In vitro assessment of a 3D segmentation algorithm based on the belief functions theory in calculating renal volumes by MRI

Comparative Study Between Functional MR Urography and Renal Scintigraphy to Evaluate Drainage Curves and Split Renal Function in Children With Congenital Anomalies of Kidney and Urinary Tract (CAKUT)

Background: Obstructive congenital anomalies of the kidney and urinary tract have a high risk of kidney failure if not surgically corrected. Dynamic renal scintigraphy is the gold standard technique to evaluate drainage curves and split renal function (SRF). Objectives: To compare functional magnetic resonance (MR) urography with dynamic renal scintigraphy in measuring volumetric SRF and in the classification of drainage curves in patients with congenital anomalies of the kidney and urinary tract. Materials and Methods: We retrospectively collected patients with hydroureteronephrosis or pelvicalyceal dilatation at renal ultrasound, who underwent both functional MR urography and dynamic renal scintigraphy (DRS) within 6 months. DRS studies were evaluated by a single nuclear medicine physician with a double reading. Functional MR urography renograms were blind evaluated twice by two radiologists. The functional MR urographyintra- and inter-reading agreements as well as the agreement between the two imaging techniques were calculated. SRF was evaluated by Area Under the Curve and Rutland-Patlak methods. Drainage curves were classified as normal, borderline or accumulation patterns by both the techniques. Results: Fifty-two children were studied, 14 with bilateral involvement. A total of 104 kidney-urinary tracts were considered: 38 normal and 66 dilated. Considering Area Under the Curve and Rutland-Patlak for SRF, the intra- and inter-reader agreements of functional MR urography had excellent and good results, respectively, and the two techniques demonstrated a good concordance (r2: 67% for Area Under the Curve and 72% for Rutland-Patlak). Considering drainage curves, the inter-readers agreement for functional MR urography and the concordance between the two techniques were moderate (Cohen's k, respectively, 55.7 and 56.3%). Conclusions: According to our results, there are no significant differences between functional MR urography and DRS in measuring volumetric SRF and in the classification of drainage curves in patients with congenital anomalies of the kidney and urinary tract.

Development and Evaluation of a Semi-automated Segmentation Tool and a Modified Ellipsoid Formula for Volumetric Analysis of the Kidney in Non-contrast T2-Weighted MR Images

Volumetric analysis of the kidney parenchyma provides additional information for the detection and monitoring of various renal diseases. Therefore the purposes of the study were to develop and evaluate a semi-automated segmentation tool and a modified ellipsoid formula for volumetric analysis of the kidney in non-contrast T2-weighted magnetic resonance (MR)-images. Three readers performed semi-automated segmentation of the total kidney volume (TKV) in axial, non-contrast-enhanced T2-weighted MR-images of 24 healthy volunteers (48 kidneys) twice. A semi-automated threshold-based segmentation tool was developed to segment the kidney parenchyma. Furthermore, the three readers measured renal dimensions (length, width, depth) and applied different formulas to calculate the TKV. Manual segmentation served as a reference volume. Volumes of the different methods were compared and time required was recorded. There was no significant difference between the semi-automatically and manually segmented TKV (p = 0.31). The difference in mean volumes was 0.3 ml (95% confidence interval (CI), -10.1 to 10.7 ml). Semi-automated segmentation was significantly faster than manual segmentation, with a mean difference = 188 s (220 vs. 408 s); p < 0.05. Volumes did not differ significantly comparing the results of different readers. Calculation of TKV with a modified ellipsoid formula (ellipsoid volume × 0.85) did not differ significantly from the reference volume; however, the mean error was three times higher (difference of mean volumes -0.1 ml; CI -31.1 to 30.9 ml; p = 0.95). Applying the modified ellipsoid formula was the fastest way to get an estimation of the renal volume (41 s). Semi-automated segmentation and volumetric analysis of the kidney in native T2-weighted MR data delivers accurate and reproducible results and was significantly faster than manual segmentation. Applying a modified ellipsoid formula quickly provides an accurate kidney volume.

Automated segmentation and volumetric analysis of renal cortex, medulla, and pelvis based on non-contrast-enhanced T1- and T2-weighted MR images

OBJECT

The aim of our study was to enable automatic volumetry of the entire kidneys as well as their internal structures (cortex, medulla, and pelvis) from native magnetic resonance imaging (MRI) data sets.

MATERIALS AND METHODS

Segmentation of the entire kidneys and differentiation of their internal structures were performed in 12 healthy volunteers based on non-contrast-enhanced T1- and T2-weighted MR images. Two data sets (each acquired in one breath-hold) were co-registered using a rigid registration algorithm compensating for possible breathing-related displacements. An automatic algorithm based on thresholding and shape detection segmented the kidneys into their compartments and was compared to a manual labeling procedure.

RESULTS

The resulting kidney volumes of the automated segmentation correlated well with those created manually (R(2) = 0.96). Average volume errors were determined to be 4.97 ± 4.08% (entire kidney parenchyma), 7.03 ± 5.56% (cortex), 12.33 ± 7.35% (medulla), and 17.57 ± 14.47% (pelvis). The variation of the kidney volume resulting from the automatic algorithm was found to be 4.76% based on the measuring of one volunteer with three independent examinations.

CONCLUSION

The results demonstrate the feasibility of an accurate and repeatable automatic segmentation of the kidneys and their internal structures from non-contrast-enhanced magnetic resonance images.

