Magnetic Resonance Urography (MRU) comprises an evolving group of techniques with the potential for allowing optimal noninvasive evaluation of many abnormalities of the urinary tract. Magnetic Resonance 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 paediatric or pregnant patients or when ionizing radiation is to be avoided.

Although Computed Tomography (CT) urography is nearing its potential in terms of spatial resolution,for tissue differentiation and elucidation of  the renal anatomy, MRU is a more nascent technology.

Many techniques such as ultrasonography, Intra Venous Urography (IVU), Micturating Cysto Uretro Graphy (MCUG), and radionuclide scintigraphy are used in assessing obstructive uropathy in children. However in uropathy, it is not always possible to reach a diagnosis with a single imaging method. Additional examinations increase the cost and result in time loss. On the other hand, there is still a need for anaesthesia for some children in scintigraphic examinations and the duration of this type of examination is generally longer than MR examinations.

MRU has become a popular imaging method in recent years because  some of the pathologies may only be seen with this and therefore its advantages override its disadvantages . Furthermore, it is also possible to quantitatively evaluate renal function with MRU.  The accuracy in the detection of urinary tract dilatation and the localization of the level of obstruction is excellent. MR Urography has been shown to be highly sensitive to the diagnosis of urinary tract obstruction. Demonstration of peri-nephric and peri-ureteric edema in obstruction helps in the differentiation of acute from non-acute urinary obstruction.

Tesla-2(T2) Weighted Magnetic Resonance Urograms simply generate static water images (static fluid MRU) the water  which we want to see is of course the urine itself, which can be regarded as an intrinsic contrast medium. This technique is independent of function, does not require the use of contrast media, and is especially successful in imaging dilated systems. The use of exclusively unenhanced T2-weighted sequences makes particular sense in non functioning hydronephrotic kidneys and in obstructive uropathy during pregnancy. Development of Magnetic Resonance Imaging (MRI) of static fluid has lead to the emergence of MRU as a potential imaging technique of the urinary system. Magnetic Resonance Urography (MRU) has been shown to be highly sensitive in the diagnosis of urinary obstruction, defining the severity of dilatation, the site and in the majority of cases the cause of obstruction.

MRU is performed by pursuing two different imaging strategies. On the one hand,  heavily T2-weighted turbo spin echo sequences are employed for obtaining  unenhanced static-water images of the urinary tract. On the other, the T1 – weighted MRU technique  imitates conventional intravenous pyelography and is, therefore, referred to as excretory MR urography. All cases of dilated  urinary tract are well visualized by MR-Urography as opposed to by drip-infusion pyelography. Thus MRU is deemed  to be an effective method  of visualizing  the dilated  urinary tract non-invasively and in a relatively short time.

MR UROGRAPHY IN DILATED URINARY TRACT DISORDERS:

The accuracy in the detection of urinary tract dilatation and the localization of the level of obstruction is excellent.(21) The determination of the type of obstruction, intrinsic versus extrinsic is 80% by IVU and 60% by MRU. MRU alone cannot specify the nature of obstruction. MRU is a non traumatic technique ,needs no iodinated contrast medium and can be widely  adopted  in the diagnosis of  urinary tract disorders.(19)Functional information about the obstructed system also cannot be obtained.

 RARE-MRU may be considered in circumstances when there are contraindications to IVU(allergy to contrast medium, severe renal failure), impairment of renal excretion and failure to locate the level of obstruction.(9) The absence of ionizing radiation favours the promotion of this procedure especially to study hydroureteronephrosis during pregnancy.(6)The development of HASTE scans which combine ultrafast acquisition with high resolution images of both renal parenchyma and dilated urinary tract improved the quality of images obtained.(22)MRU 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 detailed functional assessment.(23)

Imaging of the non-obstructed urinary tract,however, posses greater challenge because there is no obstruction and urine flow is not impeded. Hence artificial induction of stasis and distension in the system is accomplished with application   of   external    ureteral    compression    followed    by   intravenous administration of furosemide. Furosemide causes rapid diuresis, which distends the system whereas external ureteral compression slows the flow of urine enough to allow adequate imaging.

Anatomical detailing was really improved after the diuretic administration ,especially in the study of major cayceal system.(24)However the rapid diuresis induces flow of urine distal to the compression device may cause artifacts and result in poor visualization of the distal ureter and bladder. This problem may be related to the quantity of furosemide administered, but can be circumvented by means of acquisition of two separate image sets. Because the bladder is best imaged when full, it should be imaged when full before the administration of the diuretic. The patient then voids, external compression is applied and the furosemide is administered. The second set of images includes the proximal urinary tract. Thus MRU in two stages provides good visualization of the renal parenchyma in all cases of both obstructed and non-obstructed systems.

