Evaluation of RARE-MR urography in the assessment of ureterohydronephrosis

Magnetic resonance urography

Excellent contrast resolution and lack of ionizing radiation make magnetic resonance urography (MRU) a promising technique for noninvasively evaluating the entire urinary tract. While MRU currently lags behind CT urography (CTU) in spatial resolution and efficiency, new hardware and sequence developments have contributed to a resurgence of interest in MRU techniques. By combining unenhanced sequences with multiphase contrast-enhanced and excretory phase imaging, a comprehensive assessment of the kidneys, ureters, bladder, and surrounding structures is possible with image quality rivaling that obtained with other techniques. At the same time, formidable challenges remain to be overcome and further clinical validation is necessary before MRU can replace other forms of urography. In this article, we demonstrate the current potential of MRU to demonstrate a spectrum of urologic pathology involving the kidneys, ureters, and bladder while discussing the limitations and current status of this evolving technique.

MR urography: techniques and clinical applications

Magnetic resonance (MR) urography comprises an evolving group of techniques with the potential for allowing optimal noninvasive evaluation of many abnormalities of the urinary tract. MR urography is clinically useful in the evaluation of suspected urinary tract obstruction, hematuria, and congenital anomalies, as well as surgically altered anatomy, and can be particularly beneficial in pediatric or pregnant patients or when ionizing radiation is to be avoided. The most common MR urographic techniques for displaying the urinary tract can be divided into two categories: static-fluid MR urography and excretory MR urography. Static-fluid MR urography makes use of heavily T2-weighted sequences to image the urinary tract as a static collection of fluid, can be repeated sequentially (cine MR urography) to better demonstrate the ureters in their entirety and to confirm the presence of fixed stenoses, and is most successful in patients with dilated or obstructed collecting systems. Excretory MR urography is performed during the excretory phase of enhancement after the intravenous administration of gadolinium-based contrast material; thus, the patient must have sufficient renal function to allow the excretion and even distribution of the contrast material. Diuretic administration is an important adjunct to excretory MR urography, which can better demonstrate nondilated systems. Static-fluid and excretory MR urography can be combined with conventional MR imaging for comprehensive evaluation of the urinary tract. The successful interpretation of MR urographic examinations requires familiarity with the many pitfalls and artifacts that can be encountered with these techniques.

3D excretory MR urography: Improved image quality with intravenous saline and diuretic administration

PURPOSE

To assess the effect of diuretic administration on the image quality of excretory magnetic resonance urography (MRU) obtained following intravenous hydration, and to determine whether intravenous hydration alone is sufficient to produce diagnostic quality studies of nondilated upper tracts.

MATERIALS AND METHODS

A total of 22 patients with nondilated upper tracts were evaluated with contrast-enhanced MRU. All patients received 250 mL of saline intravenously immediately prior to the examination. A total of 11 patients received 10-20 mg furosemide in addition to saline. Imaging was performed with a three-dimensional (3D) and two-dimensional (2D) breathhold spoiled gradient-echo sequences. Excretory MRU images were acquired five minutes after the administration of 0.1 mmol/kg gadolinium and were independently reviewed by two radiologists, who were blinded to the MRU technique. Readers evaluated the calyces, renal pelvis, and ureters qualitatively for degree of opacification, distention, and artifacts on a four-point scale. Statistical analysis was performed using a permutation test.

RESULTS

There was no significant disagreement between the two readers (P=0.14). Furosemide resulted in significant improvement in calyceal and renal pelvis distention (P<0.005), and significant artifact reduction in all upper tract segments (P<0.001) compared to the effect of saline alone.

CONCLUSION

Intravenous furosemide significantly improves the image quality of excretory MRU studies obtained following intravenous hydration. Intravenous saline alone is insufficient to produce diagnostic quality studies of the non-dilated upper tracts.

