Robust Assessment of Macromolecular Fraction (MMF) in Muscle with Differing Fat Fraction Using Ultrashort Echo Time (UTE) Magnetization Transfer Modeling with Measured T1.

Magnetic resonance imaging (MRI) is widely regarded as the most comprehensive imaging modality to assess skeletal muscle quality and quantity. Magnetization transfer (MT) imaging can be used to estimate the fraction of water and macromolecular proton pools, with the latter including the myofibrillar proteins and collagen, which are related to the muscle quality and its ability to generate force. MT modeling combined with ultrashort echo time (UTE-MT modeling) may improve the evaluation of the myotendinous junction and regions with fibrotic tissues in the skeletal muscles, which possess short T2 values and higher bound-water concentration.

Ultrashort echo time adiabatic T (UTE-Adiab-T) is sensitive to human cadaveric knee joint deformation induced by mechanical loading and unloading.

Purpose: The development of ultrashort echo time (UTE) MRI sequences has led to improved imaging of tissues with short T relaxation times, such as the deep layer cartilage and meniscus. UTE combined with adiabatic T preparation (UTE-Adiab-T) is an MRI measure with low sensitivity to the magic angle effect. This study aimed to investigate the sensitivity of UTE-Adiab-T to mechanical load-induced deformations in the tibiofemoral cartilage and meniscus of human cadaveric knee joints.

Detecting Articular Cartilage and Meniscus Deformation Effects Using Magnetization Transfer Ultrashort Echo Time (MT-UTE) Modeling during Mechanical Load Application: Feasibility Study.

Objective: Ultrashort echo time (UTE) magnetic resonance imaging (MRI) sequences have improved imaging of short T2 musculoskeletal (MSK) tissues. UTE-MRI combined with magnetization transfer modeling (UTE-MT) has demonstrated robust assessment of MSK tissues. This study aimed to investigate the variation of UTE-MT measures under mechanical loading in tibiofemoral cartilage and meniscus of cadaveric knee joints.

Use of Multiplied, Added, Subtracted and/or FiTted Inversion Recovery (MASTIR) pulse sequences.

The group of Multiplied, Added, Subtracted and/or fiTted Inversion Recovery (MASTIR) pulse sequences in which usually two or more inversion recovery (IR) images of different types are combined is described, and uses for this type of sequence are outlined. IR sequences of different types can be multiplied, added, subtracted, and/or fitted together to produce variants of the MASTIR sequence. The sequences provide a range of options for increasing image contrast, demonstrating specific tissues and fluids of interest, and suppressing unwanted signals.

Pulse sequences as tissue property filters (TP-filters): a way of understanding the signal, contrast and weighting of magnetic resonance images.

This paper describes a quantitative approach to understanding the signal, contrast and weighting of magnetic resonance (MR) images. It uses the concept of pulse sequences as tissue property (TP) filters and models the signal, contrast and weighting of sequences using either a single TP-filter (univariate model) or several TP-filters (the multivariate model). For the spin echo (SE) sequence using the Bloch equations, voxel signal intensity is plotted against the logarithm of the value of the TPs contributing to the sequence signal to produce three TP-filters, an exponential ρ-filter, a low pass T-filter and a high pass T-filter.

Liver fat imaging-a clinical overview of ultrasound, CT, and MR imaging.

Hepatic steatosis is a frequently encountered imaging finding that may indicate chronic liver disease, the most common of which is non-alcoholic fatty liver disease. Non-alcoholic fatty liver disease is implicated in the development of systemic diseases and its progressive phenotype, non-alcoholic steatohepatitis, leads to increased liver-specific morbidity and mortality. With the rising obesity epidemic and advent of novel therapeutics aimed at altering metabolism, there is a growing need to quantify and monitor liver steatosis.

Accurate T mapping of short T tissues using a three-dimensional ultrashort echo time cones actual flip angle imaging-variable repetition time (3D UTE-Cones AFI-VTR) method.

Purpose: To develop an accurate T measurement method for short T tissues using a combination of a 3-dimensional ultrashort echo time cones actual flip angle imaging technique and a variable repetition time technique (3D UTE-Cones AFI-VTR) on a clinical 3T scanner.

