Assessment of left ventricle magnetic resonance temperature stability in patients in the presence of arrhythmias.

BACKGROUND: Magnetic resonance (MR) thermometry allows visualization of lesion formation in real-time during cardiac radiofrequency (RF) ablation. The present study was performed to evaluate the precision of MR thermometry without RF heating in patients exhibiting cardiac arrhythmia in a clinical setting. The evaluation relied on quantification of changes in temperature measurements caused by noise and physiological motion. METHODS: Fourteen patients referred for cardiovascular magnetic resonance imaging underwent an extra sequence to test the temperature mapping stability during free-breathing acquisition. Phase images were acquired using a multi-slice, cardiac-triggered, single-shot echo planar imaging sequence. Temperature maps were calculated and displayed in real-time while the electrocardiogram (ECG) was recorded. The precision of temperature measurement was assessed by measuring the temporal standard deviation and temporal mean of consecutive temperature maps over a period of three minutes. The cardiac cycle was analyzed from ECG recordings to quantify the impact of arrhythmia events on the precision of temperature measurement. Finally, two retrospective strategies were tested to remove acquisition dynamics related either to arrhythmia events or sudden breathing motion. RESULTS: ECG synchronization allowed categorization of inter-beat intervals (RR) into distinct beat morphologies. Five patients were in stable sinus rhythm, while nine patients showed irregular RR intervals due to ectopic beats. An average temporal standard deviation of temperature of 1.6°C was observed in patients under sinus rhythm with a frame rate corresponding to the heart rate of the patient. The temporal standard deviation rose to 2.5°C in patients with arrhythmia. The retrospective rejection strategies increased the temperature precision measurement while maintaining a sufficient frame rate. CONCLUSIONS: Our results indicated that real-time cardiac MR thermometry shows good precision in patients under clinical conditions, even in the presence of arrhythmia. By providing real-time visualization of temperature distribution within the myocardium during RF delivery, MR thermometry could prevent insufficient or excessive heating and thus improve safety and efficacy.

T2 -based MRI Delta-radiomics improve response prediction in soft-tissue sarcomas treated by neoadjuvant chemotherapy.

BACKGROUND: Standard of care for patients with high-grade soft-tissue sarcoma (STS) are being redefined since neoadjuvant chemotherapy (NAC) has demonstrated a positive effect on patients' outcome. Yet response evaluation in clinical trials still relies on RECIST criteria. PURPOSE: To investigate the added value of a Delta-radiomics approach for early response prediction in patients with STS undergoing NAC. STUDY TYPE: Retrospective. POPULATION: Sixty-five adult patients with newly-diagnosed, locally-advanced, histologically proven high-grade STS of trunk and extremities. All were treated by anthracycline-based NAC followed by surgery and had available MRI at baseline and after two chemotherapy cycles. FIELD STRENGTH/SEQUENCE: Pre- and postcontrast enhanced T1 -weighted imaging (T1 -WI), turbo spin echo T2 -WI at 1.5 T. ASSESSMENT: A threshold of <10% viable cells on surgical specimens defined good response (Good-HR). Two senior radiologists performed a semantic analysis of the MRI. After 3D manual segmentation of tumors at baseline and early evaluation, and standardization of voxel-sizes and intensities, absolute changes in 33 texture and shape features were calculated. STATISTICAL TESTS: Classification models based on logistic regression, support vector machine, k-nearest neighbors, and random forests were elaborated using crossvalidation (training and validation) on 50 patients ("training cohort") and was validated on 15 other patients ("test cohort"). RESULTS: Sixteen patients were good-HR. Neither RECIST status (P = 0.112) nor semantic radiological variables were associated with response (range of P-values: 0.134-0.490) except an edema decrease (P = 0.003), although 14 shape and texture features were (range of P-values: 0.002-0.037). On the training cohort, the highest diagnostic performances were obtained with random forests built on three features: Δ_Histogram_Entropy, Δ_Elongation, Δ_Surrounding_Edema, which provided: area under the curve the receiver operating characteristic = 0.86, accuracy = 88.1%, sensitivity = 94.1%, and specificity = 66.3%. On the test cohort, this model provided an accuracy of 74.6% but 3/5 good-HR were systematically ill-classified. DATA CONCLUSION: A T2 -based Delta-radiomics approach might improve early response assessment in STS patients with a limited number of features. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:497-510.

