REFERENCELESS MULTI-COIL RECONSTRUCTION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Introduction: Referenceless PRF thermometry is inherently robust to tissue motion because the subtraction of a baseline phase image acquired prior to heating is not necessary. Instead, the background phase is estimated in every individual image by fitting a polynomial to the phase outside the heating region. For this it is necessary that the phase vary slowly without discontinuities. In this project, we demonstrate a coil combination method that determines and eliminates the coil dependent phase offset of multi-coil acquisitions and generates combined images with a smooth background phase that can be used for temperature estimation with the referenceless method. Methods and Discussion: The multi-coil combination and referenceless processing was performed in MatLab. Receiver coil phase offsets from an arbitrarily chosen individual coil in an N coil array were determined using a least-squares solution. Once the differential coil offsets of the individual coils were determined, the offset is removed by multiplying each image with the corresponding complex conjugate of the phase offset. After the correction, the data can be combined into a single complex image. For a combination that minimizes the temperature uncertainty in the resulting temperature maps, the phase can be combined with a weighting by the magnitude squared. The method was demonstrated in phantoms during focused ultrasound heating.