Physics Informed Neural Networks for Estimation of Tissue Properties from Multi-echo Configuration State MRI.

This work investigates the use of configuration state imaging together with deep neural networks to develop quantitative MRI techniques for deployment in an interventional setting. A physics modeling technique for inhomogeneous fields and heterogeneous tissues is presented and used to evaluate the theoretical capability of neural networks to estimate parameter maps from configuration state signal data. All tested normalization strategies achieved similar performance in estimating and .

Evaluating the Need for Competency-Based Pharmacy Education (CBPE): The Report of the 2023-2024 Academic Affairs Standing Committee.

The 2023-2024 Academic Affairs Committee was charged to create a sense of urgency around the concept of Competency-Based Pharmacy Education and develop a "readiness for change" instrument that is based on the 5 essential elements that make up the definition of Competency-Based Pharmacy Education. This report describes the process undertaken by the committee to determine the societal needs of pharmacists and current state of pharmacy practice and pharmacy education. The practice gaps in pharmacy education and the key drivers needed to close these gaps are evaluated.

Development of an MR-Guided Focused Ultrasound (MRgFUS) Lesioning Approach for the Fornix in the Rat Brain.

Objective: High-intensity magnetic resonance-guided focused ultrasound (MRgFUS) is a non-invasive therapy to lesion brain tissue, used clinically in patients and pre-clinically in several animal models. Challenges with focused ablation in rodent brains can include skull and near-field heating and accurately targeting small and deep brain structures. We overcame these challenges by creating a novel method consisting of a craniectomy skull preparation, a high-frequency transducer (3 MHz) with a small ultrasound focal spot, a transducer positioning system with an added manual adjustment of ∼0.

MR-Guided Focused Ultrasound Thalamotomy in the Setting of Aneurysm Clip.

We report on a 75-year-old woman with a history of right MCA aneurysm clipping and medically refractive right-hand tremor. We successfully performed focused ultrasound thalamotomy of the left ventral intermediate nucleus under MR imaging-guidance at 3T. A thorough pretreatment evaluation of MR thermometry was critical to ensure that adequate precision could be achieved at the intended target.

Validation of single reference variable flip angle (SR-VFA) dynamic T mapping with T * correction using a novel rotating phantom.

Purpose: To validate single reference variable flip angle (SR-VFA) dynamic T mapping with and without T * correction against inversion recovery (IR) T measurements.

Methods: A custom cylindrical phantom with three concentric compartments was filled with variably doped agar to produce a smooth spatial gradient of the T relaxation rate as a function of angle across each compartment. IR T , VFA T , and B measurements were made on the phantom before rotation, and multi-echo stack-of-radial dynamic images were acquired during rotation via an MRI-compatible motor.

Extracranial carotid artery atherosclerotic plaque and APOE polymorphisms: a systematic review and meta-analysis.

Introduction: Carotid atherosclerotic plaque is an important independent risk factor for stroke. Apolipoprotein E (APOE) influences cholesterol levels and certain isoforms are associated with increased carotid atherosclerosis, though the exact association between APOE and carotid plaque is uncertain. The study aimed to evaluate the association between APOE and carotid plaque.

Development of an MR-guided focused ultrasound (MRgFUS) lesioning approach for small and deep structures in the rat brain.

Objective: High-intensity magnetic resonance-guided focused ultrasound (MRgFUS) is a noninvasive therapy to lesion brain tissue, used clinically in patients and preclinically in several animal models. Challenges with focused ablation in rodent brains can include skull and near-field heating and accurately targeting small and deep brain structures. We overcame these challenges by creating a novel method consisting of a craniectomy skull preparation, a high-frequency transducer (3 MHz) with a small ultrasound focal spot, a transducer positioning system with an added manual adjustment of ∼0.

The influence of bone model geometries on the determination of skull acoustic properties.

In this study, we investigated the impact of various simulated skull bone geometries on the determination of skull speed of sound and acoustic attenuation values via optimization using transmitted pressure amplitudes beyond the bone. Using the hybrid angular spectrum method (HAS), we simulated ultrasound transmission through four model sets of different geometries involving sandwiched layers of diploë and cortical bone in addition to three models generated from CT images of ex-vivo human skull-bones. We characterized cost-function solution spaces for each model and, using optimization, found that when a model possessed appreciable variations in resolvable layer thickness, the predefined attenuation coefficients could be found with low error (RMSE < 0.

Evaluation of methemoglobin as an intravascular contrast agent: T1 relaxation time effect in a rabbit model.

Objective: Alternative contrast agents for MRI are needed for individuals who may respond adversely to gadolinium, and need an intravascular agent for specific indications. One potential contrast agent is intracellular methemoglobin, a paramagnetic molecule that is normally present in small amounts in red blood cells. An animal model was used to determine whether methemoglobin modulation with intravenous sodium nitrite transiently changes the T1 relaxation of blood.

Influence of cerebrospinal fluid on power absorption during transcranial magnetic resonance-guided focused ultrasound treatment.

Background: Ultrasound beam aberration correction is vital when focusing ultrasound through the skull bone in transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS) applications. Current methods make transducer element phase adjustments to compensate for the variation in skull properties (shape, thickness, and acoustic properties), but do not account for variations in the internal brain anatomy.

Purpose: Our objective is to investigate the effect of cerebrospinal fluid (CSF) and brain anatomy on beam focusing in tcMRgFUS treatments.

MRI-compatible electromagnetic servomotor for image-guided medical robotics.

