title: Temperature mapping of frozen tissue using eddy current compensated half excitation RF pulses.
abstract: Cryosurgery has been shown to be an effective therapy for prostate cancer. Temperature monitoring throughout the cryosurgical iceball could dramatically improve efficacy, since end temperatures of at least -40 degrees C are required. The results of this study indicate that MR thermometry based on tissue R(*)(2) has the potential to provide this information. Frozen tissue appears as a complete signal void on conventional MRI. Ultrashort echo times (TEs), achievable with half pulse excitation and a short spiral readout, allow frozen tissue to be imaged and MR characteristics to be measured. However, half pulse excitation is highly sensitive to eddy current distortions of the slice-select gradient. In this work, the effects of eddy currents on the half pulse technique are characterized and methods to overcome these effects are developed. The methods include: 1) eddy current compensated slice-select gradients, and 2) a correction for the phase shift between the first and second half excitations at the center of the slice. The effectiveness of these methods is demonstrated in R(*)(2) maps calculated within the frozen region during cryoablation.
authors.affiliation: Department of Radiology, Stanford University, Stanford, California 94305, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Wansapura
authors.forename: B L
authors.initials: BL
authors.lastname: Daniel
authors.forename: J
authors.initials: J
authors.lastname: Pauly
authors.forename: K
authors.initials: K
authors.lastname: Butts
mesh_terms: D000818:Animals; D002417:Cattle; D003452:Cryosurgery; D006801:Humans; D008099:Liver / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods*