What are the reasons why stones do not show up on imaging?

Patient's question:

Everything is normal, stuck in the upper ureter, does not show up on CT, two months ago

Doctor's answer:

Patient is male, with ureteral calculus and upper ureteral stricture.
Advice: The composition of urinary calculi varies among individuals. The most common type is calcium oxalate stones, which are hard, irregular, and easily visible on plain films. The next most common types are phosphate stones, uric acid stones, and carbonate stones, which are brittle and respond well to lithotripsy. Another type is uric acid stones, which are related to uric acid metabolism, hard, smooth, and pure uric acid stones are not visible on plain films. Another type is cystine stones, a rare familial genetic disease, also not visible on plain films.
Since you have ureteral calculi, it is recommended to undergo ureterolithotomy to remove the stones while also correcting the stricture. In daily life, it is important to drink more water, avoid holding urine, and stay more active.