Abstract To quantitatively assess the influence of target temperature and ablation duration on the quality of proton resonance frequency shift (PRFS)-based MR thermometry during microwave ablation (MWA) in a controlled ex vivo model, and to identify parameter ranges associated with improved thermometry performance. Thirty-two MWAs were performed in 10 ex vivo bovine livers in a 1.5-tesla MRI system with multi-slice volumetric real-time thermometry yielding temperature and thermal dose maps. The experiments were conducted twice using all combinations of four target temperatures (60; 80; 100; 120 °C) and four ablation times (5:00; 7:30; 10:00; 15:00 min). Thermometry quality was rated on a 5‑point Likert scale. Ablation areas were compared with histopathology (hematoxylin and eosin, H&E; and nicotinamide adenine dinucleotide, NADH‑diaphorase) and correlated using Spearman coefficients. Likert scores were compared across temperatures using Kruskal-Wallis and Mann-Whitney U tests. All evaluations were performed independently by two readers. Lesion areas varied from 2.6 to 12.9 cm², increasing primarily with target temperature. Ablation areas from temperature and thermal dose maps correlated strongly with macroscopically visual necrosis (p < 0.01). Likert scores differed significantly across temperatures (p < 0.05). The highest image quality was achieved at 60 °C for 7:30 min, showing comparable scores as at 80° for 15:00 min, but significantly differing from 100 °C to 120 °C. In this controlled ex vivo setting, lower target temperatures were associated with improved MRI thermometry quality, providing more reliable visualization of ablation zones; however, ablation volumes decreased at lower temperatures. Furthermore, these empirical ex vivo observations suggest that a staged two-level approach may support a clinical workflow strategy aimed at balancing thermometry image quality and ablation volume. Given the absence of perfusion and motion effects, these findings require further validation before clinical translation.

Purpose: The primary purpose of this study was to evaluate the accuracy of an MR-thermometry sequence for monitoring prostate temperature. The secondary purposes were to analyze clinical and technical factors that may affect accuracy and testing the method in a realistic setting, with MR-guided Laser ablation on an ex vivo muscle sample. Materials and methods: An ex vivo muscle sample was subjected to Laser ablation while using a two-dimensional multislice segmented echo planar imaging sequence for MR thermometry. The MR thermometry measurements were compared with invasive sensor temperature readings to assess accuracy. Subsequently, 56 men with a median age of 70 years (age range: 53-84 years) who underwent prostate MRI examinations at 1.5- (n = 27) or 3 T (n = 24) were prospectively included. For each patient, the proportion of 'noisy voxels' (i.e., those with a temporal standard deviation of temperature [SD(T)] > 2 degrees C) in the prostate was calculated. The impact of clinical and technical factors on the proportion of noisy voxels was also examined. Results: MR-thermometry showed excellent correlation with invasive sensors during MR-guided Laser ablation on the ex vivo muscle sample. The median proportion of noisy voxels per patient in the entire cohort was 1 % (Q1, 0.2; Q3, 4.9; range: 0-90.4). No significant differences in median proportion of noisy voxels were observed between examinations performed at 1.5 T and those at 3 T (P = 0.89 before and after adjustment). No clinical or technical factors significantly influenced the proportion of noisy voxels. Conclusion: Two-dimensional real time multislice MR-thermometry is feasible and accurate for monitoring prostate temperature in patients.

Objectives To investigate and optimize the quality of magnetic resonance imaging (MRI) thermometry during microwave ablations (MWAs). Materials & Methods Thirty-two MWAs were performed in 10 ex vivo bovine livers in a 1.5-tesla MRI system with real-time three-dimensional (3D) thermometry yielding temperature and thermal dose maps. The experiments were conducted twice using all combinations of four target temperatures (60; 80; 100; 120°C) and four ablation times (5:00; 7:30; 10:00; 15:00 min). Thermometry quality was rated on a 5‑point Likert scale. Ablation areas were compared with histopathology (hematoxylin and eosin, H&E; and nicotinamide adenine dinucleotide, NADH‑diaphorase) and correlated using Spearman coefficients. Likert scores were compared across temperatures using Kruskal-Wallis and Mann-Whitney U tests. All evaluations were performed independently by two readers. Results Lesion areas varied from 2.6 to 12.9 cm², increasing primarily with target temperature. Ablation areas from temperature and thermal dose maps correlated strongly with macroscopically visual necrosis ( p < 0.01). Likert scores differed significantly across temperatures ( p < 0.05). The highest image quality was achieved at 60°C for 7:30 min, showing comparable scores as at 80° for 15:00 min, but significantly differing from 100°C and 120°C. Conclusion Lower target temperatures were associated with improved MRI thermometry quality, providing more reliable visualization of ablation zones.

