"Hi there. This is Tish from the Solis Womens Health Center. We found some things we wanted to review from your last mammogram."
The first thing that shot through my head was, "Oh great, like I don't have enough things to do and now I have to carve out time for another stupid visit to the doctor's. The perky voice continued.
"We'd like you to come back and take a few more views. When are you available tomorrow?"
Those few words sent a stream of thoughts running through my head at about the speed of light: Tomorrow? Really? Tomorrow?
It doesn't matter that I know the vast majority of callbacks reveal there is nothing to worry about and reflect medical professionals that would rather err on the side of caution. It doesn't matter that I am fortunate to have no family history of breast cancer. The thought invariably flashes through your head: What if I have cancer?
I've never understood women who don't get mammograms because they complain they are uncomfortable. They should volunteer to escort breast cancer patients to their radiation and chemo treatments. Breast cancer is a whole lot more uncomfortable than a few seconds of boob-squash. (Just for those of you who aren't part of the club: Your breast -- as much of it as possible -- is squished between two clear plastic pieces to make it as thin as possible for imaging. It's more uncomfortable than drawing blood, but less painful than intramuscular steroid injections (in my opinion).
I realized during the somewhat sleepless night that followed that I didn't actually know much about mammograms. I wanted to understand exactly what a mammogram can and can't tell you. Being a scientist, I'm a horrible patient because I want to see the proof for anything a doctor tells me.
There are basically two types of probes used in medical imaging: Those that go through the target and those that bounce off the target. I realize the professionals in the audience are pulling out their hair about now, sorry for the over simplification.
Mammograms are x-rays and belong to the first category. X-rays are part of the electromagnetic spectrum (shown at right), which means that they are made up of perpendicular electric and magnetic fields. Electromagnetic waves come in a wide, wide range of wavelengths. X-rays have wavelengths between 10 to 0.01 nanometers. (A nanometer is a billionth of a meter. The average hair is about 70,000 nanometers in diameter, so we're talking really small.)
When x-rays were discovered by Wilhelm Roentgen in 1895, he didn't realize they were electromagnetic radiation. As is often the case, Roentgen was working on something else entirely. He called them "x"-rays, since "x" stands for the unknown and no one knew the source of the x-rays. What was most surprising is that x-rays were capable of going through material. Not all materials, but tissues, muscles and other not-so-dense materials. The x-ray image at right is a picture of Mrs. Roentgen's hand. You can see the bones and her metal wedding ring, but you can't see her fingers - just a vague outline of the thickest part of her hand.
X-rays were one of the first scientific discoveries that took to the popular press with great speed. Roentgen submitted his scientific manuscript on December 28th, 1895, despite being initially unsure he had discovered anything worth mentioning. The first public announcement took place on January 5, 1896. A front-page article in Die Presse carried an extensive description of the discovery and suggested that the new kind of radiation might be useful for medical diagnoses. The news was published in other European papers, and three weeks later in London, The Electrician (a major electrical engineering journal) published an English translation of Roentgen's original scientific manuscript, "A New Kind of Ray, A Preliminary Communication".
US newspapers were freer with exclamation points than the stolid European papers: "NEW LIGHT SEES THROUGH FLESH TO BONES!" was a headline from mid-January 1896. Another screamed "HIDDEN SOLIDS REVEALED!!" Within a week, demonstrations were being set up at colleges, in high schools, and in public venues. Within the year, boys clubs were building their own x-ray sources.
X-rays captured the popular imagination. People sat for "x-ray portraits". Brides gave away x-ray pictures of their hands with their new wedding ring as wedding favors. In February 1896, a physics professor at Vanderbilt University persuaded the dean of the medical school to sit for an experimental radiograph of the skull. Three weeks later the dean's hair fell out. Now there's a way not to get tenure.
Within the first few months of 1896, researchers started realizing that the new rays were not only not understood, they perhaps needed to be treated with a little more care than they were currently being accorded. A number of the first x-ray investigators (predominantly the assistants who did the actual work) became ill, lost limbs or eventually died from exposure to x-rays. Although x-rays stopped being used for entertainment purposes, surprisingly, people still liked to 'play' with x-rays well into the 1950's. My husband remembers going to the shoe store as a kid and using an x-ray machine that allowed the salesman to look at your feet inside the shoes to make sure they fit correctly. (Apparently the thumb pressing down in search of the big toe method came later because it is hard to NIST-certify thumbs.)
Röntgen never sought honors or financial profit for his discovery. He rejected a title that would have provided entry into the German nobility, and donated the money he received from the very first Nobel Prize in physics to his University. At the time of his death, he was nearly bankrupt from the inflation that followed World War I. He asked for all of his scientific communication and records to be destroyed on his death. Sadly, they were.
