Hybrid 99mTc-magnetite tracer for dual modality sentinel lymph node mapping.

Accuracy of sentinel lymph node identification using radioactive tracers in non-superficial cancers can be limited by radiation shine through and low spatial resolution of detection systems such as intraoperative gamma probes. By utilising a dual radioactive/magnetic tracer, sensitive lymphoscintigraphy can be paired with high spatial resolution intraoperative magnetometer probes to improve the accuracy of sentinel node detection in cancers with complex multidirectional lymphatic drainage. Dextran-coated magnetite nanoparticles (33 nm mean hydrodynamic diameter) were labelled with 99mTc and applied as a lymphotropic tracer in small and large animal models. The dual tracer could be radiolabelled with 98 ± 2% efficiency after 10 min of incubation at room temperature. Biodistribution studies of the tracer were conducted in normal rats (subdermal and intravenous tail delivery, n = 3) and swine (subdermal hind limb delivery, n = 5). In rats the dual tracer migrated through four tiers of lymph node, 20 min after subdermal injection. Results from intravenous biodistribution test for radiocolloids demonstrated no aggregation in vivo, however indicated the presence of some lower-molecular weight radioactive impurities (99mTc-dextran). In swine, the dual tracer could be effectively used to map lymphatic drainage from hind hoof to popliteal and inguinal basins using intraoperative gamma and magnetometer probes. Of the eight primary nodes excised, eight were positively identified by gamma probe and seven by magnetometer probe. The high-purity dual tracer shows early promise for sentinel node identification in complex lymphatic environments by combining sensitive preoperative lymphoscintigraphy with a high-resolution intraoperative magnetometer probe.

Preparation of 68 Ga-Mg-Ca-phytate colloid and its evaluation as a liver imaging agent.

The objective of this study was to investigate the radiosynthesis of 68 Ga-Mg-Ca-phytate colloid and then characterise the formulation for radiochemical purity (RCP), radioactive particle size distribution, and biodistribution in normal rats. This radiocolloid was prepared by mixing an aqueous solution of phytic acid, 68 Ga3+ ions, a dispersant, Mg2+ and Ca2+ ions, and then heating the contents at 100°C for 5 minutes. After cooling the vial to 5°C, the solution was basified to pH 5 and stored in the cold. The resulting product contained 92±3% RCP 68 Ga-colloidal particles and a low level (8±3%) of soluble 68 Ga-Mg-Ca-phytate. Particle size experiments defined the radioactive particle population was 6±4% <20 nm, 90±6% 20 to 200 nm, and 4% were >200 nm in diameter. Intravenous injection of the 68 Ga-colloid dispersion to rats resulted in 93% uptake by the liver plus spleen, 1% lungs, 1% total blood, and 6% in the carcass after 20 minutes. This optimal formulation remained stable at 5°C for 1½ hours in vitro, and it resulted in the same biodistribution as the formulation prepared at t = 0 hours. The preclinical data so far indicate that 68 Ga-Mg-Ca-colloid has excellent potential as a liver imaging agent.

A study of radiogallium aqueous chemistry: in vitro and in vivo characterisation of (67) Ga-hydrolysed-stannous fluoride particles.

The objective of this study was to explore the aqueous chemistry of gallium using (67) Ga-chloride starting material, by radiolabelling hydrolysed(h)-stannous fluoride particles and then characterising the optimal formulation for radiochemical purity (RCP) and radioactive particle size distribution in vitro. The pilot reactions determined stannous fluoride was added to (67) Ga-acetate under nitrogen and then heated at 100 °C for 20 min to achieve ≥95% RCP and (67) Ga-particles were >3 µm in diameter. A high radioactive concentration of (67) Ga-h-SnF2 particles could be prepared similarly in ≥97% RCP with 74% as 3-5 µm and 26% >5 µm in diameter. The latter formulation had larger particles than (99m) Tc-h-SnF2 colloid (96% of 1-3 µm), and it resulted in a rat biodistribution of 41% in the lungs, 41% in the liver plus spleen and 18% in the carcass at 20 min after injection. The carcass activity was attributed to bone marrow and some (67) Ga-transferrin formed in blood. Isolated mixed human leucocytes were radiolabelled with (67) Ga-h-SnF2 particles in 100% efficiency, and the (67) Ga-cells did not release soluble (67) Ga(3+) at room temperature over 3 h. The (67) Ga-h-SnF2 particle formulation could find a use in labelling leucocyte cells for in vivo homing studies when delayed animal imaging is required.

