Global Longitudinal Strain to Predict Respiratory Failure and Death in Patients Admitted for COVID-19-Related Disease.

Evidence of the involvement of the cardiovascular system in patients with COVID-19 is increasing. The evaluation of the subclinical cardiac involvement is crucial for risk stratification at admission, and left ventricular global longitudinal strain (LVGLS) may be useful for this purpose. A total of 87 consecutive patients admitted to the COVID Center were enrolled from December 2020 to April 2021. A complete echocardiography examination was performed within 72 hours from admission. The main outcome was the need for mechanical ventilation by way of orotracheal intubation (OTI) and mortality, and the secondary outcome was the worsening of the respiratory function during hospitalization, interpreted as a decrease of the ratio between the partial pressure of oxygen and the fraction of inspired oxygen (P/F) <100. Of 87 patients, 14 had severe disease leading to OTI or death, whereas 24 had a P/F <100. LVGLS was significantly impaired in patients with severe disease. After adjustment for risk factors, by considering LVGLS as continuous variable, the latter remained significantly associated with severe acute respiratory distress syndrome (P/F <100) (hazard ratio [HR] 1.48, 95% confidence interval [CI] 1.18 to 1.88, p = 0.001) and OTI/death (HR 1.63, 95% CI 1.13 to 2.38, p = 0.012). When using an LVGLS cutoff of -16.1%, LVGLS ≥ -16.1% was independently associated with a higher risk of severe acute respiratory distress syndrome (HR 4.0, 95% CI 1.4 to 11.1, p= 0.008) and OTI/death (HR 7.3, 95% CI 1.6 to 34.1, p = 0.024). LVGLS can detect high-risk patients at the admission, which can help to guide in starting early treatment of the admitted patients.

Quality and comfort in head and neck hyperthermia: A redesign according to clinical experience and simulation studies.

PURPOSE: Clinical phase III trials have shown the benefit of adding hyperthermia to radiotherapy and chemotherapy for head and neck cancer (H&N). The HYPERcollar, a functional prototype capable of applying hyperthermia to the entire H&N region was developed. Specific absorption rate-based hyperthermia treatment planning (HTP) is used to optimise HYPERcollar treatments. Hence, besides treatment quality, reproduction and reproducibility of the HTP are also pivotal. In the current work we analysed the impact of key parameters on treatment quality and completely redesigned the mechanical layout of the HYPERcollar for improved treatment quality and patient comfort. MATERIAL AND METHODS: The requirements regarding patient position and the water bolus shape were quantified by simulation studies. The complete mechanical redesign was based on these requirements and non-modellable improvements were experimentally validated. RESULTS: From simulation studies we imposed the required positioning accuracy to be within ±5 mm. Simulation studies also showed that the water bolus shape has an important impact on treatment quality. Solutions to meet the requirements were 1) a redesign of the applicator, 2) a redesign of the water bolus, and 3) a renewed positioning strategy. Experiments were used to demonstrate whether the solutions meet the requirements. CONCLUSIONS: The HYPERcollar redesign improves water bolus shape, stability and skin contact. The renewed positioning strategy allows for positioning of the patient within the required precision of ±5 mm. By clinically introducing the new design, we aim at improving not only treatment quality and reproducibility, but also patient comfort and operator handling, which are all important for a better hyperthermia treatment quality.

Validation of MR thermometry: method for temperature probe sensor registration accuracy in head and neck phantoms.

PURPOSE: Magnetic resonance thermometry (MRT) is an attractive means to non-invasively monitor in vivo temperature during head and neck hyperthermia treatments because it can provide multi-dimensional temperature information with high spatial resolution over large regions of interest. However, validation of MRT measurements in a head and neck clinical set-up is crucial to ensure the temperature maps are accurate. Here we demonstrate a unique approach for temperature probe sensor localisation in head and neck hyperthermia test phantoms. METHODS: We characterise the proton resonance frequency shift temperature coefficient and validate MRT measurements in an oil-gel phantom by applying a combination of MR imaging and 3D spline fitting for accurate probe localisation. We also investigate how uncertainties in both the probe localisation and the proton resonance frequency shift (PRFS) thermal coefficient affect the registration of fibre-optic reference temperature probe and MRT readings. RESULTS: The method provides a two-fold advantage of sensor localisation and PRFS thermal coefficient calibration. We provide experimental data for two distinct head and neck phantoms showing the significance of this method as it mitigates temperature probe localisation errors and thereby increases accuracy of MRT validation results. CONCLUSIONS: The techniques presented here may be used to simplify calibration experiments that use an interstitial heating device, or any heating method that provides rapid and spatially localised heat distributions. Overall, the experimental verification of the data registration and PRFS thermal coefficient calibration technique provides a useful benchmarking method to maximise MRT accuracy in any similar context.

