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Real-time temperature monitoring is critical to the success of thermally ablative therapies. This work validates a 3D thermometry sequence with k-space field drift correction designed for use in magnetic resonance-guided focused ultrasound treatments for breast cancer. Fiberoptic probes were embedded in tissue-mimicking phantoms, and temperature change measurements from the probes were compared with the magnetic resonance temperature imaging measurements following heating with focused ultrasound. Precision and accuracy of measurements were also evaluated in free-breathing healthy volunteers (N = 3) under a non-heating condition. MR temperature measurements agreed closely with those of fiberoptic probes, with a 95% confidence interval of measurement difference from -2.0 °C to 1.4 °C. Field drift-corrected measurements in vivo had a precision of 1.1 ± 0.7 °C and were accurate within 1.3 ± 0.9 °C across the three volunteers. The field drift correction method improved precision and accuracy by an average of 46 and 42%, respectively, when compared to the uncorrected data. This temperature imaging sequence can provide accurate measurements of temperature change in aqueous tissues in the breast and support the use of this sequence in clinical investigations of focused ultrasound treatments for breast cancer.

Objective We seek to identify risk factors associated with abnormal umbilical artery cord gas (UACG). Study Design Secondary analysis of the multi-center Consortium for Safe Labor dataset. This study included singleton, term deliveries with UACG available. Abnormal UACG was defined as pH ≤ 7.0 or base excess > 12 mmol/L. Odds ratios calculated using a multivariable logistic regression to determine clinical factors associated with abnormal UACG. Result 18 589 patients met inclusion criteria, with approximately 2% having an abnormal UACG. Those with prior Cesarean delivery (OR 1.49, 95% CI 1.15–1.93), maternal diabetes (OR 1.67, 95% CI 1.06–2.64), magnesium sulfate use (OR 1.81, 95% CI 1.25–2.60), current Cesarean delivery (OR 2.56, CI 2.06–3.19), pre-eclampsia/HELLP syndrome (OR 2.80, 95% CI 1.79–4.36), and placental abruption (OR 4.81, 95% CI 3.35–6.91) had increased odds of having abnormal UACG at delivery compared to those without. Conclusion Patients with certain conditions may be at increased likelihood of adverse outcomes.

PURPOSE: Develop and evaluate the effectiveness of a T1-based correction method for errors in proton resonant frequency shift thermometry due to non-local field effects caused by heating in fatty breast tissues. METHODS: Computational models of human breast tissue were created by segmenting MRI data from a healthy human volunteer. MR guided focused ultrasound (MRgFUS) heating and MR thermometry measurements were simulated in several locations in the heterogeneous segmented breast models. A T1 based correction method for PRF thermometry errors was applied and the maximum positive and negative errors and the root mean squared error (RMSE) in a region around each heating location was evaluated with and without correction. The method uses T1 measurements to estimate the temperature change in fatty tissues and correct for their influence. Experimental data from a heating study in cadaver breast tissue was analyzed, and the expected PRFS error computed. RESULTS: The simulated MR thermometry had maximum single voxel errors ranging between 10 and 18% when no correction was applied. Applying the correction led to a considerable improvement, lowering the maximum error range to 2–5%. The 5(th) to 95(th) percentile interval of the temperature error distribution was also lowered with correction, from approximately 3.5 to 1°C. This correction worked even when T1 times were uniformly raised or lowered by 5–10%. The experimental data showed predicted errors of 15%. CONCLUSIONS: This simulation study demonstrates that the T1-based correction method reduces MR thermometry errors due to non-local effects from heating in fatty tissues, potentially improving the accuracy of thermometry measurements during MRgFUS treatments. The presented correction method is reliant on having a patient-specific 3D model of the breast, and may be limited by the accuracy of the fat temperatures which in turn may be limited by noise or bias present in the T1 measurements.

Academic physicians must teach elements in an Accreditation Council for Graduate Medical Education (ACGME)-mandated curriculum while balancing career development and clinical workload. Exploring educator perceptions on the learning environment and comparing two instructional methods (traditional didactics [TD] vs. flipped classroom [FC]) in one pediatric subspecialty may elucidate current challenges, barriers, and strategies to optimize learning and educator satisfaction. A randomized trial comparing effectiveness and learner preference for FC versus TD physiology teaching was conducted in ACGME-accredited neonatal-perinatal medicine (NPM) fellowship programs in 2018 to 2019. Educator preferences were elicited through online surveys pre- and postintervention. Free-text comments were provided for questions exploring strengths, challenges, and opportunities in fellowship education. Statistical analysis included comparisons of demographics and pre-post-intervention educator responses between groups. Thematic analysis of text responses was conducted to identify common subthemes. From 61 participating programs, 114 FC educators and 130 TD educators completed surveys. At baseline, all educators experienced professional satisfaction from teaching fellows, but noted challenges with time available to create and/or deliver educational content, limited content expertise amongst faculty, colleagues' limited enthusiasm toward educating fellows, and lack of perceived value of education by institutions given limited protected time or credit toward promotion. Postintervention, educators in both groups noted a preference to teach physiology using FC due to interactivity, learner enthusiasm, and learner-centeredness. FC educators had a 17% increase in preference to teach using FC ( Overall, NPM educators in a trial evaluating a standardized, peer-reviewed curriculum report professional satisfaction from teaching, but described logistical challenges with developing/delivering content. Educators preferred instruction using FC, but identified challenges with learner preparedness and ensuring adequate educator time and skill. Future efforts should be dedicated to addressing these barriers.· Many challenges exist for educators teaching neonatal-perinatal medicine fellows, including time, support, and recognition.. · Many educators preferred using flipped classroom methodology with a standardized curriculum due to interactivity and learner-centeredness.. · Benefits of a standardized, peer-reviewed curriculum include reduced preparation time, adaptability of content, and learning environment enhancement..

