Let the point \( A \) be the foot of perpendicular drawn from the point \( P(a, b, 0) \) on the line}
\[
\frac{x - 1}{2} = \frac{y - 2}{1} = \frac{z - \alpha}{3}.
\]
If the midpoint of the line segment \( PA \) is \( \left( \frac{3}{4}, \frac{4}{3}, -\frac{1}{4} \right) \), then the value of \( a^2 + b^2 + \alpha^2 \) is: