MR-sequence development involves the creation and refinement of specific imaging techniques or sequences used in Magnetic Resonance Imaging (MRI) to generate different types of image contrasts and provide valuable diagnostic information.


Our research group is at the forefront of developing advanced 3D thermometry techniques within the field of Magnetic Resonance Imaging (MRI). The cornerstone of our work lies in the creation of custom sequences that calculate temperature information from MR parameters. This innovative approach leverages the principle that temperature changes induce a shift in the frequency of protons within water-rich tissues. By understanding and harnessing this phenomenon, we can precisely map temperature variations in the body, which is pivotal for effective treatment and monitoring. 

One of our significant breakthroughs is the development of a ‘stack of spirals’ sequence [1]. This technique stands out for its efficiency in data collection, enabling simultaneous imaging and temperature measurement in real-time, even in patients who are breathing. This aspect is crucial, as it allows for continuous monitoring and adjustment during procedures like microwave ablation, ensuring both safety and efficacy. 

Currently, there is no clinically established real-time 3D thermometry sequence available, primarily due to challenges such as the impact of respiratory motion and inefficient data sampling. Our approach addresses these challenges head-on. By optimizing the data collection process, our ‘stack of spirals’ sequence minimizes the effects of respiratory motion, thereby enabling accurate and consistent temperature mapping. 

The potential impact of this technology in a clinical setting is substantial. By providing real-time, accurate temperature mapping, our sequences can revolutionize the way treatments are monitored and adjusted, leading to better outcomes and enhanced patient safety. This advancement marks a significant step forward in the field of medical imaging and opens new avenues for treatment and research in thermal therapies.


MR-Thermometry is only possible because there are multiple MR-related tissue parameters that are temperature dependent. Examples are the proton resonance frequency (PRF) or the T1 relaxation time. In practice, mostly the PRF is used for MR-Thermometry. However, the PRF shift with temperature only occurs in aqueous tissue, making it impossible to monitor temperature changes in adipose tissue. Another issue is that PRF-based methods are highly sensitive to susceptibility artifacts which can severely reduce the quality of the thermometry. It might therefore be beneficial to have information on other parameters. MR-Fingerprinting (MRF) is a novel technique which can be used to quantize multiple parameters at the same time [2]. It could therefore provide more accurate temperature maps based on a combination of more than just one tissue parameter.


In the field of medical imaging and thermometry, our team is pioneering a novel approach by combining two distinct thermometry methods: Xenon (Xe) thermometry and Proton Resonance Frequency (PRF) thermometry. This innovative amalgamation aims to capitalize on the unique strengths of each method to enhance overall temperature measurement accuracy. 

Xenon thermometry is known for its ability to measure absolute temperatures [3]. This method is highly precise and offers the distinct advantage of providing actual temperature values, which is crucial in various clinical settings. On the other hand, PRF thermometry excels in measuring relative temperature changes. While it does not provide absolute temperature readings, it is highly sensitive to even minute temperature variations within the body. 

By integrating these two techniques into 3D-Xe-PRF-Thermometry, we are able to harness the absolute temperature measurement capability of Xe thermometry and the sensitivity to temperature changes of PRF thermometry. This hybrid approach not only enhances the accuracy of temperature readings but also provides a comprehensive view of thermal changes during medical procedures. 

Shielding the Microwave Generator

In the realm of real-time 3D thermometry, particularly during microwave ablation procedures, one significant challenge has been the electromagnetic interference (EMI) from the microwave generator. This interference couples with the MRI scanner, resulting in images that are marred by noise, making accurate and real-time 3D thermometry a complex task. The noise can significantly impede the clarity of images, thus affecting the precision and effectiveness of the treatment monitoring. 

Addressing this critical issue, our research group has successfully implemented shielding measures for the microwave generator [4][5]. These measures are meticulously designed to mitigate EMI, ensuring that the noise in the MRI images is substantially reduced. By doing so, we have been able to maintain the integrity of the imaging process, allowing for clear and accurate real-time 3D thermometry even during the Microwave Ablation.

The implementation of these shielding techniques marks a pivotal advancement in the field. It enables clinicians to perform microwave ablations with greater confidence in the accuracy of the real-time 3D thermometry readings. This development not only enhances the safety and effectiveness of the procedure but also paves the way for broader applications of this technology in various clinical scenarios. The ability to conduct noise-free real-time imaging during such procedures is a testament to our group’s commitment to innovation and excellence in medical technology.


[1] Horstmann et al. 3D MR Thermometry Sequences for Abdominal Microwave Ablation Monitoring on Phantom Simulating Breathing Motion. ISMRM Proceedings 2023.
[2] Gutt et al. An MRF approach for Simultaneous T1- and PRFS-based 3D MR-Thermometry. ISMRM Proceedings 2023.
[3] Kern et al. Absolute thermometry using hyperpolarized 129Xe free-induction decay and spin-echo chemical-shift imaging in rats. Magn Reson Med 89 (2023): 54-63.
[4] Schröer et al. Addressing Electromagnetic Interference during MR-guided Ablations. IGIC Proceedings 2023.
[5] Löning et al. Reduced Electromagnetic Interference of a microwave ablation system by an external shielding enclosure. IGIC Proceedings 2021.