Isometrics

for the life of me, I cannot figure out how to translate the mouse to my isometric map. this is my code for how i'm trying to do it and the way it is used in the draw function

updateMap = function()
  tMouseX = ((mouse.x/2-mouse.y/4)/2)
  tMouseY = ((mouse.y/2-mouse.x/4)/2)
  for t in tiles
    local x = (t.x/4-t.y/2)*tWidth
    local y = (t.x/4+t.y/2)*tHeight

    if collision(t.x,t.y,1*camera.scale,1*camera.scale,tMouseX-camera.x,tMouseY-camera.y,0.1,0.1) then
      t.sprite = "port"
    else t.sprite = "tile" end
  end
end

drawMap = function()
  for t in tiles
    local x = floor((t.x/2-t.y/2)*tWidth)
    local y = floor((t.x/4+t.y/4)*tHeight)
    screen.drawSprite(t.sprite,x,y,tWidth,tHeight)
    screen.drawSprite("icon",t.x,t.y,1)
  end
  screen.drawSprite("icon",tMouseX-camera.x,tMouseY-camera.y,12,12)
end

if you know anything about isometrics, please help