OBJECTIVEDespite longstanding and recurrent calls for effective implicit bias (IB) education in health professions education as one mechanism to reduce ongoing racism and health disparities, evidence-based IB curricula for neonatal-perinatal medicine (NPM) are limited. We aim to determine the key IB curricular elements for teaching NPM fellows, advanced practice providers, and attending physicians. STUDY DESIGNA modified Delphi study was performed with content experts in IB and health disparities who had educational relationships to those working and training in the neonatal intensive care unit. RESULTThree Delphi rounds were conducted. Experts reached consensus on a variety of items for inclusion in an IB curriculum, including educational goals, learning objectives, teaching strategies, and educator principles.CONCLUSIONEssential IB curricular components for the field of neonatal medicine were defined using rigorous consensus building methodology.

Objective: This paper presents and evaluates a breast-specific magnetic resonance guided focused ultrasound (MRgFUS) system. A first-in-human evaluation demonstrates the novel hardware, a sophisticated tumor targeting algorithm and a volumetric magnetic resonance imaging (MRI) protocol. Methods: At the time of submission, N = 10 patients with non-palpable T0 stage breast cancer have been treated with the breast MRgFUS system. The described tumor targeting algorithm is evaluated both with a phantom test and in vivo during the breast MRgFUS treatments. Treatments were planned and monitored using volumetric MR-acoustic radiation force imaging (MR-ARFI) and temperature imaging (MRTI). Results: Successful technical treatments were achieved in 80 $\%$ of the patients. All patients underwent the treatment with no sedation and 60 $\%$ of participants had analgesic support. The total MR treatment time ranged from 73 to 114 minutes. Mean error between desired and achieved targeting in a phantom was 2.9 $\pm$ 1.8 mm while 6.2 $\pm$ 1.9 mm was achieved in patient studies, assessed either with MRTI or MR-ARFI measurements. MRTI and MR-ARFI were successful in 60 $\%$ and 70 $\%$ of patients, respectively. Conclusion: The targeting accuracy allows the accurate placement of the focal spot using electronic steering capabilities of the transducer. The use of both volumetric MRTI and MR-ARFI provides complementary treatment planning and monitoring information during the treatment, allowing the treatment of all breast anatomies, including homogeneously fatty breasts.

Purpose The aim was to quantitatively validate the hybrid angular spectrum (HAS) algorithm, a rapid wave propagation technique for heterogeneous media, with both pressure and temperature measurements. Methods Heterogeneous tissue-mimicking phantoms were used to evaluate the accuracy of the HAS acoustic modeling algorithm in predicting pressure and thermal patterns. Acoustic properties of the phantom components were measured by a through-transmission technique while thermal properties were measured with a commercial probe. Numerical models of each heterogeneous phantom were segmented from 3D MR images. Cylindrical phantoms 30-mm thick were placed in the pre-focal field of a focused ultrasound beam and 2D pressure measurements obtained with a scanning hydrophone. Peak pressure, full width at half maximum, and normalized root mean squared difference (RMSDn) between the measured and simulated patterns were compared. MR-guided sonications were performed on 150-mm phantoms to obtain MR temperature measurements. Using HAS-predicted power density patterns, temperature simulations were performed. Experimental and simulated temperature patterns were directly compared using peak and mean temperature plots, RMSDn metrics, and accuracy of heating localization. Results The average difference between simulated and hydrophone-measured peak pressures was 9.0% with an RMSDn of 11.4%. Comparison of the experimental MRI-derived and simulated temperature patterns showed RMSDn values of 10.2% and 11.1% and distance differences between the centers of thermal mass of 2.0 and 2.2 mm. Conclusions These results show that the computationally rapid hybrid angular spectrum method can predict pressure and temperature patterns in heterogeneous models, including uncertainties in property values and other parameters, to within approximately 10%.

