What are you saying this test is "better" then? A CT angiogram? Because it's not more accurate then a run-of-the-mill modern medicine gold standard CTA. The test may have a role in low-income countries where they don't have modern equipment and can't easily transfer patients to a place that does, however.

Sorry for your loss. Based on your description, your brother in law probably had a hemorrhagic stroke meaning the artery ruptured and bled. That type of stroke is the easiest to detect because it shows up clearly on CT imaging. This blood test is for "ischemic" stroke, which is very different and actually has the opposite treatment.