Radiopharmacokinetics, renal clearance and dosimetry of 99mTc-MAG3.

BACKGROUND: Technetium-99m-mercaptoacetyltriglycine (99mTc-MAG3) is a radiopharmaceutical for tubular function and can be prepared with 99m-technetium and the ligand Bz-MAG3 (Instituto Nacional de Investigaciones Nucleares, Mexico City). No radiopharmacokinetic parameters have been found for the healthy adult Mexican population with 99mTc-MAG3, prepared with the nationally produced or imported Bz-MAG3 kit. METHODS: The radiopharmacokinetic parameters and the clearance of 99mTc-MAG3 in seven healthy Mexican volunteers were determined by the single- and multi-sample methods. Computer programs were used for the calculations. RESULTS: Using several plasma samples from 0-43 min and the BIEXP program, it was shown that 99mTc-MAG3 follows a two-compartment model of distribution, with an apparent volume in the central compartment Vdcc = 3.8 + 0.7 l, a volume of distribution at steady state Vdss = 6.7 + 1.0 l, T1/2 alpha = 0.07 + 0.02 h-1, T1/2 beta = 0.49 + 0.15 h-1, mean residence time MRT = 0.60 + 0.17 h and clearance = 208 + 57 (ml/min)/1.73 m2. In comparison, the clearance value with a single sample drawn 43 min post-injection and calculated with Tauxe's formula was 193 +/- 59 (ml/min)/m2. CONCLUSIONS: The 15 ml difference between the two methods is neither statistically different (p = 0.11) nor important for routine clinical studies. The single-sample method is recommended because it is reliable and can be done at the same time that the dynamic renal scan is acquired. Estimated absorbed radiation dose was calculated for several organs.

Radiopharmacokinetic data for 99mTc-ABP--a new radiopharmaceutical for bone scanning: comparison with 99mTc-MDP.

Technetium-99m-labeled alendronate is a new radiopharmaceutical for bone scanning developed under strict quality control at the INNSZ. The purpose of this work was to compare the radiopharmacokinetic data and the dosimetry of 99mTc-ABP and 99mTc-MDP in 10 volunteers, after it was tested in laboratory animals. 99mTc-ABP has shorter mean residence time (MRT) and t 1/2 beta; is less protein bound; has a higher renal clearance; smaller Vdss, and similar bone uptake at 1 and 2 h. 99mTc-ABP gives less radiation exposure to the patient with a 740 MBq dose, and the quality of the bone scan is excellent. 99mTc-ABP is a better radiopharmaceutical than 99mTc-MDP for bone scanning.

[99m-Tc alendronate as a new option in bone gammagraphy]. / El 99mTc-alendronato como nueva opción en la gammagrafía ósea.

OBJECTIVE: To compare the quality of bone scans obtained with 99mTc-ABP, a new radiopharmaceutical, and 99mTc-MDP. MATERIAL AND METHODS: A comparative study within subjects was done in nine healthy volunteers, 5 female and 4 male, aged 23 to 39 years. The dose for both radiopharmaceuticals was 740 MBq; radiopharmacokinetic parameters were determined and a whole body bone scan was taken with a MultiSpect 2 gamma camera two hours post administration with a wash-out period of 72 hours between preparations. The images were independently evaluated by three nuclear medicine physicians by drawing of regions of interest (ROIs) on vertebrae, ribs, femur, sternum, joints and skull. Ratios bone/soft tissue were obtained drawing ROIs on several bones. The kappa test and the Wilcoxon rank test were used for statistical comparisons. RESULTS: The agreement on the quality of the images with Tc-ABP and Tc-MDP was fair (kappa 0.4). The femur/soft tissue ratio had a normal distribution and the Wilcoxon test showed no statistical difference between preparations. CONCLUSIONS: Even though bone uptake was higher and faster with Tc-ABP, the quality of the scans obtained with either radiopharmaceutical was similar. We recommend the use of Tc-ABP as a routine bone scan agent because of its less radiation exposure to the patient.

Technetium-99m-alendronate: a new radiopharmaceutical for bone scanning.

The purpose of this paper is to report the preparation of a new technetium-99m-radiopharmaceutical for bone scanning. The chelating agent for 99mTc is a new bisphosphonate, alendronate, 4-amino-1-hydroxy-butylidene-1, 1-bisphosphonate (ABP) used as a treatment for osteoporosis. ABP, because of its amino group, seems to be better suited to form a strong and stable complex with technetium-99m and therefore might be better than 99mTc-etidronate (HEDP) or 99mTc-medronate (MDP) for bone scanning. A sterile dry kit containing APB, a reducing agent and a stabilizer was prepared. The parameters studied were molar concentrations, pH, shelf life, labeling efficiency and radiochemical purity. The oven dried sterile kit was formulated with 5 mg ABP, 0.25 mg stannous fluoride and 0.025 mg gentisic acid at pH 2.5-3.5. The labeling efficiency with 20-1500 MBq of pertechnetate (99mTcO4-) was over 95% at room temperature and was stable for 5 h. Technetium-99m-alendronate was tested in two rabbits and it proved to be a promising new radiopharmaceutical for bone scanning. Work is underway to study 99mTc-ABP biodistribution in a statistically significant number of laboratory animals and, later on, to determine radiopharmacokinetic parameters in normal volunteers.

[Interobserver variation in region-of-interest drawing in computerized gammagraphy]. / Variabilidad interobservadores al delimitar regiones de interés en gamagramas computarizados.

BACKGROUND: Nuclear medicine uses computerized scintillation cameras for scan processing. For the radio-renogram, the main objective is to observe the passage of radionuclides through the kidneys during a given time. The new software automatically provides data of the dynamic studies, but there is one step (the drawing of regions of interest, ROI) handled by an operator. With the ROI drawings the computer integrates their radioactivity and displays it as time/activity curves, and calculates the Tmax (time to achieve maximal activity) and the T1/2 (time to eliminate half of the Tmax) of each kidney. OBJECTIVE: To evaluate inter-observer variability in drawing the ROI on renal scans. MATERIAL AND METHODS: Four observers with at least seven years of experience in the procedure drew independently the ROI of 38 renograms of 20 patients (two transplants) to obtain the Tmax and T1/2. The interobserver CV was calculated for the Tmax and the T1/2 of the 38 scans. RESULTS: Globally the interobserver variability was larger for T1/2 than for Tmax. There were four scans with small differences in Tmax and/or T1/2 but which lead to inter-observer discrepancies in the classification (normal/abnormal). The partition of the scans in three groups (1 = Tmax and T1/2 normal; 2 = only Tmax normal; 3 = both abnormal) showed significant intergroup differences in the interobserver variability (Kruskal-Wallis p = 0.032) which were caused by the larger variability in group 2 (6 of 11 scans with CV > 4%) than in the other groups (none with CV > 4%). CONCLUSIONS: 1. The interobserver discrepancies in classification were observed only in cases with parameters slightly abnormal (8-9 min in Tmax, 15-20 min in T1/2). 2. We have no explanation for the larger interobserver variability of the Tmax in group 2 study of intraobserver variability in these same four observers may help in gaining insight to some of the observations in this study.