Purpose Magnetic resonance guided focused ultrasound (MRgFUS) treatment of tumors uses inter-sonication delays to allow heat to dissipate from the skin and other near-field tissues. Despite inter-sonication delays, treatment of tumors close to the skin risks skin burns. This work has designed and evaluated an open-source, conformable, skin-cooling system for body MRgFUS treatments to reduce skin burns and enable ablation closer to the skin. Methods A MR-compatible skin cooling system is described that features a conformable skin-cooling pad assembly with feedback control allowing continuous flow and pressure maintenance during the procedure. System performance was evaluated with hydrophone, phantom and in vivo porcine studies. Sonications were performed 10 and 5 mm from the skin surface under both control and forced convective skin-cooling conditions. 3D MR temperature imaging was acquired in real time and the accumulated thermal dose volume was measured. Gross analysis of the skin post-sonication was further performed. Device conformability was demonstrated at several body locations. Results Hydrophone studies demonstrated no beam aberration, but a 5–12% reduction of the peak pressure due to the presence of the skin-cooling pad assembly in the acoustic near field. Phantom evaluation demonstrated there is no MR temperature imaging precision reduction or any other artifacts present due to the coolant flow during MRgFUS sonication. The porcine studies demonstrated skin burns were reduced in size or eliminated when compared to the control condition. Conclusion An open-source design of an MRgFUS active skin cooling system demonstrates device conformability with a reduction of skin burns while ablating superficial tissues.

Present a method to use change in phase in repeated Cartesian k-space measurements to monitor the change in magnetic field for dynamic MR temperature imaging.The method is applied to focused ultrasound heating experiments in a gelatin phantom and an ex vivo salt pork sample, without and with simulated respiratory motion.In each experiment, phase variations due to BThis work demonstrates that phase changes resulting from variations in B

Improved early detection methods and treatments have led to the reduction of breast cancer mortality, yet there remains a need for more conservative, more efficacious and less invasive breast cancer treatments. Focused ultrasound (FUS) is a promising non-invasive treatment for localized breast cancer. Magnetic resonance guided FUS leverages breast magnetic resonance imaging (MRI) to plan, monitor and assess treatments under MRI guidance to attain tumor destruction with focused ultrasound, achieving excellent cosmetic, therapeutic, and safety results. MRgFUS is one of the most attractive emerging minimally invasive procedures for breast cancer. This talk will present different focused ultrasound mechanisms that can be used to treat breast cancer and discuss the design considerations that must be considered when developing transducers, sonication protocols and imaging techniques for the treatment of breast cancer with therapeutic ultrasound. Preliminary results from ongoing breast cancer MRgFUS clinical trials will be presented and future opportunities and ongoing challenges for this exciting technology will be elucidated.

Magnetic resonance-guided focused ultrasound (MRgFUS) is a completely non-invasive technology that has been approved by FDA to treat several diseases. This report, prepared by the American Association of Physicist in Medicine (AAPM) Task Group 241, provides background on MRgFUS technology with a focus on clinical body MRgFUS systems. The report addresses the issues of interest to the medical physics community, specific to the body MRgFUS system configuration, and provides recommendations on how to successfully implement and maintain a clinical MRgFUS program. The following sections describe the key features of typical MRgFUS systems and clinical workflow and provide key points and best practices for the medical physicist. Commonly used terms, metrics and physics are defined and sources of uncertainty that affect MRgFUS procedures are described. Finally, safety and quality assurance procedures are explained, the recommended role of the medical physicist in MRgFUS procedures is described, and regulatory requirements for planning clinical trials are detailed. Although this report is limited in scope to clinical body MRgFUS systems that are approved or currently undergoing clinical trials in the United States, much of the material presented is also applicable to systems designed for other applications.

Transcranial Magnetic Resonance guided Focused Ultrasound (TcMRgFUS) has been proven to be an effective treatment for some neurological disorders such as essential and Parkinson's tremor. However, magnetic resonance guidance at 3 Tesla (3T) frequencies and using the large hemispherical transducers required for TcMRgFUS results in artifactual low-signal bands that pass through key regions of the brain. The purpose of this work was to investigate the use of a circular conductive Radio Frequency (RF) screen, that is bent to have a 12 cm radius in one direction and positioned near the top or back of the head, to reduce or remove these artifactual low-signal bands in TcMRgFUS. The impact of using an RF screen to remove these low signal bands was studied in both imaging experiments and electromagnetic simulations. Hydrophone measurements of the acoustic transparency of the bronze 2 mm diameter square mesh screen used in the imaging studies were compared with temperature measurements with and without the screen in heating studies in the TcMRgFUS system. The imaging and simulation studies both show that for the different screen configurations studied in this work, RF screen removes the low-signal bands and increases both homogeneity and signal-to-noise ratio (SNR) throughout the region of the brain. Hydrophone and heating studies indicate that even a 2 mm wire mesh provides minimal attenuation to the ultrasound beam. Simulation results also suggest that a 1 cm mesh will provide adequate artifact suppression with even less ultrasound attenuation. An RF screen that disrupts the natural waveguide nature of the transducer in the 3T MR environment can change the electromagnetic field profile to reduce unwanted artifacts and provide an imaging region which has more homogeneity and higher SNR throughout the brain.

