Abstract
The purpose of this study was to compare the diagnostic accuracy of T2-weighted (T2w) MR urography (MRU) techniques — the standard MRU using fast spin echo (FSE) and postprocessing maximum intensity projection (MIP) and the single-shot MRU — in the diagnosis of ureteric obstruction in patients with noncalcular urinary obstruction. The study included 150 patients admitted to our center between January 2005 and December 2006. There were 203 renal units with noncalcular obstruction; 53 patients had bilateral obstruction. Patients with calcular obstruction were excluded. There were 85 males and 65 females with a mean age of 50 (range: 5–83) years. All patients were examined with static MRU using both single-shot (thick slab) and multisection MRU. Using single-shot MRU, we obtained images at the direct coronal and oblique coronal, as well as sagittal, planes for each renal unit. Postprocessing MIP for the standard coronal heavy T2 source images to obtain coronal and oblique images was done. Among the obstructed 203 units, the intrinsic causes were present in 157 units (151 were stricture and six were ureteric tumors), while the extrinsic causes were present in 46 units (35 bladder tumor, four ureterocele, five retroperitoneal fibrosis, one prostatic tumor, and one local pelvic recurrence after radical cystectomy for bladder cancer). The overall accuracy of single-shot MRU was 89% and was 93% for the multisection MRU in cases of intrinsic ureteric obstruction, while in cases of extrinsic obstruction, it was 20% for single-shot MRU and 96% for multisection MRU. T2w static MRU is a very useful technique in diagnosing noncalcular ureteric obstruction. Multisection MRU has a high diagnostic accuracy and reliability over that of the single-shot technique. The single-section technique is very rapid and useful in diagnosing ureteric stricture so it could be used as a localizer, while multisection images with postprocessing MIP is mandatory, especially in cases of suspected ureteric tumors or extraureteric causes.
Highlights
The concept of MR urography (MRU) came into existence at the end of 1980s
Single-shot MRU does not have the prerequisites of intravenous urography, such as ionizing radiation, injection of contrast media, and functioning kidney, but it has been hampered by limited spatial resolution[10,11,112,13]
Whereas intravenous urography may last from 15 min to several hours, singleshot MRU is completed within a maximum of 5 min
Summary
The concept of MR urography (MRU) came into existence at the end of 1980s. The static fluid MRU (sMRU), based on heavily T2-weighted (T2w) images, visualizing static and slowly flowing fluids, was the first technique used in clinical practice[1,2].MRU was described in cases of patients with obstructive uropathy. The static fluid MRU (sMRU), based on heavily T2-weighted (T2w) images, visualizing static and slowly flowing fluids, was the first technique used in clinical practice[1,2]. T2w sequences can visualize a dilated urinary tract without injection of contrast materials because MRU selectively depicts urine in the dilated renal collecting system and ureter[3,4,5,6,7]. In the clinical practice of T2w sMRU, single-slice projection imaging using rapid acquisition with relaxation enhancement (RARE) or half-Fourier acquisition single-shot turbo spin echo (HASTE) does not have the same discernment as the multislice technique. A fast-echo pulse sequence adapted for single-shot use reduces the acquisition time for a full 250 × 256 matrix to 2.8 sec and permits selective projection of the collecting system in convenient breath holds. Postprocessing required for a selective display in T2w pulse sequences with shorter echo trains bears a high risk of introducing artifacts and lengthens time to complete the examination[9]
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