MRgFUS is a non-invasive treatment that combines high intensity focused ultrasound tissue ablation with MRI for image guidance. During treatment, ultrasound waves are emitted from a phased array transducer and focused to a small ellipsoid-shaped spot known as a sonication. Sonications can range from 1 to 10-mm in diameter and 10 to 50-mm in length. Multiple sonications, each lasting 15 to 25-seconds in duration, are needed to ablate the entire volume of targeted tissue. The focused ultrasound energy delivered to the lesion during each sonication is sufficient to cause the tissue temperature to exceed the thermal dose threshold required for coagulative necrosis.
Magnetic resonance images are used for treatment planning and ablation feedback. T2-weighted images are used to evaluate the tumor and surrounding anatomy and guide the physician in defining the treatment volume. MR thermal images (gradient echo) are taken during every sonication. These images show the relative changes in temperature during the treatment. These images also allow the physician to confirm that the heat was delivered to the targeted region and that the thermal dose threshold was reached.
The MRgFUS system keeps track of all regions that have reached the thermal dose threshold during ablation. Once the entire tumor has been ablated, the patient is given contrast agent and post-contrast MR images are used to evaluate the non-perfused volume.
No incisions are required for MRgFUS and there is no ionizing radiation. Patients are able to have multiple treatments for large lesions and for symptom recurrence due to new lesions. For applications in which patients are able to undergo the ablation with conscious sedation (such as bone, breast and fibroids), recovery time is generally less than an hour after the outpatient procedure is completed.
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