The adverse event of skin burns and the restrictions caused by multi-hour treatment times continue to limit the clinical efficacy and cost effectiveness of MRgFUS thermal therapies. This proposal directly addresses these unmet needs with two primary aims. Aim 1 includes design and fabrication of a prototype cooling device, testing of clinically identified design specifications, and initial experimental validation ex vivo tissue experiments. This conformable skin-cooling device will reduce the potential for skin burns in desmoid tumor and other MRgFUS treatments. Aim 2 will assess the skin cooling device on a pre-clinical MRgFUS system with rabbit and pig studies and will integrate the device with the clinical ExAblate 2100 system. The ultimate goal of the device design is to be MRgFUS system independent. This may require a modular design that allows for both clinical and veterinarian applications. The completion of this proposal will deliver the engineering schematic, parts list and use manual of the completed device, validation data and install a single device at the Focused Ultrasound Center of Excellence at Stanford University.Presented here are the open-source parts list and assembly files to reproduce the skin cooling device, along with the device user manual. An open-access publication on the design methods and preclinical results will be published soon.

A computer implemented method for measuring T1 in an anatomical region of interest during a dynamic procedure includes acquiring a reference MR image of the anatomical region of interest using a first flip angle. A first set of dynamic MR images of the anatomical region of interest are acquired using a second flip angle. The reference MR image and the first set are used to calculate a reference T1 value for tissue in the anatomical region of interest. During an intervention where the T1 value may change, a second set of dynamic MR images of the anatomical region of interest is acquired using the second flip angle. The reference MR image and the second set are used to calculate an estimated T1 value. The reference T1 value, the estimated T1 value, and the first and second flip angles may then be used to correct the estimated T1 value.

Purpose To evaluate the effect of a focused ultrasound transducer position and ground plane configuration on magnetic resonance image quality. Methods The effect of transducer position with respect to the MRI B0 field and the radiofrequency receive coils was evaluated in a breast-specific MRgFUS system with an integrated RF phased-array coil. Image signal-to-noise ratio was evaluated at different transducer locations. The effect of ultrasound transducer ground plane configuration was evaluated using a replica transducer with 12 ground plane configurations. All evaluations were performed at 3 Tesla. Results Both transducer position and ground plane configuration were found to have a considerable effect on overall image SNR. A 67% increase in SNR was achieved by positioning the transducer face perpendicular to the B0 field. A 25% increase in SNR was achieved by segmenting the replica transducer ground plane from one continuous plane to nine individual segments. Conclusions Advances in focused ultrasound hardware allow for integrated radiofrequency MRI coils as well as adjustable transducer positioning. The placement of the ultrasound transducer with respect to both the magnetic field and RF coils can have a considerable effect on image SNR and the resulting MR images that are used for MR-guided focused ultrasound treatment planning, monitoring and assessment.

In focused ultrasound (FUS) thermal ablation of diseased tissue, acoustic beam and thermal simulations enable treatment planning and optimization. In this study, a treatment-planning methodology that uses the hybrid angular spectrum (HAS) method and the Pennes' bioheat equation (PBHE) is experimentally validated in homogeneous tissue-mimicking phantoms. Simulated three-dimensional temperature profiles are compared to volumetric MR thermometry imaging (MRTI) of FUS sonications in the phantoms, whose acoustic and thermal properties are independently measured. Additionally, Monte Carlo (MC) uncertainty analysis is performed to quantify the effect of tissue property uncertainties on simulation results. The mean error between simulated and experimental spatiotemporal peak temperature rise was +0.33°C (+6.9%). Despite this error, the experimental temperature rise fell within the expected uncertainty of the simulation, as determined by the MC analysis. The average errors of the simulated transverse and longitudinal full width half maximum (FWHM) of the profiles were -1.9% and 7.5%, respectively. A linear regression and local sensitivity analysis revealed that simulated temperature amplitude is more sensitive to uncertainties in simulation inputs than in the profile width and shape. Acoustic power, acoustic attenuation and thermal conductivity had the greatest impact on peak temperature rise uncertainty; thermal conductivity and volumetric heat capacity had the greatest impact on FWHM uncertainty. This study validates that using the HAS and PBHE method can adequately predict temperature profiles from single sonications in homogeneous media. Further, it informs the need to accurately measure or predict patient-specific properties for improved treatment planning of ablative FUS surgeries.

