Evaluation Of Hydronephrosis By Diffusion-Weighted Imaging And Dynamic Enhanced MRI

Background and ObjectiveHydronephrosis is a common disease of urological clinical practice, which is one of the major causes of renal insufficiency and renal failure in infants and children. Up to now, there are various approaches for trying to define what obstruction really means including ultrasonography (US), intravenous urography (IVU), diuretic renal scintigraphy (DRS) and so on. However, it is difficult to identify which hydronephrotic kidneys are really obstructive. Furthermore, there exists the intense controversy surrounding the evaluation of renal function.Recently, with the development of technique MRI can provide anatomical information that exceeds those provided by ultrasound, and additionally, computer-assisted post-processing techniques can be employed to quantify objectively the function and degree of obstruction as what of DRS does. At present, the quantitative analysis of renal function using MRU has some deficiencies, especially to severe impairment of renal function. How to standardize the parametric criterion of renal anatomy and function and further validate the use of MRU parameters for predicting renal obstruction is the situation of radiologists and urologists are facing.Therefore, the main objective of this thesis is to assess the value of contrast enhanced MRI in the evaluation of hydronephrosis by static-dynamic magnetic resonance urography (MRU) and diffusion weighted imaging (DWI) including morphologic and functional information, to investigate the function of undetected obstructive hydronephrotic kidney on IVU for providing value information to the choice of time and approach on surgical intervention, and to analysis the relationship between ADC and parameters on MRU in order to provide the evidences for predicting degree of renal damage and obstruction.This thesis included two parts:1 Functional evaluation of undetected obstructive hydronephrotic kidney on IVU by dynamic enhanced MRI.2 Functional evaluation of obstructive hydronephrosis by MR imaging: relationship between apparent diffusion coefficient and functional parameters on Gd-MRU.Part OneFunctional Evaluation of Undetected Obstructive Hydronephrotic Kidney onIVU by Dynamic Enhanced MRIMaterials and MethodsMaterials Twenty-one patients with unilateral obstructive hydronephrosis weresubjected to dynamic enhanced MRI, who had already been diagnosed by ultrasoundor determined by surgery.Methods The MRI image was collected before and at 1 min, 3 min, 5 min, 10 min, 15min, 30 min, 45 min and 60 min after contrast (Gd-DTPA) injection intravenously.Relative signal intensity (RSI) was calculated at different time. IVU was performed inall patients within 1 week pre-MRI. According to whether the urinary tract was shownon IVU, all patients were divided into detected hydronephrosis group (DH, including14 patients) and undetected hydronephrosis group (UDH, including 7 patients).Statistical analysisStatistical analyses were carried out by using the Statistical Package for Social Sciences (SPSS), version 10.0 for windows. Repeated measurement data of analysis of variance was used. P-values of <0.05 were considered to be statistically significant.Results 1 The kidneys in 7 patients with poor renal function were not observed on IVU. However, dynamic enhanced MRI of suffered kidney showed the parenchyma and collecting system. In addition, it also provides valuable information about the true location of obstruction.2 In DH, there were no differences of RSIs on renal parenchyma of hydronephrosis over all time periods, and RSIs for the collecting system of hydronephrosis were less than those of control at 3, 5 minute and were greater than those of control after 30 minutes(P<0.05).3 In UDH, RSIs for the parenchyma of hydronephrosis were greater than those of control after 10 minutes (P<0.05), and RSIs for the collecting system of hydronephrosis were less than those of control after 10 minutes (P<0.05).4 Compared with 14 patients with kidney shown on IVU, the RSI of the parenchyma after 10 minutes in other 7 patients was obviously increased(P<0.05), but that of the collecting system after 5 minutes was in lower level (P<0.05).Part TwoFunctional Evaluation of Obstructive Hydronephrosis by MR Imaging:Relationship between Apparent Diffusion Coefficient and Functional Parameterson Gd-MRUMaterials and MethodsMaterials Eleven patients with obstructive hydronephrosis were subjected to the MRIexamination. Inclusion criteria were unilateral or bilateral urinary tract dilatationdepicted at US and age more than 6 weeks. The study protocol was approved by theethics committee of the University of Zhengzhou, and informed consent was obtainedfrom the parents or guardians.MRI Scan All patients were placed supine in the core of a 1.5 T superconducting MRunit (Gyroscan ACS-NT, Philips, The Netherlands). Images were acquired with thefollowing: flow-compensated T1-weighted spin-echo, flow-compensated T2-weightedturbo spin-echo, flow-compensated respiratory-triggered three-dimensional (3D)turbo spin-echo. Then, the MR pulse sequence was used for diffusion-weighted imaging. At last, sequential dynamic contrast enhanced imaging was performed using a volumetric gradient echo technique covering the entire urinary tract. This volumetric sequence was repeated continuously for the initial 3 minutes. For the subsequent 7 minutes, the same sequence was used to acquire images at 1-minute intervals. Then, two sets of dynamic images were acquired at 15 minute and 30 minute.Post processing Post-processing was carried out, including measuring ADC values of the individual kidneys were by diffusion-weighted MR imaging and reformatting of 3D volume images from the static T2-weighted sequence. MIPs in the coronal plane were automatically generated for each of the dynamic volumes, and these were generally used for the assessment of the RTT. And the dynamic sequence was also used to generate time-intensity curves from two different manually selected regions of interest (ROIs), copied automatically onto every image of the sequence. Subsequently, automatic generation of SI vs. time curve should be obtained. Several key accidents have to be pinpointed on this curve.Statistical analysisStatistical analyses were carried out by using the Statistical Package for Social Sciences (SPSS), version 10.0 for windows. Two independent-samples t test and analysis of correlation were used. P-values of <0.05 were considered to be statistically significant.Results1 T2W Static-MRU showed 2 cases on bilateral hydronephrosis and 9 cases on unilateral hydronephrosis. There were total 13 hydronephrotic kidney, included 1 calculus on UPJ, 1 postoperative midureteric stricture , 1 non-obstructive ureter and 10UPJ.2 ADC values on control group were significant higher than hydronephrosis group (P<0.05).3 Based on RTT, all kidneys were classified as 11 normal (RTT≤4 min) and 11 equivocal (4 8 min).4 There was no difference between RSI for the cortical peak (RSIc) of hydronephrosis and those of control (P>0.05). However, RSI for the medullar peak (RSIm) of hydronephrosis were less than those of control (P<0.05).5 A good negative correlation had been found between ADC values and RTT, r=-0.642 (P=0.001). RSIm had also well correlated with RTT, r=0.693(P=0.001).Conclusions1 T2W static-MRU can initially assess the obstructive site of urinary obstruction.2 Dynamic MRU can provide more useful information about configuration and accurately and sensitively reflect the renal function for the obstructive hydronephrosis therefore, it also provide the reliable and useful information in distinguishing obstructive from unobstructive dilated systems to the urologists.3 Dynamic MRU can evaluate the function about hydronephrotic kidney, while the urinary tract was not shown on IVU. The study results can provide value information to the choice of time and approach on surgical intervention.4 Diffusion-weighted MR imaging has a potential value in the evaluation of the water molecules and blood flow of hydronephrotic kidneys.5 There is a good negative relationship between ADC values and RTT and there is a good positive relationship between ADC values and RSIm. A combination of DW MR imaging and Gd-MR imaging evaluated on morphologic and functional changes of different degrees of hydronephrosis from molecular level, and it provide the evidences for predicting impairment degree and obstruction.