Ioannis Karakitsios

An integrated model-based software for FUS in moving abdominal organs

Abstract Focused ultrasound surgery (FUS) is a non-invasive method for tissue ablation that has the potential for complete and controlled local tumour destruction with minimal side effects. The treatment of abdominal organs such as the liver, however, requires particular technological support in order to enable a safe, efficient and effective treatment. As FUS is applied from outside the patient’s body, suitable imaging methods, such as magnetic resonance imaging or diagnostic ultrasound, are needed to guide and track the procedure. To facilitate an efficient FUS procedure in the liver, the organ motion during breathing and the partial occlusion by the rib cage need to be taken into account in real time, demanding a continuous patient-specific adaptation of the treatment configuration. Modelling the patient’s respiratory motion and combining this with tracking data improves the accuracy of motion predictions. Modelling and simulation of the FUS effects within the body allows the use of treatment planning and has the potential to be used within therapy to increase knowledge about the patient status. This article describes integrated model-based software for patient-specific modelling and prediction for FUS treatments of moving abdominal organs.

Feasibility study of pre-clinical Thiel embalmed human cadaver for MR-guided focused ultrasound of the spine

Abstract Background Magnetic Resonance-guided Focused Ultrasound Surgery (MRgFUS) is a non-invasive treatment option based on high acoustic absorption and minimal thermal conductivity of the bone to destroy nerves and reduce pain. There is lack of a preclinical validation tool with correct human anatomy. This work introduces usage of an ex-vivo Thiel embalmed human tissue model for preclinical verification of MRgFUS on intervertebral discs or bone metastases within the spinal body. Material and methods Thiel embalmed human cadaver was subjected to FUS sonication of the vertebra (with energies 250J, 420J, 600J) and the intervertebral disc (with energies 310J, 610J, 950J) of the lumbar spine for 20s of sonication under MR guidance. Results For the vertebra, maximum temperatures were recorded as 38 °C, 58.3 °C, 69 °C. The intervertebral disc reached maximum temperatures of 23.7 °C, 54 °C, 83 °C. The temperature measurements showed that the spinal canal and adjacent organs were not heated > 0.1 °C. Conclusions A heating pattern that can induce thermal ablation was achieved in the vertebral body and the intervertebral disc. Adjacent structures and nerves were not heated in lethal levels. Thus, the Thiel embalmed human cadaver can be a safe and efficient model for preclinical study of application of MRgFUS on the upper lumbar spine.

Thermometry during MR-guided focused ultrasound in a preclinical model based on Thiel embalmed tissue

Abstract Background: The purpose of this work was to determine the accuracy of Proton Resonance Frequency (PRF) thermometry during MR-guided Focused Ultrasound (MRgFUS) ablation on explanted Thiel embalmed human and animal liver, fresh animal liver, and compared to gel phantom. Material and methods: PRF thermometry during MRgFUS was conducted using a 1.5T MRI system. The phantom and the organs were sonicated with the following energies:300J, 600J, 1000J and 1400J. The temperature increase which was measured using PRF thermometry during sonication was compared to actual temperature rise in the same conditions measured by fibre optic thermocouple. Results: Sonication of fresh animal liver showed temperature differences varying between 0.27°C and 0.40°C, whereas the phantom results showed temperature differences from 0.23°C to 0.40°C. For the Thiel embalmed organs, the temperature difference varied from 1.17 °C to 3.13°C for the ovine liver, and from 1.3°C to 3.10°C for the human liver. Conclusion: The temperature differences measured in the fresh liver were small and similar to those found for the gel phantom. However, the temperature differences calculated for the Thiel embalmed organs were higher compared to the fresh organ. This indicates that the PRF-based temperature calibration of the Focused Ultrasound machine for Thiel embalmed tissue is necessary.

Measurement of proton resonance frequency shift coefficient during MR‐guided focused ultrasound on Thiel embalmed tissue

To estimate the value of proton resonance frequency (PRF) shift coefficient of explanted Thiel embalmed animal and human tissue used as a preclinical model for treatment with MR‐guided focused ultrasound (FUS).

