Magnetic Resonance Renography Research Articles

Motion correction of free-breathing magnetic resonance renography using model-driven registration

IntroductionModel-driven registration (MDR) is a general approach to remove patient motion in quantitative imaging. In this study, we investigate whether MDR can effectively correct the motion in free-breathing MR renography (MRR).Materials and methodsMDR was generalised to linear tracer-kinetic models and implemented using 2D or 3D free-form deformations (FFD) with multi-resolution and gradient descent optimization. MDR was evaluated using a kidney-mimicking digital reference object (DRO) and free-breathing patient data acquired at high temporal resolution in multi-slice 2D (5 patients) and 3D acquisitions (8 patients). Registration accuracy was assessed using comparison to ground truth DRO, calculating the Hausdorff distance (HD) between ground truth masks with segmentations and visual evaluation of dynamic images, signal-time courses and parametric maps (all data).ResultsDRO data showed that the bias and precision of parameter maps after MDR are indistinguishable from motion-free data. MDR led to reduction in HD (HDunregistered = 9.98 ± 9.76, HDregistered = 1.63 ± 0.49). Visual inspection showed that MDR effectively removed motion effects in the dynamic data, leading to a clear improvement in anatomical delineation on parametric maps and a reduction in motion-induced oscillations on signal-time courses.DiscussionMDR provides effective motion correction of MRR in synthetic and patient data. Future work is needed to compare the performance against other more established methods.

Analytical validation of single-kidney glomerular filtration rate and split renal function as measured with magnetic resonance renography

Analytical validation of single-kidney glomerular filtration rate and split renal function as measured with magnetic resonance renography

Aromatherapy: Activating olfactory calcium-sensing receptors impairs renal hemodynamics via sympathetic nerve-mediated vasoconstriction.

This study determines whether the activation of olfactory calcium-sensing receptor initiates a sympathetic activation-dependent neurovascular reflex subsequently contributing to renal hemodynamic depression. Immunohistochemistry and nose-loading calcium-sensitive dye were used to explore the location and function of calcium-sensing receptor on the olfactory sensory neuron. The renal sympathetic nervous activity, renal hemodynamics and the microcirculation of kidney, liver and intestine were evaluated after liquid-phase intranasal administrations of saline, lidocaine, calcium-sensing receptor agonists and antagonist in sham and bilateral renal denervated rats. Real-time renal glomerular filtration rate was measured by a magnetic resonance renography. Calcium-sensing receptors were expressed on the cilia the olfactory sensory neuron and their activation depolarized olfactory sensory neuron and induced the calcium influx in the terminal side on olfactory glomeruli. Activating olfactory calcium-sensing receptors significantly increased arterial blood pressure and renal sympathetic nervous activities and subsequently decreased renal blood flow, renal, hepatic and enteral microcirculation. Cotreatments with calcium-sensing receptor antagonist or lidocaine inhibited these physiological alterations. The renal hemodynamic depressions by olfactory calcium-sensing receptor activation were significantly blocked by bilateral renal denervation. The intranasal manganese administration decreased the glomerular filtration rate. Calcium-sensing receptor acts as a functional chemosensory receptor on olfactory sensory neuron, and its activation causes the global sympathetic enhancement contributing to systematic vasoconstriction and subsequently depresses renal blood flow and glomerular filtration rate. These data implicate a possibly clinical aspect that several environmental stimuli may activate olfactory calcium-sensing receptors to evoke a sympathetic nervous system-mediated neurovascular reflex to depress renal hemodynamics.

Diagnosis and treatment of coexisting ureteropelvic junction obstruction and ureterovesical junction obstruction

