In circle \( G, G H=6 \) and \( \mathrm{m} \angle H G I=90^{\circ} \). Find the length of \( H I \). Express your answer as a fraction times \( \pi \).

Step 1 ：1. Use the theorem that the angle subtended by a diameter in a circle is always a right angle: Since \(\mathrm{m}\angle HGI = 90^{\circ}\), we know that GI is a diameter.

Step 2 ：2. Use the Pythagorean theorem on right triangle HGI: \(GH^2+HI^2 = GI^2\)

Step 3 ：3. Calculate HI: \(HI^2 = GI^2 - GH^2\) and \(HI = \sqrt{GI^2 - GH^2}\)