ISMRM Conference logo 2020The Annual Meeting of the International Society for Magnetic Resonance in Medicine (ISMRM 2020) was held as a virtual conference and exhibition from August 8–14, 2020. This scientific and clinical meeting, which was held in conjunction with the Society of MR Radiographers & Technologists (SMRT), included nine focused ultrasound presentations and 24 posters.

The Foundation thanks Dennis Parker, PhD, Professor of Radiology and Imaging Sciences at the University of Utah, for collecting and providing commentary on the conference’s focused ultrasound content below.

ISMRM virtual Conference content is available at www.ismrm.org.

Presentations (9)

102: Dynamic PRF and T1-based 3D Thermometry in the Liver using a Variable Flip Angle Stack-of-Radial Technique

Le Zhang, Tess Armstrong, and Holden H. Wu
University of California, Los Angeles, Los Angeles, CA, United States

MR thermometry in the liver is challenged by mismatch between baseline and dynamic images caused by motion, leading to temperature errors. To address motion, previous methods had to compromise spatial coverage to increase temporal resolution. We propose a variable-flip-angle (VFA) 3D stack-of-radial technique for combined proton resonance frequency shift (PRF) and T1-based MR thermometry with volumetric coverage and high spatiotemporal resolution. Accurate VFA T1 calculation is achieved by synthesizing B1+ maps that match the liver position in dynamic images. A multi-baseline approach is used for accurate dynamic PRF measurements. Results from non-heating scans demonstrate reliable liver T1 and PRF measurements.

Comments:
The authors provide a detailed pulse sequence description. Switching between two flip angles for the dual flip angle approach while maintaining reasonable temporal resolution in T1 measurement requires some cleverness in interleaving. To improve the PRF measurements, they bin the first few images based on the phase in the respiratory cycle. For the T1 measurements, B1 maps are obtained at both ends of the respiratory cycle. PRF was best with the respiratory matched baseline image subtracted, giving under 6°C error with multi-baseline. The T1 was best with B1+ interpolated map. It would be good to test this sequence with heating speed with parallel imaging. Under 1s per 3D frame. In general, this is excellent work with further progress to be made. This group developed the stack of radial pulse sequence that we and others are using.

The methods they present are interesting, but the T1 measurement still requires two flip angles. Further, if T1 is changing rapidly during acquisition, there may be a bias error in the value obtained. A mono flip angle version of their method may increase the speed of measurement and reduce measurement bias, although that remains to be shown. Although the variance in their temperature measurements is high, this is the abdomen where motion and peristalsis are a huge challenge and their results are a great start towards an acceptable solution. Need to test this sequence with heating.


103: Simultaneous MR acoustic radiation force imaging and MR thermometry: comparison of coherent echo-shifted and RF spoiled gradient echo sequence

Yangzi Qiao, Chao Zou, Chuanli Cheng, Changjun Tie, Xin Liu, and Hairong Zheng
Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China

Simultaneous MR acoustic radiation force imaging and MR thermometry (STARFI) based on coherent echo-shifted sequence (cES) was proposed and comprehensively compared to RF spoiled gradient echo (spGRE). The calculated displacement of cES STARFI was always larger than the value of spGRE STARFI through both the simulation and experiments, while the accuracy of the temperature monitoring of cES was maintained. The temperature and displacement map acquired during HIFU heating were in good accordance with each other. The cES STARFI can be an alternative for comprehensively monitoring of HIFU treatment with increased displacement sensitivity and time efficiency compared to spGRE STARFI.

Comments: Comparing against conventional GRE simultaneous temperature and ARFI imaging allowed this group to observe that displacement-induced phase change was greater for cES ARFI but the variance in the phase was much higher than the GRE ARFI. The displacement phase also depended on T1/T2. To validate this novel idea, it would be helpful to compare the coefficient of variation of the displacements and temperature measured using cES STARFI and spGRE ARFI methods.


104: Rapid autofocusing of MR-guided focused ultrasound acoustic pressure fields using MR-ARFI with spatially coded emissions

Sumeeth Jonathan, M Anthony Phipps, Charles F Caskey, and William A Grissom
Vanderbilt University, Nashville, TN, United States

Magnetic resonance-guided focused ultrasound (MRgFUS) has many potential neurological applications, but skull-induced aberrations of the acoustic pressure field limit its specificity and safety. MR-acoustic radiation force imaging (MR-ARFI)-based methods have been proposed to refocus the pressure field in situ. However, they take too long for practical in vivo use. We propose a multi-voxel MR-ARFI-based autofocusing method for rapid aberration correction of MRgFUS acoustic pressure fields. We compare our proposed method to the canonical single-voxel MR-ARFI-based refocusing method and demonstrate that as few as two MR-ARFI acquisitions can be used to refocus a programmatically aberrated pressure field.

Comments: This presentation builds on the pioneering adaptive focusing methods of Herbert, et al. and Larrat, et al. from the Langevin program and presents and tests a much more efficient method of beam focusing through skull. Similar to the virtual transducer element of Larrat, who composed Hadamard combinations of transducer elements, Sumeeth proposed to divide the transducer into logical elements composed of groups of individual elements. Virtual elements are then obtained as Hadamard combinations of logical elements. They then use Larrat’s method without an aberrator to determine the relative phase of each logical element. The novelty of this method is that they then take an aberrated MR-ARFI image and adjust the phases of the logical elements until the magnitude of the pressure field matches the aberrated pressure field magnitude. The match is over multiple voxels and not just the desired focal point. The inverse of those phases is then used for the logical elements of the transducer during transmit. Because the displacement field is used in the fit, not just a single voxel, the quality of the aberration correction is very good with fewer excitations. Finally, they test with four logical elements and again with eight. Although not said, it is possible to have a large number of logical elements. And the method should work. It will be interesting to see how well the method will converge when applied to individual elements combined into virtual elements.


105: MRI assessment and monitoring of cavitation-based ultrasound therapy (histotripsy) for transcranial brain treatment in vivo

Dinank Gupta, Ning Lu, Jonathan Sukovich, Krisanne Litnas, Aditya Pandey, Badih Junior Daou, Timothy Hall, Zhen Xu, Scott Peltier, and Douglas Noll
University of Michigan, Ann Arbor, MI, United States

Transcranial MR-guided cavitation-based Focused Ultrasound (FUS) treatment (histotripsy) is performed in vivo for the first time on a pig brain. Transcranial histotripsy is delivered by an MRI compatible FUS transducer array inside a 3T MRI scanner. Real-time MRI monitoring with two-second temporal resolution is carried with an intra-voxel incoherent motion (IVIM) pulse sequence synchronized with the FUS array. IVIM images show the histotripsy ablation effect at the intended treatment location in real-time, and the ablation zone was confirmed by post-treatment images. This is the first study to show successful in vivo transcranial histotripsy guided by MRI.

Comments: This group encoded the complex incoherent flow that occurs during histotripsy cavitation by adding IVIM gradients to a sequence with spiral readout. The IVIM images obtained in real time showed the increase in dimensions of the hole in the tissue from histotripsy. The possibility of extravascular blood contributing to signal loss was tested in tofu.


106: Three-dimensional magnetic resonance acoustic radiation force imaging in the breast

Allison Payne, Lorne Hofstetter, Henrik Odéen, Erik Dumont, Dennis L Parker, and Jean Palussiere
University of Utah, Salt Lake City, UT, United States
Image Guided Therapy, Pessac, France
Institut Bergonie, Bordeaux, France

3D MR acoustic radiation force imaging (MR-ARFI) is a useful treatment planning and monitoring tool for magnetic resonance guided focused ultrasound (MRgFUS) treatments in the breast. MR-ARFI displacement is easily visualized in fat, fibroglandular and tumor tissues, allowing for accurate localization of the ultrasound beam and quantitative tissue assessment. The potential formation of standing shear waves in the breast requires careful optimization of the pulse sequence to ensure clear visualization of the radiation force displacement point. This effect is shown in both human breast and phantom data.

Comments: The development of an MRI-guided, breast-specific focused ultrasound system has been a major effort of our focused ultrasound lab at the University of Utah, primarily under the able leadership of Dr. Payne. This presentation is based on her experience in the first clinical trial in collaboration with Dr. Jean Palussière of l’Institut Bergonié. In summary, she demonstrated that 3D MR-ARFI was of great utility in accurately locating the ultrasound pressure pattern in the typical breast, which is primarily composed of fatty tissue that does not show heating with PRF temperature imaging. This trial is ongoing but paused because of the virus. The 3D MR-ARFI method worked very well to locate the focus in both fat and glandular tissue.


107: Deep learning for improved workflow in MRgFUS treatment planning

Pan Su, Sijia Guo, Florian Maier, Steven Roys, Himanshu Bhat, Elias R. Melhem, Dheeraj Gandhi, Rao P. Gullapalli, and Jiachen Zhuo
University of Maryland School of Medicine, Baltimore, MD, United States
Siemens Medical Solutions USA Inc, Malvern, PA, United States
Siemens Healthcare GmbH, Erlangen, Germany

Transcranial MRI-guided focused ultrasound (tcMRgFUS) is a promising technique to treat multiple diseases. Here we examined the feasibility of leveraging deep learning to convert MRI dual echo UTE images directly to synthesized CT skull images. We demonstrated that the derived model is capable of not only segmenting the UTE images to generate synthetic CT skull masks that are highly comparable to true CT skull masks but is also able to reliably predict the CT skull intensities in Hounsfield units. Furthermore, we demonstrated that synthetic CT skull can be reliably used for skull-density-ratio (SDR) determination and predicting target temperature rise in tcMRgFUS.

Comments: With a goal to use UTE MRI of the skull to predict the CT scan of the skull and ideally obtain the same skull density ratio (SDR), this group used a dual echo UTE acquisition with TEs=0.07, 4ms, TR=5ms, 60,000 views, FA=5°, matrix = 1923 resolution = 1.3mm 3. The CT scan used a 120kV, 64-slice CT scanner with a matrix of 512x512 and a resolution of 0.48 x 0.48x1 mm3. The UTE and CT were registered using FLRT. They used a U-Net deep learning architecture with 32 subjects as training, 8 as testing dataset, and a five-fold cross validation method. The predicted CT matched very well with the original CT, although not all differences were quantified. There was good agreement in spatial overlap, predicted Hounsfield number, and SDR. Simulated heating through the original and predicted CT images were nearly identical. Excellent work.


108: Real-time estimation of 2D deformation vector fields from highly undersampled, dynamic k-space for MRI-guided radiotherapy using deep learning

Maarten L Terpstra, Federico d'Agata, Bjorn Stemkens, Jan JW Lagendijk, Cornelis AT van den Berg, and Rob HN Tijssen
University Medical Center Utrecht, Utrecht, Netherlands
University of Turin, Turin, Italy

MRI-guided radiotherapy (MRgRT) enables new ways to improve dose delivery to moving tumors and the organs-at-risk (e.g. in abdomen) by steering the radiation beam based on real-time MRI. While state-of-the-art techniques (e.g. compressed sensing) can provide the required acquisition speed, the corresponding reconstruction time is too long for real-time processing. In this work, we investigate the use of multiple deep neural networks for image reconstruction and subsequent motion estimation. We show that a single motion estimation network can estimate high-quality 2D deformation vector fields from aliased images, even for high undersampling factors up to R=25.

Comments:
This interesting method shows that conventional reconstruction with deep learning motion tracking works fairly well.


113: “Propeller Beanie” Passive Antennas to Alleviate Dark Bands in Transcranial MR-Guided Focused Ultrasound

Xinqiang Yan, Steven Allen, William Grissom
Vanderbilt University, Nashville, TN
University of Virginia, Charlottesville, VA

Transcranial MR-guided focused ultrasound (tcMRgFUS) neurosurgery is a non-invasive treatment for essential tremor and many emerging applications. In the FDA-approved Insightec tcMRgFUS system, however, RF reflections inside the transducer create a curved dark band in brain images that runs through midbrain locations that are targeted for essential tremor, and signal is reduced at least 25% everywhere in the brain, which limits the set of scans that can be performed during treatment. This work proposes a simpler solution that alleviates the problem, which is to place a passive reflecting antenna or resonator above the patient’s head, with a “propeller-beanie” crossed-wire shape.

Comments: The authors performed a numerical simulation of B1+ map into the transducer. The simulations demonstrated that banding can result from destructive interference from reflection of the transmitted B1+ field by the conducting surface of the helmet. They changed the reflected pattern by placing crossed-wire over a swimming cap on the head phantom. This simple method achieved excellent movement of the dark band away from the transducer focus.


1268: Improving Image Quality in Transcranial Magnetic Resonance Guided Focused Ultrasound Using a Conductive Screen

J. Rock Hadley, Henrik Odeen, Robb Merrill, Sam Adams, Viola Rieke, Allison Payne, Dennis Parker
University of Utah, Salt Lake City, UT

This work uses an RF screen, placed over the top of a human skull phantom, to reduce image banding artifacts that are common in transcranial transducer MRI. The goals of the study are to improve imaging homogeneity over the region of the brain by changing RF field patterns that cause the artifacts, and to find a solution that doesn’t attenuate or distort the ultrasound properties of the transducer. Hydrophone and focused ultrasound heating studies are performed to measure ultrasound screen transparency and MRI studies are performed to evaluate the effects the screen has on homogeneity and artifact reduction.

Comments: This work from our group was initiated with no knowledge of the work in the above paper. Rather than crossed wires, we placed a conducting screen over the top of a human skull phantom. The result was removal of the banding artifact and an increase in the SNR and signal uniformity under the screen. Using both MRI and hydrophone experiments, we found that the screen had very little effect on focused ultrasound intensity. Artifact reduction as a function of screen mesh size was also studied (See poster 4122.)

Posters (24)

1545: A pilot study of MR–guided focused ultrasound thalamotomy for refractory essential tremor

Jianfeng He, Yongqin Xiong, Rui Zong, Dekang Zhang, Xin Zhou, Longsheng Pan, Xin Lou
Chinese PLA General Hospital, Beijing, China
Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, China

Essential tremor is the most common movement disorder and is often refractory to medical treatment, Deep brain stimulation in the thalamus has proved the efficiency for these patients. However, this treatment has risks associated with an open neurosurgical procedure. MR-guided focused ultrasound has been developed as a non-invasive means of generating precisely placed focal lesions. We examined its application to the management of refractory essential tremor. Satisfactory results were found that the mean reduction in tremor score of the treated hand was 86.7% at 1 month and 72.5% at 3 months, what’s more, no adverse events lasted beyond three months.

Comments: This group reports on treating 10 patients with MRgFUS for essential tremor. Some adverse effects all cleared by three months. Concluded that the procedure was safe and effective.


1985: Identifying the brain network underlying symptom improvement following neuromodulation in Obsessive Compulsive Disorder

Jurgen Germann, Gavin Elias, Clemens Neudorfer, Alexandre Boutet, Clement Chow, Peter Giacobbe, Se Jo Kim, Hyun Ho Jung, Walter Kucharczyk, Jin Woo Chang, Andres Lozano 
University Health Network, Toronto, ON, Canada
Sunnybrook Health Sciences Centre, Toronto, ON, Canada
Yonsei University College of Medicine, Seoul, Republic of Korea

Neuromodulatory interventions have shown promise in the treatment of obsessive-compulsive disorder (OCD). However, the nature of the aberrants circuits that cause the disease as well as the network changes that are the basis of improvement following treatment are not well understood. Here we analyzed OCD patients treated with either MRI-guided focused ultrasound capsulotomy or deep brain stimulation targeting the inferior thalamic peduncle. Using neuroimaging analysis and modeling techniques we found that a fronto-limbic network (DLPFC, dorsal ACC, and amygdala) predicts individual improvement across groups. These results provide new insight into OCD and how to possibly refine neuromodulatory therapies.

Comments: This study compares 11 patients treated for OCD with MRgFUS with five patients treated with deep brain stimulation. It includes a detailed description of the brain regions treated and seems to have positive results.


2007: 7T resting state connectivity applied to HIFU procedures for planning and efficacy

Stephen Jones, Jessica Cooperrider, Daniel Lockwood, Sean Nagel, Emmanuel Obusez, Richard Rammo, Paul Ruggieri, Andre Machado, and Mark Lowe
Cleveland Clinic, Cleveland, OH, United States

High Intensity Focused Ultrasound (HIFU) in now entering clinical practice, for example to treat essential tremor by causing small lesions in the thalamus. Due to small size of treatment lesions, treatment success depends critically on targeting, which is classically done using measurements and landmarks. We explore an alternative method using functional imaging to guide targeting, specifically using 7T resting state connectivity. We present preliminary data of the patterns of connectivity possible with 7T using a concatenated series of healthy subjects. Finally, we show the changes in connectivity in a post-HIFU patient from the thalamus to the cortex.

Comments: Functional connectivity measured at 7T might be used to predict treatment location in thalamus for essential tremor.


3219: Using QSM to Quantify Microbubble Concentrations

Barbara Dymerska, Bernard Siow, Karin Shmueli
University College London, London, United Kingdom
The Francis Crick Institute, London, United Kingdom

Microbubbles are a well-established intravascular ultrasound contrast agent. There is increasing interest in MRI-guided microbubble-mediated focused ultrasound treatments such as thermal surgery. MRI magnitude has a non-linear and non-local dependence on microbubble size and volume fraction, making it unsuitable for estimating microbubble concentrations. Quantitative Susceptibility Mapping (QSM) is a strong candidate for tracking microbubble concentration, destruction and clearance because the susceptibility depends linearly on the volumetric bubble concentration. Here, we show the first QSM of microbubbles in a phantom and observe that the measured susceptibility has a high SNR and is directly proportional to the microbubble volumetric concentration.

Comments: This is a nice demonstration that MRI quantitative susceptibility mapping can be used to measure microbubble concentration. Note that changes in susceptibility cause a change in the main magnetic field distribution around the local change. Because this is a phantom study in tubes, the spacing between the tubes is such that the effect of nearby tubes is greatly reduced. It will be interesting to see how well the measurements would correlate with microbubble concentration in tissues (not in the tubes). Do we need to deconvolve the susceptibility kernel? It works in tubes, but it remains to be shown in tissues.


3648: An MR-guided focused ultrasound software with Gadgetron reconstruction

Yangzi Qiao, Chao Zou, Jianhong Wen, Sen Jia, Xin Liu, and Hairong Zheng
Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China

An integrated focused ultrasound guidance software named MARFit was developed base on the framework of Gadgetron. The software realized automatically focus localization and real-time temperature change monitoring during HIFU therapy. These features has been evaluated in animal experiments. The software makes the post processing procedure easily translated between different vendors, and could be a powerful tool for MR guided focused ultrasound therapy.

Comments:
This group presented many applications and capabilities.


4111: A method for post-surgical evaluation of targeting accuracy in transcranial focused ultrasound thalamic ablation

Benjamin T Newman, Ana Untaroiu, and T. Jason Druzgal
University of Virginia, Charlottesville, VA, United States

MR-guided focused ultrasound ablation targets small thalamic nuclei that are frequently difficult to distinguish from surrounding tissue. The ability to accurately evaluate the success in ablating the target nuclei is essential for predicting treatment outcome and evaluating surgical performance. We show microstructural changes in the thalamus that may prevent accurate post-surgical tractography. We propose a straightforward technique that reconstructs neuronal connections in the pre-surgical brain using the post-operative lesioned area as a seed-region for constrained spherical deconvolution based tractography. The proportion of tracts leading to regions known to be connected to the target nuclei is then evaluated.

Comments: The authors developed methods to register posttreatment MRI to pretreatment tractography and compare treatment location to tracts. This method rigidly registers to pretreatment images using a circular convolution. The T1w lesion appears within 24 hours after treatment and is gone shortly after 1 week. The T2 effects remain longer. The authors found that induced anisotropy in the tissue seen after treatment impacts the accuracy of posttreatment tractography. Their solution was to register the pretreatment tractography to the posttreatment T1w image volume. Treatment success seems to relate to how well the lesion volume is found in the tracts that pass into the motor cortex.