PURPOSE:Real-time monitoring of microwave liver ablation (MWA) using MRI thermometry can be hindered by boiling-induced susceptibility artifacts. These artifacts cause large temperature measurement errors that prevent accurate lesion size prediction. This study proposes a correction methodology based on removing the contribution of this susceptibility artifact using subvoxel sources of susceptibility. METHODS:In vivo microwave ablations (N = 23) were performed on seven pig livers and the temperature was monitored using the proton resonance frequency shift (PRFS) method. The boiling-induced artifacts were observed in 11 ablation cases. To validate the proposed methodology, the thermal dose was computed from the corrected temperature maps, and the resulting lesion estimates were compared in three dimensions with ground-truth lesion segmentations derived from post-ablation T1w images. A numerical simulation was also conducted to emphasize the need for a finer spatial discretization. RESULTS:After correction, a better agreement was noticed between thermal dose prediction and lesion size. Over the 11 cases observed with boiling-induced susceptibility artifacts, the median volumetric Dice, Total Overlap, and False Negative rates changed by 4.8%, 6.2%, and -11.4%. CONCLUSION:Comparison with T1w imaging showed improvements in prediction of lesion volume. The proposed methodology takes into account partial volume effects and the contribution of adjacent slices. It was able to simulate a diverse range of deformed dipole-like artifacts observed in experimental data.

BACKGROUND:Quantitative real-time MRI-based temperature mapping techniques are hampered by abdominal motion. Intrascan motion can be reduced by rapid acquisition sequences such as 2D echo planar imaging (EPI), and inter-scan organ displacement can be compensated by image processing such as optical flow (OF) algorithms. However, motion field estimation can be seriously affected by local variation of signal intensity on magnitude images inherent to tissue heating, potentially leading to erroneous temperature estimates. PURPOSE:This study aims to characterize, in the context of clinical MRI-guided microwave ablation (MWA), a novel deformable image registration (DIR) algorithm that enhances the generation of thermal maps aligned to a reference position, a critical step for calculating cumulative thermal dose and, consequently, for the real-time evaluation of interventional procedure progress. METHODS:A retrospective image analysis was performed on 11 patients that underwent MWA of a liver tumor (primary or metastasis). Ablation duration was set to 9 ± 2 min with a 14-gauge large antenna. A stack of 13-20 contiguous slices was acquired dynamically (350 repetitions) at 1.5T using a single-shot EPI sequence. Evaluation was first performed on motion-free datasets (5 gated acquisitions using a cushion positioned in the patient abdomen) then with ones with motion (8 fixed-frequency acquisitions at 0.5 Hz). Temperature, thermal dose and lesion size were computed using three workflows: (i) standard phase subtraction (gold standard), (ii) conventional OF motion compensation, (iii) PCA-based OF motion compensation. The impact of flow field, temperature and lesion volume estimation were compared using averaged endpoint error (AEE), NRMSE and bland Altman plot, respectively. RESULTS:Intensity signal decreases (close to 50%) were observed in the vicinity of the probe during MW energy delivery. Both motion correction algorithms reduce the NRMSE of magnitude images throughout the acquisition (p < 0.005) and achieve similar results between them. Gated acquisition results. Conventional OF produced erroneous vector fields compared to the PCA-based OF, leading to higher maximal EE (3 mm vs. 1 mm) and temperature errors up to 15°C-20°C. PCA-based OF algorithm significantly reduces the NRMSE of temperature (p < 0.005). The conventional OF method underestimated the final size of lesions with a bias of 0.93 cm3 while the PCA-based OF reported a bias of 0.5 cm3. Fixed frequency acquisition results. The temperature estimation without motion correction led to strong fluctuations or loss of temperature measurement while the proposed PCA-based OF recovered both a stable and precise measurement with null bias. CONCLUSION:The deformable image registration algorithm is less sensitive to local variations of the signal. Volumetric temperature imaging without gating (20 slices/2 s) could be performed with the same accuracy, and offer trade-offs in acquisition time or volume coverage. Such a strategy is expected to increase procedure safety by monitoring large volumes more rapidly for MR-guided thermotherapy on mobile organs.