 In all cases in which obstruction is present or furosemide enhancement is used, both the collecting system and the renal parenchyma are well visualized. In cases where standard MR-Urography (no furosemide given) is performed and physiologic obstruction is not present, visualization of the collecting system varies widely. The anatomic  and functional information shown on MR urography is superior to that shown on sonography and scintigraphy and has the potential to allow understanding of the pathophysiology of PUJ obstruction.(25)

MRI is gaining more and more importance since this imaging modality allows for a comprehensive examination of almost the complete spectrum of urologic diseases.(26 )The degree and cause of ureteric obstruction can be diagnosed with high sensitivity and specificity. Paediatric and pregnant patients can be examined as well as donors before and patients after renal transplant.(27)Combining renal MR imaging and MR urography can serve as a comprehensive imaging of the renal parenchyma, collecting system and bladder in patients who cannot go to routine radiographic studies, such as pregnant or pediatric patients, patients with severe allergy to contrast media, or patients with impaired renal function.(28)However, various studies proved that, in cases of calculus diseases, Computed Tomography Scan and MRU give same accuracy. The technique has less observer variability and is more accurate than CT in detecting evidence of acute obstruction such as perirenal fluid.(29)

The role of MRU in tumor-induced stenosis of the urinary tract in coronal plane with T2-turbo-spin-echo sequence and MIP (maximum intensity projection) reconstruction is also worth praising. The level of stenosis is correctly seen.

Another MR sequence is using half-Fourier acquisition single shot turbo spin echo (HASTE) in the assessment of ureteric obstruction.(30) With HASTE-MRU, it is possible correctly to diagnose, grade and locate the level of obstruction in almost all kidneys (100%).(31)It provides in a rather short time “all in one approach” of the pathological process.(32)MRU is comparable to other imaging modalities except in identifying non obstructing calculi.(33)In all likelihood ultrasonography will continue to be used as a primary screening tool.(34)

Heavily T2-weighted fast-spin-echo sequence with post procedure MIP reconstructions can determine the presence of hydronephrosis and obstruction in all cases.(35) The cause of hydronephrosis can also correctly be identified in all cases of hydronephrosis. This MRU is a reliable non-invasive method for detecting the abnormalities of the urinary tract.

There is a possible role of MR imaging in the assessment of patients with urinary tract obstruction by combining MR-pyelography and conventional MR imaging.35 Respiratory compensated Tl-weighted spin-echo and T2 weighted TSE sequences are obtained MRP images are reconstructed with a MIP algorithm. Then excretory Urography or/and ascending pyelography is also performed. The dilated tract and level of obstruction can be accurately depicted. Additionally the cause of obstruction can also be demonstrated in 90% cases, if combined with Cine MRU.(36) In cases of obstructive hydroureteronephrosis, MR imaging, combining MR-pyelography and conventional MR sequences is an accurate technique in the assessment of the level and cause of obstruction. Oral negative contrast agent also can be used to reduce the gastrointestinal tract induced artifacts.(37)

The kidneys maintain homeostasis by filtering and excreting metabolic waste products, regulating acid base balance, and moderating blood pressure and fluid volume. Because decreasing renal function accompanies renal disease, monitoring renal function permits assessment of disease progression and prognosis and is used to guide patient management and therapy, researchers realized that MR imaging is the only single imaging modality with the potential to deliver a comprehensive anatomic and functional examination of the kidneys with minimal risk to the patient and minimal pitfalls. The MR imaging evaluation of renal function typically centers on visualizing the passage of contrast material through the kidney. The contrast agents used in MR imaging are usually gadolinium chelates, such as Gadolinium Diethylenetriamine Pentacetic Acid (Gd-DTPA). Gadolinium enhanced MRU and T(2)-wighted (HASTE) MRU turns out to be equivalent in the assessment of obstructed but normal functioning upper urinary tracts.(38)

 The paramagnetic properties of gadolinium cause a decrease in the Tl and T2 relaxation times of nearby tissues and fluids. The physiologic behaviour of gadolinium is governed by the properties of the agent to which it is chelated. DTPA is a substance that like inulin is freely filtered by the glomerulus and is neither absorbed nor secreted by the renal tubules. When tagged to gadolinium its path through the kidneys is traced with Tl weighted MR imaging. Such imaging examinations are also referred to as "MR renography". The potential of MRU when enhanced with gadolinium and furesemide is excellent and is useful if there is a dilated system with no excretory function.(39)

MRU is superior to other modalities because it provides better anatomic and functional imaging in a single setting.(11) Some other sequences in MR imaging are a T2 weighted three dimensional inversion recovery turbo spin echo sequence, dynamic MR imaging using a two dimensional Tl- weighted GRE sequence using 0.1 mmol/kg of Gd-DTPA and 0.3 mg/kg of furosemide for distension of the urinary tract, and diuretic renal scintigraphy using Technetium 99m and 0.5mg/kg of furosemide. MRU showed the level of stenosis and the more proximal urinary tract in all cases whereas IVU showed the same in only half the cases. Ultrasound almost never shows the level of obstruction. MRU is also superior to IVU and ultrasound in demonstrating the urinary tract distal to the level of obstruction. A distinct advantage of MRU is its ability to detect other findings such as various fluid collections (using the static sequence) and their causes (using the dynamic sequence to depict contrast extravasation).

