Cell Labeling topics to be coveredRed Cells: Tc-99m and Cr-51White Cells: Tc-99m and In-111Platelets: In-111
Uses of Tc-99m Red CellsFirstPass Cardiac studyGated Blood Pool studyG.I. Bleed StudyLocalization of hepatic hemangioma
Principles of Tc-99m RBC LabelingStannous ion, a powerful reducing agent, is added to red cellsSn2+ is permitted to diffuse into RBCsTc-99m pertechnetate (TcO4-) is then added to pre-tinned RBCsTc-99m diffuses into the RBCs, where it is reduced by the Sn2+ ion to Tc4+, which binds to the -globin chains of hemoglobin.
Principles of Tc-99m RBC LabelingReduced Tc-99m (Tc4+)cannot bind to the heme portion of the hemoglobin molecule since the Fe incorporated into the heme can not be displaced under physiological conditions. Tc4+ therefore binds only to the globin portion of the molecule, specifically the -globin chains.
NOW HEAR THIS!!! Every container which holds a blood sample Full Name must be labeled with the Full Name Full Name patient’s FULL NAME Syringes Full Name Test tubes Vials
Methods of Preparation of Tc-99m RBCs • In vivo/in vivo • In vivo/in vitro • In vitro/in vitro
Methods of Preparation of Tc-99m RBCs In vivo / in vivo In vivo / in vitro In vitro / in vitroRefers to Refers totinning of the radiolabelingcells, i.e., of the cells,injection of the i.e., injection ofstannous the Tc-99mpyrophosphate pertechnetate
In vivo/in vivo method1. 1 mg of Sn2+ in the form of pyrophosphate(“cold PYP”) is given IV2. 20 min wait to permit mixing of the SnPYP in body and diffusion of Sn2+ into RBC.3. IV injection of 25 mCi 99mTc pertechnetate4. 10 min waiting period to permit diffusion ofpertechnetate into RBCs where radio-labeling takes place.
In Vivo/In Vivo: Advantages/disadvantagesAdvantages: quick, simple, inexpensiveDisadvantage: lowest labeling efficiency ofall commonly used procedures, butperfectly acceptable for routine work, e.g.,MUGAs.
In vivo/in vitro method (in vivtro method) 1. 1 mg of Sn2+ in the form of pyrophosphate (“cold PYP”) is given IV 2. 20 min wait to permit mixing of the Sn PYP in body and diffusion of Sn2+ into RBC. 3. Withdrawal of 5-10 ml of blood anti- coagulated with heparin or ACD solution into a syringe containing 25 mCi Tc-99m pertechnetate
In vivo/in vitro method (in vivtro method)4. 10 min waiting period to permit diffusion of the pertechnetate into RBCs and to permit labeling to reach equilibrium.5. Reinjection of labeled cells into patient.6. Expected labeling efficiency: ~92%
In vivo/in vitro: Advantages/disadvantagesAdvantages: quick, simple, inexpensivemethod; achieves higher labeling efficiencythan in vivo/in vivo technique sinceincubation with RBC is extracorporeal. Notoptimal for GI Bleeding Studies.Disadvantages: takes extra tech time;potential for breaking sterility
Modified In vivo/in vitro method1. 1 mg of Sn2+ in the form of pyrophosphate(“cold PYP”) is given IV.2. 20 min wait to permit mixing of the SnPYP in body and diffusion of Sn2+ into RBC.3. Withdrawal of 5-10 ml of anti-coagulatedblood (heparin, ACD) into vacutainer.4. Centrifuge the vacutainer in invertedposition for 5 min at 3000 rpm.
Modified In vivo/in vitro method5. Removal of 1-2 ml of packed cellsthrough a 20 ga or larger needle.6. Aseptic addition of these tinned, packedcells to a sterile vial containing 35 mCi ofTc-99m pertechnetate.7. 10 min incubation to permit labelingreaction to go to completion. Expectedlabeling efficiency: 98-100%8. Reinjection of Tc RBC
Modified In vivo/in vitro method Advantages/disadvantagesAdvantages: quick, simple, inexpensivemethod; achieves highest labeling efficiencyof all procedures since reaction of Tc withplasma proteins has been eliminated. Ideallysuited for GI Bleeding Studies; producesexcellent delayed images.Disadvantage: takes extra tech time; requiresclinical centrifuge; potential for breakingsterility.