A planning strategy for combined motion-assisted/gated MR guided focused ultrasound treatment of the pancreas.

Objective: To develop and evaluate a combined motion-assisted/gated MRHIFU heating strategy designed to accelerate the treatment procedure by reducing the required number of sonications to ablate a target volume in the pancreas. Methods: A planning method for combined motion-assisted/gated MRHIFU using 4D-MRI and motion characterization is introduced. Six healthy volunteers underwent 4D-MRI for target motion characterization on a 3.0-T clinical scanner. Using displacement patterns, simulations were performed for all volunteers for three sonication approaches: gated, combined motion-assisted/gated, and static. The number of sonications needed to ablate the pancreas head was compared. The influence of displacement amplitude and target volume size was investigated. Spherical target volumes (8, 15, 20 and 34 mL) and displacement amplitudes ranging from 5 to 25 mm were evaluated. For this case, the number of sonications required to ablate the whole target was determined. Results: The number of required sonications was lowest for a static target, 62 on average (range 49-78). The gated approach required most sonications, 126 (range 97-159). The combined approach was almost as efficient as the hypothetical static case, with an average of 78 (range 53-123). Simulations showed that with a 5-mm displacement amplitude, the target could be treated by making use of motion-assisted MRHIFU sonications only. In that case, this approach allowed the lowest number of sonication, while for 10 mm and above, the number of required sonications increased. Conclusion: The use of a combined motion-assisted/gated MRHIFU strategy may accelerate tumor ablation in the pancreas when respiratory-induced displacement amplitudes are between 5 and 10 mm.

Improved cardiac magnetic resonance thermometry and dosimetry for monitoring lesion formation during catheter ablation.

PURPOSE: A new real-time MR-thermometry pipeline was developed to measure multiple temperature images per heartbeat with 1.6×1.6×3 mm3 spatial resolution. The method was evaluated on 10 healthy volunteers and during radiofrequency ablation (RFA) in sheep. METHODS: Multislice, electrocardiogram-triggered, echo-planar imaging was combined with parallel imaging, under free breathing conditions. In-plane respiratory motion was corrected on magnitude images by an optical flow algorithm. Motion-related susceptibility artifacts were compensated on phase images by an algorithm based on Principal Component Analysis. Correction of phase drift and temporal filter were included in the pipeline implemented in the Gadgetron framework. Contact electrograms were recorded simultaneously with MR thermometry by an MR-compatible ablation catheter. RESULTS: The temporal standard deviation of temperature in the left ventricle remained below 2 °C on each volunteer. In sheep, focal heated regions near the catheter tip were observed on temperature images (maximal temperature increase of 38 °C) during RFA, with contact electrograms of acceptable quality. Thermal lesion dimensions at gross pathology were in agreement with those observed on thermal dose images. CONCLUSION: This fully automated MR thermometry pipeline (five images/heartbeat) provides direct assessment of lesion formation in the heart during catheter-based RFA, which may improve treatment of cardiac arrhythmia by ablation. Magn Reson Med 77:673-683, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

MRI-Guided HIFU Methods for the Ablation of Liver and Renal Cancers.