4112: An efficient approach for simultaneous PRF-T1 MR thermometry and shear wave elastography to monitor MR-guided focused ultrasound therapies

Henrik Odéen, Lorne Hofstetter, and Dennis L Parker
University of Utah, Salt Lake City, UT, United States

Treatment endpoint assessment in MRgFUS is commonly performed by investigating non-perfused volume or accumulated thermal dose, but these measurements can be inaccurate and have low precision immediately after treatment and can be tissue type dependent. In this work we present a pulse sequence which can provide dynamic measurements of PRF thermometry (and hence also thermal dose), T1 and tissue mechanical properties through shear wave speed measurements. PRF and T1 can provide complete MR thermometry in all tissue types (aqueous and adipose), and together all parameters are useful in treatment endpoint assessment.

Comments: In an attempt to generate MRI pulse sequences that can efficiently assess treatment endpoints, we developed a novel sequence that allows PRF, T1, and shear wave elastography to be imaged simultaneously. Preliminary results with the sequence are presented.


4113: Intraoperative Diffusion Weighted MR Image Contrast during Focused Ultrasound Ablation in a Preclinical Swine Model

Steven P Allen, Francesco Prada, Jeremy Gatesman, Xue Feng, Helen Sporkin, Yekaterina Gilbo, Kim Butts Pauly, and Craig H Meyer
University of Virginia, Charlottesville, VA, United States
Stanford University, Stanford, CA, United States

This abstract presents a preclinical study of intraoperative diffusion weighted imaging (DWI) of focused ultrasound thermal lesions in the thalamus using a novel acquisition sequence. We found that DW imaging can visualize thermal lesions within 10 minutes of ablation. Our study indicates that MR-guided focused ultrasound lesions present a rapid and persistent decrease in apparent diffusion coefficient within minutes after ablation and that diffusion-based lesion classification methods can outperform T2-w based methods.

Comments: The authors achieved diffusion weighting with an adiabatic, twice refocused preparation with spectral spatial excitation and a multishot retraced variable density spiral readout to counter the effects of B1 inhomogeneity, off resonance, eddy currents. They also estimated and corrected for motion. Based on treated tissue as truth, they performed ROC analysis to evaluate the efficacy of ADC, DWI contrast, and T2w contrast. ROC analysis used z-scores to classify treated tissue. The ADC and DW measurements were more effective (AUC = 0.74 and 0.8) than T2-w (AUC = 0.66).


4114: MR imaging Evaluation of an Interstitial Focused Ultrasound Probe used in Robotically Assisted Brain Ablation Procedures

Matthew Tarasek, Eric Fiveland, Chitresh Bhushan, Goutam Ghoshal, Tamas Heffter, Katie Gandomi, Paulo Alberto Carvalho, Christopher Nycz, Teresa Maiette, Zahabiya Campwala, Erin Jeannotte, Michael Staudt, E Clif Burdette, Gregory Fischer, Julie Pilitsis, and Desmond Yeo
GE Global Research, Niskayuna, NY, United States
Acoustic MedSystems Inc., Savoy, IL, United States
WPI, Worcester, MA, United States
Albany Medical College, Albany, NY, United States

In this work we evaluate a newly developed catheter-based therapeutic ultrasound (US) probe used for interstitial MR-guided high intensity focused US (iMRgFUS) procedures. Specifically, we optimize and down-select MR thermal imaging protocols in order to achieve maximum temperature measurement precision and volume coverage in the presence of image artifacts arising from the iMRgFUS probe design and operation.

Comments: Experiments with an interstitial probe demonstrate a susceptibility artifact that depends on the orientation of the probe.


4115: Enhancement of the MRgHIFU therapy using endovascular sono-sensitizers demonstrated in an experimental model of perfused tissue

Orane Lorton, Ryan Holman, Pauline Guillemin, Stéphane Desgranges, Laura Gui, Lindsey A. Crowe, François Lazeyras, Antonio Nastasi, Christiane Contino-Pépin, and Rares Salomir
University of Geneva, Faculty of Medicine, Geneva, Switzerland
University of Avignon, CBSA-IBMM (UMR5247), Avignon, France
University Hospitals of Geneva, Geneva, Switzerland

Magnetic Resonance guided High Intensity Focused Ultrasound (MRgHIFU) is accepted for the non-invasive ablation of localized tumors. Thermal contrast between the target tissue and pre/post focal tissues can be improved for highly perfused tumors by injection of liquid core micro-droplets, used as endovascular sono-sensitizers. We are aiming to provide a substitution model for living organs or perfused ex vivo organs to facilitate the investigation of new sono-sensitizers and sonication paradigms. We are reporting an experimental model that is suitable for MR-guided HIFU studies, offering in situ tunable perfusion rate, multi-compartment structure, and tunable concentration of sono-sensitizers and dissolved gases.

Comments:
This is an interesting use of an in vitro perfusion model (artificial kidney) and testing of the effects of microdroplets on heating with MRgFUS. The temperature maps demonstrate that the microdroplets do increase heating.


