Thomas J. Herold

Optimal conditions of 99mTc eluate for the radiolabeling of 99mTc-sestamibi

Our nuclear pharmacy has reported that a failed radiochemical purity (RCP) (i.e., RCP < 90%) of 99mTc-sestamibi may be associated with the use of a first elution at later stages from a long-ingrowth time (i.e., > or = 72 h) wet-column generator. The primary purpose of this study was to evaluate the effects of 99mTc eluates from wet- and dry-column generators on the RCP of 99mTc-sestamibi under the above conditions. RCP values were found to be measurably higher and kit failure rates lower with the use of dry-column generator eluate. Using a dry-column generator eluate, Cardiolite kits were prepared with 11.10 GBq of 99mTc at 3, 4, and 5 h postelution and 5.55 GBq at 6, 10, 11, and 12 h postelution. Our data suggest that when 11.10 GBq of 99mTc from a dry-column generator with > or = 72-h ingrowth was used to prepare 99mTc-sestamibi, kit failure started to occur using 99mTc eluate at approximately 4 h postelution. When 5.55 GBq was used to reconstitute the kit, RCP failure began to occur using 99mTc eluate approximately 10 h postelution and wet-column generators; the failure rate can be reduced even further by avoiding the addition of high activities of 99mTc and long elution times.

Generator Eluate Effects on the Labeling Efficiency of 99mTc-Sestamibi

Our nuclear pharmacy noted that 99mTc-sestamibi kits sometimes failed radiochemical purity (RCP) testing (i.e., RCP < 90%). All failed kits had been prepared with eluate from a newly arrived generator (ingrowth time > or = 72 h) which had been eluted > or = 6 h before the kit failure. The effects of 99mTc activity and eluate volume were then investigated to help explain the reason for the low RCP values. Our results demonstrated that higher failure rates of the 99mTc-sestamibi kits were noted when higher activities of 99mTc eluates were added, and the higher failure rates of the kits were associated with lower RCP values. In addition, higher kit failure rate and lower RCP values of the 5.55-GBq kits at 12 h postelution in comparison with the 11.1-GBq kits at 6 h (same eluate volume) indicated that the 99mTc activity and volume had a less detrimental effect on the 99mTc-sestamibi kit preparation than the 99mTc eluate age. The kit failures might be explained by the higher amount of 99mTc and the production of the free radicals during the long ingrowth time prior to generator elution. In conclusion, the use of a first elution from a long-ingrowth time generator at a later stage (i.e., 11.1 GBq at 6 h and 5.55 GBq at 12 h postelution) in preparation of a 99mTc-sestamibi kit is associated with a high rate of kit failure and should therefore be avoided.

Modified radioiodination and quality control methods for [125I]sodiuin iothalamate

[125I]Sodium iothalamate can be prepared by the isotope-exchange method with the use of a contrast medium preparation (i.e. iothalamate sodium injection, USP, 80%). The initial isolation and purification of iothalamate from the contrast medium solution for radioiodination is tedious and time-consuming (i.e. 1 1/2 h for purification and overnight for drying). The new method uses iothalamic acid to replace iothalamate sodium injection as a starting material and reduces the heating time and multiple acid-washing steps during radioiodination to expedite the radiolabelling process. The radiochemical purity (RCP) of [125I]sodium iothalamate obtained from the new method was 98.9 +/- 1.3% (n = 30) versus RCP value of 99.2 +/- 1.0% (n = 25) from the old method with no significant differences between the two groups of RCP values. An RCP chromatographical system to separate and migrate the radiochemical species of [125I]sodium iothalamate from the origin is described in this paper.

