Preparation and evaluation of a new 99mTc labeled bombesin derivative for tumor imaging

A variety of human tumors like prostate and breast cancer express bombesin receptors. Due to this a new bombesin analogue was labeled with ^99mTc via HYNIC and tricine as a coligand and investigated further. Peptide was synthesized on a solid phase using Fmoc strategy. Labeling with ^99mTc was performed at 100 °C for 10 min and radiochemical analysis involved ITLC and HPLC methods. The stability of radiopeptide was checked in the presence of human serum at 37 °C up to 24 h. Internalization was studied with the human GRP receptor cell line PC-3. The biodistribution was studied in mice. Labeling yield of >98% was obtained corresponding to a specific activity of ~80.9 GBq/μmol. Radiopeptide internalization into PC-3 cells was moderate and specific (10.7 ± 1.2% at 4 h). A high and specific GRP receptor expressing mouse tumor and pancreas uptake (1.12 ± 0.08 and 1.04 ± 0.11% ID/g after 1 h respectively) was also determined.     

Evaluation of a new radiolabeled bombesin derivative with 99mTc as potential targeted tumor imaging agent

Gastrin-releasing peptide (GRP) receptors are over-expressed in various human tumor including breast and prostate which can be targeted with bombesin for diagnosis and targeted therapy. High abdominal accumulation and the poor in vivo stability of radiolabeled bombesin analogues may represent a limitation for diagnostic imaging and targeted therapy. In this study a new bombesin derivative was labeled with ^99mTc via HYNIC and tricine as a coligand and investigated further. The peptide HYNIC conjugate was synthesized on a solid phase using Fmoc strategy. Labeling with ^99mTc was performed at 100 °C for 10 min and radiochemical analysis involved ITLC and HPLC methods. The stability of radiopeptide was checked in the presence of human serum at 37 °C up to 24 h. Internalization was studied with the human GRP receptor cell line PC-3. The Biodistribution was studied in mice. Labeling yield of >98 % was obtained to correspond a specific activity of ~80.9 GBq/μmol. Radioconjugate internalization into PC-3 cells was high and specific (15.6 ± 1.9 % at 4 h). A high and specific uptake in GRP-receptor-positive organs such as mouse tumor and pancreas (2.11 ± 0.18 and 1.78 ± 0.09 % ID/g after 1 h respectively) was also determined.     

Preparation and evaluation of a new neurotensin analog labeled with 99mTc for targeted imaging of neurotensin receptor positive tumors

Neurotensin receptors are overexpressed in several human tumors and can be targets for tumors diagnosis and therapy. In this study, a new neurotensin analogue was labeled with ^99mTc via HYNIC and tricine/EDDA as coligands and investigated further. [HYNIC⁰, Gly⁷, Lys⁹, d-Tyr¹¹]-Neurotensin (7–13) was synthesized using a standard Fmoc strategy. Labeling with ^99mTc was performed at 100 °C for 10 min and radiochemical analysis involved ITLC and HPLC methods. The stability of radiopeptide was checked in the presence of humane serum at 37 °C up to 24 h. The receptor bound internalization and externalization rates were studied in neurotensin receptor expressing HT-29 cells. Biodistribution of radiopeptide was studied in nude mice bearing HT-29 tumor. Labeling yield of 98.6 ± 0.54 % (n = 3) was obtained corresponding to a specific activity of 81 MBq/nmol. Peptide conjugate showed good stability in the presence of human serum. The radioligand showed specific internalization into HT-29 cells (12.43 ± 0.52 % at 4 h). In biodistribution studies, a receptor-specific uptake was observed in neurotensin receptor positive organs so that after 1 h the uptakes in mouse intestine and tumor were 0.87 ± 0.16 and 0.63 ± 0.12 % ID/g respectively.     

Radio labeling,quality control and biodistribution of <Superscript>99m</Superscript>Tc-cefotaxime as an infection imaging agent

Cefotaxime, a cephalosporin antibiotic, used to treat bacterial infections was investigated to label with ^99mTc. Labeling was performed using sodium dithionite as a reducing agent at 100 °C for 10 min and radiochemical analysis involved ITLC and HPLC methods. The stability of labeled antibiotic was checked in the presence of human serum at 37 °C up to 24 h. The maximum radiolabeling yield was 92 ± 2%. Bacterial binding assay was performed with S. aureus and the in vivo distribution was studied in mice. Images showed minimal accumulation in non-target tissues, with an average target/non-target ratio of 2.89 ± 0.58.     

