Talk:Computed tomography

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[edit] Radiation Exposure

Suggest including comparison of the raditation in a CT scan to the background radiation in the atmosphere one recieves (i.e. ?possible 1 CT equivalent of 3 years of background radition one recieves from the atmosphere) would be interesting.216.95.114.241 06:52, 8 December 2006 (UTC)

Can someone verify the numbers for radiation exposure? I have heard that PET is much safer than CT but the numbers here don't show that... cbm 03:16, 16 Sep 2004 (UTC)

I presume the cost given for a scanner ($1.3 million) is in US Dollars? I'd add it myself but don't want to include incorrect information. --Roisterer 04:22, 5 Oct 2004 (UTC)

Radiation doses from PET and CT cover a wide range depending on the exact type of investigation being conducted but, in the UK at least, are roughly the same. Both investigations give doses several times greater than a conventional planar x-ray.

If you were planning to put this into the article, this didn't work out :-(. Do you have some more hard data (e.g. radiation exposure in Sv for every CT)? Apparently 1/1000 patients who have a CT will develop a lymphoma as a result ???? JFW | T@lk 14:23, 6 Dec 2004 (UTC)
Sorry, I was trying to put in a comment, I'm new to this. The data is available in several publications or by calculation. The important thing is that the dose from PET ranges from 10-20mSv while CT gives from approximately 5-20mSv. These numbers depend on the exact type of investigation. 2-10mSv is approximately one years background radiation in the UK(from cosmic rays, granite, etc). Papers such as the one you quote have a role, but are often mis-interpereted by the media. The lifetime risk of cancer in the UK is :approximately 1 in 3-4. Determining whether a lymphoma, or any cancer, is caused by radiation exposure is a very difficult business when the natural incidence is so high and is usually the result of a statistical study rather than any particular "radiation tag" attached to the disease. In all cases involving ionising radiation, the benefit of having the investigation should be weighed against the possible detriment of not having it. I know for a fact that if I had a a suspected serious complaint, I would not be worrying about the radiation dose from a CT scan.
Some numbers - for deterministic effects - are available in the article Radiosensitivity. Otherwise, the background radiation is typically 2-3 mSv. The numbers were assessed by UNSCEAR and ICRP. --Eleassar777 18:02, 31 May 2005 (UTC)


The following text was added to the main article. I think it would be more appropriate here:

18:33 9/3/06 (Wildcat444)-'Exception? --- Second para. above suggests multi-slice CT imposes a radioactive exposure of 500 times that of a conventional chest x-ray. Given the exposure of 0.085 mSv as that of an x-ray, multiplied by "500", the exposure of the MSCT would be 42.5 mSv for a chest scan. From my searches - as supported by 'Typical Scan Dose' - under 'Radiation Exposure' of "Article" - Computed Tomography, here in Wikipedia --- the exposure for a chest scan is shown as 5.8 mSv.
BA van der Bruggen-Bogaarts, JJ Broerse, JW Lammers, PF van Waes and J Geleijns of University Hospital Utrecht, The Netherlands report a standard CT chest scan dose of 6.5 mSv.
They also report their study produced an effective dose, using high-resolution CT (HRCT) equipment (1.5-mm slices, gap 10 mm) of "0.98 mSv"; approximately 6.5 times less than a standard chest scan or approximately 12 times that of a chest x-ray.
These values translate to 106 days of typical background radiation; not years. Other inquiry on my part suggests that the 'Dual Source CT scanners' reduce the "5.8 mSv" I've quoted above to approximately 2.9 mSv; still less than one year's exposure from natural sources. While none of the above set forth the specific variables involved in scan radiation exposures - they ARE significant.
Finally, NIH's radiation safety committee has also established guideline values for research doses that are helpful to our (their) institutional review committees in evaluating the risk versus benefit of the studies. These guidelines are 5.0 rem (50 mSv) per year, that is, 12 consecutive months for adults, and 0.5 rem for subjects younger than 18 years of age. per Dr. Jamey West National Institutes of Health

I don't think the article is significantly in error. The estimate of 0.085 mSv for a chest X-ray exam seems quite high. Surveys in the UK, and Europe, suggest that 0.02 mSv is typical. As a cardiac CT can reach doses of 13-18 mSv, I don't think the claim of 500 Chest X-rays is totally unreasonable. Although I grant that it may be misinterpreted. Perhaps the wording should be changed.