[Functional and morphological MR imaging of the upper urinary tract in the pediatric age group]

MR imaging is being increasingly used for the diagnosis of congenital urinary tract obstruction. The following conditions have to be fulfilled to provide an MR urography technique which is useful for the pediatric age group: (1) the combination of morphology and function, (2) a high-resolution morphological image, (3) a morphological image independent of kidney function, (4) reliable determination of split renal function and (5) of urinary excretion. This is best accomplished with a combination of a T1-weighted fast GE sequence post-contrast and a heavily T2-weighted 3D IR-TSE sequence. Selected sequence parameters are important for optimization as well as for a correct functional assessment. Then MR urography is superior to the conventional methods of excretory urography, ultrasound, and scintigraphy in the morphological depiction of the urinary tract even of complex malformations as well as in a detailed functional assessment. In particular, this method is useful in the situation of complicated duplex kidneys, dystopic kidneys, unclear morphology, or discrepant former results and perioperative assessment. The main advantages are avoiding radiation and obtaining a simultaneous functional-morphological diagnosis.

Imagerie de la lithiase urinaire : « Trois en un »

Urinary lithiasis is very common among the general population, with a high prevalence level. In rich countries it is mainly located inside the upper urinary tract. Helical CToperated with newer devices is the most accurate modality to provide all needed information: diagnosis of stone without contrast medium injection, morphology (size, number) and localization, diagnosis of urinary obstruction, urinary tract aspect and all kind of differential diagnosis in emergency. It must be used during follow up to diagnose residual fragments. Multiplanar reconstructions are essential for the clinicians; but diagnosis is interpreted by scrolling axial views with dynamic analysis on computer screen. Low-dose helical CT is today available. Helical CT provides an "all-in-one" examination. It should soon replace combined plain film-ultrasonography performed in an emergency context of renal colic and intravenous urography for pre- and post-treatment assessments.

[MR urography: principles, examination techniques, indications]

MR urography is an evolving and promising technique in the evaluation of the urinary tract. MR urography is currently considered the method of choice for imaging of the renal parenchyma and the collecting systems in patients who cannot undergo routine radiographic studies such as pregnant women, pediatric patients, patients allergic to iodinated contrast agents, or patients with impaired renal function. The future development of MR urography in terms of functional, cellular, and molecular imaging is presently the subject of research. The ability of MR imaging to provide quantitative functional information (e.g., on blood flow, perfusion, glomerular filtration rate, and excretion as well as urine drainage) in addition to morphologic assessment of the parenchyma and the collecting system could lead to a single, "all-in-one approach" examination technique.

Impact of magnetic resonance urography on preoperative diagnostic workup in children affected by hydronephrosis: should IVU be replaced?

PURPOSE

The aim of this study was to determine the role of magnetic resonance urography (MRU) in preoperative diagnostic workup of children with hydronephrosis in a prospective clinical study with comparison of MRU, standard diagnostic investigations, and intraoperative findings.

METHODS

Thirty-one children with hydronephrosis secondary to different causes underwent ultrasound scan (US), intravenous urography (IVU), micturation cysto-urethrography (MCU), isotope nephrography (ING) and MRU. For MRU the authors performed sagittal and coronal halve-Fourier SSFSE scans in a 1.5 Tesla MR system. T1- and T2-weighted sequences were used in axial orientation to improve morphologic information. In 24 patients, preoperative data were compared with intraoperative findings.

RESULTS

Comparison of the different imaging modalities proved MRU to be able to provide more detailed information about the correct localization of stenoses along the urinary tract and the morphology of renal parenchyma. MRU showed the highest concordance of all imaging modalities with intraoperative findings.

CONCLUSION

As a reliable investigation, MRU has the potentials to replace IVU in preoperative diagnostic workup of hydronephrosis in childhood.

Functional and morphologic evaluation of congenital urinary tract dilatation by using combined static-dynamic MR urography: findings in kidneys with a single collecting system

PURPOSE

To assess combined static-dynamic magnetic resonance (MR) urography in the evaluation of congenital urinary tract dilatation in infants and children.

MATERIALS AND METHODS

Sixty-two patients with urinary tract dilatation underwent prospective examination with combined static-dynamic MR urography. A combination examination involved use of a static T2-weighted three-dimensional inversion-recovery fast spin-echo sequence and a dynamic T1-weighted two-dimensional fast field-echo sequence with gadopentetate dimeglumine-DTPA and furosemide application. Twelve additional patients underwent examination with only static MR urography. Thus, both image quality and morphologic features were assessed in 74 patients with the use of MR urography. The results were compared with those of ultrasonography and, when available, conventional urography or surgery. In 62 patients, the dynamic sequence was used to calculate split renal function from renograms generated from parenchymal regions of interest and to assess urinary excretion from whole-kidney renograms. Results were compared with those of diuretic renal scintigraphy (DRS) for split function (Spearman rank correlation coefficient) and urinary excretion (kappa coefficient).

RESULTS

Stenoses at the ureteropelvic (n = 33) and ureterovesical (n = 31) junctions and within the ureter (n = 3) and nonstenotic dilatation (n = 23) were clearly depicted, while the normal urinary tract (n = 51) was depicted in its entirety in 47 of 51 examinations. Image quality was considered good or excellent in 95% of the kidney-ureter units. For split renal function, dynamic MR urography and DRS showed significant correlation (r = 0.92, P <.001). For urinary excretion, MR urography and DRS showed strong agreement (kappa = 0.67), with concordant classification of urinary excretion in 59 (81%) of 73 abnormal kidney-ureter units and in all 47 (100%) normal kidney-ureter units.

CONCLUSION

Combined static-dynamic MR urography provides high-quality depiction of the urinary tract in infants and children, while allowing accurate determination of single-kidney function and reliable evaluation of urinary excretion.

Moderately T2-weighted images obtained with the single-shot fast spin-echo technique: differentiating between malignant and benign urinary obstructions

The purpose of this study was to determine whether a distinction could be made between benign and malignant urinary obstructions in moderately T(2)-weighted images obtained with the single-shot fast spin-echo technique. Forty-four lesions in 39 patients with urinary obstruction were evaluated with the single-shot fast spin-echo (SSFSE) technique with an effective TE of 90-100 ms and without fat saturation. Benign and malignant lesions were compared for the presence of ureteral wall thickening and a signal intensity relative to the proximal ureteral wall. Statistically significant differences were found between benign and malignant lesions in both morphologic change (P<0.0001) and signal intensity of the lesions at the obstruction position (P<0.0001). The combination of wall thickening and increased signal intensity as a predictor of malignant disease yielded a sensitivity of 88% and a specificity of 100%. Neither increased signal intensity nor wall thickening as a predictor of benign disease yielded a sensitivity of 89% and a specificity of 88%. The moderately T(2)-weighted SSFSE technique without fat saturation can accurately distinguish between benign and malignant urinary obstructions.

The management of urinary calculi in pregnancy

When a pregnant patient presents with a urinary calculus, the customary investigations and management must change in order to take into account the well-being of the developing fetus. Transabdominal or endovaginal ultrasound should be the initial imaging modality used in order to establish the diagnosis. A plain abdominal X-ray, limited intravenous pyelography, or retrograde pyelography is used secondarily if a definitive diagnosis is lacking. The treatment of first choice for urolithiasis in pregnancy is conservative, because 70-80% of stones will pass spontaneously. If conservative management fails, or in cases of sepsis, obstruction of a solitary kidney, or bilateral ureteric obstruction, then surgical intervention is indicated. Traditional surgical management consists of draining the obstructed collecting system with a ureteral stent or percutaneous nephrostomy tube with definitive treatment of the stone in the post-partum period. Ureteroscopic lithotripsy and stone extraction is another option that has been used safely and reliably with increasing frequency in many centers. Despite recent reports of using extracorporeal shock-wave lithotripsy, this treatment is still considered contraindicated in pregnancy.

MR urography in evaluation of acute flank pain: T2-weighted sequences and gadolinium-enhanced three-dimensional FLASH compared with urography. Fast low-angle shot

OBJECTIVE

The aim of this study was to compare the usefulness of breath-hold heavily T2-weighted sequences with gadolinium-enhanced three-dimensional fast low-angle shot (3D FLASH) MR urography in the evaluation of patients with acute flank pain.