Labeling bombesin-like peptide with <Superscript>99m</Superscript>Tc via hydrazinonicotinamide: description of optimized radiolabeling conditions

Bombesin (BNN)-like peptides have very high binding affinity for the gastrin-releasing peptide (GRP) receptor. The goal of the current study was to optimize the labeling conditions of a new ^99mTc-radiolabeled BNN-like peptide based on the bifunctional chelating ligand HYNIC using different co-ligands (EDDA and tricine). The radiolabeling conditions (pH, amount of co-ligand, amount of stannous chloride, temperature and reaction time) for newly-formed ^99mTc-tricine-HYNIC-Q-Litorin and ^99mTc-EDDA-HYNIC-Q-Litorin were optimized and evaluated by RHPLC and RTLC. Radiochemical yields for ^99mTc-tricine-HYNIC-Q-Litorin and ^99mTc-EDDA-HYNIC-Q-Litorin were 98.0 ± 1.7 and 97.5 ± 2.5%, respectively. When EDDA was used as co-ligand, the labeling of ^99mTc-EDDA-HYNIC-Q-Litorin was optimal in the following reaction mixture: HYNIC-peptide: EDDA: 10 μg/5 mg, pH 3, SnCl₂ concentration: 12 μg/0.1 mL, reaction temperature: 100 °C, reaction time: 15 min. Besides, the optimum conditions were HYNIC-peptide:tricine: 10 μg/50 mg, pH 5, SnCl₂ concentration: 12 μg/0.1 mL, reaction temperature: 100 °C, reaction time: 15 min for preparing ^99mTc-tricine-HYNIC-Q-Litorin. The manufactured ^99mTc-HYNIC-Q-Litorin conjugates may offer new possibilities for imaging cancer cells expressing bombesin receptors.     

Synthesis,radiolabelling and biodistribution of HYNIC-Tyr<Superscript>3</Superscript> octreotide: a somatostatin receptor positive tumour imaging agent

In vivo imaging of tumours using radiolabelled somatostatin (SST) analogues has become an accepted clinical tool in oncology. HYNIC-Tyr³ octreotide and Tyr³ octreotide were synthesized by FMOC solid-phase peptide synthesis using a semi-automated synthesizer. These were analyzed and purified by RP-HPLC, mass spectroscopy, IR spectroscopy, ¹H NMR and ¹³C NMR. The prochelator 6-BOC-HYNIC was also synthesised and characterised indigenously. HYNIC-Tyr³ octreotide was labelled with ^99mTc using Tricine and EDDA as coligand by SnCl₂ method. Labelling with ^99mTc was performed at 100 °C for 15 min and radiochemical analysis by ITLC and HPLC methods. The radiochemical purity of the complex was over 98% and log p value was found to be −1.27 ± 0.12. The stability of radiolabelled peptide complex was checked at 37 °C up to 24 h. Blood clearance and protein-binding study was also performed. In vivo biodistribution studies in rat showed uptake of ^99mTc-HYNIC-TOC in kidney than any other organs. The blood clearance was faster with rapid excretion through kidneys and relatively low uptake in liver.     

Preparation of <Superscript>99m</Superscript>Tc-metronidazole as a model for tumor imaging

Metronidazole (MTNZ) is an antiprotozoa drug, could be labeled with the ^99mTc. MTZL could be used as an ideal vehicle to deliver radioactive decay energy of ^99mTc to the sites of tumor, thus facilitate tumor imaging. The process of labeling was done using tin chloride as reducing agent. The optimum conditions required to label 25 μg MTZL were 100 μg stannous chloride, 30 min reaction time, room temperature at pH 7–9 using 0.5 M phosphate buffer. The radiochemical purity of the labeled compound, at the above conditions, was determined using paper chromatography. The yield was about 93%. About 2.5 × l0⁶ of Ehrlich Ascites Carcinoma (EAC) was injected intrapritoneally (i.p) to produce ascites and intramuscularly (i.m) in the right thigh to produce solid tumor in female mice. Biodistribution studies were carried out by injecting solution of ^99mTc-MTZL in normal and tumor bearing mice. The uptake in ascites was over 5% of the injected dose per gram tissue body weight, at 4 h post injection and above 4% in solid tumor. These data revealed localization of the tracer in the tumor tissues with high percentage sufficient to use ^99 mTc MTZL as promising tool for diagnosis of tumor.     

