Remnant renal volume can predict prognosis of remnant renal function in kidney transplantation donors: a prospective observational study.

BACKGROUND: Safety and survival during and after donor nephrectomy (DN) are one of the main concerns in living kidney donors (LKDs). Therefore, kidney (left/right) to be procured should be determined after considering the difficulty of DN, as well as the preservation of remnant renal function (RRF). In this prospective study, we investigated the roles of computed tomography volumetry (CTV) in split renal function (SRF) and established a predictive model for RRF in LKDs. METHODS: We assessed 103 LKDs who underwent DN at our institute. The Volume Analyzer SYNAPSE VINCENT image analysis system were used as CTV. RRF was defined as the estimated glomerular filtration rate (eGFR) 12 months after DN. The association between various factors measured by CTV and RRF were investigated, and a role of CTV on prediction for RRF was assessed. RESULTS: The median age and the preoperative eGFR were 58 years and 80.7 mL/min/1.73m2, respectively. Each factor measured by CTV showed an association with RRF. The ratio of remnant renal volume to body surface area (RRV/BSA) could predict RRF. In addition, RRV/BSA could predict RRF more accurately when used together with age and 24-h creatinine clearance (CrCl). CONCLUSIONS: Our findings suggest that RRV/BSA measured by CTV can play an important role in predicting RRF, and a comprehensive assessment including age and CrCl is important to determine the kidney to be procured.

Time changes of renal dimensions and variations of glomerular filtration rate in chronic kidney disease patients.

BACKGROUND: The aim of this longitudinal prospective study was to search if even in the absence of total or partial nephrectomy the kidney size can increase as the kidney function improves. METHODS: We randomly enrolled 80 adult patients with various degrees of chronic renal failure but non-dialysis dependent neither totally or partially nephrectomized nor affected by any of the pathological conditions that can increase kidney size. The patients underwent a first examination comprehensive of a blood sample and renal ultrasonography and then were submitted to a therapeutic intervention aimed at removing all nephrotoxic agents to finally be subjected to a last similar medical examination. RESULTS: The statistical analysis displayed a strong positive correlation between the percentage variation of the renal diameters' average and the time changes of the GFR (r 0.731; p < 0.01) as well as the percentage variation of the GFR and the time changes variations of the right (r 0.487; p < 0.01) and left cortical kidney thickness (r 0.519; p < 0.01) and finally a strong negative correlation between the removal of nephrotoxic agents and the percentage variation of the renal diameters' average (r - 0.293; p < 0.01) and the time changes of the GFR (r - 0.429; p < 0.01). CONCLUSIONS: In patients with chronic kidney disease, even in the absence of total or partial nephrectomy, under the stimulus of the removal of any nephrotoxic agents, there may be a limited increase in renal size according to a model that sees them vary according to the changes in GFR.

Medullary and cortical thick ascending limb: similarities and differences.

The thick ascending limb of the loop of Henle (TAL) is the first segment of the distal nephron, extending through the whole outer medulla and cortex, two regions with different composition of the peritubular environment. The TAL plays a critical role in the control of NaCl, water, acid, and divalent cation homeostasis, as illustrated by the consequences of the various monogenic diseases that affect the TAL. It delivers tubular fluid to the distal convoluted tubule and thereby affects the function of the downstream tubular segments. The TAL is commonly considered as a whole. However, many structural and functional differences exist between its medullary and cortical parts. The present review summarizes the available data regarding the similarities and differences between the medullary and cortical parts of the TAL. Both subsegments reabsorb NaCl and have high Na+-K+-ATPase activity and negligible water permeability; however, they express distinct isoforms of the Na+-K+-2Cl- cotransporter at the apical membrane. Ammonia and bicarbonate are mostly reabsorbed in the medullary TAL, whereas Ca2+ and Mg2+ are mostly reabsorbed in the cortical TAL. The peptidic hormone receptors controlling transport in the TAL are not homogeneously expressed along the cortical and medullary TAL. Besides this axial heterogeneity, structural and functional differences are also apparent between species, which underscores the link between properties and role of the TAL under various environments.