CT radiation dose depends on many factors, not just the length covered. A cardiac scan is a very different protocol to a chest scan, and a 'high-resolution' chest CT is very different to a 'normal' chest CT.

Cardiac CT is difficult because the heart moves, but to ensure diagnostic images the data for image reconstruction must be obtained at the same point in the cardiac cycle. This invariably means that the scanner must discard some of the data it gathers (e.g. when the heart is contracting), or it must scan the area multiple times. A typical approach is to scan slowly through the heart, so that the entire heart is covered about 4 times over about 5-10 beats. This increases the radiation burden significantly. Additionally, because cardiac CT needs high spatial resolution, and high contrast resolution, a high radiation exposure is needed to achieve this (due to shot noise effects).

'High-resoution' chest CT has a considerably lower radiation dose than a 'normal' chest CT because it is a different technique. Most commonly in chest CT, you are looking for soft-tissue abnormalities, or small abnormalities - e.g. tumous, infection, enlarged lymph nodes. This needs good contrast resolution, and also requires that the entire chest is covered (so that a small tumor isn't missed). 'High-resolution' CT takes extremely fine sections through the chest so that high z-axis resolution is obtained - this allows the fine detail in the airspaces of the lungs to be seen. Additionally, because you are looking at air spaces, there is naturally very high contrast between the tissue and air. High inherent contrast means that less radiation exposure is necessary to obtain a diagnostic contrast-noise ratio. Additionally, because HR CT is only looking for generalised lung disease, it isn't necessary to scan the whole chest - it's typical to take 1mm sections every 10 mm (so you only scan 10% of the chest).

Modern MSCT scanners do allow the option of scanning the entire-chest in 'high-resolution' mode - but they do so by destroying the dose advantage.

Dual source scanners do have the potential to bring significant dose benefits - because their faster acquisition means that less data must be discarded due to movement. Some manufacturers are looking at volumetric CT for their next-gen products - it has been reported that a 256 slice volumetric scanner can perform an entire cardiac study in the time between 2 beats. The advantage of this is that there is no repeated exposure, and a significantly reduced radiation dose. ChumpusRex 19:08, 4 September 2006 (UTC)




you r dumb

[edit] Electron beam

I don't know why electron-beam CT is given a whole photograph. These scanners are very rare and one could easily remove all reference to it. Otherwise, why not talk about all the other forms of CT?


The term "CAT" has not been used by professionals for 20 years: it is called "CT"

20 years? Isn't that an exaggeration? "CAT Scan" is still used by the general public. In any case, we need an explanation about why (and when) the name was changed. What was the history of this?


  • I'm not sure EBCT is particularly relevant here. These were an interesting design intended to solve the particular problem of cardiac imaging, but because of their high cost, and single-purpose use, very few have been installed. It may be that these are on the verge of obsolescence, due to the development of the much cheaper and more flexible multi-detector CT scanners (especially the new dual-source scanners). Nevertheless, the bulk of the evidence on CT assessment of heart disease is based on EBCT, not MDCT so, for this reason alone, the technique is certainly not dead. I'm tempted to remove the long paragraph about EBCT, instead briefly mentioning the technology and linking to the EBCT page. ChumpusRex 13:34, 4 March 2006 (UTC)

[edit] body section roentgenography

Be careful with this term. There is a very old film-based (non-digital) method for making tomographic images and the term "body section roentgenography" may refer to this.

[edit] dose decrease?

"overall radiation dose has decreased"

Actually, I believe the overall dose has increased. This is a result of using very thin slices on the multislice (volume) CT scanners.

Advances in technology have meant that reproducing the image quality seen in scans acquired three or four years ago is now possible with significantly less dose. Unfortunately, the trend is to use these imporvements to full effect often increasing the dose. It is possible to achieve an adequate scan with a much reduced dose or a exquisite scan with a greatly increased dose. Whether doses increase or decrease will depend on the attitude of the referring radiologist most likely --5pints

People, sign yourself. Three or four tildes ~~~~. Thanks very much. --Eleassar777 18:02, 31 May 2005 (UTC)