Methods: First, the longitudinal magnetization mapping function of the excitation pulse was obtained with the 3D UTE-Cones AFI method, which provided information about excitation efficiency and B inhomogeneity. Then, the derived mapping function was substituted into the VTR fitting to generate accurate T maps.

Yet more evidence that myelin protons can be directly imaged with UTE sequences on a clinical 3T scanner: Bicomponent T2* analysis of native and deuterated ovine brain specimens.

Purpose: UTE sequences with a minimal nominal TE of 8 µs have shown promise for direct imaging of myelin protons (T , < 1 ms). However, there is still debate about the efficiency of 2D slice-selective UTE sequences in exciting myelin protons because the half excitation pulses used in these sequences have a relatively long duration (e.g.

Sources of systematic error in proton density fat fraction (PDFF) quantification in the liver evaluated from magnitude images with different numbers of echoes.

The purpose of this work was to investigate sources of bias in magnetic resonance imaging (MRI) liver fat quantification that lead to a dependence of the proton density fat fraction (PDFF) on the number of echoes. This was a retrospective analysis of liver MRI data from 463 subjects. The magnitude signal variation with TE from spoiled gradient echo images was curve fitted to estimate the PDFF using a model that included monoexponential R * decay and a multi-peak fat spectrum.

Ultrashort echo time T2 values decrease in tendons with application of static tensile loads.

In early stages of tendon disease, mechanical properties may become altered prior to changes in morphological anatomy. Ultrashort echo time (UTE) magnetic resonance imaging (MRI) can be used to directly detect signal from tissues with very short T2 values, including unique viscoelastic tissues such as tendons. The purpose of this study was to use UTE sequences to measure T2, T1 and magnetization transfer ratio (MTR) variations of tendon samples under static tensile loads.

Repeatability and reproducibility of 2D and 3D hepatic MR elastography with rigid and flexible drivers at end-expiration and end-inspiration in healthy volunteers.

Purpose: To evaluate the repeatability and reproducibility of 2D and 3D hepatic MRE with rigid and flexible drivers at end-expiration and end-inspiration in healthy volunteers.

Materials And Methods: Nine healthy volunteers underwent two same-day MRE exams separated by a 5- to 10-min break. In each exam, 2D and 3D MRE scans were performed, each under four conditions (2 driver types [rigid, flexible] × 2 breath-hold phases [end-expiration, end-inspiration]).

Multisite, multivendor validation of the accuracy and reproducibility of proton-density fat-fraction quantification at 1.5T and 3T using a fat-water phantom.

Purpose: To evaluate the accuracy and reproducibility of quantitative chemical shift-encoded (CSE) MRI to quantify proton-density fat-fraction (PDFF) in a fat-water phantom across sites, vendors, field strengths, and protocols.

Methods: Six sites (Philips, Siemens, and GE Healthcare) participated in this study. A phantom containing multiple vials with various oil/water suspensions (PDFF:0%-100%) was built, shipped to each site, and scanned at 1.

Novel 3D Magnetic Resonance Elastography for the Noninvasive Diagnosis of Advanced Fibrosis in NAFLD: A Prospective Study.

Objectives: Recent studies show two-dimensional (2D)-magnetic resonance elastography (MRE) is accurate in diagnosing advanced fibrosis (stages 3 and 4) in nonalcoholic fatty liver disease (NAFLD) patients. Three-dimensional (3D)-MRE is a more advanced version of the technology that can image shear-wave fields in 3D of the entire liver. The aim of this study was to prospectively compare the diagnostic accuracy of 3D-MRE and 2D-MRE for diagnosing advanced fibrosis in patients with biopsy-proven NAFLD.

Ultrasound Elastography and MR Elastography for Assessing Liver Fibrosis: Part 2, Diagnostic Performance, Confounders, and Future Directions.

Objective: The purpose of the article is to review the diagnostic performance of ultra-sound and MR elastography techniques for detection and staging of liver fibrosis, the main current clinical applications of elastography in the abdomen.