Background Clinical Laser-Induced Thermotherapy (LITT) currently lacks precise control of tissue temperature increase during the procedure. This study presents a new method to automatically regulate the maximum temperature increase in vivo at different positions by adjusting LITT power delivered by multiple laser probes using real-time volumetric MR-thermometry. Methods The regulation algorithm was evaluated in vivo on a pig leg muscle. Temperature regulation was performed in volumes surrounding each laser probe tip. The power delivered to each laser probe was automatically adjusted every second using a feedback control algorithm by processing on-the-fly MR-thermometry images (10 slices/second) on a 1.5 T clinical scanner (1.56 mm × 1.56 mm x 3 mm resolution), using the proton-resonance frequency (PRF) shift technique. Several experimental conditions were tested with predefined temperature-time profiles corresponding to conditions of thermal ablation (+30 °C above body temperature) or moderate hyperthermia (+10 and + 15 °C). Control images were acquired after injection of Gadolinium at the end of experiment and were compared with the thermal dose images calculated from the thermometry images. Results The mean difference and root mean squared error between target temperatures and measured ones remained below 0.5 °C and 2 °C respectively, for 5 min duration. Lesion sizes observed on thermal dose and on images acquired after gadolinium injection were in good agreement. Conclusion Automatic regulation of in vivo temperature increase during LITT procedures with multiple laser emitters control is feasible. The method provides an adaptative solution to improve the safety and efficacity of such clinical procedures.

Background & Aims:MRI guidance offers better lesion targeting for microwave ablation of liver lesions with higher soft-tissue contrast, as well as the possibility of real-time thermometry. This study aims to evaluate the correlation of real-time MR thermometry-predicted lesion volume with the ablation zone in postprocedural first-day images. Methods:This single-center retrospective analysis evaluated prospectively included patients who underwent MRI-guided microwave ablation with real-time thermometry between December 2020 and July 2023. All procedures were performed under general anesthesia on a 1.5 T MRI scanner. Real-time thermometry data were acquired using multi-slice gradient-echo echoplanar imaging sequences, and thermal dose maps (CEM43 of 240 min as a threshold) were created. The volume of tissue exposed to a lethal thermal dose in MR thermometry (thermal dose) was compared with the ablation zone volume in portal phase T1w MRI on the postprocedural first day using the Pearson correlation test, and visual quantitative assessment by radiologists was performed to evaluate the similarity of shapes and volumes. Results:Out of 30 patients with 33 lesions with thermometry images, six (18.1%) lesions were excluded because of artifacts limiting interpretation of thermal dose volume. Twenty-four patients with 27 lesions (20 male, age 63.1 ± 9.1 years) were evaluated for the volume correlation. The volume of thermal dose-predicted lesions and the postprocedural first-day ablation zones showed a strong correlation (R = 0.89, p <0.001). Similarly, visual similarity of molecular resonance thermometry-predicted shape and the ablation zone shape was graded as perfect in 23 (85.1%) lesions. Conclusions:Real-time thermal dose-predicted volumes show very good correlation with the ablation zone volumes in images obtained 1 day after the procedure, which could reduce the local recurrence rates with the possibility of re-ablating lesions within the same procedure. Impact and implications:Heat-based ablation is an established treatment for liver tumors; however, there is a considerable rate of incomplete treatment because of the lack of real-time visualization of the treated area during treatment. Our results show that MRI-guided ablation enables the visualization of the treatment area in real-time with high accuracy using a special technique of MR thermometry in patients with liver tumors.

