STEREO X-RAYS OF SEA SHELLS by Peter Abrahams The images posted to illustrate this essay include integrated pairs (parallel format & a few cross eyed format,) and single images. Except for the first group, these are large files, too big for standard size monitor screens. These images are available for anyone to use for non profit purposes, provided attribution is given. If images are processed to create an integral pair, or if an image is created of smaller size, that is viewable on a small screen, please e-mail a copy so it can be posted on this site. See below for credits for this project. The first four are stereo pairs rendered by Monte Ramstad, to view on a standard monitor, smaller files than those following: http://www.europa.com/~telscope/busycss1.jpg Busycon canaliculatum (Channeled Whelk) http://www.europa.com/~telscope/busycss2.jpg Busycon canaliculatum (Channeled Whelk) --reversed http://www.europa.com/~telscope/epitonss.jpg Epitonium scalare (Precious Wentletrap) http://www.europa.com/~telscope/tonnass.jpg Tonna sulcosa (Banded Tun) 1. Tonna sulcosa (Banded Tun) http://www.europa.com/~telscope/tonna2.jpg the pair (John Toeppen, Vrex DDS & Photoshop) http://www.europa.com/~telscope/tonnax.jpg the pair, cross eyed (Harold Kaiman) http://www.europa.com/~telscope/tonnal.jpg left side (Shab Levy) http://www.europa.com/~telscope/tonnar.jpg right side (SL) 2. Busycon canaliculatum (Channeled Whelk) http://www.europa.com/~telscope/busycnPr.jpg the pair (SL) http://www.europa.com/~telscope/busycon2.jpg the pair (JT) http://www.europa.com/~telscope/bsycnang.jpg the pair, red/blue anaglyph (Steve Berezin) http://www.europa.com/~telscope/bsycnprx.jpg the pair, cross-eyed, with JPS header (using plug-in, allows view as an anaglyph, with shutter glasses, cross-eyed or wall eyed) (SB) http://www.europa.com/~telscope/busyconl.jpg left side (SL) http://www.europa.com/~telscope/busyconr.jpg right side (SL) 3. Epitonium scalare (Precious Wentletrap) http://www.europa.com/~telscope/epitonm2.jpg the pair (JT) http://www.europa.com/~telscope/epitonml.jpg left side (SL) http://www.europa.com/~telscope/epitonmr.jpg right side (SL) Stereo x-rays are a standard technique, used by radiographers to locate bullets, tumors, and other items of interest inside a body. In an article written in 1896, Elihu Thomson described an experiment with stereo pairs of radiographs, 'The effect is very curious...two heavily insulated wires twisted together...the wires alone are seen, standing apart in space.' He also suggested stereo fluoroscopy (motion pictures,) and his paper was followed by others on the topic in both English and French Journals. The discoverer of x-rays, Wilhelm Roentgen, took at least one stereo photograph, a self portrait with his wife. Discussion of this subject on the on-line Photo-3d Digest elicited some very interesting responses. Stereo fluoroscopy was tried at the Mayo clinic in the 1950s, using an x-ray tube with two foci and spinning polarizing filters in front of the viewer; and switching LCD glasses are used in modern systems. At a Naval laboratory, the effect on the spine of impacts from ejection seats is studied using stereo x-rays. In England, the technique has been developed for scanning luggage at airports. Radiographic pairs of flowers were featured at a recent NSA convention and in Stereo World magazine. William Conklin, a radiologist in South Carolina, has done hundreds of ‘flat’ x-rays of seashells, that are very beautiful images of the delicate spirals and detail within a shell. This inspired a project that created stereo pairs of radiographs of shells. The generosity of two organizations permitted this work; Portland Community College’s Department of Radiology allowed use of their equipment, and members of the Oregon Society of Conchologists loaned many unusual and exquisite shells for the project. There were many technical puzzles to be solved, since shells are of widely varying densities and thicknesses, and to capture the thin edge along with the many layers of material in the center was a constant challenge. Penetration by x-rays involves a balance between kilovolts of power and milli ampere seconds, mAs. A rough analogy with light is that kilovolts corresponds to color (frequency or wavelength) and mAs to brightness. To preserve contrast in the exposure, some materials must be penetrated with higher kilovolts and others with higher mAs. Although the film is not too expensive, lab time is at a great premium, and to our delight the very first stereo we took was successful. The inner layers of the shell could be seen to arch up from the film surface, each layer demarcated from the next, a truly complex and inspiring construction. Some of the most beautiful shells had an uninteresting inner structure, and the