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Temperature monitoring plays a central role in improving clinical effectiveness of adjuvant hyperthermia. The potential of magnetic resonance thermometry for treatment monitoring purposes led to several MR-guided hyperthermia approaches. However, the proposed solutions were sub-optimal due to technological and intrinsic limitations. These hamper achieving target conformal heating possibilities (applicator limitations) and accurate thermometry (inadequate signal-to-noise-ratio (SNR)). In this work, we studied proof of principle of a dual-function hyperthermia approach based on a coil array (64 MHz, 1.5 T) that is integrated in-between a phased array for heating (434 MHz) for maximum signal receive in order to improve thermometry accuracy. Hereto, we designed and fabricated a superficial hyperthermia mimicking planar array setup to study the most challenging interactions of generic phased-array setups in order to validate the integrated approach. Experiments demonstrated that the setup complies with the superficial hyperthermia guidelines for heating and is able to improve SNR at 2-4 cm depth by 17%, as compared to imaging using the body coil. Hence, the results showed the feasibility of our dual-function MR-guided hyperthermia approach as basis for the development of application specific setups.

Purpose: To develop a head and neck hyperthermia phased array system compatible with a 1.5 T magnetic resonance (MR) scanner for noninvasive thermometry. Methods: We designed a dielectric-parabolic-reflector antenna (DiPRA) based on a printed reflector backed dipole antenna and studied its predicted and measured performance in a flat configuration (30 mm thick water bolus and muscle equivalent layer). Thereafter, we designed a phased array applicator model (‘MRcollar’) consisting of 12 DiPRA modules placed on a radius of 180 mm. Theoretical heating performance of the MRcollar model was benchmarked against the current clinical applicator (HYPERcollar3D) using specific (3D) head and neck models of 28 treated patients. Lastly, we assessed the influence of the DiPRA modules on MR scanning quality. Results: The predicted and measured reflection coefficients (S 11) of the DiPRA module are below −20 dB. The maximum specific absorption rate (SAR) in the area under the antenna was 47% higher than for the antenna without encasing. Compared to the HYPERcollar3D, the MRcollar design incorporates 31% less demineralized water (−2.5 L), improves the predicted TC25 (target volume enclosed by 25% iso-SAR contour) by 4.1% and TC50 by 8.5%, while the target-to-hotspot quotient (THQ) is minimally affected (−1.6%). MR experiments showed that the DiPRA modules do not affect MR transmit/receive performance. Conclusion: Our results suggest that head and neck hyperthermia delivery quality with the MRcollar can be maintained, while facilitating simultaneous noninvasive MR thermometry for treatment monitoring and control.

Temperature monitoring is essential for a controlled application of hyperthermia in the head & neck to counteract the heterogeneous thermoregulation. Magnetic resonance (MR) thermometry can be used to monitor the 3D temperature pattern, so we are developing the world’s first hyperthermia applicator for MR guided treatment of head & neck cancers. To maximize imaging signal-to-noise (SNR) but also allow an independent choice of the radiofrequencies for imaging and heating, our approach is based on integrating heating antenna- and imaging coil-arrays into one device. In this work, we developed and experimentally assessed the dual-function using a 3channel receiver-only coil array designed for a 1.5T MR scanner (64 MHz) integrated into one of the two MRcollar shells containing six antennas operating at 434 MHz. Vector network analyzer measurements showed an average S ii equal to -14dB and S ij equal to -12dB with a 2cm geometric overlap. MR imaging experiments showed an average SNR improvement of +40 dB when comparing the proposed coil to the conventional body coil. Results show the feasibility of the approach, and therefore paves the way for a clinical prototype for testing our dual-function approach in phantoms, volunteers and patients.

MR compatible hyperthermia devices exploit MR thermometry capabilities for non-invasive treatment monitoring. These devices, which have been tested to be MR-safe, can potentially influence the MR image quality. One such device is the Pyrexar BSD-2000 3D/MR applicator. In this study, we quantitatively evaluated the impact of the applicator for different setups on MR imaging by B1 + and signal-to-noise (SNR) measurements. Our results show 30% decrease in the B1 + transmit efficiency and 20% decrease in the SNR. We have found the biggest impact was caused by the device's water bolus. This effect can be overcome by increasing the B1 transmit gain or using a thinner water bolus in the device design.

