Hybrid referenceless and multibaseline subtraction MR thermometry for monitoring thermal therapies in moving organs

Abstract

Purpose: Magnetic resonance thermometry using the proton resonance frequency ͑PRF͒ shift is a promising technique for guiding thermal ablation. For temperature monitoring in moving organs, such as the liver and the heart, problems with motion must be addressed. Multi-baseline subtraction techniques have been proposed, which use a library of baseline images covering the respiratory and cardiac cycle. However, main field shifts due to lung and diaphragm motion can cause large inaccuracies in multi-baseline subtraction. Referenceless thermometry methods based on polynomial phase regression are immune to motion and susceptibility shifts. While referenceless methods can accurately estimate temperature within the organ, in general, the background phase at organ/ tissue interfaces requires large polynomial orders to fit, leading to increased danger that the heated region itself will be fitted by the polynomial and thermal dose will be underestimated. In this paper, a hybrid method for PRF thermometry in moving organs is presented that combines the strengths of referenceless and multi-baseline thermometry. Methods: The hybrid image model assumes that three sources contribute to image phase during thermal treatment: Background anatomical phase, spatially smooth phase deviations, and focal, heat-induced phase shifts. The new model and temperature estimation algorithm were tested in the heart and liver of normal volunteers, in a moving phantom HIFU heating experiment, and in numerical simulations of thermal ablation. The results were compared to multi-baseline and referenceless methods alone. Results: The hybrid method allows for in vivo temperature estimation in the liver and the heart with lower temperature uncertainty compared to multi-baseline and referenceless methods. The moving phantom HIFU experiment showed that the method accurately estimates temperature during motion in the presence of smooth main field shifts. Numerical simulations illustrated the method's sensitivity to algorithm parameters and hot spot features. Conclusions: This new hybrid method for MR thermometry in moving organs combines the strengths of both multi-baseline subtraction and referenceless thermometry and overcomes their fundamental weaknesses.

Magnetic resonance thermometry: Methodology, pitfalls and practical solutions

“…Any intra-scan motion leading to misregistration with the reference phase image results in temperature errors. These errors might be caused by respiratory, cardiac, peristaltic or bulk motion with standard deviations of >±10°C even without any application of heat (25,73). Structural changes of the treatment area due to tissue coagulation during an ablation procedure (40) This library is used to link the phase measured during thermal therapy to the correct reference image by means of an acquired navigator echo (22), non-similarity coefficients (77) or intercorrelation coefficients (78,79).…”

“…Since the advent of MR thermometry (17,18), the first decade of development culminated in techniques allowing for qualitative temperature assessment in thermal therapies (19)(20)(21). The second decade of development advanced the capabilities of MR thermometry towards more robust and reliable in vivo applications (22)(23)(24)(25). The future target of MR thermometry developments is clearly formed around novel methodology and hardware that supports accurate absolute temperature readings in vivo with the current developments already pushing into this direction (26)(27)(28)(29)(30)(31).…”

Motion Correction Techniques for MR-Guided HIFU Ablation of Abdominal Organs

“…35,36 A discussion about the inherent advantages and drawback of these methods can be found in Ref. [35].…”

MRI use for atrial tissue characterization in arrhythmias and for EP procedure guidance

“…Whereas this method is widely used in other body regions to obtain high spatial-resolution temperature maps, its sensitivity to motion is large, due to its dependence on small changes in the magnetic field, so its use in the heart may be difficult, although methods have been proposed for resolving these issues 60 . Success of the PRS method in predicting the extent of RF ablation was demonstrated in the left ventricle of canine models 61 , with excellent correlation to LGE and histology results.…”