[edit] Requested move

  • I suggest moving the article to a new heading, computed tomography, currently a redirect here. Computed tomography means the same, but is a much more used and more simple term.
  • Support --Eleassar777 18:12, 31 May 2005 (UTC)
  • Support. — Knowledge Seeker দ 18:27, 31 May 2005 (UTC)
  • Oppose. --Dragons flight 21:16, May 31, 2005 (UTC)
  • Oppose. --Quuxplusone 00:58, 1 Jun 2005 (UTC)
  • Oppose. --AjAldous 19:56, 1 Jun 2005 (UTC)
  • Support. --JFW | T@lk 20:26, 1 Jun 2005 (UTC)
  • Support. --TenOfAllTrades (talk/contrib) 21:01, 1 Jun 2005 (UTC)
  • Support. --Alex.tan 12:04, 2 Jun 2005 (UTC)
  • Support. violet/riga (t) 20:30, 6 Jun 2005 (UTC)

This article has been renamed as the result of a move request. violet/riga (t) 20:30, 6 Jun 2005 (UTC)

[edit] Discussion

The terms are not identical. There are plenty of uses of "computed tomography" in geology and materials science which are not axial. This article appears to be solely discussing the axially oriented medical technology, and I don't see any reason to block the more general term, which could at some future date develop into a general article on computed tomographic techniques. Dragons flight 21:16, May 31, 2005 (UTC)

I second "Dragons flight"'s comments, noting that the first paragraph would have to be rewritten if the page were no longer about axial scans. Also, "CAT scan" is a common phrase in American English; "CT scan" isn't. :) --Quuxplusone 00:58, 1 Jun 2005 (UTC)
I don't know how it is used among lay people, but I haven't heard the term "CAT scan" since I was young, but definitely not used in a classroom or in a hospital. We always use "CT scan" (I'm from Chicago; perhaps it is different in other parts of the country). — Knowledge Seeker দ 06:43, 1 Jun 2005 (UTC)
I concur with Knowledge Seeker's comments. I do research in a medical biophysics department and deal with radiologists and imaging specialists on a regular basis. At least in Canada, the acronym CT is used exclusively; I've never heard the acronym CAT used by a professional. (It does still show up in the lay press on occasion, however.) --TenOfAllTrades (talk/contrib) 21:01, 1 Jun 2005 (UTC)
But this is not a medical textbook. CAT Scan is in fact the common name and should be identified as such. Current medical jargon is not the sole deciding factor for this encyclopedia. What happens when someone looks up the common name and finds nothing?
Perhaps this article should be split into two, a general information page and a more technically detailed page for medical professionals (and interested others) or better still reorganize the current article into sections.
Why wasn't CAT simply changed to CaT rather than the longer to pronounce CT? Most phrases are usually shortened for speed.

In the event of moving it, at least, preserve the current page as a redirect. Else, it'll break the interwiki links, for example the one from our Tamil wiki. -- Sundar (talk • contribs) 06:23, Jun 1, 2005 (UTC)

When pages are moved, the former page is automatically made a redirect to a new one. Otherwise, as far as I know, "computed tomography" most often refers to medical imaging technique and is the most often used term in this context. I think it would be best to move the page and to put This article refers to a medical imaging technique. For other meanings, see computed tomography (disambiguation) at the top of the article when moved. --Eleassar777 08:03, 1 Jun 2005 (UTC)
In my experience CAT and CT scans refer to X-ray transmission tomography - there are other modalities utilising tomography e.g. single photon emission computed tomography and positron emission tomography that need a computer to perform the reconstruction. Therefore computed tomography shouldn't be moved to this article. --AjAldous 19:56, 1 Jun 2005 (UTC)
I think we've done the right thing--the See also section of this article includes links to SPECT and PET, so we're covered for the other types of computed tomography. As AjAldous says, when radiologists (or most anyone else) refers to CT, they're talking about X-ray transmission CT and not one of the other flavours. --TenOfAllTrades (talk/contrib) 21:01, 1 Jun 2005 (UTC)

As far as I can tell, the most common usage by far of the term computed tomography is in radiology. If someone starts an article on the use of CT in other fields, we can always create Computed tomography (disambiguation), and link to it from the main Computed tomography article: this one. --TenOfAllTrades (talk/contrib) 21:01, 1 Jun 2005 (UTC)

[edit] References to real companies: when is it an ad?

I am new to Wikipedia, and yesterday I had my first go.

I don't like ads myself, but yesterday I added a few lines about microtomography and even nanotomography and I thought that it would be interesting to add a link to my company Skyscan, since I also found out that there was a link to "Creative Technology Ltd." on that same page. Also searching for Dell and IBM I found references to machines they sell, so I am wondering why that Skyscan link was removed? (I am just wondering, no hard feelings)

I understand the intention of this Wikipedia to be free of ads, and to be accurate as possible but at Skyscan we are not a pure commercial company, we also help in a lot of research, especially bone research. We work together with universities. A lot of papers have been published by our people and we do develop very interesting new technology like our nano-ct scanner that has a pixel resolution about 150...250 nanometers. And our scanners are not exactly a mass product.

