Re: [pinhole-discussion] Pinhole Camera for medical purposes
- Original Message - From: > I am working as a Medical Physicist for my summer Co-op position. One of the projects I am working on is an attempt to use a x-ray flouroscopy screen and a thick piece of lead with a hole drilled through the center to try and image the position of a point source of radiation in a radiation therapy procedure. The radiation used is gamma-radiation which is an electromagnetic wave like light so it has most of the same properties. Interesting project you young people have the chance to work on, a young friend of mine flew to Switzerland just yesterday to work on the installation of a new particle detector at CERN. Let me congratulate you on your summer job position. > I am trying to optimize the Field of View and the Resolution and can't find _any_ resources for pinhole imaging with the pinhole in a thick material. (The thickness is required, otherwise the strength of the radiation will over-expose the screen and all we will see is white.) Any knowledge, links or even idle speculation would be appreciated. I am less than a neophyte on this stuff, but that doesn't prevent me from posting this: if what you have is a pinhole on a very thick piece of lead, this is basically a gamma rays collimator, it would allow only gamma rays parallel to the pinhole walls to reach the detector (fluoroscopy screen in this case?), therefore your point source of gamma rays would have to be in axis with the pinhole "tunnel" in order for an image of the source of rays to form. It seems to me that if the aim is to image the position of the source, no matter where it is, a collimator consisting in an array of pinholes should be used, in this case, an image of the source will be formed by the pinhole whose axis happen to be in line with the source of rays. As for the field of view, a pinhole drilled in any thick material precludes any field of view, due to simple geometry of the set up. Resolution: gamma rays have such a high frequency that probably any pinhole you are able to make will be much bigger than what any Lord Rayleigh derived optimum pinhole formula would give you (assuming they obey to the same diffraction laws as visible spectrum wavelength), therefore loss of resolution due to diffraction could be disregarded and all you have is geometric resolution given by the diameter of the pinhole. What I would do is to do google searches and send emails to researches and scientists with web pages on similar topics. I know the above is of no help to you, but wish you the best of luck in your endeavor, Guillermo
Re: [pinhole-discussion] Pinhole Camera for medical purposes
Jenn, I know nothing of optics, but frequently I am a problem solver in areas where my knowledge is void. You didn?t mention the thickness of lead, the focal length or the field of view angle you require. I pose this question to my pinhole colleagues: Can the metal be precision machined from both sides with a conical bore to create a negative space in the shape of an hourglass? A steeper angle, will create thicker shielding down to the point of the pinhole. Obviously the boring cannot penetrate through the midpoint of the metal but should stop short several .001s of an inch short to allow for a precise pinhole to be drilled. The light passing through the hole will be focused and properly exposed. Perhaps there might be a corona, but it seems that should taper off as the lead?s thickness begins to block undesired radiation. Mike Atwell Get advanced SPAM filtering on Webmail or POP Mail ... Get Lycos Mail! http://login.mail.lycos.com/r/referral?aid=27005
Re: [pinhole-discussion] Pinhole Camera for medical purposes
Even more speculation here. But hey its worth a try. Would it be possible to work this problem in a reverse per say. Meaning if your gamma radiation functions similar to light then how does one adjust light when they cannot stop down their aperture? Either use a neutral density filter or a slower film emulsion. Since I do not know what type of material you are exposing and you say that you need the thickness of lead then would it be possible to find some kind of gamma radiation neutral density filter material and then reduce the thickness of the pinhole plate? Or place this neutral density material over the exposed material and then thin out the lead pinhole plate? Just my few words. Granted they are more to ponder I suppose. On 5/13/03 02:39 PM, "Nick Dvoracek" wrote: > Jenn, > > Probably in the realm of idle speculation here. > > Field of view would be dependent on focal length just like visible > light. > > Resolution is also a function of the size of the pinhole based on the > standard circle of confusion arguments, The smaller the pinhole, the > greater f is, therefore the sharper the image. > > On the lower limit, optimal pinhole size is a function of the > wavelength and focal length. Since the wavelength of gamma rays is so > short, it would be pretty hard to get a hole small enough for this to > come in to play. > > The thick piece of lead is going to be your biggest problem. The ideal > pinhole is in a planar surface. In actual practice, this means as > thin a material as is opaque to the radiation involved. I 'm afraid I > don't know the arguments, but when the hole becomes a tunnel, image > quality fails, first because it restricts the field of view (strictly a > geometry thing again) , and secondly because of internal reflections > inside the tunnel (but I don't think gamma rays will reflect normally > off a lead surface). There's gotta be some other reason also, the > Victorian authors I've read make a big deal about the thinness of the > material. > > Some of the first high energy astronomy detectors were clusters of > tunnels like this that didn't form an image exactly, just restricted > the field of view so much that they detected that there was a source of > light somewhere in the direction the tunnel was pointing. > > Interesting idea though. > > On Tuesday, May 13, 2003, at 12:01 PM, jennem...