A new versatile MR-guided high-intensity focused ultrasound (HIFU) device for the treatment of musculoskeletal tumors

High-intensity focused ultrasound-a needleless management for osteoid osteoma: a systematic review

Osteoid osteoma is one of the most frequent benign musculoskeletal neoplasm. Radiofrequency ablation is the method of choice for non-conservative treatment of osteoid osteoma. Recently, high-intensity focused ultrasound (HIFU) has been proposed as a safer option. The objective of this study is to review the efficacy and side effects of HIFU in the management of osteoid osteoma. A comprehensive search was conducted in PubMed, Science Direct, and Clinical Key until June 30, 2022. Demographic data, baseline characteristics, success rates, pre- and post-procedure pain scores, recurrences, and complications were recorded. Eleven studies were included in this systematic review. Pooled analysis that involved 186 subjects resulted in an overall success rate of 91.94%. Recurrence was reported in two studies, in which it occurred in 4/177 (2.26%) subjects. Skin burn was found in 1 (0.54%) patients. No major or other complications were reported. Three studies compared the success rate of HIFU and RFA. Success rate was slightly higher in the RFA group with insignificant difference (p = 0.15). High-intensity focused ultrasound showed promising results. It offers a safer treatment approach for osteoid osteoma, especially in children, and can be considered for recalcitrant cases after RFA. Nonetheless, more studies are expected in the future.

Magnetic Resonance Acoustic Radiation Force Imaging (MR-ARFI) for the monitoring of High Intensity Focused Ultrasound (HIFU) ablation in anisotropic tissue

OBJECTIVE

We introduce a non-invasive MR-Acoustic Radiation Force Imaging (ARFI)-based elastography method that provides both the local shear modulus and temperature maps for the monitoring of High Intensity Focused Ultrasound (HIFU) therapy.

MATERIALS AND METHODS

To take tissue anisotropy into account, the local shear modulus μ is determined in selected radial directions around the focal spot by fitting the phase profiles to a linear viscoelastic model, including tissue-specific mechanical relaxation time τ. MR-ARFI was evaluated on a calibrated phantom, then applied to the monitoring of HIFU in a gel phantom, ex vivo and in vivo porcine muscle tissue, in parallel with MR-thermometry.

RESULTS

As expected, the shear modulus polar maps reflected the isotropy of phantoms and the anisotropy of muscle. In the HIFU monitoring experiments, both the shear modulus polar map and the thermometry map were updated with every pair of MR-ARFI phase images acquired with opposite MR-ARFI-encoding. The shear modulus was found to decrease (phantom and ex vivo) or increase (in vivo) during heating, before remaining steady during the cooling phase. The mechanical relaxation time, estimated pre- and post-HIFU, was found to vary in muscle tissue.

DISCUSSION

MR-ARFI allowed for monitoring of viscoelasticity changes around the HIFU focal spot even in anisotropic muscle tissue.

Advanced liposome and polymersome-based drug delivery systems: Considerations for physicochemical properties, targeting strategies and stimuli-sensitive approaches

Liposomes and polymersomes are colloidal vesicles that are self-assembled from lipids and amphiphilic polymers, respectively. Because of their ability to encapsulate both hydrophilic and hydrophobic therapeutics, they are of great interest in drug delivery research. Today, the applications of liposomes and polymersomes have expanded to a wide variety of complex therapeutic molecules, including nucleic acids, proteins and enzymes. Thanks to their chemical versatility, they can be tailored to different drug delivery applications to achieve maximum therapeutic index. This review article evaluates liposomes and polymersomes from a perspective that takes into account the physical and biological barriers that reduce the efficiency of the drug delivery process. In this context, the design approaches of liposomes and polymersomes are discussed with representative examples in terms of their physicochemical properties (size, shape, charge, mechanical), targeting strategies (passive and active) and response to different stimuli (pH, redox, enzyme, temperature, light, magnetic field, ultrasound). Finally, the challenges limiting the transition from laboratory to practice, recent clinical developments, and future perspectives are addressed.

Monitoring MR-guided high intensity focused ultrasound therapy using transient supersonic shear wave MR-elastography

Objective.The aim of the paper is to propose an all-in-one method based on magnetic resonance-supersonic shear wave imaging (MR-SSI) and proton resonance frequency shift (PRFS) to monitor high intensity focused ultrasound (HIFU) thermal ablations.Approach.Mechanical properties have been shown to be related to tissue damage induced by thermal ablations. Monitoring elasticity in addition to temperature changes may help in ensuring the efficacy and the accuracy of HIFU therapies. For this purpose, an MR-SSI method has been developed where the ultrasonic transducer is used for both mechanical wave generation and thermal ablation. Transient quasi-planar shear waves are generated using the acoustic radiation force, and their propagation is monitored in motion-sensitized phase MR images. Using a single-shot gradient-echo echo-planar-imaging sequence, MR images can be acquired at a sufficiently high temporal resolution to provide an update of PRFS thermometry and MR-SSI elastography maps in real time.Main results.The proposed method was first validated on a calibrated elasticity phantom, in which both the possibility to detect inclusions with different stiffness and repeatability were demonstrated. The standard deviation between the 8 performed measurements was 2% on the background of the phantom and 11%, at most, on the inclusions. A second experiment consisted in performing a HIFU heating in a gelatin phantom. The temperature increase was estimated to be 9 °C and the shear modulus was found to decrease from 2.9 to 1.8 kPa, reflecting the gel softening around the HIFU focus, whereas it remained steady in non-heated areas.Significance.The proposed MR-SSI technique allows monitoring HIFU ablations using thermometry and elastography simultaneously, without the need for an additional external mechanical exciter such as those used in MR elastography.

High Intensity Focused Ultrasound for Treatment of Bone Malignancies-20 Years of History

High Intensity Focused Ultrasound (HIFU) is the only non-invasive method for percutaneous thermal ablation of tissue, with treatments typically performed either under magnetic resonance imaging or ultrasound guidance. Since this method allows efficient heating of bony structures, it has found not only early use in treatment of bone pain, but also in local treatment of malignant bone tumors. This review of 20 years of published studies shows that HIFU is a very efficient method for rapid pain relief, can provide local tumor control and has a very patient-friendly safety profile.