most beautiful radiographs were of less glamorous shells. Many had to be imaged using a ‘mask’, a thick wedge of plasticene clay that blocked more radiation on one side of the image, and allowed the thin lip of the shell to appear on the image. We now have about 70 successful pairs, the beginning of an ongoing project. Sharing these radiographs with the public has posed some problems. These are 8 x 10 transparencies, and few can freeview such dimensions. Radiologists use Wheatstone style viewers with large mirrors, and public use of one inevitably results in fingerprints on the first surface mirrors. (A very unusual stereoscopic antique is the General Electric Orthostereoscope, a radiograph viewer that uses two large rhomboid prisms to effectively widen the interocular distance.) Another problem is backlighting these exposures. An enormous lightbox would be the ideal solution, and sheets of frosted mylar taped to windows have been an inadequate substitute. The delicate contrast and fine detail of these exposures will be difficult to capture in the pictures that accompany this article. Realist format duplicates will also be attempted. There are other natural forms that would be interesting to view as a stereo radiograph, but few could match the beauty of these seashells. I am indebted to some very helpful people for this project. The seashells belonged to members of the Oregon Society of Conchologists, especially Jeannine Baird. The radiologist was Dan Holmes, who did much background work to find the best films, and then spent long sessions with masks, screens, and experimenting with exposure. We were allowed to use the facilities of Portland Community College, Sylvania Campus. Radiographs were converted to 35 mm film by John Dennis. This film was scanned & processed by Shab Levy. At each step of the process, I was amazed at how well these artists retained the contrast and detail of the originals. ======================== Further Notes. There is a very nicely made CD of shell radiographs, not stereo, but an excellent presentation of well done images. SEASHELL ARCHITECTURE, 1112 N. FLOYD ROAD, RICHARDSON, TEXAS 75080 (214) 351-6303 ( CREDIT CARD ORDERS SHIPPED THE FOLLOWING DAY ) http://home.att.net/~crowmd/ CD was 21.95 in 1998. "I began collecting, photographing, and x-raying seashells while I was in Hawaii," according to Steven Crow, MD. "The x-rays were all taken with Kodak X-ray films and were exposed in cardboard cassettes to provide the highest level of detail. Initially, I made contact prints of the x-rays, but now with all the technical gizmos available I have been able to create some more imaginative programs." All the x-rays have been scanned at high resolution using an HP ScanJet 4c with transparancy adapter. The seashells were scanned directly on the flatbed, taking advantage of the built in depth of field that scanners have. The black background for the shell images is a result of keeping the scanner lid up during the scan. All the images were then imported into Adobe® Photoshop 4.0® and "cleaned up". Only dust spots had to be removed and there was no "doctoring" of the images themselves. Finally, the x-ray images were all inverted in Photoshop to change the image from a "negative" to a "positive" image. ================================================================== Posts on this subject from the 'photo3d' e-mail list: 3d sonography: www.3dsono.org www.medison.co.kr =============== Date: Thu, 07 Mar 1996 21:33:33 -0600 From: johnroll@uic.edu (John D. Roll) I found your discussion of stereo radiography interesting. To answer your question about stereo fluoroscopy, a General Electric service man who recently retired told me about fluoroscopy equipment he helped to install back in the 1950's at the Mayo Clinic. This unit I believe had two focal spots in the xray tube and polarizing filters that spun in front of the viewer. The radiologist wore polarized glasses to view. The service man thought that this might have been the only one made. I don't think it worked real well. He said he might be able to find the blue prints for me but he could not find them. I did my Radiology residency and neuroradiology fellowship at the University of Minnesota from 1981 to 1986. That is a seperate training institution from the Mayo Clinic but we were close to them so I was aware that the Mayo Clinic still routinely did stereo chest xrays. There are still occasions where stereo xrays can be useful. In the past, there were many stereo xray machines made for certain exams such as the antiquated pneumoencephalogram. About a year ago I heard that Toshiba has come out with a stereo fluoroscopy system I believe for angiography and radiology interventional procedures. I think this uses switching LCD glasses. There may also be other