Michael Garwood

University of Minnesota | UMN · Center for Magnetic Resonance Research

Highly portable and accessible MRI technology will allow researchers to conduct field-based MRI research in community settings. Previous guidance for researchers working with fixed MRI does not address the novel ethical, legal, and societal issues (ELSI) of portable MRI (pMRI). Our interdisciplinary Working Group (WG) previously identified 15 core...

Besides being responsible for olfaction and air intake, the nose contains abundant vasculature and autonomic nervous system innervations, and it is a cerebrospinal fluid clearance site. Therefore, the nose is an attractive target for functional MRI (fMRI). Yet, nose fMRI has not been possible so far due to signal losses originating from nasal air-t...

Brain imaging MRI comprises a significant proportion of MRI scans, but the requirement for including the shoulders in the magnet bore means there is not a significant size reduction in the magnet compared to whole-body magnets. Here we present a new design approach for brain imaging MRI magnets targeting ±20 kHz B0 variation over the imaging volume...

Understanding the effects of white matter (WM) axon fibre microstructure on T1 relaxation is important for neuroimaging. Here, we have studied the interrelationship between T1 and axon fibre configurations at 3T and 7T. T1 and S0 (=signal intensity at zero TI) were computed from MP2RAGE images acquired with six inversion recovery times. Multishell...

Introduction Subcutaneous macroencapsulation devices circumvent disadvantages of intraportal islet therapy. However, a curative dose of islets within reasonably sized devices requires dense cell packing. We measured internal PO2 of implanted devices, mathematically modeled oxygen availability within devices and tested the predictions with implanted...

Purpose To improve intraoral transverse loop coil design for high‐resolution dental MRI. Methods The transverse intraoral loop coil (tLoop) was modified (mtLoop) by overlapping the feed port conductors, bending the posterior section, introducing a parallel plate capacitor, optimizing the insulation thickness, and using it in receive‐only mode. In...

Purpose Recent studies indicate that T1 in white matter (WM) is influenced by fiber orientation in B0. The purpose of the study was to investigate the interrelationships between axon fiber orientation in corpus callosum (CC) and T1 relaxation time in humans in vivo as well as in rat brain ex vivo. Methods Volunteers were scanned for relaxometric a...

Purpose To expand on the previously developed B1+$$ {\mathrm{B}}_1^{+} $$‐encoding technique, frequency‐modulated Rabi‐encoded echoes (FREE), to perform accelerated image acquisition by collecting multiple lines of k‐space in an echo train. Methods FREE uses adiabatic full‐passage pulses and a spatially varying RF field to encode unique spatial in...

Purpose To correct image distortions that result from nonlinear spatial variation in the transmit RF field amplitude (B1+$$ {B}_1^{+} $$) when performing spatial encoding with the method called frequency‐modulated Rabi encoded echoes (FREE). Theory and Methods An algorithm developed to correct image distortion resulting from the use of nonlinear s...

Liver cryopreservation has the potential to enable indefinite organ banking. This study investigated vitrification—the ice-free cryopreservation of livers in a glass-like state—as a promising alternative to conventional cryopreservation, which uniformly fails due to damage from ice formation or cracking. Our unique “nanowarming” technology, which i...

Deep-seated tumors of the liver, brain, and other organ systems often recur after initial surgical, chemotherapeutic, radiation, or focal treatments. Repeating these treatments is often invasive and traumatic. We propose an iron oxide nanoparticle (IONP)-enhanced precipitating hydrophobic injectable liquid (PHIL, MicroVention inc.) embolic as a loc...

Understanding the link between the brain activity and behavior is a key challenge in modern neuroscience. Behavioral neuroscience, however, lacks tools to record whole-brain activity in complex behavioral settings. Here we demonstrate that a novel Multi-Band SWeep Imaging with Fourier Transformation (MB-SWIFT) functional magnetic resonance imaging...

