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Inorganic Imaging Agents Used In Medicine
Inorganic chemistry can be applied to multiple areas of medicine due to the diversity
of these molecules and the continual improvement to the medicinal industry
...
Medicine also involves the use of inorganic molecules as
mineral supplements, for example Calcium, Zinc and Iron can all be used to boost the
body’s natural functions
...

It is used widely for the remarkable spatial resolution and sensitivity of the
images it takes
...
However due to the short half-lives of these
radionuclides, in order to form the relevant radiopharmaceutical, the
labelling needs to happen relatively quickly5
...
Inorganic imaging agents are normally based on a
gamma-emitting nuclide which will localise in a particular tissue/organ once a small
quantity has been introduced (intravenously) into the body, leaving cells unharmed
...
A “highly specific biodistribution” and low radiation dosage are
necessary to ensure the imaging agent used reaches the target quickly and with as
little damage to the body as possible2
...
The wide variety of radioisotopes allows for the “precise
tailoring” of the radioisotope’s physical half-life to the biological half-life of the
vectors involved3
...

It is essential that radionuclides and radiopharmaceuticals used in diagnostic imaging
meet a specific set of physical, chemical and biological properties in order to be both
efficient and safe for use, including:







Type of
Imaging

Procedure
Time (min)

Tumour

PET/CT

30-60

Cardiac

PET

30-60

Brain

unreactive4
...

There must be a thorough understanding of the coordination chemistry of
metals used1
...

The clearance of the imaging agents should be relatively rapid4
...

All daughter products formed from the radionuclide must be stable1
...
It is a positron
emitter which is “predominantly used as a label” for positron emission
tomography and is normally produced by a nuclear reaction7
...
This positron
travels a short distance before encountering an electron, in order to
produce its normal annihilation with two gamma photons (“both with
an energy of 511keV”) being “emitted at 180o”8
...

Furthermore, while Fluorine18 is was not widely used in medicine after
its approval in 1972 (10 years after its introduction), due to the high
cost and limited supply, it has re-emerged with the development of
PET/CT scanning10
...
This is because tumours require a
large amount of glucose to be used for
energy, therefore tumorous cells have higher
numbers of glucose-transporters
...
The
radiopharmaceutical however does not
undergo metabolism as quickly as glucose so
remains “trapped in the cells” in a
proportionate manner to the rate at which
glucose is metabolised fully14
...
The localisation and distribution of
the imaging agent varies however due to different
amounts of blood being transported to each part of
the body, and therefore the bone in these areas12
...
This information demonstrates that the
initial uptake of any 18F-Sodium Fluoride is wholly
dependent upon the surface area of exposed bone
and the blood flow around the body16
...

A rapid and large osseous uptake11
...


Figure 6- Whole body PET scan using 18Fluorine-FDG 8

Figure 2- Table of common radionuclides which emit positrons13

View
Whole Body
Chest
Head
Whole Body

Table comparing the different imaging with Fluorine18 and procedures12:
The glucose analogue, 18F-fluorodeoxyglucose is commonly used for imaging the brain and heart though it can be
used in the diagnosis of epilepsy and cancer
...






Conflictions
(Medication/Examination)

Figure 4Spliting of
the two
y-photons
evenly8

In conclusion Fluorine18 based radiopharmaceuticals, in conjunction with PET and PET/CT, are superior
inorganic imaging agents used in the diagnosis of multiple diseases, due to them giving a better quality and
more sensitive image of the body
...


Although, for the past 30 years, the standard method for the
detection of skeletal metastases has been Technetium99m
methylene diphosphonate when this is compared to 18F-Sodium
Fluoride PET/CT the latter is shown to be superior
...
This is because 18FNaF PET/CT
gives an image with a higher resolution than that of 99mTcMDP
SPECT and so can be used to identify skeletal metastases more
effectively
...
18FFDG PET/CT though inferior at detecting skeletal
metastases (bone lesions detected in 16/52 patients) was found to
be excellent at imaging extra-skeletal lesions (which were identified
in 28 out of the 52 patients)
...

Figure 7Kinetic model
of 18FluorineNaF14

Another comparison between 99mTc MDP and 18F-NaF which
supports Fluorine18 being a superior imaging agent is the time it
takes for the radiopharmaceutical to reach its target site and
how long it takes from administration to imaging
...
This is because while Fluorine18Sodium Fluoride is dependent on the surface area of any exposed
bone and the blood flow, Technetium99m-Methylene Diphosphate
has many more factors which affect its uptake; for instance
metabolic activity, the calcium content of bone and the
extracellular surface area18
...


1
...
Gaynor, D
...
Griffith, Dalton Trans
...


R
...
Mackay, W
...
, 2002, pp 556-558

3
...
M
...
L
...
J
...
Viola-Villegas, J
...
Lewis, Inorg
...
, 2014, 53, pp 1880- 1899

4
...
N
...


Radiopharmaceuticals for Positron Emission Tomography, ed
...
Stocklin, Kluwer Academic Publishers, Netherlands, 1993, pp 1-20

6
...
A
...
G
...


Paediatric Nuclear Medicine and Molecular Imaging, ed
...
T
...
, 2014, pp 33-38

8
...
Le Bars, J
...
Chem
...


S
...
Dixit, Dalton Trans
...


H
...
Desai, P
...
Conti, Sem
...
Med
...


D
...
Fisher, Sem
...
Med
...


P
...
R
...
, 2008, pp 125-127

13
...
A
...
R
...
J
...
, 2012, pp 10-11

14
...
Czernin, N
...
Schiepers, J
...
Med
...


K
...
Kurdziel, J
...
Shih, A
...
Apolo, L
...
Mena, Y
...
McKinney, S
...
Adler, B
...
Dahut, J
...
Gulley, R
...
Madan, O
...
L
...
Nuc
...
, 2012, 53, pp 1177-1184

16
...
Blau, R
...
A
...
Nuc
...
1972, 2, pp 31-37

17
...
Iagaru, E
...
W
...
S
...
Imaging
...
, 2012, 14, pp 252-25

18
...
W
...
, 2007, pp 1-13

19
...
Lim, F
...
Fahey, L
...
Drubach, L
...
Connolly, S
...
Treves, J
...
Orthop
...


Practical Paediatric PET Imaging, Ed
...
Charron, Springer, United States of America, 2006, pp 1-20



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