technetium vs thallium stress tests 
Author Message
 technetium vs thallium stress tests

Can a technetium stress test be usefully compared on the same person
to a previous thallium stress test as evidence of change?

Given the 12 times difference in isotope lifetime and hence safe 10
times higher dosing (activity), surely the technetium scan is more
accurate. Smaller error in nuclear counting statistics.

                                             Kemp Randolph



Thu, 14 Oct 1999 03:00:00 GMT
 technetium vs thallium stress tests


Quote:

>Can a technetium stress test be usefully compared on the same person
>to a previous thallium stress test as evidence of change?

>Given the 12 times difference in isotope lifetime and hence safe 10
>times higher dosing (activity), surely the technetium scan is more
>accurate. Smaller error in nuclear counting statistics.

>                                             Kemp Randolph

Please; someone knowledgeable give some attention to this general question
and this one? How do Thallium Treadmill Scan,Cardiolyte (Tc) Scan and pet
compare? Do they not all measure tomographically the angular distribution
of gamma radiations from a short lived isotope? I once was told that all
were positron emitters, but have also been told that this is not correct.
Having had both Thallium and Cardiolyte scans, I know that the protocals are
surprisingly different, at least so they seem to me. If I could learn the
isotopic masses I could figure out the nuclear physics, but the protocals
(particularly the milk drinking after Cardiolyte) are beyond me. The
relative merits of Tc versus Th have been argued before in this group, but
not to my understanding.


Fri, 15 Oct 1999 03:00:00 GMT
 technetium vs thallium stress tests


Quote:

>>Can a technetium stress test be usefully compared on the same person
>>to a previous thallium stress test as evidence of change?

>>Given the 12 times difference in isotope lifetime and hence safe 10
>>times higher dosing (activity), surely the technetium scan is more
>>accurate. Smaller error in nuclear counting statistics.

No this is completely untrue. In the UK the maximum allowable
acitivity of Thallium that can be administered is 80 MBq (approx
2mCi). This one injection allows both stress images and redistribution
(similar to rest but not identical) images to be obtained. With the
newer technetium compounds eg tetrofosmin (myoview) or sestamibi
(cardiolite) the total injected acitivity is typically 1000 MBq.
However in order to obtain stress and rest images two injections are
required. This is usually involves 1 injection of 250 MBq followed by
a further injection of 750 MBq 3-4 hours later, in the hope that the
larger injection swamps the earlier dose. It is also possible to
adminster 2 injections of 500 MBq on seperate days but this is not
practical for many centres and patients. There are advantages and
disadvantages of stress followed by rest or vice versa.
In our experience an injection of 250 MBq of tetrofosmin leads  to
less than twice as many counts detected from the myocardium compared
to that with 80 MBq of thallium. I believe sestamibi to be slightly
worse but do not have experience to back this up.
The reason for this is that a much smaller fraction of the injected
tetrofosmin is extracted from the {*filter*} by the myocardium. Uptake is
also very slow compared to thallium which leads to other serious
problems for stress imaging.

A factor of 2 in counting statistics is unlikely to be significant.

Additionally there are many other differences between thallium and
technetium (eg mechanism of uptake and degree of attenuation in
tissue)  which mean technetium and thallium scans should not be
directly compared. This is why new normal ranges should be established
if a centre switches from thallium to technetium or vice versa.

Quote:
>Please; someone knowledgeable give some attention to this general question
>and this one? How do Thallium Treadmill Scan,Cardiolyte (Tc) Scan and pet
>compare? Do they not all measure tomographically the angular distribution
>of gamma radiations from a short lived isotope? I once was told that all

Thallium and technetium are both gamma emitters ( well strictly
thallium emits x-rays) which are detected by a gamma camera to form an
image. This is not always done tomographically, some centres still
believe in planar imaging as there is no convincing evidence to
suggest that tomographic imaging gives better results.
The isotopes used in pet imaging are positron emitters.

Quote:
>were positron emitters, but have also been told that this is not correct.
>Having had both Thallium and Cardiolyte scans, I know that the protocals are
>surprisingly different, at least so they seem to me. If I could learn the
>isotopic masses I could figure out the nuclear physics, but the protocals
>(particularly the milk drinking after Cardiolyte) are beyond me. The
>relative merits of Tc versus Th have been argued before in this group, but
>not to my understanding.

The main reason for differences in protocol is the fact that there is
high liver uptake of cardiolite (and tetrofosmin). This  is a big
problem as it can often overlap with the myocardium making the images
unreportable. Even in cases where there is no overlap or in tomography
where overlapping structures can be separated it is still a problem
due to scatter. Therefore it is necessary to wait an hour or even 90
mins between injecting sestamibi and imaging (with tetrofosmin waiting
time is approx 40 mins). The suppliers of sestamibi also recommend a
fatty meal to help clear the liver - hence the milk.
With thallium, imaging must start immediately after injection as
redistribution occurs relatively quickly.