A radically new method to accomplish magnetic resonance imaging (MRI), called sweep imaging with Fourier transformation (SWIFT), was proposed in 2006. SWIFT stands alone from any other MRI techniques due to its unique image acquisition protocol (pulse sequence), which involves exciting spins with a frequency‐swept pulse and simultaneously acquiring...

To extend the preservation of donor hearts beyond the current 4–6 h, this paper explores heart cryopreservation by vitrification—cryogenic storage in a glass‐like state. While organ vitrification is made possible by using cryoprotective agents (CPA) that inhibit ice during cooling, failure occurs during convective rewarming due to slow and non‐unif...

Purpose Reduce expense and increase accessibility of MRI by eliminating pulsed field (B0) gradient hardware. Methods A radiofrequency imaging method is described that enables spatial encoding without B0 gradients. This method, herein referred to as frequency‐modulated Rabi‐encoded echoes (FREE), utilizes adiabatic full passage pulses and a gradien...

Vitrification can dramatically increase the storage of viable biomaterials in the cryogenic state for years. Unfortunately, vitrified systems ≥3 mL like large tissues and organs, cannot currently be rewarmed sufficiently rapidly or uniformly by convective approaches to avoid ice crystallization or cracking failures. A new volumetric rewarming techn...

Understanding the link between the brain activity and behavior is a key challenge in modern neuroscience. Behavioral neuroscience, however, lacks tools to record whole-brain activity in complex behavioral settings. Here we demonstrate that a novel Multi-Band SWeep Imaging with Fourier Transformation (MB-SWIFT) functional magnetic resonance imaging...

Model-based reconstruction methods have emerged as a powerful alternative to classical Fourier-based MRI techniques, largely because of their ability to explicitly model (and therefore, potentially overcome) moderate field inhomogeneities, streamline reconstruction from non-Cartesian sampling, and even allow for the use of custom designed non-Fouri...

Simultaneous Transmit and Receive (STAR) requires high decoupling between the RF transmitter and receiver. Current methods for this include, but are not limited to: geometric isolation, active RF leakage cancellation and metamaterial decoupling. The presented method uses a passive, four-port, tunable canceller circuit to achieve upwards of 40 dB of...

Smaller, more affordable, and more portable MRI brain scanners offer exciting opportunities to address unmet research needs and long-standing health inequities in remote and resource-limited international settings. Field-based neuroimaging research in low- and middle-income countries (LMICs) can improve local capacity to conduct both structural and...

High-fidelity control of spin ensemble dynamics is essential to many fields, spanning from quantum computing to optical, coherent, and nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI). However, attaining robust and high-fidelity quantum spin operations remains an unmet challenge. Using a combination of an evolutionary algorithm and a...

Purpose The ability to use dual polarity encoded MRI with the missing pulse steady‐state free precession (MP‐SSFP) sequence is demonstrated to perform robust MRI with low radiofrequency (RF) amplitude, where the field is distorted by embedding metallic screws in an agar phantom. Image‐based estimation of the 3D ΔB0 map and image distortion correcti...

Objective: In dental MRI intraoral coils provide higher signal-to-noise ratio (SNR) than coils placed outside the mouth. This study aims to design an intraoral dipole antenna and demonstrates the feasibility of combining it with an extraoral coil. Methods: Dipole antenna design was chosen over loop design, as it is open toward the distal; theref...

Purpose To develop a 3D composite adiabatic spectral‐spatial pulse for refocusing in spin‐echo spectroscopy acquisitions and to compare its performance against standard acquisition methods. Methods A 3D composite adiabatic pulse was designed by modulating a train of parallel transmit–optimized 2D subpulses with an adiabatic envelope. The spatial a...

Purpose We demonstrate the feasibility of MRI with missing‐pulse steady‐state free precession (MP‐SSFP) in a 4T magnet with artificially degraded homogeneity. Methods T1, T2, and diffusion contrast of MP‐SSFP was simulated with constant and alternate radiofrequency (RF) phase using an extended phase graph. To validate MP‐SSFP performance in human...

