CONSISTENCY OF SIGNAL INTENSITY AND R2* IN FROZEN PORCINE KIDNEY AND LIVER

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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: MR-guided cryoablation is a promising method for the minimally invasive therapy of prostate, liver, and kidney tumors. MRI beautifully depicts the iceball edge as the frozen tissue has decreased signal intensity. Although it is known that the relaxation rate R2* increases in frozen tissue, it is not known how consistent these MR parameters are between tissue types. The purpose of this work was to quantify and compare the MR parameters of freshly excised ex vivo frozen tissue of two different types, kidney and liver. Methods and Discussion: Three liver and four kidney tissue samples were imaged in a Signa SP 0.5T interventional scanner. A receive only endorectal coil was placed adjacent to the tissue samples of dimensions 10x10x25mm which were placed on a plexi-glass plate between two 12x12x65mm copper blocks 25mm apart. A cryo probe was inserted 35mm into each copper block. Four fiber-optic temperature were placed into the tissue sample 5 mm apart. A non slice-selective pulse sequence was used for imaging (TR = 200ms, FOV = 200mm, flip angle = 60¿ and BW of 31.25 kHz). Images were acquired at echo times of 210us, 310us, and 610us. Imaging was repeated as the tissue was cooled from room temperature to -40¿C in 5¿C increments. Signal Intensity (SI) and R2* were calculated from a region of interest surrounding each temperature sensor. SI data from the four kidney experiments were grouped together as well as data for the three liver experiments. SI was fit to separate curves between 0¿C and -4¿C (linear fit) and below -6¿C (exponential fit). For R2* data, a linear fit was used. The difference between the slopes is within one standard deviation. However the intersects for two curves had a greater variability. Consistency of SI and R2* values was also studied within tissue types. The R2*(T) linear fits for three liver experiments and for four kidney experiments had little variability in slope, but considerable uncertainty in intersect values between the subjects. Grant #: RO1 CA09061