Iodine-125-terbutaline (125ITB): A new β2- adrenoceptor probe for lung imaging

Article abstract of DOI:10.1002/jlcr.2935

Development of a selective β₂-adrenoceptor tracer for single photon emission tomography is important for imaging of the lungs. Iodine-125-terbutaline (¹²⁵ITB) was prepared by the reaction of terbutaline with iodine-125 in the presence of chloramine-T as the oxidizing agent. The reaction was completed by incubation of the reaction mixture at 70°C for 15 minutes at pH 7. The biodistribution study in mice indicated the ability of the tracer to bind β-adrenoceptors in lungs, liver, heart, and spleen. The localization of the tracer in the lungs was high (85%/g at 60 minutes post-injection) and the highest lung/blood/g ratio was 19.8% at 60 minutes post-injection. The selectivity of the tracer for the β₂-adrenoceptor was examined by blocking with both β₁ and β₂-adrenoceptor selective antagonists. The results showed reduction of both heart and lung uptake of the ¹²⁵ITB tracer, indicating a moderate (not absolute) selectivity for the β₂-adrenoceptor. Copyright

Full text of DOI:10.1002/jlcr.2935

Research Article
Received 21 December 2011,
Revised 05 May 2012,
Accepted 10 May 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jlcr.2935
Iodine-125-terbutaline (125ITB): a new b2-
adrenoceptor probe for lung imaging
A. M. Amin
Development of a selective b2-adrenoceptor tracer for single photon emission tomography is important for imaging of
the lungs. Iodine-125-terbutaline (125ITB) was prepared by the reaction of terbutaline with iodine-125 in the presence
of chloramine-T as the oxidizing agent. The reaction was completed by incubation of the reaction mixture at 70ꢀC for
15 minutes at pH 7. The biodistribution study in mice indicated the ability of the tracer to bind b-adrenoceptors in lungs,
liver, heart, and spleen. The localization of the tracer in the lungs was high (85%/g at 60 minutes post-injection) and the
highest lung/blood/g ratio was 19.8% at 60 minutes post-injection. The selectivity of the tracer for the b2-adrenoceptor
was examined by blocking with both b1 and b2-adrenoceptor selective antagonists. The results showed reduction of
both heart and lung uptake of the 125ITB tracer, indicating a moderate (not absolute) selectivity for the b2-adrenoceptor.
Keywords: terbutaline; Iodine-125; biodistribution; lungs imaging; radiolabelling; I-125
release of neurotransmitters; or a mixed action involving both
Introduction
of the aforementioned examples (examples are phenylpropano-
lamine and ephedrine).12
Radionuclide imaging is one method by which physiological
aspects of lung function are evaluated. The most widely
Lung function in the sense of gas exchange is determined by
used techniques are the following: lung perfusion imaging using
the regional matching of ventilation and perfusion. In addition, it
technetium-99 m macroaggregates of albumin labeled perfusion
is also controlled by the endothelial receptor systems, enzyme
agents and lung ventilation imaging using either radioactive
function, and metabolic processes. Neural control of airway
gasses such as 133Xe, 127Xe, 81mKr, 13N, or technetium-99 m
smooth muscle resulting in contraction and relaxation is an
important determinant of airway caliber in health and disease.13
labeled aerosols. The clinical indications are mainly the diagnosis
of pulmonary embolism and the semi-quantitative assessment
Several neurotransmitters in airway nerves and receptors on
of the left–right distribution of pulmonary perfusion before
airway smooth muscle cells have been identified. One of them
is b-adrenoceptors (b2,bronchodilatation), which modulate their
performing major lung surgery such as lung transplantation or
pulmonary volume reduction surgery in emphysema patients.1
action via stimulation by b2 agonists, including terbutaline,
A number of different imaging modalities can be employed to
resulting in activation of adenylate cyclase via the stimulatory
analyze ventilation and perfusion, including nuclear scintigraphy,2
Gs protein followed by the formation of the second messenger,
single photon emission computed tomography (SPECT),3–5 mag-
netic resonance imaging (MRI),6 and computed tomography
(CT).7,8 Positron emission tomography (PET) is another nuclear
medicine imaging modality. It uses specially chosen positron
emitters. The most commonly used radionuclide in PET is 18 F.9,10
The b-adrenergic receptors are present on the surface of
mammalian cells. These receptors are stimulated physiologically
by the neurotransmitter, norepinephrine, and the adrenal
medullary hormone, epinephrine. There are three subtypes of
adrenergic receptors, namely, b1, b2, and b3; the pharmacological
and physiological responses of an individual cell result from the
particular mixture of the three b-adrenergic receptor subtypes
present on that cell. Species-specific structure (amino acid
sequence) also causes modification of the function of a given
b-adrenergic receptors subtype.11
cyclic adenosine monophosphate (AMP).14 Cyclic AMP accumula-
tion leads via a cascade of processes to relaxation of smooth
muscle cells in the wall of the airway. Such relaxation seems to
be impaired in humans with pulmonary dysfunction, for example,
in patients suffering from asthma. In addition, b-adrenoceptors
are involved in numerous functions such as mucous secretion,
ion transport across airway epithelium, and permeability of
pulmonary blood vessels.
