Usefulness of contrast kinetics for predicting and monitoring tissue changes in muscle following thermal therapy in long survival studies

Abstract

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 (K trans ) and leakage space (v e ), were correlated to T 2 -weighted MR and histology.Results: Images of K trans and v e 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 v e , whereas the borders of inflammation are shown on K trans . The total lesion extent is relatively stable over the 7 days posttherapy and can be predicted by v e or T 2 -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.

MRI‐based prediction of pulsed high‐intensity focused ultrasound effect on tissue transport in rabbit muscle

“…These results are consistent with observations reported in Cheng et al where a similar region encircling the central coagulative necrosis was labeled “Zone I” for its inflammation. That study suggests that Zone I is broken down and ingested by neutrophils and macrophages and repaired within 1 week . Although we did not study tissue recovery in great detail, our results largely agree with these observations.…”

MRI methods for the evaluation of high intensity focused ultrasound tumor treatment: Current status and future needs

“…Cheng et al used DCE‐MRI to assess delayed effects of HIFU treatment of rabbit thigh muscles. At 40 h and 3 days after treatment, a pronounced ring of inflammatory edema, that was characterized by high K trans values, was observed around the central zone of ablation .…”

“…A significant decrease in tumor K trans was reported after HIFU treatment of subcutaneous rat tumors . Cheng et al performed an extensive analysis of the K trans and v e values in HIFU‐treated rabbit skeletal muscle tissue (Fig. ).…”

A new MRI method, tested in vitro for the assessment of thermal coagulation and demonstrated in vivo on focused ultrasound ablation

“…It is important to try to predict the final size of the coagulated area after completion of the treatment (26)(27)(28), because the full extent of cell death might be clear only days after thermal treatment. An investigation of the value of MEXI in such a prediction is warranted.…”