J. Rock Hadley

Multiple-region gradient arrays for extended field of view, increased performance, and reduced nerve stimulation in magnetic resonance imaging

This article presents a novel design for magnetic resonance imaging (MRI) gradient systems. This design may allow the development of MRI scanners that are capable of imaging large regions with high performance while minimizing the potential for nerve stimulation. The general concept of the gradient system is that spatial oscillation is incorporated such that each gradient coil creates multiple, approximately linear gradient regions that oscillate in gradient polarity. Separate radiofrequency (RF) coil arrays are designed to be sensitive to the signals within each linear region and thus allow signal measurements to be obtained separately from each region. Enabling image acquisition in the transition region that separates each pair of adjacent linear regions requires a second gradient system with imaging regions that overlap and coincide with the transition regions of the first gradient system. Imaging the extended field of view (FOV) is accomplished by interleaved operation of the two gradient systems. Simulated annealing is used to create designs for both longitudinal and transverse gradient systems with two imaging regions. Magn Reson Med, 2006.

A three-coil comparison for MR angiography

The purpose of this work was to compare intracranial magnetic resonance angiography (MRA) image quality using three different radiofrequency coils. The three coil types included a reduced volume quadrature birdcage coil with endcap, a commercially available quadrature birdcage head coil, and a four‐element phased‐array coil. Signal‐to‐noise ratio (SNR) measurements were obtained from comparison studies performed on a uniform cylindrical phantom. MRA comparisons were performed using data acquired from 15 volunteers and applying a thick‐slab three‐dimensional time‐of‐flight sequence. Analysis was performed using the signal difference‐to‐noise ratio, a quantitative measure of the relative vascular signal. The reduced‐volume endcap and phased‐array coils, which were designed specifically for imaging the intracranial volume of the head, improved the image SNR and vascular detail considerably over that obtained using the commercially available head coil. The endcap coil configuration provided the best vascular signal overall, while the phased‐array coil provided the best results for arteries close to the coil elements. J. Magn. Reson. Imaging 2000;11:458–468.

Phase reconstruction from multiple coil data using a virtual reference coil

This study develops a method to obtain optimal estimates of absolute magnetization phase from multiple‐coil MRI data.

A 3 T sodium and proton composite array breast coil

The objective of this study was to determine whether a sodium phased array would improve sodium breast MRI at 3 T. The secondary objective was to create acceptable proton images with the sodium phased array in place.

Longitudinal Assessment of Hyperplasia Using Magnetic Resonance Imaging without Contrast in a Porcine Arteriovenous Graft Model

RATIONALE AND OBJECTIVES Chronic hemodialysis requires a vascular access that provides high blood-flow rates for the extracorporeal recirculation of blood. Synthetic arteriovenous (AV) grafts often fail because of clotting caused by underlying hyperplasia formation. The authors report the use of magnetic resonance (MR) imaging (MRI) without contrast agent to monitor tissue hyperplasia formation as well as luminal area in a porcine model of AV graft stenosis. MATERIALS AND METHODS Expanded reinforced polytetrafluoroethylene grafts were surgically placed between the common carotid artery and the external jugular vein, bilaterally, in pigs. Animals underwent MRI in a 3-T scanner at 3, 4, or 6 weeks after graft placement, followed by euthanasia and the collection of grafts and adjacent tissues for histologic analysis. Two animals underwent sequential scanning at 1, 2, 3, 5, and 7 weeks after graft placement, followed by histologic analysis. RESULTS Measurements of hyperplasia obtained from the MR images were compared with, and correlated well with, measurements obtained from the histologic cross-sections (r = 0.932, P = .02). The MR images provided a more complete view of the venous hyperplasia throughout the graft compared with histology. The MR images could be examined from multiple angles and were unaffected by histologic preparation artifacts. CONCLUSION Unlike histology, MRI provided longitudinal 3-dimensional views of hyperplasia within the AV grafts. This ability of MRI to more completely identify the geometry of hyperplasia and to quantify the tissue volume in vivo could provide benefits over histologic analysis in assessing the pathology of AV graft failure and the efficacy of antihyperplasia interventions.

