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Rationale and Objectives An in vivo evaluation of a new trimodality breast localization marker was performed with magnetic resonance imaging (MRI), ultrasound (US), x-ray, and histopathology. The evaluation of the marker in animal tests should help define its utility for surgical biopsy localization in humans. Materials and Methods Five rabbits were used and sacrificed at 2 days, 1 week, 2 weeks, 4 weeks, and 7 weeks after marker implantation. The marker placement and tissue biopsies were performed under US guidance. MRI, US, and x-ray imaging were performed to monitor the contrast of the marker, track marker migration. The biologic compatibility of the marker was demonstrated by histopathologic analysis. Results The contrast of the marker was clear and stable on each imaging modality over the 7-week study period. Acute inflammation was visible by 2 days after marker injection, with evidence of granulation tissue and angiogenesis at 2 weeks after implantation. A modest degree of chronic inflammation and angiogenesis remained evident at 4 weeks after procedure, and fibrosis persisted 7 weeks after procedure with no further tissue changes. These results suggest that the new marker is biocompatible and can remain interstitial for up to 7 weeks. Furthermore, very little marker migration was observed. On removal, the marker was found to be mechanically stable. Conclusion This in vivo animal study demonstrates that the new marker may be appropriate for in vivo human testing and as an alternative to traditional wire localization currently used for breast surgery.

Purpose To investigate Gd-DTPA kinetics as predictors of histopathological changes following focused ultrasound (FUS) thermal ablation for improved planning and assessment. Materials and Methods Twenty-nine FUS lesions were created in the thigh muscle of eight rabbits under MR-guidance at 1.5 Tesla. Three rabbits were killed at four hours; and 11 lesions were analyzed with histopathology. Temperature-sensitive MRI using proton-resonant frequency-shift was used for time-dependent temperature measurements. Analysis of the uptake kinetics of Gd-DTPA was performed after Gd-DTPA injection, within 20 minutes after heating and again at two hours after heating. The resulting kinetic maps, permeability (Ktrans) and leakage space (ve), were correlated to peak temperatures, T2-weighted MR, and histopathology. Results Images of Ktrans and ve reveal regions of histopathological change not visible on conventional post-therapy MR. At early times after heating, ve predicts the area of injury more accurately than T2 (7 ± 2% vs. 25 ± 6% underestimation). A circular region of extensive structural/vascular disruption is indicated only on Ktrans maps. The sharp decrease in Ktrans at the boundary of this region occurs at 47.5 ± 0.5°C, and may be a better estimate of cell death than the conventional method of temperature threshold (55°C for coagulation) used in therapy planning. Conclusion Our results suggest Gd-DTPA kinetics can predict different histopathological changes following FUS ablation and may be valuable for early prediction. J. Magn. Reson. Imaging 2003;18:585–598. © 2003 Wiley-Liss, Inc.

The purpose of this experiment was to use MRI to monitor microwave heating and thermal damage of brain tissue in vivo. Interstitial microwave antennas were implanted into the cerebral hemispheres of seven anesthetized rabbits. Variable power of 30 to 100 W was applied for periods of 5 to 15 minutes and tissue temperature was monitored continuously. MR images were obtained throughout the procedure at 20-second intervals, using a spoiled gradient-echo sequence, without significant artifact. Magnitude, phase, and complex difference images all demonstrated temperature-related signal changes during heating. The findings were better visualized on the phase and complex difference images. Phase difference image analysis revealed an approximately linear relationship between phase change and temperature. Post-treatment thermal lesions measured up to 2.0 cm in size on pathologic specimens and exhibited a zonal pattern on spin-echo MR images.

Objective. To investigate the effects of chronic calcium pyrophosphate dihydrate (CPPD) synovitis on the development of osteoarthritic (OA) lesions in an animal model. Methods. OA was induced in the right knees of 30 male New Zealand white rabbits by partial lateral meniscectomy and section of the fibular collateral and sesamoid ligaments (PLM/LS), followed by 8 weekly intraarticular (IA) injections of 1 mg (low-dose) or 10 mg (high-dose) of CPPD crystals in 3 sets of experiments (10 rabbits each). The contralateral left knees served as controls: experiment 1 PLM/LS alone, experiment 2 8 weekly IA injections of CPPD crystals alone, and experiment 3 sham surgery plus 8 weekly IA injections of CPPD crystals. Results. At 8 weeks, repeated IA injections of low-dose and high-dose CPPD crystals into meniscectomized right knees resulted in more severe OA than in meniscectomized but noninjected left knees (experiment 1) (P = 0.003 and P = 0.001, respectively). One-fourth of the meniscectomized knees (11 of 40), both CPPD-injected and noninjected, showed embedded synovial cartilage shards. Conclusion. The data demonstrate a worsening effect of chronic CPPD crystal-induced synovitis on experimental OA produced in the rabbit knees by PLM/LS, and support a possible role for CPPD microcrystalline inflammation in the progression of OA lesions in clinical CPPD crystal deposition disease.

Purpose To investigate Gd-DTPA kinetics as indicators of subacute and subchronic histopathological changes following focused ultrasound (FUS) thermal therapy for improved evaluation. Materials and Methods A total of 18 FUS lesions were created in the thigh muscle of five rabbits under magnetic resonance (MR) guidance at 1.5 Tesla. The rabbits were killed at different times: 40 hours, three days, and seven days. All lesions were analyzed histologically. An analysis of the uptake kinetics of Gd-DTPA, injected within two hours postheating and before sacrifice, was performed. The resulting kinetic maps, permeability (Ktrans) and leakage space (ve), were correlated to T2-weighted MR and histology. Results Images of Ktrans and ve better differentiate subacute and subchronic changes not visible on conventional MR in the days following therapy and are consistent with the histopathology observed. In particular, the border between nonviable and viable tissue is well demarcated. The extent of damage is best indicated on ve, whereas the borders of inflammation are shown on Ktrans. The total lesion extent is relatively stable over the 7 days posttherapy and can be predicted by ve or T2-weighted MR at early times after heating. Conclusion Our results suggest that Gd-DTPA kinetics can complement conventional MR for improved evaluation of FUS thermal therapy by providing finer differentiation of necrotic states, inflammation, and repair processes. J. Magn. Reson. Imaging 2004;19:329–341. © 2004 Wiley-Liss, Inc.