The generator matrix

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

generates a code of length 18 over F4[X,sigma]/(X^2) who´s minimum homogenous weight is 50.

Homogenous weight enumerator: w(x)=1x^0+216x^50+240x^51+24x^52+144x^54+36x^56+216x^58+144x^59+3x^64

The gray image is a linear code over GF(4) with n=72, k=5 and d=50.
This code was found by Heurico 1.16 in 3.24e-008 seconds.