SUBJECTS AND METHODS

Forty consecutive patients with symptoms of acute flank pain underwent MR urography followed immediately by excretory urography. Heavily T2-weighted (combined thin-slice half-Fourier acquisition single-shot turbo spin-echo [HASTE] and thick-slab single-shot turbo spin-echo) and 3D FLASH sequences were evaluated separately and independently by two experienced radiologists for the presence, cause, level, and degree of obstruction. Interobserver agreement was calculated using the kappa statistic. Excretory urography and the final clinical diagnosis were used as reference.

RESULTS

Twenty-six patients were found to have unilateral obstruction caused by ureteral stones. Both MR urography methods were excellent for detecting obstruction. In the detection of stones 3D FLASH was superior, with a sensitivity of 96.2% and 100% and specificity of 100% and 100% for observers A and B, respectively, compared with a sensitivity of 57.7% and 53.8% and a specificity of 100% and 100%, respectively, for T2-weighted sequences. The best degree of obstruction was seen with 3D FLASH, and the interobserver agreement was excellent for stone detection (kappa = 0.97).

CONCLUSION

T2-weighted sequences alone are not sufficient for examining patients with acute flank pain. However, the combined use of both T2-weighted and 3D FLASH sequences will ensure better confidence in the evaluation of acute suspected renal colic. MR urography can replace conventional excretory urography when the latter is contraindicated or undesirable.

MR virtual endoscopy of the upper urinary tract

OBJECTIVE

We investigated the feasibility of applying surface-rendered virtual endoscopy to the visualization of the upper urinary tract by processing unenhanced MR urography data sets.

SUBJECTS AND METHODS

Twenty-six patients, having neoplastic lesions (n = 9), calculi (n = 8), pelviureteric junction stenoses (n = 4), postoperative fibrotic strictures (n = 3), and extrinsic compressions of the ureter (n = 2), underwent unenhanced MR urography. Virtual endoscopy of the upper urinary tract was obtained using a thresholding technique and surface-rendering MR urography data sets.

RESULTS

Virtual endoscopy of the renal pelvis and calices was feasible in all cases on the side of the urinary obstruction. Virtual endoscopy of the ureter was obtained for a diameter of at least larger than 5 mm. The nondilated side could be partially explored in 11 cases (43%). The mean virtual endoscopy threshold required for the visualization of the urinary tract was 157.36-159.94. The mean time for virtual endoscopy was 13.8 min. Endoluminal masses were found in three (12%) of 26 cases on the renal pelvis (corresponding to neoplastic lesions), and occlusions, in 23 (88%) of 26 on the pelviureteric junction and ureter (neoplastic lesions and other abnormalities).

CONCLUSION

Virtual endoscopy of MR urography data sets is feasible in patients with urinary tract dilatation. Virtual endoscopy displays the renal pelvis, calices, and ureter and, moreover, can show endoluminal changes caused by abnormalities.

Magnetic resonance urography enhanced by gadolinium and diuretics: a comparison with conventional urography in diagnosing the cause of ureteric obstruction

OBJECTIVE

To compare the ability of magnetic resonance urography (MRU), enhanced using gadolinium and frusemide diuresis, and conventional intravenous urography (IVU) to diagnose the cause of ureteric obstruction.

PATIENTS AND METHODS

The study included 82 patients in whom IVU showed or suggested obstruction and who also underwent MRU. The images from both methods were interpreted by various investigators independently; two evaluated the IVU and two others the MRU, the latter being unaware of the diagnosis after IVU. If the diagnosis remained unclear, further investigations (e.g. computed tomography, retrograde pyelography or ureteroscopy) were conducted.

RESULTS

The diagnoses were ureteric calculi in 72 patients, ureteric tumours in eight and extra-ureteric tumours in two. In those with urolithiasis, the diagnosis was correct with IVU in 49 patients and with MRU in 64. The diagnosis in this group was incorrect with MRU in only two patients. The main reason for the failure of IVU was absent contrast medium excretion. Three of eight patients with ureteric tumours were correctly diagnosed by IVU but in three patients the diagnosis was incorrect. MRU correctly diagnosed seven of the eight patients in this group, with no false diagnosis.

CONCLUSION

IVU is currently likely to remain the standard procedure for imaging the upper urinary tract, but this study shows the potential of MRU when enhanced with gadolinium and frusemide. MRU may be helpful if there is a dilated system with no excretory function, in pregnant women, in children and in those with contrast medium allergy.

