Biodistribution and dosimetry of [(18)F]fluorodeoxyglucose labelled leukocytes in normal human subjects.

SUMMARY: This study was performed in order to assess [(18)F]fluorodeoxyglucose white blood cell ((18)F-FDG WBC) dosimetry in normal human subjects. Using previously reported methods, mixed cell suspensions of autologous leukocytes were prepared from four normal volunteers. Leukocytes were labelled in heparin-saline by incubation with (18)F-FDG at 37 degrees C for 20 min. After washing and resuspension, (18)F-FDG WBCs (225-315 MBq) were administered by intravenous injection. Whole-body imaging was performed at 0.5, 1, 2, 4 and 6 h using a GE Varicam with 511 keV collimation. Blood samples were obtained at corresponding times as well as fractionated urinary collection. Whole-body anterior and posterior images were used for calculation of organ dosimetry. Uptake of (18)F-FDG WBCs occurred predominantly within the reticulo-endothelial system. Plasma activity, urinary excretion (9.9+/-2.3% at 6 h), and brain uptake (1.7+/-0.4%) were consistent with partial elution of (18)F-FDG. Positron emission tomography imaging performed at 5-6 h after injection yielded good quality images of reticulo-endothelial uptake. Whole-body and organ dosimetry for (18)F-FDG WBCs in doses of 225-250 MBq are comparable with reported results for conventional doses of (111)In oxine labelled leukocytes. Further studies of (18)F-FDG WBC as an agent for positron emission tomography imaging of inflammatory disease appear warranted.

Inverse associations between plasma lycopene and other carotenoids and prostate cancer.

Although dietary intake of tomatoes and tomato products containing lycopene has been reported to reduce the risk of prostate cancer, few studies have been done on the relationship between plasma lycopene and other carotenoids and prostate cancer. This case-control study was conducted to investigate the effects of plasma lycopene, other carotenoids, and retinol, as well as alpha- and gamma-tocopherols on the risk of prostate cancer. The study included 65 patients with prostate cancer and 132 cancer-free controls; all of them were interviewed using a standard epidemiological questionnaire at the Memorial Sloan-Kettering Cancer Center from 1993 to 1997. Plasma levels of carotenoids, retinol, and tocopherols were measured by high performance liquid chromatography. An unconditional logistic regression model was used in bivariate and multivariate analyses using Statistical Analysis System (SAS). After adjusting for age, race, years of education, daily caloric intake, pack-years of smoking, alcohol consumption, and family history of prostate cancer, significantly inverse associations with prostate cancer were observed with plasma concentrations of the following carotenoids: lycopene [odds ratio (OR), 0.17; 95% confidence interval (CI), 0.04-0.78; P for trend, 0.0052] and zeaxanthin (OR, 0.22; 95% CI, 0.06-0.83; P for trend, 0.0028) when comparing highest with lowest quartiles. Borderline associations were found for lutein (OR, 0.30; 95% CI, 0.09-1.03; P for trend, 0.0064) and beta-cryptoxanthin (OR, 0.31; 95% CI, 0.08-1.24; P for trend, 0.0666). No obvious associations were found for alpha- and beta-carotenes, retinol, and alpha- and gamma-tocopherols. Our study confirmed the inverse associations between lycopene, other carotenoids such as zeaxanthin, lutein, and beta-cryptoxanthin, and prostate cancer. This study provides justification for further research on the associations between lycopene and other antioxidants and the risk of prostate cancer.

Regulation of the compounding of positron emission tomography drugs.

Controversial aspects of the regulatory framework for compounding drug products used in positron emission tomography (PET) are discussed. The Food and Drug Administration Modernization Act of 1997 (FDAMA), which amends the Federal Food, Drug, and Cosmetic Act (FFDCA), required that FDA establish approval (new drug application [NDA] and abbreviated new drug application [ANDA]) procedures and current good manufacturing practice (CGMP) requirements for PET drugs; this seems to conflict with differentiation between manufacturing and compounding in FFDCA. Compounding by pharmacists is implied in the FDAMA section on PET, but specific mention of "pharmacist" needs to be included. Congress apparently did not intend for compounded PET drugs to be regulated differently from other drugs. Although FDA has waived NDA and ANDA fees for three PET radiopharmaceuticals, revision of FDAMA to exempt PET drug products from regulations placed on manufacturing is needed. Without relief from the current regulations, many academic PET centers are likely to close; this would violate FDAMA's stated intent of making PET available to patients at reasonable cost. Also problematic is FDAMA's prohibition of compounding "regularly or in inordinate amounts" a product that is commercially available; the common PET radiopharmaceutical fludeoxyglucose F 18 injection, for example, is commercially available. A sensible alternative to NDA or ANDA and CGMP requirements would be the enforcement of USP standards for PET drugs by state boards of pharmacy.