Knowing where x-rays come from, we know you don't want to get exposed to more of them than you really need. X-rays are ionizing radiation, which means the radiation can remove one or more electrons from an atom. X-rays can convert harmless organic molecules into much-more-reactive ions (like free radicals) that wreak havoc in the body. Low doses of radiation can damage cell DNA, mutate cells and can cause cancer. Like any technology, x-rays can be used smartly or poorly. Used smartly, x-rays can also save your life.
Of course, the American health care system being as screwed up as it is (due in large part to people wanting magic answers and magic pills instead of doing the hard work of taking better care of themselves), Americans get much more x-ray exposure than people in the rest of the world. If you look worldwide at all the advanced procedures that require radiation, Americans account for fully half of them. The average American's dose keeps growing, too: you've probably had six times as much radiation as your grandparents ever did. Doctors order CAT scans (a type of x-ray) more than sonograms or MRI's, neither of which expose you to ionizing radiation. There's no central accounting that keeps track of your exposures. Even if your doctor has a complete list of the x-rays you've had, he or she generally doesn't have any way to calculate your cumulative dose.
Dose - the amount of radiation absorbed by your body - is the important thing here. The measurement unit is the mrem (millirem). Most people typically get about 360 mrem each year from incidental sources (flying, radon exposure, cosmic radiation, etc.)
|Dental x-ray||10 mrem|
|Round trip NYC-LAX||5 mrem|
|Electron-Beam CT scan for coronary angiography||85-105 mrem|
All atoms have their electrons arranged in shells (remember atomic counting: 2s1 2s2 2p6...?) Inner shells (ones numbered 1 or 2, for example) have lower energy than outer shells. Electrons in the inner shells have less energy than electrons in the outer shells. X-rays are generated by shooting electrons at a metal like copper. The electrons hit the metal atoms and can knock out inner-shell electrons. Since all electrons like being in their lowest possible energy state (don't we all), an electron from a higher energy level will drop into the vacant spot in the low-energy shell. The energy that electron sheds comes off as an electromagnetic wave -- an x-ray.
The x-rays in my diffractometer are generated from a copper target and have a wavelength of about 0.15 nanometers. They are pretty high energy because I don't use x-rays for imaging, but for diffraction. Most medical x-rays are used for imaging and are generated using a tungsten target, so they have a bigger wavelength and smaller energy. Mammograms, which only have to pass through tissue, most often use a molybdenum source with a wavelength of 0.709 nm (Angstroms - thank you Michael!), so mammograms are even lower energy than regular x-rays.
X-rays are the "shooting something through" type of probe, so the images they produce are essentially shadows. Dense areas block more x-rays, which is why you can see Mrs. Roetgen's ring and bones in the x-ray, but not the tendons and muscles in her hand. The less dense material blocks fewer x-rays, allowing some of the film to be exposed. You've probably all see x-rays where the bones are white and the rest is black - that's a negative, which is why it's inverted. The absolute color isn't the most important thing: the contrast is.
The mammogram image at right shows a typical breast. Breast tissue isn't homogeneous - you can see the milk ducts (near the nipple), and the fibrous tissue that makes up most of the breast. The red arrow on the x-ray shows the type of thing a doctor "reading" a mammogram would tag for follow-up. Notice how the tumor is so much whiter - it is much denser than the fibrous breast tissue that surrounds it. (And no, this is not mine.)
A white spot on a mammogram isn't an automatic indication of cancer. A lot of normal (and abnormal) processes can produce questionable features in a mammogram. For example, microcalcifications occur when cells in breast tissue start dividing rapidly. Most cells contain calcium and the cell growth can produce small residual calcium deposits. Certain patterns of microcalcifications, like a series of nodes clumped together or in a line as opposed to randomly scattered, may be a sign of breast cancer.
Or not, because calcium deposits are very common (especially after menopause). They can be caused by fluid from a benign cyst, prior injuries to the breast or even dermatitis. You are instructed not to use deodorant or talcum powder or anything else the day of a mammogram because residue from these types of products can show up looking just like microcalcifications.
If you're in the Plano area, I highly recommend Solis for mammography because they have a great set up: current machines, very nice surroundings and -- most importantly -- they take the time to answer your questions. In my case, that's not a trivial task. When I went for the followup mammogram, they did indeed confirm some abnormal looking spots that might be microcalcifications - or cysts, or remnants of cysts. Or cancer. I was surprised when they took me into another room for a sonogram. To me, a sonogram seems rather low tech compared to a mammogram. Mammograms are high resolution (especially with digital detection). Sonograms bring to mind those fuzzy pictures people show me that I have to pretend look like cute babies.