68 Ga-Ca-phytate particles: A potential lung perfusion agent of synthetic origin prepared in a cold kit format.

The objective of this study was to investigate the radiosynthesis of 68 Ga-Ca-phytate particles and then characterize the formulation for radiochemical purity, radioactive particle size distribution, and biodistribution in normal rats. This radiotracer was prepared using a commercial phytate cold kit after reconstitution with saline, 68 Ga-chloride generator eluent, calcium chloride, and air, then heating at 100°C for 30 minutes to achieve 99% radiochemical purity of 68 Ga-particles that were 21% 3-5 µm, 8% 5-15 µm, and 71% >15 µm in diameter. This optimal formulation was stable for 2 hours at room temperature. Intravenous administration of 68 Ga-particles in rats resulted in an uptake of 93% in the lungs, 4% in the liver plus spleen, and 3% in the carcass after 20 minutes. Two-thirds of the carcass activity was radioactive blood, likely to be 68 Ga-transferrin. The positron emission tomography image was superior than the 99m Tc-MAA image because it displayed high lung uptake against a low background. Low uptake by the liver, spleen did not interfere with the diagnostic quality, and faint activity in the submandibular (salivary) glands was due to 68 Ga-transferrin. The preclinical data so far indicate that 68 Ga-Ca-phytate particles have good potential as a lung perfusion imaging agent.

An improved assay for (68)Ga-hydroxide in (68)Ga-DOTATATE formulations intended for neuroendocrine tumour imaging.

The objective of this study was to identify a more rapid assay for (68)Ga(OH)3 impurity in (68)Ga-DOTATATE formulations. Three methods were used to prepare (68)Ga(OH)3 reference material (pharmacopoeial, bench titration and automated radiosynthesis), and four quality control methods for its assessment (thin layer chromatography, membrane filtration, HPLC and solid phase extraction). The optimal method of preparing (68)Ga(OH)3 was by titrating (68)Ga(3+) with buffered sodium hydroxide solutions to pH 5.6 ± 0.2. The precipitate was quantitatively isolated by membrane filtration (0.02 µm)/hydrochloric acid (HCl; pH 5.6) solvent, and also it remained 100% at the origin on instant thin layer chromatography with silica gel paper/HCl (pH 5.6) solvent. For (68)Ga-DOTATATE samples, the thin layer chromatography technique was used with a single paper strip developed separately on two occasions, once in HCl (pH 5.6) and next in methanol solvent. This so-called double-developed (DD) method separated (68)Ga(OH)3 impurity located at the origin, from (68)Ga-DOTATATE plus (68)Ga(3+) at ~Rf 0.4, and it was superior to the other methods. It assayed for the impurity similarly to the pharmacopoeial method. The advantages of the DD method were that it required inexpensive test materials and it reproducibly determined % (68)Ga(OH)3 in (68)Ga-DOTATATE in 12 min, 13 min earlier than the pharmacopoeial method. This time efficiency resulted in a surplus of 12% (68)Ga-DOTATATE counts in the product vial, and this provided a contingency of radioactivity or time for the injection/imaging processes in the Nuclear Medicine Department.

Radiotracers used for the scintigraphic detection of infection and inflammation.

Over the last forty years, a small group of commercial radiopharmaceuticals have found their way into routine medical use, for the diagnostic imaging of patients with infection or inflammation. These molecular radiotracers usually participate in the immune response to an antigen, by tagging leukocytes or other molecules/cells that are endogenous to the process. Currently there is an advancing effort by researchers in the preclinical domain to design and develop new agents for this application. This review discusses radiopharmaceuticals used in the nuclear medicine clinic today, as well as those potential radiotracers that exploit an organism's defence mechanisms to an infectious or inflammatory event.

Lymphoscintigraphy is more effective using higher specific activity (99m)Tc-antimony trisulfide colloid in the rat.

