Mild hydronephrosis, right; up to mid-ureter consider possible partially obstucting lucent ureterolithiasis. what it means?

Stones: You probably have a stone obstructing your right kidney's urine outflow tract that has caused the tract to become enlarged (hydronephrosis). Lucent just implies that the stone is not visible on xray or ultrasound. A ct scan should still be able to pick it up though.

Stone, scar, etc: I see you take potassium citrate so i must assume you have had kidney stone experiences previously. A non-calcified stone may be present although these typically show up on ct scan. Ureteral scarring or a small blood clot could also cause this. Urological evaluation is advised.