MRI-guided High Intensity Focused Ultrasound (MRI-HIFU) is a promising method for the non-invasive ablation of pathological tissue in many organs, including mobile organs such as liver and kidney. The possibility to locally deposit thermal energy in a non-invasive way opens a path towards new therapeutic strategies with improved reliability and reduced associated trauma, leading to improved efficacy, reduced hospitalization and costs. Liver and kidney tumors represent a major health problem because not all patients are suitable for curative treatment with surgery. Currently, radio-frequency is the most used method for percutaneous ablation. The development of a completely non-invasive method based on MR guided high intensity focused ultrasound (HIFU) treatments is of particular interest due to the associated reduced burden for the patient, treatment related patient morbidity and complication rate. The objective of MR-guidance is hereby to control heat deposition with HIFU within the targeted pathological area, despite the physiological motion of these organs, in order to provide an effective treatment with a reduced duration and an increased level of patient safety. Regarding this, several technological challenges have to be addressed: Firstly, the anatomical location of both organs within the thoracic cage requires inter-costal ablation strategies, which preserve the therapeutic efficiency, but prevent undesired tissue damage to the ribs and the intercostal muscle. Secondly, both therapy guidance and energy deposition have to be rendered compatible with the continuous physiological motion of the abdomen.

Recruitment of endocytosis in sonopermeabilization-mediated drug delivery: a real-time study.

Microbubbles (MBs) in combination with ultrasound (US) can enhance cell membrane permeability, and have the potential to facilitate the cellular uptake of hydrophilic molecules. However, the exact mechanism behind US- and MB-mediated intracellular delivery still remains to be fully understood. Among the proposed mechanisms are formation of transient pores and endocytosis stimulation. In our study, we investigated whether endocytosis is involved in US- and MB-mediated delivery of small molecules. Dynamic fluorescence microscopy was used to investigate the effects of endocytosis inhibitors on the pharmacokinetic parameters of US- and MB-mediated uptake of SYTOX Green, a 600 Da hydrophilic model drug. C6 rat glioma cells, together with SonoVue(®) MBs, were exposed to 1.4 MHz US waves at 0.2 MPa peak-negative pressure. Collection of the signal intensity in each individual nucleus was monitored during and after US exposure by a fibered confocal fluorescence microscope designed for real-time imaging. Exposed to US waves, C6 cells pretreated with chlorpromazine, an inhibitor of clathrin-mediated endocytosis, showed up to a 2.5-fold significant increase of the uptake time constant, and a 1.1-fold increase with genistein, an inhibitor of caveolae-mediated endocytosis. Both inhibitors slowed down the US-mediated uptake of SYTOX Green. With C6 cells and our experimental settings, these quantitative data indicate that endocytosis plays a role in sonopermeabilization-mediated delivery of small molecules with a more predominant contribution of clathrin-mediated endocytosis.

Feasibility of fast MR-thermometry during cardiac radiofrequency ablation.

Online MR temperature monitoring during radiofrequency (RF) ablation of cardiac arrhythmias may improve the efficacy and safety of the treatment. MR thermometry at 1.5 T using the proton resonance frequency (PRF) method was assessed in 10 healthy volunteers under normal breathing conditions, using a multi-slice, ECG-gated, echo planar imaging (EPI) sequence in combination with slice tracking. Temperature images were post-processed to remove residual motion-related artifacts. Using an MR-compatible steerable catheter and electromagnetic noise filter, RF ablation was performed in the ventricles of two sheep in vivo. The standard deviation of the temperature evolution in time (TSD) was computed. Temperature mapping of the left ventricle was achieved at an update rate of approximately 1 Hz with a mean TSD of 3.6 ± 0.9 °C. TSD measurements at the septum showed a higher precision (2.8 ± 0.9 °C) than at the myocardial regions at the heart-lung and heart-liver interfaces (4.1 ± 0.9 °C). Temperature rose maximally by 9 °C and 16 °C during 5 W and 10 W RF applications, respectively, for 60 s each. Tissue temperature can be monitored at an update rate of approximately 1 Hz in five slices. Typical temperature changes observed during clinical RF application can be monitored with an acceptable level of precision.

Deep Learning for the Automatic Quantification of Pleural Plaques in Asbestos-Exposed Subjects.

