Open-source, small-animal magnetic resonance-guided focused ultrasound system

Poorman, Megan E.; Chaplin, V.; Wilkens, Ken; Dockery, Mary D.; Giorgio, Todd D.; Grissom, William A.; Caskey, Charles F.

doi:10.1186/s40349-016-0066-7

Cited by 23 publications

(15 citation statements)

References 43 publications

(29 reference statements)

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“…Three baseline preheating images were acquired of all slices before triggering the laser(s) for a 30 seconds INI heating image. The acquired images were zero‐padded in‐plane to a 512 × 512 matrix (0.055 × 0.055 × 0.25 mm voxels) and temperature maps were computed from the resulting images using baseline‐subtracted proton resonance frequency‐shift MR thermometry which was adapted to run on the scanner .…”

Section: Methodsmentioning

confidence: 99%

Identifying the Role of Block Length in Neural Heat Block to Reduce Temperatures During Infrared Neural Inhibition

et al. 2019

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Background and Objectives The objective of this study is to assess the hypothesis that the length of axon heated, defined here as block length (BL), affects the temperature required for thermal inhibition of action potential propagation applied using laser heating. The presence of such a phenomenon has implications for how this technique, called infrared neural inhibition (INI), may be applied in a clinically safe manner since it suggests that temperatures required for therapy may be reduced through the proper spatial application of light. Here, we validate the presence of this phenomenon by assessing how the peak temperatures during INI are reduced when two different BLs are applied using irradiation from either one or two adjacent optical fibers. Study Design/Materials and Methods Assessment of the role of BL was carried out over two phases. First, a computational proof of concept was performed in the neural conduction simulation environment, NEURON, simulating the response of action potentials to increased temperatures applied at different full‐width at half‐maxima (FWHM) along axons. Second, ex vivo validation of these predictions was performed by measuring the radiant exposure, peak temperature rise, and FWHM of heat distributions associated with INI from one or two adjacent optical fibers. Electrophysiological assessment of radiant exposures at inhibition threshold were carried out in ex vivo Aplysia californica (sea slug) pleural abdominal nerves ( n = 6), an invertebrate with unmyelinated axons. Measurement of the maximum temperature rise required for induced heat block was performed in a water bath using a fine wire thermocouple. Finally, magnetic resonance thermometry (MRT) was performed on a nerve immersed in saline to assess the elevated temperature distribution at these radiant exposures. Results Computational modeling in NEURON provided a theoretical proof of concept that the BL is an important factor contributing to the peak temperature required during neural heat block, predicting a 11.7% reduction in temperature rise when the FWHM along an axon is increased by 42.9%. Experimental validation showed that, when using two adjacent fibers instead of one, a 38.5 ± 2.2% (mean ± standard error of the mean) reduction in radiant exposure per pulse per fiber threshold at the fiber output (P = 7.3E−6) is measured, resulting in a reduction in peak temperature rise under each fiber of 23.5 ± 2.1% ( P = 9.3E−5) and 15.0 ± 2.4% ( P = 1.4E−3) and an increase in the FWHM of heating by 37.7 ± 6.4% ( P = 1E−3), 68.4 ± 5.2% ( P = 2.4E−5), and 51.9 ± 9.9% ( P = 1.7E−3) in three MRT slices. Conclusions This study provides the first experimental evidence for a phenomenon during the heat block in which the temperature for inhibition is dependent on the BL. While more work is needed to further reduce the temperature during INI, the results highlight that spatial application of the temperature rise during INI must be considered. Optimized implementation of INI may leverage this cellular response to provide optical modul...