I also see that some companies have here a complete description about when they were started up, who is in charge… is that not an ad?

Again, I have no hard feelings that the link was removed, but I wanted to extend the microtomography and nanotomography since I did not find any references in here. And writing about is very hard to do if I cannot reference to my company or avoid the name Skyscan.

PS: I am not a sales person, just IT. ;-) But we do create wonderful stuff here that is very interesting for scientific minded people. I just want to share that information.

Any tips and hints are welcome. :-)


[edit] Proton CT

What about Proton CT? Why is there no information on this? It could be a seperate page, but this page acts like the only CT is photon. I perform research in proton CT and could provide some text, if I got suggestions on where to put it. This page, or link to seperate page?

If it is likely to be short, a paragraph here will do. It is a form of CT, isn't it. If you plan to write a longer article, please make a new page with a link from here. Don't forget to cite your sources! JFW | T@lk 09:15, 11 December 2005 (UTC)

[edit] Is this information really correct?

I actually do CT scans and I am concerned that the info in this article is way off. We take 2 dimensional images of internal organs and we can reconstruct them into 3D images with special software (that not every CT scanner is connected to). Also, the "axial" is not included in the name very often because the data is actually collected in a spiral or helical plane and then made "axial" by the computer.

16:49, 9 March 2006 (UTC) Christopher B. RT(R)(CT pending) CT is 3 Dimentional. The CT image uses what's called "voxels" (a volume of pixels). The "matrix" is what the technologist views. The matrix is composed of all the voxels the the scanner sees, and reconstructs into the image on the screen. Yes, we can use the information to make a true 3D image, but even though the technologist sees a 2D image, the scanner is aquiring the information 3D. For example, say I take a slice with a thickness of 5mm. The voxel will be 5mm deep, even though I'm looking at a flat screen or image. Especially now with Multi-Detector Scanners, we can reconstruct that 5mm image into whatever thickness we want. For simplicity, if I cut the 5mm voxel in half, I'll get two 2.5mm images. There are 3 planes used in Radiology (Axial, Sagital, Coronal). The scanners still aquire the images in the axial plane. With helical/spiral (similar terms, different brand -- Siemens: Helical GE: Spiral)scanning, rather than the sequential step by step style of imaging, the scanner will continuously scan and image the patient while moving the patient through the scanner.


The use of the word "axial" is still applicable to helical medical CT as the tube and detector still rotate around a fixed axis. Strictly speaking the data collected during a medical CT exam is 3-dimensional but it is misleading to suggest that thie 3D sampling is regular, as in the case of MRI. Reconstruction algorithms are now very complex and the basic examples quoted in many cases are becoming less and less applicable. 80.189.7.248 16:09, 14 September 2006 (UTC)5pints

[edit] misleading

I'd like to kindly point out the term CT does not necessarily mean an imaging technique strictly in the *medical* field. It's a broadly used technique spanning many fields. To show and talk about only the instruments of this technique used in *one* aspect of the medical field misleads the audience into thinking that this is a very narrow topic. Such is not the case. Please consider revamping this topic. Perhaps the main CT page could discuss the mathematics and history, then sub-topics could be broken out; astronomy, oceanography, reconnaissance, microscopy, as seen in the current page, etc... I do realise that this subject has been rapidly expanding in several fields for years now and the terminology is a mess. It won't be cleaned up anytime soon, so why worry about it.

--Gatohaus 01:29, 29 January 2006 (UTC)
The usual technique in such an instance is to create a disambiguation page that lists the other uses of the term and links to the relevant articles. Since the biggest use of the term 'computed tomography' is probably still in medical imaging by a good margin, we would leave this article, computed tomography, here. At the top, add a link of the form
This article discusses medical imaging. For other uses of computed tomography, see computed tomography (disambiguation).
The dab (disambiguation) page would then link to other articles that use the term. TenOfAllTrades(talk) 18:15, 9 March 2006 (UTC)

