Stress Test/Thallium Scan 
Author Message
 Stress Test/Thallium Scan

This is a follow-up to the conversation on thallium scans.  I recently had a
combination stress test/thallium scan.  The stress test (treadmill) was done in
the normal fashion, and when I had reached my maximum rate a dose of thallium
isomer was injected through a previously-placed catheter.  A series of scans
were then taken over the next 1/2 hour.  I was asked to return to the X-ray lab
3 hours  later, at which time another injection of thallium was given, and the
series of  scans was repeated.  I should add that I have had cardiac by-pass
twice, and two MI's.
My question involves the interpretation of the test.  What is the reason for the  
second injection and the second series of scans?  I understand (I think!) that
healthy heart muscle takes  up radioactive thallium preferentially over damaged
muscle, and that the scan shows a 'picture' of the damaged areas of the heart.  
Why the second go-around?  Also,  is there a value in comparing results of
thallium/stress tests from year to year?  Thanks in advance for your responses!

--  
Uucp: ...{gatech,ames,rutgers}!ncar!asuvax!stjhmc!273!708!Hal.Hersh



Thu, 11 Nov 1993 00:56:59 GMT
 Stress Test/Thallium Scan
+This is a follow-up to the conversation on thallium scans.  I recently had a
+combination stress test/thallium scan.  The stress test (treadmill) was done in
+the normal fashion, and when I had reached my maximum rate a dose of thallium
+isomer was injected through a previously-placed catheter.  A series of scans
+were then taken over the next 1/2 hour.  I was asked to return to the X-ray lab
+3 hours  later, at which time another injection of thallium was given, and the
+series of  scans was repeated.  I should add that I have had cardiac by-pass
+twice, and two MI's.
+My question involves the interpretation of the test.  What is the reason for the  
+second injection and the second series of scans?  I understand (I think!) that
+healthy heart muscle takes  up radioactive thallium preferentially over damaged
+muscle, and that the scan shows a 'picture' of the damaged areas of the heart.  
+Why the second go-around?  Also,  is there a value in comparing results of
+thallium/stress tests from year to year?  Thanks in advance for your responses!

  The first injection was to see what portions of the myocardium take up or
fail to take up the tl-201 when the heart is under stress (meaning that the
heart muscle, which is working harder than at rest, will need more {*filter*}
supply).  If there are ischemic or infarcted areas, there will be a much
greater contrast between normal and compromised areas than when the heart is
at rest.  That's the point of doing a _stress_ test.

  The second injection was to see how well (or if) there are compromised
areas that fill in when the heart is at rest, when the myocardium is doing a
minimal amount of work and therefore needing less {*filter*} supply than when it
is racing along.  Areas of little uptake on the exercise study may show
"normal" uptake (relative to true-normal myocardium) when the vessels don't
have to try to provide heavy-duty circulation to the muscle.

  A combined rest/exercise study is an alternative to a variation in which
there is a exercise/redistribution study. (Note: when the tl-201 is
injected, there is maximal uptake in the first few minutes, and then the
myocardium "releases" some of the tl-201 back into the {*filter*} stream.  Over a
period of 3-4 hours, the material has gone in and out of the myocardium, and
thus has more opportunity for compromised areas to fill in, hence the name
"redistribution study".)  This method has the advantages of one injection
instead of two (besides the discomfort for the patient, bear in mind that a
2.2 milliCurie dose has a list price of about $125), less radiation dose,
and often gives the clinician all the answers he needs.  You should ask your
doctor why in your specific case that a dual injection study (which is by no
means unusual to do) was preferred over doing an exercise/redistribution
study.  Note also that many institutions may "only" do rest/exercise studies
or that others may "only" do exercise/redistribution studies, which may
explain why you had an rest/ex instead of a ex/redist.

  (To those people who are wondering how an aged person with bad hips/legs,
or an amputee, or the otherwise unable-to-exercise are provided with an
"exercise" study, we sometimes use {*filter*} like persantin and, lately,
adenosine, to stress the heart.  There are some other methods like emotional
stress and and "bicycle grip squeeze" that haven't panned out too well.)

Hope this helps.

--
Kim L. Greer                      

Div. Nuclear Medicine  POB 3949          voice: 919-681-5894
Durham, NC 27710                         fax: 919-681-5636



Mon, 15 Nov 1993 20:04:56 GMT
 
 [ 2 post ] 

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