Radiosynthesis and biological evaluation of <Superscript>99m</Superscript>TcN-sitafloxacin dithiocarbamate as a potential radiotracer for <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> infection

Sitafloxacin dithocarbamate (SFDE) was synthesized, radiolabeled with technetium-99m (^99mTc) using [^99mTc-N]²⁺ core and evaluated its biological efficacy as a potential radiotracer for Staphylococcus aureus (S. aureus) infection in artificially infected rats (AIRT) and rabbits (AIRB). The radiochemical stability of the ^99mTc labeled SFDE (^99mTcN-SFDE) in saline and serum was determined by radio-HPLC and TLC methods, respectively. After, 1 min of reconstitution the value of radiochemical purity (RCP) was 99.00 ± 0.20% and was remained more than 90% unwavering even after 240 min of the radiolabeling. The ^99mTcN-SFDE complex showed similar radiochemical permanence behavior in serum at 37 °C. The complex showed almost six fold higher specific in vitro binding with living than heat killed S. aureus. Biodistribution behavior was evaluated in S. aureus AIRT and whole body imaging (WBI) in AIRB, respectively. Seven fold up take was observed in infected muscle of the AIRT as compared to inflamed and normal muscles. The disappearance of activity from blood and appearance in urinary system indicated normal route of excretion of the complex. Scintigraphically, it was confirmed that the labeled SFDE was higher accumulated in the infected muscle higher than in inflamed and normal muscle. The high radiochemical stability in saline and serum, specific in vitro binding with S. aureus, precise in vivo distribution in S. aureus AIRT and targeted WBI in AIRB confirmed the possibility of the ^99mTcN-SFDE complex as a potential and promising S. aureus infection radiotracer.     

<Superscript>99m</Superscript>Tc-exorphin C: A new peptide radiopharmaceutical for tumor imaging

Summary The aim of this study was to label exorphin C with ^99mTc and to examine its usefulness as opioid receptor binding radiopharmaceutical in Albino Wistar rats. Exorphin C, which is a peptide with 5 aminoacids, was labeled with ^99mTc using glucoheptonate (GH) as a bifunctional chelating agent. Labeling efficiency was higher than 98%. The compound was stable for at least 5 hours at room temperature. Mammary tumor bearing Albino Wistar rats were imaged using gamma-camera. Biodistribution studies were also performed. Results demonstrated that ^99mTc-glucoheptonate-exorphin C (^99mTc-GE) analogs may be useful as a new class of receptor-binding peptides for the diagnosis and therapy of some cancer diseases related with opioid receptor-expressing tissues.     

Synthesis and biodistribution of a novel <Superscript>99m</Superscript>Tc-DMSA-metronidazole ester as a potential tumor hypoxia imaging agent

The dimercaptosuccinic acid metronidazole ester (DMSAMe) was synthesized and radiolabeled with ^99mTc to form the ^99mTc-DMSAMe complex in high yield. The radiochemical purity of the ^99mTc-DMSAMe complex was over 90%, as measured by TLC and by HPLC, without any notable decomposition at room temperature over a period of 6 h. Its partition coefficient indicated that it was a lipophilic complex. The tumor cell experiment and the biodistribution in mice bearing S 180 tumor showed that the ^99mTc-DMSAMe complex had a certain hypoxic selectivity and accumulated in the tumor with high uptake and good retention. The tumor/blood and tumor/muscle ratios increased with time, suggesting it would be a possible tumor hypoxia imaging agent.     

A novel electrochemical <Superscript>99</Superscript>Mo/<Superscript>99m</Superscript>Tc generator

A novel electrochemical process to avail clinical grade ^99mTc from (n,γ)⁹⁹Mo has been demonstrated. The electrochemical parameters were optimized to maximize the ^99mTc yield with minimal ⁹⁹Mo contamination. ⁹⁹Mo/^99mTc generators containing up to 29.6 GBq (800 mCi) ⁹⁹Mo were developed and their performance were extensively evaluated for 10 days without changing the operating conditions. Very high radioactive concentration of ^99mTcO₄ ⁻ of acceptable quality, commensurate with hospital radiopharmacy requirements could be availed from the system with >90% yield. The compatibility of the product for the formulation of ^99mTc labeled radiopharmaceuticals such as ^99mTc-DMSA and ^99mTc-EC was found to be satisfactory in terms of high labeling yields. The proposed route represents an important step for enhancing the scope of accessing clinical grade ^99mTc from low specific activity (n, γ)⁹⁹Mo.     