Several b-adrenoceptors ligands have been labeled with
iodine-123 for SPECT imaging and with fluorine-18 and
carbon-11 for PET imaging.15–19 Radioactive tracer techniques
are applied not only for diagnostic purposes but also for research
and better understanding of normal physiology and pathology.
Labeled Compounds Department, Hot Lab. Center, Atomic Energy Authority
13759 Cairo, Egypt
The structures of the stimulants closely mimic the structure of
the neurotransmitters and are thus able to interact with the
receptor site. Adrenergic stimulants may have three modes of
action: direct interaction with specific receptors (examples are
*Correspondence to: Abeer Amin, Labeled Compounds Department, Hot Lab.
Center, Atomic Energy Authority, P. No. 13759 Egypt.
epinephrine and phenylephrine); indirect action by stimulating E-mail: ab_amin@hotmail.com
J. Label Compd. Radiopharm 2012
Copyright © 2012 John Wiley & Sons, Ltd.

A. M. Amin
The high incoming cost and isotopes unavailability for routinely chromatographic analysis. The total reaction volume (210 ml) is con-
producing receptor-specific imaging agents with these isotopes stant in all experiments. The different parameters that affect the
provide the impetus for similar agents labeled with the more radiochemical yield of 125ITB were investigated. In the process of
widely available iodine.
labeling, trials and errors were performed for each factor under
Accordingly, there is an urgent need for improved PET and investigation till obtaining the optimum value. The experiment
SPECT radioligands that home to specific tissue and allow detec- was repeated with all factors kept at optimum values except the
tion and diagnosis. Because the chemistry and the pharmacologic factor under study until the optimal conditions were achieved.
effects of beta-adrenergic agonists have been well-documented,
Determination of radiochemical yield and purity
we have chosen one of these drugs (terbutaline - Figure 1) that
selectively bind to and activate beta-adrenergic receptors as the
compound for radio-iodination with the radioisotope 125I, which
is commercially available as a label for molecular probes and
utilized by researchers in small animal studies.20
In this work, the factors affecting the radio-iodination of
terbutaline were investigated to obtain a high radiochemical
yield of radio-iodoterbutaline, and the biodistribution of the
labeled product was studied.
The radiochemical yield of the labeled terbutaline was deter-
mined using aluminum-backed silica gel-60 sheet (20 ꢁ 20 cm).
It was cut into 1 ꢁ 13-cm strips. The strips were previ-
ously impregnated with Na2S2O3 to inhibit the oxidation of
radio-iodide to a volatile form. A volume of 5ml of the reaction
mixture was spotted on the start line, then the strip was chro-
matographed using n-butanol: acetic acid: water (4:1:1, v/v/v) as
a developing system. The strips were removed, dried, cut into
1-cm segments, and assayed for radioactivity using gamma counter
connected with a well-type NaI (TI) crystal. The free iodide remains
at the origin with Rf = 0.1–0.2, whereas the labeled terbutaline
migrates with the solvent front with Rf = 0.8–1.0.
Experimental
Materials
All chemicals and laboratory reagents used during this work were
of the highest purity grade. In all cases, the water used was double
distilled. Terbutaline and chloramine-T (CAT) (N-chloro-p-toluene
sulfonamide sodium salt, CAT) were purchased from Sigma-Aldrich,
Activity of labeled product ꢁ 100
Radiochemical yield;% ¼
Total activity
Germany. Iodine-125 as no carrier added solution (Na125
I
HPLC analysis
(185 MBq/5 mL) in diluted NaOH, pH 7–11) was purchased from
Institute of Isotopes, Budapest, Hungary. Animals, Male Swiss
Albino mice weighing 25–30 gm were purchased from the
Research Center, Cairo, Egypt.