OBJECTIVE: This study aimed to develop and validate an automated artificial intelligence (AI)-driven quantification of pleural plaques in a population of retired workers previously occupationally exposed to asbestos. METHODS: CT scans of former workers previously occupationally exposed to asbestos who participated in the multicenter APEXS (Asbestos PostExposure Survey) study were collected retrospectively between 2010 and 2017 during the second and the third rounds of the survey. A hundred and forty-one participants with pleural plaques identified by expert radiologists at the 2nd and the 3rd CT screenings were included. Maximum Intensity Projection (MIP) with 5 mm thickness was used to reduce the number of CT slices for manual delineation. A Deep Learning AI algorithm using 2D-convolutional neural networks was trained with 8280 images from 138 CT scans of 69 participants for the semantic labeling of Pleural Plaques (PP). In all, 2160 CT images from 36 CT scans of 18 participants were used for AI testing versus ground-truth labels (GT). The clinical validity of the method was evaluated longitudinally in 54 participants with pleural plaques. RESULTS: The concordance correlation coefficient (CCC) between AI-driven and GT was almost perfect (>0.98) for the volume extent of both PP and calcified PP. The 2D pixel similarity overlap of AI versus GT was good (DICE = 0.63) for PP, whether they were calcified or not, and very good (DICE = 0.82) for calcified PP. A longitudinal comparison of the volumetric extent of PP showed a significant increase in PP volumes (p < 0.001) between the 2nd and the 3rd CT screenings with an average delay of 5 years. CONCLUSIONS: AI allows a fully automated volumetric quantification of pleural plaques showing volumetric progression of PP over a five-year period. The reproducible PP volume evaluation may enable further investigations for the comprehension of the unclear relationships between pleural plaques and both respiratory function and occurrence of thoracic malignancy.

Real-time volumetric MRI thermometry of focused ultrasound ablation in vivo: a feasibility study in pig liver and kidney.

MR thermometry offers the possibility to precisely guide high-intensity focused ultrasound (HIFU) for the noninvasive treatment of kidney and liver tumours. The objectives of this study were to demonstrate therapy guidance by motion-compensated, rapid and volumetric MR temperature monitoring and to evaluate the feasibility of MR-guided HIFU ablation in these organs. Fourteen HIFU sonications were performed in the kidney and liver of five pigs under general anaesthesia using an MR-compatible Philips HIFU platform prototype. HIFU sonication power and duration were varied. Volumetric MR thermometry was performed continuously at 1.5 T using the proton resonance frequency shift method employing a multi-slice, single-shot, echo-planar imaging sequence with an update frequency of 2.5 Hz. Motion-related suceptibility artefacts were compensated for using multi-baseline reference images acquired prior to sonication. At the end of the experiment, the animals were sacrificed for macroscopic and microscopic examinations of the kidney, liver and skin. The standard deviation of the temperature measured prior to heating in the sonicated area was approximately 1 °C in kidney and liver, and 2.5 °C near the skin. The maximum temperature rise was 30 °C for a sonication of 1.2 MHz in the liver over 15 s at 300 W. The thermal dose reached the lethal threshold (240 CEM(43) ) in two of six cases in the kidney and four of eight cases in the liver, but remained below this value in skin regions in the beam path. These findings were in agreement with histological analysis. Volumetric thermometry allows real-time monitoring of the temperature at the target location in liver and kidney, as well as in surrounding tissues. Thermal ablation was more difficult to achieve in renal than in hepatic tissue even using higher acoustic energy, probably because of a more efficient heat evacuation in the kidney by perfusion.

Improved 18-FDG PET/CT diagnosis of multiple myeloma diffuse disease by radiomics analysis.