18F-FDG labelling of human leukocytes.

Radiolabelled leukocytes are useful for the imaging of inflammation and infection, and 18F-fluorodeoxyglucose (18F-FDG) is known to concentrate in metabolically active cells. We evaluated the feasibility of leukocyte labelling with 18F-FDG using ACD and heparin anticoagulants at 20 degrees C and 37 degrees C, with and without gentle mixing during incubation. With leukocytes (WBC) harvested from 20 ml blood, studies were performed using 18F-FDG in concentrations of 3.7-74 MBq (0.1-2.0 mCi). 18F-FDG WBC stability in platelet-poor plasma was assessed at 1-4 h. Satisfactory labelling efficiency was achieved with incubation in heparin-saline at 37 degrees C for 30 min (62.7+/-1.6%), and was further enhanced by mixing during incubation (78.1+/-3.9%). Cell labelling was predominantly of granulocytes (78.5+/-1.4%). 18F-FDG WBC was relatively stable in platelet-poor plasma for up to 4 h, and no cell staining was observed in viability studies using trypan blue. These results indicate the feasibility of leukocyte labelling with 18F-FDG, providing an approach that may be useful in PET imaging of inflammation and infection.

The relationship between elution time and eluate volume using the Ultra-TechneKow DTE technetium-99m generator.

OBJECTIVE: The new Ultra-TechneKow Dry Ship Top Elute 99mTc generator (UTK-DTE generator; Mallinckrodt Medical, Inc., St. Louis, MO) was devised to facilitate fractionated elution with an ergonomically designed elution shield. Fractionation is accomplished traditionally by visually observing the eluted volume through 2 layers of leaded glass windows located in a lighted elution shield and generator auxiliary shield. The goal of our study was to use elution time to determine the endpoint for obtaining the required volume of 99mTc-eluate from a UTK-DTE generator. METHODS: After triplicate elution at several predetermined elution times, the initial weight of the evacuated collecting vial was subtracted from the total weight after elution to determine the elution volume. RESULTS: A quadratic relationship was established between the eluate volume (v, mL) and elution time (t, s) (v = 0.3594 + 0.1889 t - 0.0009 t2). This equation is suitable for use with the 10-mL elution vial. This formula may not be accurate for the first elution since the UTK-DTE generator is a dry-column generator when shipped. The following elution times were calculated for some commonly eluted volumes: 2 mL (9 s), 4 mL (22 s), 5 mL (28 s), 7 mL (45 s), and 10 mL (88 s). CONCLUSION: Our calculated elution time method can be used to predict the eluate volume from a UTK-DTE generator.

Nuclear pharmacy, Part II: Nuclear pharmacy practice today.

OBJECTIVE: Nuclear pharmacy is a specialty within the profession of pharmacy that focuses on the proper use of radiopharmaceuticals. This article reviews various features of contemporary nuclear pharmacy practice. After reading this article the nuclear medicine technologist should be able to: (a) describe nuclear pharmacy training and certification; (b) discuss nuclear pharmacy practice settings; (c) discuss nuclear pharmacy practice activities; (d) list professional organizations; and (e) describe activities associated with job satisfaction. In addition, the reader should be able to discuss regulatory issues of current concern.

Biodistribution and radiation dosimetry of stabilized 99mTc-exametazine-labeled leukocytes in normal subjects.