The radiochemical purity of 125ITB was determined by direct
injection of 5–10 ml, of the reaction mixture at the optimum
conditions for obtaining the highest radiochemical yield, into
the column (RP18 – 250 ꢁ 4 mm, 5 mm, Lischrosorb) built in HPLC
Shimadzu model consisting of pumps LC-9A with a Rheohydron
injector and U.V. spectrophotometer detector (SPD-6A) adjusted
to the wave length 254 nm. The column was eluted with the
isocratic solvent using methanol: H2O (70: 30 v/v) as a mobile
phase and the flow rate was adjusted to 1 ml/minute. The
labeled compound was collected by using a fraction collector
and its activity was counted by using a well-type NaI (Tl) crystal
connected with single channel analyzer.
Method
Preparation of labeled terbutaline
The iodination process was achieved by using CAT as oxidizing
agent. All experiments were carried out in a convenient round
bottom flask that could be tightly closed by rubber stopper. In
the flask, 10 ml Na125I (7–14 MBq) were added and dried by a
vacuum line, then a specific concentration of oxidizing agent in
100-ml double distilled water and a specific concentration of
the terbutaline in 100-ml suitable medium (0.05 M phosphate
buffer pH7) were added. The flask was immersed in a thermosta-
tically controlled water bath. The reaction mixture was heated to
specific temperature within suitable time. The pH value of
Radiochemical yield was determined by thin layer chromato-
graphy, and radiochemical purity was determined by HPLC.
Preparation and structure confirmation of non-radioactive
iodoterbutaline
the reaction mixture (pH 2–11) was varied using different buffer The non-radioactive iodoterbutaline is prepared by the same
systems. After a specified interval of time, the reaction was iodination method on a larger scale (to provide enough iodoter-
quenched by using 100-ml [0.2 N] sodium metabisulphate (Na2S2O3) butaline) to allow isolation and characterization. Unlabeled iodo-
solutions to ensure that the unreacted iodine is reduced before terbutaline is characterized by proton NMR.
Figure 1. The chemical structure of terbutaline and adrenergic beta-2-receptor, surface crystallographic structure of the b2-adrenergic receptor21,22
.
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Copyright © 2012 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2012

A. M. Amin
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1HNMR spectrum of iodoterbutaline in (DMSO-d6) revealed
signals at d (ppm) = 5.99(m, 2H, benzene), 5.0(2H, OH. aromatic),
4.74(t,1H, CH. methine), 2.90–3.15(d,2H, CH2.methylene), 2.0(1H,
NH. amine), 2.0(1H,OH. alcohol), 1.10(3S, 9H, 3(CH3) methyl)) as
shown in Figure 2.
The resolution of preparative and analytical techniques was
insufficient, so the uncertainty in the identity of the iodoterbuta-
line may affect the purification of the labeled compound from
any iodo-isomers.
Biodistribution in mice
Three mice per group were used for each biodistribution study. A
solution of 0.1 ml containing 2.5–3 MBq of radioactive tracer was
injected into the tail vein. The mice were sacrificed at the time
indicated by cardiac excision under ether anesthesia. Organs of
interest were removed, weighed, and the radioactivity was
counted. The results were expressed as percent injected dose
per organ (%ID/organ) and percent injected dose per gram
tissue (%ID/g) and were calculated by a comparison of the tissue
counts to the standard solution of the labeled terbutaline
measured at the same time.
0
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100
150
200
250
300
Terbutaline amount ( g)
Figure 3. The radiochemical yield of 125ITB as a function of substrate amount.
Effect of CAT amount
Because of its efficiency, CAT is the most widely used oxidizing
agent in the labeling of organic compounds with iodine.23,24
CAT is used in the range of 25–250 mg in this labeling reaction.
The data presented in Figure 4 indicated the inability of 25 mg
of CAT to oxidize all the iodine found in the reaction mixture,
and as a result, the free iodine was detected in high percent
(21.5%). These results may be explained by the fact that at low
concentration of CAT, not all the iodide is converted to iodonium
ion which is involved in the substitution reaction and thus the
The selectivity of 125ITB for the b1 and b2 receptor subytypes
was investigated by performing in vivo competitive binding
experiments. The mice were injected with 2 mg/kg, I.V. atenolol
(a b1selective blocking agent) or 2 mg/kg and I.V. butoxamine
(a b2 selective blocking agent) at 30 minutes prior to the injec-
tion of 125ITB. The animals were sacrificed and the distribution
of radioactivity calculated as described earlier.
