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Cardio Diabetes Medicine 2017 345

uptake is directly proportional to the blood flow are 64 Cu labelled VEGF analog to image VEGF receptor
required and the PET tracer, O-water (t 2.06 min) in angiogenesis), thanks to their favourable complex-
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which diffuses freely across myocyte membranes, ation characteristics. This advantage can be further
with 100% extraction fraction,would be the ideal trac- harnessed for development in future of a myocardi-
er for the purpose. However, its use is limited due al perfusion PET tracer. The superior resolution PET
to practical disadvantages including the very short images, and greater quantitation capability of PET,
half-life of 2.06 minutes. Among the other myocardi- are key drivers to explorefurther in the evolution of
al perfusion PET tracers, Rb and NH , are the ones myocardial imaging agents.
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used despite their non-ideal myocardial extraction
fractions. Rb derived from a generator, has edge Markers for myocardial metabolism and
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over NH ,and hence preferred currently for CFR es- myocardial viability
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timation.
The growth in hybrid imaging using PET-CT,and avail- Iodine-123 labelled fatty acid analogs:
ability of CT along with PET,offered an advantage for Fatty acid is the primary source of energy for myo-
estimation of another important parameter Fractional cardium, and thus radiolabelled (e.g. radioiodinated)
Flow Reserve(FFR). Recent advances in computation- analogues of fatty acid derivatives (such as ortho/
al fluid dynamics and image-based modeling have para Iodo phenyl pentadecanoic acid (IPPA)) were at-
made it possible to calculate FFR non-invasively tractive carrier molecules for myocardial imaging, e.g.
without the need for additional imaging, modifica- 123 I-IPPA. Thus an early development in NM involved
tion of acquisition protocols, or administration of using iodine-123 fatty acid analogues, as tracer for
medications. This added possibility to PET-CT imag- myocardial metabolism imaging. However, this did
ing studies is yet another boost to the value-addition not live up to its full potential. I (13.3 h half-life; Eg
123
available fromnuclear cardiology. 159 keV (84%)), though an ideal agent for imaging
with gamma camera and SPECT, posed demanding
Additional PET tracers - Potential for production logistics (very highly enriched 124 Xe tar-
Development: get use) as well as high cost. Furthermore, the then
mindset was that 13.3 hours half-life of 123 I is too
The generator produced PET tracer Ga (68 min half- short for facile transportation. These factors severe-
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life) is being increasingly used in NM, mostly for tu- ly impacted the exploitation of the utility of I-based
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mour imaging. The availability of Ga from long shelf- myocardial agent. It is ironical that despite growth in
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life Ge- Ga generator is an important advantage, as the deployment of MC, and the paradigm-shift with
it obviates the need for on-site MC or dependence on respect to half-life of radionuclides in use nowadays
daily shipments. This aspect together with the amena- (e.g. the widespread distribution and use of 110 min
bility of trivalent gallium ion for complexation by a half-life F), interest in production and use of I has
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variety of chelating moieties have accelerated R&D remained low. F labelled fatty acid analogs have
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efforts for using Ga. Thus a welcome development been reported in the quest for a PET tracer for myo-
in the evolution of myocardial agents will be develop- cardial metabolism imaging, but with limited success.
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ment of a Ga product for MP PET imaging in near In light of emerging use of PET radioiodine tracer I
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future. Although several synthetic cationic complex- (4.18 d), one can also consider using I-IPPA in future.
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es of Ga(III) have been explored as Ga PET tracers
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for MPI (e.g. gallium(III)-(bis(3-isopropoxy-2-phenolate
-benzylidene)-N,N’-bis(2,2-dimethyl-3-amino-propyl) PET tracers:
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ethylenediamine), Ga-based product with biochem- The role of nuclear medicine to directly show the ex-
ical and pharmacokinetic properties well-suited for tent of viability in the suspect segments or damaged
PET MPI, with high contrast perfusion images of the or injured myocardium has been well-recognised,
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heart combined with rapid clearance from the liver,is especially after F-2-fluoro-2-deoxy glucose ( FDG)
yet to be achieved. entered clinical NM practice. Now that medical cy-
clotrons (MC) and PET tracer like FDG have become
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Another positron emitter with high potential for ex- commonplace items (16 MC and over 120 PET-CT now
ploitation is Copper-64, which is already being much in India), NM’s value addition to managing cardiac
investigated for tumour imaging. The 12.4 h half-life patients by demonstrating myocardial viability in an
of Cu makes it more attractive for production and unequivocal manner can be more increasingly put to
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distribution logistics. Ga and Cu have been used clinical use. The blood flow starved lesion(s) shown
in NM with effective linker molecules to biologically on the MP images with 99m Tc + SPECT, lighting up
(or biochemically) interesting carrier molecule (e.g.
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