Clinical integration of software tool VEDO for adaptive and quantitative application of phased array hyperthermia in the head and neck.

BACKGROUND AND PURPOSE: In Rotterdam, patient-specific hyperthermia (HT) treatment planning (HTP) is applied for all deep head and neck (H&N) HT treatments. In this paper we introduce VEDO (the Visualisation Tool for Electromagnetic Dosimetry and Optimisation), the software tool required, and demonstrate its value for HTP-guided online complaint-adaptive (CA) steering based on specific absorption rate (SAR) optimisation during a H&N HT treatment. MATERIALS AND METHODS: VEDO integrates CA steering, visualisation of the SAR patterns and mean tumour SAR (SAR(target)) optimisation in a single screen. The pre-calculated electromagnetic fields are loaded into VEDO. During treatment, VEDO shows the SAR pattern, overlaid on the patients' CT-scan, corresponding to the actually applied power settings and it can (re-)optimise the SAR pattern to minimise SAR at regions where the patient senses discomfort while maintaining a high SAR(target). RESULTS: The potential of the quantitative SAR steering approach using VEDO is demonstrated by analysis of the first treatment in which VEDO was used for two patients using the HYPERcollar. These cases show that VEDO allows response to power-related complaints of the patient and to quantify the change in absolute SAR: increasing either SAR(target) from 96 to 178 W/kg (case 1); or show that the first SAR distribution was already optimum (case 2). CONCLUSION: This analysis shows that VEDO facilitates a quantitative treatment strategy allowing standardised application of HT by technicians of different HT centres, which will potentially lead to improved treatment quality and the possibility of tracking the effectiveness of different treatment strategies.

Design of a wideband multi-channel system for time reversal hyperthermia.

PURPOSE: To design and test a wideband multi-channel amplifier system for time reversal (TR) microwave hyperthermia, operating in the frequency range 300 MHz-1 GHz, enabling operation in both pulsed and continuous wave regimes. This is to experimentally verify that adaptation of the heating pattern with respect to tumour size can be realised by varying the operating frequency of the antennas and potentially by using Ultra-wideband (UWB) pulse sequences instead of pure harmonic signals. MATERIALS AND METHODS: The proposed system consists of 12 identical channels driven by a common reference signal. The power and phase settings are applied with resolutions of 0.1 W and 0.1°, respectively. Using a calibration procedure, the measured output characteristics of each channel are interpolated using polynomial functions, which are then implemented into a system software algorithm driving the system feedback loop. RESULTS: The maximum output power capability of the system varies with frequency, between 90 and 135 W with a relative power error of ± 6%. A phase error in the order of ± 4° has been achieved within the entire frequency band. CONCLUSIONS: The developed amplifier system prototype is capable of accurate power and phase delivery, over the entire frequency band of the system. The output power of the present system allows for an experimental verification of a recently developed TR-method on phantoms or animals. The system is suitable for further development for head and neck tumours, breast or extremity applications.

Microwave applicator for hyperthermia treatment on in vivo melanoma model.

In this article, we evaluated a planar microwave applicator for in vivo superficial hyperthermia treatments on small tumors in the mouse mimicking treatments for human neoplasms. The design of the applicator, was challenged by the small dimensions of the tumors and unwanted diffusion of heating in the tumor-bearing animals. The required solution was to limit the penetration of microwaves in the depth of the tissue maintaining the full efficacy of hyperthermia. The study was firstly performed by computer simulations of SAR distribution inside a flat homogeneous phantom, considering various thicknesses of the integrated water bolus. Simulations, validated by the measurements, were also used to evaluate the impedance matching. Further tests were performed on homogeneous agar phantom to simulate the temperature distribution in the biological tissue and to preliminary assess the possible modality and schedule of microwave hyperthermia delivery. The in vivo experiments showed the evidence of direct microwave-induced heating and damage of the melanoma tissue in a range of penetration coherent both with computer simulations and phantom studies. The described approach appears perspective for designing limited-microwave-delivery applicators tailored for treatments of human superficial tumors and pre-tumoral lesions.

Slot-line applicator for microwave hyperthermia.

Electromagnetic field interaction with biological tissues and their applications in cancer treatment research has become of growing interest. This paper describes the possibility of using a slot-line type applicator for microwave hyperthermia treatment in oncology. What we aim to show in this paper is that this type of applicator is particularly suitable for the treatment of superficial cancers with depths 2-3 cm below the body surface. To support this thesis, a 3D electromagnetic field simulator has been used to predict the specific absorbed ratio (SAR), and the consequent temperature distribution in the area under treatment. The results of the simulations are supported by experimental temperature measurements made with the help of an infrared thermo-camera on a homogeneous agar phantom. The possibility to use an array configuration of this applicator in order to treat bigger areas is also analyzed using computer simulation of SAR distribution.