The generator matrix

 1  0  0  1  1  1 (a+1)X  1  1  1  1  1  1  1  1  1  1  1
 0  1  0 (a+1)X  1 (a+1)X+1  1  X X+1 X+a aX+a  a a+1 aX+1 (a+1)X+a+1 aX+a+1 aX (a+1)X
 0  0  1  1 X+1  X  1 (a+1)X+a (a+1)X+a+1 aX aX+1 aX+a (a+1)X+1  a (a+1)X X+1 a+1 X+a+1

generates a code of length 18 over F4[X,sigma]/(X^2) who´s minimum homogenous weight is 48.

Homogenous weight enumerator: w(x)=1x^0+195x^48+216x^49+528x^50+240x^51+390x^52+432x^53+480x^54+156x^56+504x^57+528x^58+144x^59+282x^60

The gray image is a linear code over GF(4) with n=72, k=6 and d=48.
This code was found by Heurico 1.16 in 0.015 seconds.