Vandiver Chaplin

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

BackgroundMR-guided focused ultrasound or high-intensity focused ultrasound (MRgFUS/MRgHIFU) is a non-invasive therapeutic modality with many potential applications in areas such as cancer therapy, drug delivery, and blood-brain barrier opening. However, the large financial costs involved in developing preclinical MRgFUS systems represent a barrier to research groups interested in developing new techniques and applications. We aim to mitigate these challenges by detailing a validated, open-source preclinical MRgFUS system capable of delivering thermal and mechanical FUS in a quantifiable and repeatable manner under real-time MRI guidance.MethodsA hardware and software package was developed that includes closed-loop feedback controlled thermometry code and CAD drawings for a therapy table designed for a preclinical MRI scanner. For thermal treatments, the modular software uses a proportional integral derivative controller to maintain a precise focal temperature rise in the target given input from MR phase images obtained concurrently. The software computes the required voltage output and transmits it to a FUS transducer that is embedded in the delivery table within the magnet bore. The delivery table holds the FUS transducer, a small animal and its monitoring equipment, and a transmit/receive RF coil. The transducer is coupled to the animal via a water bath and is translatable in two dimensions from outside the magnet. The transducer is driven by a waveform generator and amplifier controlled by real-time software in Matlab. MR acoustic radiation force imaging is also implemented to confirm the position of the focus for mechanical and thermal treatments.ResultsThe system was validated in tissue-mimicking phantoms and in vivo during murine tumor hyperthermia treatments. Sonications were successfully controlled over a range of temperatures and thermal doses for up to 20 min with minimal temperature overshoot. MR thermometry was validated with an optical temperature probe, and focus visualization was achieved with acoustic radiation force imaging.ConclusionsWe developed an MRgFUS platform for small-animal treatments that robustly delivers accurate, precise, and controllable sonications over extended time periods. This system is an open source and could increase the availability of low-cost small-animal systems to interdisciplinary researchers seeking to develop new MRgFUS applications and technology.

Neuromodulation of sensory networks in monkey brain by focused ultrasound with MRI guidance and detection

Focused ultrasound (FUS) has gained recognition as a technique for non-invasive neuromodulation with high spatial precision and the ability to both excite and inhibit neural activity. Here we demonstrate that MRI-guided FUS is capable of exciting precise targets within areas 3a/3b in the monkey brain, causing downstream activations in off-target somatosensory and associated brain regions which are simultaneously detected by functional MRI. The similarity between natural tactile stimulation-and FUS- evoked fMRI activation patterns suggests that FUS likely can excite populations of neurons and produce associated spiking activities that may be subsequently transmitted to other functionally related touch regions. The across-region differences in fMRI signal changes relative to area 3a/3b between tactile and FUS conditions also indicate that FUS modulated the tactile network differently. The significantly faster rising (>1 sec) fMRI signals elicited by direct FUS stimulation at the targeted cortical region suggest that a different neural hemodynamic coupling mechanism may be involved in generating fMRI signals. This is the first demonstration of imaging neural excitation effects of FUS with BOLD fMRI on a specific functional circuit in non-human primates.

Design and characterization of an MR-compatible FUS randomized array for transcranial neuromodulation

Transcranial focused ultrasound (FUS) is a noninvasive technique for therapy and study of brain neural activation. Here we report on the design and characterization of a new MR-guided FUS transducer for neuromodulation in nonhuman primates at 650kHz. Focus size and grating lobes during electronic steering were quantified using hydrophone measurements in water and a three-axis stage. Pressure output vs. power was characterized and shown to agree with design simulations.

A random phased-array for MR-guided transcranial ultrasound neuromodulation in non-human primates

Transcranial focused ultrasound (FUS) is a non-invasive technique for therapy and study of brain neural activation. Here we report on the design and characterization of a new MR-guided FUS transducer for neuromodulation in non-human primates at 650 kHz. The array is randomized with 128 elements 6.6 mm in diameter, radius of curvature 7.2 cm, opening diameter 10.3 cm (focal ratio 0.7), and 46% coverage. Simulations were used to optimize transducer geometry with respect to focus size, grating lobes, and directivity. Focus size and grating lobes during electronic steering were quantified using hydrophone measurements in water and a three-axis stage. A novel combination of optical tracking and acoustic mapping enabled measurement of the 3D pressure distribution in the cortical region of an ex vivo skull to within ~3.5 mm of the surface, and allowed accurate modelling of the experiment via non-homogeneous 3D acoustic simulations. The data demonstrates acoustic focusing beyond the skull bone, with the focus slightly broadened and shifted proximal to the skull. The fabricated design is capable of targeting regions within the S1 sensorimotor cortex of macaques.