A sonogram uses sound waves. Sound waves are fundamentally different than electromagnetic waves. Sound waves cause the molecules in a solid, liquid or gas to move back and forth. When I speak, the molecules closest to my mouth start oscillating back and forth, in the direction the wave is traveling. That causes the molecules next to them to start moving, and the molecules next to them, etc. Finally, the molecules next to your ear start to oscillate, which starts your eardrum oscillating and you hear what I said. Sound waves are pressure waves, alternating regions of dense and not-so-dense regions, as shown to the right.
Sound waves can travel through liquids, solids and gases, being fastest in solids because the atoms in solids are connected together much more strongly. When you bump one atom, it affects the atoms around it much more immediately than in a gas, where the atoms are more spread out. In a gas, it takes a little while for the motion to be transmitted. (And this is why, in space, no one can hear you scream. No molecules means no sound.) That's also why they spread jelly over the area they are going to image: the jelly couples the sound waves better to the tissue to be imaged than air would, which gives a stronger signal.
Unlike x-rays, sound waves don't have the energy to pass through bone or tissue. Sound waves are part of the 'bouncing back' class of imaging techniques, working much like radar, where you send out a wave, it bounces into things that change its wavelength and/or speed, and then returns to be detected. The soundwaves used in medical imaging are silent - they are normally in the range of 2-20 MHz (MegaHertz). A typical hearing range goes up to about 0.02 MHz (20 kiloHertz).
A mammogram is a two-dimensional projection of a three-dimensional object, so it doesn't tell you anything about the inside of an object. When you focus sound waves into something heterogeneous, like tissue, the sound waves are partially reflected when there is a density change. It's similar to how light is partially reflected from a plate of glass. That means a sonogram can distinguish between a solid object (like a tumor) and a hollow or fluid-filled object of the same shape (like a cyst). Higher frequencies have smaller wavelengths, which means better resolution. Sonography on breasts generally uses 7-18 MHz sound waves. There is a trade-off in that higher frequencies don't penetrate as deeply into the body as lower-frequency sound waves. If you're after something deeper in the body, you have to use lower-frequency sound.
I should also not that the resolution is not as good when the subject talks during the measurement. (Another benefit of working with Gadolinium.) The features that had raised concern in the mammogram didn't look like they were solid, so after the sonogram (which the technician was kind enough to let me watch while it was being taken), I was told that, although the chances were that they were harmless mineralizations or cysts, I should return in six months to monitor for any changes that might indicate they were growing. Just in case.
I started writing this blog in January, the day after the followup confirmed that I needed more than the usual yearly or every-other-year mammogram schedule. In February, my Mom was diagnosed with ovarian cancer. She died in April. She hadn't had a pelvic exam in at least five years: she said they were "uncomfortable" and couldn't even remember when the last one was.
While we still don't know what causes cancer and we still don't know how to cure it, we do know that the earlier we catch it, the higher the likelihood of beating it. Even with my recent experience with my Mom, I was still a month late on my six-month follow up. My excuse: I got busy. I meant to get to it. Really. I had a few moments between appointments the other day, found myself in the neighborhood and stopped in to make my appointment. Finally.
You know those stickers they give you when you vote - the ones that proclaim "I VOTED!"? They're designed to remind people who see it that they need to vote, too. That gave me an idea.
Every woman should do a monthly breast self-exam. If nothing else, it keeps the idea of your own health in your mind. I've designed an image to be printed out - you can print it on adhesive address labels, or a piece of paper or whatever. (I'm a crappy artist, so maybe someone out there can design something better and we'll make something easy to print.)
The day of the month you do your breast self exam, wear a sticker. It's a pink ribbon - everyone knows what that means. When other women ask what the sticker is for, ask them what day of the month they do their breast self-exam. If they can't tell you, suggest they pick TODAY to start.
Medicine seems to scare people. I know some people make a big difference between medicine and science, but to me, so much of medicine involves really interesting (and useful!) physics and chemistry. The more science you know, the better position you're in to stand up for yourself, your sisters, your mothers and your friends.
I just got back from that "6-month" followup. Another benefit to modern mammography: They know the results right away. The suspicious features they had been watching are essentially gone, which means they probably were microcalcifications or cysts. I promised myself as I saw in the car getting ready to head back to work that I was going to be better about my health this year. Y'all should too: We want all of you to be around for our Cocktail Parties.