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CT-monitored Percutaneous Cryoablation in a Pig Liver Model: Pilot Study¹

¹ From the Departments of Radiology (F.T.L., S.G.C., J.E.K.), Pathology (T.F.W.), and Surgery (D.M.M.), University of Wisconsin, E3/311 CSC, 600 Highland Ave, Madison, WI 53792; and the Department of Radiology, Wayne State University, Detroit, Mich (P.J.L.). Received May 7, 1998; revision requested July 7; revision received August 7; accepted November 6. F.T.L., P.J.L., and D.M.M. supported in part by Endocare, Irvine, Calif. F.T.L. supported by the RSNA Research and Education Foundation as a GE/RSNA Scholar. Address reprint requests to F.T.L. (e-mail: ftlee@facstaff.wisc.edu).

View larger version (164K): [in a new window]   Figure 1a. (a–e) CT images demonstrate percutaneous cryoablation procedure. (a) Guide wires (arrows) are placed on either side of an agar-filled balloon that functions as a target. The small metal balloon valve is a bright spot (arrowhead) surrounded by the lower-attenuation agar. (b) Cryoablation at 2 minutes into the freezing process. The guide wires have been replaced by cryoprobes (straight solid arrows) by using the Seldinger technique. Note the markedly hypoattenuating appearance of the ice balls (curved arrows) with smooth, clearly demarcated borders. Cryoprobes exhibit some beam-hardening artifact, but not enough to interfere with the monitoring of tissue destruction. The target balloon is not yet covered by ice because of the cleft between the two ice balls (open arrow). Ascitic fluid (*) surrounding the liver is saline solution from intraabdominal irrigation intended to insulate the diaphragm and the thoracic structures from potential freezing damage. (c) Image obtained at 5 minutes depicts the cleft (arrow) in the progressing cryolesion. (d) Image obtained at 20 minutes shows that ice has filled the cleft (arrow) and has covered the lesion and an ablative margin. (e) Postprocedure contrast material–enhanced image demonstrates the ablated zone of the liver. Note the high-attenuation cellulose packing material in the probe tracts (arrowheads). The portion of the liver peripheral to the cryolesion has been temporarily devascularized (curved arrows) by the ice ball and does not enhance with contrast material. The agar lesion (straight arrow) is still evident within the cryolesion. (f) Gross axial section corresponding to the CT images. The cryolesion (straight arrows) is ovoid with a smooth, clearly demarcated border and appears deep red. The targeted agar lesion (arrowhead) and an ablative margin have been completely encompassed. The cryolesion is bordered by a thin white rim of tissue (curved arrows) corresponding to infiltration by leukocytes and is surrounded by normal-appearing parenchyma.

View larger version (182K): [in a new window]   Figure 1b. (a–e) CT images demonstrate percutaneous cryoablation procedure. (a) Guide wires (arrows) are placed on either side of an agar-filled balloon that functions as a target. The small metal balloon valve is a bright spot (arrowhead) surrounded by the lower-attenuation agar. (b) Cryoablation at 2 minutes into the freezing process. The guide wires have been replaced by cryoprobes (straight solid arrows) by using the Seldinger technique. Note the markedly hypoattenuating appearance of the ice balls (curved arrows) with smooth, clearly demarcated borders. Cryoprobes exhibit some beam-hardening artifact, but not enough to interfere with the monitoring of tissue destruction. The target balloon is not yet covered by ice because of the cleft between the two ice balls (open arrow). Ascitic fluid (*) surrounding the liver is saline solution from intraabdominal irrigation intended to insulate the diaphragm and the thoracic structures from potential freezing damage. (c) Image obtained at 5 minutes depicts the cleft (arrow) in the progressing cryolesion. (d) Image obtained at 20 minutes shows that ice has filled the cleft (arrow) and has covered the lesion and an ablative margin. (e) Postprocedure contrast material–enhanced image demonstrates the ablated zone of the liver. Note the high-attenuation cellulose packing material in the probe tracts (arrowheads). The portion of the liver peripheral to the cryolesion has been temporarily devascularized (curved arrows) by the ice ball and does not enhance with contrast material. The agar lesion (straight arrow) is still evident within the cryolesion. (f) Gross axial section corresponding to the CT images. The cryolesion (straight arrows) is ovoid with a smooth, clearly demarcated border and appears deep red. The targeted agar lesion (arrowhead) and an ablative margin have been completely encompassed. The cryolesion is bordered by a thin white rim of tissue (curved arrows) corresponding to infiltration by leukocytes and is surrounded by normal-appearing parenchyma.