Shear wave elastography in the evaluation of renal parenchymal stiffness in patients with chronic kidney disease.

OBJECTIVE: To investigate the use of shear wave elastography (SWE)-derived estimates of Young's modulus (YM) as an indicator to detect abnormal renal tissue diagnosed by estimated glomerular filtration rate (eGFR). METHODS: The study comprised 106 chronic kidney disease (CKD) patients and 203 control subjects. Conventional ultrasound was performed to measure the kidney length and cortical thickness. SWE imaging was performed to measure renal parenchymal stiffness. Diagnostic performance of SWE and conventional ultrasound were correlated with serum creatinine, urea levels and eGFR. RESULTS: Pearson's correlation coefficient revealed a negative correlation between YM measurements and eGFR (r = -0.576, p < 0.0001). Positive correlations between YM measurements and age (r = 0.321, p < 0.05), serum creatinine (r = 0.375, p < 0.0001) and urea (r = 0.287, p < 0.0001) were also observed. The area under the receiver operating characteristic curve for SWE (0.87) was superior to conventional ultrasound alone (0.35-0.37). The cut-off value of less or equal to 4.31 kPa suggested a non-diseased kidney (80.3% sensitivity, 79.5% specificity). CONCLUSION: SWE was superior to renal length and cortical thickness in detecting CKD. A value of 4.31 kPa or less showed good accuracy in determining whether a kidney was diseased or not. Advances in knowledge: On SWE, CKD patients show greater renal parenchymal stiffness than non-CKD patients. Determining a cut-off value between normal and diseased renal parenchyma may help in early non-invasive detection and management of CKD.

Molecular phenotypes of the human kidney: Myoid stromal cells/telocytes and myoepithelial cells.

The connective stromal and epithelial compartments of the kidney have regenerative potential and phenotypic flexibility. A few studies have shown that cells appertaining to both compartments can exhibit myoid phenotypes. The purpose of our study was to investigate the myoid pattern of kidney and its association with the kidney niches containing stromal cells/telocytes (SC/TCs). We performed an immunohistochemical study using a panel of endothelial, myoid, mesenchymal and stem/progenitor markers, namely CD31, CD34, CD105 (endoglin), CD117/c-kit, nestin, desmin, α-smooth muscle actin (α-SMA) and the heavy chain of smooth muscle myosin (SMM). We used histologically normal kidney samples, obtained after nephrectomy, from nine adult patients. The capsular SC/TCs had a strong CD34 and partial nestin and CD105 immunopositivity. Subcapsular and interstitial SC/TCs expressed c-kit, nestin, CD105, but also α-SMA and SMM, therefore having a myoid phenotype. The endothelial SC/TCs phenotype was CD31+/CD34+/CD105+/nestin±/SMM±/α-SMA±. All three myoid markers were expressed in periendothelial SC/TCs. We also found a scarce expression of nestin in parietal epithelial cells of Bowman's capsule, and in podocytes. In epithelial cells, we found a positive expression for CD31, CD117/c-kit, desmin, CD34, SMM, and CD105. In epithelial tubular cells, we found a predominant basal expression of the myoid markers (SMM and desmin). In conclusion, myoepithelial tubular cells, myoid endothelial cells and myoid SC/TCs are normal constituents of the kidney.

CorteXpert: A model-based method for automatic renal cortex segmentation.

This paper introduces a model-based approach for a fully automatic delineation of kidney and cortex tissue from contrast-enhanced abdominal CT scans. The proposed framework, named CorteXpert, consists of two new strategies for kidney tissue delineation: cortex model adaptation and non-uniform graph search. CorteXpert was validated on a clinical data set of 58 CT scans using the cross-validation evaluation strategy. The experimental results indicated the state-of-the-art segmentation accuracies (as dice coefficient): 97.86% ±â€¯2.41% and 97.48% ±â€¯3.18% for kidney and renal cortex delineations, respectively.