Purpose Implement and evaluate a 3D MRI method to measure temperature changes with high spatial and temporal resolution and large field of view. Methods A multiecho pseudo-golden angle stack-of-stars (SOS) sequence with k-space weighted image contrast (KWIC) reconstruction was implemented to simultaneously measure multiple quantities, including temperature, initial signal magnitude M(0), transverse relaxation time ( T2*), and water/fat images. Respiration artifacts were corrected using self-navigation. KWIC artifacts were removed using a multi-baseline library. The phases of the multiple echo images were combined to improve proton resonance frequency precision. Temperature precision was tested through in vivo breast imaging (N = 5 healthy volunteers) using both coronal and sagittal orientations and with focused ultrasound (FUS) heating in a pork phantom using a breast specific MR-guided FUS system. Results Temperature measurement precision was significantly improved after echo combination when compared with the no echo combination case (spatial average of the standard deviation through time of 0.3–1.0 and 0.7–1.9°C, respectively). Temperature measurement accuracy during heating was comparable to a 3D seg-EPI sequence. M(0) and T2* values showed temperature dependence during heating in pork adipose tissue. Conclusion A self-navigated 3D multiecho SOS sequence with dynamic KWIC reconstruction is a promising thermometry method that provides multiple temperature sensitive quantitative values. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Advances in imaging and early cancer detection have increased interest in magnetic resonance (MR) guided focused ultrasound (MRgFUS) technologies for cancer treatment. MRgFUS ablation treatments could reduce surgical risks, preserve organ tissue/function, and improve patient quality of life. However, surgical resection and histological analysis remain the gold standard to assess cancer treatment response. For non-invasive ablation therapies such as MRgFUS, the treatment response must be determined through MR imaging biomarkers. However, current MR biomarkers are inconclusive and have not been rigorously evaluated against histology via accurate registration. Existing registration methods rely on anatomical features to directly register in vivo MR and histology. For MRgFUS applications in anatomies such as liver, kidney, or breast, anatomical features independent from treatment features are often insufficient to perform direct registration. We present a novel MR to histology registration workflow that utilizes intermediate imaging and does not rely on these independent features. The presented workflow yields an overall registration accuracy of 1.00 +/- 0.13 mm. The developed registration pipeline is used to evaluate a common MRgFUS treatment assessment biomarker against histology. Evaluating MR biomarkers against histology using this registration pipeline will facilitate validating novel MRgFUS biomarkers to improve treatment assessment without surgical intervention., Comment: 12 pages, 5 figures, 2 tables

Noninvasive MR-guided focused ultrasound (MRgFUS) treatments are promising alternatives to the surgical removal of malignant tumors. A significant challenge is assessing the viability of treated tissue during and immediately after MRgFUS procedures. Current clinical assessment uses the nonperfused volume (NPV) biomarker immediately after treatment from contrast-enhanced MRI. The NPV has variable accuracy, and the use of contrast agent prevents continuing MRgFUS treatment if tumor coverage is inadequate. This work presents a novel, noncontrast, learned multiparametric MR biomarker that can be used during treatment for intratreatment assessment, validated in a VX2 rabbit tumor model. A deep convolutional neural network was trained on noncontrast multiparametric MR images using the NPV biomarker from follow-up MR imaging (3-5 days after MRgFUS treatment) as the accurate label of nonviable tissue. A novel volume-conserving registration algorithm yielded a voxel-wise correlation between treatment and follow-up NPV, providing a rigorous validation of the biomarker. The learned noncontrast multiparametric MR biomarker predicted the follow-up NPV with an average DICE coefficient of 0.71, substantially outperforming the current clinical standard (DICE coefficient = 0.53). Noncontrast multiparametric MR imaging integrated with a deep convolutional neural network provides a more accurate prediction of MRgFUS treatment outcome than current contrast-based techniques., 11 pages, 12 figures

To characterize behavior of 2-year-old children based on the severity of bronchopulmonary dysplasia (BPD).We studied children born at 22-26 weeks of gestation and assessed at 22-26 months of corrected age with the Child Behavior Checklist (CBCL). BPD was classified by the level of respiratory support at 36 weeks of postmenstrual age. CBCL syndrome scales were the primary outcomes. The relationship between BPD grade and behavior was evaluated, adjusting for perinatal confounders. Mediation analysis was performed to evaluate whether cognitive, language, or motor skills mediated the effect of BPD grade on behavior.Of 2310 children, 1208 (52%) had no BPD, 806 (35%) had grade 1 BPD, 177 (8%) had grade 2 BPD, and 119 (5%) had grade 3 BPD. Withdrawn behavior (P .001) and pervasive developmental problems (P .001) increased with worsening BPD grade. Sleep problems (P = .008) and aggressive behavior (P = .023) decreased with worsening BPD grade. Children with grade 3 BPD scored 2 points worse for withdrawn behavior and pervasive developmental problems and 2 points better for externalizing problems, sleep problems, and aggressive behavior than children without BPD. Cognitive, language, and motor skills mediated the effect of BPD grade on the attention problems, emotionally reactive, somatic complaints, and withdrawn CBCL syndrome scales (P values .05).BPD grade was associated with increased risk of withdrawn behavior and pervasive developmental problems but with decreased risk of sleep problems and aggressive behavior. The relationship between BPD and behavior is complex. Cognitive, language, and motor skills mediate the effects of BPD grade on some problem behaviors.

