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Physics Medical Physics

  1. Oct 6, 2003 #1
    Having been an occasional member of this forum for a while, I find myself dissapointed by the lack of discussion about medical physics. It really is an exciting field (I would say that...) and is usually totally shadowed by all of the other applications to physics. Space science and astronomy are great, but medical phyiscs is very down to earth (forgive the pun) subject, and is a fascinating and rewarding career path. I personally work in Radiotherapy, but many other applications are available, and there is much research to be done in this importnat and fast expanding field.

    Am I the only person on the forum interested? Does anyone want to know more about medical physics as a career?
  2. jcsd
  3. Oct 6, 2003 #2


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    I’m familiar with Radiotherapy from the bioengineering aspect and would agree that medical physics could be an exiting field. Besides the various positions in a hospital environment, there is also a bio-industry need. From my own experiences, working with a physician on a daily basis can be frustrating. Hospital politics is unique to say the least. The medical physicist, I think, would benefit from having an introductory circuit and mechanical design course included in their curriculum. Of course today’s world requires as much computer expertise as one can manage.
  4. Oct 6, 2003 #3

    Chi Meson

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    As a teacher I would love to follow interesting threads on the lastest uses of physics in the medical realm. Lasers, MRIs, CAT scans, PET scans, ultrasound, etc etc... It seems that the most worthwile outcome of physics is in the medical applications. I see it as something to counter the stigma of "The Bomb."
  5. Oct 6, 2003 #4


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    Chi Meson – There is no artifact that lacks an underlying knowledge of physics in its creation. Actually all the devices you mention have been in use since the 1970’s, and the supporting physics known decades earlier. Imaging technologies owe their existence to the mathematical algorithms, programmers, and faster almost single chip computers (less expensive to manufacture) that became available then.

    While PET produces an image of body metabolism it is not an anatomical image. The superimposing of its image with that of an MRI or a CT is really impressive. The early use of ultra sound in medicine was to precisely locate the pituitary gland as an aid to diagnosing a concussion. Visiting the NIH (1972), I met a pioneer in the field of ultrasound. He had PhD’s in physics, and engineering, a doctorate in medicine and looked to be less than 25 years old. To image with ultrasound the beam must be moved similar to an automobiles windshield wiper’s pattern. Then it was done mechanically. Now some 64 or more transponders are used with beam steering done by controlling the phase relationship of the sound pulses. This technology probably is derived from a process to direct the radar beam in military aircraft. I once toyed with a surgical laser. The device used a helium laser as an aiming beam (visible red) and an 80-watt, infrared CO2 laser for the knife. The beams were transmitted through an articulated arm and focused on a point several inches away. I removed the focusing optics, and using some other borrowed optics, I achieved a focal point about 10 feet away. I was able to burn tiny holes in IBM cards at that distance. I hid under a desk as I did this because I did not know if the IR beam would be focused using normal optics or if they would crack from the heat. Without any optics, it made the paint discolor on the ceiling. I always wondered what the painters thought about all those little round spots on the ceiling. Surgery is also done with high frequency electric currents. Tissue and muscle response to high frequency current is almost non-existent, whereas at 60hz there is a lot of twitching with a high probability of causing cardiac fibrillation. Hi currents are achieved at the surgical site by use of a very pointed instrument. Exit current density is kept low by using a large dispersing plate and conductive gel.

    I could go on forever as there’s so much material.
  6. Oct 7, 2003 #5
    I have to agree about hospital politics. I haven't been working in my current place of work very long and so try not to get involved, but it always ends up affecting you.

    Although my work involves routine things; calibtrations of linacs used for RT, QA etc. I also involve myself in project work quite significantly. My dissertation for my degree for example involved 3D image registration via different algorithms when applied to MRI, CT and SPECT images. I am currently working on a gynae brachytherapy (insertion of radioactive sources to treat cancer of the ovaries and cervix) related-project, which is mainly programming at the moment.

    When asked what my job is, people always wonder what possible application physics couild have to medicine. It's a very understaed profession.

    Teachers could (and should!) throw in the odd comment about MP when teaching. It's very easy to come up with examples related to space science or televisions or other technology, but the first time I heard my own blood flowing in my neck (doppler ultrasound) I was instantly hooked, and wanted to know how it worked.

    I dont think enough time is spent promoting physics and all of the things that it can be applied to. Lack of links with real-life applications leads to a lack of interest from students. The more applications they are exposed to, the better.

    Ok, end of ranting.
  7. Oct 7, 2003 #6

    Chi Meson

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    This is partly due to many physics teachers spending too much time on mechanics, never getting to heat, light, sound, and electricity. TO most of the country (US) Physics is associated with cars crashing, and cannonballs being fired off mountains. I always make a point of truncating mechanics as soon as we hit the halfway point. I'm thinking of ditching projectile motion completely because optics, sound, and thermodynamics seems to be more applicable.