OBJECTIVES: In multiple myeloma, the diagnosis of diffuse bone marrow infiltration on 18-FDG PET/CT can be challenging. We aimed to develop a PET/CT radiomics-based model that could improve the diagnosis of multiple myeloma diffuse disease on 18-FDG PET/CT. METHODS: We prospectively performed PET/CT and whole-body diffusion-weighted MRI in 30 newly diagnosed multiple myeloma. MRI was the reference standard for diffuse disease assessment. Twenty patients were randomly assigned to a training set and 10 to an independent test set. Visual analysis of PET/CT was performed by two nuclear medicine physicians. Spine volumes were automatically segmented, and a total of 174 Imaging Biomarker Standardisation Initiative-compliant radiomics features were extracted from PET and CT. Selection of best features was performed with random forest features importance and correlation analysis. Machine-learning algorithms were trained on the selected features with cross-validation and evaluated on the independent test set. RESULTS: Out of the 30 patients, 18 had established diffuse disease on MRI. The sensitivity, specificity and accuracy of visual analysis were 67, 75 and 70%, respectively, with a moderate kappa coefficient of agreement of 0.6. Five radiomics features were selected. On the training set, random forest classifier reached a sensitivity, specificity and accuracy of 93, 86 and 91%, respectively, with an area under the curve of 0.90 (95% confidence interval, 0.89-0.91). On the independent test set, the model achieved an accuracy of 80%. CONCLUSIONS: Radiomics analysis of 18-FDG PET/CT images with machine-learning overcame the limitations of visual analysis, providing a highly accurate and more reliable diagnosis of diffuse bone marrow infiltration in multiple myeloma patients.

Deciphering tumour tissue organization by 3D electron microscopy and machine learning.

Despite recent progress in the characterization of tumour components, the tri-dimensional (3D) organization of this pathological tissue and the parameters determining its internal architecture remain elusive. Here, we analysed the spatial organization of patient-derived xenograft tissues generated from hepatoblastoma, the most frequent childhood liver tumour, by serial block-face scanning electron microscopy using an integrated workflow combining 3D imaging, manual and machine learning-based semi-automatic segmentations, mathematics and infographics. By digitally reconstituting an entire hepatoblastoma sample with a blood capillary, a bile canaliculus-like structure, hundreds of tumour cells and their main organelles (e.g. cytoplasm, nucleus, mitochondria), we report unique 3D ultrastructural data about the organization of tumour tissue. We found that the size of hepatoblastoma cells correlates with the size of their nucleus, cytoplasm and mitochondrial mass. We also found anatomical connections between the blood capillary and the planar alignment and size of tumour cells in their 3D milieu. Finally, a set of tumour cells polarized in the direction of a hot spot corresponding to a bile canaliculus-like structure. In conclusion, this pilot study allowed the identification of bioarchitectural parameters that shape the internal and spatial organization of tumours, thus paving the way for future investigations in the emerging onconanotomy field.

Motion correction in MR thermometry of abdominal organs: a comparison of the referenceless vs. the multibaseline approach.

Reliable temperature and thermal-dose measurements using proton resonance frequency shift-based magnetic resonance (MR) thermometry for MR-guided ablation of abdominal organs require a robust correction of artefacts induced by the target displacement through an inhomogeneous and time-variant magnetic field. Two correction approaches emerged recently as promising candidates to allow continuous real-time MR-thermometry under free-breathing conditions: The multibaseline correction method, which relies on a pre-recorded correction table allowing to correct for periodic phase changes, and the referenceless method, which depends on a background phase estimation in the target area based on the assumption of a smooth spatial variation of the phase across the organ. This study combines both methods with real-time in-plane motion correction to permit both temperature and thermal-dose calculations on the fly. Subsequently, the practical aspects of both methods are compared in two application scenarios, a radio frequency-ablation and a high-intensity focused ultrasound ablation. A hybrid approach is presented that exploits the strong points of both methods, allowing accurate and precise proton resonance frequency-thermometry measurements during periodical displacement, even in the presence of spontaneous motion and strong susceptibility variations in the target area.

Real-time 3D target tracking in MRI guided focused ultrasound ablations in moving tissues.

