Hi, 3 Years Back My Father Had MRI Scan In

hi,
3 years back my father had MRI scan in which he was diagnosed with multiple chronic lacunar infarcts.
The MRI scan reports:
There are bilateral peri ventricular and sub cortical white matter foci of signal alteration are seen eliciting hyperintense signal on T2WI'S AND T2 FLAIR sequences and iso intense on TI WI'S.There is no associated mass effect or diffusion restriction.
Bilateral ganglio-capsular foci eliciting hyperintense signal on T2WI'S AND T2 flair sequence and iso intense on TI WI's.There is no associated mass effect or diffusion restriction.
and it says other parts of brain are normal ventricles ,grey white matter differentiation ,craniocervical junction ,corpus callosum,cerebellopontine angles are intact.
doctors told us that there is brain damage and it is irreversible he has been taking aspirin regularly from 3 years and he has no diabetes,cholestrol and hypertension.
But i dont understand the reason of stroke and i want to know how can we prevent further damage to brain.
please help me and reply soon.