c# random generated values within a certain range that can only be generated once

I'm trying to chose between 15 array values on a random base. The problem i'm facing is the fact that i want a value to only be generated once during the program. Once all 15 numbers are generated, the programs ends.

So my question is, how do you make sure a value is only generated once during the program.

       int[] ImageValues = new int[15];
       ImageValues[0] = 1;
       ImageValues[1] = 2;
       ImageValues[2] = 3;
       ImageValues[3] = 4;
       ImageValues[4] = 5;
       ImageValues[5] = 6;
       ImageValues[6] = 7;
       ImageValues[7] = 8;
       ImageValues[8] = 9;
       ImageValues[9] = 10;
       ImageValues[10] = 11;
       ImageValues[11] = 12;
       ImageValues[12] = 13;
       ImageValues[13] = 14;
       ImageValues[14] = 15;

       Random randomize = new Random();
       int initialValue = randomize.Next(0, 15);
       int finalValue = ImageValues[initialValue];