Genito-urinary Imaging Figure 1: Renal Tuberculosis
breath-hold. As suggested by the CT Urography Working Group of the European Society of Urogenital Radiology (ESUR),6
urography is a dedicated multiphasic CT scanning technique that is optimized for imaging the urinary tract. Intravascular contrast medium is used and high-resolution images of the renal parenchyma and urinary tract (including the bladder) are obtained. The development of multidetector CT urography means this technique is now used for all of the clinical indications previously addressed by excretory urography.
Maximum-intensity projection computed tomography urography showing renal medullary necrosis (arrow) in one of the renal calyces of the lower group.
Figure 2: Renal Tuberculosis on Computed Tomography Urography
Typically, CT urography consists of a multiphasic helical CT protocol. A preliminary unenhanced CT scan is obtained from the upper pole of the kidney to the lower edge of the symphysis pubis to detect calculi, reveal the unenhanced appearance of masses (throughout the urinary tract), and provide a baseline attenuation value to calculate enhancement of masses and other abnormalities. Unenhanced images are also useful for evaluating masses for fat or calcium. The number of CT urography phases in the single-bolus technique generally varies between two and four: an unenhanced phase of the abdomen and pelvis, a nephrographic phase of the kidney, and an excretory phase of the abdomen and pelvis. Only a few groups employ a corticomedullary phase, since the arterial-phase information is not needed routinely. Some extend the nephrographic phase to the pelvis, especially when the patient is at increased risk for malignancy. Such a nephrographic phase facilitates complete tumor staging or evaluation of associated findings. Because of the high radiation dose of CT urography, the number of phases should be kept to a minimum.
3D images are created interactively by radiologists on a 3D workstation. Thin-slab volume-rendering (VR), average-intensity projection (AIP), or maximum-intensity projection (MIP) 3D images can be used for interactive image evaluation.
In our department we employ the so-called ‘split-bolus’ technique, which is probably the most widely used technique; also, it limits the radiation exposure to the patient. Instead of obtaining two (nephrographic- and excretory-phase) separate scans after intravenous contrast material administration, the split-bolus technique reduces the total number of scans from three to two, and therefore reduces radiation exposure.7
The split-bolus technique allows two-phase CT
urography with a synchronous nephrographic and pyelographic excretory phase.8,9
Once the patient is positioned on the table,
Maximum-intensity projection showing segmental dilatation of the upper urinary tract owing to fibrosclerosing tuberculosis, with a tuberculous stricture at the superior infundibulum with regional hydrocalycosis (arrow).
the upper urinary tract, including its involvement in renal tuberculosis. CT urography provides the ability to obtain thin (sub-millimeter) collimated data of the entire urinary tract during a short single
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furosemide is administered intravenously (0.1 mg/kg) and an unenhanced scan is acquired from the upper pole of the kidneys to the bladder base. The contrast agent is then injected in two boluses, for a total patient dose of 600 mgI/kg. A first bolus of 400 mgI/kg is injected, followed by a second bolus of 200 mgI/kg after a six-minute delay and a saline flush. Two minutes after the second bolus, a second scan is acquired of the entire abdomen and pelvis, which affords both an effective nephrographic-phase image (thanks to the second bolus of contrast material) and good opacification and distension of the urinary tract (thanks to the time delay after the first bolus).
The advantage of split-bolus administration is that it allows a combined nephro–pyelographic phase to be obtained instead of two separate phases, leading to a relatively reduced radiation exposure. Radiation exposure is a critical issue and further optimization is achieved by using low-dose protocols and tube-current modulation.
US RADIOLOGY multidetector CT
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