Objective To explore the diagnosis, treatment options and outcomes of patients with ureteropelvic junction obstruction(UPJO) and ureterovesical junction obstruction(UVJO). Methods Clinical records of 12 children with UPJO and UVJO who received treatment in Children′s Hospital of Nanjing Medical University from April 2008 to December 2015 were reviewed.Presentations included prenatal hydronephrosis and symptoms caused by urinary tract infections.Ultrasonography, intravenous pyelography, magnetic resonance imaging and renography were performed before surgery. Results Four patients underwent nephrostomy, followed by pyeloplasty and eventually, ureteroneocystostomy.Five patients underwent heterochronic pyeloplasty plus ureteroneocystostomy.Two patients received pyeloplasty only.And another patient underwent heterochronic nephrostomy plus ureteroneocystostomy.The 12 patients received a 2.0 months to 2.5 years′ follow-up.Recurrent urinary tract infection and abdominal pain were relieved after the treatment.Ultrasonography showed hydronephrosis reduced obviously after the surgery. Conclusions UVJO patients with unparallel hydronephrosis should be considered with the coexistence of UPJO.Retrograde pyelography(RPG) is recommended for the diagnosis.And the treatment includes both pyeloplasty and ureteroneocystostomy.The patients diagnosed with UPJO should be first managed with pyeloplasty or nephrostomy instead of RPG.Subsequently anterograde pyelography can be performed to decide if the patients need additional ureteroneocystostomy. Key words: Child; Hydronephrosis; Ureteropelvic junction obstruction; Ureterovesical junction obstruction; Urography

Can Hyperpolarized 13C-Urea be Used to Assess Glomerular Filtration Rate? A Retrospective Study.

This study investigated a simple method for calculating the single-kidney glomerular filtration rate (GFR) using dynamic hyperpolarized 13C-urea magnetic resonance (MR) renography. A retrospective data analysis was applied to renal hyperpolarized 13C-urea MR data acquired from control rats, prediabetic nephropathy rats, and rats in which 1 kidney was subjected to ischemia-reperfusion. Renal blood flow was determined by the model-free bolus differentiation method, GFR was determined using the Baumann–Rudin model method. Reference single-kidney and total GFRs were measured by plasma creatinine content and compared to 1H dynamic contrast-enhanced estimated GFR and fluorescein isothiocyanate-inulin clearance GFR estimation. In healthy and prediabetic nephropathy rats, single-kidney hyperpolarized 13C-urea GFR was estimated to be 2.5 ± 0.7 mL/min in good agreement with both gold-standard inulin clearance GFR (2.7 ± 1.2 ml/min) and 1H dynamic contrast-enhanced estimated GFR (1.8 ± 0.8 mL/min), as well as plasma creatinine measurements and literature findings. Following ischemia-reperfusion, hyperpolarized 13C-urea revealed a significant reduction in single-kidney GFR of 57% compared with the contralateral kidney. Hyperpolarized 13C MR could be a promising tool for accurate determination of GFR. The model-free renal blood flow and arterial input function-insensitive GFR estimations are simple to implement and warrant further translational adaptation.

Movement correction in DCE-MRI through windowed and reconstruction dynamic mode decomposition

Images of the kidneys using dynamic contrast-enhanced magnetic resonance renography (DCE-MRR) contains unwanted complex organ motion due to respiration. This gives rise to motion artefacts that hinder the clinical assessment of kidney function. However, due to the rapid change in contrast agent within the DCE-MR image sequence, commonly used intensity-based image registration techniques are likely to fail. While semi-automated approaches involving human experts are a possible alternative, they pose significant drawbacks including inter-observer variability, and the bottleneck introduced through manual inspection of the multiplicity of images produced during a DCE-MRR study. To address this issue, we present a novel automated, registration-free movement correction approach based on windowed and reconstruction variants of dynamic mode decomposition (WR-DMD). Our proposed method is validated on ten different healthy volunteers’ kidney DCE-MRI data sets. The results, using block-matching-block evaluation on the image sequence produced by WR-DMD, show the elimination of 99% of mean motion magnitude when compared to the original data sets, thereby demonstrating the viability of automatic movement correction using WR-DMD.

Gd-Dots with Strong Ligand-Water Interaction for Ultrasensitive Magnetic Resonance Renography.

Magnetic resonance imaging contrast agents with both significantly enhanced relaxivity and minimal safety risk are of great importance for sensitive clinical diagnosis, but have rarely been reported. Herein, we present a simple strategy to improve relaxivity by introducing surface ligands with strong interaction to water molecules. As a proof of concept, NaGdF4 nanoparticles (NPs) capped by poly(acrylic acid) (PAA) show superior relaxivity to those capped by polyethylenimine and polyethylene glycol, which is attributed to the strong hydrogen-bond capacity of PAA to water molecules as revealed by theoretical calculation. Furthermore, benefiting from PAA and ultrasmall particle size, Gd-dots, namely PAA-capped GdOF NPs (2.1 ± 0.2 nm), are developed as a high-performance contrast agent, with a remarkable ionic relaxivity of ∼75 mM-1 s-1 in albumin solution at 0.5 T. These Gd-dots also exhibit efficient renal clearance with <3% of injected amount left 12 h post-injection. Ultrasensitive MR renography achieved with Gd-dots strongly suggests their great potential for practical applications.