4116: Feasibility of rapid diffusion-weighted imaging for monitoring of MR-guided prostate high intensity focused ultrasound ablation

Elena Kaye, Oguz Akin
Memorial Sloan Kettering Cancer Center, New York, NY, United States

MR-guided high-intensity focused ultrasound (HIFU) treatment of prostate cancer is a promising non-invasive approach. The outcomes of these treatments can be improved with more accurate visualization of ablative necrosis surrounding a tumor. Diffusion-weighted imaging (DWI) could provide valuable information about tissue viability without injection of contrast. However, currently DWI requires high number of excitations (NEX), averages, takes several minutes and is not practical for intraprocedural monitoring. To make DWI a practical tool for monitoring of prostate HIFU, we propose to replace high NEX DWI acquisitions, with NEX=2 acquisitions and subsequent deep-learning denoising of these image.

Comments:
This group trained their model on 103 patients and then validated it on 15 patients. The images are much better, and the apparent diffusion coefficient (ADC) values are closer to those obtained using diagnostic imaging.


4117: Monitoring of Focused Ultrasound Induced Stable Cavitation by Using Magnetic Resonance Imaging: In Vivo Experiments

Yu-Ting Jiang, Cheng-Tao Ho, Po-Hung Hsu, Hao-Li Liu, Chih-Kuang Yeh, and Hsu-Hsia Peng
National Tsing Hua University, Hsinchu, Taiwan
Chang Gung Memorial Hospital, Taoyuan, Taiwan

We aimed to monitor the focused ultrasound (FUS)-induced stable cavitation (SC) by using single-shot turbo spin-echo based sequence in in vivo experiments. The FUS were transmitted to the cortex ~2‐mm beneath the superior sagittal sinus of rats with acoustic pressure=0.5 or 0.8 MPa. A cavitation index map was computed to highlight the occurrence of SC at focus. In conclusion, the simultaneous acquisitions of spin-echo based images during FUS transmission and the proposed CI map can immediately localize the position occurring SC. The relevant information can be feedbacked to FUS facility for improving the procedure of BBB opening.

Comments: Unfortunately, this abstract interchanged cavitation index (CI) with IC, making the results somewhat unclear.


4118: Evaluate thrombolysis effect of focused ultrasound in different thrombus ages by MRI

Yu-Ting Jiang, Po-Hung Hsu, Hao-Li Liu, Chih-Kuang Yeh, and Hsu-Hsia Peng
National Tsing Hua University, Hsinchu, Taiwan
Chang Gung Memorial Hospital, Taoyuan, Taiwan

We aimed to evaluate the thrombolysis effect with variant focused ultrasound (FUS) and microbubbles (MB) conditions in different thrombus ages by MRI. Compared to one-week thrombi, 2-days thrombi presented longer T1 and similar T2, while the total iron content increased with thrombus ages. However, with identical thrombolysis conditions, there is no significant difference of weight loss between two different thrombi ages groups. In conclusion, to characterize the T1 and T2 relaxation times of thrombi with different ages can be helpful for evaluation of the thrombolysis effect with variant UK and FUS conditions in different thrombi ages.

Comments: These observations are hard to follow. Results did not seem to be consistent, possibly due to inconsistent progression of thrombus at low temperature.


4119: Selective fast focal switching of high-contrast-ratio magnetocaloric MRI labels with focused ultrasound

G. Wilson Miller, Yekaterina Gilbo, Stephen Dodd, Alan P Koretsky, Hatem ElBidweihy, and Mladen Barbic
University of Virginia, Charlottesville, VA, United States
National Institutes of Health, Bethesda, MD, United States
United States Naval Academy, Annapolis, MD, United States
HHMI - Janelia Research Campus, Ashburn, VA, United States

We describe the use of MRI-compatible focused ultrasound (FUS) for selective fast focal switching of high-contrast-ratio magnetocaloric MRI particle labels. Lanthanum-Iron-Silicon (La-Fe-Si) particles that have sharp first-order magnetic phase transitions at physiological temperatures and MRI field strengths were used as MRI labels. Non-invasive rapid thermal switching of these magnetocaloric MRI particle labels with focused ultrasound was clearly demonstrated at physiological temperatures within a clinical 1.5T MR scanner. We have thereby shown that high differential contrast ratio magnetocaloric MRI labels can be switched non-invasively, rapidly, and selectively under conditions relevant to clinical MRI.

Comments:
This study shows a novel observation. Iron rodium switches on as temperature increases. Lanthanum-Iron-Silicon switches off as temperature increases. The team used focused ultrasound to switch particle labels on and off. These are clever ideas that may lead to the development of useful temperature-sensitive agents.


4120: Improving in situ acoustic intensity estimation by augmenting MR acoustic radiation force imaging with MR elastography

Ningrui Li, Pooja Gaur, and Kim Butts Pauly
Stanford University, Stanford, CA, United States

MR acoustic radiation force imaging (MR-ARFI) can be used to localize the focal spot for non-thermal transcranial ultrasound therapies. The acoustic radiation force is proportional to the applied acoustic intensity, meaning that tissue displacements measured with MR-ARFI can potentially be used to estimate the acoustic intensity at the target. However, variable brain stiffness is an obstacle to obtaining accurate acoustic intensity estimates. Using gelatin phantoms with varying stiffnesses, we demonstrate that stiffness information from MR elastography can be used in combination with MR-ARFI to improve in situ estimates of acoustic intensity. This could enable safer and more effective treatments.