A perspective on <Superscript>99m</Superscript>Tc and <Superscript>125/131</Superscript>I labeled receptor targeted compounds and their in vitro/in vivo affinities

A novel quinoline derivative, 2,2′-[(5-chloro-8-hydroxyquinoline-7-yl) methylazanediyl] diacetic acid (CHQMADA) was labeled with ^99mTc using SnCl₂·2H₂O as a reducing agent to give a complex with a labeling yield 94 %. Also [^99mTc(H₂O)₃(CO)₃]⁺ was prepared by heating at 100 °C for 30 min using 2 mg CHQMADA at pH 8 to give a labeling yield >99 %. ^99mTc-(CO)₃ CHQMADA and ^99mTc-Sn(II)-CHQMADA showed tissue uptake (target to non target T/NT = 6.80 ± 0.22) and (T/NT = 5.65 ± 0.34) respectively in Escherichia coli induced infection, which is higher than the commercially available ^99mTc-ciprofloxacin (T/NT = 3.80 ± 0.80). In conclusion, both complexes were able to differentiate between septic and aseptic inflammation with superiority of [^99mTc-(CO)₃ CHQMADA].     

Radiosynthesis and characterization of the <Superscript>99m</Superscript>Tc-fleroxacin complex: a novel <Emphasis Type="Italic">Escherichia coli</Emphasis> infection imaging agent

Radiocomplexation of fleroxacin (FXN) with technetium-99m and its characterization in terms of in vitro stability in saline and serum solutions, in vitro binding with live and heat-killed Escherichia coli, and biodistribution in male Wistar rats (MWR) artificially infected with live and heat-killed E. coli was studied. The ^99mTc-FXN complex showed a radiochemical purity (RCP) yield of 98.10 ± 0.24% at 30 min using 125 μg of stannous fluoride, 74 MBq of sodium pertechnetate, and 2 mg of FXN. The complex was found to be more than 90% stable up to 4 h after constitution in normal saline. In serum, the emergence of 16.50% undesirable species was observed within 16 h of incubation at 37 °C. The ^99mTc-FXN complex showed saturated in vitro binding with E. coli with a maximum value of 65.00% at 90 min. A fivefold increase in uptake of the complex was noted in the infected when compared with the inflamed and normal muscle of the MWR infected with live E. coli. The stable radiochemical profile in saline and serum, saturated in vitro binding with E. coli and increased uptake in the infected muscle, confirmed the potential of the ^99mTc-FXN complex as an E. coli infection imaging agent.     

Synthesis,radiochemical and biological characteristics of <Superscript>99m</Superscript>Tc-8-hydroxy-7-substituted quinoline complex: a novel agent for infection imaging

2,2′-[(8-hydroxyquinolin-7-yl)methylazanediyl]diacetic acid (HQMADA) was synthesized via reaction of 8-hydroxyquinoline with iminodiacetic acid in presence of paraformaldehyde with a yield of 27%. The obtained compound was well characterized via different analytical techniques. Labeling of the synthesized compound with technetium-99m in pertechnetate form (^99mTcO₄ ⁻) in the presence of stannous chloride dihydrate was carried out via chelation reaction. The reaction parameters that affect the labeling yield such as HQMADA concentration, stannous chloride dihydrate concentration, pH of the reaction mixture, and reaction time were studied to optimize the labeling conditions. Maximum radiochemical yield of ^99mTc-HQMADA complex (91.9%) was obtained by using 1.5 mg HQMADA, 50 μg SnCl₂·2H₂O, pH 8 and 30 min reaction time. Biodistribution studies in mice were carried out in experimentally induced infection in the left thigh using E. coli. ^99mTc-HQMADA complex showed higher uptake (T/NT = 5.5 ± 0.3) in the infectious lesion than the commercially available ^99mTc-ciprofloxacin (T/NT = 3.8 ± 0.8). Biodistribution studies for ^99mTc-HQMADA complex in Albino mice bearing septic and aseptic inflammation models showed that ^99mTc-HQMADA complex able to differentiate between septic and aseptic inflammation.     

