Principles Of T2weighted Mr Urography Staticfluid Mr Urography

T2-weighted MR urography simply provides water images of the urinary tract by acquisition of heavily T2-weighted turbo spin-echo (TSE) sequence techniques. The water we intend to visualize is the urine itself, which may be regarded as an "intrinsic contrast medium.'' T2-weighted MR urography is well suited for imaging of obstructive urinary tract disorders, because the large amount of static fluid generates a good SNR (Fig. 1). Moreover, T2-weighted MR urography offers a diagnostic tool that is independent of the renal excretory function. Static-fluid MR urography may even provide excellent urographic views of hydronephroses associated with severe kidney malfunction (2,5-10).

Moderate or marked dilatation is often indicative of advanced-stage urinary tract obstruction. On the other hand, early-stage intrinsic or extrinsic tumor lesions often do not cause obstruction and are therefore not necessarily associated with an increase of static fluid. The value of T2-weighted MR urography for the visualization of the nondilated urinary system is limited (Fig. 1) (7,8,11-13). Thus, several authors evaluating T2-weighted MR urography recommend supplementary measures for increasing the fluid load of the nondilated collecting system, including the use of a compression device plus intravenous diuretics (6,14) or saline

Figure 1 T2-weighted MR urogram of a male patient with a left-sided ureterohydronephrosis developed after prostatectomy. The large amount of static fluid on the left provides a good visualization of the dilated urinary tract on a heavily T2-weighted MR image. The unobstructed collecting system on the right remains invisible because of the lack of static fluid without application of a compression device. This MR urogram was obtained during a breath-hold of eight seconds by acquisition of a single-slice projection MR image with a thickness of 85mm. Abbreviation: MR, magnetic resonance.

Figure 1 T2-weighted MR urogram of a male patient with a left-sided ureterohydronephrosis developed after prostatectomy. The large amount of static fluid on the left provides a good visualization of the dilated urinary tract on a heavily T2-weighted MR image. The unobstructed collecting system on the right remains invisible because of the lack of static fluid without application of a compression device. This MR urogram was obtained during a breath-hold of eight seconds by acquisition of a single-slice projection MR image with a thickness of 85mm. Abbreviation: MR, magnetic resonance.

infusion plus intravenous diuretics; e.g., 0.3 mg furosemide per kg bodyweight combined with 20 mL saline infusion per kg (15). However, even the administration of an intravenous dose of 20 mg of furosemide cannot constantly ensure sufficient visualization of the nondilated urinary tract on T2-weighted MR urograms (11).

A second limitation of static-fluid MR urography is the inability of deriving functional information about the renal excretion and the urine flow through the collecting system and ureters (2,5,8,9).

The former objection that superimposed intestinal fluid collections may degrade the conspicuity of the urinary tract on T2-weighted MR urograms is nowadays less relevant because modern image postprocessing techniques, such as vector-of-interest editing, allow the elimination of fluid-filled bowel loops from MR urographic source images.

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