Friday, August 27, 2010

Don’t throw away the cane

In Chapter 1 of the 4th edition of Intermediate Physics for Medicine and Biology, Russ Hobbie and I quote the article “Don’t Throw Away the Cane” by Walter Blount (Journal of Bone and Joint Surgery, Volume 38, Pages 695–708, 1956).
The patient with a wise orthopedic surgeon walks with crutches for six months after a fracture of the neck of the femur. He uses a stick for a longer time—the wiser the doctor, the longer the time. If his medical adviser, his physical therapist, his friends, and his pride finally drive him to abandon the cane while he still needs one, he limps. He limps in a subconscious effort to reduce the strain on the weakened hip. If there is restricted motion, he cannot shift his body weight, but he hurries to remove the weight from the painful hip joint when his pride makes him reduce the limp to a minimum. The excessive force pressing on the aging hip takes its toll in producing degenerative changes. He should not have thrown away the stick.
I recently looked up the full article, which is delightful. It was listed as a JBJS classic in 2003 (Volume 85, Page 380). Here are a few more quotes. I suggest you read the entire paper.
As the causes of premature death are conquered one by one, man is given a longer life in which to grow old gracefully. In the twilight years that his forefathers rarely knew, he needs help in seeing, hearing, chewing, and walking. Gradually we are coming to look upon eye glasses, hearing devices, and dentures as welcome aids to gracious living rather than as the stigmata of senility. They should be accepted eagerly as components of a richer life. The cane, too, should be restored to favor as a means of preventing fatigue and a halting gait, rather than maligned as a sign of deterioration.

The use of the cane in order to prevent strain upon an ailing hip or knee is not generally accepted. In the patient's mind there is a nice distinction between the permissible use of a stick postoperatively and the adoption of this humble support for no other reason than the relief of a slight physical infirmity. A fat lady may waddle like a duck when she laboriously walks a few steps, but she resents the suggestion that she carry a cane. She would look much better with a stick than with the limp; and with support she could walk enough to get some exercise. More walking would help with weight reduction. But no! she is not ready for a cane yet! The patient with residual disability after poliomyelitis and with a fatiguing, unsightly lurch needs a cane. Early degenerative hip disease may require no treatment other than weight reduction and a stick in the opposite hand; however it takes an impressive orthopaedic surgeon to sell the idea…

As Pauwels has shown so well (Fig. 8), the use of a cane in the left hand reduces the pressure on the right femoral head without the need for limping. The support afforded by the stick greatly lessens the pull required of the abductor muscles in helping to support the body weight. The cane works through a long lever, so that a moderate push on the stick greatly relieves the strain on the hip [my boldface]. The relative forces are shown in Table I. Pauwels estimated that during the stance phase of walking, without the support of a cane, an average person exerts a static force of 385 pounds on the stationary hip. This weight can be reduced to 220 pounds by pushing down on a stick with the opposite hand the equivalent of 20 pounds. The cane is really an efficient mechanical device…

I should rather be remembered as a thoughtful surgeon than as a bold one. I submit that a well planned sequence of lesser operations with long intervals between, and the use of a cane as needed, may prove better for the patient and productive of a more desirable end result than some more heroic surgical procedure. There is a tendency among orthopaedic surgeons to exchange simple methods for dramatic treatment that will not require the use of the cane. The surgeon looks for a single, definitive, bridge-burning operation that will cure the patient completely for the rest of his life. Too often, this goal is not reached. The patient still needs the stick (or even crutches) after this heroic operation. If a satisfactory arthroplasty or reconstruction operation is performed, how much better it would be for most patients to urge the continued use of a cane in order to preserve the function of the reshaped bone by taking the strain off the hip for years, not for months only.
Blount was a leading physician and surgeon in orthopedics. His grandfather was a civil war surgeon, his mother was a physician and surgeon, and his sister was a pediatrician. He attended the University of Illinois and Rush Medical College. He helped develop the Milwaukee brace for spinal malalignment, was an expert on fractures in children, and introduced tibial stapling for epiphyses. In 1954 he became president of the American Academy of Orthopedic Surgeons.