In vitro/in vitro method Ultratag Kits 1. To vial containing Sn2+ compound, add 3- 5 ml of anticoagulated blood 2. Incubate 15 min 3. add 25 mCi Tc-99m pertechnetate 4. add Na hypochlorite (NaClO) to destroy extracellular Sn2+ ion 5. Add Citrate Buffer 6. incubate 20 min. Expected labeling efficiency >98%
In vitro/in vitro (Ultratag): Advantages/disadvantagesAdvantages: quick, simple, inexpensivemethod; achieves higher labeling efficiencythan in vivo/in vivo technique since incubationwith RBC is extracorporeal. Ideally suited forGI Bleeding Studies; produces excellentdelayed images.Disadvantage: takes extra tech time; slightpotential for breaking sterility
Quality Control for Tc-99m RBCsTake 0.2 mL of labeled RBC suspensionAdd to 2 mL 0.9% NaCl; mix gentlyCentrifuge 5 min. Pipette off diluted plasmaCount Radioactivity in plasma and in packed RBC% RBC Labeling = CountsRBC x 100% CountsRBC + CountsPlasma
Heat Damaged Tc-99m RBCsUsed for spleen imaging –Accessory spleen –Splenic remnants after splenectomyPrepare Tc-99m RBCs by one of the in vitro methodsIncubate 30 minutes at 50ºCHeat damaged RBCs are removed from circulation by the spleen
Tc-99m Labeled WBCsUsed for localizing infection and abscessesPrinciple of labeling –Tc-99m Ceretec is lipophilic and crosses lipid bilayer of cell membranes –Inside the cell the Ceretec complex is broken down and the resulting charged Tc-99m species is trapped in the cell –All cell types are labeled by Ceretec so prior leukocyte separation is necessary
Tc-99m WBC Labeling ProcedureCheck patient’s white count (must be > 2K)Obtain ~50 mL anticoagulated whole blood from pt (larger volume if WBC count is low)Optional: add Hetastarch as a sedimentation aidCentrifuge at 15 x g for 10 min
Tc-99m WBC Labeling ProcedureAseptically remove the platelet-rich & leukocyte-rich supernatantCentrifuge at 200 x g for 10 min.Decant platelet-rich plasma and then wash cells with 0.9% NaClAdd ~40 mCi freshly prepared Tc-99m Ceretec dropwise to leukocyte pellet and incubate for 20 min. Do NOT use Methylene Blue.
Tc-99m WBC Labeling ProcedureCentrifuge, remove unbound Tc- 99m, and wash pellet.Resuspend labeled WBC in either platelet poor plasma or 0.9% NaClLabeling 50 - 80 %.Draw up dose and inject patient. If patient has been on dialysis, wait until procedure is complete
Quality Control of Tc-99m WBCPlace a drop of labeled cells on a hemocytometerAdd a drop of Trypan Blue dyeAdd a cover slip and examine under microscopeViable cells exclude dye; dead cells are stained blueIf >10% are dead or large clumps are present, don’t use
Labeling In-111 WBCUsed for localizing infection and abscessesPrinciple of labeling –In-111 Oxine is lipophilic and crosses lipid bilayer of cell membranes –Inside the cell the Oxine complex is broken down and the resulting charged In- 111 species is trapped in the cell –All cell types are labeled so prior leukocyte separation is necessary
In-111 WBC Labeling ProcedureCheck patient’s WBC count; adjust if necessarySeparate WBC fraction as previously describedAdd 500-1000 µCi In-111 Oxine.Radiolabel as previously described. Labeling typically 50-95%.QC is the same as for Tc-99m WBC
WBC Separation by Osmotic LysisRBCs are more susceptible to lysis from osmotic pressure than WBCsAdd sterile H2O to WBC pellet contaminated w/ RBCs – This lowers the concentration of ions, etc. – The result is increased pressure in cells – RBCs lyse (burst open and die)Quickly add 5% NaCl to restore tonicity
WBC Separation by Osmotic Lysis Centrifuge WBC sediment, Platelets and RBC debris remain in supernatant Remove supernatant Resuspend WBC Label WBC with Tc-99m or In-111
Labeled PlateletsSeparate platelets from whole blood by centrifugationLabel by incubation with lipophilic complexes of Tc-99m or In-111Uses –Localization of thrombi –Platelet survival studies
Cr-51 Labeled RBCsUses –RBC Mass –RBC Survival and SequestrationProperties of Cr-51 –Half-life = 28 days –Gamma energy = 320 keV
Principle of Labeling Cr-51RBCs Cr-51 in the form of Na2CrO4 (+6 oxidation state) is incubated with RBCs Cr-51 binds to RBCs Reaction terminated by adding a reducing agent such as ascorbic acid
Procedure for Labeling Cr-51 RBCsObtain 25-30 mL of anticoagulated bloodCombine blood with 75 - 150 µCi Cr-51Incubate 20-30 minutes at 37ºC or at room tempAdd 100 mg ascorbic acid and incubate 5 more minutesRemove and use the labeled cells
Summary and Conclusions1. Multiple methods are available for labeling RBCs with Tc-99m. All are simple, rapid, inexpensive, and reliable2. GI Bleeding studies are optimally performed with Tc-99m RBCs prepared using the packed cell technique or the UltraTag kit.
Summary and Conclusions3. It is easy to label WBCs with either Tc-99m or In-111. Both preparations involve isolation of the WBCs and incubation with a lipophilic intermediate to effect labeling.4. It is very easy to label red cells with Cr-51. Isolation of RBCs is not required.5. Most labeling procedures can be performed in any laboratory by a person knowledgeable about aseptic technique.