Purpose To develop and demonstrate in vitro and in vivo, a single interventional MR-active device that integrates the functions of precise identification of a tissue site with the delivery of RF energy for ablation, high-resolution thermal mapping to monitor thermal dose, and with quantitative MRI relaxometry to document ablation-induced tissue changes for characterizing ablated tissue. Materials and Methods All animal studies were approved by our Institutional Animal Care and Use Committee. A loopless MRI antenna comprised of a tuned micro-cable either 0.8 or 2.2mm in diameter with an extended central conductor, was switched between a 3T MRI scanner and an RF power source, to monitor and perform RF ablation in bovine muscle and human artery samples in vitro, and in rabbits in vivo. High-resolution (250–300μm) proton resonance frequency shift MR thermometry was interleaved with ablations. Quantitative spin-lattice (T1) and spin-spin (T2) relaxation time MRI mapping was performed pre- and post-ablation, and compared with gross tissue examination of the region of ablated tissue, post-MRI. Results High-resolution MRI afforded temperature mapping in under 8s for monitoring ablation temperatures exceeding 85°C delivered by the same device, producing irreversible thermal injury and necrosis. Quantitative MRI relaxation time maps revealed up to a two-fold variation in mean regional T1 and T2 post-vs. pre-ablation. Conclusion A simple, integrated, minimally-invasive interventional probe that provides image-guided therapy delivery, thermal mapping of dose and the detection of ablation-associated MRI parametric changes was developed and demonstrated. This single-device approach avoided coupling-related safety concerns associated with multiple conductor approaches.

BackgroundAtherosclerosis is prevalent in cardiovascular disease, but present imaging modalities have limited capabilities for characterizing lesion stage, progression and response to intervention. This study tests whether intravascular magnetic resonance imaging (IVMRI) measures of relaxation times (T1, T2) and proton density (PD) in a clinical 3 Tesla scanner could characterize vessel disease, and evaluates a practical strategy for accelerated quantification.MethodsIVMRI was performed in fresh human artery segments and swine vessels in vivo, using fast multi-parametric sequences, 1–2 mm diameter loopless antennae and 200–300 μm resolution. T1, T2 and PD data were used to train a machine learning classifier (support vector machine, SVM) to automatically classify normal vessel, and early or advanced disease, using histology for validation. Disease identification using the SVM was tested with receiver operating characteristic curves. To expedite acquisition of T1, T2 and PD data for vessel characterization, the linear algebraic method (‘SLAM’) was modified to accommodate the antenna’s highly-nonuniform sensitivity, and used to provide average T1, T2 and PD measurements from compartments of normal and pathological tissue segmented from high-resolution images at acceleration factors of R ≤ 18-fold. The results were validated using compartment-average measures derived from the high-resolution scans.ResultsThe SVM accurately classified ~80% of samples into the three disease classes. The ‘area-under-the-curve’ was 0.96 for detecting disease in 248 samples, with T1 providing the best discrimination. SLAM T1, T2 and PD measures for R ≤ 10 were indistinguishable from the true means of segmented tissue compartments.ConclusionHigh-resolution IVMRI measures of T1, T2 and PD with a trained SVM can automatically classify normal, early and advanced atherosclerosis with high sensitivity and specificity. Replacing relaxometric MRI with SLAM yields good estimates of T1, T2 and PD an order-of-magnitude faster to facilitate IVMRI-based characterization of vessel disease.Electronic supplementary materialThe online version of this article (doi:10.1186/s12968-017-0399-6) contains supplementary material, which is available to authorized users.

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Purpose High-resolution intravascular (IV) MRI is susceptible to degradation from physiological motion and requires high frame-rates for true endoscopy. Traditional cardiac-gating techniques compromise efficiency by reducing the effective scan rate. Here we test whether compressed sensing (CS) reconstruction and ungated motion-compensation employing projection shifting, could provide faster motion-suppressed, IVMRI. Theory and Methods CS reconstruction is developed for under-sampled Cartesian and radial imaging using a new IVMRI-specific cost function to effectively increase imaging speed. A new motion correction method is presented wherein individual IVMRI projections are shifted based on the IVMRI detector's intrinsic amplitude and phase properties. The methods are tested at 3T in fruit, human vessel specimens, and a rabbit aorta in vivo. Images are compared using Structural-Similarity and ‘Spokal-Variation’ indices. Results Although some residual artifacts persisted, CS acceleration and radial motion compensation strategies reduced motion artefact in vitro and in vivo, allowing effective accelerations of up to eightfold at 200-300μm resolution. Conclusion 3T IVMRI detectors are well-suited to CS and motion correction strategies based on their intrinsic radially-sparse sensitivity profiles and high signal-to-noise ratios. While benefits of faster free-breathing high-resolution IVMRI and reduced motion sensitivity are realized, there are costs to spatial resolution, and some motion artifacts may persist.