Real-time volumetric MR thermometry using 3D echo-shifted sequence under an open source reconstruction platform

PurposeThe aim of this work is to implement real-time 3D MR thermometry for high intensity focused ultrasound (HIFU) monitoring.MethodsVolumetric MR thermometry was implemented based on a 3D echo-shifted sequence with short TR to improve temperature sensitivity. The 3D acquisition was accelerated in two phase encoding directions with controlled aliasing in volumetric parallel imaging (CAIPIRINHA). Image reconstruction was run in an open source reconstruction platform (Gadgetron).ResultsPhantom experiments showed the proposed volumetric thermometry was comparable to the fiber optical thermometer. In-vivo animal experiments in rabbit thigh showed that the temperature error before and after 4× acceleration was less than 0.65 °C. Finally, real-time 3D thermometry with temporal resolution ~3 s and spatial resolution 2 × 2 × 5 mm³ (spatial coverage 192 × 192 × 80 mm³) was achieved with Gadgetron reconstruction.ConclusionReal-time temperature monitoring was achieved in-vivo by using parallel imaging accelerated 3D echo-shifted sequence with Gadgetron reconstruction.     

Real-time cardiac magnetic resonance cine imaging with sparse sampling and iterative reconstruction for left-ventricular measures: Comparison with gold-standard segmented steady-state free precession

BackgroundSegmented cine imaging with a steady-state free-precession sequence (Cine-SSFP) is currently the gold standard technique for measuring ventricular volumes and mass, but due to multi breath-hold (BH) requirements, it is prone to misalignment of consecutive slices, time consuming and dependent on respiratory capacity. Real-time cine avoids those limitations, but poor spatial and temporal resolution of conventional sequences has prevented its routine application. We sought to examine the accuracy and feasibility of a newly developed real-time sequence with aggressive under-sampling of k-space using sparse sampling and iterative reconstruction (Cine-RT).MethodsStacks of short-axis cines were acquired covering both ventricles in a 1.5 T system using gold standard Cine-SSFP and Cine-RT. Acquisition parameters for Cine-SSFP were: acquisition matrix of 224 × 196, temporal resolution of 39 ms, retrospective gating, with an average of 8 heartbeats per slice and 1–2 slices/BH. For Cine-RT: acquisition matrix of 224 × 196, sparse sampling net acceleration factor of 11.3, temporal resolution of 41 ms, prospective gating, real-time acquisition of 1 heart-beat/slice and all slices in one BH. LV contours were drawn at end diastole and systole to derive LV volumes and mass.ResultsForty-one consecutive patients (15 male; 41 ± 17 years) in sinus rhythm were successfully included. All images from Cine-SSFP and Cine-RT were considered to have excellent quality. Cine-RT-derived LV volumes and mass were slightly underestimated but strongly correlated with gold standard Cine-SSFP. Inter- and intra-observer analysis presented similar results between both sequences.ConclusionsCine-RT featuring sparse sampling and iterative reconstruction can achieve spatial and temporal resolution equivalent to Cine-SSFP, providing excellent image quality, with similar precision measurements and highly correlated and only slightly underestimated volume and mass values.     

Orientational analysis of the Achilles tendon and enthesis using an ultrashort echo time spectroscopic imaging sequence

Tendons and entheses are magnetic resonance (MR) “invisible” when imaged with conventional clinical pulse sequences. When the highly ordered, collagen-rich fibers in tendons and entheses are placed at the magic angle, dipolar interactions are decreased and their T2s are often considerably increased. The bulk magnetic susceptibility of tendons and entheses also varies with orientation to B₀, leading to a direction-dependent resonance frequency shift. Ultrashort echo time (UTE) sequences with a minimum TE of 8 μs provide high signal from both tendons and entheses. The combination of a UTE sequence with an interleaved undersampled variable TE acquisition scheme provides a new approach for fast spectroscopic imaging of short T2 tissues. This UTE spectroscopic imaging (UTESI) technique provides quantitative information including T2?, chemical shift and resonance frequency shift due to bulk susceptibility effect. In this article, the orientational effects on tendons and entheses were investigated using a UTESI sequence on a clinical 3-T scanner. T2? was found to increase fivefold for tendons and twofold for entheses due to the magic angle effect. A resonance frequency shift up to 1.2 ppm was observed for both tendons and entheses due to the bulk susceptibility effect when their orientation was changed from 0° to 90° relative to B₀.     

Reduced capillary perfusion and permeability in human tumour xenografts treated with the VEGF signalling inhibitor ZD4190: an in vivo assessment using dynamic MR imaging and macromolecular contrast media

We describe the use of perfusion-permeability magnetic resonance imaging (ppMRI) to study hemodynamic parameters in human prostate tumor xenografts, following treatment with the vascular endothelial growth factor-A (VEGF) receptor tyrosine kinase inhibitor, ZD4190. Using a macromolecular contrast agent (P792), a fast MR imaging protocol and a compartmental data analysis, we were able to demonstrate a significant simultaneous reduction in tumor vascular permeability, tumor vascular volume and tumor blood flow (43%, 30% and 42%, respectively) following ZD4190 treatment (100 mg/kg orally, 24 h and 2 h prior to imaging). This study indicates that MR imaging can be used to measure multiple hemodynamic parameters in tumors, and that tumor vascular permeability, volume and flow, can change in response to acute treatment with a VEGF signaling inhibitor.