systems under development. Of course there are other 3d and stereo applications currently being used. I have made my own stereo pairs from 3d volume sets form CT, MR, and nuclear medicine. I have even used this to help an orthopedic surgeon prepare for surgery on a complex pelvic fracture. John D. Roll, M.D., Rockford, IL, USA ------------------------------------------------------------ Date: Wed, 06 Mar 1996 18:32:04 -0600 (CST) In regard to stereo X-rays, I do that all the time at the Naval BioDynamics Labs here in New Orleans. I designed the X-ray technique (from descriptions in papers published by others in Photogrammetric Engineerin)g. Stuff works great! What's really neat is looking inside somebody to view (& triangulate)a point on a guy's spine - inside the thorascic (sp?) cavity. I published a couple \papers a few years ago in the Annual Procedings...nothing specially new for a Photogrammetrist, but nevertheless it's really near fantastic to view in stereo. P.S. Of course, the u.S.Navy has the good judgement to use my software... Clifford J. Mugnier (cjmce@uno.edu), Topographic Engineering Laboratory Department of Civil & Environmental Engineering, University of New Orleans New Orleans, Louisiana 70148, Voice: (504) 286-7095, FAX: 286- 5586 ---------------------- Date: Fri, 08 Mar 1996 08:43:01 -0600 (CST) At the U.S. Naval BioDynamics Laboratories (NBDL) here in New Orleans, they have been shooting sailors out of ejection seats for about 25 years on a regular basis. These sailors are Human Research Volunteers (HRVs) generally referred to as "Lab Rats" (not a slur but a good-natured nickname). They get strapped into Impact Accelerators (ejection seats) and withstand 1g to 16g impacts to study the relation of the human head and neck with respect to the first thorascic vertebral element (T-1). Since it is not possible to surgically implant visible targets into a person's spine, a method of targeting the T-1 vertebrae was devised with non-invasive targets in concert with stereo X-Rays. With much experimentation, I had their machine shop fabricate an "X-Ray Chair" that had the exact dimensions and mechanical ajustments as the aluminum seats used in the accelerators. The difference was, though, it was made out of X-Ray transparent plexiglas. The harness system used on the accelerators was duplicated with transparent fittings and straps so that the only things that would appear on the resultant X-Rays was the HRV and my control points (small lead shot or BBs). Initial stereo was achieved by simple lateral shifting of the HRV in the chair in AP views (Anterior-Posterior) - face to the X-Ray source. Problem with that was the anterior wall of T-1 was too thin to perceive in stereo - it washed out. We then rotated the subject 45 degrees and did lateral shifts with success; we COULD see the anterior wall in stereo! We then rotated the subject the opposite direction 45 degrees and got another stereopair successfully. With that, we established a standard procedure to obtain two stereopairs of each HRV which was then measured and photogrammetrically triangulated to determine the "Body Anthropometric Coordinate System". ... with my software, of course. (PC Giant) Accuracy achieved: +/- 2.7mm in each component X-Y-Z (Variance-Covariance Matrix used for Eigenvector/Eigenvalue determination). Clifford J. Mugnier (cjmce@uno.edu) University of New Orleans ------------------------------------------------------------ Tilting would only work for relatively singular small objects. Seashells are complex and you need to have consistent patterning in order for the stereo effect to be present and strongly coincident. You might practice this effect by using translucent objects and a single light source. Photograph the shadows that result and see if keeping the light source consistently aligned doesn't provide a higher quality of results. It would give you a much better feel for things when you get back to the Xray machine. Larry Berlin ============================== >The images had a relatively high percentage of areas that weren't expressed >equally in both left and right views. Yes, if I get a chance to do these again, I will decrease the disparity between R & L. The x-ray techs tilt the gun maybe 5 degrees to the R of vertical and 5 to the left to make a stereo pair, a really radical amount, the subject is only about two feet away. Probably this is because they are trying to locate the z axis placement of some tumor or bullet, and will strain their eyes a little to do this if necessary. It's particularly noticeable because you're seeing the front & the back surfaces. The simpler shells, with a clean spiral form, needed this disparity, but the images of the complex shells had lots of areas that were white on one side and black on the other, creating