Clinical effectiveness of hyperthermia treatments, in which tumor tissue is artificially heated to 40–44 °C for 60–90 min, can be hampered by a lack of accurate temperature monitoring. The need for noninvasive temperature monitoring in the head and neck region (H&amp, N) and the potential of MR thermometry prompt us to design an MR compatible hyperthermia applicator: the MRcollar. In this work, we validate the design, numerical model, and MR performance of the MRcollar. The MRcollar antennas have low reflection coefficients (&lt, −15 dB) and the intended low interaction between the individual antenna modules (&lt, −32 dB). A 10 °C increase in 3 min was reached in a muscle-equivalent phantom, such that the specifications from the European Society for Hyperthermic Oncology were easily reached. The MRcollar had a minimal effect on MR image quality and a five-fold improvement in SNR was achieved using the integrated coils of the MRcollar, compared to the body coil. The feasibility of using the MRcollar in an MR environment was shown by a synchronous heating experiment. The match between the predicted SAR and measured SAR using MR thermometry satisfied the gamma criteria [distance-to-agreement = 5 mm, dose-difference = 7%]. All experiments combined show that the MRcollar delivers on the needs for MR—hyperthermia in the H&amp, N and is ready for in vivo investigation.

The potential of MR thermometry (MRT) fostered the development of MRI compatible radiofrequency (RF) hyperthermia devices. Such device integration creates major technological challenges and a crucial point for image quality is the water bolus (WB). The WB is located between the patient body and external sources to both couple electromagnetic energy and to cool the patient skin. However, the WB causes MRT errors and unnecessarily large field of view. In this work, we studied making the WB MRI transparent by an optimal concentration of compounds capable of modifying T 2 * relaxation without an impact on the efficiency of RF heating. Three different T 2 * reducing compounds were investigated, namely CuSO 4 , MnCl 2 , and Fe 3 O 4 . First, electromagnetic properties and T 2 * relaxation rates at 1.5 T were measured. Next, through multi-physics simulations, the predicted effect on the RF-power deposition pattern was evaluated and MRT precision was experimentally assessed. Our results identified 5 mM Fe 3 O 4 solution as optimal since it does not alter the RF-power level needed and improved MRT precision from 0.39 ∘ C to 0.09 ∘ C. MnCl 2 showed a similar MRT improvement, but caused unacceptable RF-power losses. We conclude that adding Fe 3 O 4 has significant potential to improve RF hyperthermia treatment monitoring under MR guidance.

Clinical outcome of hyperthermia depends on the achieved target temperature, therefore target conformal heating is essential. Currently, invasive temperature probe measurements are the gold standard for temperature monitoring, however, they only provide limited sparse data. In contrast, magnetic resonance thermometry (MRT) provides unique capabilities to non-invasively measure the 3D-temperature. This study investigates MRT accuracy for MR-hyperthermia hybrid systems located at five European institutions while heating a centric or eccentric target in anthropomorphic phantoms with pelvic and spine structures. Scatter plots, root mean square error (RMSE) and Bland&ndash, Altman analysis were used to quantify accuracy of MRT compared to high resistance thermistor probe measurements. For all institutions, a linear relation between MRT and thermistor probes measurements was found with R2 (mean &plusmn, standard deviation) of 0.97 &plusmn, 0.03 and 0.97 &plusmn, 0.02, respectively for centric and eccentric heating targets. The RMSE was found to be 0.52 &plusmn, 0.31 &deg, C and 0.30 &plusmn, 0.20 &deg, C, respectively. The Bland-Altman evaluation showed a mean difference of 0.46 &plusmn, C and 0.13 &plusmn, 0.08 &deg, C, respectively. This first multi-institutional evaluation of MR-hyperthermia hybrid systems indicates comparable device performance and good agreement between MRT and thermistor probes measurements. This forms the basis to standardize treatments in multi-institution studies of MR-guided hyperthermia and to elucidate thermal dose-effect relations.

The estimation of electrical properties of living biological tissues is relevant to several medical applications ranging from hyperthermia treatment planning to dosimetry and, more in general, is pivotal for a fundamental understanding of bioclectromagnetic interactions. Non-invasive electromagnetic imaging, either based on the processing of electric fields measured via microwave tomography or magnetic fields acquired in magnetic resonance is suitable to pursue this goal. In this framework, the possibility of imaging without the need of phase information would be extremely relevant, as it would enable simpler and more reliable devices and would avoid limiting assumptions typically used in the literature. With reference to the canonical yet significant 2D case, in this paper we propose an inverse scattering approach for tissue characterization from only-amplitude electromagnetic data, which, by virtue of a unified mathematical framework, is viable for both microwave tomography and magnetic resonance imaging. The key feature of the method is the innovative use of morphological maps derived by other medical imaging modalities as prior spatial information, In particular, these images arc exploited to define a convenient and effective patient-specific representation of the unknowns. The approach is tested against simulated data derived from anatomically realistic scenarios.