Frequency-modulated (FM) pulses can provide several advantages over conventional amplitude-modulated pulses in the field of MRI; however, the manner in which spins are manipulated imprints a quadratic phase on the resulting magnetization. Historically this was considered a hindrance and slowed the widespread adoption of FM pulses. This article seek...

Despite its importance as a clinical imaging modality, magnetic resonance imaging remains inaccessible to most of the world’s population due to its high cost and infrastructure requirements. Substantial effort is underway to develop portable, low-cost systems able to address MRI access inequality and to enable new uses of MRI such as bedside imagin...

Purpose Spatial encoding for MRI is generally based on linear x, y, and z magnetic field gradients generated by a set of dedicated gradient coils. We recently introduced the dynamic multicoil technique (DYNAMITE) for B0 field control and demonstrated DYNAMITE MRI in a preclinical MR environment. In this study, we report the first realization of DYN...

Cryopreservation technology allows long‐term banking of biological systems. However, a major challenge to cryopreserving organs remains in the rewarming of large volumes (>3 mL), where mechanical stress and ice formation during convective warming cause severe damage. Nanowarming technology presents a promising solution to rewarm organs rapidly and...

Purpose Herein, we evaluate the use of MRI as a tool for assessing iron oxide nanoparticle (IONP) distribution within IONP perfused organs and vascularized composite allografts (VCAs) (i.e., hindlimbs) prepared for cryopreservation. Methods Magnetic resonance imaging was performed on room‐temperature organs and VCAs perfused with IONPs and were as...

Functional magnetic resonance imaging (fMRI) studies in animal models provide invaluable information regarding normal and abnormal brain function, especially when combined with complementary stimulation and recording techniques. The echo planar imaging (EPI) pulse sequence is the most common choice for fMRI investigations, but it has several shortc...

This work evaluates MRI relaxation and the specific absorption rate properties of iron oxide nanoparticles (IONPs) as a function of diameter (6-32 nm). We conclude that the ideal IONP diameter for image guided heating applications is dependent on the magnetic field strength of the MRI for the intended application. <br

For decades iron oxide nanoparticles (IONPs) have been exploited to treat anemia and to generate contrast for magnetic resonance imaging (MRI). More recently, in combination with magnetic fluid hyperthermia (MFH), IONPs have transitioned into the clinic as a cancer therapy. Review of the safety profile of IONPs as new clinical applications emerge i...

Large magnetic field inhomogeneity can be a significant cause of spatial flip-angle variation when using ordinary, limited-bandwidth RF pulses. Multidimensional RF pulses are particularly sensitive to inhomogeneity due to their extended pulse length, which decreases their bandwidth. Previously, it was shown that, by breaking a 2D pulse into multipl...

Background Magnetic resonance imaging (MRI) research at the University of Minnesota has resulted in notable advancements, including capture of signal from densely calcified tissues. Application of this technology to address dental questions plus efforts to minimize the cost and size of MRI scanners suggests the potential adoption of MRI in regular...

Applications of multidimensional spatially-selective pulses are sometimes limited by their long pulse durations resulting from the need to execute a modulated gradient waveform in concert with RF transmission. Here, we introduce a method to design two-dimensional selective adiabatic pulses using a Cartesian k-space trajectory. The full pulse can be...

Purpose The sweep imaging with Fourier transformation (SWIFT) imaging technique has been shown to provide positive contrast from diluted cell suspensions labeled with super‐paramagnetic iron oxide (SPIO) in a tissue, as an alternative to T2*‐weighted imaging. Here we demonstrate a variation of the SWIFT technique that yields a hyperintense signal f...

The Ferrozinen assay is applied as an accurate and rapid method to quantify the iron content of iron oxide nanoparticles (IONPs) and can be used in biological matrices. The addition of ascorbic aqcid accelerates the digestion process and can penetrate an IONP core within a mesoporous and solid silica shell. This new digestion protocol avoids the ne...