MR real-time tracking of hepatic motion during respiration in a Thiel Soft-fix cadaver

Thiel Soft-fix cadavers represent an alternative to more traditional formaldehyde cadaveric embalmment, preservatives sustain tissue flexibility, colouring, plus integrity therefore, Thiel cadavers simulate anatomically correct models for the purposes of human research, education and training. The purpose of this study was to track hepatic movement during artificial respiration with Magnetic Resonance Imaging (MRI).

Ex vivo ovine liver model simulating respiratory motion and blood perfusion for validating image-guided HIFU systems.

The effect of moving organs and blood perfusion on image guided procedures such as focused ultrasound is challenging therefore we have developed ex vivo ovine liver phantoms to simulate respiratory motion and blood perfusion. The simulator was used to validate ultrasound image-guided HIFU treatment when the target tissue was moving.

Reference-less MR thermometry on pre-clinical thiel human cadaver for liver surgery with MRgFUS

Abstract Purpose: Reference-less MR thermometry can be a promising technique for temperature mapping during liver treatment with Magnetic Resonance-guided Focused Ultrasound (MRgFUS), as it is more robust to breathing motion than Proton Resonance Frequency MR thermometry. However, there is a lack of a pre-clinical model for repeatable testing of reference-less thermometry. The purpose of this work was to verify the explanted Thiel embalmed human liver and whole Thiel embalmed human cadaver for application of a custom made reference-less thermometry algorithm during MRgFUS sonication. Material and methods: Phase maps were generated during sonication as an input to the algorithm. A square Region-of-Interest (ROI) was designed around the heated area. The ROI was interpolated using a two-dimensional polynomial to the surrounding phase map to calculate the background phase. Results: Using the phase information from the images, the temperature rise was measured. Validation of the methodology showed accordance of temperatures with actual temperatures. Conclusions: The explanted liver and the whole cadaver constitute a promising and feasible model to study reference-less techniques for thermometry during MRgFUS, before clinical trials.

Acoustic characterization of Thiel liver for magnetic resonance-guided focused ultrasound treatment

Abstract Background: The purpose of this work was to measure the essential acoustic parameters, i.e., acoustic impedance, reflection coefficient, attenuation coefficient, of Thiel embalmed human and animal liver. The Thiel embalmed tissue can be a promising, pre-clinical model to study liver treatment with Magnetic Resonance-guided Focused Ultrasound (MRgFUS). Material and methods: Using a single-element transducer and the contact pulse-echo method, the acoustic parameters, i.e., acoustic impedance, reflection coefficient and attenuation coefficient of Thiel embalmed human and animal liver were measured. Results: The Thiel embalmed livers had higher impedance, similar reflection and lower attenuation compared to the fresh tissue. Conclusions: Embalming liver with Thiel fluid affects its acoustic properties. During MRgFUS sonication of a Thiel organ, more focused ultrasound (FUS) will be backscattered by the organ, and higher acoustic powers are required to reach coagulation levels (temperatures >56 °C).

Thiel soft embalmed Porcine Kidney Perfusion Model for focused ultrasound therapy

Thiel soft embalmed porcine kidneys have been used to study the effect of artificial blood flow on focused ultrasound (FUS) therapy. A significant temperature drop is observed when a perfusion is established within the porcine kidneys, compared with the no-flow condition FUS leads to a 2 ~ 4 °C higher temperature rising. The influence of Thiel soft embalmed Porcine Kidney Perfusion Model for Focused Ultrasound Therapy e effect from blood flow must be considered.

Ultrasound tracked motion compensated focused ultrasound system evaluated on ex vivo ovine livers

The application of FUS in abdominal organs such as the liver or the kidneys is impeded by a number of complications. One of the most challenging is organ motion due to breathing. To achieve ablation in a target within a moving organ the FUS system has to be steered to focus on the same anatomical position. We present a prototypical system that tracks the motion of an ex vivo ovine liver via diagnostic ultrasound (US) and adjusts the focal spot to a fixed anatomical position.