A system, comprising: a display ; and a processor , configured: to modify an image slice , by: identifying portions of the image slice that correspond to anatomical cavities ; and filling each identified portion with a representation of a wall of the corresponding anatomical cavity, thus giving each anatomical cavity a three-dimensional appearance; the processor being further configured to perform the steps of overlaying an icon that represents an intrabody tool on a portion of the modified image slice that corresponds to a location of the intrabody tool within the anatomical cavity; and overlaying a marker on a portion of the representation of the wall that corresponds to a location at which the intrabody tool would meet the wall, were the intrabody tool to continue moving toward the wall in a direction in which the intrabody tool is pointing, and to display the modified image slice and the overlaid icon and marker on the display . a display ; and a processor , configured: to modify an image slice , by: identifying portions of the image slice that correspond to anatomical cavities ; and filling each identified portion with a representation of a wall of the corresponding anatomical cavity, thus giving each anatomical cavity a three-dimensional appearance; the processor being further configured to perform the steps of overlaying an icon that represents an intrabody tool on a portion of the modified image slice that corresponds to a location of the intrabody tool within the anatomical cavity; and overlaying a marker on a portion of the representation of the wall that corresponds to a location at which the intrabody tool would meet the wall, were the intrabody tool to continue moving toward the wall in a direction in which the intrabody tool is pointing, and to display the modified image slice and the overlaid icon and marker on the display . to modify an image slice , by: identifying portions of the image slice that correspond to anatomical cavities ; and filling each identified portion with a representation of a wall of the corresponding anatomical cavity, thus giving each anatomical cavity a three-dimensional appearance; the processor being further configured to perform the steps of overlaying an icon that represents an intrabody tool on a portion of the modified image slice that corresponds to a location of the intrabody tool within the anatomical cavity; and overlaying a marker on a portion of the representation of the wall that corresponds to a location at which the intrabody tool would meet the wall, were the intrabody tool to continue moving toward the wall in a direction in which the intrabody tool is pointing, and identifying portions of the image slice that correspond to anatomical cavities ; and filling each identified portion with a representation of a wall of the corresponding anatomical cavity, thus giving each anatomical cavity a three-dimensional appearance; the processor being further configured to perform the steps of overlaying an icon that represents an intrabody tool on a portion of the modified image slice that corresponds to a location of the intrabody tool within the anatomical cavity; and overlaying a marker on a portion of the representation of the wall that corresponds to a location at which the intrabody tool would meet the wall, were the intrabody tool to continue moving toward the wall in a direction in which the intrabody tool is pointing, and to display the modified image slice and the overlaid icon and marker on the display . <EOS>