The quantitative analysis of MR-renography data in the anatomic and functional evaluation of kidneys of patients with suspected unilateral hydronephrosis is specific for specific clinical settings, like acute flank pain.(40) It consists of three 8mm thick coronal sections acquired with a fast spoiled GRH sequence following injection of 0.05 mmol/kg of gadolinium-based contrast. The medullary enhancement pattern is delayed in hydronephrotic as compared with normal kidneys.MR pyelography ,made with ultrafast breath-hold sequences,provides the chance to pyonephrosis requiring an immediate drainage of the kidney before major complications develop.(41)

To summarize static MRU is performed using a heavily T2 - weighted pulse sequence to obtain static-fluid images of the urinary tract. T2-weighted MRU has proved to be excellent in the visualization of the markedly dilated urinary tract, even if the renal excretory function is quiescent.(16) Static-fluid MRU is less suitable for imaging of disorders that occur in the non-dilated collecting system. Gadolinium excretory MRU allows obtaining high-quality images of both non-dilated and obstructed urinary tracts in patients with normal or moderately impaired renal function.

A major limitation of MRU is the detection of urinary calculi, which, generally appear as filling defects, or signal voids on both heavily T2 weighted and contrast enhanced three dimensional spoiled gradient images.(42)These findings are not specific for calculi and may represent blood clot, gas, fungal ball and sloughed papilla. Furthermore, it is very difficult to visualize small calculus. On occasion the distinction of ureteral stone from vascular impression and physiologic peristalsis may be difficult.

Another limitation is relatively poor spatial resolution. Current MRU  techniques do not provide visualization of anatomic detail of the calyces, infundibula and ureters equivalent to IVU or CT Urography. It is possible that small urothelial tumors go unnoticed.(42)

In addition to obvious mechanical causes from obstruction; eg. - ureteral calculus, ureteral tumor, ureteral ligation, obstruction may sometimes be functional. The functional conditions produce increased resistance to the outflow of urine from the urinary tract, not by specific mechanical block but by interference with the physiologic processes that normally transports the urine in the antegrade direction. Such conditions include deficiency of ureteral peristaltic activity, presence of retrograde peristalsis and the presence of vesico-ureteric reflux due to incompetence of uretero-vesical valve mechanism.(42)

Rare congenital anomalies, e.g. Bladder agenesis, bladder hypoplasia are usually not compatible with life. Extrophy of urinary bladder includes many variations, commonest being classical variety which includes epispadic complex and separation of pubic bones more than 10mm.

Inflammatory diseases of urinary bladder can cause chronic obstruction to the flow of urine. Common causes being granulomatous cystitis, cystitis emphysematosa, cystitis cystica, cystitis glandularis, Koch's, Malakoplasia etc.

Bladder calculi are also common causes of urinary obstruction. Bladder calculi are usually composed of a mixture of Magnesium, ammonium and phosphate apatite or of uric acid mixed with urates. Most bladder calculi are missed on plain film as they are non-opaque (uric acid). But these can be detected on T2W MRI, although finding is not so specific.

Primary bladder tumors are mostly epithelial in origin.(15) All epithelial tumors are malignant, the majority being of the transitional cell type, with squamous cell carcinoma (1.5-10%) and adenocarcinoma (1%) being relatively uncommon. Non-epithelial tumors may be benign (leiomyoma, fibroma) or malignant (leiomyosarcoma and rhabdomyosarcoma). MR Urography is a very specific modality to diagnose as well as grade the urothelial tumors.

Source of data: In my study, total of 35 patients have taken part after elaborate discussion with them and after informing about the study design and protocol. Patients, included in my study group were inpatients, out patients and referrel patients of Sri Chamundeshwari Medical College Hospital and research institute ,channapatna who detected to have signs and symptoms of obstructive uropathy based mainly on the clinical background. Some of the patients also underwent Ultrasonography, which showed dilatation of the renal pelvi-calyceal system. Study participants were randomly chosen who were detected to have signs of obstructive uropathy on clinical background. The study was conducted after getting clearance from the ethical committee. Method of collection of data : a) Study Design :Descriptive study b) Study Place : Department of Radio Diagnosis, Sri Chamundeshwari Medical College Hospital and research institute, channapatna c) Study duration :Sep 2024 to June 2026 d) Sample Size :35. Inclusion criteria are: a) Patients presented with acute urinary symptoms. b) Patients with biochemical abnormalities. c) Non-conclusive other radiological investigations. d) Some cases are contraindicated for X-Ray and CT Urography , specially pregnant patients and female patients in child bearing age are also included in our study group. Exclusion criteria are: a) Patients with metallic implants in their bodies. b) Patients with prosthetic heart valves or pace-marker c) Patients with suspected metallic foreign body and any organ of the body, especially eye. d) Those cases of obstructive uropathy where the cause is distal to the urinary bladder, e.g., in the urethra or in the prostate.