Recently introduced 3D radial MRI pulse sequence entitled Multi-Band SWeep Imaging with Fourier Transformation (MB-SWIFT) having inherently zero acquisition delay was used to obtain functional MRI (fMRI) contrast in rat's brain at 9.4 Tesla during deep brain stimulation (DBS). The results demonstrate that MB-SWIFT allows images free of susceptibili...

Purpose: Iron-oxide nanoparticles (IONPs) have shown tremendous utility for enhancing image contrast and delivering targeted therapies. Quantification of IONPs has been demonstrated at low concentrations with gradient echo (GRE) and spin echo (SE), and at high concentrations with echoless sequences such as swept imaging with Fourier transform (SWI...

Vitrification, a kinetic process of liquid solidification into glass, poses many potential benefits for tissue cryopreservation including indefinite storage, banking, and facilitation of tissue matching for transplantation. To date, however, successful rewarming of tissues vitrified in VS55, a cryoprotectant solution, can only be achieved by convec...

Purpose: Conventional T2 -weighted MRI produces a hypointense signal from iron-labeled cells, which renders quantification unfeasible. We tested a SWeep Imaging with Fourier Transformation (SWIFT) MRI pulse sequence to generate a quantifiable hyperintense signal from iron-labeled cells. Methods: Mesenchymal stem cells (MSCs) were labeled with di...

Purpose: To estimate the accuracy of predicting response to neoadjuvant chemotherapy (NACT) in patients with locally advanced breast cancer using MR spectroscopy (MRS) measurements made very early in treatment. Materials and methods: This prospective Health Insurance Portability and Accountability Act (HIPAA)-compliant protocol was approved by t...

Electrodeposited Fe and Fe-Au nanowires were studied for potential as MRI contrast agents, especially for T2-weighted imaging. Transverse relaxivities up to r2 = 77.1 mM-1s-1(at 1.5 T) were achieved when Fe-Au nanowires were coated with thiol and carboxylic acid functionalized poly(ethyleneglycol). T2-weighted images (9 T) verified successful contr...

Purpose: To present a practical scheme of a simultaneous radiofrequency (RF) transmit (Tx) and receive (Rx) (STAR) system for MRI, discuss the challenges and solutions, and show preliminary in vivo MR images obtained with this new technique. Methods: A remotely controlled STAR system was built and tested with a transverse electromagnetic head co...

Purpose: To use contrast based on longitudinal relaxation times (T1 ) or rates (R1 ) to quantify the biodistribution of iron oxide nanoparticles (IONPs), which are of interest for hyperthermia therapy, cell targeting, and drug delivery, within primary clearance organs. Methods: Mesoporous silica-coated IONPs (msIONPs) were intravenously injected...

Three-dimensional phosphorus MR images (31P MRI) of teeth are obtained at a nominal resolution of 0.5 mm in less than 15 minutes using acquisition pulse sequences sensitive to ultra-short transversal relaxation times. The images directly reflect the spatially resolved phosphorus content of mineral tissue in dentin and enamel; they show a lack of si...

Objectives: To evaluate the limit of tooth crack width visualization by two magnetic resonance imaging (MRI) pulse sequences in comparison with cone-beam CT (CBCT). Methods: Two extracted human teeth with known crack locations and dimensions, as determined by reference standard microCT, were selected for experimental imaging. Crack location/dime...

Purpose: The frequency-swept pulse known as the hyperbolic-secant (HS) pulse is popular in NMR for achieving adiabatic spin inversion. The HS pulse has also shown utility for achieving excitation and refocusing in gradient-echo and spin-echo sequences, including new ultrashort echo-time imaging (e.g., Sweep Imaging with Fourier Transform, SWIFT) a...

Purpose: To use quantitative susceptibility mapping (QSM) to investigate changes in cartilage canals in the distal femur of juvenile goats after their surgical transection. Methods: Chondronecrosis was surgically induced in the right medial femoral condyles of four 4-day-old goats. Both the operated and control knees were harvested at 2, 3, 5, a...

