T1 relaxivity of core-encapsulated gadolinium liposomal contrast agents--effect of liposome size and internal gadolinium concentration.
OBJECTIVE
Long circulating core-encapsulated gadolinium (CE-Gd) liposomal nanoparticles that have surface conjugated polyethylene glycol are a promising platform technology for use as blood pool T1-based magnetic resonance (MR) contrast agents. The objective of this study was to investigate the effect of liposome size and internal (core) Gd concentration on the T1 relaxivity of CE-Gd liposomes.


METHODS
Twelve different liposomal formulations were synthesized and characterized, resulting in a size (50, 100, 200, and 400 nm) and core Gd-concentration (200, 350, and 500 mM) "matrix" of test samples. Subsequently, CE-Gd liposomes were diluted in deionized water (four diluted samples) and molar T1 relaxivity (r1) measurements were performed at 2- and 7-T MR field strengths.


RESULTS
The r1 of CE-Gd liposomes was inversely related to the liposome size. The largest change in r1 was observed between liposomes that were extruded through 50- and 100-nm filter membranes. At both field strengths, the variation in internal gadolinium concentration did not show any significant correlation (alpha < or = 0.05) with r1.


CONCLUSIONS
The size of CE-Gd liposomal nanoparticles significantly affects the T1 relaxivity. An inverse relation was observed between liposome size and T1 relaxivity. The T1 relaxivity did not change significantly with core Gd concentration over the measured concentration range.
Ghaghada
Ketan
K
Department of Radiology, Box 3808, Duke University Medical Center, Durham, NC 27710, USA.
Hawley
Catherine
C
Kawaji
Keigo
K
Annapragada
Ananth
A
Mukundan
Srinivasan
S
D003287:Contrast Media / Q000737:chemistry*; D004337:Drug Carriers / Q000737:chemistry*; D005682:Gadolinium / Q000737:chemistry*; D007089:Image Enhancement / Q000379:methods*; D008081:Liposomes / Q000737:chemistry*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D010316:Particle Size; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D003287:Contrast Media; D004337:Drug Carriers; D008081:Liposomes; D005682:Gadolinium
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