Abstract Background Interventional magnetic resonance imaging (MRI) can provide a comprehensive setting for microwave ablation of tumors with real-time monitoring of the energy delivery using MRI-based temperature mapping. The purpose of this study was to quantify the accuracy of three-dimensional (3D) real-time MRI temperature mapping during microwave heating in vitro by comparing MRI thermometry data to reference data measured by fiber-optical thermometry. Methods Nine phantom experiments were evaluated in agar-based gel phantoms using an in-room MR-conditional microwave system and MRI thermometry. MRI measurements were performed for 700 s (25 slices; temporal resolution 2 s). The temperature was monitored with two fiber-optical temperature sensors approximately 5 mm and 10 mm distant from the microwave antenna. Temperature curves of the sensors were compared to MRI temperature data of single-voxel regions of interest (ROIs) at the sensor tips; the accuracy of MRI thermometry was assessed as the root-mean-squared (RMS)-averaged temperature difference. Eighteen neighboring voxels around the original ROI were also evaluated and the voxel with the smallest temperature difference was additionally selected for further evaluation. Results The maximum temperature changes measured by the fiber-optical sensors ranged from 7.3 K to 50.7 K. The median RMS-averaged temperature differences in the originally selected voxels ranged from 1.4 K to 3.4 K. When evaluating the minimum-difference voxel from the neighborhood, the temperature differences ranged from 0.5 K to 0.9 K. The microwave antenna and the MRI-conditional in-room microwave generator did not induce relevant radiofrequency artifacts. Conclusion Accurate 3D real-time MRI temperature mapping during microwave heating with very low RMS-averaged temperature errors below 1 K is feasible in gel phantoms. Relevance statement Accurate MRI-based volumetric real-time monitoring of temperature distribution and thermal dose is highly relevant in clinical MRI-based interventions and can be expected to improve local tumor control, as well as procedural safety by extending the limits of thermal (e.g., microwave) ablation of tumors in the liver and in other organs. Key Points Interventional MRI can provide a comprehensive setting for the microwave ablation of tumors. MRI can monitor the microwave ablation using real-time MRI-based temperature mapping. 3D real-time MRI temperature mapping during microwave heating is feasible. Measured temperature errors were below 1 °C in gel phantoms. The active in-room microwave generator did not induce any relevant radiofrequency artifacts. Graphical Abstract

We present here a method to automatically regulate heat deposition during Laser Interstitial Thermal Therapy to precisely control temperature evolution during the procedure. The method relies on real-time rapid volumetric thermometry using the Proton Resonance Frequency Shift technique and a regulation algorithm that adjusts every second the emitted power by the laser to force temperature to follow a predefined temperature-time profile.

Precise control of tissue temperature during Laser-Induced Thermotherapy (LITT) procedures has the potential to improve the clinical efficiency and safety of such minimally invasive therapies. We present a method to automatically regulate in vivo the temperature increase during LITT using real-time rapid volumetric Magnetic Resonance thermometry (8 slices acquired every second, with an in-plane resolution of 1.4 mmx1.4 mm and a slice thickness of 3 mm) using the proton-resonance frequency (PRF) shift technique. The laser output power is adjusted every second using a feedback control algorithm (proportional-integral-derivative controller) to force maximal tissue temperature in the targeted region to follow a predefined temperature–time profile. The root-mean-square of the difference between the target temperature and the measured temperature ranged between 0.5 °C and 1.4 °C, for temperature increases between + 5 °C to + 30 °C above body temperature and a long heating duration (up to 15 min), showing excellent accuracy and stability of the method. These results were obtained on a 1.5 T clinical MRI scanner, showing a potential immediate clinical application of such a temperature controller during MR-guided LITT.

PURPOSE In presence of respiratory motion, temperature mapping is altered by in-plane and through-plane displacements between successive acquisitions together with periodic phase variations. Fast 2D Echo Planar Imaging (EPI) sequence can accommodate intra-scan motion, but limited volume coverage and inter-scan motion remain a challenge during free-breathing acquisition since position offsets can arise between the different slices. METHOD To address this limitation, we evaluated a 2D simultaneous multi-slice EPI sequence with multiband (MB) acceleration during radiofrequency ablation on a mobile gel and in the liver of a volunteer (no heating). The sequence was evaluated in terms of resulting inter-scan motion, temperature uncertainty and elevation, potential false-positive heating and repeatability. Lastly, to account for potential through-plane motion, a 3D motion compensation pipeline was implemented and evaluated. RESULTS In-plane motion was compensated whatever the MB factor and temperature distribution was found in agreement during both the heating and cooling periods. No obvious false-positive temperature was observed under the conditions being investigated. Repeatability of measurements results in a 95% uncertainty below 2 °C for MB1 and MB2. Uncertainty up to 4.5 °C was reported with MB3 together with the presence of aliasing artifacts. Lastly, fast simultaneous multi-slice EPI combined with 3D motion compensation reduce residual out-of-plane motion. CONCLUSION Volumetric temperature imaging (12 slices/700 ms) could be performed with 2 °C accuracy or less, and offer tradeoffs in acquisition time or volume coverage. Such a strategy is expected to increase procedure safety by monitoring large volumes more rapidly for MR-guided thermotherapy on mobile organs.