a rivalry. If the right side has an area of exposure (black) & the left is white, then the thickness of the shell that the x rays passed through is different by that amount, thin on the right and thick on the left. ================================= Date: Tue, 29 Jul 1997 20:32:41 -0500 From: P3D Clifford J. Mugnier I did about a hundred or so people in the early nineties with stereo X- rays, each person getting two stereopair (2 shots tilted to the left, 2 shots tilted to the right) in order to get convergent (4-ray solutions) of a particular point on the anterior (front) surface of the T-1 vetebral element (first thoracic vertebrae). The stuff was for an analytical photogrammetric analysis of people (male and female sailors) for ejection-seat testing at the National (then Naval) Bio Dynamics Laboratory (NBDL) here in New Orleans. For a guy used to doing stereo aerial photo stuff for topographic mapping, this was really, really weird stuff to look at in stereo. Anyway, the opposite tilts were at about 15 degrees each, and were not viewable in the convergent case, but each tilt was done with a pair, laterally separated so that a left-tilted pair was easily viewable in stereo. Points were identified in stereo (marked and measured) for the left-tilted pair, and then the same for the right-tilted pair. Results yielded X-Y-Z positions inside the body cavity with accuracies typically 0.1 to 0.2 mm in all three components. The lab is now part of the University of New Orleans Cliff Mugnier ============================================= Alignment has been a real problem, which could probably be corrected nicely via digitization....BUT: It's trickier than you might think. These are helical shaped objects. To align with say Photoshop, you might pick the upper point, and the lower point, in L & R, and rotate until they match. But, because it's helical, the highest point in the L exposure is lower than the highest point in the R (just an example, might not be 'true'). Does that make sense? Imagine a stereo pair of a coiled spring, and a single point on the L side of that spring. The R eye would see that point a little higher than the L. The problem was resolved by me because when they're aligned, all the complex curves & lines just meld together & form a stereo object that jumps up off the film. It's hard to tell otherwise. --Peter ======================================== Date: Mon, 17 May 1999 06:09:01 -0400 From: Harold Kaiman I read your answer to the photo-3D question about 3d radiology with interest. I was planning to respond in a similar manner. I assume you are a radiologist or technologist. I am a radiologist practicing in Cleveland, Ohio and have had an interest in stereo imaging also. My interest began as a resident at Mallinckrodt Institute where stereo Water's views of the paranasal sinuses were a part of our routine. We had dedicated units (I forget the name) for skull work that were capable of shifting laterally and exposing left and right views on the same film (8x10?). We all learned to free view by crossing our eyes. I have seen some of the old viewers for chest films ( I think Mayo's did them routinely for years) but never really have had any experience using them. Ronald L. Eisenberg published a beautiful book, Radiology. An Illustrated History in 1992 which has a chapter (#5 page 79-82) entitled "Stereoscopic Radiology" in which he quotes Thomson's 1896 article and reproduces the stereo self photos made by Roentgen as well as a few other examples of early stereo images. The closing sentence of Eisenberg's chapter states "The development of modern cross-sectional imaging effectively marked the end of the stereoscopic era in diagnostic radiology." I would be interested in seeing your work with the sea shells. Several years ago (before I had met George Themelis) I made a few 2d Xerographs of shells which I still have. I don't know how old you are, but xerograms were not so susceptible to variable densities (therefore, their popularity for mammography). Harold Kaiman, M.D. =========================== Date: Mon, 17 May 1999 22:46:44 -0700 From: Ray Zone In 1987 I worked for a short time with Dr. Arthur Fielder, a chiropracter in Torrance, California who was making 3-D X-Rays and viewing the 8 x 10 stereo pairs on a large Wheatstone chiropractic stereoscope. The stereo pair was produced by taking one x-ray and then moving the emission head of the x-ray machine laterally to produce the second eye view; side-step 3-D x-rays. The 3-D produced was somewhat hyper but this was not a drawback with applications that were primarily diagnostic. Using this technique Dr. Fielder and I produced a stereo x-ray of my hands and I subsequently duped these images to 35 mm film for use in my (twin 35mm) 3-D slide shows along with other