Rotating frame spin–lattice relaxation, with the characteristic time constant T1ρ, provides a means to access motion-restricted (slow) spin dynamics in MRI. As a result of their restricted motion, these spins are sometimes characterized by a short transverse relaxation time constant T2 and thus can be difficult to detect directly with conventional...

Image blurring due to off-resonance and fast T 2 * signal decay is a common issue in radial ultrashort echo time MRI sequences. One solution is to use a higher readout bandwidth, but this may be impractical for some techniques like pointwise encoding time reduction with radial acquisition (PETRA), which is a hybrid method of zero echo time and sin...

Purpose: To evaluate multiple MRI parameters in a surgical model of osteochondrosis (OC) in goats. Methods: Focal ischemic lesions of two different sizes were induced in the epiphyseal cartilage of the medial femoral condyles of goats at 4 days of age by surgical transection of cartilage canal blood vessels. Goats were euthanized and specimens h...

Purpose: To introduce a method of designing two-dimensional (2D) frequency-modulated pulses that produce phase coherence in a spatiotemporal manner. Uniquely, this class of pulses provides the ability to compensate for field inhomogeneity using a spatiotemporally dependent trajectory of maximum coherence in a single-shot. Theory and methods: A p...

SWeep Imaging with Fourier Transformation (SWIFT) with gradient modulation and DC navigator retrospective gating is introduced as a 3D cine magnetic resonance imaging (MRI) method for the lung. The quasi-simultaneous excitation and acquisition in SWIFT enabled extremely high sensitivity to the fast-decaying parenchymal signals (TE=~4 μs), which are...

We combine a modified phase based dipole matched filter to count dipole sources in the field of view with model based dipole source decomposition of the phase offsets in 3D radial sampled data. Due to the spherical polar symmetry of the secular dipole field, the dipole source decomposition is most conveniently carried out using decimated radial k-s...

Insulin-like growth factors (IGFs) and insulin acting via the type I IGF receptor (IGF1R) and insulin receptor (IR) respectively regulate biology of estrogen positive (ER+) and triple negative (TN) breast cancer cells. In animal models, inhibition of IGF1R alone with antibodies has demonstrated significant inhibition of tumor growth and/or metastas...

Although preliminary clinical trials are ongoing, successful the use of iron-oxide magnetic nanoparticles (IONP) for heatbased cancer treatments will depend on advancements in: 1) nanoparticle platforms, 2) delivery of a safe and effective alternating magnetic field (AMF) to the tumor, and 3) development of non-invasive, spatially accurate IONP ima...

PurposeMethods designed to image fast-relaxing spins, such as sweep imaging with Fourier transformation (SWIFT), often utilize high excitation bandwidth and duty cycle, and in some applications the optimal flip angle cannot be used without exceeding safe specific absorption rate (SAR) levels. The aim is to reduce SAR and increase the flexibility of...

Brain myelin plays an important role in normal brain function. Demyelination is involved in many degenerative brain diseases, thus quantitative imaging of myelin has been under active investigation. In previous work, we demonstrated the capability of the method known as Relaxation Along a Fictitious Field (RAFF) in the rotating frame of rank n (RAF...

Purpose: SWIFT (SWeep Imaging with Fourier Transformation) is a non-Cartesian MRI method with unique features and capabilities. In SWIFT, radiofrequency (RF) excitation and reception are performed nearly simultaneously, by rapidly switching between transmit and receive during a frequency-swept RF pulse. Because both the transmitted pulse and data...

A magnetic resonance image is produced by shifting a gap during acquisition of spin data for a specimen. The spin data is generated by a gapped excitation sequence.

The majority of MRI phase imaging is based on gradient recalled echo (GRE) sequences. This work studies phase contrast behavior due to small off-resonance frequency offsets in brain using SWIFT, a FID-based sequence with nearly zero acquisition delay. 1D simulations and a phantom study were conducted to describe the behavior of phase accumulation i...