The complexity of the MRI protocol is one of the factors limiting the clinical adoption of MR temperature mapping for real-time monitoring of cardiac ablation procedures and a push-button solution would ease its use. Continuous gradient echo golden angle radial acquisition combined with intra-scan motion correction and undersampled temperature determination could be a robust and more user-friendly alternative than the ultrafast GRE-EPI sequence which suffers from sensitivity to magnetic field susceptibility artifacts and requires ECG-gating. The goal of this proof-of-concept work is to establish the temperature uncertainty as well as the spatial and temporal resolutions achievable in an Agar-gel phantom and in vivo using this method. GRE radial golden angle acquisitions were used to monitor RF ablations in a phantom and in vivo in two sheep hearts with different slice orientations. In each case, 2D rigid motion correction based on catheter micro-coil signal, tracking its motion, was performed and its impact on the temperature imaging was assessed. The temperature uncertainty was determined for three spatial resolutions (1 × 1 × 3 mm3, 2 × 2 × 3 mm3, and 3 × 3 × 3 mm3) and three temporal resolutions (0.48, 0.72, and 0.97 s) with undersampling acceleration factors ranging from 2 to 17. The combination of radial golden angle GRE acquisition, simultaneous catheter tracking, intra-scan 2D motion correction, and undersampled thermometry enabled temperature monitoring in the myocardium in vivo during RF ablations with high temporal (< 1 s) and high spatial resolution. The temperature uncertainty ranged from 0.2 ± 0.1 to 1.8 ± 0.2 °C for the various temporal and spatial resolutions and, on average, remained superior to the uncertainty of an EPI acquisition while still allowing clinical monitoring of the RF ablation process. The proposed method is a robust and promising alternative to EPI acquisition to monitor in vivo RF cardiac ablations. Further studies remain required to improve the temperature uncertainty and establish its clinical applicability.

PurposeTo propose a MR-thermometry method and associated data processing technique to predict the maximal RF-induced temperature increase near an implanted wire for any other MRI sequence.MethodsA dynamic single shot echo planar imaging sequence was implemented that interleaves acquisition of several slices every second and an energy deposition module with adjustable parameters. Temperature images were processed in real time and compared to invasive fiber-optic measurements to assess accuracy of the method. The standard deviation of temperature was measured in gel and in vivo in the human brain of a volunteer. Temperature increases were measured for different RF exposure levels in a phantom containing an inserted wire and then a MR-conditional pacemaker lead. These calibration data set were fitted to a semi-empirical model allowing estimation of temperature increase of other acquisition sequences.ResultsThe precision of the measurement obtained after filtering with a 1.6x1.6 mm2 in plane resolution was 0.2°C in gel, as well as in the human brain. A high correspondence was observed with invasive temperature measurements during RF-induced heating (0.5°C RMSE for a 11.5°C temperature increase). Temperature rises of 32.4°C and 6.5°C were reached at the tip of a wire and of a pacemaker lead, respectively. After successful fitting of temperature curves of the calibration data set, temperature rise predicted by the model was in good agreement (around 5% difference) with measured temperature by a fiber optic probe, for three other MRI sequences.ConclusionThis method proposes a rapid and reliable quantification of the temperature rise near an implanted wire. Calibration data set and resulting fitting coefficients can be used to estimate temperature increase for any MRI sequence as function of its power and duration.

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.

