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Among many methods in tumor treatment, ultrasound hyperthermia is characterized by non-invasiveness, and it has been proven very effective for clinical treatment. But the problem of monitoring temperature limits its development. MRI-based temperature mapping techniques are safe compared with invasive methods and have been applied to detect temperature changes for a variety of applications. Among these techniques, the proton resonance frequency (PRF) method is relatively advanced. With a temperature measuring experiment and experiment conducted on tumors inside rabbit legs, the effectiveness of PRF method has been proved. This paper is to introduce an MRI guided ultrasound superficial tumor hyperthermia instrument based on PRF method.

Proton resonance frequency (PRF) change is used to measure tissue heating, but also distorts the image and causes geometric distortions in temperature estimates in the same manner as other chemical shift distortions if left uncompensated. We propose an algorithm that produces PRF temperature maps free of these distortions by fitting a signal model directly to acquired k-space data that accounts for PRF-induced phase both up to and during the readout. We also introduce a faster method compatible with Cartesian data that corrects distortions from image-domain temperature maps. Gel heating experiments show the proposed CS compensation algorithms correct magnitude image artifacts and hotspot distortions. Without CS compensation, thermal dose values are overestimated in spiral data, and are spatially offset in 2DFT and EPI data. Compensating for heat-induced CS distortions improves the accuracy of temperature change and thermal dose measurements, and can have a significant positive impact on clinical and resea...

Proton resonance frequency shift (PRFS)‐based MR thermometry is hampered by temporal field changes. Temporal changes in the susceptibility distribution lead to field changes and are therefore a possible source of errors. The susceptibility of fat, χfat, is temperature dependent, in the same order of magnitude as the temperature dependence of the chemical shift of water (0.01 ppm/° C). PRFS‐based temperature measurements may therefore be corrupted by non‐local field effects due to temperature induced susceptibility changes in fatty tissue. We performed simulations to quantify the influence of dχfat/dT on PRFS‐based MR temperature maps during thermal interventions in the breast. Susceptibility distributions were calculated for a 3D breast model without and with a stationary Gaussian temperature distribution and a maximum temperature of 57° C. Subsequently, the magnetic field was calculated in Fourier‐domain from these susceptibility distributions. Changes in the magnetic field distribution were quantified b...

A new rapid application development platform has been used to develop a system for MRI guided HIFU therapies with real‐time automatic feedback control and visualizations to monitor treatment progression. As the treatment dose is being administered to the patient, the MRI system calculates the Proton Resonance Frequency (PRF) based temperature measurements and sends them to our application over a TCP/IP network. The current thermal dose distribution and the next desired SAR pattern are immediately calculated. As the next dose is administered to the patient, the application applies a 1D color map to visualize thermal dose and a 2D color map to visualize temperature and SAR. The user is able to move 3D planes through the visualizations during the treatment in order to monitor treatment progression.

Successful HIFU surgery demands accurate and reliable temperature monitoring. Heating affects acoustic properties of biological tissues changing the acoustic field and consequent heat deposition. As a result, HIFU thermal lesions grow asymmetrically from the focus toward the transducer and perpendicularly to the beam axis. If the growth process is not monitored, the healthy tissues located on the beam path can be damaged. We propose an improved approach to MRI temperature mapping designed for the real‐time guidance of HIFU surgery, which is based on the acquisition of images along the HIFU beam and allows monitoring and analyzing heat deposition and distribution patterns. Our method visualizes the heat deposition site and shows its evolution during the surgery. In‐vitro HIFU experiments have been performed under real‐time MRI temperature monitoring using the Proton Resonance Frequency Shift method. A set of mathematical operations has been applied to MRI temperature maps, which revealed the HIFU thermal focus (which not always coincides with the geometrical focus) as well as the focus’ shape, size and displacements during sonications. The operations also visualized the HIFU beam waist as well as the hot area borders and main heat transfer directions. Our approach provides information for on‐line prevention of undesirable heat deposition resulting from intra‐operative changes of tissue acoustic properties. Since making small sharp HIFU lesions demands the usage of short high‐power sonications, predicting the thermal lesion growth resulting from the next sonication becomes highly desirable. Our method has a potential to supply the information necessary for such predictions, which can increase the safety and improving the clinical outcome of the HIFU surgery.

Proton resonance frequency shift based temperature mapping in the breast is hindered by local magnetic field inhomogeneities. We quantified field disturbances caused by regular respiration, maximum capacity respiration and cardiac motion at 3T and found disturbances of 0.2, 0.3 and 0.02 ppm respectively.

Referenceless proton resonance frequency (PRF) shift thermometry provides a means to measure temperature changes during minimally invasive thermotherapy that is inherently robust to motion and tissue displacement. However, if the referenceless method is used to determine temperature changes during prostate ablation, phase gaps between water and fat in image regions used to determine the background phase can confound the phase estimation. We demonstrate an extension to referenceless thermometry which eliminates this problem by allowing background phase estimation in the presence of phase discontinuities between aqueous and fatty tissue. In this method, images are acquired with a multi‐echo sequence and binary water and fat maps are generated from a Dixon reconstruction. For the background phase estimation, water and fat regions are treated separately and the phase offset between the two tissue types is determined. The method is demonstrated during in vivo thermal ablation of canine prostate.

The purpose of this work is to demonstrate how temperature can be derived from MRE data. A 1.5% agarose phantom was heated slowly during this temperature trial. The temperature was measured using a fluorescent thermometer while MRE data were acquired. The phase average from the MRE acquisition was used to calculate the phase shift induced by the proton resonance frequency shift (PRF shift) associated with the temperature change. Our data correlate well with the temperature change recorded by thermometer.