Effect of Iodinated Contrast Media on Renal Function Evaluated with Dynamic Three-dimensional MR Renography

To assess the hemodynamic effect of iodinated contrast media (CM) on glomerular filtration rate (GFR) by using dynamic three-dimensional magnetic resonance (MR) renography in a rabbit model. This study was approved by the university animal care and use committee. Twelve healthy male New Zealand rabbits (body mass range, 2.5-3.0 kg) were included. Two of them were sacrificed before MR examination to obtain renal histologic samples as controls. The other ten rabbits completed 4-minute dynamic contrast material-enhanced MR imaging 24 hours before and 20 minutes after intravenous injection of iopamidol (370 mg of iodine per milliliter) at a dose of 6 mL per kilogram of body weight. Blood volume (V(B)), GFR, and tubule volume (V(E)) of the renal cortex were determined with a two-compartment kinetic model. Maximum upslope (K(m)), peak concentration (P(c)), and initial 60-second area under the curve (IAUC) of the whole kidney renogram curve were measured with semiquantitative analysis. The self-control data were compared by using the Student paired t test. Iopamidol significantly decreased cortical V(B) (mean, 42.53% ± 10.16 [standard deviation] before CM administration vs 27.23% ± 16.13 after CM administration; P < .01), V(E) (mean, 22.40% ± 11.69 before CM administration vs 11.51% ± 6.58 after CM administration; P < .01), and GFR (mean, 31.92 mL/100 g per minute ± 12.52 before CM administration vs 21.48 mL/100 g per minute ± 10.02 after CM administration; P < .01). Results of whole-kidney renogram analysis showed a decrease in K(m), P(c), and IAUC caused by iopamidol administration. High-dose iopamidol resulted in a marked decrease in renal function, which could be detected at dynamic three-dimensional MR renography.

Dynamic Contrast-Enhanced Magnetic Resonance Imaging Measurement of Renal Function in Patients Undergoing Partial Nephrectomy

To evaluate changes in single-kidney glomerular filtration rate (SK-GFR) using low-dose dynamic contrast-enhanced magnetic resonance (MR) renography (MRR) in patients undergoing partial nephrectomy for renal masses. In this Health Information Patient Protection Act-compliant prospective study, 18 patients with renal masses underwent preoperative MR imaging at 1.5 T for renal mass evaluation and low-dose gadolinium-enhanced MRR. Magnetic resonance renography was repeated approximately 48 to 72 hours and 6 months after partial nephrectomy. Single-kidney glomerular filtration rate was calculated from the MRR images, and the right and left kidney values were summed for total MR-GFR. Postoperative changes in SK-GFR and MR-GFR were compared with changes in estimated glomerular filtration rate calculated using modification of diet in renal disease formula, renal lesion characteristics, ischemia type (warm vs cold), and ischemia time. A decrease in the operated kidney SK-GFR was seen in 15 of the 18 patients, with a mean (SD) loss of 31% (23%), whereas estimated glomerular filtration rate decreased in 13 of the 18 patients with mean (SD) decrease of 19% (14%). Decrease in SK-GFR was greatest in the patients with warm ischemia time greater than 40 minutes and least in the patients with cold ischemia. In the immediate postoperative period, 6 of 7 patients (86%) with preoperative MR-GFR less than 60 mL/min per 1.73 m failed to demonstrate compensatory increase in SK-GFR in the nonoperated kidney, whereas 5 of 11 patients with baseline MR-GFR more than 60 mL/min per 1.73 m showed compensatory increase in nonoperated kidney SK-GFR. Magnetic resonance renography can demonstrate functional loss in the operated kidney and compensatory increase in the function of the contralateral kidney, thus enabling evaluation of various surgical techniques on kidney function.

