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Experimental Studies |
1 From the Department of Radiology, Harvard Medical School and Brigham and Women’s Hospital, 221 Longwood Ave, LMRC 007C, Boston, MA 02115 (N.M., H.M., N.V., K.H.); and Amersham Health, Oslo, Norway (S.L.F., H.R.). From the 2002 RSNA scientific assembly. Received December 18, 2002; revision requested February 7, 2003; final revision received June 14; accepted July 15. Supported by NIH grants CA 46627 and CA 089017. Address correspondence to N.M. (e-mail: njm@bwh.harvard.edu).
PURPOSE: To evaluate by using in vivo magnetic resonance (MR) imaging the functionality of a liposomal paramagnetic contrast agent with T1 relaxivity that rapidly and markedly increases at temperatures above the gel-to-liquid crystalline phase transition temperature (Tc) of the liposome membrane.
MATERIALS AND METHODS: Liposomal gadolinium diethylenetriaminepentaacetic acid bis(methylamide) was injected intravenously at a dose of 0.4 or 1.2 mL (containing 10 or 30 µmol of gadolinium, respectively) per kilogram of body weight shortly before the application of focused ultrasound in liver (seven rabbits) or kidney (three rabbits). VX2 tumors had been implanted in liver in four of the rabbits. Eighteen locations in liver (13 in normal tissue, five in tumor) and 12 locations in kidney were sonicated. MR thermometry was performed during sonications. Signal intensity enhancement was evaluated on T1-weighted images acquired after the tissue cooled, and enhanced zones were compared with isotherms at Tc of the liposome membrane (approximately 57°C) by using Bland-Altman analysis. In liver, enhanced zones also were compared with areas of histologically verified thermal damage. The threshold temperature of enhancement at T1-weighted imaging was verified by monitoring the signal intensity increase after 10 sonications at varied powers in two locations in normal liver tissue.
RESULTS: Persistent enhancement was observed on T1-weighted images at all sonicated liver locations. In liver, enhanced zones on T1-weighted images were contiguous both with 57°C isotherms (25 measurements; mean difference ± SD, 0.4 mm ± 1.2) and with histologically verified areas of necrosis (seven measurements; mean difference ± SD, 0.1 mm ± 0.9). The threshold temperature of enhancement at T1-weighted imaging in normal liver was 53°–57°C. In kidney, enhanced zones on T1-weighted images did not match the isotherms.
CONCLUSION: The liposomal contrast agent was effective at in vivo MR thermometry in liver but not in kidney.
© RSNA, 2004
Index terms: Animals • Magnetic resonance (MR), experimental studies, 76.1291, 81.1291 • Magnetic resonance (MR), temperature monitoring, 76.12149, 81.12149 • Ultrasound (US), therapeutic, 76.12989, 81.12989
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