Hope this makes sense and is of use

Graham Wright




Thu, 21 Oct 1999 03:00:00 GMT
 technetium vs thallium stress tests

Quote:



>>>Can a technetium stress test be usefully compared on the same person
>>>to a previous thallium stress test as evidence of change?

>>>Given the 12 times difference in isotope lifetime and hence safe 10
>>>times higher dosing (activity), surely the technetium scan is more
>>>accurate. Smaller error in nuclear counting statistics.
>No this is completely untrue. In the UK the maximum allowable
>acitivity of Thallium that can be administered is 80 MBq (approx
>2mCi). This one injection allows both stress images and redistribution
>(similar to rest but not identical) images to be obtained. With the
>newer technetium compounds eg tetrofosmin (myoview) or sestamibi
>(cardiolite) the total injected acitivity is typically 1000 MBq.
>However in order to obtain stress and rest images two injections are
>required. This is usually involves 1 injection of 250 MBq followed by
>a further injection of 750 MBq 3-4 hours later, in the hope that the
>larger injection swamps the earlier dose. It is also possible to
>adminster 2 injections of 500 MBq on seperate days but this is not
>practical for many centres and patients. There are advantages and
>disadvantages of stress followed by rest or vice versa.
>In our experience an injection of 250 MBq of tetrofosmin leads  to
>less than twice as many counts detected from the myocardium compared
>to that with 80 MBq of thallium.

Here sestambi with 30 mC stress with gating,  10 mCi rest two days
later versus 1 mCi for thallium though I've not yet seen the printed
report on the latter. So a  little better.

Quote:
>I believe sestamibi to be slightly
>worse but do not have experience to back this up.
>The reason for this is that a much smaller fraction of the injected
>tetrofosmin is extracted from the {*filter*} by the myocardium. Uptake is
>also very slow compared to thallium which leads to other serious
>problems for stress imaging.

"Uptake" , meaning extravascular or (misnomer, I'd say) to
microcirculation? Aren't both assays designed to assay  total
"myocardial" {*filter*} volume, that is,both in the chambers of the heart
and the microvasculature of the heart muscle? You make it sound like
the "uptake" is the source of the counts and that it's to the heart
tissue itself.

Quote:
>A factor of 2 in counting statistics is unlikely to be significant.

Probably, though I had a little more and was told the technetium was
more accurate.

Quote:
>Additionally there are many other differences between thallium and
>technetium (eg mechanism of uptake and degree of attenuation in
>tissue)  which mean technetium and thallium scans should not be
>directly compared.

Not understanding this uptake issue yet, I'll still ask:  would it be
fair to say the tests, properly normalized, assay different mixtures
of macrovascular and microvascular cardiac status?

Quote:
>This is why new normal ranges should be established
>if a centre switches from thallium to technetium or vice versa.
>>Please; someone knowledgeable give some attention to this general question
>>and this one? How do Thallium Treadmill Scan,Cardiolyte (Tc) Scan and pet
>>compare? Do they not all measure tomographically the angular distribution
>>of gamma radiations from a short lived isotope? I once was told that all
>Thallium and technetium are both gamma emitters ( well strictly
>thallium emits x-rays) which are detected by a gamma camera to form an
>image. This is not always done tomographically, some centres still
>believe in planar imaging as there is no convincing evidence to
>suggest that tomographic imaging gives better results.
>The isotopes used in pet imaging are positron emitters.

If this is the deoxyglucose assay then that presumably measures the
metabolic level of the heart muscle, that is how live it is AND how
well perfused.

- Show quoted text -

Quote:
>>were positron emitters, but have also been told that this is not correct.
>>Having had both Thallium and Cardiolyte scans, I know that the protocals are
>>surprisingly different, at least so they seem to me. If I could learn the
>>isotopic masses I could figure out the nuclear physics, but the protocals
>>(particularly the milk drinking after Cardiolyte) are beyond me. The
>>relative merits of Tc versus Th have been argued before in this group, but
>>not to my understanding.

>The main reason for differences in protocol is the fact that there is
>high liver uptake of cardiolite (and tetrofosmin). This  is a big
>problem as it can often overlap with the myocardium making the images
>unreportable. Even in cases where there is no overlap or in tomography
>where overlapping structures can be separated it is still a problem
>due to scatter. Therefore it is necessary to wait an hour or even 90
>mins between injecting sestamibi and imaging (with tetrofosmin waiting
>time is approx 40 mins). The suppliers of sestamibi also recommend a
>fatty meal to help clear the liver - hence the milk.
>With thallium, imaging must start immediately after injection as
>redistribution occurs relatively quickly.
>Hope this makes sense and is of use

Yes, indeed

                                          Kemp Randolph
                                          Long Island



Fri, 22 Oct 1999 03:00:00 GMT
 technetium vs thallium stress tests

Quote:

>Here sestambi with 30 mC stress with gating,  10 mCi rest two days
>later versus 1 mCi for thallium though I've not yet seen the printed
>report on the latter. So a  little better.