Abstract A086: Real-time in vivo characterization of spatiotemporal immunotherapeutic response to high intensity focused ultrasound with a novel NF-kB reporter model of human breast cancer

Detailed temporal characterization of in vivo response to anti-tumor immunotherapies are limited by the frequency and volume of tissue that can be practically collected. We have successfully generated a novel double-transgenic murine model, which incorporates a nuclear factor-kappaB (NF-kB) reporter transgene (NGL) into the polyoma virus middle T oncogene (PyVT) model, a widely accepted transgenic mouse with spontaneous tumor formation and disease progression comparable to that of human breast cancer. The reporter transgene uses luciferase to quantitatively indicate NF-kB activation, which is central to immunomodulatory inflammation. In vivo imaging systems (IVIS) were used for luminescent imaging of luciferase activity as a spatial reporter of NF-kB activation that was carried out repeatedly on individual double transgenic (Py-NGL) mice. Magnetic resonance thermometry (MRT) was used to guide therapeutic, high intensity focused ultrasound (HIFU) for quantitatively repeatable, sub-ablative thermal dosing as an inflammatory stimulus. Py-NGL mice were treated with the MRT-HIFU system at a sub-ablative level of 42 °C for up to 25 minutes. Mice were imaged with IVIS before treatment and every twelve hours after treatment until the collection of tissues. The untreated tumors, treated tumors, and spleens were collected, digested, and quantitatively analyzed with flow cytometry for immunophenotyping and cytokine expression. Py-NGL mice have a peak in NF-kB activation, spatially correlated with the administration of MRT-guided HIFU, between 48-96 hours post treatment. Preliminary measures of inflammation by NF-kB activity demonstrate up to a 20-fold increase from baseline in the HIFU treated tissue. Following treatment, NF-kB activity increased from baseline as early as 24 hours and reached a peak between 48 and 96 hours, consistent with recruitment and activation of inflammatory cell phenotypes as a consequence of MRT-HIFU treatment. Elevated NF-kB activity remained localized in the HIFU-treated tissue throughout the measurement period, and smoothly declined towards, but remained above, baseline levels following the activation peak. Immunophenotyping data reveals changes in immune cell infiltrates following treatment, including the number and phenotypes of T cells and macrophages. This novel murine model enabled real-time, quantitative live-animal imaging of spatially specific, time-dependent NF-kB activation. Measurement of NF-kB response to controlled-dose HIFU provides the first opportunity to correlate induced inflammation with immune cell and cytokine characterization of the tumors. The objective is to quantitatively elucidate the spatiotemporal immunologic response to inflammatory stimulus in tumors. In this way, therapeutic methods based on elevating inflammation in tumors can be assessed for reversal of the immunosuppressive microenvironment and the generation of functional anti-tumor immunotherapy. Citation Format: Mary D. Dockery, Megan E. Poorman, Vandiver L. Chaplin, Ryan A. Spears, Charles F. Caskey, William A. Grissom, Todd D. Giorgio. Real-time in vivo characterization of spatiotemporal immunotherapeutic response to high intensity focused ultrasound with a novel NF-kB reporter model of human breast cancer. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A086.

Abstract A06: Novel NF-kB reporter murine model of spontaneous, metastatic breast cancer for spatiotemporal monitoring of local and systemic therapeutic response

Characterization of therapeutic response in primary and metastatic tumors is limited by endpoint studies and tissue collection. We have successfully developed a unique double-transgenic mouse model, which combines the polyoma virus middle T oncogene (PyVT), a model of human breast cancer, with a nuclear factor-kappaB (NF-kB) reporter model (NGL). PyVT mice spontaneously form primary mammary fat pad tumors, with 80% of mice developing metastatic lesions in the lungs. The reporter is luciferase, driven by NF-kB activation, to provide quantitative bioluminescent measurements of spatially-specific NF-kB activity. The resulting double transgenic (PyNGL) mice were monitored using in vivo imaging systems (IVIS) multiple times, before and after treatment, to quantitatively and spatially characterize NF-kB therapeutic response, both locally and systemically. High intensity focused ultrasound (HIFU) was guided by magnetic resonance (MR) thermometry for tumor-localized hyperthermia which was dosage-controlled by the thermal feedback MR guided HIFU (MRgHIFU) system. A single primary mammary tumor in each PyNGL was treated with sub-ablative hyperthermia of 42⁰ for up to 25 minutes. Pre-treatment IVIS measurements were collected to determine baseline NF-kB activity within each mouse, followed by IVIS imaging every twelve hours after treatment until tissue collection. Treated tumor, contralateral (untreated) tumors, and spleens were collected for immunophenotyping and cytokine analysis using flow cytometry. PyNGL mice exhibited decreased NF-kB activity, spatially correlated with HIFU treatment, as early as 12 hours. In contrast, NF-kB increased in contralateral tumors as early as 24 hours following treatment. Immunophenotyping reveals changes in tumor infiltrating leukocyte populations in HIFU-treated and contralateral tumors, including quantity and phenotype of T cells. The unique murine model developed allowed quantitative, temporal characterization of local and distant tumor response to MFgHIFU. The spontaneous, metastatic nature of PyVT tumor formation in concert with the non-destructive, spatiotemporal imaging capabilities of the NF-kB reporter transgene make the PyNGL model an unparalleled tool for research in metastatic disease. Citation Format: Mary Dockery, Megan Poorman, Stephanie Dudzinski, Whitney Barham, Vandiver Chaplin, Ryan Spears, Jiro Kusunose, Fiona Yull, Charles Caskey, William Grissom, Todd Giorgio. Novel NF-kB reporter murine model of spontaneous, metastatic breast cancer for spatiotemporal monitoring of local and systemic therapeutic response. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr A06.