Comments: This work is a nice demonstration that MR-ARFI can be used to obtain estimates of acoustic intensity. The independent estimate of tissue stiffness, obtained from MRE, is needed.


4121: Focused Ultrasound Enhances Connectivity of Default Mode Network in Rat Brain

Chia-Yu Huang, Yi-Cheng Wang, Wen-Yen Chai, Sheng-Min Huang, Hao-Li Liu, and Fu-Nien Wang
National Tsing Hua University, Hsinchu, Taiwan
Chang Gung University, Taoyuan, Taiwan

Focused ultrasound is a noninvasive, deep-penetrating, and spatially well-defined modality to modulate the neural activity. In this study, we used resting state functional MRI (rs-fMRI) to investigate the functionally connectivity after stimulation in the brain. Rats underwent focused ultrasound stimulation targeted unilaterally to the ventral posteromedial and ventral posterolateral thalamic nuclei (VPM/VPL) in the left thalamic region. The default mode network (DMN) showed hyper-correlation after sonication, and as time proceed, the correlation has a tendency to decline slowly in about 3 days.


4122: Designing RF Screens for MRI guided Focused Ultrasound Applications

Rock Hadley, Henrik Odeen, Robb Merrill, Sam Adams, Viola Rieke, Allison Payne, and Dennis Parker
University of Utah, Salt Lake City, UT, United States

This work evaluates screens with different hole size in their ability to pass ultrasound and their ability to shield RF in a Transcranial MR guided Focused Ultrasound experiment. Hydrophone and radiation force balance studies were used to measure attenuation and peak pressure when passing ultrasound through the screens compared to water-only measurements. Electromagnetic simulations and MRI experiments were performed to measure RF shielding effectiveness of the screens by comparing their ability to change known artifacts in a transcranial transducer compared to a solid conductor.

Comments: This is our work to design an RF screen that eliminates the signal loss band artifact in transcranial MRgFUS. We are continuing this work and plan to submit a paper this fall.


4123: Brain Volumetric Changes following MR Guided Focused Ultrasound Treatment for Parkinson’s Disease

Justin Schumacher, Li Jiang, Jiachen Zhuo, Howard Eisenberg, Paul Fishman, Dheeraj Gandhi, and Rao Gullapalli
University of Maryland School of Medicine, Baltimore, MD, United States

MR Guided Focused Ultrasound (MRgFUS) is a novel technique used to noninvasively lesion the brain for treatment of Parkinson’s Disease (PD). In this study 12 PD patients with asymmetric motor symptoms underwent MRgFUS pallidotomy and cortical thicknesses and subcortical volumes were measured pre and post treatment. Subcortical gray matter volume increases were observed 24 hours post treatment with bilateral decreases in basal ganglia gray matter volume 3-6 months post treatment. Cortical thicknesses decreases were observed in the frontal and temporal cortices of right-sided treated patients 3-6 months post treatment. These regions may play a role in the management of dyskinesias.

Comments: These interesting observations describe how some brain regions change volume (some acutely, possibly due to edema) after focused ultrasound treatment.


4124: MR guided blood-brain-barrier opening induced by focus ultrasound on Non-human primate

Hui Zhou, Yang Liu, Chao Zou, Xiaojing Long, Xin Liu, and Hairong Zheng
Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China

Magnetic Resonance Imaging (MRI) is highly recommended for estimation of the feasibility and safety of BBB opening. We opened BBB in three different deep brain areas of a non-human primate with a single element ultrasound transducer working at 300kHz without detectable edema, hemorrhage and abnormal behavior. We found that the BBB in gray matter was easier to be disrupted than that in white matter, suggesting that for a local BBB opening in deep brain on non-human primate and human subjects, array transduces with relative large assemble surface are required to avoid the BBB disruption in cerebral cortex.

Comments:
A short abstract on safe BBB opening in three macaques.


4125: Effects of mild hyperthermia and pulsed high intensity focused ultrasound in a mouse models of Pancreatic Ductal Adenocarcinoma

Ravneet Vohra, Yak-Nam Wang, Helena Son, Stephanie Totten, Joo Ha Hwang, and Donghoon Lee
University of Washington, Seattle, WA, United States
Stanford University, Stanford, CA, United States

Pancreatic cancer is expected to become the second leading cause of the cancer related deaths in the USA by 2020. The ineffectiveness of conventional chemotherapeutics in Pancreatic Ductal Adenocarcinoma (PDA) is thought to be largely due to the extensive stromal desmoplasia which inadvertently increases the interstitial fluid pressure. High intensity focused ultrasound (HIFU) sonication was performed with temperature monitored by MRI. The aim of this study was to develop a target treatment of pulsed HIFU treatment combined with mild hyperthermia on PDA and to monitor the response to the therapy using multi-parametric MRI as a non-invasive biomarker.