Conclusion: Technical and instrument-related factors and biologic and patient-related factors may constitute potential confounders of stiffness measurements for assessment of liver fibrosis. Future developments may expand the scope of elastography for monitoring liver fibrosis and predict complications of chronic liver disease.

Ultrasound Elastography and MR Elastography for Assessing Liver Fibrosis: Part 1, Principles and Techniques.

Objective: The purpose of this article is to provide an overview of ultrasound and MR elastography, including a glossary of relevant terminology, a classification of elastography techniques, and a discussion of their respective strengths and limitations.

Conclusion: Elastography is an emerging technique for the noninvasive assessment of mechanical tissue properties. These techniques report metrics related to tissue stiffness, such as shear-wave speed, magnitude of the complex shear modulus, and the Young modulus.

Magnetic resonance imaging of the pulleys of the flexor tendons of the toes at 11.7 T.

Objective: We obtained high-resolution 11.7-T MR images of the pulleys of the flexor tendons in cadaveric toe specimens. A detailed understanding of toe pulley anatomy as seen with MR is likely to be of benefit in recognizing disease and the effects of trauma.

Rotator cuff tendon ultrastructure assessment with reduced-orientation dipolar anisotropy fiber imaging.

Objective: The anisotropic fibrous structure of collagen can significantly affect MRI signal intensity. Use of this magic angle effect as a contrast mechanism has been previously termed "dipolar anisotropy fiber imaging." The goal of this pilot study was to use a reduced-orientation version of dipolar anisotropy fiber imaging to study rotator cuff tendon internal fiber structure.

Ultrashort echo time (UTE) magnetic resonance imaging of the short T2 components in white matter of the brain using a clinical 3T scanner.

White matter of the brain contains a majority of long T2 components as well as a minority of short T2 components. These are not detectable using clinical magnetic resonance imaging (MRI) sequences with conventional echo times (TEs). In this study we used ultrashort echo time (UTE) sequences to investigate the ultrashort T2 components in white matter of the brain and quantify their T2*s and relative proton densities (RPDs) (relative to water with a proton density of 100%) using a clinical whole body 3T scanner.

Dipolar anisotropy fiber imaging in a goat knee meniscus.

This study describes a method of utilizing unaveraged dipolar effects to characterize and compute collagen fiber tracks using magnetic resonance imaging. The technique yields information about fiber structure with some similarities to what can be obtained in brain using diffusion tensor imaging, but relies on a completely different physical mechanism, namely, unaveraged homonuclear dipolar interactions. The method is probably only appropriate for highly ordered collagen rich tissues.

Ultrashort TE T1rho (UTE T1rho) imaging of the Achilles tendon and meniscus.

In this study, we report the use of a novel ultrashort echo time T(1)rhoT(1) sequence that combines a spin-lock preparation pulse with a two-dimensional ultrashort echo time sequence of a nominal echo time 8 microsec. The ultrashort echo time-T(1)rho sequence was employed to quantify T(1)rho in short T(2) tissues including the Achilles tendon and the meniscus. T(1)rho dispersion was investigated by varying the spin-lock field strength.

Neural resources associated with perceptual judgment across sensory modalities.

Electrophysiological and brain imaging studies have shown that different populations of neurons contribute to perceptual decision making. Perceptual judgment is a complicated process that has several subprocesses, including the final step of a discrete choice among available possibilities. Using the psychophysical paradigm of difference scaling combined with functional magnetic resonance imaging, we identify an area within a distributed representation that is consistently invoked in perceptual decision.

Effects of hyperoxia on human sensorimotor cortex activity produced by electrical stimulation of the median nerve: a functional magnetic resonance imaging study.

This study investigated the effect of hyperoxia on sensorimotorcortical activity resulting from electrical stimulation of the median nerve, using functional magnetic resonance imaging (fMRI). Nine volunteers underwent stimulation at 5 and 100 Hz while breathing 21% FIO(2) (fraction of inspired oxygen) or 100% FIO(2). fMRI data were correlated with a stimulus predictor curve, transformed into Talairach space and averaged by group.