Magnetic resonance imaging-guided high intensity focused ultrasound is a promising method for the noninvasive ablation of pathological tissue in abdominal organs such as liver and kidney. Due to the high perfusion rates of these organs, sustained sonications are required to achieve a sufficiently high temperature elevation to induce necrosis. However, the constant displacement of the target due to the respiratory cycle render continuous ablations challenging, since dynamic repositioning of the focal point is required. This study demonstrates subsecond 3D high intensity focused ultrasound-beam steering under magnetic resonance-guidance for the real-time compensation of respiratory motion. The target is observed in 3D space by coupling rapid 2D magnetic resonance-imaging with prospective slice tracking based on pencil-beam navigator echoes. The magnetic resonance-data is processed in real-time by a computationally efficient reconstruction pipeline, which provides the position, the temperature and the thermal dose on-the-fly, and which feeds corrections into the high intensity focused ultrasound-ablator. The effect of the residual update latency is reduced by using a 3D Kalman-predictor for trajectory anticipation. The suggested method is characterized with phantom experiments and verified in vivo on porcine kidney. The results show that for update frequencies of more than 10 Hz and latencies of less then 114 msec, temperature elevations can be achieved, which are comparable to static experiments.

Rapid motion correction in MR-guided high-intensity focused ultrasound heating using real-time ultrasound echo information.

The objective of this study was to evaluate the feasibility of integrating real-time ultrasound echo guidance in MR-guided high-intensity focused ultrasound (HIFU) heating of mobile targets in order to reduce latency between displacement analysis and HIFU treatment. Experiments on a moving phantom were carried out with MRI-guided HIFU during continuous one-dimensional ultrasound echo detection using separate HIFU and ultrasound imaging transducers. Excellent correspondence was found between MR- and ultrasound-detected displacements. Real-time ultrasound echo-based target tracking during MR-guided HIFU heating is shown with the dimensions of the heated area similar to those obtained for a static target. This work demonstrates that the combination of the two modalities opens up perspectives for motion correction in MRI-guided HIFU with negligible latency.

A method for MRI guidance of intercostal high intensity focused ultrasound ablation in the liver.

PURPOSE: High intensity focused ultrasound (HIFU) is a promising method for the noninvasive treatment of liver tumors. However, the presence of ribs in the HIFU beam path remains problematic since it may lead to adverse effects (skin burns) by absorption and reflection of the incident beam at or near the bone surface. This article presents a method based on magnetic resonance (MR) imaging for identification of the ribs in the HIFU beam, and for selection of the transducer elements to deactivate. METHODS: The ribs are visualized on anatomical images acquired prior to heating and manually segmented. The resulting regions of interest surrounding the ribs are projected onto the transducer surface by ray tracing from the focal point. The transducer elements in the "shadow" of the ribs are then deactivated. The method was validated ex vivo and in vivo in pig liver during breathing under multislice real-time MR thermometry, using the proton resonance frequency shift method. RESULTS: Ex vivo and in vivo temperature data showed that the temperature increase near the ribs was substantial when HIFU sonications were performed with all elements active, whereas the temperature was reduced with deactivation of the transducer elements located in front of the ribs. The temperature at the focal point was similar with and without deactivation of the transducer elements, indicative of no loss of heat efficiency with the proposed technique. CONCLUSIONS: This method is simple, rapid, and reliable, and enables intercostal HIFU ablation while sparing ribs and their surrounding tissues.

Biomechanical quality assurance criteria for deformable image registration algorithms used in radiotherapy guidance.

Image-guided radiation therapy (IGRT) allows radiation dose deposition with a high degree of geometric accuracy. Previous studies have demonstrated that such therapies may benefit from the employment of deformable image registration (DIR) algorithms, which allow both the automatic tracking of anatomical changes and accumulation of the delivered radiation dose over time. In order to ensure patient care and safety, however, the estimated deformations must be subjected to stringent quality assurance (QA) measures. In the present study we propose to extend the state-of-the-art methodology for QA of DIR algorithms by a set of novel biomechanical criteria. The proposed biomechanical criteria imply the calculation of the normal and shear mechanical stress, which would occur within the observed tissues as a result of the estimated deformations. The calculated stress is then compared to plausible physiological limits, providing thus the anatomical plausibility of the estimated deformations. The criteria were employed for the QA of three DIR algorithms in the context of abdominal conebeam computed tomography and magnetic resonance radiotherapy guidance. An initial evaluation of organ boundary alignment capabilities indicated that all three algorithms perform similarly. However, an analysis of the deformations within the organ boundaries with respect to the proposed biomechanical QA criteria revealed different degrees of anatomical plausibility. Additionally, it was demonstrated that violations of these criteria are also indicative of errors within the dose accumulation process. The proposed QA criteria, therefore, provide a tissue-dependent assessment of the anatomical plausibility of the deformations estimated by DIR algorithms, showcasing potential in ensuring patient safety for future adaptive IGRT treatments.