Particle-Size and Radiochemical Purity Evaluations of Filtered 99mTc-Sulfur Colloid Prepared with Different Heating Times

Sentinel node lymphoscintigraphy using colloidal particles has become common practice at many institutions. The ideal particle size for colloids such as filtered 99mTc-sulfur colloid (99mTc-FSC) in sentinel node studies is 15–100 nm. It is reported that the use of a reduced heating time during the reconstitution process results in an increased number of smaller particles (<30 nm). However, it is unclear whether these smaller particles (>15 nm) would be of benefit in sentinel node studies. This study sought to better define particle size by using electron microscopy, as well as to evaluate the radiochemical purity (RCP) of 99mTc-FSC at various time points after filtration. Methods: One group of 99mTc-sulfur colloid (99mTc-SC) preparations was reconstituted using the standard heating time of 5 min, and another group was prepared using a reduced heating time of 3 min. The 99mTc-SC preparations were passed through a 0.2-μm filter, and retained filter activity was measured. RCP values were collected at 0, 1, 3, and 6 h after filtration, and the particle sizes were measured at 0 and 6 h after filtration. Results: Average RCP values (± SD) for 99mTc-FSC with 5-min heating were 98.4% ± 3.0% and 98.3% ± 1.8% for 0 h and 6 h, respectively (n = 6). Average RCP values for 99mTc-FSC with 3-min heating were 98.4% ± 4.1% and 96.9% ± 3.1% for 0 h and 6 h, respectively (n = 6). Electron microscopy data showed that median particle sizes for the 3-min heating at 0 and 6 h were 24 and 35 nm, respectively. Median particle sizes for the 5-min heating at 0 and 6 h were 29 and 27 nm, respectively. The proportion of particles within the ideal range for sentinel node lymphoscintigraphy was similar between the heating methods (91.1% for 3-min heating at 0 h and 88.8% for 5-min heating at 0 h, P = 0.1851). Conclusion: Our results indicate that although there are slight significant differences in RCP value, particle size, and particle number for 99mTc-FSC prepared using either a standard or a reduced heating time, both methods produce particles within the optimum range for sentinel node studies.

Trends of Radiopharmaceutical Use at Mayo Clinic Rochester

The field of radiology is continuously changing. The purpose of this study was to identify the effect of technologic advances on nuclear medicine during the past 15 y. Methods: The number of radiopharmaceutical doses dispensed at Mayo Clinic (Rochester, Minnesota) from 1990 through 2004 was tracked. The number of doses was equivalent to the number of scans performed. Results: Since 1990, the number of bone scans decreased by 38%. Brain scans using 99mTc have increased by 166%. The number of cardiac doses dispensed increased 184% from 1990 through 1999 but decreased 3% between 2000 and 2004. The number of lung scans decreased 52% from 1992 through 1999 and increased 66% from 1999 through 2004. The number of kidney scans decreased 67% since 1990. Since its introduction in 1993, the use of 111In-pentetreotide has increased 16-fold. PET data showed a 602% increase in the number of procedures from 2001 through 2004. Conclusion: The number of bone, lung, and kidney scans has decreased because of advances in other imaging modalities. Although the number of cardiac imaging scans increased during most of the study period, the recent rate of growth has declined, possibly because of the availability of alternative procedures such as stress echocardiography. The number of brain and lung scans performed has increased, partially because of the development of new protocols. PET and tumor imaging have shown a substantial increase because of increasing numbers of approved indications and Medicare reimbursement.

Faster and easier radiochemical purity testing for [125I]sodium iothalamate☆

A previous method for determination of the radiochemical purity (RCP) value of [125I]sodium iothalamate uses two paper strips and solvents (total developing time is approximately 2.5 h). To simplify and shorten the RCP testing procedure, our laboratory has developed a single-strip chromatography method that not only distributes free 125I and [125I]sodium iothalamate to different relative front (Rf) locations, but is also faster and easier to perform. RCP of [125I]sodium iothalamate was determined with the use of a 10-cm instant thin-layer chromatography strip impregnated with polysilicic acid gel (ITLC-SA) as the solid phase, and a mobile phase of 2-butanol:acetic acid:water (140:2.5:70, v/v). By using autoradiography and counting the strip segments in a gamma counter, our results indicated that free 125I migrated to Rf = 0.89-1.00 while the [125I]sodium iothalamate moved to Rf = 0.44-0.67. The total developing time for the single-strip ITLC-SA system was approximately 1 h.