In this contribution, an original approach for invivo estimation of electrical properties of biological tissues is presented. Such an estimation represents an essential step in hyperthermia treatment planning, wherein typically magnetic resonance or computerized tomography images are exploited and turned into electric parameters, based on available ex-vivo measured properties, to predict the effects of the treatment. As parameters change from patient to patient and can be quite different from the ex-vivo ones, the proposed approach is based on the solution of an inverse scattering problem, processing backscattered data measured from the patient and conveniently exploiting the morphological information on tissues available from medical images, to overcome the well-known issues arising in the solution of inverse problems.

Clinical studies have shown the benefit of hyperthermia as a strong adjuvant to conventional cancer treatments but a tight control of the administered heating still represents an open challenge. Planning the hyperthermia treatment is the way to deliver a target conformal specific absorption rate (SAR) deposition over the target area while keeping the SAR bounded in normal tissue. This task is even more challenging in case of large and irregularly shaped target volumes. Motivated by this need, the so-called multi-target focusing via constrained power optimization was developed. In the current study, we investigated the effective gain in terms of heating profile of the proposed approach using simulations of 3D clinical patient specific models. Results indicate an average median temperature gain of 0.8°C with respect to standard FOCO.

The estimation of conductivity and permittivity of biological tissues is fundamental in the determination of the specific absorption rate (SAR) and electromagnetic field intensity distribution in hyperthermia treatment planning. In this contribution, an original approach for the in-vivo estimation of these parameters is introduced. The proposed approach is based on the solution of an inverse scattering problem and the innovative use of the morphological map of biological tissue exacting by medical images, obtained by means of magnetic resonance imaging or computed tomography.

The possibility of uniformly shaping the SAR deposition over a target area while avoiding normal tissue to be undesirably heated represents one of the main open challenges in hyperthermia treatment planning. This task is even more challenging when dealing with large targets generally characterized by irregular shapes. Two innovative SAR shaping strategies, aimed at addressing the above-mentioned need, have been recently proposed. These strategies take advantage from the use of more target points and are respectively based on two well-known focusing techniques. In this communication, both the approaches are firstly given under a common mathematical framework and then tested on anatomically and electromagnetically realistic phantoms.

This communication describes the ongoing efforts towards the assessment of microwave imaging as a tool for real-time monitoring of thermal ablation treatments. In particular, the ex-vivo experimental set-up adopted for the validation is described, and the results of a preliminary experiment are shown. Notably, by analyzing pre- and post-ablation treatment data it is possible to recognize the footprint of the interface between the ablated and not-ablated tissue, making it possible to estimate the boundary of the treated area.

In this communication, we present a full-wave numerical study aimed at showing the potential of microwave tomography as a tool to monitor microwave ablation of solid tumors. The goal is to track the changes in dielectric properties of the tissue undergoing the treatment, in order to appraise the evolving dimension and shape of the thermally ablated area surrounding the applicator. Such an in-line monitoring capability would entail a significant improvement in the therapeutic effectiveness of cancer treatments exploiting microwave ablation, both in terms of optimization/personalization of the therapeutic protocol and of reduction of unwanted side effects due to the unwanted increase of temperature in healthy tissues. The numerical study involves a scenario inspired by an existing experimental set-up, already used for the ex-vivo assessment of microwave ablation treatments. Hence, the promising results we have obtained, fully motivate us to progress towards the experimental demonstration of the concept in ex-vivo conditions. © 2017 Euraap.

Microwave thermal ablation is a cancer treatment that exploits local heating caused by a microwave electromagnetic field to induce coagulative necrosis of tumor cells. Recently, such a technique has significantly progressed in the clinical practice. However, its effectiveness would dramatically improve if paired with a noninvasive system for the real-time monitoring of the evolving dimension and shape of the thermally ablated area. In this respect, microwave imaging can be a potential candidate to monitor the overall treatment evolution in a noninvasive way, as it takes direct advantage from the dependence of the electromagnetic properties of biological tissues from temperature. This paper explores such a possibility by presenting a proof of concept validation based on accurate simulated imaging experiments, run with respect to a scenario that mimics an ex vivo experimental setup. In particular, two model-based inversion algorithms are exploited to tackle the imaging task. These methods provide independent results in real-time and their integration improves the quality of the overall tracking of the variations occurring in the target and surrounding regions.