The Usefulness of T2-weighted MR Urography and Contrast Enhanced MR Urography in the Evaluation of Obstructive Uropathy: Comparisonal Study with Antegrade Pyelography1

PURPOSE: To compare the efficacy of contrast-enhanced and T2-weighted magnetic resonance urography (MRU) for the depiction of obstruction and evaluation of the causes of obstructive uropathy with that of antegrade pyelography. MATERIALS AND METHODS: Twenty-five patients with obstructive uropathy who underwent percutaneous nephrostomy (PCN) and antegrade pyelography (AGP) were included in the study. We performed MR urography, comprising half-Fourier acquisition single-shot turbo spin-echo (HASTE) T2-weighted imaging and 3-D fast imaging with steady state precession (3-D FISP) T1-weighted imaging after gadolinium enhancement and compared the quality of the images of both the HASTE and 3-D FISP MRU techniques in terms of their depiction of the dilated pelvocalyceal system, and the level, type, and causes of obstruction. RESULTS: In terms of anatomical depiction of the pelvocalyceal system (p=0.002) and the causes of obstruction (p=0.003), T1-weighted MRU using 3D-FISP was significantly better than T2-weighted MRU using the HASTE sequence. Regarding level of obstruction, T2-weighted MRU using the HASTE sequence and contrastenhanced T1-weighted MRU using 3D-FISP showed an accuracy of 76% (19/25) and 84% (21/25), respectively. In terms of type of obstruction, the accuracy of T2-weighted MRU and T1-weighted CEMRU was 72%(18/25) and 88% (22/25), respectively. CONCLUSION: T2-weighted MRU and T1-weighted CEMRU provided both anatomical information and that relating to impaired renal function. The two modelities played a complementary role and their use could decrease the unnecessary use of invasive diagnostic examination for the evaluation of obstructive uropathy.

Excretory MR Urography Using Breathhold Three-dimensional FISP: Comparison with MR Urography Using HASTE Technique

PURPOSE: To compare the usefulness of gadolinium-enhanced excretory MR urography using breath-hold three-dimensional fast imaging with steady state precession (3-D FISP) with conventional MR urography using the half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence in the evaluation of obstructive uropathy. MATERIALS AND METHODS: Twenty-three patients in whom ultrasonography (US) and/or intravenous urography(IVU) revealed signs of urinary obstruction were enrolled in this study. Fifteen were men and eight were women, and their mean age was 54 (range, 21 -80) years. All MR images were obtained using a 1.5-T MR unit. MR urography using the HASTE technique (MRU) and gadolinium-enhanced excretory MR urography using the 3D-FISP technique were performed, and in all cases, reconstructions involved maximum intensity projection. For contrast-enhanced MR urography (CEMRU), images were obtained 3, 5, 20, and 30 minutes after the administration of intravenous contrast media, and for selected cases, additional images were obtained until 24 hours after contrast media injection. For qualitative analysis, two experienced radiologists compared CEMRU and MRU in terms of their diagnostic value as regards the level and cause of urinary obstruction, and morphologic accuracy. In addition, signal to noise ratio (SNR) and contrast to noise ratio (CNR) of the urinary tract at each anatomic level were quantitatively analysed. RESULTS: Quantitative analysis showed that in terms of SNR and CNR of the urinary tract at the level of the mid and distal ureter, CEMRU using 3-D FISP was better than MRU using HASTE (p<0.05). Qualitative analysis indicated that for the depiction of the whole length of normal ureter, and detection of the level of obstruction, anatomic anomalies and intrinsic tumors, 3-D FISP was superior to HASTE. There was, however, no difference between these two modalities in the diagnosis of ureteral stone and the degree of hydronephrosis. In addition, 3-D FISP was better than HASTE for the assessment of filling defect, but the difference was not statistically significant. CONCLUSION: Breath hold 3-D FISP is a very valuable tool in the evaluation of obstructive uropathy. It not only depicts very clearly the anatomy of the urinary tract system, but also provides qualitative information on renal function. We believe that CEMRU using 3-D FISP is a valuable diagnostic approach which can be added to those already available for the workup of obstructive uropathy.