stereographs Dr. Fielder had produced of the neck, spine and head. The inventor of modern Chiropractry, Edwin Palmer, in his multivolume set on the subject (written in the early years of the 20th century) with the volume titled "Modern X-Ray Practice and Chiropractic Spinography" has a separate chapter for "The Chiropractic Stereoscope." This chapter includes a photograph of a Wheatstone stereoscope created for chiropractic purposes. The stereoscope uses two vertically mounted backlit lightboxes upon which the (negative) x-ray films are placed at either end for stereographic viewing. r3dzone@earthlink.net ------------------------------ From: "Ray Moxom" Just to add a bit on the topic of 3D X-Rays. I have a World War I medical book (printed in 1916) titled "Localization by X Rays and Stereoscopy" by Sir James MacKenzie Davidson. more than 20 images in the book The technique included viewing relatively small X-Ray prints in a Holmes type viewer to assist in the location of bullets and bomb fragments. =================== From: "Greg Wageman" >how about 3-D Ultra-sound? Has this been done? When I worked for a 3D medical imaging company a few years back, their scientists were experimenting with this (for purposes of volumetric rendering, though, not for stereoscopy). The results were unsatisfactory because of the graininess of ultrasound (low signal-to-noise ratio). Registration is also difficult because the ultrasound transceiver is hand-held, so there is no fixed point of reference (unlike, say, CT and MRI which are very precisely and repeatably aligned so long as the patient lies still). Unfortunately you can get rotational errors (roll, pitch, yaw) in addition to simple translation in one or more axes. ===== From: Tom Hubin Once upon a time I earned my keep by designing noncontact distance measuring equipment. I used lasers and CCD cameras but other methods are possible. If you have 3 points on the handheld ultrasound device that you can locate in space then you know where the device is and how it is oriented. It could be as simple as 3 strings tied to 3 points on the device. The other end of each sting would pass through a known point. The 3 strings then form the edges for the triangular sides of a pyramid. The triangular base is formed by the 3 known string feed points. When you crunch the numbers there are always 2 possible places where the ultrasound device could be. But one of those is on the wrong side of the base. This is called trilateration since distances are involved rather than angles. It is not triangulation. Tom Hubin ========================================================== From: Harold Kaiman Xeroradiography...... is now an extinct modality but has an interesting history and was very significant in the development of Mammography as a screening test for breast cancer during the 60's. Technique and Localization of Breast Lesions (no author) Chester F. Carlson in 1937 developed the pro- cess of xerography, a process of photoelectric imaging. At the outset he had great difficulty in interesting the leading corporations of the coun- try in his discovery, consensus being only that it was an interesting process. It was not until the Batille Institute became interested that xerog- raphy found its place in business, first as the Haloid Corporation and then as the Xerox Cor- poration. The success of the company was astro- nomical. In 1952, searching for other uses of the copying process, Carlson suggested medical usage. Roach did extensive work in the field, particularly in ostology. During this same period there was national concern over the possibility of an atomic war. Civilian defense centers were being built. It was theorized that if an atomic attack occurred all film would be exposed and be useless. As a result of the effective use of xeroradiography in bone lesions, this process was thought to be the answer to the atomic bomb exposure problem. The Gen- eral Electric Company, at the request of the federal government, built a number of xel oradi- ographic units for storage in defense centers. As the atomic scare waned, interest in the centers waned; Ruzicka was able to obtain one of the units and used it effectively in mammog- raphy. There were so many technical problems with the surgical field type equipment that he became frustrated and stopped using the equipment. At the same time Wolfe was extremely interested in mammography and obtained Ruz- icka's unit in 1966 for the Hutzel Hospital in Detroit. Through dedication and as a labor of love, Wolfe did mammography with a field unit, and at the International Mammography Confer- ence in San Juan, Puerto Rico, in April of 1967, presented his initial results. Considerable enthu- siasm was generated by many mammographers for xeroradiography after hearing Wolfe's