The soft-tissue imaging capabilities of magnetic resonance imaging (MRI) combined with high precision robotics has the potential to improve the precision and safety of a wide range of image-guided medical procedures. However, functional MRI-compatible robotics have not yet been realized in part because conventional electromagnetic servomotors can become dangerous projectiles near the strong magnetic field of an MRI scanner. Here we report an electromagnetic servomotor constructed from non-magnetic components, where high-torque and controlled rotary actuation is produced via interaction between electrical current in the servomotor armature and the magnetic field generated by the superconducting magnet of the MRI scanner itself.

Simultaneous proton resonance frequency T - MR shear wave elastography for MR-guided focused ultrasound multiparametric treatment monitoring.

Purpose: To develop an efficient MRI pulse sequence to simultaneously measure multiple parameters that have been shown to correlate with tissue nonviability following thermal therapies.

Methods: A 3D segmented EPI pulse sequence was used to simultaneously measure proton resonance frequency shift (PRFS) MR thermometry (MRT), T relaxation time, and shear wave velocity induced by focused ultrasound (FUS) push pulses. Experiments were performed in tissue mimicking gelatin phantoms and ex vivo bovine liver.

Validation of a drift-corrected 3D MR temperature imaging sequence for breast MR-guided focused ultrasound treatments.

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.

Correction of heat-induced susceptibility changes in respiratory-triggered 2D-PRF-based thermometry for monitoring of magnetic resonance-guided hepatic microwave ablation in a human-like porcine model.

Purpose: To develop and evaluate susceptibility corrected 2D proton resonance frequency (PRF)-based magnetic resonance (MR)-thermometry for the accurate assessment of the ablation zone of hepatic microwave ablation (MWA).

Methods And Materials: Twelve hepatic MWA were performed in five LEWE minipigs with human-like fissure-free liver. Temperature maps during ablation of PRF-based MR-thermometry were corrected by modeling heat induced susceptibility changes.

Association between high-risk extracranial carotid plaque and covert brain infarctions and cerebral microbleeds.

Purpose: Covert brain infarctions (CBIs) and cerebral microbleeds (CMBs) represent subclinical sequelae of ischemic and hemorrhagic cerebral small vessel disease, respectively. In addition to thromboembolic stroke, carotid atherosclerosis has been associated with downstream vascular brain injury, including inflammation and small vessel disease. The specific plaque features responsible for this are unknown.

Factors Associated with Refractory Status Epilepticus Termination Following Ketamine Initiation: A Multivariable Analysis Model.

Background: In this study, we identify factors associated with ketamine success in the treatment of refractory status epilepticus (SE). We also evaluate for adverse events including systemic and cerebral hemodynamic stability and fluid volume overload.

Methods: In this retrospective, large, single-center, observational study over a 10-year period, 879 consecutive patients receiving intravenous (IV) ketamine were reviewed, and 81 patients were identified as receiving IV ketamine for the treatment of SE.

A k-space-based method to measure and correct for temporal B field variations in MR temperature imaging.

Purpose: 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.

Methods: 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.

Results: In each experiment, phase variations due to B field drift and respiration were readily apparent in the measured phase difference.

Effects of T * on accuracy and precision of dynamic T measurements using the single reference variable flip angle method: a simulation study.

Purpose: To study in simulation and in theory the accuracy and precision of dynamic T measurements obtained using the previously published single-reference variable flip angle (SR-VFA) technique, with a focus on the effects of dynamic changes in T * on the calculation.

Methods: Monte Carlo simulations were performed over 1000 noisy iterations for the VFA method, the SR-VFA method, and a proposed method, SR-VFA with a T * correction (SR-VFA-T *). Dynamic T estimates were calculated analytically for each method, with signals modeled by the steady-state spoiled gradient echo equation.

Quasistatic Solutions versus Full-Wave Solutions of Single-Channel Circular RF Receive Coils on Phantoms of Varying Conductivities at 3 Tesla.

Purpose: Although full-wave simulations could be used to aid in RF coil design, the algorithms may be too slow for an iterative optimization algorithm. If quasistatic simulations are accurate within the design tolerance, then their use could reduce simulation time by orders of magnitude compared to full-wave simulations. This paper examines the accuracy of quasistatic and full-wave simulations at 3 Tesla.

Carotid Compliance and Parahippocampal and Hippocampal Volume over a 20-Year Period.

Introduction: We evaluated the association between carotid compliance, a measure of arterial stiffness, to parahippocampal volume (PHV) and hippocampal volume (HV) over 20 years later in the Atherosclerosis Risk in the Community study.

Methods: We included participants with common carotid compliance measurements at visit 1 (1987-1989) and volumetric brain MRI at visit 5 (2011-2013). The primary outcomes are pooled bilateral PHV and HV.

Differentiation of symptomatic and asymptomatic carotid intraplaque hemorrhage using 3D high-resolution diffusion-weighted stack of stars imaging.

Ischemic events related to carotid disease are far more strongly associated with plaque instability than stenosis. 3D high-resolution diffusion-weighted (DW) imaging can provide quantitative diffusion measurements on carotid atherosclerosis and may improve detection of vulnerable intraplaque hemorrhage (IPH). The 3D DW-stack of stars (SOS) sequence was implemented with 3D SOS acquisition combined with DW preparation.

A T1-based correction method for proton resonance frequency shift thermometry in breast tissue.

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.

AAPM Task Group 241: A medical physicist's guide to MRI-guided focused ultrasound body systems.

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.

Optimal Carotid Plaque Features on Computed Tomography Angiography Associated With Ischemic Stroke.

Background Stenosis has historically been the major factor used to determine carotid stroke sources. Recent evidence suggests that specific plaque features detected on imaging may be more highly associated with ischemic stroke than stenosis. We sought to determine computed tomography angiography (CTA) imaging features of carotid plaque that optimally discriminate ipsilateral stroke sources.

Magnetic resonance shear wave elastography using transient acoustic radiation force excitations and sinusoidal displacement encoding.

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.