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Results and discussion
Effect of substrate amount
This experiment was carried out by adding the iodine activity
(10 MBq) to a mixture of terbutaline (20, 50, 100, 200, and
300 mg) in 100-ml phosphate buffer pH7 and 150-mg CAT. The
reaction mixture was incubated in a water bath at 70ꢀC for
15 minutes. The data of this experiment is presented in Figure 3,
which clearly pointed to the possibility of using terbutaline in
the range of 100–300 mg without significant change in the
radiochemical yield of 125ITB. This may be attributed to the fact
that the yield reaches the saturation value because the entire
generated iodonium ions in the reaction are captured at these
concentrations of terbutaline. Below 100 mg of terbutaline, the
radiochemical yield decreased to below 80%.
0
50
100
150
200
250
Chloramine-T amount ( g)
Figure 4. The radiochemical yield of 125ITB as a function of chloramine-T amount.
Figure 2. 1HNMR spectrum of iodo-terbutaline.
J. Label Compd. Radiopharm 2012
Copyright © 2012 John Wiley & Sons, Ltd.
www.jlcr.org

A. M. Amin
yield decreased. Increasing the amount of CAT gradually caused
an increase in the radiochemical yield up to 97% at 150 mg of
oxidizing agent. As mentioned, 150 mg of oxidizing agent no
significant increase in the radiochemical yield of 125ITB was
obtained. Excess of oxidizing agent is not recommended in this
labeling reaction to avoid a number of undesirable side reactions
including chlorination.25–27
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Effect of reaction time
The experiment was carried out by adding (10 MBq) Na125I to a
mixture of 200-mg terbutaline and 150-mg CAT in phosphate
buffer at pH 7 in a closed vial. The reaction mixture was kept
at 70ꢀC for different intervals of time up to 60 minutes. The
gathered data is presented in Figure 5, which clearly shows that
the optimum reaction time required to attain the maximum
radiochemical yield is 15 minutes. Increasing the reaction time
to 60 minutes does not affect the radiochemical of yield 125ITB.
0
10 20 30 40 50 60 70 80 90 100
Reaction temperature(°C)
Figure 6. The radiochemical yield of 125ITB as a function of reaction temperature.
Effect of reaction temperature
The reaction temperature in most electrophilic substitution reac- on the labeling yield. The radiochemical yield of 125ITB was
tions plays an important role, as it is very important in the buildup relatively poor at pH 2 and 4, as a result of the predominance
of a new covalent bond between the iodonium ion and the carbon of ICl species, which have low oxidation potential than HOCl
atom in the molecule. The radio-iodination reaction of terbutaline species.28 At pH 7, the radiochemical yield of 125ITB reaches a
with iodine-125 was carried out using 200-mg terbutaline and maximum value of 97%. When the pH increased towards the
150-mg CAT at different temperatures, Figure 6. The radiochemical alkaline side (9 and 11), the radiochemical yield decreased. This
125
yield of ITB was found to be 45.3% at 25ꢀC and increased to may be attributed to the decrease in HOI*, which is responsible
for the electrophilic substitution reaction29. The data is summar-
ized in Figure 7. The high radiochemical yield of 125ITB at pH 7
may be because of the efficiency of CAT at this pH value.30
77.1% and 97% on heating the reaction mixture to 50 and 70ꢀC,
respectively at 15 minutes reaction time. This is because of the
fact that the leaving hydronium ion requires some energy to break
the C–H bond and to initiate the introduction of the radioactive
iodonium ion into the TB ring. By raising the reaction temperature
to 100ꢀC, the radiochemical yield of 125ITB decreased indicating
the decomposition of the labeled compound.
HPLC analysis
A radiochromatogram for the iodination of terbutaline obtained
after HPLC separation on RP-18 column at the optimum condi-
tions (200-mg terbutaline in 100-ml phosphate buffer pH 7,
150 mg of CAT, and the reaction mixture was heated at 70ꢀC for
15 minutes) is shown in Figure 8. Two peaks were obtained.
