In Chapter 15 of the 4th edition of Intermediate Physics for Medicine and Biology, Russ Hobbie and I discuss the interaction of radiation with matter, a topic that is crucial for understanding the medical use of X-rays. Twenty years ago, Russ wrote a computer program called MacDose that provides a two-dimensional simulation of the photoelectric effect, Compton scattering, and pair production; the primary mechanisms of X-ray interaction. MacDose runs on any Macintosh with OS-9 or earlier, including Classic in OS-X. You can download a copy of MacDose, including a student manual and instructors guide, at our book’s website. To learn more about MacDose, see Hobbie’s article in Computers in Physics (Volume 6, Pages 355–359, 1992).
You can also download a 26 minute Quicktime movie in which Russ demonstrates MacDose and explains various concepts related to the attenuation and absorption of X-rays (you can view the movie on either a PC or a Mac). With help from my daughter Stephanie, I have uploaded this movie onto Youtube. Because of a limit on the duration of Youtube videos, Stephanie had to split the movie into three parts. Search on YouTube for “MacDose” and you should find all three. Then pop some popcorn, pour yourself a drink, find a seat, and watch Hollywood’s leading man Russ Hobbie explain how radiation interacts with matter.
In the 1940s and 50s, Alan Hodgkin and Andrew Huxley discovered the ionic basis for nerve conduction, work that resulted in their sharing the 1963 Nobel Prize in Physiology or Medicine. Chapter 6 in the 4th edition of Intermediate Physics for Medicine and Biology describes the Hodgkin-Huxley model in detail. Yet, no textbook can replace the experience of peering over Hodgkin's shoulder while he performs the voltage clamp experiments on a squid nerve axon that were crucial for their discoveries. Fortunately, a movie was made of these experiments, and clips from it can be found online, at a website for a neurophysiology class at Smith College. I particularly recommend the clip “Dissection and Anatomy” showing the dissection of the giant axon from a squid by J. Z. Young, and “Voltage Clamping” by P. F. Baker and Hodgkin himself.
When I teach Biological Physics at Oakland University, I like to have my students read Hodgkin and Huxley's classic paper “A Quantitative Description of Membrane Current and its Application to Conduction and Excitation in Nerve” (Journal of Physiology, Volume 117, Pages 500–544, 1952). A pdf of this article is available online. However, if you encourage your students to read it, be sure to warn them that the definition of the transmembrane potential is different than is used now, with their definition being the outside minus the inside voltage, and zero being rest. (Nowadays, researchers typically use inside minus outside, with rest corresponding to -65 mV). Writing a program to simulate the Hodgkin and Huxley model is the best way to learn about it (we have a sample of such a program in Fig. 6.38 or our textbook), but those who are not programmers might want to try this applet that allows online simulation of a nerve action potential.
The quotes below are taken from the American Association of Physicists in Medicine Golden Anniversary website.
Many of the greatest inventions in modern medicine were developed by physicists who imported technologies such as X rays, nuclear magnetic resonance, ultrasound, particle accelerators and radioisotope tagging and detection techniques into the medical domain. There they became magnetic resonance imaging (MRI), computerized tomography (CT) scanning, nuclear medicine, positron emission tomography (PET) scanning, and various radiotherapy treatment methods. These contributions have revolutionized medical techniques for imaging the human body and treating disease.
Now, in 2008, the American Association of Physicists in Medicine (AAPM), the premier scientific and professional association of medical physicists, is celebrating its 50th anniversary and is calling attention to the field of medical physics achievements.
In the coming year, the AAPM will be calling attention to the many ways in which medical physics has revolutionized medicine. A few highlights include:
1. USING PARTICLE ACCELERATORS TO DEFEAT CANCER 2. BETTER DETECTION OF BREAST CANCER 3. MATTER/ANTIMATTER COLLISION IMAGING 4. ENSURING THE SAFETY OF PEOPLE WHO GET CT SCANS 5. MEDICAL PHYSICS MOMENTS IN HISTORY
This year, the AAPM journal, Medical Physics, will celebrate the 50th anniversary with a year-long celebration. Every issue published in 2008 will have an article devoted to history and reviews of special topics intended to recognize this anniversary, and will carry the AAPM anniversary logo.
The AAPM is a scientific, educational, and professional nonprofit organization whose mission is to advance the application of physics to the diagnosis and treatment of human disease. The association encourages innovative research and development, helps disseminate scientific and technical information, fosters the education and professional development of medical physicists, and promotes the highest quality medical services for patients. In 2008, AAPM will celebrate its 50th year of serving patients, physicians, and physicists.