2194 PREDICTING DIFFERENTIAL RENAL FUNCTION AND OBSTRUCTION WITH DYNAMIC CONTRAST-ENHANCED MR RENOGRAPHY (MRR) IN PATIENTS WITH URETEROPELVIC JUNCTION OBSTRUCTION (UPJO)

INTRODUCTION AND OBJECTIVES: To evaluate contrastenhanced magnetic resonance renography (MRR) for evaluation of renal function in patients with ureteropelvic junction (UPJ) obstruction as it correlates with diuretic nuclear renography (NR). METHODS: 13 patients with diagnosis of UPJ underwent dynamic MRR and lasix NR. Split renal function and assessment of mechanical or function obstruction on NR served as reference. MRR was processed to generate cortical-and-medullary enhancement curves. Bauman-Rudin model was applied to generate single-kidney renal function (SK-GFR). Split renal function ratio (Obstructed SK-GFR/ Obstructed Non-obstructed SK-GFR) obtained with MRR was compared to NR. Region-of-interest placed in renal pelvis of the obstructed kidney on MRR acquisition was used to calculate upslope-rate (signalintensity change over time divided by baseline signal-intensity). This was compared between functionally and mechanically obstructed renal units. RESULTS: There was excellent correlation between MRR and NR measure of split renal function ratio (r 0.91; p 0.01) with mean difference of less than 10%. Upslope-rate in mechanically obstructed units was significantly lower than functionally obstructed units (0.38 vs. 2.18 min-1; p 0.005). Upslope-rate cutoff of 0.85 min-1 could diagnose mechanical and functional obstruction with accuracy of 92% (12/13 patients). We were also able to calculate absolute measure of renal function (MR-GFR) which underestimates eGFR calculated with the Modification in Diet in Renal Disease (MDRD) equation. CONCLUSIONS: MRR can assess split renal function and discriminate mechanical from functional obstruction with high accuracy. A ‘one-stop-shop’ MR exam may be able to replace NR due to the ability to determine type of obstruction and also provide a pre-operative road map given the ability of MR to delineate vascular and renal anatomy to aid in surgical planning.

1431 USE OF MAGNETIC RESONANCE RENOGRAPHY TO EVALUATE CHANGES IN FUNCTIONAL RENAL VOLUME AND GLOMERULAR FILTRATION RATES IN KIDNEYS FOLLOWING PARTIAL NEPHRECTOMY FOR RENAL TUMORS

INTRODUCTION AND OBJECTIVES: Volume of functional renal parenchyma (FRP) is an important factor in glomerular filtration rate (GFR) following partial nephrectomy (PN), but is commonly overlooked. The loss of FRP may occur secondary to a variety of causes including surgical excision as well as ischemic/reperfusion injury and acute tubular necrosis following PN. Conventional imaging studies (CT and MRI) can estimate kidney volumes, but cannot measure FRP. Magnetic resonance renography (MRR) is a novel, clinically practical method of measuring single kidney GFR (SK-GFR) as well as the volume of FRP. In this study, we aim to investigate the impact of operative factors and tumor characteristics on FRP and SK-GFR loss as measured by MRR. METHODS: Between October 2009 and August 2011, 15 patients (mean age 54.5, range 33-73) receiving PN for kidney tumors underwent pre-op and early (48 hours) post-op MRR in an IRBapproved, prospective study. MRR was performed at 1.5 T using coronal 3D imaging with TWIST after administration of 4mL of gadolinium contrast. Semi-automated in-house software was used to generate FRP volume and signal curves of the aorta, cortex and medulla, with conversion to SK-GFR using a tracer kinetic model as previously described. Linear regression and unpaired t-tests were utilized for statistical analysis. Tumor characteristics were quantified using nephrometry score. RESULTS: Mean decrease in FRP volume was significantly correlated with mean decrease in SK-GFR (r 0.51, p 0.031). Nephrometry score did not have a significant correlation with FRP loss and decrease in SK-GFR (r 0.4, 0.35), however, nearness to the collecting system had the strongest association with SK-GFR decrease (p 0.002) in the immediate post-op period. Volume loss of FRP was a mean of 17 cc greater with warm ischemia compared to cold ischemia (p 0.031), and demonstrated moderate correlation with ischemia time (r 0.46, p 0.05). CONCLUSIONS: A significant correlation exists between loss of FRP and decrease in SK-GFR immediately after PN. Nearness to the collecting system appears to be associated with an increased loss of FRP and SK-GFR. Pre-operative MRR to assess baseline SK-GFR and tumor characteristics may be useful in preventing unnecessary FRP loss by appropriately modifying surgical technique as well as factors such as ischemia type and time.