View larger version (181K): [in a new window]   Figure 1c. (a–e) CT images demonstrate percutaneous cryoablation procedure. (a) Guide wires (arrows) are placed on either side of an agar-filled balloon that functions as a target. The small metal balloon valve is a bright spot (arrowhead) surrounded by the lower-attenuation agar. (b) Cryoablation at 2 minutes into the freezing process. The guide wires have been replaced by cryoprobes (straight solid arrows) by using the Seldinger technique. Note the markedly hypoattenuating appearance of the ice balls (curved arrows) with smooth, clearly demarcated borders. Cryoprobes exhibit some beam-hardening artifact, but not enough to interfere with the monitoring of tissue destruction. The target balloon is not yet covered by ice because of the cleft between the two ice balls (open arrow). Ascitic fluid (*) surrounding the liver is saline solution from intraabdominal irrigation intended to insulate the diaphragm and the thoracic structures from potential freezing damage. (c) Image obtained at 5 minutes depicts the cleft (arrow) in the progressing cryolesion. (d) Image obtained at 20 minutes shows that ice has filled the cleft (arrow) and has covered the lesion and an ablative margin. (e) Postprocedure contrast material–enhanced image demonstrates the ablated zone of the liver. Note the high-attenuation cellulose packing material in the probe tracts (arrowheads). The portion of the liver peripheral to the cryolesion has been temporarily devascularized (curved arrows) by the ice ball and does not enhance with contrast material. The agar lesion (straight arrow) is still evident within the cryolesion. (f) Gross axial section corresponding to the CT images. The cryolesion (straight arrows) is ovoid with a smooth, clearly demarcated border and appears deep red. The targeted agar lesion (arrowhead) and an ablative margin have been completely encompassed. The cryolesion is bordered by a thin white rim of tissue (curved arrows) corresponding to infiltration by leukocytes and is surrounded by normal-appearing parenchyma.

View larger version (177K): [in a new window]   Figure 1d. (a–e) CT images demonstrate percutaneous cryoablation procedure. (a) Guide wires (arrows) are placed on either side of an agar-filled balloon that functions as a target. The small metal balloon valve is a bright spot (arrowhead) surrounded by the lower-attenuation agar. (b) Cryoablation at 2 minutes into the freezing process. The guide wires have been replaced by cryoprobes (straight solid arrows) by using the Seldinger technique. Note the markedly hypoattenuating appearance of the ice balls (curved arrows) with smooth, clearly demarcated borders. Cryoprobes exhibit some beam-hardening artifact, but not enough to interfere with the monitoring of tissue destruction. The target balloon is not yet covered by ice because of the cleft between the two ice balls (open arrow). Ascitic fluid (*) surrounding the liver is saline solution from intraabdominal irrigation intended to insulate the diaphragm and the thoracic structures from potential freezing damage. (c) Image obtained at 5 minutes depicts the cleft (arrow) in the progressing cryolesion. (d) Image obtained at 20 minutes shows that ice has filled the cleft (arrow) and has covered the lesion and an ablative margin. (e) Postprocedure contrast material–enhanced image demonstrates the ablated zone of the liver. Note the high-attenuation cellulose packing material in the probe tracts (arrowheads). The portion of the liver peripheral to the cryolesion has been temporarily devascularized (curved arrows) by the ice ball and does not enhance with contrast material. The agar lesion (straight arrow) is still evident within the cryolesion. (f) Gross axial section corresponding to the CT images. The cryolesion (straight arrows) is ovoid with a smooth, clearly demarcated border and appears deep red. The targeted agar lesion (arrowhead) and an ablative margin have been completely encompassed. The cryolesion is bordered by a thin white rim of tissue (curved arrows) corresponding to infiltration by leukocytes and is surrounded by normal-appearing parenchyma.

View larger version (161K): [in a new window]   Figure 1e. (a–e) CT images demonstrate percutaneous cryoablation procedure. (a) Guide wires (arrows) are placed on either side of an agar-filled balloon that functions as a target. The small metal balloon valve is a bright spot (arrowhead) surrounded by the lower-attenuation agar. (b) Cryoablation at 2 minutes into the freezing process. The guide wires have been replaced by cryoprobes (straight solid arrows) by using the Seldinger technique. Note the markedly hypoattenuating appearance of the ice balls (curved arrows) with smooth, clearly demarcated borders. Cryoprobes exhibit some beam-hardening artifact, but not enough to interfere with the monitoring of tissue destruction. The target balloon is not yet covered by ice because of the cleft between the two ice balls (open arrow). Ascitic fluid (*) surrounding the liver is saline solution from intraabdominal irrigation intended to insulate the diaphragm and the thoracic structures from potential freezing damage. (c) Image obtained at 5 minutes depicts the cleft (arrow) in the progressing cryolesion. (d) Image obtained at 20 minutes shows that ice has filled the cleft (arrow) and has covered the lesion and an ablative margin. (e) Postprocedure contrast material–enhanced image demonstrates the ablated zone of the liver. Note the high-attenuation cellulose packing material in the probe tracts (arrowheads). The portion of the liver peripheral to the cryolesion has been temporarily devascularized (curved arrows) by the ice ball and does not enhance with contrast material. The agar lesion (straight arrow) is still evident within the cryolesion. (f) Gross axial section corresponding to the CT images. The cryolesion (straight arrows) is ovoid with a smooth, clearly demarcated border and appears deep red. The targeted agar lesion (arrowhead) and an ablative margin have been completely encompassed. The cryolesion is bordered by a thin white rim of tissue (curved arrows) corresponding to infiltration by leukocytes and is surrounded by normal-appearing parenchyma.

