Thanks for writing to HCM
Mild lobulated cortical outlines are normal findings. Lobulations are formed during embryogenesis of kidneys.
Optimal cortico-medullary differentiation is also normal finding.
your measurement of kidney is also normal.
Echogenic foci measuring 3.5 mm in interpolar reason may be calculus. It may be confirmed by non contrast CT scan
,if there is any confusion in USG.
Treatment of renal calculus is both medical and surgical. It is not very serious condition.so don't worry.