    So... legitimate question: what is that radioactive tracer that is injected into the blood, and what is the specific application? I remember it made my arm very cold.
  8. Oct 7, 2003 #7
    It depends on which organ they were looking at. Different organs take up different chemicals better than others. 131I, 132I, and 123I are all used, but for instance 131I has a half-life of 8 days which is longer than any test will last so its more ideal to use 123I. Different compounds containing these iodine isotopes can be taken up by different organs. There are other elements beside iodine that are used but I'm not familiar with them all. I think Tc is used also.

    LSU ( where I go to school ) has a medical physics program. Here is their "links" page http://www.nuclear.lsu.edu/links.htm
  9. Oct 8, 2003 #8
    You are absolutely right:

    It really depends what the area of interest was in your body. Isotopes of Iodine are commonly used, especially for testing (and sometimes treating) thyroid gland function. Cr-51 also often used.

    By far the most commonly used isotope, as you mention, is a metastable isotope of Tecnecium, Tc-99m. It is especially used in conjunction with gamma cameras since it offers the best overall tradeoff between the factors that make up the "ideal" medical isotope (shortbut usable halflife, fairly monoenergetic gammas with no betas or alphas, easily made etc.). It can also be bound to different molecules, and so can be sent to whichever bit of the body is required.

    I've never had one, but have had a few beasty injections, and they were damn cold. It feels weird, I must admit.

    Most people who have iodine usually have to drink it. By all accounts it just tastes like water. They should mix it with coke or something...

  10. Oct 8, 2003 #9
    I wonder why 99mTc has an "m" in the mass number. Does anyone know?
  11. Oct 9, 2003 #10
    The m stands for metastable, as I mentioned in one of my above posts.

    A metastable state is effectively a quantum mechanical energy state which has an unusual exited > ground relaxation process. I think it has something to do with a quantum number mismatch. Anyway, the basic effect is that the half-life changes. Tc-99 has a halflife of about 20000 years; Tc-99m has a half-life of around 6 hours.

    It is produced via a radioisotope generator (we have one here in this hospital), the "parent" being Mo-99.

    The generator is simply a big ol' shielded thing, in which Mo-99 is placed (it gets replenished periodically). It has a half life of about 3 days I think, and the daughter, Tc-99m, is flushed away from the core with saline, which can then be taken away for activity measurments before going into a patient. It needs to be made on site because it has such a short effictive lifetime; good for the patient, but creates transit problems.

    Here in the hospital I work in, we supply about 4 other hospitals with the radioisotopes they need, genally on a daily basis. They are all a fairly short distance away, so they can be sent off in the early hours and used that day.

    I don't actually work in radioisotopes (I did last summer for a few months at a different hospital); I work in radiotherapy, so please forgive any mistakes in the information.

  12. Oct 9, 2003 #11
    In my watching of TV I recall having seen the first of the images, made by a PET scan, of the active dynamics of the Human brain, at work. I suspect that, since then, they have changed the radioisotope employed, as the original one was a dual photon(*) emitter and it was not the "safest" but the dynamic pictures of the brain, actively thinking, were really neat to watch, and does it ever act fast.
    (*)(They used a dual positron(?) or photon(?) emitter which they later found out had some rather not so nice side effects)

    Do they still have the ability to generate active (visually real time dynamic) brain scans using PET's?
  13. Oct 9, 2003 #12
    Absolutely. I dont know a great deal about it, but I know that it is particularly useful in cardiac monitoring. They commonly use Rb-82 as the radioisotope. I don't know about the brain application.

    PET is chiefly used to monitor function an metabolism, as opposed to anatomy. You can guess this just by looking at a PET scan because it looks vaugely like what you would expect but with very poor resolution.

    The process is actually very interesting: The radioisotope decays into (among other things) an unstable positron, which travels for a short distance before destructing into a photon pair, which in turn travel in opposite directions (to conform to the conservation of energy).

    The dectector array design is very clever because it utilises this fact in order to create the 3D image (it knows where the destruction has taken place because of comparison of time of flights for the photons).

    Interestingly, the lack of resolution is mainly due to the short distance travelled by the positron before it destructs.

    SPECT scans are similar, but I'm sure you can guess what the 'S' stands for...


    Who wants a medical physics forum on this site? Meeeeeee!!
  14. Oct 10, 2003 #13
    I enjoy mechanics and things of this nature. It is really easy to forget the other branches of physics like the medical field. ATB for starting a thread on it. Medical physics has lead to great devices like the MRI. IMO it is among the most interesting devices in physics only topped by tesla coils and particle accelerators. Anyway, besides the hair raising name like Magnetic Resonance Imaging, it has really aided in the diagnosis of ailments which is never a bad thing.
  15. Oct 10, 2003 #14
    MRI is indeed very clever.

