Can someone help me interpret at these images? I find the subtle changes in kidneys difficult to parse out between normal aging variation and disease processes.

First:

• 6 year old mn DSH cat
• History of relinquishing to vet hospital due to bladder stones chronic urinary issues
• Stones disappeared on SO while in hospital
• Recent onset of acute bladder pain about 1 week after rehoming
• Radiograph post u/s was negative for stones in urethra, cat is not blocked but does not empty bladder fully