PURPOSE Treating uterine fibroids with less invasive therapies such as magnetic resonance-guided focused ultrasound (MRgFUS) is an attractive alternative to surgery. Treatment planning can improve MRgFUS procedures and reduce treatment times, but the tissue properties that currently inform treatment planning tools are not adequate. This study aims to develop an ex vivo uterine fibroid model that can emulate the in vivo environment allowing for characterization of the uterus and fibroid MR, acoustic, and thermal tissue properties while maintaining viability for the necessary postsurgical histopathological assessments. METHODS Women undergoing a hysterectomy due to fibroid-related symptoms were invited to undergo a preoperative pelvic MRI and to permit postoperative testing of their uterine specimen. Patients that declined or could not be scheduled for a pre-operative MRI were still able to allow post-operative testing of their excised tissue. Following surgical removal of the uterus, nonmorcellated tissues were reperfused with a Krebs-Henseleit buffer solution. An MR-compatible perfusion system was designed to maintain tissue viability inside the MR suite during scanning. MR imaging protocols utilized preoperatively were repeated on whole sample, reperfused ex vivo uterus specimens. Thermal properties including thermal diffusivity and thermal conductivity of the uterus and fibroids were determined using an invasive needle sensor device in 50% of the specimens. Acoustic property measurements (density, speed of sound and attenuation) were obtained for approximately 20% of the tissue samples using both through-transmission and radiation force balance techniques. Differences between fibroid and uterus and in vivo and ex vivo measurements were evaluated with a two-tailed Student t test. RESULTS Fourteen patients participated in the study and measurements were obtained from 22 unique fibroids. Of the 16 fibroids available for preoperative MRI testing, 69% demonstrated classic hypo-intensity relative to the myometrium, with the remainder presenting with iso- (25%) or hyper-intensity (6%). While thermal diffusivity was not significantly different between fibroid and myometrium tissues (0.217 ± 0.047 and 0.204 ± 0.039 mm2 /s, respectively), the acoustic attenuation in fibroid tissue was significantly higher than myometrium (0.092 ± 0.021 and 0.052 ± 0.023 Np/cm/MHz, respectively). When comparing in vivo with ex vivo MRI T1 and T2 measurements in fibroids and myometrium tissue, the only difference was found in the fibroid T2 property (P

A magnetic resonance (MR) shear wave elastography technique that uses transient acoustic radiation force impulses from a focused ultrasound (FUS) transducer and a sinusoidal-shaped MR displacement encoding strategy is presented. Using this encoding strategy, an analytic expression for calculating the shear wave speed in a heterogeneous medium was derived. Green’s function-based simulations were used to evaluate the feasibility of calculating shear wave speed maps using the analytic expression. Accuracy of simulation technique was confirmed experimentally in a homogeneous gelatin phantom. The elastography measurement was compared to harmonic MR elastography in a homogeneous phantom experiment and the measured shear wave speed values differed by less than 14%. This new transient elastography approach was able to map the position and shape of inclusions sized from 8.5 to 14 mm in an inclusion phantom experiment. These preliminary results demonstrate the feasibility of using a straightforward analytic expression to generate shear wave speed maps from MR images where sinusoidal-shaped motion encoding gradients are used to encode the displacement-time history of a transiently propagating wave-packet. This new measurement technique may be particularly well suited for performing elastography before, during, and after MR-guided FUS therapies since the same device used for therapy is also used as an excitation source for elastography.