    One great expereince that always sticks in my mind about MR is when I was in my first year undergrad. My MRI/CT lecturer took me (I was the only one on my course!) to the hospital, the very one at which I now work, to show me the MR scanners. There are 2, one 1T machine and one 1.5T machine, which I'm sure you all know is a rather strong magnet. I had to remove all metal from my person and fill out a form about pacemakers and past surgery as well.

    He showed me the hidden bits of the machine, such as the liquid He cooling system and the power generator. Then he took me into the room, taking out of his pocket a pair of scissors on a piece of string. I swear that thing lept up and pointed at the core of the scanner, and the string was pulled tight (and twangable). Next he took out a paperclip and told me to hold it in my hand. I then put my hand into the scanner, and it squirmed insode my hand and was twisted beyond recognition.

    The images we gain from MRI these days are very high definition, and you can pick out individual cross sections of small veins and the like. It is invaluable in oncology and diagnosis of many nerve and brain disesases like multiple sclerosis and alzheimers disease.

    What I do remember is that it was also the hardest and most complicated medical physics module I studied. Very intersting, but applied quantum mechanics and fourier transforms made for a daunting combination.

  16. Oct 10, 2003 #15
    Personally, I enjoy mechanics because it has helped me many times in everyday life.

    Medical Physics is what I'd like to read up/study a bit sometime but I think I'm more into the Physics that will be "seen"/used in everyday life. Every once too often, I will indulge in the Philosophical/Theoritical side of Physics but to be quite honest, haven't looked too deeply into the medical side of things. While I plan to, it doesn't seem quite as interesting to me. Maybe you can prove me wrong?

    So, with you being in the medical industry, what is the most effective cure for cancer?
  17. Oct 10, 2003 #16
    Prevention, and sorry, I realize the question isn't meant for me, but having some little knowledge on the subjects, I thought.
    (And "no" it isn't a joke, either)
  18. Oct 10, 2003 #17
    No problem, it's a forum. Your opinion and knowledge is valued.

    I ahve to agree with Mr. R.P, because ultimately that's right. Unfortunately there are many cancers for which this is not possible. A lot of cancer conditions are unrelated to lifestyle, and so some people are just unlucky.

    As for the best treatment for cancer? I'm a physicist, not an oncology doctor, so I'm not in a position to answer that, especially since chemotherapy plays an important part in cancer treatment: this of course has nothing to do with medical physics.

    It also depends on the type of cancer. There are several forms of radiotherapy, each having different pros and cons for different cancers in different parts of the body.

    Unfortunatley, many patients receive radiotherapy with no hope of ever being cured; the treatment is simply prolonging life or pain management. These cases are always the hardest to work with because you know (and they know) that they do not have long to live. It's a matter of making them comfortable and maximising the time they have left.

    On the other hand, you can be impaired by a patients wishes. Just last week, a patient with Hodgkins disease (a type of brain cancer) was admitted to us. She is only 20 years old, and refuses stright up to lose her hair. She went on an unusual course of chemotherapy to prevent hair loss, knowing it would make her sterile, which it did. She now has the choice (radiotherapy) of 95% survival with 80% hair loss, or certain death (within 15 years or so) with no hair loss. I'm not kidding. It's maddening to see things like that. A total waste of life just because she doesn't want to lose her hair.

  19. Oct 11, 2003 #18
    A life for a bunch of hair?! Thats rediculus.

    There was this thing we learnt in Physics last year, that you can fire an (electromagnetic) beam from three different places concentrating on one are of the brain to get of a brain tumour. Can't quite remember what it was though.

    Gamma rays?
  20. Oct 11, 2003 #19
    Know someone that that was performed upon, as experimentation, (Stereotactic was what it was called then) "cured" (rather stopped the growth, killed the tumor) the cancer, but left the person in, well, not the best of 'living' realities.
    My Dad Died of cancer, lung then brain, and given that it is genetically based and very idiosyncratic, "curing" cancer seems a little bit of a misnomer as it is a part of the systems built in protection(s) just with an 'error' in place.
    As for the hair part, did something like that when I was younger, twice actually, shaved my head bald to see if I had the strength of character to live like that, it was interesting.
  21. Oct 11, 2003 #20


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    Hi Jonathan. I'm wicked glad you brought this up. At the moment I'm trying to get into the field. I'm educated as a physicist and due to my recent bout with cancer I've been wanting to get into the field you're in. In particular I'd like to get into Radiological Oncology, but I'm flexible. I'm up for a position as a dosimetrist (waiting for second interview) and am crossing my fingers.

    Any pointers you can give me to get into the field would be greatly appreciated.

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