RE: A Question for Power Reactor Types and others with portal monitors.

[John Jacobus <crispy_bird@YAHOO.COM>]

I picked a bone imaging agent as the Tc-99m labeled

compound has a fairly long retention in the bone.  The

limiting factor in this case is the half-life of the

Tc-99m.  (Also, the number I gave assumes all is taken

up in the bone.  Generally, the patient empties their

bladder before the first image is taken).  Obviously,

other imaging compounds would have shorter effective

half lives. 



Thallium is analgous to potassium, so its effective

half life will be based on both the excretion of

potassium and the half life of the radioisotope. 

Generally, you see the Tl-204 for quite sometime.  



One possible reason for more heart scans using Tl-201

is the ease of the procedure.  There have also been

articles recommending that patients who arrive at

Emergency Rooms demonstrating heart problems be given

a nuclear medicine scan prior to admission.  If the

patient does not show signs of heart disease, they are

not admitted.  Saves hundreds of bucks.



Have you ever done a spectral analysis of the Tc-99m

injected patients to see what the radionuclide is?  



--- "Flood, John" <FloodJR@NV.DOE.GOV> wrote:

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

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

> Sent: Thursday, April 08, 2004 10:51 AM

> 

> "If a patient is given a bone scan

> with 30 mCi of Tc-99m, after 3 days there may still

> be

> 7 microcuries of activity present."

> 

> Actually, there may be AS MUCH AS 7 uCi remaining. 

> The effective half-life

> will also include the biological elimination rate,

> and varies greatly from

> individual to individual.

> 

> "Tl-201 is only used for heart scans.  While it is

> has

> a half life of 3 days, there are Tl-202 and Tl204

> contaminates.  However, you do not retain thallium

> chloride."

> 

> Again, this is heavily related to biological

> elimination rates.  Our

> experience is that Tc-99m is rarely detectable for

> more than 10 days and

> usually undetectable in a week or less, but Tl-201

> cases remain detectable

> longer.  The longest lived of our cases (a month

> each) were both Tl-201

> stress tests.

> 

> And our experience probably mimics others - the

> overwhelming majority of

> detectable medical uses are Tc-99m, with Tl-201

> second - the stress test

> business is booming (thanx to baby boomers, no

> doubt).

> 

> The other big player is therapeutic I-131 thyroid

> treatments - not only can

> they last a long time, they are detectable from a

> great distance.

> 

> Bob Flood

> Nevada Test Site





=====

+++++++++++++++++++

"Those who have not known the joy of standing up for a great cause of justice have not known what makes living worthwhile."

Paul Painleve, regarding the Dreyfus Affair, 1895



-- John

John Jacobus, MS

Certified Health Physicist

e-mail:  crispy_bird@yahoo.com



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