IVUS ray intersection improvements

[rmolazem]

Improve IVUS simulation by correctly handling ray intersections with catheter and vessel walls.

• Step 1 — Offset rays using catheter radius

Objective: Make rays start outside the catheter surface so that the IVUS image can be debugged easily. Currently, rays produce only one intersection, which hits the catheter wall.

Actions: Use a configurable r_catheter to offset ray origins from catheter surface.

Expected outcome:

• Rays will intersect the vessel wall instead of the catheter.

• Debug hit points show a realistic lumen (empty interior) in generated IVUS images.

• Step 2 — Allow multiple intersections per ray

Objective: Record both catheter and vessel wall intersections.

Actions: Modify ray intersection logic to collect all intersections along the ray.

• Filter intersections by distance:

d <= r_catheter → catheter wall

d > r_catheter → vessel wall

• Store separately for debugging and visualization.

Expected outcome:

IVUS images will contain a bright circle which indicates the catheter.