RE: Digital X-Ray Can Scan Body in 13 Seconds

[John Jacobus <crispy_bird@YAHOO.COM>]

Hobart,

You are correct.  All interactions in diagnostic

radiology, Rayleigh, photoelectric, and Comptom

scattering involve interactions with electrons.  Since

the electron density of a diamond, with a higher

atomic density, has more electrons, you will get

increased scattering.  Most biological molecules are

composed of low Z elements.  And, as you noted, the

greater differences in density, the greater the

scattering.  



I tried to keep the discussion as simple as possible.



I am thinking that the device is like a bone

densimmetry scanner, using a beam with a small cross

sectional area that tracks back and forth over the

worker.  I have seen backscatter units advertised,

such as http://www.rapiscan.com/secure1000.html  It

would be no big trick to develop a system to scan a

workers abdomen.  Again, this is a screening device,

not a diagnostic tool.  I still question the need to

resolve sources as small as 2 mm.  You are looking for

workers stealing ore with diamonds in the matrix, not

separated diamonds.



As for your calculations, I assumed an average photon

energy of 40 keV, and calculated an attenuation ratio

of 0.948 (diamond) to 0.829 (water) for a 2 mm thick

diamond.  The ratio being 1.15.  Again, I question the

presumption that the stone would be so small.



--- "Shackford, Hobart W" <hshackford@rwmc.org> wrote:

> John:

> 

> Actually medical images rely a on the photoelectric

> effect which is a cubic

> function of effective atomic number (Z) and

> proportional to physical

> density.  Thus bone has a contrast over soft tissue

> of about 6 due to the Z

> difference and the density difference. Carbon has

> essentially the same Z as

> soft tissue so only the density difference will

> provide the subject contrast

> as you suggest. 

> 

> I am not familiar with this device but it sounds

> like this device would be a

> projection-type imager that is perhaps set up in a

> portal. In that case I

> think you would rapidly loose the 3.5 density ratio

> since the equivalent

> tissue path through a 2 mm diamond would be about

> 30.5 cm vs. the adjacent

> soft tissue of 30 cm which, if I did the math right

> is an attenuation ratio

> of about 1.05. It would be very hard to see small

> objects in a film-based

> system with that kind of contrast but with some

> digital enhancement...maybe

> (but I doubt it in a screening situation,

> particularly when you are viewing

> the whole body).

> 

> I would be interested to see some studies of the

> medical applications

> mentioned in the original post.

> 

> Hobie Shackford

> Chief Medical Physicist

> Roger Williams Medical Center

> Providence, RI 02908

> (401) 456-6528

> Fax: (401) 456-6540

> hshackford@rwmc.org

> 

> 

> 

> -----Original Message-----

> From: John Jacobus [mailto:crispy_bird@YAHOO.COM]

> Sent: Tuesday, June 17, 2003 9:39 AM

> To: Douglas and Shirley Jackson

> Cc: RADSAFE

> Subject: Re: Digital X-Ray Can Scan Body in 13

> Seconds

> 

> 

> An x-ray image shows objects due to differences in

> density.  Water has a density of 1.00, a diamond has

> a

> density of 3.51, graphite of 2.25, and bone of

> 1.7-2.0

> 

. . .



=====

-- John

John Jacobus, MS

Certified Health Physicist

e-mail:  crispy_bird@yahoo.com



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