Quantitative Evaluation of Acute Renal Transplant Dysfunction with Low-Dose Three-dimensional MR Renography

To assess prospectively the ability of quantitative low-dose three-dimensional magnetic resonance (MR) renography to help identify the cause of acute graft dysfunction. This HIPAA-compliant study was approved by the institutional review board, and written informed consent was obtained. Between December 2001 and May 2009, sixty patients with transplanted kidneys (41 men and 19 women; mean age, 49 years; age range, 22-71 years) were included. Thirty-one patients had normal function and 29 had acute dysfunction due to acute rejection (n = 12), acute tubular necrosis (ATN) (n = 8), chronic rejection (n = 6), or drug toxicity (n = 3). MR renography was performed at 1.5 T with three-dimensional gradient-echo imaging. With use of a multicompartment renal model, the glomerular filtration rate (GFR) and the mean transit time (MTT) of the tracer for the vascular compartment (MTT(A)), the tubular compartment (MTT(T)), and the collecting system compartment (MTT(C)) were calculated. Also derived was MTT for the whole kidney (MTT(K) = MTT(A) + MTT(T) + MTT(C)) and fractional MTT of each compartment (MTT(A/K) = MTT(A)/MTT(K), MTT(T/K) = MTT(T)/MTT(K), MTT(C/K) = MTT(C)/MTT(K)). These parameters were compared in patients in the different study groups. Statistical analysis was performed by using analysis of covariance. There were significant differences in GFR and MTT(K) between the acute dysfunction group (36.4 mL/min ± 20.8 [standard deviation] and 177.1 seconds ± 46.8, respectively) and the normal function group (65.9 mL/min ± 27.6 and 140.5 seconds ± 51.8, respectively) (P < .001 and P = .004). The MTT(A/K) was significantly higher in the acute rejection group (mean, 12.7% ± 2.9) than in the normal function group (mean, 8.3% ± 2.2; P < .001) or in the ATN group (mean, 7.1% ± 1.4; P < .001). The MTT(T/K) was significantly higher in the ATN group (mean, 83.2% ± 9.2) than in the normal function group (mean, 72.4% ± 10.2; P = .031) or in the acute rejection group (mean, 69.2% ± 6.1; P = .003). Low-dose MR renography analyzed by using a multicompartmental tracer kinetic renal model may help to differentiate noninvasively between acute rejection and ATN after kidney transplantation.

Comparison of Gd‐DTPA and Gd‐BOPTA for studying renal perfusion and filtration

To measure the systematic error in perfusion and filtration parameters derived from magnetic resonance (MR) renography caused by protein binding of MR contrast agents. Eight healthy Danish Landrace pigs were examined with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). In four pigs a bolus of gadopentetate-dimeglumine (Gd-DTPA; no protein binding) was injected, followed by gadobenate-dimeglumine (Gd-BOPTA; 10% protein binding). The order was reversed in the other four pigs. A two-compartment filtration model was generalized to allow for protein binding and fitted to whole-cortex region of interest (ROI) curves. Single-kidney plasma flow and volume, tubular flow (or GFR), and tubular transit time of both agents were compared. The data show a strong systematic underestimation (P < 0.001) in GFR by Gd-BOPTA (33 ± 7.2%), and no significant differences (P > 0.05) in plasma flow (2.2 ± 18%), plasma volume (-1.7 ± 7.8%) and tubular transit time (3.1 ± 7.2%). The order of injection had no significant effect. Theory and experiments agree that perfusion parameters of both agents are comparable, whereas GFR is underestimated with Gd-BOPTA due to the dependence of relaxivity on protein content. Hence, GFR cannot be measured with protein-bound contrast agents, but the proposed dual-agent protocol may produce new functional indices measuring protein filtration.