UNLABELLED: Labeling leukocytes with 99mTc-exametazime is a validated technique for imaging infection and inflammation. A new radiolabeling technique has recently been described that enables leukocyte labeling with a more stable form of 99mTc-exametazime. A normal value study of stabilized 99mTc-exametazime-labeled leukocytes has been performed, including biodistribution and dosimetry estimates in normal subjects. METHODS: Ten volunteers were injected with stabilized 99mTc-exametazime-labeled autologous leukocytes to study labeled leukocyte kinetics and dosimetry in normal subjects. Serial whole-body imaging and blood sampling were performed up to 24 h after injection. Cell-labeling efficiency and in vivo viability, organ dosimetry, and clearance calculations were obtained from the blood samples and imaging data as well as urine and stool collection up to 36 h after injection. RESULTS: Cell-labeling efficiency of 87.5% +/- 5.1% was achieved, which is similar to or better than that reported with the standard preparation of 99mTc-exametazime. In vivo stability of the radiolabeled leukocytes was also similar to in vitro results with stabilized 99mTc-exametazime and better than previously reported in vivo stability for nonstabilized 99mTc-exametazime-labeled leukocytes. Organ dosimetry and radiation absorbed doses were similar with a whole-body absorbed dose of 1.3 x 10(-3) mGy/ MBq. Urinary and fecal excretion of activity was minimal, and visual assessment of the images showed little renal parenchymal activity and no bowel activity up to 2 h after injection. CONCLUSION: Cell labeling and in vivo stability appear improved compared with the leukocytes labeled with the nonstabilized preparation of 99mTc-exametazime. There are advantages in more cost-effective preparation of the stabilized 99mTc-exametazime and an extended window for clinical usage, with good visualization of abdominal structures on early images. No significant increase in specific organ and whole-body dosimetry estimates was noted compared with previous estimates using nonstabilized 99mTc-exametazime-labeled leukocytes.

Evaluation of macroaggregated albumin particle sizes for use in pulmonary shunt patient studies.

OBJECTIVE: To assess commercial macroaggregated albumin (MAA) reagent kits for compliance with particle-size parameters needed for proper clinical evaluation of pulmonary shunts (right-to-left). DESIGN: Comparative trial. SETTING: Nuclear pharmacy (laboratory setting). PATIENTS AND OTHER PARTICIPANTS: Not applicable. INTERVENTIONS: Minimally, 90% of the particles contained within an MAA reagent kit should be within the 10 to 90 microns range with minimal variation in particle size distribution and as few small particles (i.e., < 10 microns) as possible. Five separate vials from five commercial brands of MAA reagent kits were obtained, and 500 to 517 particles were analyzed for each sample. An additional study was performed on one of the MAA reagent kit brands, using five vials from each of five different lot numbers to determine the variability between lots. MAIN OUTCOME MEASURES: Long axis (maximum, micron), short axis (minimum, micron), and the area (micron 2) of each MAA particle. RESULTS: One MAA brand had the lowest percentage of unacceptable MAA particle sizes and maintained consistent particle sizes between vials. However, the same MAA reagent kit brand showed that only two of five lots had a low percentage of MAA particle sizes below the 10-micron limit. CONCLUSION: Particle sizes varied among the five different brands of MAA reagent kits, as did different lots of the best-performing kit. This variability in particle sizes may affect the accuracy and reproducibility of pulmonary shunt patient studies.

Evaluation of an alternative radiochemical purity testing method for technetium-99m sestamibi.

OBJECTIVE: Our study evaluated the accuracy and reliability of 3 radiochemical purity (RCP) measurement methods of 99mTc-sestamibi. A regular-sized (1.0 cm x 9.0 cm) Whatman 31 ET Chr paper strip (regular 31 ET) also was included in our evaluation because of its ease in handling. METHODS: The miniaturized and regular 31 ET methods were compared with the standard RCP testing method (aluminum oxide-coated plastic thin-layer chromatography [TLC] plate, with > or = 95% ethanol as the developing solvent). A total of 30 experimental runs were performed in triplicate (n = 90) over an RCP range of 82%-98%. The 99mTc-sestamibi preparations were reconstituted purposely to ensure that 50% of the tested samples had RCP values below the 90% limit. RESULTS: The evaluated RCP ranges were 89.9% +/- 6.3%, 91.0% +/- 3.8%, and 91.4% +/- 4.3% for the TLC, miniature 31 ET, and regular 31 ET methods, respectively (n = 30 each). A strong correlation was found between the TLC and miniature 31 ET methods (r = 0.92), as well as between the TLC and regular 31 ET methods (r = 0.94). Both alternative methods tended to overestimate RCP value as determined by the TLC method, especially in an RCP range below 95%. This resulted in a false-positive rate of 27% for the miniature 31 ET method and 33% for the regular 31 ET method. The test/retest reliability was 99% for both the TLC and regular 31 ET methods, and 91% for the TLC and miniature 31 ET methods. CONCLUSION: The miniature and regular 31 ET methods produced a high false-positive rate, which makes them unacceptable for the determination of RCP value of 99mTc-sestamibi.

