Blood-pool imaging using technetium-99m-labeled liposomes.
This study evaluated two 99mTc-liposome formulations as potential blood-pool agents in comparison with standard 99mTc-red cells and 99mTc-human serum albumin (HSA).


METHODS
Liposomes with no surface modification or coated with polyethylene glycol (PEG) were labeled with 99mTc using the lipophilic chelator, HMPAO. Autologous red cells were labeled with 99mTc using in vitro or in vivo techniques. Technetium-99m-HSA was supplied commercially. Rabbits were injected intravenously with 99mTc-liposomes, 99mTc-red cells or 99mTc-HSA. Static images were acquired and blood samples collected.


RESULTS
Technetium-99m-liposome images showed prominent blood-pool activity compared to lung and liver activities, which were similar to those acquired for 99mTc-red cells, but better than 99mTc-HSA. Heart-to-lung ratios were not significantly different between 99mTc-liposome formulations or for either formulation compared to 99mTc-red cells. The ratios were higher, however, than for 99mTc-HSA. Heart-to-liver ratios were higher for PEG 99mTc-liposomes than they were for neutral 99mTc-liposomes and 99mTc-HSA, but were not significantly different than 99mTc-red cells. Bladder activities for both 99mTc-liposome formulations were 3-6 times lower than for the other agents. PEG 99mTc-liposomes remained in circulation 1.6 times longer than any of the other agents.


CONCLUSIONS
Technetium-99m-liposomes, independent of surface modification, had excellent circulation persistence and in vivo stability when compared to 99mTc-red cells and 99mTc-HSA. PEG 99mTc-liposomes performed better than neutral 99mTc-liposomes due to lower liver background activity. Advantages of PEG 99mTc-liposomes compared to 99mTc-red cells include: (a) only one venipuncture, (b) little exposure to patient's blood, (c) excellent in vitro and in vivo stability and (d) lack of drug interference.
Goins
B
B
Department of Radiology, University of Texas Health Science Center at San Antonio, Texas 78284-7800, USA.
Phillips
W T
WT
Klipper
R
R
D000818:Animals; D004912:Erythrocytes; D015637:Gated Blood-Pool Imaging; D006321:Heart / Q000000981:diagnostic imaging; D007553:Isotope Labeling; D008081:Liposomes / Q000493:pharmacokinetics; D008099:Liver / Q000000981:diagnostic imaging; D008168:Lung / Q000000981:diagnostic imaging; D008297:Male; D015609:Organotechnetium Compounds; D010091:Oximes; D011092:Polyethylene Glycols; D011817:Rabbits; D013667:Technetium / Q000493:pharmacokinetics; D013668:Technetium Tc 99m Aggregated Albumin; D019690:Technetium Tc 99m Exametazime; D014018:Tissue Distribution; D001743:Urinary Bladder / Q000000981:diagnostic imaging
D008081:Liposomes; D015609:Organotechnetium Compounds; D010091:Oximes; D013668:Technetium Tc 99m Aggregated Albumin; D019690:Technetium Tc 99m Exametazime; D011092:Polyethylene Glycols; D013667:Technetium