Role of MR renography in the evaluation of acute upper urinary tract obstruction

PurposeTo present the role of MR renography in diagnosis of upper urinary tract obstruction (UTO) with evaluation of diagnostic criteria for acute obstruction. Material and methodsThirty consecutive patients with obstructive anuria were included in our study. For identification of the cause of obstruction, all patients were subjected to plain abdominal X-ray (KUB), gray scale ultrasonography, non-contrast CT for the abdomen and pelvis (NCCT). There were five patients with bilateral obstruction and 25 with obstructed solitary functioning kidney, so the study included 35 units. All patients were subjected to radioisotope diuretic renography and magnetic resonance renography (MRR) before relief of obstruction and 3days after drainage. Of the 30 patients included, 20 were men and 10 women. ResultsAmong our patients the mean serum creatinine at time of presentation was 7±4.5mg/dl (range 2.4–12) and GFR ranged from 33 to 48ml/min (mean±SD; 38±4.2). All the renal units have hydronephrosis. The mean pre drainage SI values 133±22 (range 120–180). The mean time to peak (TP) for each unit was 171.6±78s and at isotope renography it was 320±66s. There was good corticomedullary differentiation (CMD) in 31 units and the remaining 4 showed loss of CMD differentiation. The CMD crossing time was 163.6±70.4s. Post kidney drainage the parenchymal SI was increased in 30 units, in 3 units there was drop and no change in 2 (r=0.29). There is relative reduction in the time to peak, it becomes 67±79s after drainage (r=0.76). ConclusionMR renography is a clinically valuable technique that provides diagnostic criteria to diagnose the acute urinary obstruction and allows follow up of renal function.

1080 PRE- AND POST-OPERATIVE MEASUREMENT OF SINGLE KIDNEY FUNCTION IN PARTIAL NEPHRECTOMY FOR RENAL MASSES USING MAGNETIC RESONANCE RENOGRAPHY

You have accessJournal of UrologyKidney Cancer: Localized1 Apr 20111080 PRE- AND POST-OPERATIVE MEASUREMENT OF SINGLE KIDNEY FUNCTION IN PARTIAL NEPHRECTOMY FOR RENAL MASSES USING MAGNETIC RESONANCE RENOGRAPHY Stella Kang, Aron Bruhn, Hersh Chandarana, Jeff Zhang, Vivian Lee, Michael Stifelman, and William Huang Stella KangStella Kang New York, NY More articles by this author , Aron BruhnAron Bruhn New York, NY More articles by this author , Hersh ChandaranaHersh Chandarana New York, NY More articles by this author , Jeff ZhangJeff Zhang New York, NY More articles by this author , Vivian LeeVivian Lee New York, NY More articles by this author , Michael StifelmanMichael Stifelman New York, NY More articles by this author , and William HuangWilliam Huang New York, NY More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2011.02.1118AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Partial nephrectomy (PN) and preservation of renal function is an integral part of managing patients with localized renal tumors. Current estimates of kidney function, including estimated GFR (eGFR) based on serum creatinine, have limited sensitivity and accuracy, and cannot assess single kidney GFR (SK-GFR). Magnetic resonance renography (MRR) has been shown to accurately and reliably estimate SK-GFR. The goal of this pilot study was to determine the feasibility of using MRR in pre- and post-operative evaluation of SK GFR in patients undergoing PN. METHODS In this IRB-approved, prospective study 13 patients with renal neoplasms underwent PN with preoperative and early (48 hrs) post-operative MRR, and 5/13 returned for 6-month post-operative MRR. eGFR was calculated using the Modification of Diet in Renal Disease equation. MRR was performed at 1.5 T using coronal TWIST after administration of 4 mL gadolinium contrast. Signal curves of the aorta, cortex, and medulla were converted to MR-GFR using a tracer kinetic model as previously described. RESULTS Preoperative MR-GFR ranged from 43 to 112 mL/min/1.73 m2 overall.11 patients showed decreased postoperative SK-GFR (mean -45%), detected by eGFR in only 7 patients. The greatest decrease in SK-GFR was seen in patients with warm ischemia time > 40 min (Table 1). Contralateral kidney SK-GFR increased in 4 patients and decreased in 4 patients (Fig 1). Only 1/5 with pre-op CKD had a compensatory response to surgery in the contralateral kidney at 48 hours. At 6 months, 3 of 5 patients recovered function to near-baseline MR-GFR. Table 1. Ischemia Type Baseline MR-GFR (mL/min/1.73 m2) Baseline Operated Kidney SK-GFR (mL/min/1.73 m2) Early Decrease in Operated Kidney SK-GFR (%) Cold Ischemia 76 33 26 +/- 28 Warm Ischemia (all cases) 73 36 41 +/- 27 Warm Ischemia (< 40 min) 69 32 34 +/- 25 Warm Ischemia (> 40 min) 82 44 57 +/- 30 CONCLUSIONS MRR is useful for evaluating patients with renal masses as an adjunct to anatomic imaging, providing single kidney function with only 5 minutes of additional scan time and minimal contrast. MRR may be useful tool in assessing proper patient selection, surgical technique (warm vs. cold ischemia), as well as current and future renal protective strategies for patients undergoing PN. © 2011 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 185Issue 4SApril 2011Page: e434-e435 Advertisement Copyright & Permissions© 2011 by American Urological Association Education and Research, Inc.MetricsAuthor Information Stella Kang New York, NY More articles by this author Aron Bruhn New York, NY More articles by this author Hersh Chandarana New York, NY More articles by this author Jeff Zhang New York, NY More articles by this author Vivian Lee New York, NY More articles by this author Michael Stifelman New York, NY More articles by this author William Huang New York, NY More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Kidney Function: Glomerular Filtration Rate Measurement with MR Renography in Patients with Cirrhosis