This study was conducted in the Department  of  Radio  Diagnosis, Sri Chamundeshwari Medical College Hospital  and research institute, channapatna  from September 2024 to June 2026  The study comprised of a total of 35 patients after elaborate discussion with them and after informing about the study design and protocol.

35 patients underwent MRU who showed the clinical signs of hydronephrosis and hydroureter. Out of these 35 patients, all patients were detected to have hydronephrosis and/or hydroureter and MR Urography could be able to locate the cause of dilatation of pelvi-calyceal system. One case showed no detectable cause for dilated collecting system. However clinical history proved that they had suffered from recent passage of calculus.

 MRU using heavily T2 weighted sequences is very accurate in demonstrating the cause, level of obstruction and degree of dilatation of the collecting system in all the patients without ionising radiation and without the use of IV contrast media.  Only case showed no detectable cause for dilated collecting system. However clinical history proved that the patient had suffered from recent passage of calculus and the cause of dilated collecting system was post passage residual dilatation.  Hence MRU is a useful non-invasive method for assessing a variety of urinary tract disorders.  It is also useful in the evaluation of pediatric and pregnant patients without the use of ionising radiation, patients with allergy to contrast media and patients with biochemical abnormalities  So, in near future it may emerge as an alternative to the other available radiological investigations.  Etiological findings in cases of dilated urinary system Etiology in cases of unilateral hydronephrosis Etiology in cases of bilateral Hydronephrosis Summary This study entitled "Role of Magnetic Resonance Urography in dilated urinary tract disorders” included 35 patients The MR urography was performed using 1.5 Tesla MRI Machine (Siemens Magetom sepra ) with phased array body coils. Dilated urinary tract or hydronephrosis is found to be more commonly unilateral (80%) and the commonest age group is 11-20 years. Males are more commonly affected (M:F = 1.9:1) Among the various clinical presentation, the most common is only pain abdomen (54.28%). 31.4% of patients presented with two or more clinical symptoms. The commonest cause of unilateral hydronephrosis is calculus disease (34.18%) followed by pelvi-ureteric junction obstruction (20%) and stricture ureter (20%). Majority of unilateral hydronephrosis is on the left side (52.3%) and with mild degree dilated collecting system (61.9%). Male predominance is noted (M:F = 2:1) in case of unilateral hydronephrosis . The commonest cause of bilateral hydronephrosis is stricture ureter(37.71%), followed by pelvi-ureteric junction obstruction (21.42%). Majority of the patients with bilateral hydronephrosis presented with severe degree dilatation of collecting system (42.85%). Male predominance is noted (M:F = 1.8:1) in case of bilateral hydronephrosis . Majority of the patients suffering from calculus diseases presented with two or three clinical features.(50%) and majority of them show mild hydronephrosis (75%). The commonest location of calculi is in the vesicoureteric junction (41.6%). Males are affected more commonly (M:F~5.:1). Calculi are found to be common on left side (66.6%). The most common clinical presentation in patients with pelvi-ureteric junction obstruction is only pain abdomen (71.42%) and majority show severe hydronephrosis (71.42%). Males are affected for more commonly (M:F-2.5:1).Majority of the patients show unilateral obstruction with equal incidence on right and left side (57.15%) and to present with normal blood urea level. Majority of the patients with ureteral stricture showed moderate hydronephrosis (57.14%). Female predominance is noted (F:M-2.5:1).Majority of the patients show bilateral obstruction (71.4%). 2 cases of carcinoma bladder with infiltration of the ureteral orifice and distal ureter was well demonstrated by MRU and 2 cases of bladder diverticulum pressing on the distal ureter causing mild dilatation of the collecting system were well depicted. Static fluid MRU also proved useful in diagnosing anomalies of urinary tract like megaureter and ectopic malrotated kidney. MRU could also demonstrate bilateral severe dilatation of the collecting system in a female patient with uterine prolapse with bladder base herniation. One female patient who had ureterocele , MRU could well demonstrate focal dilatation of the distal ureter abutting the bladder base. Only one case with mild degree hydronephrosis show no obvious pathology that could be picked up by MRU. However, after taking proper clinical history, it was found to be due to post passage residual dilatation.

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