Comparison of four 1-mL syringes for administering first-pass radionuclide angiography doses.

OBJECTIVE: For optimal imaging in first-pass radionuclide angiography (FPRNA) studies, 1.11 GBq (30 mCi) 99mTc-sestamibi doses are drawn up in volumes of 0.1-0.3 mL. A single bolus injection of this small volume is important to obtain accurate time-activity curves. Because of the small volume and concentrated radioactivity, it is undesirable for study effectiveness and image quality to have a significant amount of residual activity remaining in the syringe after injection. The purpose of this study was to compare the amount of residual activity in 4 different 1-mL syringes. METHODS: Each test syringe (n = 20) was filled with a volume (0.2 mL) of approximately 1.11 GBq (approximately 30 mCi) 99mTc-sestamibi. Initial activity was measured, and the dose was injected back into a vial only once, simulating bolus injection into a patient. The remaining activity was measured, followed by the calculation of percent residual activity. RESULTS: The two 25-G x 5/8-in. permanent needles had a low percent of residual activity, as well as a much sturdier needle for injection. However, one of these syringes is more expensive. CONCLUSION: The results of our comparison studies showed that the syringe with a 25-G x 5/8-in. permanent needle is ideal for FPRNA doses because of its sturdiness, low residual activity, and the quality of the bolus and resulting images.

Comparison of three cold kit reconstitution techniques for the reduction of hand radiation dose.

In the performance of conventional nuclear pharmacy work, personnel usually receive the highest hand radiation dose during reconstitution of 99Tcm-labelled radiopharmaceuticals. This study was conducted to compare the hand radiation doses incurred during the preparation of 99Tcm-labelled radiopharmaceuticals using three different reconstitution procedures: (1) the standard reconstitution method (i.e. withdrawing 99Tcm activity and normal saline [NS] into the same syringe before adding to the cold kit) (standard); (2) an alternative reconstitution procedure using two syringes to add normal saline separately before 99Tcm activity to the cold kit (NS/Tc); and (3) a standard reconstitution procedure using a robotic system (Amercare Syringe Fill Station, model NuMed SFS 3a, Amercare Ltd, Oxon, UK) (robot). Radiation doses were monitored by thermoluminescent dosimeters (Landauer Inc., Glenwood, IL, USA) on the base of the fourth finger (i.e. ring finger) of the non-dominant hand and on the mid-portion of the second finger (i.e. index finger) of the dominant hand. Three sets of ring badges were measured for each procedure, with 10 stimulated or real reconstitutions per set. Two different radiopharmaceutical kits were evaluated: 99Tcm-MDP, as it is the most frequently used radiopharmaceutical in the majority of nuclear medicine departments (all three reconstitution methods; i.e. standard, NS/Tc and robot), and 99Tcm-sestamibi, as it is not only reconstituted with the highest amount of radioactivity but is also the most frequently dispensed radiopharmaceutical in our laboratory (standard and robot). All kits were prepared from an elution vial containing a standardized amount of 99Tcm activity (i.e. 104.4 +/- 3.6 GBq). To each of the cold MDP and sestamibi kits, 20.7 +/- 1.2 GBq and 44.2 +/- 0.7 GBq of 99Tcm activity were added, respectively. Average accumulated radiation doses for 10 reconstitutions to the fingers (non-dominant/dominant) for the preparations of 99Tcm-MDP were as follows: 14.2 +/- 0.9 mSv/2.8 +/- 0.8 mSv (standard), 10.0 +/- 0.6 mSv/2.7 +/- 0.2 mSv (NS/Tc), and 0.6 +/- 0.1 mSv/1.3 +/- 0.1 mSv (robot). For 99Tcm-sestamibi, the average accumulated radiation doses for 10 reconstitutions to the fingers (non-dominant/dominant) were 6.7 +/- 0.7 mSv/4.6 +/- 0.5 mSv (standard) and 1.1 +/- 0.1 mSv/3.1 +/- 0.4 mSv (robot). When compared to the standard reconstitution method, our results show that the NS/Tc method slightly reduced radiation dose to the non-dominant hand, without any significant reduction for the dominant hand. However, the robot has proved to be the most effective method to considerably reduce radiation dose to both hands. A robotic system should be a useful ALARA (as low as reasonably achievable) tool to prepare other high-activity 99Tcm-labelled radiopharmaceuticals, as well as therapeutic and PET radiopharmaceuticals.

