Balanced-force shim system for correcting magnetic-field inhomogeneities in the heart due to implanted cardioverter defibrillators.

Background: In the US, 1.4 million people have implanted ICDs for reducing the risk of sudden death due to ventricular arrhythmias. Cardiac MRI (cMR) is of particular interest in the ICD patient population as cMR is the optimal imaging modality for distinguishing cardiac conditions that predispose to sudden death, and it is the best method to plan and guide therapy.

MR-Safe Cartesian Platform for Active Cardiac Shimming: Preliminary Validation.

Objective: Implanted Cardioverter Defibrillators (ICDs) induce a large (100 parts per million) inhomogeneous magnetic field in the magnetic resonance imaging (MRI) scanner which cannot be corrected by the scanner's built-in shim coils, leading to significant image artifacts that can make portions of the heart unreadable. To compensate for the field inhomogeneity, an active shim coil capable of countering the field deviation in user-defined regions was designed that must be optimally placed at patient-specific locations. We aim to develop and evaluate an MR-safe robotic solution for automated shim coil positioning.

A portable single-sided magnet system for remote NMR measurements of pulmonary function.

In this work, we report initial results from a light-weight, low field magnetic resonance device designed to make relative pulmonary density measurements at the bedside. The development of this device necessarily involves special considerations for the magnet, RF and data acquisition schemes as well as a careful analysis of what is needed to provide useful information in the ICU. A homogeneous field region is created remotely from the surface of the magnet such that when the magnet is placed against the chest, an NMR signal is measured from a small volume in the lung.

Single-breath xenon polarization transfer contrast (SB-XTC): implementation and initial results in healthy humans.

Purpose: To implement and characterize a single-breath xenon transfer contrast (SB-XTC) method to assess the fractional diffusive gas transport F in the lung: to study the dependence of F and its uniformity as a function of lung volume; to estimate local alveolar surface area per unit gas volume S(A)/V(Gas) from multiple diffusion time measurements of F; to evaluate the reproducibility of the measurements and the necessity of B(1) correction in cases of centric and sequential encoding.

Materials And Methods: In SB-XTC three or four gradient echo images separated by inversion/saturation pulses were collected during a breath-hold in eight healthy volunteers, allowing the mapping of F (thus S(A)/V(Gas)) and correction for other contributions such as T(1) relaxation, RF depletion and B(1) inhomogeneity from inherently registered data.

Results: Regional values of F and its distribution were obtained; both the mean value and heterogeneity of F increased with the decrease of lung volume.

Skeletal muscle mitochondrial function is associated with longitudinal growth velocity in children and adolescents.

Context: Periods of rapid growth require an increase in energy use and substrate formation. Mitochondrial function contributes to each of these and therefore may play a role in longitudinal growth.

Methods: Twenty-nine children and adolescents of ages 8-15 yr were enrolled in a comprehensive longitudinal assessment of glucose homeostasis and mitochondrial function.

Bone mineral imaged in vivo by 31P solid state MRI of human wrists.

Purpose: To implement solid state (31)P MRI ((31)P SMRI) in a clinical scanner to visualize bone mineral.

Materials And Methods: Wrists of seven healthy volunteers were scanned. A quadrature wrist (31)P transmit/receive coil provided strong B(1) and good signal-to-noise ratio (SNR).

Increased skeletal muscle phosphocreatine recovery after sub-maximal exercise is associated with increased carotid intima-media thickness.

Background: The association between skeletal muscle mitochondrial function and CVD risk in healthy subjects is unknown.

Methods: Forty subjects were evaluated for CVD risk with lipid profile, oral glucose tolerance test and measurement of carotid intima-media thickness (cIMT). Skeletal muscle mitochondrial function was determined by phosphocreatine recovery after sub-maximal exercise with (31)Phosphorous-MRS and represented as τPCr.

The association of growth hormone parameters with skeletal muscle phosphocreatine recovery in adult men.

Context: Previous studies have suggested a relationship between GH and mitochondrial function. However, little is known about the relationship of specific GH indices and in vivo measures of mitochondrial function in humans.

Objective: The objective of this study was to determine the association between GH, IGF-I, and phosphocreatine (PCr) recovery, a measure of mitochondrial function, in otherwise healthy adults.

Skeletal muscle phosphocreatine recovery after submaximal exercise in children and young and middle-aged adults.

Context: Elderly subjects have reduced mitochondrial function. However, it remains unclear whether the decline in mitochondrial function begins earlier in the life span.

Objective: The objective of the study was to determine skeletal muscle mitochondrial oxidative phosphorylation by (31)phosphorous-magnetic resonance spectroscopy (MRS) across a variety of age groups.