Feasibility and utility of respiratory-gated, gadolinium-enhanced T1-weighted magnetic resonance urography in children

RATIONALE AND OBJECTIVES

To evaluate the feasibility and utility of respiratory-gated, gadolinium-enhanced T1-weighted magnetic resonance (MR) urography in children.

METHODS

In a prospective study, 30 consecutive children, aged 3 weeks to 13.8 years, underwent MR urography. After intravenous injection of low-dose furosemide and gadopentetate dimeglumine, respiratory-gated, coronal, T1-weighted 3D-gradient-echo sequences were obtained at 1.5 T 5 to 30 minutes after contrast administration. Postprocessing of the data was performed using a maximum-intensity projection algorithm. In addition, precontrast half-Fourier rapid acquisition with relaxation enhancement MR urograms were obtained in 29 children.

RESULTS

Respiratory-gated, T1-weighted MR urography was successfully performed in all children without the need for sedation. Compared with the final diagnosis, prospective analysis of MR urography images revealed the correct diagnosis in 56 of 58 pelvicaliceal systems (96%). The ureteral morphology was correctly evaluated in 59 of 64 ureters (92%). The method showed limited efficiency for evaluating nonfunctioning renal units.

CONCLUSIONS

Respiratory-gated, gadolinium-enhanced T1-weighted MR urography is a feasible and effective diagnostic tool in the assessment of upper urinary tract morphology in children. It is especially useful in depicting nondilated collecting systems and ureters.

Early report: comparison of breath-hold MR excretory urography, Doppler ultrasound and isotope renography in evaluation of symptomatic hydronephrosis in pregnancy

AIM

To compare assessment by MR excretory urography (MREU), Doppler ultrasound and isotope renography of women with symptomatic hydronephrosis in pregnancy and to define its cause.

MATERIALS AND METHODS

Eleven women at 19-34 weeks of gestation were studied prospectively with gadolinium-enhanced breath-hold gradient echo MREU and transabdominal Doppler ultrasound compared with a 'gold standard' of isotope renography employing frusemide challenge. All studies were performed within 24 h, were reported independently in a blinded fashion and employed clearly defined criteria. Obstetric and infant outcomes were obtained.

RESULTS

There were no adverse reactions to gadolinium administration in pregnancy and no adverse obstetric or infant outcomes. Three of the 11 women were unable to tolerate the complete MREU protocol. Ultrasound indices could not be used to predict ureteric obstruction as shown by isotope renography. MREU agreed with renographic findings in five of the six cases with obstruction and in two without obstruction. MREU directly demonstrated hydronephrosis to result from extrinsic compression of the ureter between the gravid uterus and iliopsoas muscle.

CONCLUSION

MR excretory urography is a promising technique which affords equivalent functional and additional anatomical information to isotope renography. It is more accurate than Doppler ultrasound in the assessment of ureteric obstruction in pregnancy.Spencer, J. A. (2000). Clinical Radiology55, 446-453.

MR imaging-guided percutaneous nephrostomy and use of MR-compatible catheters in the nondilated porcine urinary tract

PURPOSE

To investigate technique and practicability of MR-guided percutaneous nephrostomy (MRPCN) and to test magnetic resonance (MR)-compatible catheters inside the urinary tract.

MATERIALS AND METHODS

In 10 healthy pigs, a percutaneous nephrostomy tube was placed into the nonobstructed pelvicaliceal system with use of exclusive MR guidance with a standard 1.5-T magnet. The urinary tract was visualized by intravenous injection of Gd-DTPA in combination with low-dose furosemide. The procedure was controlled with use of a T1-weighted turbo gradient-echo sequence in two orthogonal planes. The equipment for MRPCN included an 18-gauge MR-compatible puncture needle, a nitinol guide wire, and different 5-F MR catheters.

RESULTS

In all 10 animals, the puncture needle was safely directed into the nondilated target calix. Slight deviations of the needle were detected on both MR image planes, which enabled immediate correction. This technique achieved a "first attempt" puncture of the targeted calix in each animal. MR images accurately demonstrated the dysprosium labelled tip of the different inserted catheters. It proved essential to inject a gadolinium-insaline solution via these catheters to preserve the endoluminal contrast enhancement as long as necessary. Balloon catheters were directed and inflated inside the ureter under exclusive MR guidance. Complications such as perforation and leakage were visualized by MR imaging.