Pulmonary function monitoring during adenosine myocardial perfusion scintigraphy in patients with chronic obstructive pulmonary disease.

OBJECTIVE: To determine whether adenosine could be safely administered to patients with chronic obstructive pulmonary disease (COPD) for coronary vasodilatation during perfusion scintigraphy without causing bronchospasm. MATERIAL AND METHODS: The study was divided into two phases. In the monitoring phase, patients with COPD were pretreated with an inhaled bronchodilator (albuterol) and had pulmonary function monitored during the infusion of a graduated dose of adenosine. Eligibility for entry into this phase of the study was determined on the basis of results of pulmonary function testing (PFT) during resting. Once we had shown that adenosine could be safely administered to patients with COPD, an implementation phase was begun. Entry did not require resting PFT, and patients were administered adenosine without monitoring of pulmonary function. Differences between patients with normal pulmonary function or mild COPD and those with more severe COPD were analyzed statistically. RESULTS: Of 94 patients entered into the monitoring phase, none had obvious bronchospasm. The dosage of adenosine was reduced in four patients because of a decrease in forced expiratory volume in 1 second (FEV1) of 20% in comparison with baseline (FEV1 before administration of albuterol). The mean FEV1 decreased slightly from 1.83 L after administration of albuterol to 1.78 L during the maximal adenosine dose. Patients with a remote history of asthma, positive result of a methacholine challenge test, or mild COPD (FEV1 60 to 80% of the maximal predicted value for age) did not differ significantly in their response to infusion of adenosine from those with moderate or severe COPD (FEV1 30 to 59% of the maximum predicted for age). Of 117 patients in the implementation phase, 2 had bronchospasm during infusion of adenosine that was quickly terminated by stopping the administration in one patient and reducing the dose of adenosine in the other. CONCLUSION: This study shows that adenosine can be safely administered intravenously to selected patients with known or suspected COPD to produce coronary vasodilatation for myocardial perfusion imaging. Patients who are within the guidelines established for this study should be considered for adenosine coronary vasodilatation with use of bronchodilator pretreatment, a graduated dose of adenosine, and regular chest auscultation during the infusion.

Effects of alternative reconstitution procedures on the labelling efficiency and in vitro stability of 99Tcm-labelled radiopharmaceuticals.

Adding normal saline (NS) separately before 99Tcm-sodium pertechnetate to MDP cold kits has been shown to reduce substantially the radiation dose to the hand. A similar dose reduction will probably prove to be valid with the preparation of most other 99Tcm-labelled radiopharmaceuticals. However, it is unknown how this altered reconstitution procedure may affect the labelling efficiency and in vitro stability of the 99Tcm-labelled radiopharmaceuticals. We have evaluated the effects on the labelling efficiency and in vitro stability of 99Tcm-labelled MDP, mertiatide and sestamibi reconstituted with three different methods: adding normal saline before 99Tcm activity (NS/Tc); adding 99Tcm activity before normal saline (Tc/NS); and the standard reconstitution method of adding both 99Tcm activity and normal saline together. The labelling efficiency and in vitro stability were evaluated by measuring the radiochemical purity of each radiopharmaceutical tested at 0, 1, 3, 6, 12 (except 99Tcm-MDP) and 24 h after reconstitution. For 99Tc-mertiatide, there was a very slight difference in the labelling efficiency, mostly due to the Tc/NS method being approximately 0.29% lower across time post-reconstitution than the standard method. For 99Tcm-labelled MDP and sestamibi, there were no differences between the three methods in terms of labelling efficiency and in vitro stability. In conclusion, both alternative methods (i.e. NS/Tc and Tc/NS) appear not to have any detrimental effect on the labelling efficiency and in vitro stability of the 99Tcm-labelled radiopharmaceuticals that we tested. However, of the two alternative kit reconstitution methods, we recommend the NS/Tc method, since it may reduce the hand radiation dose.

Practical methods for reducing radioactive contamination incidents in the nuclear cardiology laboratory.