Clinical application of calculated split renal volume using computed tomography-based renal volumetry after partial nephrectomy: Correlation with technetium-99m dimercaptosuccinic acid renal scan data.

OBJECTIVE: To evaluate the clinical application of computed tomography-based measurement of renal cortical volume and split renal volume as a single tool to assess the anatomy and renal function in patients with renal tumors before and after partial nephrectomy, and to compare the findings with technetium-99m dimercaptosuccinic acid renal scan. METHODS: The data of 51 patients with a unilateral renal tumor managed by partial nephrectomy were retrospectively analyzed. The renal cortical volume of tumor-bearing and contralateral kidneys was measured using ImageJ software. Split estimated glomerular filtration rate and split renal volume calculated using this renal cortical volume were compared with the split renal function measured with technetium-99m dimercaptosuccinic acid renal scan. RESULTS: A strong correlation between split renal function and split renal volume of the tumor-bearing kidney was observed before and after surgery (r = 0.89, P < 0.001 and r = 0.94, P < 0.001). The preoperative and postoperative split estimated glomerular filtration rate of the operated kidney showed a moderate correlation with split renal function (r = 0.39, P = 0.004 and r = 0.49, P < 0.001). The correlation between reductions in split renal function and split renal volume of the operated kidney (r = 0.87, P < 0.001) was stronger than that between split renal function and percent reduction in split estimated glomerular filtration rate (r = 0.64, P < 0.001). CONCLUSIONS: The split renal volume calculated using computed tomography-based renal volumetry had a strong correlation with the split renal function measured using technetium-99m dimercaptosuccinic acid renal scan. Computed tomography-based split renal volume measurement before and after partial nephrectomy can be used as a single modality for anatomical and functional assessment of the tumor-bearing kidney.

[Investigation of renal corticomedullary differentiation with age-related change on non-contrast-enhanced MRI].

OBJECTIVE: To evaluate the relationship between renal corticomedullary differentiation, renal cortical thickness and age-related changes with non-contrast-enhanced steady-state free precession(SSFP) magnetic resonance imaging (MRI) and spatially selective inversion recovery(IR) pulse technology as well as its applied value . METHODS: A total of 76 healthy volunteers had been recruited from August 2014 to June 2015 in First Hospital of China Medical University.All volunteers were divided into three groups: 2-40 years old, 41-60 years old, 61-80 years old. All 76 volunteers underwent non-contrast-enhanced steady-state free precession(SSFP) 3.0 T MRI scan using variable inversion times (TIs)(TI=1 000, 1 100, 1 200, 1 300, 1 400, 1 500, 1 600, 1 700 ms). The renal corticomedullary differentiation was observed and the signal intensity of renal cortex and medulla were measured respectively as well in order to calculate renal corticomedullary contrast ratio. Besides, renal cortical thickness and renal size were measured. RESULTS: All 76 volunteers were successfully performed all the sequences of MRI scan, including 152 useful imaging of kidney in total. The renal corticomedullary differentiation was clearly shown in all subjects. There was negative correlation between the optimal inversion time(TI) and age(r=-0.65, P<0.01). Similarly, negative correlation was observed between renal corticomedullary contrast ratio and age(r=-0.35, P<0.01). The mean renal cortical thickness of all subjects was (5.33±0.71)mm and there were statistically significant difference among those different groups, which was negative-related with age(r=-0.79, P<0.01). There was no statistically significant difference between sexuality and renal cortical thickness.Additionally, renal cortical thickness had no statistically significant difference in both sides of kidneys. CONCLUSION: The renal corticomedullary differentiation is depicted clearly by means of non-contrast-enhanced steady-state free precession MRI with spatially selective inversion recovery pulse technology. The optimal inversion time decreases along with the increase of age. In the meanwhile, the renal cortical thickness could be measured truthfully and accurately.