Technetium-99m-antimony trisulfide colloid ((99m)Tc-ATC) was investigated with varying specific activity in the rat lymphatic system, as well as its binding to rat blood cells in vitro. Low, moderate and high doses of (99m)Tc-ATC were subdermally injected into tails of rats (n=3) and 30min later whole body lymphoscintigraphic images were acquired. (99m)Tc-ATC was incubated for 30min at 37°C with whole blood (n=4) as for control, at 4°C as for hypothermia, as opsonized at 37°C and lipopolysaccharide (LPS) at 37°C. Cell types were separated by gradient centrifugation to assay for cell bound-radioactivity. These experiments were repeated using mixed leukocytes that were erythrocytes-free. Images showed direct drainage of (99m)Tc-ATC from the tail to the popliteal nodes, sacral node and beyond, along the para-aortic chain, and to a left inguinal lymph node that drained into the axillia. The higher specific activity dose resulted in more visible lymph nodes after 30min. (99m)Tc-ATC was predominantly not cell-bound. In rat whole blood (99m)Tc-ATC-neutrophils were only present to the extent of 3% for the control, 3% for the hypothermia test, 4% for the opsonized and 7% for the LPS test. In the erythrocytes-free samples, (99m)Tc-ATC-leukocytes were present to the extent of 5% (control), 4% (hypothermia), 6% (opsonized) and 11% (LPS). In conclusion, a higher specific activity radiocolloid may identify the sentinel lymph node sooner during lymphoscintigraphy, and there may be an advantage in detecting more counts with the γ-probe. Retention of (99m)Tc-ATC in lymph nodes in vivo is likely because of binding on macrophage surfaces, rather than from internalization by phagocytosis within a time frame of 30min after injection.

Lymphatic mapping with 99mTc-Evans Blue dye in sheep.

OBJECTIVE: 99mTc-Evans Blue (EB) is an agent that contains both radioactive and color signals in a single dose. Earlier studies in animal models have suggested that this agent when compared with the dual-injection technique of radiocolloid/blue dye can successfully discriminate the sentinel lymph node. The aim of this study was to investigate the potential of 99mTc-EB as an agent to map the lymphatic system in an ovine model. METHODS: Doses of 99mTc-EB (23 MBq) containing EB dye (4 mg) were administered intradermally to the limbs of four anesthetized sheep, and they were then imaged over 20-30 min using a gamma camera. The study protocol was repeated using 99mTc-antimony trisulfide colloid (ATC) and Patent Blue V dye. The lymph nodes (popliteal, inguinal, and iliac for hind limbs or prescapular for fore limbs) were identified with a gamma probe during the operative exposure, then dissected and counted in a large volume counter. RESULTS: Simple and complex (dual) drainage patterns were visible on the scans, and the sentinel node was more radioactive than higher tier nodes in a chain, for both radiotracers. For 99mTc-EB, maximum radioactive uptake was achieved at 3-6 min for popliteal lymph nodes, 12-14 min for iliac nodes, and 13-14 min for prescapular nodes. 99mTc-ATC resulted in maximum radioactive uptake at 4-6 min for popliteal lymph nodes, 13 min for an inguinal node, 13-20 min for iliac nodes, and 18 min for a prescapular node. Following 99mTc-EB injection, 15/15 lymph nodes harvested were all radioactive and blue. For 99mTc-radiocolloid/Patent Blue V injection, 8/14 nodes were radioactive and blue, and 6/14 nodes were radioactive only. CONCLUSIONS: The soluble radiotracer 99mTc-EB appeared to be a useful lymphoscintigraphic agent in sheep, in which radioactive counts from superficial lymphatic channels and lymph nodes were sufficient for planar imaging. In comparison with 99mTc-antimony trisulfide colloid, both tracers discriminated the sentinel lymph node up to 50 min after administration; however, 99mTc-EB had the advantage of providing radioactive (gamma probe) and color signals simultaneously during the operative exposure.

Colonic transit studies with 99mTc-rhenium sulfide colloid in live rats. A preliminary study.