Friday, August 20, 2010

The Anger Camera

In Section 17.12 of the 4th edition of Intermediate Physics for Medicine and Biology, Russ Hobbie and I discuss the gamma camera, used in to produce images during nuclear medicine procedures. The gamma camera often goes by another name, the Anger camera, after its inventor Hal Anger (1920–2005). Anger’s contributions to medical physics imaging rank him with giants of the field such as Godfrey Hounsfield, Allan Cormack, and Paul Lauterbur. Yet, it is harder to find information about Anger than about these other luminaries. His obituary in the New York Times stated
Mr. Anger was known in his field for inventing the gamma camera, which was first exhibited in 1958 at a meeting of the Society of Nuclear Medicine. The device, also known as a scintillation camera and later as the Anger camera, produced images of internal processes by tracking tiny amounts of radioactive substances, known as radiopharmaceuticals, given to patients.

The invention and later improvements represented a major advance in the diagnosis and treatment of brain tumors, bone marrow disorders and other life-threatening diseases.
Another obituary in the IEEE publication The Institute wrote
Seen by many as a quiet genius who shaped the future of nuclear medicine, Hal took a hands-on approach to science that also led to his invention of the well counter, which is used daily in nuclear medical labs worldwide to measure small quantities of radioactive substances. He also invented the whole-body scanner, the positron camera, and the multiplane tomographic scanner.

Nuclear medicine has been profoundly affected by Hal Anger. Millions of patients have benefited from diagnosis and treatment that depended on the Anger camera and the innovations made possible by its development.
Anger described his invention in a paper titled simply “Scintillation Camera” (Review of Scientific Instruments, Volume 29, Pages 27–33, 1958). The abstract is reproduced below.
A new and more sensitive gamma-ray camera for visualizing sources of radioactivity is described. It consists of a lead shield with a pinhole aperture, a scintillating crystal within the shield viewed by a bank of seven photomultiplier tubes, a signal matrix circuit, a pulse-height selector, and a cathode-ray oscilloscope. Scintillations that fall in a certain range of brightness, such as the photopeak scintillations from a gamma-ray-emitting isotope, are reproduced as point flashes of light on the cathode-ray tube screen in approximately the same relative positions as the original scintillations in the crystal. A time exposure of the screen is taken with an oscilloscope camera, during which time a gamma-ray image of the subject is formed from the flashes that occur. One of many medical and industrial uses is described, namely the visualization of the thyroid gland with I131.

Friday, August 13, 2010

The barn

Figure 15.2 of the 4th edition of Intermediate Physics for Medicine and Biology shows the cross section for the interaction of photons with carbon versus photon energy. The caption of the figure says “The cross section is given in barns: 1 b = 10−28 m2.” Where did this strange unit come from?

The July 1972 issue of Physics Today published a letter by M. G. Holloway and C. P Baker, explaining “How the Barn was Born.”
Some time in December of 1942, the authors, being hungry and deprived temporarily of domestic cooking, were eating dinner in the cafeteria of the Union Building of Purdue University. With cigarettes and coffee the conversation turned to the topic uppermost in their minds, namely cross sections. In the course of the conversation, it was lamented that there was no name for the unit of cross section of 10−24 cm2. It was natural to try to remedy this situation.

The tradition of naming a unit after some great man closely associated with the field ran into difficulties since no such person could be brought to mind. Failing in this, the names Oppenheimer and Bethe were tried, since these men had suggested and made possible the work on the problem with which the Purdue project was concerned. The “Oppenheimer” was discarded because of its length, although in retrospect an “Oppy” or “Oppie” would seem to be short enough. The “Bethe” was thought to lend itself to confusion because of the widespread use of the Greek letter. Since John Manley was directing the work at Purdue, his name was tried, but the “Manley” was through to be too long. The “John” was considered, but was discarded because of the use of the term for purposes other than as the name of a person. The rural background of one of the authors then led to the bridging of the gap between the “John” and the “barn.” This immediately seemed good and further it was pointed out that a cross section of 10−24 cm2 for nuclear processes was really as big as a barn. Such was the birth of the “barn.”