presen- tation. A group of radiologists, with the help of the American College of Radiology Committee on mammography and the American Cancer So- ciety, asked Xerox to reopen investigation into xeroradiography to determine whether this was an effective method of finding breast cancer. In 1968 a program of investigation was launched with Wolfe as the primary investigator. The first extensive clinical trials were done by Wolfe in Detroit and Martin in Houston, both serving as consultants to Xerox Corporation. The process proved to be effective in finding breast cancer and has become widely accepted. The process of xerography depends on an ef- fective photoconductor, and selenium has the best properties of tested photoconductors for the copying process. Unfortunately, selenium proved more difficult to use in medical applications, and it was deter-mined early that selenium had to be in a more purified form. In xeroradiography, a selenium-coated alumi- num plate is used as the photoconductor. Sele- nium will retain an electrical charge which, when exposed to the radiation spectrum, whether x- ray, light, or some other, will discharge differen- tially, the charge on the plate being altered by the amount of radiation. In its medical applica- tion, the surface of the plate is electrically charged in the processor, placed in a radiographic casette, and used as film is used. Tn examination of the breast, as soon as x-ray exposure occurs, the x-rays are selectively absorbed by the sele- nium plate, leading to the allocation of the elec- trical charge. At this time a latent image is on the plate, made possible by the photoconductive properties of selenium. The latent image is then transformed into a visible image by being exposed to a powder cloud of charged particles (Fig. 6.1.). If a negative image is desired the toner cloud charge is positive; if a positive image is desired the toner cloud is neg- ative. The particles settle on the plate in amounts necessary to complete the photoconductive ac- tion. At this time a readable image is present on the selenium plate. Fine detail is present; how- ever, reading from the plate is impractical. The powder image is then transferred to a sheet of paper and heat-fused and becomes archival. This is the method which has become so convenient to the radiologist for reading and storage. Edge effect, resolution, and latitude are the major attributes of the diagnostic image. Edge effect is the most important of these, for in adjacent structures with areas of different den- sity, the borders are clearly delineated. The high level of contrast which produces this effect is proportionate to the variability of changes of density of adjacent structures. Structures such as calcifications are then clearly delineated, whereas periductal connective tissue, being the same density as mammary ducts, cannot be dif- ferentially separated from the ducts. Because of edge effect, the slightest variable of density makes different structures visible. This effect can be appreciated in many cysts, fibroadenomas, and cancers partially hidden by stromal connec- tive tissues. Numerous resolution point tests have proved the superiority of xeroradiography in demon- strating particles as small as 0.08 mm in tissue equivalents of 2.7 cm. The latitude of the process enables imaging of skin, subcutaneous structures, and structures deep in the breasts on a single image. Xeroradiography in medical usage has been limited primarily to mammography. A moderate amount of extremity and soft tissue techniques are used. Tomography, chest, and abdominal examinations can be valuable, but the high dos- age exposures, when compared to the lower ex- posures with film and particularly rare earth screens, negate its use for these procedures in most circumstances. The extremity and soft tis- sue uses are still valid; sometimes on extremity examinations a fracture can be verified by the use of xeroradiography that is only suspected on film studies. =============================== From: abram klooswyk As is clear from Peter Abrahams excerpt, the first stereo X-rays were made just a few month after Roentgen had discovered the rays. Remember that in the late 19th century stereoviews were normal in the parlors, and probably up to a half of all photography was in stereo, so the idea of stereo X-rays was only self evident. They indeed played a great role in getting bomb fragments out off people in World War I, and this role was activated again when fragmentation bombs were used in Vietnam. The purpose of stereo X-rays of course is localization in the third dimension, for in any plain X-ray all anatomical structures are in superimposed on the film. But this role nowadays largely has been superseded by imaging techniques which provides slices: Computed