How can I scale an SVG while maintaining whole pixels?

I have a pixelart-style image which intend to scale to 4x size with SVG. However, the following code blurs the pixels of the image:

<image x="0" y="0" width="1024" height="1024"
    image-rendering="optimizeSpeed"
    xlink:href="pixelart.bmp" />

Is there some attribute which will resolve this?