Assessment of kidney volumes from MRI: acquisition and segmentation techniques

OBJECTIVE

The prevalence of chronic kidney disease (CKD) is increasing worldwide. In Europe alone, at least 8% of the population currently has some degree of CKD. CKD is associated with serious comorbidity, reduced life expectancy, and high economic costs; hence, early detection and adequate treatment of kidney disease are important.

CONCLUSION

We review state-of-the-art MRI acquisition techniques for CKD, with a special focus on image segmentation methods used for the estimation of kidney volume.

Assessing renal parenchymal volume on unenhanced CT as a marker for predicting renal function in patients with chronic kidney disease

OBJECTIVES

To estimate renal volume in chronic kidney disease (CKD) patients using a semiautomated software and compare them with split renal function estimates from radionuclide renogram (RR). We proposed that renal volume from unenhanced computed tomography (CT) scans may serve as surrogate marker for assessing renal function in CKD patients.

MATERIALS AND METHODS

Unenhanced multidetector CT scans of 26 patients with CKD (estimated glomerular filtration rate [eGFR] <60 mL/kg/body surface area [BSA]) and 10 controls (eGFR >60 mL/kg/BSA) were analyzed to calculate renal volumes using a semiautomated software (AMIRAV5.2.0). Volumes obtained were then correlated with corresponding eGFR and split renal function estimates from RR. Volumes were also compared with those obtained on enhanced scans in 10 cases (five disease group, five controls). Bland-Altman analysis was used to assess agreement between methods.

RESULTS

A moderately positive correlation was found between renal volume obtained on unenhanced CT and eGFR (r = 0.65, P < .0001), whereas a significantly high correlation with split function estimates from RR (r = 0.95, P < .001) was found. Bland-Altman analysis revealed a good agreement between renal volume from CT and renal function from RR (34/36 observations were within 95% CI and there were two outliers). Correlation between volumes obtained from unenhanced and enhanced CT scans was also significant (r = 0.96).

CONCLUSION

In patients with CKD, renal volume derived from unenhanced CT can possibly serve as a surrogate marker for assessing and monitoring renal function reserves to plan further management.

[Imaging evaluation of renal function: principles and limitations]

The kidney performs multiple functions. Glomerular filtration is the most studied of these functions. In clinical practice, the surgical indication for patients with unilateral uropathy is frequently based on the split renal function as demonstrated by scintigraphy. MRI is not yet validated as a technique but nonetheless offers an interesting non-radiating alternative to achieve both morphological and functional renal evaluation. Recent pulse sequences such as diffusion, arterial spin labeling, and blood oxygenation dependent imaging may also provide additional information. CT and US remain of limited value for the evaluation of renal function.

Kidney function: glomerular filtration rate measurement with MR renography in patients with cirrhosis

PURPOSE

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.

MATERIALS AND METHODS

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.

RESULTS

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).

CONCLUSION

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.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101338/-/DC1.

An algorithm for calculi segmentation on ureteroscopic images

PURPOSE

The purpose of the study is to develop an algorithm for the segmentation of renal calculi on ureteroscopic images. In fact, renal calculi are common source of urological obstruction, and laser lithotripsy during ureteroscopy is a possible therapy. A laser-based system to sweep the calculus surface and vaporize it was developed to automate a very tedious manual task. The distal tip of the ureteroscope is directed using image guidance, and this operation is not possible without an efficient segmentation of renal calculi on the ureteroscopic images.

METHODS

We proposed and developed a region growing algorithm to segment renal calculi on ureteroscopic images. Using real video images to compute ground truth and compare our segmentation with a reference segmentation, we computed statistics on different image metrics, such as Precision, Recall, and Yasnoff Measure, for comparison with ground truth.

RESULTS

The algorithm and its parameters were established for the most likely clinical scenarii. The segmentation results are encouraging: the developed algorithm was able to correctly detect more than 90% of the surface of the calculi, according to an expert observer.

CONCLUSION

Implementation of an algorithm for the segmentation of calculi on ureteroscopic images is feasible. The next step is the integration of our algorithm in the command scheme of a motorized system to build a complete operating prototype.

MR urography in children. Part 1: how we do the F0 technique

MR urography (MRU) has been widely accepted as a substitute to intravenous urography for investigating children with a dilated urinary tract after preliminary assessment by US and voiding cystourethrography. Hydronephrosis is by far the main indication for MRU because upper tract dilatation is a frequent condition in infants and children. Recent advances in technology have allowed MR to go beyond morphology and to assess renal function parameters such as split renal function and drainage. In this article we report our routine practice of the F0 MRU technique. The main advantages of our protocol are no requirement for general anaesthesia, no bladder catheterization, use of low-dose gadolinium-based contrast agent (0.05-0.1 mmol/kg) and total acquisition time of 30 min or less.

MR urography in children. Part 2: how to use ImageJ MR urography processing software

MR urography (MRU) is an emerging technique particularly useful in paediatric uroradiology. The most common indication is the investigation of hydronephrosis. Combined static and dynamic contrast-enhanced MRU (DCE-MRU) provides both morphological and functional information in a single examination. However, specific post-processing must be performed and to our knowledge, dedicated software is not available in conventional workstations. Investigators involved in MRU classically use homemade software that is not freely accessible. For these reasons, we have developed a software program that is freely downloadable on the National Institute of Health (NIH) website. We report and describe in this study the features of this software program.