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

["Shackford, Hobart W" <hshackford@rwmc.org>]

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





--- Douglas and Shirley Jackson <g2v13a@SWBELL.NET>

wrote:

> My I ask the dumb question of the day ?????

> 

> Can you actually see the diamonds (as is implied) in

> this x-ray ?

> 

> I have seen many foreign object x-rays of the

> abdomen over the years and 

> ... the rings show nicely, but the diamonds would

> have been missed 

> without the metal ring.

> . . .





=====

-- John

John Jacobus, MS

Certified Health Physicist

e-mail:  crispy_bird@yahoo.com



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