CONCLUSIONS

MRPCN is a promising technique for puncturing the pelvicaliceal system. The ability to successfully enter the urinary tract, even when it is nondilated, underscores the accuracy achievable with multiplanar MR imaging.

Diagnostic pitfalls of breath-hold MR urography in obstructive uropathy

Breath-hold MR urography (MRU) is being used with increasing frequency to evaluate urinary tract pathology. Although multiple studies have documented the accuracy of breath-hold MRU in the evaluation of obstructive uropathy, pitfalls associated with this technique may result in diagnostic errors. This essay illustrates both technical and interpretive pitfalls of MRU and suggests strategies for their recognition and avoidance.

Prospective comparison of unenhanced spiral computed tomography and intravenous urogram in the evaluation of acute flank pain

OBJECTIVES

To prospectively compare the diagnostic ability of unenhanced spiral computed tomography (NCCT) and intravenous urogram (IVU) in the evaluation of adults with acute flank pain.

METHODS

After giving informed consent, 106 adult patients with acute flank pain suspected of having urolithiasis underwent NCCT followed by IVU. Subsequent follow-up was scheduled within 72 hours in the Urology Clinic. Each NCCT was read by a single radiologist who was unaware of clinical history and IVU results. Each IVU was read by a different radiologist who was unaware of clinical history and NCCT results. Sensitivity, specificity, and positive and negative predictive values were determined for NCCT and IVU.

RESULTS

The diagnosis of ureterolithiasis was defined as unequivocal evidence of urolithiasis on either NCCT or IVP. Seventy-five of 106 patients evaluated were diagnosed with ureterolithiasis. Clinical follow-up was available in 74 (98%) stone patients and in 31 (100%) of 31 non-stone patients. In 72 of the 75 patients diagnosed with ureteral calculi, the NCCT made the diagnosis. IVU made the diagnosis in 65 of the 75 patients. Of the 31 patients without ureterolithiasis, the NCCT was negative in all cases. IVU was negative in 29 of the 31 cases. Unenhanced spiral CT was 96% sensitive and 100% specific (P <0.001). IVU was 87% sensitive and 94% specific (P <0.001). Compared with IVU, using the log odds ratio and Fisher's exact test, NCCT was significantly better able to predict the presence of urolithiasis (P=0.015).

CONCLUSIONS

NCCT accurately diagnoses ureterolithiasis in patients presenting with acute flank pain. NCCT is significantly better than IVU in determining the presence of urolithiasis.

Use of magnetic resonance urography

OBJECTIVES

Magnetic resonance urography (MRU) is a new technique that uses heavily weighted T2 coronal images with fat suppression pulse. Urine appears white on MRU, resembling an intravenous urogram (IVU). Contrast agents are not necessary. This study describes the use of MRU in the diagnosis and treatment of patients with hematuria.

METHODS

One hundred six patients with microscopic or gross hematuria and 6 normal volunteers underwent MRU between 1992 and 1995. A modified, heavily weighted T2 technique with intravenous administration of furosemide and ureteral compression was used. Thirty-two patients had other imaging techniques as well for comparison.

RESULTS

MRU provided high-resolution images in almost all cases; 73 (69%) had a normal MRU. Significant findings in the 33 patients with abnormalities included renal cysts in 17 (51%), renal cell carcinoma in 6 (18%), transitional cell carcinoma in 5 (15%), ureteropelvic junction obstruction in 3 (9%), and stones causing obstruction in 6 (18%). Five patients with renal failure also had good visualization of the entire urinary tract. MRU was comparable to other imaging modalities except in identifying nonobstructing calculi.

CONCLUSIONS

MRU provides an alternative to conventional imaging of the urinary tract, especially in those patients who have contraindications to ionizing radiation and contrast agents. Improvements in resolution, technique, and cost have to be addressed before it can be used regularly in urologic practice.

Contrast-enhanced magnetic resonance urography. First experimental results with a polymeric gadolinium bloodpool agent

RATIONALE AND OBJECTIVES

The authors investigated the feasibility of contrast-enhanced excretory magnetic resonance urography to visualize the nonobstructed urinary tract with a macromolecular gadolinium-based bloodpool agent.

METHODS

Excretory magnetic resonance imaging was performed in seven pigs using a T1-weighted three dimensional fast-field-echo sequence before and up to 120 minutes after administration of a gadolinium bloodpool prototype agent.

RESULTS

During the first 15 minutes after injection, the urographic effect was predominantly poor. Visualization of the entire urinary tract was excellent in four pigs and incomplete but satisfactory in three 105 minutes after injection. Furosemide application was tested in one case, which improved image quality effectively. Corresponding to the physiological excretion rate, signal measurements in the renal parenchyma revealed a gradual decrease of the initially distinct contrast enhancement.

CONCLUSIONS

T1-weighted contrast-enhanced magnetic resonance urography using a polymeric gadolinium bloodpool allows detailed visualization of the normal urinary tract, while information about the excretory function is obtained simultaneously. However, application of a diuretic seems to be essential to prevent lengthy examination duration.

Perirenal MR high signal--a new and sensitive indicator of acute ureteric obstruction

PURPOSE

This study was carried out to determine the incidence of perirenal magnetic resonance (MR) high signal in acute ureteric obstruction as demonstrated by half-Fourier acquisition single shot turbo spin-echo (HASTE) MR. In addition, we evaluated the sensitivity of this perirenal MR high signal as a predictor of acute ureteric obstruction.

MATERIALS AND METHODS

A prospective evaluation of 55 consecutive patients with suspected ureteric obstruction was carried out using the HASTE MR sequence. Images were compared to concurrent IV urography (IVU) or to computed tomography (CT) where these were available. Acute and chronic ureteric obstruction were differentiated by clinical evaluation.

RESULTS

Forty-one patients had obstructed kidneys. HASTE MR accurately predicted the presence of acute ureteric obstruction in 20/23 (87%) based on presence of perirenal MR high signal. None of these showed evidence of contrast medium extravasation on the concurrent i.v. urogram. 15/18 (83%) chronically obstructed kidneys demonstrated no perirenal high signal on HASTE MR, and the remaining three showed only a trace of perirenal high signal. CT showed perirenal stranding in only 2/8 patients with acutely obstructed kidneys.

CONCLUSION

In acute ureteric obstruction, HASTE MR shows perirenal high signal intensity much more commonly than IVU shows extravasation or CT showing perirenal stranding. The origin of this MR signal is uncertain but may represent oedema, lymphatic distension or free fluid from forniceal rupture. HASTE MR can accurately distinguish between acute and chronic ureteric obstruction based on the degree of perirenal high signal.

Fast MR imaging techniques: impact in the abdomen

The increased efficiency of MRI data acquisition has had a substantial impact on clinical MRI of the abdomen. Five particular applications that have thus been affected include breath-hold imaging of liver lesions (including detection, characterization, and biopsy), MR cholangiopan- creatography, practical chemical shift imaging (including liver and adrenal glands), dynamic imaging after contrast media injection, and MR angiography.

Fast imaging MR assessment of ureterohydronephrosis during pregnancy

PURPOSE

to assess the value of the fast imaging sequence called RARE-MR-Urography (RMU) for the diagnosis of pathologic ureterohydronephrosis during pregnancy.

MATERIALS AND METHODS

15 pregnant women with an acute flank pain were examined with RMU. Results were compared with those of ultrasonography (US), X-rays, and the evolution of symptoms.

RESULTS

the accuracy of RMU in the detection of urinary tract dilatation and the localization of the level of obstruction was excellent (100%). The determination of the type of obstruction, intrinsic vs. extrinsic, was always exact. RMU alone cannot specify the exact nature of the intrinsic obstruction. Ultrasonography gave less sensitive information in terms of level (60%) and type of obstruction (53%).

CONCLUSION

RMU is able to differentiate a physiological from a pathologic ureterohydronephrosis during pregnancy. It could be considered as a procedure of choice for special cases when US failed to establish this differential diagnosis.