Are you sure it was only 1mCi of thallium? I think that is an usually
low dose. 40 mCi of sestamibi is also very high and would not be
allowed in the UK routinely. You do not need that level to allow
gating - we routinely gate thallium scans with less than 2mCi.

Quote:
>"Uptake" , meaning extravascular or (misnomer, I'd say) to
>microcirculation? Aren't both assays designed to assay  total
>"myocardial" {*filter*} volume, that is,both in the chambers of the heart
>and the microvasculature of the heart muscle? You make it sound like
>the "uptake" is the source of the counts and that it's to the heart
>tissue itself.

I'm not sure I understand what you are asking here. The idea of both
tests is to measure myocardial perfusion at stress and rest. Thallium
and sestamibi are both extracted by myocytes (by different mechanisms)
in proportion to {*filter*} flow. Therefore images of thallium or sestamibi
distribution represent myocardial perfusion.

Graham Wright




Sun, 31 Oct 1999 03:00:00 GMT
 technetium vs thallium stress tests

Quote:

>>Here sestambi with 30 mC stress with gating,  10 mCi rest two days
>>later versus 1 mCi for thallium though I've not yet seen the printed
>>report on the latter. So a  little better.

>Are you sure it was only 1mCi of thallium? I think that is an usually
>low dose. 40 mCi of sestamibi is also very high and would not be
>allowed in the UK routinely. You do not need that level to allow
>gating - we routinely gate thallium scans with less than 2mCi.

You're right. 3 mC thallium at peak exercise,  an extra 1 mC for the
equilibrium.  But 30 mC for the technetium.

Quote:
>>"Uptake" , meaning extravascular or (misnomer, I'd say) to
>>microcirculation? Aren't both assays designed to assay  total
>>"myocardial" {*filter*} volume, that is,both in the chambers of the heart
>>and the microvasculature of the heart muscle? You make it sound like
>>the "uptake" is the source of the counts and that it's to the heart
>>tissue itself.

>I'm not sure I understand what you are asking here. The idea of both
>tests is to measure myocardial perfusion at stress and rest. Thallium
>and sestamibi are both extracted by myocytes (by different mechanisms)
>in proportion to {*filter*} flow. Therefore images of thallium or sestamibi
>distribution represent myocardial perfusion.

Now that I have two dimensional thallium images to look at, most just
showing wall sources, not chamber sources ,I understand .

 Is most of that signal (radiation) then coming from the
radionucliotide in the {*filter*} or in the extravascular (myocardium)
tissue?  (If from the tissue then the agent with greater uptake gets
an enhanced sensitivity to factor in with activity differences as
relating to the original question. )

                                        Kemp Randolph
                                        Long Island



Tue, 02 Nov 1999 03:00:00 GMT
 technetium vs thallium stress tests



Quote:

>You're right. 3 mC thallium at peak exercise,  an extra 1 mC for the
>equilibrium.  But 30 mC for the technetium.

Sounds like you had something called a reinjection thallium scan. A
single injection of thallium allows peak stress + equilibrium images
to be taken as thallium redistributes. A further injection is
occaisonally given when looking for something called hibernating
myocardium. This is an area that is very poorly understood and
reinjection thallium scans may or may not identify hibernation.

Quote:
>Now that I have two dimensional thallium images to look at, most just
>showing wall sources, not chamber sources ,I understand .

> Is most of that signal (radiation) then coming from the
>radionucliotide in the {*filter*} or in the extravascular (myocardium)
>tissue?  (If from the tissue then the agent with greater uptake gets
>an enhanced sensitivity to factor in with activity differences as
>relating to the original question. )

Yes the purpose of a thallium (or sestamibi) scan is to measure
myocardial perfusion. Uptake of the tracer is an indication of the
{*filter*} flow to the muscle. Most of the injected thallium (approx
80-90%) is cleared from the {*filter*} within 1 min of injection. This is
why you will have had to exercise for a further minute post injection
- to ensure most uptake occurs when the heart is at peak stress.
With setamibi uptake from the {*filter*} is much slower and therefore there
is a danger that much of the uptake will not be at peak stress. This
is a serious problem for stress imaging.

In relation to the injected activities ~4% of injected thallium ends
up in the myocardium compared to ~1.5% of sestamibi.

Graham Wright



Thu, 11 Nov 1999 03:00:00 GMT
 
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