[edit] History of CT

The history of transmission CT, both for medical as well as non-medical applications, goes much farther back than currently mentioned in the article. First, medical X-ray tomography (known as 'Conventional Tomography' or 'Classical Tomography') was used for many years prior to the advent of CT (apparently since the 1920's), with the principle of mechanically moving the film and/or X-ray tube during a prolonged exposure in such a way as to blur out all object voxels except the ones lying in a pre-defined focal plane. This was used quite extensively at the time, for example to detect brain pathology in conjuction with the injection of air into the ventricular system (obviously a very traumatic procedure), called pneumoencephalography. In 1942, Gabriel Frank was issued US patent 02281931 for a CT-like X-ray scanning apparatus that performed reconstruction from projections using analog techniques. It is not clear whether the disclosed device was ever built or used. In 1961, Malvin Howard Kalos, a professor of physics at Columbia University in NY, invented a technique for scanning vapor pipes with gamma radiation in nuclear reactors to determine their consistency. This was the first known application of the principle of computerized tomography and was part of work funded by the US Atomic Energy Commission (see: "Conceptual Design of a Vapor Volume Fraction Instrument", Kalos, AEC Contract AT(30-1)-2303(IX), Apr. 1961. ) Apparently Prof. Kalos did recognize the potential of this technique for medical applications, and reportedly went over to the nearby Memorial Sloan Kettering Cancer Center to try to talk the radiologists there into possibly using his invention to replace the traumatic pneumoencephalography procedure for their patients. The story goes that he was laughed out of the building and lost his interest in pursuing this further. In the mid 1960's Allan Cormack came up with his independent concept for CT, and by the late 1960's Godfrey Hounsfield invented and developed his version. Apparently all these individuals, as well as others in various parts of the world, were unaware of each other at that point (WWW and Google being some years away ;) ). Hounsfield's main advantage was that he actually put his invention to practical use wheras the others just had the concept. By the way, Hounsfield used an iterative computational method to reconstruct an image from projections, whereas Kalos and the others used direct analytical techniques, the latter also being used today.

Anybody that knows more about this subject is welcome to add. I suggest a section about this be added to the main History section. tomos1

Found some CT History here [1]
(see the section titled: "A BRIEF HISTORY OF COMPUTED TOMOGRAPHY (CT) SCANNING"). It adds Prof. Oldendorf (in 1961) and does not mention Prof. Kalos. Crum375 01:04, 5 May 2006 (UTC)
Made minor wording edit in Article to implicitly reflect the fact that prior CT inventors existed since Gabriel Frank - but did not include him or any of the above history for now. Crum375 16:43, 18 May 2006 (UTC)

[edit] Example images

Many of the example CT images included (and linked to) are poorly windowed (brightness and contrast both too low) - as a result very little detail is visible. This applies to both the chest and cranial images on the main page and a linked example [[2]]. In the case of the linked site, the window settings aren't even consistent between neighboring images in the series.

It would be nice to have appropriately windowed examples, to illustrate the anatomic detail available with CT. Could we perhaps ask the owner of the original data to prepare new images from the raw data, or perhaps another contributor could provide some new images. Unfortunately, simply adjusting the web-ready images would be unsatisfactory as much of the contrast detail will have been discarded in the conversion to 8-bit images. ChumpusRex 17:54, 10 May 2006 (UTC)

[edit] CT imaging as graphic art

I removed this section because I saw no supporting sources for it. If someone does have the correct secondary sources for it then it could be included. Thanks, Crum375 00:07, 18 June 2006 (UTC)

[edit] Removing my beautiful art / the author's response

I wrote that section. What is wrong with it? Please explain. I accept your removing the section and the image if your have any objection against their quality. Please let me know if this is the case. Then I will shut my mouth up. However, I do not accept this removal if your only reason is the lack of references. How can I provide you with any source if I was the original creator of the text and the image. And one more word: I do not have time to read through the elaborated rules about secondary and other kinds of references. My image is simply an original piece of art that I donated to the World. If you do not like it then let me know. PLEASE.Otherwise I will act like an idiot and you will suggest to excomunicate me. I am from the seventeenth sentury so I rather choose excommunication than learning the stupid IP rights when I am the owner. Please respond!!!! excommunicandus

Zgyorfi, please read the relevant WP policies that pertain to sourcing, such as WP:RS.

I will try to touch some key issues here, but you really should do your own detailed reading.