To the best knowledge of the authors, the first public (if it may be called that) use of the barn was in Report LAMS-2 (28 June, 1943) in which the barn was defined as a cross section of 1 × 10−24 cm2.

The authors would like to insist that the “barn” is spelled just that way, that no capital “b” is needed, and that the plural is “barns” with no letter “e” involved, and that the symbol be a small “b.” The meanings of “millibarn” and “kilobarn” are obvious.

Friday, August 6, 2010

Iron, Nature’s Universal Element

Iron, Nature's Universal Element:  Why People Need Iron and Animals Make Magnets,  by Eugenie Mielczarek, superimposed on Intermediate Physics for Medicine and Biology.
Iron, Nature's Universal Element:
Why People Need Iron
and Animals Make Magnets
by Eugenie Mielczarek.
A few months ago in this blog, I mentioned that I put the book Iron, Nature’s Universal Element: Why People Need Iron and Animals Make Magnets, by Eugenie Mielczarek and Sharon McGrayne, on my list of things to read this summer. Well, I finished this book, and I recommend it. Russ Hobbie and I cite the book in Chapter 8 of the 4th edition of Intermediate Physics for Medicine and Biology.
Magnetism is used for orientation by several organisms. A history of studies in this area is provided in a very readable book by Mielczarek and McGrayne (2000).
My favorite part of Iron, Nature’s Universal Element was Chapter 4, on magnetotactic bacteria. Russ and I discussed these interesting little creatures in Section 8.8.3
Several species of bacteria contain linear strings of up to 20 particles of magnetite, each about 50 nm on a side encased in a mambrane [Frankel et al. (1979); Moskowitz (1995)]. Over a dozen different bacteria have been indentified that synthesize these intracellular, membrane-bound particles or magnetosomes (Fig. 8.25). Bacteria in the northern hemisphere have been shown to seek the north pole. Because of the tilt of the earth’s field, they burrow deeper into the environment in which they live. Similar bacteria in the southern hemisphere burrow down by seeking the south pole. In the laboratory the bacteria align themselves with the local field.
The caption to our Figure 8.25 reads
The small black dots are magnetosomes, small particles of magnetite in the magnetotactic bacterium Aquaspirillum magnetotacticum. The vertical bar is 1 [micron] long. The photograph was taken by Y. Gorby and was supplied by N. Blakemore and R. Blakemore, University of New Hampshire.
Mielczarek and McGrayne provide a colorful description of how magnetotactic bacteria were discovered.
“I see it crystal clearly,” Richard Blakemore said, recalling the evening he discovered Earth’s smallest living magnets. “I get excited every time I look at them.”

It was already dark outside the laboratory as Blakemore, peering through his microscope, searched through mud samples for bacteria. At twenty-three, Blakemore was a second-year graduate student in microbiology at the University of Massachusetts in Amherst. In 1975, fledgling microbiologists there were often assigned such simple tasks as identifying the material between their teeth or analyzing organisms in mud. His professor had collected the mud from a Massachusetts marsh, and asked Blakemore to learn everything possible about some large spiral bacteria in it. But that night, Blakemore said, “other organisms forced their existence on me...”

So while Blakemore looked through the scope, [advanced graduate student John Bresnick] picked up a magnetic stirrer lying beside the microscope and brought it up behind the swimmers. “Fortunately,” Blakemore recalled, “he had the end of the magnet pointing toward them so that it attracted them. And—all of a sudden—en masse—this whole massive population of bacteria swims in exactly the opposite way across the microscope stage. It was incredible, just incredible, and no one even believed my response. They thought I was kidding—until they looked in...” At that point, John Bresnick said, “I think you’ve discovered something...” “From then on,” Blakemore said, still starry-eyed more than twenty years later, “it was a night of incredulity...”

Blakemore’s microbiology professor was in Italy at the time, and Blakemore was exploding with the news, so he raced home to tell his wife Nancy. Abandoning all grammar in the joy of the memory, Blakemore said “It couldn’t have been perfecter. I didn’t really—hardly—know how to take it in.”