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Three-Dimensional Assessment of MRI-Guided Percutaneous Cryotherapy of Liver Metastases

Stuart G. Silverman1, Maryellen R. M. Sun1, Kemal Tuncali1, Paul R. Morrison1, Eric vanSonnenberg1, Sridhar Shankar1,2, Kelly H. Zou1 and Simon K. Warfield1

1 Department of Radiology, Division of Abdominal Imaging and Intervention, Brigham and Women's Hospital, 75 Francis St., Boston, MA 02115.
2 Department of Radiology, University of Massachusetts, 5 Lake Ave., Worcester, MA 01604.



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  		Fig. 1A. —Segmentation of structures from multiple 2D MR images to generate 3D models for volume calculations and 3D assessment of liver tumor ablations. Postprocedural enhanced axial MR image (T1-weighted fast multiplanar spoiled gradient-echo; TR/TE, 310/1.6; flip angle, 75°; section thickness, 5 mm; field of view, 40 cm) obtained at 48 hr shows teardrop-shaped nonenhancing region of cryonecrosis (arrow). Tumor is seen as hyperintense structure (arrowhead) relative to ablated tissue.

 


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  		Fig. 1B. —Segmentation of structures from multiple 2D MR images to generate 3D models for volume calculations and 3D assessment of liver tumor ablations. Three-dimensional models of structures of interest are shown including tumor (green), liver (brown), and cryonecrosis (blue).

 


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  		Fig. 1C. —Segmentation of structures from multiple 2D MR images to generate 3D models for volume calculations and 3D assessment of liver tumor ablations. Structures outside liver (gallbladder in yellow, colon in purple, and kidney in red) add perspective and provide guidance in planning interventional access.

 


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  		Fig. 2A. —Computer generation of target volume from tumor volume. Schematic of principle is shown in two dimensions; segmented tumor (green) has diameter of DT, which is supplemented by 1-cm ablation margin to establish total target (yellow) with diameter DT+ 2 cm.

 


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  		Fig. 2B. —Computer generation of target volume from tumor volume. Segmented tumor (green) from patient 9 is shown.

 


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  		Fig. 2C. —Computer generation of target volume from tumor volume. Three-dimensional target volume (gray halo) is generated by extending 1 cm in all directions.

 


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  		Fig. 2D. —Computer generation of target volume from tumor volume. Target volume (yellow) is displayed in context of 3D depiction of tumor (green), cryonecrosis (blue), and liver (brown).

 


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  		Fig. 3. —Schematic 2D depiction of range of values for Dice similarity coefficient (DSC), metric used to assess intersection of cryonecrosis and target volumes. A and B show that if two volumes do not intersect, regardless of their relative sizes, DSC is zero. C and D show that for volumes that intersect minimally, whether because of minimal overlap or large differences in size, DSC is low. E and F show that DSC equals 1 if volumes are equal and intersection is complete.

 


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  		Fig. 4. —58-year-old woman with colorectal carcinoma metastatic to liver (patient 1). Cryonecrosis (blue) is shown relative to tumor (green) and target (yellow). Inferior pole of tumor and target were treated, but superior portion was not. Percentage of tumor coverage was 29.8%; percentage of target volume coverage was 24.7%. Undercoverage of target was reflected in low Dice similarity coefficient value (0.27).

 


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  		Fig. 5. —63-year-old man (patient 8) with colorectal carcinoma metastatic to liver. Percentage of tumor coverage is 100%, and percentage of target volume coverage is 93.2%. Cryonecrosis (blue) incorporates some normal liver tissue (brown) as it extends outside target volume (yellow), but Dice similarity coefficient is relatively high (0.71).

 


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  		Fig. 6. —64-year-old man (patient 9) with lung cancer metastatic to liver. Both percentage of tumor coverage and percentage of target (yellow) volume coverage are high (100% and 99.8%, respectively). In contrast to patient 8 shown in Figure 5, involvement of normal liver (brown) by cryonecrosis (blue) is greater and results in relatively low Dice similarity coefficient of 0.56 [8].

 

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