Synthesis and biological evaluation of fatty acid derivatives for myocardial imaging containing [<Superscript>99m</Superscript>Tc(CO)<Subscript>3</Subscript>]<Superscript>+</Superscript>

Radiolabeled fatty acids as myocardial metabolic agent are used for detecting ischemic heart disease, however, no ^99mTc-labeled fatty acids have potential use in clinical diagnosis. In this work, five fatty acid analogues labeled with ^99mTc were firstly synthesized and characterized, their biological behaviors were investigated. All Radiotracers had good stability when incubated in rat serum for 3 h at 37 °C. ^99mTc -CpT-12-ODPPA (8b) showed higher initial myocardial uptake (8.17% ID/g at 1 min postinjection) and good heart/blood ratio (2.58 at 30 min postinjection). ^99mTc-11-dpa-OUFA (2b) as positively charged lipophilic compounds had reasonable heart uptake (5.59% ID/g at 1 min postinjection) and good retention (1.89% ID/g at 60 min postinjection). Unfortunately, no great improvement was obtained by the five ^99mTc-labeled fatty acid analogues for the short myocardial retention and poor heart/liver ratios.     

Synthesis,labeling and biodistribution of <Superscript>99m</Superscript>Tc-3-amino-2-quinoxalin-carbonitrile 1,4-dioxide in tumor bearing mice

3-Amino-2-quinoxalincarbonitrile 1,4-dioxide (AQCD) is a quinoxaline derivative, which was synthesized by condensation method. AQCD was labeled with ^99mTc with labeling yield above 90% investigated by paper chromatography. ^99mTc-AQCD was prepared using stannous chloride as reducing agent at pH 7 and 10 min reaction time. ^99mTc-AQCD should be freshly prepared, otherwise the yield significantly decreased after 15 min post labeling. Stability study of ^99mTc-AQCD reflected the short time stability of Biodistribution study of ^99 mTc-AQCD in tumor bearing mice reflected that its uptake in tumor sites in both ascites and solid tumor sites. This uptake of ^99mTc-AQCD in tumor sites was sufficient to radioimage the inoculated sites.     

The interaction of <Superscript>99m</Superscript>Tc with pyrimidine compounds

The reaction of ^99mTc of different oxidation states (+7, +4) with 2-thiouracil and 5-nitrobarbituric acid have been studied at different temperatures, pH and concentrations. The reaction mixtures have been analyzed at different times using thin layer chromatography (TLC) and a radio detector to show the peaks at the plates. ^99mTc is obtained from the Mo generators with oxidation state (+7). The use of SnCl₂ as a reducing agent gave ^99mTc with oxidation state (+4). It is very difficult to separate the complexes formed from the reactions in very small concentration. The percentage of ^99mTc and its oxidation state involved in the complexes can be determined. The labeling efficiencies (percentage of complex) in the reaction of ^99mTc⁺⁷ with 5-nitro-barbituric-acid increases mostly at pH  10. Both oxidation states of ^99mTc(+7, +4) can be detected at pH’s 4 and 10, but at pH  4, the reduced form ^99mTCO₂, is more pronounced. At pH  7 no complexes were detected and most of ^99mTc remains as ^99mTCO₄ ⁻ . By increasing the ligand concentration, the labeling efficiencies of the complex increases. For the reaction of ^99mTc of oxidation states (+4, +7) with 2-thiouracil at different temperatures and analytical times it is concluded that several complexes with different R_f values were observed in equilibrium and most of these complexes were unstable.     

Preparation of <Superscript>99m</Superscript>Tc-PQQ and preliminary biological evaluation for the NMDA receptor

