifies rapidly growing cells, like cancer. Simplistically, rapidly growing cells require more energy, so they suck up more of the sugar in the tracer which then accumulates more heavily in areas with hungry, fast growing cells. The camera detects those heavier accumulations and malignancies light up as "hot spots" on the image.
Dr. Ella Kazerooni, Professor of Radiology and the Director of the Division of Cardiothoracic Radiology at the University of Michigan, further explains how CTs and PET's impart different, complementary information. "On a CT, we're basically looking at size, and the assumption has always been that if something got smaller, it's better, and when it got larger, it's worse. With a PET scan, we know that you can have a tumor that does not change in size on a CT, but the amount of PET agent it takes up falls dramatically or goes away, which tells us that the tumor is non-active — that treatment has killed it, but it just hasn't shrunk yet."
On the other hand, she adds, "We might have an area that we're watching on CT that doesn't change in size over time, but now it develops a new area of PET uptake in it, so even though it hasn't changed in size, something may be going on in it that we wouldn't know from the CT. So size has always been used as the measure of tumor response, but we know, in the last decade particularly, that different information provided by PET can more accurately know if a tumor really is getting better or worse."
The newest PET scanners combine PET and CT, so that we now have the PET/CT which gives doctors the metabolic information from PET superimposed on the anatomic information from CT. And in 2008, the first PET/MRI was installed.
Dr. Alan Waxman of Cedars-Sinai gives a more detailed explanation of PET for the Society of Nuclear Medicine:

So which modality is best? That depends on what our doctors want to see and what type of cancer we have. CT's, MRI's and PET's — and other imaging devices — have specific applications and are used for different needs. One is not better than the other for all things. Some types of cancer, for example, don't appear on PET scans, so they're not appropriate for all types, and PET can characterize a tumor as benign or malignant, but benign conditions as well as scar tissue can resemble cancer. Clearly, each of these tests requires careful interpretation by highly trained specialists.
One thing is certain. Before the advent of these devices, millions of people underwent exploratory surgery when abnormalities were suspected. My dad was one of them, and if he were alive today, he'd be quite amazed that machines offer so much information without using a single scalpel. Indeed, medical imaging devices have revolutionized the way cancer is diagnosed and even treated.

Previous installments of Candid Cancer are archived here.
Betsy de Parry is the author of The Roller Coaster Chronicles, a book about her experience with cancer and the shorter, serialized version she wrote for annarbor.com. Find her on Facebook or email her.

Betsy's book is available to purchase by clicking the link of her book to the right of this column