1- Overhydration/ inadequate dehydration :
Causes dilution of the contrast material (Note that the kidneys may be entirely normal).2- Polyuria :
Excretion of large volumes of hypotonic urine due to diuretic therapy, diabetes insipidus (lack of antidiuretic hormone ADH secreted by the posterior lobe of the pituitary gland), diabetes mellitus, and intrinsic renal diseases. 3- Renal failure (uremia) :
Severely decreased renal function due to a variety of underlying causes. 4- Nephrosclerosis :
Long-standing hypertension causes narrowing of extraand intrarenal arteries with prolonged intrarenal circulation time and decreased excretion of contrast material.
Malignant nephrosclerosis. Nephrotomogram obtained 5 minutes after the injection of contrast material shows minimum opacification of small, smooth kidneys.
5- Technical :
Injection of an inadequate dose of contrast material.