To assess the accuracy of glomerular filtration rate (GFR) measurements obtained with low-contrast agent dose dynamic contrast material-enhanced magnetic resonance (MR) renography in patients with liver cirrhosis who underwent routine liver MR imaging, with urinary clearance of technetium 99m ((99m)Tc) pentetic acid (DTPA) as the reference standard. This HIPAA-compliant study was institutional review board approved. Written informed patient consent was obtained. Twenty patients with cirrhosis (14 men, six women; age range, 41-70 years; mean age, 54.6 years) who were scheduled for routine 1.5-T liver MR examinations to screen for hepatocellular carcinoma during a 6-month period were prospectively included. Five-minute MR renography with a 3-mL dose of gadoteridol was performed instead of a routine test-dose timing examination. The GFR was estimated at MR imaging with use of two kinetic models. In one model, only the signal intensities in the aorta and kidney parenchyma were considered, and in the other, renal cortical and medullary signal intensities were treated separately. The GFR was also calculated by using serum creatinine levels according to the Cockcroft-Gault and modification of diet in renal disease (MDRD) formulas. All patients underwent a (99m)Tc-DTPA urinary clearance examination on the same day to obtain a reference GFR measurement. The accuracies of all MR- and creatinine-based GFR estimations were compared by using Wilcoxon signed rank tests. The mean reference GFR, based on (99m)Tc-DTPA clearance, was 74.9 mL/min/1.73 m(2) ± 27.7 (standard deviation) (range, 10.3-120.7 mL/min/1.73 m(2)). With both kinetic models, 95% of MR-based GFRs were within 30% of the reference values, whereas only 40% and 60% of Cockcroft-Gault- and MDRD-based GFRs, respectively, were within this range. MR-based GFR estimates were significantly more accurate than creatinine level-based estimates (P < .001). GFR assessment with MR imaging, which outperformed the Cockcroft-Gault and MDRD formulas, adds less than 10 minutes of table time to a clinically indicated liver MR examination without ionizing radiation. http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101338/-/DC1.

Compartmental modelling for magnetic resonance renography

A basic formalism is presented for generating and interpreting compartmental models for dynamic contrast-enhanced MRI data in the kidney. A graphical convention is introduced to represent and design compartmental models in a transparent and physically intuitive manner. A systematic system of notations and a simple set of rules allows direct translation of the graphical representation into a mathematical solution. The rules are derived from the physical principle of mass conservation, and the interpretation provided by the general tracer-kinetic theory of linear and stationary systems. The power of the formalism is illustrated using examples of models that have been proposed in the literature on perfusion MRI, and by generating a number of advanced models that may be of use in the kidney.