The first peak was at 3 minutes, whereas the second peak was
at 6 minutes retention time. The first peak corresponds to free
iodide, whereas the second peak corresponds to the 125ITB.
125ITB is not completely separated from terbutaline or any
iodo-isomers in Figure 8 that clarifies the short retentions. The
eluted fractions containing the labeled compound are pooled
Effect of pH
This experiment was carried out using different buffer systems to
obtain the required pH values; citrate buffer for pH 2 and 4,
phosphate buffer for pH 7 and 9, and bicarbonate buffer for
pH 11. The optimum amount of terbutaline was added to the
buffer system and then 150-ml CAT (150 mg) followed by Na125I.
The reaction mixture was heated to 70ꢀC for 15 minutes. The
results indicate the effectiveness of pH of the reaction mixture
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0
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pH
8
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0
10
20
30
40
50
60
Reaction time(min.)
Figure 7. Effect of pH of the reaction medium on the percent radiochemical yield
Figure 5. The radiochemical yield of 125ITB as a function of reaction time.
of 125ITB.
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Copyright © 2012 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2012

A. M. Amin
10000
9000
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7000
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5000
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3000
2000
1000
0
reaches a maximum at 60minutes before decreasing at 120 and
240 minutes is an indicative of the renal clearance. Although initial
blood levels of radioactivity were moderately high (8.4% ID/g at
30minutes), this tissue displayed ~40% radioactivity clearance
between 30 and 60 minutes. Organs of interest, liver, spleen, heart,
and lungs (organs that contain b-adrenoceptors) showed high
accumulation of radioactivity 31.5%, 6.9%, 3.3%, and 60.5%/g
at early time post-injection (30 minutes), respectively. Uptake in
organs with different dominant receptor subtypes is relevant
to receptor density and ratio of receptor subtypes. The lungs
that are the main target of 125ITB showed high binding percen-
tage and reached its maximum at 60 minutes post-injection
(85%ID/g) because b-adrenoceptors density in human peripheral
lung is normally 100–130 fmol/mg protein and the ratio of
the b1: b2 is about 30:70.31 The built-up of radioactivity in
the spleen, as time passed post-injection, was because of the
dominance of b2 subtype adrenoceptor,32 whereas the less
heart uptake was attributed to the dominance of b1 subtype
in the heart.33 Blocking studies with atenolol and butoxamine
were performed to determine a better selectivity of terbutaline
to b2-adrenoceptor.
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10
15
20
Retention Time(min.)
Figure 8. HPLC radiochromatogram of 125I-terbutaline.
together, and the radiochemical purity of the isolated 125ITB
(99.1%) was determined using thin layer chromatography. These
collected fractions were evaporated to dryness. The residue
was dissolved in physiological saline and then sterilized by
filtration through 0.22-mm Millipore filter to give specific activity
of 15 MBq/mg of 125ITB. The125ITB is then suitable for use in
biodistribution studies.
Moderate radioactivity uptake was seen in thyroid (maximal
uptake of 1.3% ID/g at 4 hours) indicating that the radioligand
is relatively stable towards in vivo de-iodination.
Blocking studies
The 125ITB binds to b1 and b2-adrenoceptors, then the uptake of