View larger version (77K): [in a new window]   Figure 1f. (a–e) CT images demonstrate percutaneous cryoablation procedure. (a) Guide wires (arrows) are placed on either side of an agar-filled balloon that functions as a target. The small metal balloon valve is a bright spot (arrowhead) surrounded by the lower-attenuation agar. (b) Cryoablation at 2 minutes into the freezing process. The guide wires have been replaced by cryoprobes (straight solid arrows) by using the Seldinger technique. Note the markedly hypoattenuating appearance of the ice balls (curved arrows) with smooth, clearly demarcated borders. Cryoprobes exhibit some beam-hardening artifact, but not enough to interfere with the monitoring of tissue destruction. The target balloon is not yet covered by ice because of the cleft between the two ice balls (open arrow). Ascitic fluid (*) surrounding the liver is saline solution from intraabdominal irrigation intended to insulate the diaphragm and the thoracic structures from potential freezing damage. (c) Image obtained at 5 minutes depicts the cleft (arrow) in the progressing cryolesion. (d) Image obtained at 20 minutes shows that ice has filled the cleft (arrow) and has covered the lesion and an ablative margin. (e) Postprocedure contrast material–enhanced image demonstrates the ablated zone of the liver. Note the high-attenuation cellulose packing material in the probe tracts (arrowheads). The portion of the liver peripheral to the cryolesion has been temporarily devascularized (curved arrows) by the ice ball and does not enhance with contrast material. The agar lesion (straight arrow) is still evident within the cryolesion. (f) Gross axial section corresponding to the CT images. The cryolesion (straight arrows) is ovoid with a smooth, clearly demarcated border and appears deep red. The targeted agar lesion (arrowhead) and an ablative margin have been completely encompassed. The cryolesion is bordered by a thin white rim of tissue (curved arrows) corresponding to infiltration by leukocytes and is surrounded by normal-appearing parenchyma.

View larger version (176K): [in a new window]   Figure 2a. (a) Positive margin identified at CT. CT image shows the target balloon (arrowhead) clearly is not covered by the small hypoattenuating cryolesion (arrows). In this case, failure of the anterior probe because of overuse of single-use probes in our animal laboratory resulted in an ice ball of insufficient size. Because of time constraints, a new probe was not placed. (b) Pathologic examination of the corresponding section confirms the positive margin. Area of frozen liver (straight arrows) is not large enough to encompass the anterior margin of the balloon (arrowhead). Note the invagination of the ice ball by a patent vessel (curved arrow). (Scale is in centimeters. Image is oriented to allow correlation to a, irrespective of ruler orientation.)

View larger version (86K): [in a new window]   Figure 2b. (a) Positive margin identified at CT. CT image shows the target balloon (arrowhead) clearly is not covered by the small hypoattenuating cryolesion (arrows). In this case, failure of the anterior probe because of overuse of single-use probes in our animal laboratory resulted in an ice ball of insufficient size. Because of time constraints, a new probe was not placed. (b) Pathologic examination of the corresponding section confirms the positive margin. Area of frozen liver (straight arrows) is not large enough to encompass the anterior margin of the balloon (arrowhead). Note the invagination of the ice ball by a patent vessel (curved arrow). (Scale is in centimeters. Image is oriented to allow correlation to a, irrespective of ruler orientation.)

View larger version (149K): [in a new window]   Figure 3. Histologic view of cryolesion border, from left to right: normal liver (L), transition zone between normal liver and cryoablated liver (T), and cryolesion (C). The normal liver (L) contains cells with healthy nuclei and readily identifiable lobules. At the outer edge of the cryolesion transition zone (T) are calcified, necrotic hepatocytes (arrows). Inner border of the transition zone (T) contains degenerating polymorphonuclear leukocytes (arrowheads). The transition zone defined by these two lines corresponds to the thin white rim at gross inspection. Within the cryolesion (C), tissue demonstrates complete homogeneous necrosis corresponding to the area of deep red hemorrhage seen at gross inspection. Individual cellular details are ablated, and no nuclei are present. (Hematoxylin-eosin stain; original magnification, x20.)