Gadolinium-enhanced Excretory MR Urography: Comparison with MR Urography Using HASTE Technique

PURPOSE: To compare the feasibility of gadolinium-enhanced excretory MR urography(GEMRU) and conven-tional MR urography using the half-Fourier acquisition single-shot turbo spin-echo(HASTE) sequence in pa-tients with hydronephrosis or non-visualized kidney. MATERIALS AND METHODS: Fifteen patients with hydronephrosis or non-visualized kidney, as demonstrated by ul-trasonography or intravenous urography, were enrolled in this study. Nine were men and six were women, and their age ranged from 18 to 77 (mean, 60.6) years. For all MR examinations, a 1.5-T MR unit was employed. For breath-hold MR urography, the HASTE technique(MRU) was used, and reconstruction involved the use of a maximum intensity-projection (MIP) algorithm. For gadolinium-enhanced excretory MR urography, the fast low angle shot(FLASH) 3-D method was used and images were obtained at 5, 10, 20, and 30 minutes, and recon-struction again involved the use of an MIP algorithm. In some cases, additional GEMRU was obtained 24 hours after contrast material injection, and an MIP algorithm was used for reconstruction. MRU and GEMRU were independently interpreted by two radiologists who for quantitative analysis compared SNR with CNR, and at each anatomic level qualitatively analysed morphologic accuracy and diagnostic value of the lesions. RESULTS: In quantitative analysis, SNR and CNR differences between the two sequences at the renal pelvis and the level of the ureter were not significant (p>0.05). In qualitative analysis, GEMRU was superior to M-RU for the assessment of evaluated ureter at each level(p<0.05), anatomic anomaly and intrinsic tumor. Ureteral stones, however, were more easily diagnosed with MRU. CONCLUSION: For assessment of the ureter GEMRU is superior to MRU and has the advantage of evaluating renal function. We believe that for evaluation of the urinary tract, especially the distal ureter, GEMRU may be a valuable adjunct to routine MR urography.

MR Urography Using HASTE Imaging: Comparison with Intravenous Urography

PURPOSE: To evaluate the usefulness of MR urography(MRU) using Half-Fourier acquisition single-shot turbospin-echo(HASTE) sequence compared with conventional intravenous urography(IVU). MATERIALS AND METHODS: Thirtyfive lesions of 32 patients who underwent MRU because of delayed excretion or nonvisualization of the ureter wereincluded in this study. HASTE MR urography was performed with a 1.0 MR imaging unit. Coronal images includingthose of the kidney, ureter and bladder were obtained in every patient using the multislice technique, and werepostprocessed by means of the maximal intensity projection technique. Scan time was 17-19 seconds. We analyzed theresults of MRU, focusing on level of obstruction, incidence of stone, ureter dilatation, and motion artifact, andin each case compared MRU findings with those of IVU. RESULTS: In 12 of 35 lesions(34.2%), MRU more effectivelydiagnosed causes of obstruction than did IVU, while in seven lesions(20%), MRU and IVU were similar. In eightlesions(22.9%), all of which were caused by a stone, IVU was better than MRU, and in a further eight, neithermodality was able to diagnose the cause. For diagnosis of the level of obstruction, MRU was better than IVU in 20of 35 lesions(57.1%), and similar to IVU in seven(20%). In three lesions(8.6%), neither modality was able todetect the level of obstruction. Four lesions not related to obstruction were polycystic renal disease, cysticrenal change, vesicovaginal fistula and extra-renal pelvis. Dilatation of the ureter was seen in 23lesions(65.8%) on MRU and in seven lesions on IVU. Thus, MRU revealed dilatation of for the ureter more efectivelythan IVU. CONCLUSION: MRU using HASTE was valuable for the detection of underlying causes and levels ofobstruction in the urinary tract, and of abnormalities in surrounding structures in patients with non-visualization of the kidney or delayed contrast excretion of the ureter, as seen on delayed IVU urogram.

Usefulness of MR Urography in the Diagnosis of Hydroureteronephrosis

PURPOSE: To evaluate the clinical usefulness of the MR urography (MRU) in the diagnosis of hydroureteronephrosis. MATERIALS AND METHODS: Twenty-five patients with hydronephrosis (26 cases) underwent MR urography, using a 1.5T MR scanner (Signa Horizon, GE Medical Systems, Milwaukee, U.S.A). The causes of hydronephrosis included benign ureteral stricture (12), ureteral stones (8) and malignant strictures (6), and were confirmed by operation, biopsy, conventional urography or clinical follow up. For MRU, a fat suppressed, respiratory-triggered, heavily T2-weighted fast spin echo (FSE) pulse sequence was used, and the 3-dimensional MR images were subsequently processed by a maximum-intensity-projection algorithm. We evaluated the success rate of MRU and its accuracy in determining the level and cause of obstruction, and compared the degree of hydroureteronephrosis seen on MRU with that seen on conventional urography. RESULTS: In all cases, a urogram was successfully obtained. In determining the degree of hydroureteronephrosis and the level of obstruction (in the upper ureter in 11 cases, in the mid-ureter in four, and in the lower ureter in 11), MRU findings matched those of conventional urography. In 24/26 cases (92%), MRU accurately determined the cause of urinary tract obstruction ; the two exceptions were in cases involving ureteral stones. CONCLUSION: MRU is a promising, noninvasive diagnostic method for evaluating hydroureteronephrosis, especially in children, pregnant women and patients with an allergic reaction to iodinated contrast material.