Abnormal colonic motility is associated with clinical relevant conditions such as irritable bowel syndrome or constipation. Accurate assessment of colonic transit in an animal model would be useful in studying these conditions and screen potential drug candidates. The aim of this study was to assess if scintigraphic analyses could reliably evaluate total and segmental colonic transit as a measure of colonic motility of a non-absorbable radiotracer in rats. Normal Lewis rats (250-300 g) were given oral technetium-99m-rhenium sulfide colloid (15-20 MBq; 0.5 mL; n=4) followed by a rinse with water for injection (1.0 mL). Rats were fed and hydrated ad libitum. After 30 min, each rat was contained inside an 'imaging' tube then placed on a g-camera collimator. Whole body 5 min static images were acquired every 30 min up to 9 h, and then finally at 25 hours. Region of interest analyses were applied to the caecum/proximal colon, sigmoidal loop and distal colon/rectum. The tracer entered into the colon at approximately 4 hours, and the rats remained static to permit 'live' imaging. At 4 hours the % whole body activity was: 51% caecum/proximal colon, 39% sigmoidal loop, 6% distal colon/rectum; at 8 hours, 30% caecum/proximal colon, 13% sigmoidal loop, 7% distal colon/rectum. In the whole colon there was < or =1% of total activity present at 25 hours, and the half clearance time was determined as 4.0 hours. These results suggest this is a reliable technique of measuring regional colonic transit as a measure of colonic motility in normal rats. This methodology might be well suited to screen potential motility effects of drug candidates.

18-Fluoride labeled sodium fluoride positron emission tomography with computer tomography: the impact of pretreatment staging in intermediate- and high-risk prostate cancer.

BACKGROUND: 18-Fluoride labeled sodium fluoride (Na-18-F) positron emission tomography with computer tomography (PET/CT) has a better sensitivity and specificity than whole body bone scan (WBBS) in detecting osseous metastatic prostate cancer. We performed a pilot study of 20 men to examine what level of impact Na-18-F PET/CT has on management plans when used for staging newly diagnosed prostate cancer. MATERIALS AND METHODS: Twenty men were prospectively enrolled into the study in South Australia. Men were eligible if they had newly diagnosed, untreated, and biopsy-confirmed intermediate- or high-risk prostate cancer (D'Amico classification). WBBS and Na-18-F PET/CT scans were performed within 1 week of each other. Following review of the WBBS, treatment type and intent was documented by the treating urologist. The Na-18-F PET/CT scan was then reviewed. The impact of the Na-18-F PET/CT was measured on whether treatment modality or intent was subsequently altered: high impact = treatment intent or modality was changed; medium impact = treatment modality was modified; low impact = no change in treatment. RESULTS: In 18 men (90%), the WBBS and Na-18-F PET/CT were negative for osseous metastases. In one man (5%), the WBBS demonstrated widespread osseous metastases which were similarly demonstrated on the Na-18-F PET/CT. One man (5%) had a normal WBBS; however, the Na-18-F PET/CT demonstrated widespread osseous metastases. Subsequently, in 19 men (95%), the results of the two scans were congruent and the addition of the Na-18-F PET/CT scan demonstrated a low impact on management. In one man (5%), the addition of the Na-18-F PET/CT had a high impact as treatment type and intent was altered. CONCLUSIONS: Our pilot study is the first of its kind in Australia, and our findings suggest that Na-18-F PET/CT is a safe and feasible modality for staging prostate cancer. However, its true impact on prostate cancer management warrants further investigation.

The tissue distribution of Evans blue dye in a sheep model of sentinel node biopsy.

BACKGROUND: Tc-Evans blue is a 'single dose' agent for lymphatic mapping combining radioactivity and blue dye for sentinel node identification. The mechanism and distribution of blue dye retention in the lymph node is not clearly understood. OBJECTIVE: To demonstrate the cellular distribution of Tc-Evans blue in sheep sentinel lymph nodes by measuring the radioactivity of different tissue components and correlating this with pathological examination. METHODS: Tc-Evans blue was used to identify sheep lymph nodes. Part of each node was sent for pathological examination including imprint cytology, and frozen and permanent section examination. Sections were examined without stains, with only red stains and conventional haematoxylin & eosin staining. The remaining nodal tissue was homogenized and components separated by enzymatic digestion and density gradient centrifugation. Fractions representing each tissue component were counted in a gamma counter and the distribution of Tc-Evans blue calculated. RESULTS: A dispersed population of blue staining cells was found. Their distribution, number and size indicated that they were histiocytes such as macrophages or antigen presenting cells. Radioactivity was distributed throughout the lymph node. Over 70% remained in the plasma, 19% in the leukocyte layer, and 10% was associated with erythrocytes and undigested tissue. CONCLUSION: The accumulation of radioactivity and blue colour in the lymph nodes indicates the mechanism of retention is a result of the binding interaction between Tc-Evans blue-protein and lymph node histiocytes including macrophages and antigen presenting cells.