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Section: Methodsmentioning

confidence: 99%

Identifying the Role of Block Length in Neural Heat Block to Reduce Temperatures During Infrared Neural Inhibition

et al. 2019

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“…For example, voxel temperatures were allowed to exceed the mild range since feedback control was not used. Our group has experience with mild hyperthermia feedback (e.g., Poorman et al [ 31 ]) but the present study was instead designed to observe the onset of cavitation at matched powers, and we showed that it is less likely to occur in multi-focusing at a given input power.…”

Section: Discussionmentioning

confidence: 80%

Multi-focal HIFU reduces cavitation in mild-hyperthermia

Chaplin

Caskey

2017

J Ther Ultrasound

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BackgroundMild-hyperthermia therapy (40–45 °C) with high-intensity focused ultrasound (HIFU) is a technique being considered in a number of different treatments such as thermally activated drug delivery, immune-stimulation, and as a chemotherapy adjuvant. Mechanical damage and loss of cell viability associated with HIFU-induced acoustic cavitation may pose a risk during these treatments or may hinder their success. Here we present a method that achieves mild heating and reduces cavitation by using a multi-focused HIFU beam. We quantify cavitation level and temperature rise in multi-focal sonications and compare it to single-focus sonications at the transducer geometric focus.MethodsContinuous wave sonications were performed with the Sonalleve V2 transducer in gel phantoms and pork at 5, 10, 20, 40, 60, 80 acoustic watts for 30 s. Cavitation activity was measured with two ultrasound (US) imaging probes, both by computing the raw channel variance and using passive acoustic mapping (PAM). Temperature rise was measured with MR thermometry at 3 T. Cavitation and heating were compared for single- and multi-focal sonication geometries. Multi-focal sonications used four points equally spaced on a ring of either 4 mm or 8 mm diameter. Single-focus sonications were not steered.ResultsMulti-focal sonication generated distinct foci that were visible in MRI thermal maps in both phantoms and pork, and visible in PAM images in phantoms only. Cavitation activity (measured by channel variance) and mean PAM image value were highly correlated (r > 0.9). In phantoms, cavitation exponentially decreased over the 30-second sonication, consistent with depletion of cavitation nuclei. In pork, sporadic spikes signaling cavitation were observed with single focusing only. In both materials, the widest beam reduced average and peak cavitation level by a factor of two or more at each power tested when compared to a single focus. The widest beam reduced peak temperature by at least 10 °C at powers above 5 W, and created heating that was more spatially diffuse than single focus, resulting in more voxels in the mild heating (3–8 °C) range.ConclusionsMulti-focal HIFU can be used to achieve mild temperature elevation and reduce cavitation activity.

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“…Currently, the only device that can do this 20 uses phased arrays, which steer the beam electronically. To our knowledge, there is another single‐element transducer system for small animals 31 but with a completely different design. The design of the system is simpler yet as effective as phased arrays, and the production cost is affordable, since sonications are performed via a monoelement focused transducer.…”

Section: Discussionmentioning

confidence: 99%

Magnetic Resonance Imaging–Guided Focused Ultrasound Positioning System for Preclinical Studies in Small Animals

Drakos

Giannakou

Menikou

et al. 2020

J of Ultrasound Medicine

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Objectives A positioning device compatible with magnetic resonance imaging (MRI) used for preclinical studies in small animals was developed that fits in MRI scanners up to 7 T. The positioning device was designed with two computer‐controlled linear stages. Methods The positioning device was evaluated in an agar‐based phantom, which mimics soft tissues, and in a rabbit. Experiments with this positioning device were performed in an MRI system using the agar‐based phantom. The transducer used had a diameter of 50 mm, operated at 0.5 MHz, and focused energy at 60 mm. Results Magnetic resonance thermometry was used to assess the functionality of the device, which showed adequate deposition of thermal energy and sufficient positional accuracy in all axes. Conclusions The proposed system fits in MRI scanners up to 7 T. Because of the size of the positioning device, at the moment, it can be used to perform preclinical studies on small animals such as mice, rats, and rabbits.

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Open-source, small-animal magnetic resonance-guided focused ultrasound system

Cited by 23 publications

References 43 publications

Identifying the Role of Block Length in Neural Heat Block to Reduce Temperatures During Infrared Neural Inhibition

Identifying the Role of Block Length in Neural Heat Block to Reduce Temperatures During Infrared Neural Inhibition

Multi-focal HIFU reduces cavitation in mild-hyperthermia

Magnetic Resonance Imaging–Guided Focused Ultrasound Positioning System for Preclinical Studies in Small Animals

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