Pyrroloquinoline quinone (PQQ), an essential nutrient, antioxidant, redox modulator and nerve growth factor found in a class of enzymes called quinoproteins, was labeled with ^99mTc by using stannous fluoride (SnF₂) method. Radiolabeling qualification, quality control and characterization of ^99mTc-PQQ and its biodistribution studies in mice were performed and discussed. Effects of pH values, temperature, time and reducing agents concentration on the radiolabeling yield were investigated. The quality control procedure of ^99mTc-PQQ was determined by thin layer chromatography (TLC), radio high-performance liquid chromatography (RHPLC) and paper electrophoresis methods. The average radiolabeling yield was 94 ± 1% under optimum conditions of 0.99 mg of PQQ, 30 μg of SnF₂, 0.5 mg of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and 18.5 MBq of Na^99mTcO₄ at pH 6 and 25 °C with a response volume of 1 ± 0.1 mL. ^99mTc-PQQ was stable and anionic. Lipid–water partition coefficient of ^99mTc-PQQ was −1.49 ± 0.16. The pharmacokinetics parameters of ^99mTc-PQQ were t _1/2α = 18.16 min, t _1/2β = 100.45 min, K ₁₂ = 0.013 min⁻¹, K ₂₁ = 0.017 min⁻¹, K _e = 0.016 min⁻¹, AUC (area under the curve) = 1040.78 ID% g⁻¹ min and CL (plasma clearance) = 0.096 mL min⁻¹. The dual-exponential equation was Y = 10.88e^−0.038t  + 5.21e^−0.0069t . The biodistribution of ^99mTc-PQQ was studied in ICR (Institute for Cancer Research 7701 Burhelme Are., Fox Chase, Philadelphia, PA 1911 USA) mice. In vitro autoradiographic studies clearly showed that the ^99mTc-PQQ radioactivity accumulated predominantly in the hippocampus and cortex, which had a high density of N-methyl-d-aspartate Receptor (NMDAR). The enrichment can be blocked by NMDAR redox modulatory site antagonists-ebselen (EB) and ^99mTc-PQQ is therefore a promising candidate for the molecular imaging of NMDAR. To date, however, there have been no studies characterizing ^99mTc-PQQ.     

<Superscript>99</Superscript>Mo/<Superscript>99m</Superscript>Tc generators based on aluminum molybdate gel matrix prepared by nano method

A procedure for preparation of ⁹⁹Mo/^99mTc radioisotope generator based on low specific activity neutron activated ⁹⁹Mo was developed. Aluminum molybdate(VI)-⁹⁹Mo of high Mo(VI) content (~?364 mg/g Al⁹⁹Mo) was prepared by mixing low specific activity molybdate(VI)-⁹⁹Mo and aluminum mixture solution with isoamyl alcohol. Al⁹⁹Mo gel matrix was precipitated when the pH of the mixture solution was raised to ~?5 by addition of NaOH to the mixture. Radiometric measurements indicate the strong fixation of Molybdate(VI)-⁹⁹Mo species in the form of the sparingly insoluble Al⁹⁹Mo gel matrix. The prepared AlMo gel matrix was physiochemically characterized. Al⁹⁹Mo gel matrix was used as a base material for preparation of ⁹⁹Mo/^99mTc generator. The ^99mTc eluted from ⁹⁹Mo/^99mTc radioisotope generator was found to have relatively high elution yield (84?±?2.3%), radionuclidic (≥?99.99%), radiochemical (98.1?±?0.9%) and chemical purity.     

Two novel procedures of preparation for [Tc(CO)<Subscript>2</Subscript>(NO)]<Superscript>2+</Superscript>labeled by EHIDA and its biodistribution

To develop potential new Tc radiopharmaceuticals, a novel compound [^99mTc(CO)₂(NO)(EHIDA)]⁰ (EHIDA: 2,6-diethylphenylcarbamoylmethyliminodiacetic acid) has been prepared by reacting [^99mTc(CO)₃)(EHIDA)]⁻ with NOBF₄ both in water and acetonitrile. The conversion of [^99mTc(CO)₃)(EHIDA)]⁻ to [^99mTc(CO)₂(NO)(EHIDA)]⁰ was supported by TLC, HPLC and eletrophoresis. The radiochemical purity (more than 99%) was proved by TLC and HPLC. The biodistribution in mice demonstrated that [Tc(CO)₂(NO)(EHIDA)]⁰ showed higher uptake in blood, kidney and lung (15 min, blood: 19.24±2.95; kidney: 13.61±3.49; lung: 10.81±1.09.) but a lower uptake in liver (15 min, 5.73±0.74). The slower clearances (120 min, blood: 12.75±1.34; kidney: 13.61±3.49) from blood and kidney were also found. This research describes two methods for the conversion of [^99mTc(CO)₃]⁺ into [^99mTc(CO)₂)(NO)]²⁺ by using NOBF₄ as the source of NO⁺ both in organic solvent and water. The latter method offers the possibility to introduce the NO-group in high yield in water.