Hi Virginia

As far as i know it wouldn't work as both of them will emit beta plus and therefore gamma ray s of same energy (511 keV) but you can play with the period...11C signal will be removed quickly and then copper and finally only 89Zr will remain but it will complicate somehow the data.

Multiple isotopes observation was already reported in SPECT but as far as i know not in PET.

Best regards

Yes, they could, but they can not be discriminated since all the emitted photons have an energy of 511 KeV. This technique has been suggested to be useful when you using very specific radiotracers, (i.e. primary tumor + metastasis), but it has not been probed. As Patrice said, another possibility for the discrimination might be half life, but has difficulties . Dual isotope is a much more suitable technique for SPECT, when energies are different.

Good inputs, thank you very much for your ideas.

Some combinations can be resolved. One is when there is an added imagable gamma from one of the PET tracers, It is also possible if the two tracers are the same, and are injected in sequence before the first has fully decayed. Thereby allowing probing of processes where an intervention has intervened.The other was demonstrated by the group at Donner lab, when there is a s time delay between the injections. Then one can separate the two path ways given knowledge of the late kinetics of the first injected tracer, that can be subtracted, especially when the two PET tracers have different half-lives.

Hi,

there is actually quite some literature on this issue (e.g. Kadrmas DJ1, Hoffman JM. . Methodology for quantitative rapid multi-tracer PET tumor characterizations. Theranostics. 2013 Oct 4;3(10):757-73. doi: 10.7150/thno.5201). However, IMHO, it did not make it yet into reality. What we do quite often is the injection of a tracer (such as a blood flow agent) "on top" of a metabolic agent after the latter reached a steady state and then do a regional "background correction".

It might be possible to distinguish the contribution of the two radioisotopes to the images on the basis of their kinetics in the brain. If you have two ligands with well characterised kinetic profiles, then your tissue concentration of ligand build-up will be comprised of a sum of these two profiles. If sufficiently different, you could model this mathematically: the impulse response in the tissue would be a sum of two exponentials rather than one. Non-linear least squares algorithms are best suited for this sort of component analysis. Spectral analysis and principle component analysis of time-activity curves is already being used to look at PET ligand binding to two separate subtypes of the GABA receptor, so it is doable!

In this kind of analysis, the difference in isotope is not important, just the difference in brain behaviour. In fact, doing it with two different isotopes would make things harder: you could do the ligand comparison, but quantification would be hard given your problem with decay-correction.

Different isotopes have been used to label the DA Transporter in humans and non human primates with [123I]FP-CIT SPECT.(Ioflupane;DATScan).[18 F] has eplaced the [I123] for PET imaging(Chally et al. J.Nucl.Med & Biol 1996);[11C] also fo Pet imaging,Wang et al.Synapse 1993).and [125I] also in SPECT imaging ( Scanley et al.Eur.J.Nucl.Med. 1995). These isotopes have not been used at the same time for brain imaging however.

There is a new emerging method of multi-isotope PET that relies on 'triple coincidence'. The method does work in vivo and new papers are coming out soon! Here's a glimpse at the concept behind it:

http://mvisionconsortium.mit.edu/teamPET

Hi Virginia.

In the case of PET, as many of my coleages pointed out, it is not possible to distiguish the gamma photons emited by the different radiotracers. The reason is that all of them share the same energy (511 keV).

In the case of SPECT it may be possible. But in most of the cases, it is not. The reason is the energy resolution of the scintillator crystals (>10% FWHM). This low energy resolution does not allow to discard scatter events which can amount up to 50% of your signal (and that is using a single radiotracer, imagine using multiple).

By using semiconductor detectors (Ge,Si,CdTe,...) it is possible to distinguish radiotracers with different energies and use them simultaneously in the case of SPECT or Compton camera.

Here is a link to an article of the 2007 IEEE NSS/MIC conference where multiple radiotracers are used simultaneously with a mouse. The scanner is a prototype Compton camera.