Background: Transcranial focus ultrasound applications applied under MRI-guidance benefit from unrivaled monitoring capabilities, allowing the recording of real-time anatomical information and biomarkers like the temperature rise and/or displacement induced by the acoustic radiation force. Having both of these measurements could allow for better targeting of brain structures, with improved therapy monitoring and safety. Method: We investigated the use of a novel MRI-pulse sequence described previously in Bour a al., (2017) to quantify both the displacement and temperature changes under various ultrasound sonication conditions and in different regions of the brain. The method was evaluated in vivo in a non-human primate under anesthesia using a single-element transducer (f = 850 kHz) in a setting that could mimic clinical applications. Acquisition was performed at 3 T on a clinical imaging system using a modified single-shot gradient echo EPI sequence integrating a bipolar motion-sensitive encoding gradient. Four slices were acquired sequentially perpendicularly or axially to the direction of the ultrasound beam with a 1-Hz update frequency and an isotropic spatial resolution of 2-mm. A total of twenty-four acquisitions were performed in three different sets of experiments. Measurement uncertainty of the sequence was investigated under different acoustic power deposition and in different regions of the brain. Acoustic simulation and thermal modeling were performed and compared to experimental data. Results: The sequence simultaneously provides relevant information about the focal spot location and visualization of heating of brain structures: 1) The sequence localized the acoustic focus both along as well as perpendicular to the ultrasound direction. Tissue displacements ranged from 1 to 2 pm. 2) Thermal rise was only observed at the vicinity of the skull. Temperature increase ranged between 1 and 2 degrees C and was observed delayed relative the sonication due to thermal diffusion. 3) The fast frame rate imaging was able to highlight magnetic susceptibility artifacts related to breathing, for the most caudal slices. We demonstrated that respiratory triggering successfully restored the sensitivity of the method (from 0.7 pm to 0.2 pm). 4) These results were corroborated by acoustic simulations. Conclusions: The current rapid, multi-slice acquisition and real-time implementation of temperature and displacement visualization may be useful in clinical practices. It may help defining operational safety margins, improving therapy precision and efficacy. Simulations were in good agreement with experimental data and may thus be used prior treatment for procedure planning.

Current crowd behavior analyses based on 'live' visual or audiovisual camera streams require numerous personnel and is error prone due to human mistakes. Hence, automatic crowd behavior detection is urgently needed, in particular for crowded public spaces that need 24/7 monitoring. However, the complex nature of crowd behaviors and real-life constraints debase the advantages in sophisticated computer vision and analytics algorithms when they are applied in crowed monitoring systems. It is evident that crowd behavior analysis and recognition are critical to many important applications including surveillance, robotics, information retrieval, psychology, entertainment (movies, CGI, games, etc.) and market research. Automated crowd behavior analysis has been a topic of great interest in computer vision and cognitive sciences. Recently, with the growth of crowd phenomena in the real world, this area of research has attracted much attention. Therefore, over the past few years the number of works on crowd behavior analysis increased covering macroscopic (holistic) and microscopic (object-based) approaches, including techniques based on motion patterns, tracking, activity analysis and modeling, anomaly detection, and density estimation. In this chapter state-of-the-art techniques on this topic are outlined. An overview of the related challenging tasks is provided and existing and popular solutions as well as evaluation metrics and datasets are discussed.

Described here is a study of transesophageal thermal ablation of isolated and perfused beating hearts and non-human primates. An endoscope integrating a transesophageal echocardiography probe and a high-intensity focused ultrasound transducer was built and tested on five Langendorff-isolated hearts and three 30-kg baboons. B-Mode ultrasound, passive elastography and magnetic resonance imaging were performed to monitor thermal lesions. In isolated hearts, continuous and gated sonication parameters were evaluated with acoustic intensities of 9–12 W/cm2. Sonication parameters of gated exposures with 12 W/cm2 acoustic intensity for 5 min consistently produced visible lesions in the ventricles of isolated hearts. In animals, left atria and ventricles were exposed to repeated continuous sonications (4–15 times for 16 s) at an acoustic intensity at the surface of the transducer of 9 W/cm2. Clinical states of the baboons during and after the treatment were good. One suspected lesion in the left ventricle could be evidenced by elastography, but was not confirmed by magnetic resonance imaging. The transesophageal procedure therefore has the potential to create thermal lesions in beating hearts and its safety in clinical practice seems promising. However, further technical exploration of the energy deposition in the target would be necessary before the next pre-clinical experiments.