First, let me say that the fact that you are eager to help and improve WP is greatly appreciated by all of us, so please don't be discouraged by anything I am about to say. But to contribute in a productive and useful way you have to understand what WP is about. Again, please read the various policies, e.g. WP:NOT, WP:OR and many more. I'll mention one classical NOT - WP is not a place where artists may arbitrarily upload original work. If you have created a beautiful masterpiece, you can't just upload it to WP regardless of the purity of your altruistic intentions. WP is an encyclopedia - that means it is essentially a summary of notable work that has been published and thereby became notable elsewhere. Such a publication (e.g. an art book reviewed and published by a reputable publisher - not self publishing), when verifiable and reliable would be considered a secondary source, while the work or art (say) itself is considered a primary source. WP itself would then become a tertiary source when citing this secondary source art book. In this specific case of CT related art, you would have to cite a publisher that actually published this work and made it notable. Please feel free to ask me (or anyone else) any question, but I really encourage you to read on your own and become an expert on the subject of what WP is and what it is not. Thanks again, (and please sign all your messages with 4 tildes - it makes life easier for everyone) Crum375 00:22, 19 June 2006 (UTC)

[edit] Commerical Sites in External Links

I just removed a few barnacles. Please do not add spam there - WP is an encyclopedia. If you have a site that is non-commercial (not selling anything and not favoring a company or group of companies) and adds important information to the article, it may belong there. Note that if the information is so important - it may belong directly in the text anyway. Otherwise, any spam or ads will be reverted. Crum375 13:31, 26 June 2006 (UTC)

[edit] Power and voltage

The image in the "process" section claims that CT scanners use up to 150kW of power, while in the main article under "Further Advances" it is claimed that up to 150kV is needed, at a power of up to 100kW. These should be consistent. Perhaps the information in the image is incorrect, and needs to be changed to 100kW or "150kV at 100kW". I don't know the field, so I don't know if the maximum power is 100kW or 150kW. --Mike Van Emmerik 23:45, 20 September 2006 (UTC)

They're talking about slightly different things. 100 kW is the maximum power that may be delivered to the actual X-ray tube. 150 kW may be the power needed to supply the entire scanner (including inefficiency of the high-voltage power supply unit). In the case of the picture, the caption refers to power being transmitted to the rotating scanner gantry (so, this means low voltage power supplied to the power conversion unit, as well as power needed for the detector array and other electronics).
The situation is more complicated with the development of dual-source scanners - as contemporary models use 2 independently controlled 80 kW rated tubes. Once inefficiency in power conversion and ancillary motors/electronics are considered - the power consumption could be over 200 kW.ChumpusRex 11:05, 21 September 2006 (UTC)

[edit] No Sources

There's no doubt that this a well-written article, and I don't dispute its accuracy, but there are still no sources, either after facts or in a section. Sloverlord 17:30, 5 November 2006 (UTC)

The stuff that I contributed (regarding risks from the radiocontrast agents, esp. nephrotoxicity and slight risk of anaphylactic shock) was stuff from personal experience, which I guess you could construe as original research. When I get around to it, I will try to provide more formal citations for those sections. --Kyoko 18:02, 5 November 2006 (UTC)

[edit] history section removed?

An anonymous user removed the history section of this article on Nov 7th. Someone who knows more about this should take a look at the deleted material and determine if it should have been deleted or not. 64.81.115.243 03:08, 11 November 2006 (UTC)

The last place I found the history was in the August 22 version; it seems to have been removed on August 23. I just restored that version for now. Crum375 03:23, 11 November 2006 (UTC)

[edit] Whole body scans

Most visitors won't understand what the problem is with having to follow up on "incidental findings" of a whole body scan. This should be explained succinctly, but I don't know how. An example of a problem is as follows, as I understand it. A scan incidentally shows a small carcinoma somewhere. Conventional medical practice would not have discovered the tumor and there is no clinical experience with such a finding so it is not known whether such early, small, occult lesions are likely to grow or metastasize or whether they spontaneously disappear. Therefore there is no way to compare cost versus benefit of surgical intervention and all we have to go on is anxiety. On the public health level, many unproductive tests and procedures would be conducted out of fear, ignorance and excessive risk avoidance policies, diverting resources from where they be more beneficial. On the individual patient level, someone with enough money would feel compelled to spend it and someone without may impoverish themselves or worry themselves into considerable trouble. Clarification of when whole body scans are worthwhile awaits scientific research and perhaps should be discouraged for now unless there is a pretty good special reason for doing one. How can this be expressed neatly? Myron 11:25, 10 January 2007 (UTC)

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