PURPOSE To develop a method for rapid prediction of the geometric focus location in MR coordinates of a focused ultrasound (US) transducer with arbitrary position and orientation without sonicating. METHODS Three small tracker coil circuits were designed, constructed, attached to the transducer housing of a breast-specific MR-guided focused US (MRgFUS) system with 5 degrees of freedom, and connected to receiver channel inputs of an MRI scanner. A one-dimensional sequence applied in three orthogonal directions determined the position of each tracker, which was then corrected for gradient nonlinearity. In a calibration step, low-level heating located the US focus in one transducer position orientation where the tracker positions were also known. Subsequent US focus locations were determined from the isometric transformation of the trackers. The accuracy of this method was verified by comparing the tracking coil predictions to thermal center of mass calculated using MR thermometry data acquired at 16 different transducer positions for MRgFUS sonications in a homogeneous gelatin phantom. RESULTS The tracker coil predicted focus was an average distance of 2.1 ± 1.1 mm from the thermal center of mass. The one-dimensional locator sequence and prediction calculations took less than 1 s to perform. CONCLUSION This technique accurately predicts the geometric focus for a transducer with arbitrary position and orientation without sonicating. Magn Reson Med 77:2424-2430, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Purpose: This simulation study evaluates the effects of phase aberration in breast MR-guided focused ultrasound (MRgFUS) ablation treatments performed with a phased-array transducer positioned laterally to the breast. A quantification of these effects in terms of thermal dose delivery and the potential benefits of phase correction is demonstrated in four heterogeneous breast numerical models. Methods: To evaluate the effects of varying breast tissue properties on the quality of the focus, four female volunteers with confirmed benign fibroadenomas were imaged using 3T MRI. These images were segmented into numerical models with six tissue types, with each tissue type assigned standard acoustic properties from the literature. Simulations for a single-plane 16-point raster-scan treatment trajectory centered in a fibroadenoma in each modeled breast were performed for a breast-specific MRgFUS system. At each of the 16 points, pressure patterns both with and without applying a phase correction technique were determined with the hybrid-angular spectrum method. Corrected phase patterns were obtained using a simulation-based phase aberration correction technique to adjust each element’s transmit phase to obtain maximized constructive interference at the desired focus. Thermal simulations were performed for both the corrected and uncorrected pressure patterns using a finite-difference implementation of the Pennes bioheat equation. The effect of phase correction was evaluated through comparison of thermal dose accumulation both within and outside a defined treatment volume. Treatment results using corrected and uncorrected phase aberration simulations were compared by evaluating the power required to achieve a 20 °C temperature rise at the first treatment location. The extent of the volumes that received a minimum thermal dose of 240 CEM at 43 °C inside the intended treatment volume as well as the volume in the remaining breast tissues was also evaluated in the form of a dose volume ratio (DVR), a DVR percent change between corrected and uncorrected phases, and an additional metric that measured phase spread. Results: With phase aberration correction applied, there was an improvement in the focus for all breast anatomies as quantified by a reduction in power required (13%–102%) to reach 20 °C when compared to uncorrected simulations. Also, the DVR percent change increased by 5%–77% in seven out of eight cases, indicating an improvement to the treatment as measured by a reduction in thermal dose deposited to the nontreatment tissues. Breast compositions with a higher degree of heterogeneity along the ultrasound beam path showed greater reductions in thermal dose delivered outside of the treatment volume with correction applied than beam trajectories that propagated through more homogeneous breast compositions. An increasing linear trend was observed between the DVR percent change and the phase-spread metric (R2 = 0.68). Conclusions: These results indicate that performing phase aberration correction for breast MRgFUS treatments is beneficial for the small-aperture transducer (14.4 × 9.8 cm) evaluated in this work. While all breast anatomies could benefit from phase aberration correction, greater benefits are observed in more heterogeneous anatomies.

PURPOSE: Implement simultaneous proton resonance frequency (PRF) shift and T(1) measurements with equivalent temporal resolution using a single reference variable flip angle (VFA) method. This novel method allows for simultaneous thermometry in both aqueous and fatty tissue. METHODS: This method acquires a single reference image at the lower flip angle and all dynamic images at the higher angle. T(1) is calculated using a single reference VFA method, which accounts for the reference image temperature remaining constant. Monte Carlo simulations determined the optimal dynamic flip angle for combined PRF and T(1) measurements. This method was evaluated in MR guided focused ultrasound heating experiments using a gelatin phantom and human cadaver breasts. In vivo measurement precision was demonstrated in healthy female volunteers under non-heating conditions. RESULTS: Temperature rise during MRgFUS heating was measured in aqueous tissue with both PRF and T(1). Both measures show good qualitative agreement in both space and time in aqueous tissue. The T(1) change due to temperature increase was measured in fat, demonstrating the expected temporal response. The dynamic flip angle that produces optimal SNR for PRF measurements is lower than the optimal angle for T(1) measurements, necessitating the selection of a compromise angle. CONCLUSION: The single reference VFA method provides a reliable way to simultaneously measure PRF temperature and T(1) change and overcomes PRF’s inability to simultaneously monitor temperature in aqueous and adipose tissues. Future work will calibrate T1 change to temperature enabling real-time temperature in fat, increasing patient safety and treatment efficacy during thermal interventional treatments.

For thermal modeling to play a significant role in treatment planning, monitoring, and control of magnetic resonance-guided focused ultrasound (MRgFUS) thermal therapies, accurate knowledge of ultrasound and thermal properties is essential. This study develops a new analytical solution for the temperature change observed in MRgFUS which can be used with experimental MR temperature data to provide estimates of the ultrasound initial heating rate, Gaussian beam variance, tissue thermal diffusivity, and Pennes perfusion parameter. Simulations demonstrate that this technique provides accurate and robust property estimates that are independent of the beam size, thermal diffusivity, and perfusion levels in the presence of realistic MR noise. The technique is also demonstrated in vivo using MRgFUS heating data in rabbit back muscle. Errors in property estimates are kept less than 5% by applying a third order Taylor series approximation of the perfusion term and ensuring the ratio of the fitting time (the duration of experimental data utilized for optimization) to the perfusion time constant remains less than one.