@mad.scientist.com > wrote: > >> Hello, >> >> I'm working on a project that I thought might interest people here and >> I could certainly use input from people with more experience than I. >> >> I am working as a Medical Physicist for my summer Co-op position. One >> of the projects I am working on is an attempt to use a x-ray >> flouroscopy screen and a thick piece of lead with a hole drilled >> through the center to try and image the position of a point source of >> radiation in a radiation therapy procedure. The radiation used is >> gamma-radiation which is an electromagnetic wave like light so it has >> most of the same properties. >> >> I am trying to optimize the Field of View and the Resolution and can't >> find _any_ resources for pinhole imaging with the pinhole in a thick >> material. (The thickness is required, otherwise the strength of the >> radiation will over-expose the screen and all we will see is white.) >> Any knowledge, links or even idle speculation would be appreciated. >> >> Thanks, >> Jenn >> __ >> Quantum Mechanics: The dream stuff is made of >> >> -- >> __ >> Sign-up for your own FREE Personalized E-mail at Mail.com >> http://www.mail.com/?sr=signup >> >> >> ___ >> Post to the list as PLAIN TEXT only - no HTML >> Pinhole-Discussion mailing list >> Pinhole-Discussion@p at ??? >> unsubscribe or change your account at >> http://www.???/discussion/ >> >> > -- > Nick Dvoracek dvora...@uwosh.edu > Director of Media Services Voice: 920-424-7363 > University of Wisconsin OshkoshFax: 920-424-7324 > http://idea.uwosh.edu/media_services/home.html > http://idea.uwosh.edu/nick/handouts.htm > > > ___ > Post to the list as PLAIN TEXT only - no HTML > Pinhole-Discussion mailing list > Pinhole-Discussion@p at ??? > unsubscribe or change your account at > http://www.???/discussion/
Re: [pinhole-discussion] Pinhole Camera for medical purposes
Jenn, Probably in the realm of idle speculation here. Field of view would be dependent on focal length just like visible light. Resolution is also a function of the size of the pinhole based on the standard circle of confusion arguments, The smaller the pinhole, the greater f is, therefore the sharper the image. On the lower limit, optimal pinhole size is a function of the wavelength and focal length. Since the wavelength of gamma rays is so short, it would be pretty hard to get a hole small enough for this to come in to play. The thick piece of lead is going to be your biggest problem. The ideal pinhole is in a planar surface. In actual practice, this means as thin a material as is opaque to the radiation involved. I 'm afraid I don't know the arguments, but when the hole becomes a tunnel, image quality fails, first because it restricts the field of view (strictly a geometry thing again) , and secondly because of internal reflections inside the tunnel (but I don't think gamma rays will reflect normally off a lead surface). There's gotta be some other reason also, the Victorian authors I've read make a big deal about the thinness of the material. Some of the first high energy astronomy detectors were clusters of tunnels like this that didn't form an image exactly, just restricted the field of view so much that they detected that there was a source of light somewhere in the direction the tunnel was pointing. Interesting idea though. On Tuesday, May 13, 2003, at 12:01 PM, jennem...@mad.scientist.com wrote: Hello, I'm working on a project that I thought might interest people here and I could certainly use input from people with more experience than I. I am working as a Medical Physicist for my summer Co-op position. One of the projects I am working on is an attempt to use a x-ray flouroscopy screen and a thick piece of lead with a hole drilled through the center to try and image the position of a point source of radiation in a radiation therapy procedure. The radiation used is gamma-radiation which is an electromagnetic wave like light so it has most of the same properties. I am trying to optimize the Field of View and the Resolution and can't find _any_ resources for pinhole imaging with the pinhole in a thick material. (The thickness is required, otherwise the strength of the radiation will over-expose the screen and all we will see is white.) Any knowledge, links or even idle speculation would be appreciated. Thanks, Jenn __ Quantum Mechanics: The dream stuff is made of -- __ Sign-up for your own FREE Personalized E-mail at Mail.com http://www.mail.com/?sr=signup ___ Post to the list as PLAIN TEXT only - no HTML Pinhole-Discussion mailing list Pinhole-Discussion@p at ??? unsubscribe or change your account at http://www.???/discussion/ -- Nick Dvoracek dvora...@uwosh.edu Director of Media Services Voice: 920-424-7363 University of Wisconsin Oshkosh Fax: 920-424-7324 http://idea.uwosh.edu/media_services/home.html http://idea.uwosh.edu/nick/handouts.htm
[pinhole-discussion] Pinhole Camera for medical purposes
Hello, I'm working on a project that I thought might interest people here and I could certainly use input from people with more experience than I. I am working as a Medical Physicist for my summer Co-op position. One of the projects I am working on is an attempt to use a x-ray flouroscopy screen and a thick piece of lead with a hole drilled through the center to try and image the position of a point source of radiation in a radiation therapy procedure. The radiation used is gamma-radiation which is an electromagnetic wave like light so it has most of the same properties. I am trying to optimize the Field of View and the Resolution and can't find _any_ resources for pinhole imaging with the pinhole in a thick material. (The thickness is required, otherwise the strength of the radiation will over-expose the screen and all we will see is white.) Any knowledge, links or even idle speculation would be appreciated. Thanks, Jenn __ Quantum Mechanics: The dream stuff is made of -- __ Sign-up for your own FREE Personalized E-mail at Mail.com http://www.mail.com/?sr=signup