Scintigraphic imaging of experimental colitis with technetium-99m-infliximab in the rat.

The radiolabeled monoclonal antibody (99m)Tc-infliximab was assessed as an inflammation imaging agent in a rat colitis model in comparison with (99m)Tc-tin colloid-labeled-leucocytes. (99m)Tc-infliximab and (99m)Tc-tin fluoride colloid-labeled-leucocytes were administered to (n>3) rats previously exposed to 2,4,6-trinitrobenzenesulfonic acid by rectal instillation. Whole body scintigraphic images were acquired and physiological organ assays were performed to obtain quantitative data. Histological examination of colon samples was performed to assess the site and severity of the colitis. In the inflamed colon, (99m)Tc-infliximab resulted in inflamed target (T) to control (C) colon tracer uptake ratios of 2.7 +/- 1.0 (n=5) and 2.6 +/- 0.3 (n=5) at 1 and 4 h post tracer injection respectively. (99m)Tc-leucocytes gave higher ratios of 19.5 +/- 9.9 (n=3) and 41.2 +/- 16.1 (n=5) respectively. (99m)Tc-leucocytes gave higher ratios of 19.5 +/- 9.9 and 41.2 +/- 16.1 at the corresponding time points. (99m)Tc-infliximab accumulated at sites of inflammation in this rat model but not due to a specific tumor necrosis factor-alpha binding mechanism. Although the tracer uptake was lower than radioactive leucocytes, this easily prepared (99m)Tc-monoclonal antibody may have some advantages in imaging inflammatory bowel disease in humans based on its biological activity.

Regenerating lizard tails: a new model for investigating lymphangiogenesis.

Impaired lymphatic drainage in human limbs causes the debilitating swelling termed lymphoedema. In mammals, known growth factors involved in the control of lymphangiogenesis (growth of new lymph vessels) are vascular endothelial growth factors-C and -D (VEGF-C/D). Here we characterize a model of lymphangiogenesis in which the tail of lizards is regenerated without becoming oedematous. Three weeks after the tail is shed (autotomy), there are a small number of large diameter lymphatic vessels in the regenerated tail. Thereafter, the number increases and the diameter decreases. A functional lymphatic network, as determined by lymphoscintigraphy, is established 6 wk after autotomy. The new network differs morphologically and functionally from that in original tails. This lymphatic regeneration is associated with an up-regulation of a reptilian homologue of the VEGF-C/D protein family (rVEGF-C/D), as determined by Western blot analysis using a human reactive VEGF-C polyclonal antibody. Regenerating lizard tails are potentially useful models for studying the molecular basis of lymphangiogenesis with a view to developing possible treatments for human lymphoedema.

An improved (99m)Tc-aprotinin kit formulation: quality control analysis of radiotracer stability and cold kit shelf life.

(99m)Tc-aprotinin scintigraphy has been demonstrated to be a useful noninvasive imaging technique for amyloid deposits located in extraabdominal regions of patients. The aim of this study was to develop an improved aprotinin cold kit formulation, to validate the kit for long-term stability, as well as to assess the radiotracer stability by novel quality control methods. The aprotinin cold kit formulation of Trasylol, pyrophosphate (PYP)-chelated stannous reductant and an alkaline buffer, was dispensed into nitrogen-filled vials and aliquots frozen at -20 degrees C. After 0, 1, 2, 3 and 6 months of storage, three samples were reconstituted with 750-850 MBq of (99m)Tc-pertechnetate, followed by quality control analyses by paper chromatography methods at 25, 85 and 265 min postreconstitution (pr). Cation-exchange cartridge quality control methods were also investigated. The cold kits proved to be stable to long-term storage for up to 6 months, and the radiotracer was stable for at least 4 h pr. (99m)Tc-aprotinin was formed at greater than 95% efficiency at all time points tested with (99m)TcO2 present as the major impurity (1-4%) and (99m)Tc-pertechnetate and (99m)Tc-PYP present in trace amounts. An alternative, rapid, safe and reliable method was found in Oasis MCX-BSA-treated cartridges using saline as the eluting solution to assay for (99m)Tc-aprotinin.