Real-time geometric distortion correction for interventional imaging with echo-planar imaging (EPI).

Many MR-guided interventional procedures rely on fast imaging sequences for providing images in real-time with a precise relation between the target position in the image and its true position. Echo-planar imaging (EPI) methods are very fast but prone to geometric distortions. Here, we propose a correction method designed for real-time conditions, adapting existing approaches based on dual EPI acquisition with varying echo times. The method is demonstrated with MR-thermometry for guiding thermal therapies. The proposed approach imposes a small penalty in acquisition speed but adds negligible latency to data processing, an important element for interventions of mobile organs.

Online real-time reconstruction of adaptive TSENSE with commodity CPU/GPU hardware.

Adaptive temporal sensitivity encoding (TSENSE) has been suggested as a robust parallel imaging method suitable for MR guidance of interventional procedures. However, in practice, the reconstruction of adaptive TSENSE images obtained with large coil arrays leads to long reconstruction times and latencies and thus hampers its use for applications such as MR-guided thermotherapy or cardiovascular catheterization. Here, we demonstrate a real-time reconstruction pipeline for adaptive TSENSE with low image latencies and high frame rates on affordable commodity personal computer hardware. For typical image sizes used in interventional imaging (128 x 96, 16 channels, sensitivity encoding (SENSE) factor 2-4), the pipeline is able to reconstruct adaptive TSENSE images with image latencies below 90 ms at frame rates of up to 40 images/s, rendering the MR performance in practice limited by the constraints of the MR acquisition. Its performance is demonstrated by the online reconstruction of in vivo MR images for rapid temperature mapping of the kidney and for cardiac catheterization.

Three-dimensional spatial and temporal temperature control with MR thermometry-guided focused ultrasound (MRgHIFU).

High-intensity focused ultrasound (HIFU) is an efficient noninvasive technique for local heating. Using MRI thermal maps, a proportional, integral, and derivative (PID) automatic temperature control was previously applied at the focal point, or at several points within a plane perpendicular to the beam axis using a multispiral focal point trajectory. This study presents a flexible and rapid method to extend the spatial PID temperature control to three dimensions during each MR dynamic. The temperature in the complete volume is regulated by taking into account the overlap effect of nearby sonication points, which tends to enlarge the heated area along the beam axis. Volumetric temperature control in vitro in gel and in vivo in rabbit leg muscle was shown to provide temperature control with a precision close to that of the temperature MRI measurements. The proposed temperature control ensures heating throughout the volume of interest of up to 1 ml composed of 287 voxels with 95% of the energy deposited within its boundaries and reducing the typical average temperature overshoot to 1 degrees C.

Numerical workflow of irreversible electroporation for deep-seated tumor.

The paper provides a numerical workflow, based on the 'real-life' clinical workflow of irreversible electroporation (IRE) performed for the treatment of deep-seated liver tumors. Thanks to a combination of numerical modeling, image registration algorithm and clinical data, our numerical workflow enables to provide the distribution of the electric field as effectively delivered by the clinical IRE procedure. As a proof of concept, we show on a specific clinical case of IRE ablation of liver tumor that clinical data could be advantageously combined to numerical simulations in a near future, in order to give to the interventional radiologists information on the effective IRE ablation. We also corroborate the simulated treated region with the post-treatment MRI performed 3 d after the treatment.