Estimates of glomerular filtration rate from MR renography and tracer kinetic models

To compare six methods for calculating the single-kidney glomerular filtration rate (GFR) from T(1)-weighted magnetic resonance (MR) renography (MRR) against reference radionuclide measurements. In 10 patients, GFR was determined using six published methods: the Baumann-Rudin model (BR), the Patlak-Rutland method (PR), the two-compartment model without bolus dispersion (2C) and with dispersion (2CD), the three-compartment model (3CD), and the distributed parameter model (3C-IRF). Reference single-kidney GFRs were measured by radionuclide renography. The coefficient of variation of GFR (CV) was determined for each method by Monte Carlo analyses for one healthy and one dysfunctional kidney at a noise level (sigma(n)) of 2%, 5%, and 10%. GFR estimates in patients varied from 6% overestimation (BR) to 50% underestimation (PR and 2CD applied to cortical data). Correlations with reference GFRs ranged from R = 0.74 (2CD, cortical data) to R = 0.85 (BR). In simulations, the lowest CV was produced by 3C-IRF in healthy kidney (1.7sigma(n)) and by PR in diseased kidney ((2.2-2.4)sigma(n)). In both kidneys the highest CV was obtained with 2CD ((5.9-8.2)sigma(n)) and with 3CD in diseased kidney (8.9sigma(n) at sigma(n) = 10%). GFR estimates depend on the renal model and type of data used. Two- and three-compartment models produce comparable GFR correlations.

Functional assessment of the kidney from magnetic resonance and computed tomography renography: Impulse retention approach to a multicompartment model

A three-compartment model is proposed for analyzing magnetic resonance renography (MRR) and computed tomography renography (CTR) data to derive clinically useful parameters such as glomerular filtration rate (GFR) and renal plasma flow (RPF). The model fits the convolution of the measured input and the predefined impulse retention functions to the measured tissue curves. A MRR study of 10 patients showed that relative root mean square errors by the model were significantly lower than errors for a previously reported three-compartmental model (11.6% +/- 4.9 vs 15.5% +/- 4.1; P < 0.001). GFR estimates correlated well with reference values by (99m)Tc-DTPA scintigraphy (correlation coefficient r = 0.82), and for RPF, r = 0.80. Parameter-sensitivity analysis and Monte Carlo simulation indicated that model parameters could be reliably identified. When the model was applied to CTR in five pigs, expected increases in RPF and GFR due to acetylcholine were detected with greater consistency than with the previous model. These results support the reliability and validity of the new model in computing GFR, RPF, and renal mean transit times from MR and CT data.

A Comparison of Low-Dose and Normal-Dose Gadobutrol in MR Renography and Renal Angiography

ObjectiveIt has been advocated that a reduced injection volume with highly concentrated (1 M) contrast material can produce a sharper bolus peak and an increased intravascular first-pass gadolinium concentration when compared with the use of a lower concentration (0.5 M). A higher concentration would also cause a reduction in dose. The purpose of our study was to test the use of a low dose (0.05 mmol/kg) of gadobutrol in magnetic resonance renography and angiography and compare the findings with a dose of 0.1 mmol/kg.Materials and MethodsOne-hundred-thirty-four patients referred for magnetic resonance angiography for suspected renovascular disease participated in the study. Contrast enhanced MR renography and angiography were performed after administration of a bolus of 0.1 mmol/kg or 0.05 mmol/kg gadobutrol in randomized patients. The relative signal intensity-time curves of the aorta, peripheral cortex and parenchyma, were obtained. Two radiologists evaluated the angiographic images and evaluated the quality of angiography.ResultsThe signal intensity with a low dose of gadobutrol was significantly lower in early phases, in the peripheral cortex (for 36, 54, 72 and 90 seconds), the parenchyma (for 36, 54, 72 seconds) and the aorta (for 18, 36, 54, 72 seconds). The decreases in the early phase obtained with a low dose of gadobutrol caused blunter time intensity curves. The difference in the quality scores of the readers for the angiographic images for the use of the two different doses was not statistically significant (p > 0.05).ConclusionA lower dose of gadobutrol can be used for MR renal angiography, but for MR renography the normal dose should be used.