Tomography (CT), Ultrasound (echo) and Magnetic Resonance Imaging (MR or MRI). However, I remember that some 20 years ago stereo X-rays were a standard procedure for a number of difficult areas: the skull (especially the orbit, the sella turcica and the inner ear) and the neck. I know a professor of neurosurgery who had a large collection of stereo X-rays of neck fractures and dislocations. Not all of them are lethal, and superimposed left and right sides can only clearly be identified on lateral X-rays when seen in stereo. On these films the left side of the neck was marked by taping *two* small lead corns to that side, and *one* at the right side (no colors on X-rays, so no red and green mark!). Marking is necessary, for with X-rays there is no real pseudoscopy! "Transposing" lateral stereo X-rays swaps left and right, but you cannot tell if it has been done when there is no indication how the films were taken. You cannot tell whether the side closest to you is left or right when the lead corns are omitted. Hugo de Wijs has been in touch with a professor of radiology who advocated stereo X-ray in the Netherlands, in the time before the modern slicing techniques were available, and at the exhibition of Hugo's stereo work, last year at the ISU congress in the Netherlands, he had an old X- ray stereoscope from about 1920 on display, for which I provided some stereo X-rays. Another funny thing is that there is a reasonable chance that stereo X-rays of yourself exist! When at least two chest X-rays of you have been made, not too far apart in time, there is a great chance that these differ in projection and that at least a part of them can be seen in stereo. The reason is that the vertical position of the X-ray tube is chosen by the radiographer, and often at a retake a month or a year later the tube is positioned several cm lower or higher than the first one. Then there is a vertical parallax, which results in stereo effects when both films are free viewed after rotating them over 90 degrees. Admittedly this only occasionally gives a fine stereo view, and mostly only ribs stand out in 3D, but sometimes also lung vessels look like a stereo of a shrub in winter. The proliferation of X-ray CT investigations on the one hand has made stereo X-rays old fashioned, but on the other hand 3D rendering of series of CT images is flourishing, and again two 3D rendered images differing some 5 degrees in rotation form a stereopair, and indeed commercial radiological imaging work stations can display such images more or less semi-automatically in stereo, with LCD shutter glasses. Now for stereo Ultrasound (US), this is possible, and I have made a few examples. The technique is complex, for normal ultrasound images again are cuts, slices through an anatomical structure. As you can imagine, two different slices from a cake never make a stereopair. The first thing is to get an ultrasound image which isn't a slice but an image of a surface, or a superposition of a volume as seen from some distance. Second, this view has to be rotated to get the pair of views required for stereo. Now the latter technique is implemented in a variation of the Doppler mode of some machines. In this mode blood vessels can be seen (because the blood moves), and vessels in a small volume can be imaged by rotating the US transducer over a small angle. Then the software permits to give two different projections of the volume, and then the vessel pattern can be seen in stereo. But to be honest, the results are not very impressive. Abram Klooswyk ------------------------------ From: abram klooswyk The first page says "mass", this is mostly spelled: mAs, from (milliAmpere x second), X-ray tube current x time. [You probably know that the units meter, gram, second are spelled in lower case, Ampere, Volt etc upper case, prefixes lower case again, so it's kV, mAs] Abram =============================== Date: Thu, 24 Jun 1999 16:07:35 +0100 (BST) From: David Spacey Last night "Tomorrow's World" (a *very* long running science and technology show over here) featured stereoscopic X-Ray devices for airport security. The conveyor belt passed under two beams, natch, arranged in an inverted V. Presumably the computer allowed for the delay to get two views of the same case. The display looked like it was using a full-screen lcs system, since the presenter and demo guy were using simple crossed- polariser funnyglasses. Hey, the presenter even knew they were crossed polarisers! It was being presented as a faster and better way to identify "suspect" packages. In another demonstration it made it easier to locate contraband once identified. They didn't have to search the whole case for the gun, they could see which pocket it was in. Dave Spacey ====================================================