the tracer may be non-selective which leads the need for in vivo
blocking experiments to determine selectivity. The use of b1
Biodistribution studies
The uptake of radioactivity in selected tissues was determined fol- selective blocking agent (atenolol) diminished myocardial and
lowing intravenous administration of 125ITB to albino mice. Mice pulmonary uptake of the radioligand as clear from Figure 9. In
were injected intravenously with 2.5–3 MBq of 125ITB and sacrificed contrast, the use of b2 selective blocking agent (Butoxamine)
at designated time intervals (30 minutes, 1 hour, 2 hours, and reduced the uptake of 125ITB in the lungs (an organ that contains
4 hours post-injection). The complete biodistribution results are more b2 receptors) with great rate and slight affect on binding in
presented in Table 1. The high initial 125ITB uptake in kidney that the heart (an organ that contains more b1 receptors) as clear
Table 1. Biodistribution of 125I-terbutaline in mice (x ꢂ SD, n = 3), expressed as % injected dose/total tissue and injected dose/g
tissue
Time post-injection (minutes)
30
60
120
240
Tissue
%ID/organ
% ID/g
%ID/organ
% ID/g
%ID/organ
% ID/g
%ID/organ
% ID/g
Blood
Bone
19.3 ꢂ 2.1
3.4 ꢂ 0.3
3.6 ꢂ 0.2
12.9 ꢂ 1.2
0.2 ꢂ --
8.4 ꢂ 0.3
1.1 ꢂ 0.2
0.2 ꢂ --
31.5 ꢂ 2.4
6.9 ꢂ 0.3
3.3 ꢂ 0.2
60.5 ꢂ 2.5
25.3 ꢂ 2.1
0.7 ꢂ 0.1
0.5 ꢂ 0.1
------
9.9 ꢂ 0.4
3.1 ꢂ 0.1
3.9 ꢂ 0.2
12.3 ꢂ 1.1
0.39 ꢂ 0.1
0.3 ꢂ 0.1
11.6 ꢂ 0.8
26.9 ꢂ 1.4
0.6 ꢂ 0.1
0.2 ꢂ --
4.3 ꢂ 0.3
1.0 ꢂ 0.2
0.3 ꢂ ---
30.0 ꢂ 2.2
13.0 ꢂ 1.3
5.0 ꢂ 0.4
85.0 ꢂ 1.9
67.3 ꢂ 2.4
4.0 ꢂ 0.3
0.5 ꢂ 0. 1
----
6.3 ꢂ 0.4
2.3 ꢂ 0.2
3.1 ꢂ 0.3
12.0 ꢂ 1.5
0.58 ꢂ 0.2
0.2 ꢂ --
2.7 ꢂ 0.2
0.72 ꢂ 0.1
0.19 ꢂ --
29.3 ꢂ 2.4
19.3 ꢂ 1.6
3.3 ꢂ 0.4
45.5 ꢂ 2.7
11.8 ꢂ 1.2
0.7 ꢂ 0.3
1.5 ꢂ 0.2
-----
3.7 ꢂ 0.2
1.6 ꢂ 0.1
2.3 ꢂ 0.4
7.8 ꢂ 0.8
0.88 ꢂ 0.1
0.1 ꢂ --
1.6 ꢂ 0.2
0.5 ꢂ 0.1
0.14 ꢂ 0.1
19.0 ꢂ 0.9
29.3 ꢂ 2.4
1.6 ꢂ 0.3
18.0 ꢂ 1.2
10.8 ꢂ 1.5
1.3 ꢂ 0.1
3.2 ꢂ 0.2
Muscle
Liver*
Spleen*
Heart*
Lungs*
Kidneys
Thyroid
Brain
0.2 ꢂ --
12.1 ꢂ 1.3
10.1 ꢂ 0.7
0.1 ꢂ --
9.1 ꢂ 0.6
4.7 ꢂ 0.4
0.1 ꢂ --
3.6 ꢂ 0.3
4.3 ꢂ 0.3
0.2 ꢂ --
0.2 ꢂ --
0.6 ꢂ 0.1
26.3 ꢂ 1.3
1.3 ꢂ 0.1
38.0 ꢂ 1.4
Urine
L/Bl
B/Bl
15.8 ꢂ 2.1
21.6 ꢂ 1.7
7.2
0.06
19.8
0.1
16.9
0.55
11.25
2.0
*Organs of interest L: Lungs; Bl: Blood; B: Brain.
J. Label Compd. Radiopharm 2012
Copyright © 2012 John Wiley & Sons, Ltd.
www.jlcr.org

A. M. Amin
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100-ml phosphate buffer pH 7, 150mg of CAT, and the reaction
mixture was heated at 70ꢀC for 15minutes. Biodistribution studies
show uptake in organs known to contain adrenoceptors with high
localization in the lungs (85%/g at 60 minutes post-injection). In
vivo blocking experiments have indicated the moderate selectivity
of the 125ITB to b2-adrenoceptor. For practical application,123I-
labeled terbutaline is used for lung imaging. A more efficient
preparative purification system would be needed to ensure that
the iodoterbutaline was separated from any iodo-isomers or any
unlabeled terbutaline.
Heart before blocking
Heart after blocking
Lung before blocking
Lung after blocking
Acknowledgement
The author wishes to thank the editor and the referees of the
JLCR for the cooperation and valuable comments.
Conflict of Interest
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Time post injection (Hour)
The authors did not report any conflict of interest.
Figure 9. Lung & Heart uptake of 125ITB tracer before and after the IV administra-
tion of atenolol (selective b1 blocking agent) 30 minutes before the administration
of 125ITB.
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