Anyone who teaches college students or has teenage children knows that the first place they go to for information is Wikipedia, the free online encyclopedia that anyone can edit. I, too, find Wikipedia useful. It’s extraodinarily simple to search for information, and surprisingly accurate. But sometimes, for technical information, you may prefer a more authoritative source. Now you have it: Scholarpedia. Like Wikipedia, Scholarpedia is online, free, and simple to use. The main difference with Wikipedia is that in Scholarpedia articles are authored and maintained by experts and undergo peer review. Anyone can edit Scholarpedia, but all changes must be approved by the “curator” (often the author) of the article, who’s responsible for its content.
Physics is changing the way medicine is practised. While a doctor will still use a stethoscope, a diagnosis now often requires devices that make use of sophisticated physics and engineering. The importance of physics in medicine may be best displayed when a physicist needs to visit their doctor: we seem to be the only people who can intimidate doctors as we are the ones who actually know how their devices work. As a consequence of the technological evolution of the discipline, medical schools are admitting more and more students who major in physics or engineering.
Almost all major engineering schools will now have a department of biomedical engineering. There are numerous opportunities in academia in medical physics and biomedical engineering. Students interested in becoming an academic physicist now have a fast-growing field to aim for, a field that is providing more and more opportunities. The industrial sector in biomedical engineering is also advancing and evolving quickly. Physicists and engineers can find numerous and lucrative opportunities with companies.
With all of these opportunities it is no wonder that undergraduates are very interested in knowing more about medical physics. Partly due to student interest, and partly due to the faculty’s desire to provide interesting physics classes, Carleton College offered an intermediate level course in medical physics. This was a course open to students who have completed the first year physics courses. We deliberately designed the medical physics course so that the curriculum would be advanced, thereby negating the possibility that this course alone would satisfy a pre-medical school requirement. At this level we then attracted physics majors and pre-medical students who had a genuine interest in studying more physics.
For instance, a video from December 2007 titled “Baby Thinking” describes a technique using diffuse optical tomography to study brain activity in children. Diffuse optical tomography is based on the diffusion of infrared and visible light through biological tissue, a topic examined in Chapter 14 of Intermediate Physics for Medicine and Biology. The November 2007 video titled “Safer MRI Scans for Heart Patients” explains how magnetic resonance images can be obtained safely in patients with implanted pacemakers and defibrillators. Pacemakers are described in Chapter 7, and MRI is explained in Chapter 18, of our textbook.
For those teachers who spend a lecture on the technical aspects of, say, optical diffusion may want to end the class with a 90 second video describing a potential application to modern medicine. It could help make the the basic science learned from Intermediate Physics for Medicine and Biology more relevant to the students.
The exponential function is one of the most important and widely occurring functions in physics and biology. In biology, it may describe the growth of bacteria or animal populations, the decrease of the number of bacteria in response to a sterilization procedure, the growth of a tumor, or the absorption or excretion of a drug... In physics, the exponential function describes the decay of radioactive nuclei, the emission of light by atoms, the absorption of light as it passes through matter, the change in voltage or current in some electrical circuits, the variation of temperature with time as a warm object cools, and the rate of some chemical reactions.
The Essential Exponential! For the Future of Our Planet,
by Albert Bartlett.
Albert Bartlett has written a fascinating collection of essays about the exponential function: The Essential Exponential! For the Future of Our Planet. He claims that “the greatest shortcoming of the human race is our inability to understand the exponential function.” You can see Bartlett talking about the exponential and its implications for population growth on Youtube.
e: The Story of a Number,
by Eli Maor.
The exponential function is often written using the number e = 2.718... (If you want better precision, go to Google and search for "e"). This may be the most famous number, besides Ï€, that’s not an integer. If you would like to read about the history of e, try Eli Maor’s delightful book e: The Story of a Number.
I’m a skeptic when it comes to “alternative medicine.” Often the claims of alternative medicine conflict with the basic laws of physics—and in the end, physics always wins. In particular, there are many dubious health claims about the biological effects of electric and magnetic fields. For instance, I don’t know of any research supporting the idea that magnets in your shoes or jewelry have health benefits, nor can I think of any plausible mechanism underlying such an effect. Are there companies that really promote such silliness? Go to Google and search for “magnetic therapy” and you’ll find that, indeed, there are.
Voodoo Science: The Road from Foolishness to Fraud,
by Robert Park.
“Natural” remedies [such as magnetic therapy] are presumed by their proponents to be somehow both safer and more powerful than science-based medicine. Fortunately, most natural medicine is in itself relatively harmless, aside from the financial damage done by paying eighty-nine dollars for a refrigerator magnet... It can, however, become dangerous if it leads people to forego needed medical treatment. Worse, alternative medicine reinforces a sort of upside-down view of how the world works, leaving people vulnerable to predatory quacks.
