invoke.sass

.logo
  +at2x(logo-mams, 74px, 84px)

mixin.sass

=at2x($image_name, $w: auto, $h: auto, $extention: '.png')
  background-image: image-url($image_name + $extention)
  $x2img : $image_name + '@2x' + $extention
 
  @media all and (-webkit-min-device-pixel-ratio : 1.5)
    background-image: image-url($x2img)
    background-size: $w $h

output.css

.logo {
  background-image: url('/images/logo-mams.png');
}
 
@media all and (-webkit-min-device-pixel-ratio: 1.5) {
  .logo {
    background-image: url('/images/logo-mams@2x.png');
    background-size: 74px 84px;
  }
}