Bone matrix imaged in vivo by water- and fat-suppressed proton projection MRI (WASPI) of animal and human subjects.

Purpose: To demonstrate water- and fat-suppressed proton projection MRI (WASPI) in a clinical scanner to visualize the solid bone matrix in animal and human subjects.

Materials And Methods: Pig bone specimens and polymer pellets were used to optimize the WASPI method in terms of soft-tissue suppression, image resolution, signal-to-noise ratio, and scan time on a 3T MRI scanner. The ankles of healthy 2-3-month-old live Yorkshire pigs were scanned with the optimized method.

Quantitative (31)P NMR spectroscopy and (1)H MRI measurements of bone mineral and matrix density differentiate metabolic bone diseases in rat models.

In this study, bone mineral density (BMD) of normal (CON), ovariectomized (OVX), and partially nephrectomized (NFR) rats was measured by (31)P NMR spectroscopy; bone matrix density was measured by (1)H water- and fat-suppressed projection imaging (WASPI); and the extent of bone mineralization (EBM) was obtained by the ratio of BMD/bone matrix density. The capability of these MR methods to distinguish the bone composition of the CON, OVX, and NFR groups was evaluated against chemical analysis (gravimetry). For cortical bone specimens, BMD of the CON and OVX groups was not significantly different; BMD of the NFR group was 22.

Mitochondrial function and insulin resistance in overweight and normal-weight children.

Background: Obesity has become an epidemic in children, associated with an increase in insulin resistance and metabolic dysfunction. Mitochondrial function is known to be an important determinant of glucose metabolism in adults. However, little is known about the relationship between mitochondrial function and obesity, insulin resistance, energy expenditure, and pubertal development in children.

Quantitative bone matrix density measurement by water- and fat-suppressed proton projection MRI (WASPI) with polymer calibration phantoms.

The density of the organic matrix of bone substance is a critical parameter necessary to clinically evaluate and distinguish structural and metabolic pathological conditions such as osteomalacia in adults and rickets in growing children. Water- and fat-suppressed proton projection MRI (WASPI) was developed as a noninvasive means to obtain this information. In this study, a density calibration phantom was developed to convert WASPI intensity to true bone matrix density.

Human pulmonary imaging and spectroscopy with hyperpolarized 129Xe at 0.2T.

Rationale And Objectives: Using a novel (129)Xe polarizer with high throughput (1-2 L/hour) and high polarization (approximately 55%), our objective was to demonstrate and characterize human pulmonary applications at 0.2T. Specifically, we investigated the ability of (129)Xe to measure the alveolar surface area per unit volume of gas, S(A)/V(gas).

Hyperpolarized (129)Xe MRI: a viable functional lung imaging modality?

The majority of researchers investigating hyperpolarized gas MRI as a candidate functional lung imaging modality have used (3)He as their imaging agent of choice rather than (129)Xe. This preference has been predominantly due to, (3)He providing stronger signals due to higher levels of polarization and higher gyromagnetic ratio, as well as its being easily available to more researchers due to availability of polarizers (USA) or ease of gas transport (Europe). Most researchers agree, however, that hyperpolarized (129)Xe will ultimately emerge as the imaging agent of choice due to its unlimited supply in nature and its falling cost.

Water- and fat-suppressed proton projection MRI (WASPI) of rat femur bone.

Investigators often study rats by microCT to investigate the pathogenesis and treatment of skeletal disorders in humans. However, microCT measurements provide information only on bone mineral content and not the solid matrix. CT scans are often carried out on cancellous bone, which contains a significant volume of marrow cells, stroma, water, and fat, and thus the apparent bone mineral density (BMD) does not reflect the mineral density within the matrix, where the mineral crystals are localized.

Effects of a nucleoside reverse transcriptase inhibitor, stavudine, on glucose disposal and mitochondrial function in muscle of healthy adults.

Mitochondrial dysfunction may contribute to the development of insulin resistance and type 2 diabetes. Nucleoside reverse transcriptase inhibitors (NRTIs), specifically stavudine, are known to alter mitochondrial function in human immunodeficiency virus (HIV)-infected individuals, but the effects of stavudine on glucose disposal and mitochondrial function in muscle have not been prospectively evaluated. In this study, we investigated short-term stavudine administration among healthy control subjects to determine effects on insulin sensitivity.

An open magnet utilizing ferro-refraction current magnification.

Ferro-refraction is the field magnification that is obtained when a current segment is near a high magnetic permeable boundary. It is shown that ferro-refraction may be used in the design of magnets for NMR or MRI to increase the efficiency of these magnets. The field may be modeled analytically with the Biot--Savart law and the inclusion of mirror image currents.