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From: Tim Williams on 16 Jan 2010 14:08 Except infinite depth-of-field lenses (e.g. Frazier). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms "Androcles" <Headmaster(a)Hogwarts.physics_r> wrote in message news:4Ng4n.34845$6V1.34777(a)newsfe30.ams2... > > "RichD" <r_delaney2001(a)yahoo.com> wrote in message > news:524e9de7-330d-40fd-90f5-0d671ec9ce7d(a)j19g2000yqk.googlegroups.com... >> is it possible to design a subcutaneous x ray? >> A surgeon might want to see a depth just below >> where he intends to cut. >> >> The point is, I thought only bones are opaque to x rays. > > The problem is focus. > Hold a page of text up at normal reading distance and focus on a few > words. Note that background and peripheral objects, although noticeable, > are out of focus. Now focus on a background object and note that the > writing on the paper is no longer in focus. All lenses, including those in > your eyes, have limited distances or ranges in which two objects on > different planes (focal planes) may be simultaneously in focus. > The solution has been MRI. > >
From: Joerg on 16 Jan 2010 14:43 Androcles wrote: > "RichD" <r_delaney2001(a)yahoo.com> wrote in message > news:524e9de7-330d-40fd-90f5-0d671ec9ce7d(a)j19g2000yqk.googlegroups.com... >> is it possible to design a subcutaneous x ray? >> A surgeon might want to see a depth just below >> where he intends to cut. >> >> The point is, I thought only bones are opaque to x rays. > > The problem is focus. > Hold a page of text up at normal reading distance and focus on a few words. > Note that background and peripheral objects, although noticeable, are out of > focus. Now focus on a background object and note that the writing on the > paper is no longer in focus. All lenses, including those in your eyes, have > limited distances or ranges in which two objects on different planes (focal > planes) may be simultaneously in focus. > The solution has been MRI. > Ultrasound machine had dynamic focusing since the 70's :-) What this means is "on-the-fly" focusing, like a lens that bends to the correct shape while the echoes are coming back from deeper and deeper regions. Easy on receive, but for transmit you need to do several shots and stitch the resulting horizontal image slices together. That's a whole science unto itself but nowadays very much standard procedure. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Androcles on 16 Jan 2010 14:55 "Joerg" <invalid(a)invalid.invalid> wrote in message news:7rej86Fd03U1(a)mid.individual.net... > Androcles wrote: >> "RichD" <r_delaney2001(a)yahoo.com> wrote in message >> news:524e9de7-330d-40fd-90f5-0d671ec9ce7d(a)j19g2000yqk.googlegroups.com... >>> is it possible to design a subcutaneous x ray? >>> A surgeon might want to see a depth just below >>> where he intends to cut. >>> >>> The point is, I thought only bones are opaque to x rays. >> >> The problem is focus. >> Hold a page of text up at normal reading distance and focus on a few >> words. Note that background and peripheral objects, although noticeable, >> are out of focus. Now focus on a background object and note that the >> writing on the paper is no longer in focus. All lenses, including those >> in your eyes, have limited distances or ranges in which two objects on >> different planes (focal planes) may be simultaneously in focus. >> The solution has been MRI. >> > > Ultrasound machine had dynamic focusing since the 70's :-) > > What this means is "on-the-fly" focusing, like a lens that bends to the > correct shape while the echoes are coming back from deeper and deeper > regions. Easy on receive, but for transmit you need to do several shots > and stitch the resulting horizontal image slices together. That's a whole > science unto itself but nowadays very much standard procedure. Yes, I wouldn't doubt it. I have no medical degree and very little knowledge in that field, my only use of ultrasound has been in an electronics cleaning bath. My experience with MRI is a yearly check up when I'm injected with something that makes me feel hot and want to pee! Thanks for the info.
From: Joerg on 16 Jan 2010 14:58 Androcles wrote: > "Joerg" <invalid(a)invalid.invalid> wrote in message > news:7rej86Fd03U1(a)mid.individual.net... >> Androcles wrote: >>> "RichD" <r_delaney2001(a)yahoo.com> wrote in message >>> news:524e9de7-330d-40fd-90f5-0d671ec9ce7d(a)j19g2000yqk.googlegroups.com... >>>> is it possible to design a subcutaneous x ray? >>>> A surgeon might want to see a depth just below >>>> where he intends to cut. >>>> >>>> The point is, I thought only bones are opaque to x rays. >>> The problem is focus. >>> Hold a page of text up at normal reading distance and focus on a few >>> words. Note that background and peripheral objects, although noticeable, >>> are out of focus. Now focus on a background object and note that the >>> writing on the paper is no longer in focus. All lenses, including those >>> in your eyes, have limited distances or ranges in which two objects on >>> different planes (focal planes) may be simultaneously in focus. >>> The solution has been MRI. >>> >> Ultrasound machine had dynamic focusing since the 70's :-) >> >> What this means is "on-the-fly" focusing, like a lens that bends to the >> correct shape while the echoes are coming back from deeper and deeper >> regions. Easy on receive, but for transmit you need to do several shots >> and stitch the resulting horizontal image slices together. That's a whole >> science unto itself but nowadays very much standard procedure. > > Yes, I wouldn't doubt it. I have no medical degree and very little > knowledge in that field, my only use of ultrasound has been > in an electronics cleaning bath. My experience with MRI is a > yearly check up when I'm injected with something that makes me > feel hot and want to pee! > Thanks for the info. > Yearly? Wow! I was never in an MRI, so far. One reason why ultrasound is preferred is that MRI is hugely expensive while an ultrasound scan is typically reimbursed at the two-digit Dollar level. MRI is usually four-digit. The underlying reason is equipment cost. A good MRI machine costs millions while a decent ultrasound scanner can be had for under $50k. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Phil Hobbs on 16 Jan 2010 15:05
On 1/16/2010 5:31 AM, Androcles wrote: > "RichD"<r_delaney2001(a)yahoo.com> wrote in message > news:524e9de7-330d-40fd-90f5-0d671ec9ce7d(a)j19g2000yqk.googlegroups.com... >> is it possible to design a subcutaneous x ray? >> A surgeon might want to see a depth just below >> where he intends to cut. >> >> The point is, I thought only bones are opaque to x rays. > > The problem is focus. > Hold a page of text up at normal reading distance and focus on a few words. > Note that background and peripheral objects, although noticeable, are out of > focus. Now focus on a background object and note that the writing on the > paper is no longer in focus. All lenses, including those in your eyes, have > limited distances or ranges in which two objects on different planes (focal > planes) may be simultaneously in focus. > The solution has been MRI. > > There are lots of solutions to this. In optical microscopy, you can take images at several depths and combine them, choosing the level that shows the most contrast at each position. Zeiss has been selling systems like that for years. In confocal microscopy(*), you can just sum the images taken from different depths, since out-of-focus planes hardly contribute to the image at all. There's also phase-coded imaging, which uses an artistically designed phase plate to allow 3D reconstruction from a single image. (It's really a beautiful technique, which I'd like to understand better than I do.) So the old classical optics limitations are being overcome all over the place. Cheers Phil Hobbs (*)My thesis was on a phase sensitive laser scanning confocal microscope, and I helped invent the modern real-time confocal. -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs at electrooptical dot net http://electrooptical.net |