Ultrasound in Medicine and Biology最新文献

Objective: Alternative coupling baths for transcranial MR-guided focused ultrasound (tMRgFUS) procedures have been investigated for the purpose of improving image quality. This study characterizes the physical properties and assesses the cavitation properties of an improved coupling media consisting of poly(methacrylic acid)-coated iron oxide nanoparticles synthesized with optimized Fe³⁺ to Fe²⁺ molar ratios for improved magnetic properties and purified with tangential flow filtration for improved manufacturability.

Methods: A 380 mL volume of 73 mM Fe iron-based coupling medium (IBCM) was synthesized and diluted into 4 concentrations of interest (3.5, 7, 17.5 and 35 mM Fe) and characterized to determine their physical properties. Thereafter, cavitation thresholds (pressure at which probability of cavitation = 0.5) were determined under histotripsy parameters (<1% duty cycle, <20 μs duration, single-cycle pulses) with a 500 kHz transducer at peak negative pressures ranging from 0 to 35 MPa to determine the acoustic feasibility of the coupling media.

Results: The IBCM produced in this study consisted of particles with a similar size distribution (31-37 nm intensity average hydrodynamic diameters) to prior IBCM formulations but exhibited better r₁ and r₂ relaxivity values (18.9 mM^-1 s^-1 and 63.6 mM^-1 s^-1 compared to 8.15 mM^-1 s^-1 and 58.4 mM^-1 s^-1). Cavitation threshold pressures of the IBCM did not significantly differ from the water controls, ranging from ∼26-29 MPa.

Conclusion: These findings support the feasibility of the IBCM as a replacement for the degassed water bath to improve imaging quality of tMRgFUS procedures without introducing negative acoustic effects.

This study numerically assesses the feasibility of magnetic resonance imaging (MRI)-corrected transspinal focused ultrasound (FUS). Eleven ex vivo thoracic vertebrae were imaged with computed tomography (CT) and zero echo time (ZTE) magnetic resonance imaging. ZTE images were converted to pseudo-CT (pCT) with a linear fit from the literature (-2085×ZTE+2329). Transspinal focusing was simulated with a 256-element array (400 kHz, focal full-width-at-half-maximum ∼20 mm axial, 4 mm lateral) using five correction methods: no correction; pCT-corrected, homogeneous acoustic properties; pCT-corrected, heterogeneous properties; CT-corrected, homogeneous properties; and CT-corrected, heterogeneous properties (gold standard). Pressure fields generated using each correction method were evaluated against the gold standard. Compared to no correction, heterogeneous pCT-corrected focusing reduced mean spatial maximum shift (1.5 ± 2.0 mm vs. 3.5 ± 4.1 mm), increased Sørensen-Dice similarity of the 50% contour (0.75 ± 0.10 vs. 0.57 ± 0.18), and improved the change in driving efficiency relative to the gold standard (-12% ± 11% vs. -21% ± 25%). pCT-corrected with homogeneous properties performed similarly to the heterogeneous case. CT-corrected with homogeneous properties approached the gold standard, with a mean spatial shift of 0.8 ± 1.7 mm, Dice coefficient of 0.91 ± 0.06, and little change in driving efficiency (1% ± 3%). MR-corrected focusing using ZTE-derived acoustic properties outperformed uncorrected focusing but did not match gold-standard CT-corrected focusing. Similarities in the performance of heterogeneous versus homogeneous pCT correction, along with the strong performance of homogeneous CT-corrected focusing, suggest that accurate morphological representation of the spine is key to accurate MR-corrected transspinal focused ultrasound.