Update on Clinical Magnetic Resonance-Guided Focused Ultrasound Applications

Abstract

In this review, several clinical applications of magnetic resonance (MR)-guided focused ultrasound (FUS) are updated. MR-guided FUS is used clinically for thermal ablation of uterine fibroids and bone metastases. Thousands of patients have successfully been treated. Transcranial MR-guided FUS has received CE certification for ablation of deep, central locations in the brain. Thermal ablation of specific parts of the thalamus can result in relief of the symptoms in a number of neurological disorders. Several approaches have been proposed for ablation of prostate and breast cancer and clinical trials should show the potential of MR-guided FUS for these and other applications.

Keywords: Bone metastasis pain management; Brain disease; Breast cancer; Focused ultrasound; MR imaging; Thermal ablation prostate cancer; Uterine fibroids.

Figure 1

A 45-year-old woman with a 418-cm³ fibroid experiencing gradually worsening pelvic pressure and hypermenorrhea. A) Sagittal T2-weighted MR image obtained before treatment shows predominantly hypo-intense fibroid (type 1). B) Sagittal contrast-enhanced fat-suppressed MR image before treatment shows homogeneous enhancement of vital fibroid tissue. C) Sagittal contrast-enhanced fat-suppressed MR image acquired immediately following treatment shows a completely non-perfused fibroid tissue. [From Trumm CG, Stahl R, Clevert D-A, et al. Magnetic Resonance Imaging–Guided Focused Ultrasound Treatment of Symptomatic Uterine Fibroids: Impact of Technology Advancement on Ablation Volumes in 115 Patients. Invest Radiol. 2013;48(6):359–365, with permission.]

Figure 2

Images of a 64-year-old woman with iliac bone metastasis from breast cancer. A) Axial computed tomography (CT) image shows the presence of a wide lytic lesion located in the right anterior superior iliac spine (arrows) with evidence of focal cortical erosion causing severe pain (pain severity score, 10). B) Axial T1-weighted sequence acquired following contrast agent injection at the end of the MR-guided FUS treatment shows the presence of some small areas of NPV (arrows) inside the lesion and at the periosteal margin. C) At the 2-month follow-up, axial CT identified the presence of some focal areas of de novo mineralization inside the treated tissue with partial restoration of cortical borders (arows). D) At 3 months post treatment, the lesion showed further de novo remineralization of the ablated tissue (arrows). [From Napoli A, Anzidei M, Marincola BC, et al. Primary pain palliation and local tumor control in bone metastases treated with magnetic resonance-guided focused ultrasound. Invest Radiol. 2013;48(6):351–358, with permission.]

Figure 3

Screenshots from transcranial MR-guided FUS treatment planning workstation. A) Coronal T2-weighted images of the patient in the transcranial MR-guided FUS device. The target of the current sonication is indicated by the blue rectangle. The water filling the space between the patient’s shaved head and the transducer can be seen. B) Pretreatment computed tomography (CT) scan data of the cranium is registered the intra-treatment MRI scans. The cranium is automatically segmented from the CT scan and displayed as a green region on top of the MR images used for treatment planning. Any registration errors can be seen on these images and corrected by the user by using a graphical tool. MR tracking coils integrated into the transducer are used to register the transcranial MR-guided FUS system coordinates with the imaging coordinates. Acoustic models taking into account the patient-specific cranium geometry and density are used to correct for aberrations to the ultrasound beam. C) The beam paths for each phased-array element are superimposed on the images, allowing the user to verify that no beams pass through undesired structures. D and E) Pretreatment contrast-enhanced T1-weighted images, which can be useful for defining tumor margins, acquired the day before treatment can also be registered to the intratreatment images. Axial and sagittal images are also acquired, allowing for treatment planning in three dimensions. F) Sagittal T2-weighted image. [From McDannold N, Clement GT, Black P, Jolesz F, Hynynen K. Transcranial magnetic resonance imaging-guided focused ultrasound surgery of brain tumors: initial findings in 3 patients. Neurosurgery. 2010;66(2):323–332; discussion, with permission.]

Figure 4

A) Color-coded MR thermometry acquired during real-time MR–guided FUS treatment shows a definite area of temperature increase corresponding to >60 °C (red area). B) A contrast-enhanced MRI scan acquired immediately after treatment shows an area of NPV in the exact location of the delivered sonication. The control MRI also shows the absence of rectal wall injuries or unexpected side effects. C) This macroscopic section after radical prostatectomy demonstrates an extensive coagulative necrosis at the site of sonication. D) This microscopic image (haematoxylin and eosin stained) demonstrates tissue necrosis with a peripheral layer of inflammatory infiltrates. [From Napoli A, Anzidei M, De Nunzio C, et al. Real-time Magnetic Resonance–guided High-intensity Focused Ultrasound Focal Therapy for Localised Prostate Cancer: Preliminary Experience. Eur Urol. 2013;63(2):395–398, with permission.]

Figure 5

T1-weighted contrast enhanced subtraction image pretreatment (top) and post-treatment (bottom). In the top image, the tumor (arrow) is clearly identified. In the bottom image, the tumor (arrow) is non-enhancing. The hyper-intense areas in the edges of the treated region are hyperemia. [From Furusawa H, Namba K, Thomsen S, et al. Magnetic Resonance–Guided Focused Ultrasound Surgery of Breast Cancer: Reliability and Effectiveness. J Am Coll Surg. 2006;203(1):54–63, with permission.]