Finding all Namespaces in an assembly using Reflection (DotNET)

I've got an assembly (loaded as ReflectionOnly) and I want to find all the namespaces in this assembly so I can convert them into "using" ("Imports" in VB) statements for an auto-generated source code file template.

Ideally I'd like to restrict myself to top-level namespaces only, so instead of:

using System;
using System.Collections;
using System.Collections.Generic;

you'd only get:

using System;

I noticed there is a Namespace property on the System.Type class, but is there a better way to collect Namespaces inside an assembly that doesn't involve iterating over all types and culling duplicate namespace strings?

Much obliged, David