Pharmacokinetics and normal scintigraphic appearance of 99mTc aprotinin.

OBJECTIVE: To confirm the pharmacokinetics and biodistribution of 99mTc aprotinin in normal volunteers and to determine the optimum time for scanning post-injection, prior to further investigations of 99mTc aprotinin as an imaging agent for amyloidosis. METHODS: Five patients (three men and two women, average age 49 years, age range 38-66 years) without a history of amyloidosis or any of the associated diseases, were included in this prospective study. Blood and urine were collected and images were performed of the whole body and wrists. CONCLUSIONS: Normal biodistribution of 99mTc aprotinin includes early cardiac and lung activity in the blood pool phase with subsequent hepatic activity and renal excretion with variable splenic activity. There is variable bowel uptake on later images. The best quality images were obtained 90 min post-intravenous administration, and this is likely to be the optimum time for clinical imaging.

Characterization and quality control analysis of 99mTc-bicisate.

The aim of this study was to investigate the mini cartridge versus paper chromatography quality control methods for determining the radiochemical purity (RCP) of (99m)Tc-bicisate. The 4 methods that were compared with the manufacturer's method included Whatman 17 paper/ethyl acetate solvent, instant thin-layer chromatography (ITLC) silica gel paper/saline solvent, reverse-phase C18 mini cartridge/saline solvent, and strong anion exchange mini cartridge/water solvent. At 30 min after reconstitution, (99m)Tc-bicisate was formed at 97%-98% RCP as assayed by the paper and cartridge methods, and the strong anion exchange/water for injection (WFI) system slightly underestimated the percentage at 96%. A significantly lower RCP was obtained for the C18/saline method when a faster flow rate was used. The lipophilic complex moved with ethyl acetate on Whatman 17, was separated from origin impurities on ITLC silica gel/saline, and remained on the column with C18/saline. For strong anion exchange/WFI, components in the radioactive formulation are likely to have influenced the percentage of (99m)Tc-bicisate. The time disadvantage for ITLC silica gel/saline analysis made the method less than ideal. The C18 mini cartridge/saline method was found to be the simplest and fastest; a result was obtained in 2 min with use of a safe solvent of elution.

Radiolabelling and biodistribution of 111In-antimony trisulphide colloid.

The aim of this study was to prepare 111In-antimony trisulphide colloid (111In-ATC) and evaluate its chemical properties in comparison with 99mTc-ATC. After reconstitution of an antimony trisulphide cold Kit with 111In-chloride, 111In-ATC was formed with >95% radiochemical purity in the presence of neutralising phosphate buffer. The product was found to be stable for 4.7 days when stored at room temperature, 80% of radioactive particles were < 20 nm in diameter and the mouse biodistribution assay was identical to that of 99mTc-ATC. In conclusion, pharmaceutical-grade 111In-ATC was successfully prepared and assessed to have properties that are suitable for dual-isotope lymphoscintigraphy studies at the clinical level.

Why certain dyes are useful for localizing the sentinel lymph node.

UNLABELLED: Location of the sentinel lymph node in malignant melanoma and early breast cancer patients requires separate injections of radiocolloid and blue dye. These agents are administered at alternative times because of their different rates of transit. This study has elucidated why particular dyes are absorbed by the lymphatic system from an investigation of dye molecular structure as a function of protein binding ability. METHODS: A dye-protein binding assay was developed using size-exclusion chromatography and ultraviolet spectrophotometry and applied to a series of 20 sulfonic acid group-containing dyes. Radiochemical analyses were also used with 3 99mTc-labeled dyes to rationalize which functional groups are involved in the protein binding reaction. RESULTS: Methylene blue resulted in no protein affinity at 37 degrees C, whereas disulfonate dyes separated by 1 atom such as Patent blue or Indigo carmine gave <30% binding. Optimum protein binding (84%-100%) was achieved with those dyes containing at least 2 sulfonic acid groups separated by 2-6 atoms in their chemical structure. Seven symmetric tetrasulfonic acid azo dyes were examined, including Evans blue, to result in 59%-71% binding. CONCLUSION: Ionizable groups (sulfonic acids) that are present in the structure of dyes are directly involved in dye-protein binding. At the molecular level, there is a sulfonation reaction between sulfonic acid dyes and amino groups on the protein surface to form sulfonamide complexes. This reaction shows how the soluble dyes Evans blue and Patent blue are trapped in lymph after subdermal injection during the sentinel node biopsy procedure.

Sentinel node biopsy and lymphoscintigraphy with a technetium 99m labeled blue dye in a rabbit model.

BACKGROUND: Lymphatic mapping for sentinel node biopsy in breast cancer and melanoma usually involves initial peritumoral injection of a radioisotope, gamma camera detection of the sentinel lymph node several hours prior to the operation, and separate perioperative injection of a blue dye. We have developed a combined approach using technetium 99m labeled blue dye (Evans Blue) for use in lymphoscintigraphy that may be injected as a single dose just prior to the operation. METHODS: In an anesthetized rabbit model we dissected a hind limb to display the popliteal node and afferent lymphatic. Technetium 99m Evans Blue ((99m)Tc-EB) (22 MBq; 0.5 mL) was injected subdermally in the dorsum of the paw. Simultaneous digital and gamma camera images were obtained at 14 time intervals to 30 minutes post injection. For each of these time intervals the percentage of radioactivity and percentage blueness of the popliteal node were determined. Urine and afferent lymphatic fluid were analyzed by chromatography. The popliteal node was excised post mortem, placed into solvent solutions and analyzed for blueness and radioactivity. RESULTS: Time-activity curves for radioactivity and time-blueness curves for Evans Blue uptake showed strong correlation (r = 0.958). Lymph analysis suggested (99m)Tc-EB is mainly bound to endogenous proteins. Urine was radioactive but not colored, (99m)Tc-EB being metabolized and excreted in the urine as 1,7-diamino-8-naphthol-2,4-disulfonic acid. Prolonged exposure of node to solvents did not dissociate any blue coloration or radioactivity. CONCLUSIONS: (99m)Tc-EB and Evans Blue are simultaneously retained and concentrated in the sentinel lymph node. This process is rapid and reproducible. (99m)Tc-EB migrates at the same rate as Evans Blue in lymph, where it is transported as bound to endogenous proteins. These dye molecules are metabolized by reductive cleavage in the liver and then excreted renally as colorless, radioactive metabolites. This novel agent has the potential to facilitate lymphatic mapping and subsequent sentinel node biopsy for a range of solid malignancies including breast cancer and melanoma.

A simple and effective technique to reduce staff exposure during the preparation of radiopharmaceuticals.

OBJECTIVE: In the preparation of radiopharmaceuticals, staff receive considerable radiation exposure to the hands during withdrawal of activity from the elution vial, from a combination of the syringe and elution vial activities. In an attempt to reduce the radiation burden to the hands, a simple technique was developed that utilizes a modified lead pot lid and a syringe bearing a long needle with a sterile needle guide. METHODS: An elution vial in a lead pot with an attached syringe was secured at an angle of 45 degrees, simulating the action of withdrawing (99m)Tc-pertechnetate from the elution vial. The (99m)Tc activity ratio of vial to syringe was 20:1. A gamma- camera detector without collimator was positioned at the syringe plunger and count profiles were obtained after 10 min of data acquisition. The experiment was repeated using the same set-up with (a) the modified lid on the lead pot and (b) a cold syringe to determine the contribution of the radioactive syringe to the count profile. Each experiment was repeated at the vertical position, simulating the normal action of redispensing (99m)Tc activity into the elution vial. RESULTS: The modified lid reduced exposure from the elution vial, with a count reduction of >98% for both orientations. The contributions of vial radioactivity to the total count profile were 76% and 84% for vertical and 45 degrees orientations, respectively. The contributions of syringe activity were 24% and 16% for vertical and 45 degrees orientations, respectively. CONCLUSION: A reduction in the photon flux to the hands of up to 84% (with an associated reduction in hand dose) can be achieved by withdrawing activity through a modified lid on the lead pot housing the elution vial, without significantly altering normal work practices.