In vivo and ex vivo measurements of the mean ADC values of lipid necrotic core and hemorrhage obtained from diffusion weighted imaging in human atherosclerotic plaques

To determine the apparent diffusion coefficient (ADC) values of lipid and hemorrhage in atherosclerotic plaque in human carotid arteries in vivo and compare the values obtained from ex vivo carotid endarterectomy specimens.

Initial feasibility testing of limited field of view magnetic resonance thermometry using a local cardiac radiofrequency coil.

The visualization of lesion formation in real time is one potential benefit of carrying out radiofrequency ablation under magnetic resonance (MR) guidance in the treatment of atrial fibrillation. MR thermometry has the potential to detect such lesions. However, performing MR thermometry during cardiac radiofrequency ablation requires high temporal and spatial resolution and a high signal‐to‐noise ratio. In this study, a local MR coil (2‐cm diameter) was developed to investigate the feasibility of performing limited field of view MR thermometry with high accuracy and speed. The local MR coil allowed high‐resolution (1 × 1 × 3 mm3) image acquisitions in 76.3 ms with a field of view 64 × 32 mm2 during an open‐chest animal experiment. This represents a 4‐fold image acquisition acceleration and an 18‐fold field of view reduction compared to that achieved using external MR coils. The signal sensitivity achieved using the local coil was over 20 times greater than that achievable using external coils with the same scan parameters. The local coil configuration provided fewer artifacts and sharper and more stable images. These results demonstrate that MR thermometry can be performed in the heart wall and that lesion formation can be observed during radiofrequency ablation procedures in a canine model. Magn Reson Med, 70:994–1004, 2013.

Increased Vessel Depiction of the Carotid Bifurcation with a Specialized 16-Channel Phased Array Coil at 3T

The purpose of this work was to design and construct a multichannel receive‐only radiofrequency coil for 3T magnetic resonance imaging of the human carotid artery and bifurcation with optimized signal‐to‐noise ratio (SNR) in the carotid vessels along the full extent of the neck. A neck phantom designed to match the anatomy of a subject with a neck representing the body habitus often seen in subjects with carotid arterial disease was constructed. Sixteen circular coil elements were arranged on a semirigid fiberglass former that closely fit the shape of the phantom, resulting in a 16‐channel bilateral phased array coil. Comparisons were made between this coil and a typical 4‐channel carotid coil in a study of 10 carotid vessels in five healthy volunteers. The 16‐channel carotid coil showed a 73% average improvement in SNR at the carotid bifurcation. This coil also maintained an SNR greater than the peak SNR of the 4‐channel coil over a vessel length of 10 cm. The resulting increase in SNR improved vessel depiction of the carotid arteries over an extended field of view, and demonstrated better image quality for higher parallel imaging reduction factors compared to the 4‐channel coil. Magn Reson Med, 2013.

Sodium MRI radiofrequency coils for body imaging

The proliferation of high‐field whole‐body systems, advances in gradient performance and refinement of signal‐to‐noise ratio (SNR)‐efficient short‐TE sequences suitable for sodium imaging have led to a resurgence of interest in sodium imaging for body applications. With this renewed interest has come increased demand for SNR‐efficient sodium coils. Efficient coils can significantly increase SNR in sodium imaging, allowing higher resolutions and/or shorter scan times. In this work, we focus on body imaging applications of sodium MRI, and review developments in MRI radiofrequency (RF) coil topologies for sodium imaging. We first provide a brief discussion of RF coil design considerations in sodium imaging. This is followed by an overview of common coil topologies, their advantages and disadvantages, and examples of each. Copyright

Diffusion tensor imaging of extraocular muscle using two-dimensional single-shot interleaved multiple inner volume imaging diffusion-weighted EPI at 3 tesla.

To evaluate the feasibility of diffusion tensor imaging (DTI) for the medial and lateral rectus extraocular muscle (EOM) evaluation, to investigate the normal DTI parameters of the medial and lateral rectus EOM, and to compare with other skeletal muscle.