Routine application of fractionated HMPAO stored at -70 degrees C for WBC scintigraphy.

The radiochemical purity of 99mTc-HMPAO prepared from fractions of reconstituted HMPAO stored at -70 degrees C and its application in the radiolabeling of human granulocytes was investigated. Upon reconstitution of a vial of HMPAO with 1 ml of saline and subsequent freezing at -70 degrees C, small fractions were obtained on each of four consecutive days with the vial being refrozen after each dispensing. Following radiolabeling of the HMPAO fractions with pertechnetate, mean radiochemical purity results met or exceeded manufacturers' specifications for the radiopharmaceutical on each of the four days. Imaging with radiolabeled granulocytes using 99mTc-HMPAO prepared by this technique resulted in high quality clinical studies. These results demonstrate that a vial of HMPAO can be fractionated, after storage at -70 degrees C with no loss of clinical utility for radiolabeling granulocytes and considerable cost savings.

Chromium-51 labeling of sheep red blood cells.

The failure of sheep red blood cells (RBCs) labeled with Chromium-51 (Cr-51) using the ascorbic acid technique to act as a suitable intravascular marker of blood volume in a septic sheep model prompted us to investigate the technique of radiolabeling sheep erythrocytes with this isotope. Consequently, we studied thirteen sheep in which the labeling efficiency of Cr-51 as sodium chromate and hemoglobin typing was determined for each animal. Mean Cr-51 labeling efficiency of sheep RBCs was 67.5% (n = 13). Although 5 of the 13 sheep were discovered to have two types of hemoglobin (Hb) as determined by electrophoresis, overall labeling efficiency of sheep RBCs was determined to be independent of the type of hemoglobin present. However, when two types of Hb were present (Hb-A and Hb-B), Cr-51 had a higher affinity for Hb-B (80%) than Hb-A (20%) even though both Hb types are present in similar proportions (Hb-A = 53%, Hb-B = 46%). The results of this study indicate that sheep RBCs express a lower labeling efficiency for Cr-51 than do human RBCs and that Cr-51 has a higher affinity for Hb-B than for Hb-A when both hemoglobin types are present. This difference is noteworthy when interpreting Cr-51 RBC data in experimental sheep models. Furthermore, caution should be exercised when extrapolating established human protocols to animal models.

In vivo red blood cell compatibility testing using indium-113m tropolone-labeled red blood cells.

In vivo radionuclide crossmatch is a method for identifying compatible blood for transfusion when allo- or autoantibodies preclude the use of conventional crossmatching techniques. A technique for labeling small volumes of donor red blood cells with [113mIn]tropolone is reported. The use of 113mIn minimizes the accumulation of background radioactivity and the radiation dose especially so when multiple crossmatches are performed. Labeling red cells with [113mIn]tropolone is faster and easier to perform than with other radionuclides. Consistently high labeling efficiencies are obtained and minimal 113mIn activity elutes from the labeled red blood cells. A case study involving 22 crossmatches is presented to demonstrate the technique. The radiation dose equivalent from 113mIn is significantly less than with other radionuclides that may be used to label red cells.

Polymorphonuclear leukocytes labeled with technetium-99m HMPAO. A potential bone marrow imaging agent.

A case of multifocal avascular necrosis of the bone complicating systemic lupus erythematosis is presented in which the extent of involvement was incidentally identified by Tc-99m HMPAO leukocyte imaging. Leukocytes labeled with Tc-99m HMPAO may be an excellent bone marrow imaging agent.