Convert it with imagemagick to format XnView can read.
I can be difficult to preserve the 16 bit depth however.
You will have to find a suitable format that can represent the depth and can be exported
by imagemagick and imported by XnView.
As a start I would try TIFF, it supports 16 bit and is supported by imagemagick as well as XnView. The conversion will blow up the single channel into three channels with identical values.
To read you file in imagemagick you'll probably have to use the following options:
GRAY Raw gray samples
Use -size and -depth to specify the image
width, height, and depth.
convert -endian LSB -size 513x513 -depth 16 gray:image image.tiff
Convert back to 16 bit single channel:
convert image.tiff -depth 16 -type grayscale gray:image