T quantification in brain using 3D fast spin-echo imaging with long echo trains.

Purpose: Three-dimensional fast spin-echo (FSE) sequences commonly use very long echo trains (>64 echoes) and severely reduced refocusing angles. They are increasingly used in brain exams due to high, isotropic resolution and reasonable scan time when using long trains and short interecho spacing. In this study, T quantification in 3D FSE is investigated to achieve increased resolution when comparing with established 2D (proton-density dual-echo and multi-echo spin-echo) methods.

Bloch modelling enables robust T2 mapping using retrospective proton density and T2-weighted images from different vendors and sites.

T2 quantification is commonly attempted by applying an exponential fit to proton density (PD) and transverse relaxation (T2)-weighted fast spin echo (FSE) images. However, inter-site studies have noted systematic differences between vendors in T2 maps computed via standard exponential fitting due to imperfect slice refocusing, different refocusing angles and transmit field (B1) inhomogeneity. We examine T2 mapping at 3T across 13 sites and two vendors in healthy volunteers from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database using both a standard exponential and a Bloch modelling approach.

T and T quantification from standard turbo spin echo images.

Purpose: To extract longitudinal and transverse (T and T ) relaxation maps from standard MRI methods.

Methods: Bloch simulations were used to model relative signal amplitudes from standard turbo spin-echo sequences: proton density weighted, T -weighted, and either T -weighted fluid attenuated inversion recovery or T -weighted images. Simulations over a range of expected parameter values yielded a look-up table of relative signal intensities of these sequences.

Limitations of skipping echoes for exponential T fitting.

Background: Exponential fitting of multiecho spin echo sequences with skipped echoes is still commonly used for quantification of transverse relaxation (T ).

Purpose: To examine the efficacy of skipped echo methods for T quantification against computational modeling of the exact signal decay.

Study Type: Prospective comparison of methods.

Recovery of accurate T from historical 1.5 tesla proton density and T-weighted images: Application to 7-year T changes in multiple sclerosis brain.

Objective: To determine accurate quantitative transverse relaxation times (T) using retrospective clinical images and apply it to examine 7-year changes in multiple sclerosis (MS) brain.

Methods: A method for T mapping from retrospective proton density (PD) and T-weighted fast spin echo images was recently introduced, but requires measurement of flip angles. We examined whether 1.

Transverse relaxation and flip angle mapping: Evaluation of simultaneous and independent methods using multiple spin echoes.

Purpose: To evaluate transverse relaxation (T2) and flip angle maps derived from signal pathway modeling of multiple spin echoes using simultaneous or independent T2 and flip angle fitting.

Methods: We examined different approaches to indirect and stimulated echo compensated T2 relaxometry from multiple spin echoes to evaluate both T2 and flip angle accuracy in simulation, phantom, and human brain. Signal pathways were modeled with or without independent flip angle maps using either Bloch simulations, or Extended Phase Graph (EPG) with Fourier or Shinnar-Le Roux approximation of slice profiles.

Multi-modal magnetic resonance imaging and histology of vascular function in xenografts using macromolecular contrast agent hyperbranched polyglycerol (HPG-GdF).

Macromolecular gadolinium (Gd)-based contrast agents are in development as blood pool markers for MRI. HPG-GdF is a 583 kDa hyperbranched polyglycerol doubly tagged with Gd and Alexa 647 nm dye, making it both MR and histologically visible. In this study we examined the location of HPG-GdF in whole-tumor xenograft sections matched to in vivo DCE-MR images of both HPG-GdF and Gadovist.

T2 quantification from only proton density and T2-weighted MRI by modelling actual refocusing angles.

Proton density and transverse relaxation (T2)-weighted fast spin echo images are frequently acquired. T2 quantification is commonly performed by applying an exponential fit to these two images, despite recent evidence that an exponential fit is insufficient to correctly quantify T2 in the presence of imperfect RF refocusing due to standard 2D slice selection or use of reduced refocusing angles. Here we examine the feasibility of accurate two echo fitting using standard proton density and T2-weighted images by utilizing Bloch equation simulations and prior knowledge of refocusing angles.

Hyperbranched polyglycerols as trimodal imaging agents: design, biocompatibility, and tumor uptake.

Combining various imaging modalities often leads to complementary information and synergistic advantages. A trimodal long-circulating imaging agent tagged with radioactive, magnetic resonance, and fluorescence markers is able to combine the high sensitivity of SPECT with the high resolution of MRI over hours and days. The fluorescence marker helps to confirm the in vivo imaging information at the microscopic level, in the context of the tumor microenvironment.

Bilateral filtering of magnetic resonance phase images.

High-pass filtering is required for the removal of background field inhomogeneities in magnetic resonance phase images. This high-pass filtering smooths across boundaries between areas with large differences in phase. The most prominent boundary is the surface of the brain where areas with large phase values inside the brain are located close to areas outside the brain where the phase is, on average, zero.