Purpose To develop reliable three-dimensional (3D) segmented echo planar imaging (seg-EPI) proton resonance frequency (PRF) temperature monitoring in the presence of respiration-induced B0 variation. Methods A free induction decay (FID) phase navigator was inserted into a 3D seg-EPI sequence before and after EPI readout to monitor B0 field variations. Using the field change estimates, the phase of each k-space line was adjusted to remove the additional phase from the respiratory induced off-resonance. This correction technique was evaluated while heating with MR-guided focused ultrasound (MRgFUS) in phantoms with simulated breathing and during nonheating conditions in healthy in vivo breasts. Results With k-space phase correction, the standard deviation of magnitude images and PRF temperature measurements in breast from five volunteers improved by an average factor of 1.5 and 2.1, respectively. Improved accuracy of temperature estimates was observed after correction while heating with MRgFUS in phantoms. Conclusion Phase correction based on two FID navigators placed before and after the echo train provides promising results for implementing 3D monitoring of thermal therapy treatments in the presence of field variations due to respiration. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.

This study presents a new approach for evaluating bioheat transfer equation (BHTE) models used in treatment planning, control and evaluation of all thermal therapies. First, 3D magnetic resonance temperature imaging (MRTI) data are used to quantify blood flow-related energy losses, including the effects of perfusion and convection. Second, that information is used to calculate parameters of a BHTE model; in this paper the widely used Pennes BHTE. As a self-consistency check, the BHTE parameters are utilized to predict the temperatures from which they were initially derived. The approach is evaluated with finite-difference simulations and implemented experimentally with focused ultrasound heating of an ex vivo porcine kidney perfused at 0, 20 and 40 ml/min (n = 4 each). The simulation results demonstrate accurate quantification of blood flow-related energy losses, except in regions of sharp blood flow discontinuities where the transitions are spatially smoothed. The smoothed transitions propagate into estimates of the Pennes perfusion parameter but have limited effect on the accuracy of temperature predictions using those estimates. Longer acquisition time periods mitigate the effects of MRTI noise, but worsen the effect of flow discontinuities. For the no-flow kidney experiments, the estimates of a uniform, constant Pennes perfusion parameter are approximately zero, and at 20 and 40 ml/min, the average estimates increase with flow rate to 3.0 and 4.2 kg/m3/s, respectively. When Pennes perfusion parameter values are allowed to vary spatially, but remain temporally constant, BHTE temperature predictions are more accurate than when using spatially uniform, constant Pennes perfusion values, with reductions in RMSE values of up to 79%. Locations with large estimated perfusion values correspond to high flow regions of the kidney observed in T1-weighted MR images. This novel, MRTI-based technique holds promise for improving understanding of thermal therapy biophysics and for evaluating biothermal models.

The Person-Centered Hospital Discharge Program (PCHDP) was offered by the Centers for Medicare and Medicaid Services as a way to improve care to Medicare and Medicaid beneficiaries in Maryland. The PCHDP used a care nurse/coordinator to facilitate the successful transition of patients at risk for becoming eligible for Medicaid. The purpose of this study was to examine the outcomes of the PCHDP pilot, explore factors that influenced hospital and long-term care admissions following hospital discharge, and obtain operational data to develop new programs with related objectives. Area Agencies on Aging were provided with a care coordinator who obtained patient data, developed an individualized care plan, and determined visit frequency and length of services. Multivariate analysis of variance was conducted to examine differences between those hospitalized or admitted to a skilled nursing facility during the follow-up period. The sample consisted of 359 at-risk patients, and the mean length of follow-up was approximately two months. Most patients did not go to the emergency room (N = 319, 88%) during the period of follow-up and were not admitted to an acute care setting (N = 301, 84%) or skilled nursing home (N = 322, 86%). Those who were rehospitalized were slightly younger and had more visits from the care coordinator. We anticipate that the care coordinators identified individuals at greatest need for follow-up and support. Future research should explore ways in which these care coordinators can intervene to prevent hospital readmission and long-term nursing home care.

Purpose Evaluate effects of model parameter inaccuracies (thermal conductivity, k, and ultrasound power deposition density, Q), k-space reduction factor (R), and rate of temperature increase ( ) in a thermal model-based reconstruction for MR-thermometry during focused-ultrasound heating. Methods Simulations and ex vivo experiments were performed to investigate the accuracy of the thermal model and the model predictive filtering (MPF) algorithm for varying R and , and their sensitivity to errors in k and Q. Ex vivo data was acquired with a segmented EPI pulse sequence to achieve large field-of-view (192 × 162 × 96 mm) four-dimensional temperature maps with high spatiotemporal resolution (1.5 × 1.5 × 2.0 mm, 1.7 s). Results In the simulations, 50% errors in k and Q resulted in maximum temperature root mean square errors (RMSE) of 6°C for model only and 3°C for MPF. Using recently developed methods, estimates of k and Q were accurate to within 3%. The RMSE between MPF and true temperature increased with R and . In the ex vivo study the RMSE remained below 0.7°C for R ranging from 4 to 12 and of 0.28–0.75°C/s. Conclusion Errors in MPF temperatures occur due to errors in k and Q. These MPF temperature errors increase with increase in R and , but are smaller than those obtained using the thermal model alone. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.