Another source of useful information is the magazine Skeptical Inquirer. In particular, see the article “Magnet Therapy, A Billion-dollar Boondoggle” by Bruce Flamm (July 2006), where he claims that there exists “a worldwide epidemic of useless magnet therapy.” Also, see Stephen Barrett’s article “Magnet Therapy: A Skeptical View” published by Quackwatch, Inc., a nonprofit corporation whose purpose is to combat health-related frauds, myths, fads, fallacies, and misconduct. Barrett’s bottom line is that “there is no scientific basis to conclude that small, static magnets can relieve pain or influence the course of any disease. In fact, many of today’s products produce no significant magnetic field at or beneath the skin’s surface.” How can you distinguish the legitimate from nonsense? I suspect the layman will have a hard time telling the difference between “magnetic therapy” (bogus) and “magnetic stimulation” (a well-understood technique to excite nerves in the brain). The only way I know to sort out the good from the bad is to educate yourself on the underlying physics as it applies to biology and medicine. One place to start is the 4th edition of Intermediate Physics for Medicine and Biology. Whether you consult our book or another source of information, beware of suspicious claims about the benefits of electric and magnetic fields. Bioelectricity and biomagnetism are vibrant and important fields of study (see Chapters 6–9 of our book), but there’s a lot of baloney out there too.
I recently finished readingThe World Is Flat by Thomas Friedman. This fascinating book is an “account of the great changes taking place in our time, as lightning-swift advances in technology and communications put people all over the globe in touch as never before.” I recommend it highly.
Is the world of medical physics flat? That I can write this blog about the 4th edition of the textbook Intermediate Physics for Medicine and Biology and have it read immediately, anywhere, by anyone in the world is amazing, and suggests how our world is flattening.
One example that Friedman presents is the outsourcing of reading x-rays and MRIs to India and other countries. On pages 15–16, Friedman quotes an email from Bill Brody, president of Johns Hopkins University:
Dear Tom, I am speaking at a Hopkins continuing education medical meeting for radiologists (I used to be a radiologist)... I have just learned that in many small and some medium-sized hospitals in the US, radiologists are outsourcing reading of CAT scans to doctors in India and Australia!!! Most of this evidently occurs at night (and maybe weekends) when the radiologists do not have sufficient staffing to provide in-hospital coverage... Since CAT (AND MRI) images are already in digital format and available on a network with standardized protocol, it is no problem to view the images anywhere in the world... Best, Bill
For now, the practical effect on radiology is small. At its highest levels, the United States health care system may be the best the world has ever known. India doesn’t even have many radiologists today, let alone a large number who measure up to American standards. But that’s going to change. Eventually, Indian doctors will be able to do the preliminary diagnoses that are a big part of radiology.
...to one degree or another, health care experiences the same market forces as do other industries. Whether in manufacturing, accounting, law, research science, or medicine, ultimately efficient markets will carry business activity to the lowest-cost and highest-quality supplier. At the current time, radiology is particularly vulnerable to outsourcing because of recent technologic developments. Other specialties, such as pathology, may soon follow suit. As the level of education rises in other countries, it is likely that medical tourism will also grow. If nothing else, American medicine should expect some major changes in its way of doing business in the coming years.
Outsourcing can be good or bad, depending on your perspective. Take a look at the website of the company Outsource2India to get the Indian view on outsourcing.
What is the bottom line? Outsourcing in radiology is a complex issue that I cannot resolve here. Generally I favor free trade, so I don’t view these developments with fear. One thing I can say with reasonable certainty is that, like it or not, the world of medical physics is becoming flatter.
Happy birthday to the 4th edition of Intermediate Physics for Medicine and Biology! Determining the precise date to celebrate is difficult, but one year ago this week (March 2) I received an email from my coauthor Russ Hobbie saying that an advance copy of our textbook had arrived at his house. This first anniversary is an appropriate time to thank all our readers for their support and encouragement. Without our dear readers, writing our book would have been a pointless exercise. Russ and I have heard from several instructors who are using our text for a class on biological or medical physics. We are grateful that you chose our book for your class. To the students in those classes, we hope we’ve not caused you too much grief. To all of you who have offered your kind words and compliments, they are greatly appreciated. And a special thank you to those who have pointed out and helped us correct mistakes. You can find a list of known mistakes, and other information, at the book’s website.
Two weeks ago another landmark passed unnoticed. February 21 was the 6-month anniversary of this blog. I will keep posting weekly entries as long as I have anything useful to say (and perhaps longer). I hope the blog has served as a valuable supplement to the book.
I am an emeritus professor of physics at Oakland University, and coauthor of the textbook Intermediate Physics for Medicine and Biology. The purpose of this blog is specifically to support and promote my textbook, and in general to illustrate applications of physics to medicine and biology.
