URINARY TRACT COMPUTED TOMOGRAPHY

urinary tract Computed tomography :
Widely used for investigation of urological symptoms and disease. It can detect very small differences in X-ray absorption values of tissues, providing a very wide range of densities (and therefore differentiation between tissues) when compared with plain radiography. The computer calculates the absorption value (attenuation) of each pixel, and reconstructs this into an image. The attenuation values are expressed on a scale from -1000 to +1000 Hounsfield units (water = 0, air =  1000, bone = +1000). More recently, advances in computing power have enabled the data to be reformatted so that images can be produced in sagittal and coronal planes as well as in the more familiar horizontal plane (Figs. 3.11 and 3.12).
 Plain CT scans (without contrast) can detect calcification and calculi within the urinary tract and administration of intravenous contrast is used to evaluate the nature of solid renal lesions and to determine the nature of soft tissue masses (e.g. to differentiate bowel from lymph nodes in cancer staging CTs).  Spiral or  helical CT is very rapid scanning while the table on which the patient is lying is moved though the scanner. A large volume of the body can be imaged in a single breath hold, thus eliminating movement artifact particularly useful for identifying suspected ureteric stones in patients with acute loin pain.

Uses of CT
Renal
- Investigation of renal masses characterizes solid from cystic lesions; differentiates benign (e.g. angiomyolipoma) from malignant solid masses (e.g. renal cell carcinoma)
- Staging of renal cancer (establishes local, nodal, and distant spread)
- Assessment of stone size and location (within the collecting system or within the parenchyma of the kidney)
- Detection and localization of site of intrarenal and perirenal collections of pus (pyonephrosis, perinephric abscess)
- Staging (grading) of renal trauma
- Determination of cause of hydronephrosis

Ureters
- Locates and measures size of ureteric stones

Bladder
- Bladder cancer staging (establishes local, nodal, and distant spread)

Uses of MRI
- Staging of pelvic cancer bladder and prostate cancer staging (establishes local, nodal, and distant spread). As with CT, oedema and fibrosis cannot be reliably distinguished from tumour within the bladder wall, leading to  overstaging of cancer. Again, as with CT, microscopic disease cannot be identified, leading to  understaging of cancer.
- Localization of undescended testes.
- Identification of ureteric stones, where ionizing radiation is best avoided (e.g. pregnant women with loin pain).