Comments: This group used focused ultrasound to induce mild hyperthermia in a mouse model (n=8) of pancreatic ductal adenocarcinoma. The observed increase in T2, decrease in magnetization transfer (MTR), and increase in ADC (diffusion coefficient) were all consistent with increased perfusion and possible depletion of tumor stroma.


4128: Development of T1-based Skull Thermometry using a 3D Spiral Ultra-Short Echo Time Sequence

Yekaterina K Gilbo, Helen Sporkin, Samuel W Fielden, John P Mugler, Grady W Miller, Steven P Allen, and Craig H Meyer
University of Virginia, Charlottesville, VA, United States
Department of Imaging Sciences & Innovation, Geisenger, Danville, PA, United States

Skull temperature monitoring is important for MR-guided focused ultrasound (MRgFUS), as the skull is highly absorptive to acoustic energy. T1 thermometry uses T1 mapping to observe a linear increase in T1 with temperature but requires long acquisitions. Here we compare T1-weighted thermometry with T1 thermometry using a 3D spiral ultra-short-echo time sequence and show that T1 thermometry is feasible, but requires further acceleration, whereas T1-weighted thermometry results are nonlinear and inconsistent.

Comments:
Katya demonstrates nicely that T1 is linear with temperature. Excellent digital poster presentation. Katya has done a lot of work and is getting consistent results. We hope to be repeating this with our fast methods in the very near future.


4145: 4D-MRI of Thorax and Abdomen with Variable Contrast at 1.5T

Orso Andrea Pusterla, Francesco Santini, Grzgorz Bauman, Rahel Heule, Alina Giger, Philippe Claude Cattin, Sairos Safai, Sebastian Kozerke, and Oliver Bieri
Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
University Hospital Basel, Basel, Switzerland
University of Basel, Allschwil, Switzerland
Max Planck Institute for Biological Cybernetics, Tübingen, Germany
Paul Scherrer Institute, Villigen-PSI, Switzerland

Time-resolved volumetric imaging (4D-MRI) of moving organs is essential for several clinical applications, e.g., in interventional treatments, radiation therapies, and high-intensity focused ultrasound ablations. In this work, an interleaved time-resolved data-navigator acquisition strategy for 4D-MRI with flexible contrast is developed offering versatile settings for thoracic and abdominal imaging: for both, image and navigator, not only the flip angle but also the basic acquisition type (pulse sequence kernel) can be chosen independently from either balanced SSFP (i.e., T2/T1-weighted) or spoiled gradient echo (i.e., T1-weighted).

Comments: This abstract presents a method to track motion in the thorax and abdomen in a 1.5T MRI to assist MR-guided interventions (including focused ultrasound).


4173: Magnetic Resonance Imaging-guided Focused Ultrasound ablation of lumbar facet joints of a patient with a MRI non-conditional pacemaker at 1.5T

Jacinta Browne, Christin A Tiegs-Heiden, Vance T Lehman, Zaiyang Long, Robert E Watson, Gina K Hesley, and Krzysztof R Gorny
Mayo Clinic, Rochester, MN, United States

An MRgFUS ablation treatment of lumbar facet joints in a patient with a traditional MRI non-conditional pacemaker was completed. A risk-benefit analysis by a coordinated multi-disciplinary team prior to this treatment was performed to account for the risks associated with traditional MRI non-conditional pacemaker. The treatment was successfully performed as per our institution established cardiac implanted electronic device (CIED) MRI practice and the patient had no adverse cardiac event during or following this procedure. By careful use of our institutional CIED MR-practice guidelines, we demonstrated that such treatments can be safely achieved for patients with CIEDs on a case-by-case basis.

Comments: This is a case report of using MRgFUS to ablate the nerve in a facet joint. The procedure time was 2.5 hours for 22 individual sonications with treatment doses of 40 to 60W. Multidisciplinary team.


4752: Imaging and pain response in extra vs intra-pelvic recurrent gynaecological tumours treated with MR guided HIFU: a pilot study

Georgios Imseeh, Sharon L Giles, Ian Rivens, Alexandra Taylor, Gail ter Haar, Erica Scurr, and Nandita M deSouza
Institute of Cancer Research, Sutton, Surrey, United Kingdom
The Royal Marsden NHS Foundation Trust, London, United Kingdom

MR guided High Intensity Focused Ultrasound in 10 patients with symptomatic recurrent gynecological tumors treated for pain palliation resulted in higher temperatures in shallower extra-pelvic tumors compared to intra-pelvic ones (62.9±11.7oC vs. 49.4±2.8oC over median 16 sec sonication) despite lower energy delivery in them (39.1±23.6 kJ vs. 72.1±24.3 kJ). In 3 of 5 extra-pelvic tumors, an increase in the non-perfused tumor volume immediately after treatment was seen, indicating edema. At Day 30, 5 patients met the criteria of pain response, 3 with extra-pelvic tumors and 2 with intra-pelvic tumors.

Comments:
This group treated 10 patients with the Philips Sonalleve V2 system integrated into a 3T Achieva MRI scanner. There was a range of different tumors, and 50% of the patients experienced improved pain relief. There was no control group.

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