OBJECTIVE: The purpose of this study was to determine the extent and cause of radioactive contamination in our nuclear cardiology laboratory, and to develop possible solutions to minimize future occurrence. METHODS: We conducted a retrospective review to determine the underlying causes of the 15 minor radioactive contamination events that have occurred in the exercise areas of our laboratory since 1986. Of the 15 documented events, 8 were caused by failure of intravenous apparatus and 7 were due to syringe mishandling. Based on a staff questionnaire, we determined the most prevalent causes of radioactive contamination. Other than problems associated with intravenous setup, the causes were lack of experience by the individual performing the injection, followed closely by radioactive syringe disposal problems, injection technique, and unclear designation of duties during the exercise procedure. RESULTS: Based on these findings, we formulated a 4-part plan: a training program; a closely inspected intravenous apparatus; a mobile radioactive waste container; and a clear designation of duties for personnel to be included in the exercise procedure protocol. CONCLUSION: We have implemented a sensible and practical plan for reducing radioactive contamination, which is currently being evaluated.

Sensible approaches to avoid needle stick accidents in nuclear medicine.

OBJECTIVE: Needle sticks are a continuous concern in the health care environment because of the prevalence of bloodborne pathogens in today's society. Radioactive contamination is another concern with needle sticks during nuclear medicine and nuclear pharmacy procedures. In our institution, substantial efforts have been made to prevent needle sticks, but they still occur occasionally. The purpose of this project was to analyze different practices and products to determine the best protocol in an effort to avoid further needle sticks. METHODS: The nuclear medicine technologists were surveyed to determine how many needle sticks have occurred and the situation behind each occurrence. Using our initial survey, the circumstances involved in each incident were reviewed, suggestions considered, and various means of protection analyzed. Five options were presented in a second survey. RESULTS: The results of the second survey showed that technologists favored the newly designed needle-capping blocks for preventing needle sticks in their daily routine procedures. CONCLUSION: The newly designed needle-capping block is best suited for both nuclear medicine and nuclear pharmacy laboratories. We will continue to monitor the effectiveness of this new approach in preventing needle sticks.

The use of human glutathione S-transferase A1 in the detection of cystic fibrosis liver disease.

OBJECTIVE: To determine the value of serum human glutathione S-transferase A1 (hGST A1) in the detection of cystic fibrosis liver disease (CFLD). METHODS: Sixty-three children (aged 0.5-16 years) with cystic fibrosis (CF) were screened prospectively for evidence of hepatobiliary abnormalities between February 1993 and February 1996. Comparison was made between clinical examination, abdominal ultrasonic scan, measurement of conventional liver enzymes (LFTs) and serum hGST A1 concentration in the detection of hepatobiliary abnormalities in children with CF. RESULTS: The 5-95% concentration of serum hGST A1 was 1.7-4.27 micrograms L-1 for the control group. The hGST A1 levels in the CF patients were significantly higher than in the non-CF group. Thirty-eight (60%) children had detectable hepatobiliary abnormalities. Ultrasound scanning detected the highest number of abnormalities (41%), followed by hGST A1 (30%). The presence of clinical liver disease was found in 19% of the children. The estimated sensitivities of detecting CFLD by clinical method, ultrasound scan, serum hGST A1, and LFTs would be 32%, 68%, 50% and 16%, respectively. CONCLUSIONS: Serum hGST A1 measurement increases the sensitivity of detecting hepatic abnormalities when included with clinical and ultrasound evaluation although, in some cases with advanced liver disease, serum hGST A1 may be normal. Conventional liver enzyme tests add little information in the detection of CF liver disease.

Activated charcoal as a potential radioactive marker for gastrointestinal studies.

The scintigraphic measurement of colonic transit is currently performed using 111In ion exchange resin pellets delivered to the colon in a capsule coated with a pH sensitive polymer, methacrylate, which dissolves in the distal ileum. However, in the USA, this requires an investigational drug permit. Our aim was to evaluate the in vitro binding characteristics of activated charcoal in milieus that mimicked gastric and small intestinal content. The in vitro incubation of activated charcoal was performed with Na99Tc(m)O4, 99Tc(m)-DTPA, 111InCl3, 111In-DTPA, 201TlCl and 67Ga-citrate in the pH range 2-4 and pH 7.2 at 37 degrees C. We estimated the association of radiopharmaceuticals with the activated charcoal over a 3 h in vitro incubation. With the exception of 67Ga-citrate, the association of activated charcoal with the other radiopharmaceuticals was approximately 100% throughout the 3 h incubation. In conclusion, activated charcoal appears to adsorb avidly with common radioisotopes, and appears promising as an alternative to resin ion exchange pellets used for the measurement of gastrointestinal transit by scintigraphy.