Diffusion-weighted perinatal postmortem magnetic resonance imaging as a marker of postmortem interval.

OBJECTIVE: To evaluate perinatal body organ apparent diffusion coefficient (ADC) values at postmortem magnetic resonance imaging (PMMR) in order to evaluate postmortem changes. METHODS: Postmortem diffusion-weighted imaging (DWI) of the thorax and abdomen were performed with diffusion gradient values b = 0, 500, and 1000 s/mm(2) on 15 foetal and childhood cases (mean 33.3 ± 7.8 weeks gestation) compared to 44 live infants (mean age 75.5 ± 53.4 days). Mean ADC values were calculated from regions of interest (ROIs) for the lungs, liver, spleen and renal cortex, compared to normative live infantile body ADC values of similar gestational age. RESULTS: Mean ADC values were significantly lower in postmortem cases than in normal controls for liver (0.88 10(-3) mm(2)/s ± SD 0.39 vs. 1.13 ± 0.13; p < 0.05) and renal cortex (0.85 ± 0.26 vs. 1.19 ± 0.13; p < 0.05) but not spleen or muscle. Mean lung ADC values were significantly higher than normal controls (1.06 ± 0.18 vs. 0 ± 0; p < 0.001), and there was a significant correlation between postmortem interval and lung ADC (R(2) = 0.55). CONCLUSION: Lung PMMR ADC values are related to postmortem interval, making them a potential marker of time since death. Further research is needed to understand the organ-specific changes which occur in the postmortem period. KEY POINTS: • Liver and spleen PM ADC values were lower than controls. • Lung ADC changes correlate with PM interval. • These findings may be useful in medicolegal cases.

MRI quantification of non-Gaussian water diffusion in normal human kidney: a diffusional kurtosis imaging study.

Our aim was to prospectively evaluate the feasibility of diffusional kurtosis imaging (DKI) in normal human kidney and to report preliminary DKI measurements. Institutional review board approval and informed consent were obtained. Forty-two healthy volunteers underwent diffusion-weighted imaging (DWI) scans with a 3-T MR scanner. b values of 0, 500 and 1000 s/mm(2) were adopted. Maps of fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (D⊥), axial diffusivity (D||), mean kurtosis (MK), radial kurtosis (K⊥) and axial kurtosis (K||) were produced. Three representative axial slices in the upper pole, mid-zone and lower pole were selected in the left and right kidney. On each selected slice, three regions of interest were drawn on the renal cortex and another three on the medulla. Statistical comparison was performed with t-test and analysis of variance. Thirty-seven volunteers successfully completed the scans. No statistically significant differences were observed between the left and right kidney for all metrics (p values in the cortex: FA, 0.114; MD, 0.531; D⊥, 0.576; D||, 0.691; MK, 0.934; K⊥, 0.722; K||, 0.891; p values in the medulla: FA, 0.348; MD, 0.732; D⊥, 0.470; D||, 0.289; MK, 0.959; K⊥, 0.780; K||, 0.287). Kurtosis metrics (MK, K||, K⊥) obtained in the renal medulla were significantly (p <0.001) higher than those in the cortex (0.552 ± 0.04, 0.637 ± 0.07 and 0.530 ± 0.08 in the medulla and 0.373 ± 0.04, 0.492 ± 0.06 and 0.295 ± 0.06 in the cortex, respectively). For the diffusivity measures, FA of the medulla (0.356 ± 0.03) was higher than that of the cortex (0.179 ± 0.03), whereas MD, D⊥ and D|| (mm(2) /ms) were lower in the medulla than in the cortex (3.88 ± 0.09, 3.50 ± 0.23 and 4.65 ± 0.29 in the cortex and 2.88 ± 0.11, 2.32 ± 0.20 and 3.47 ± 0.31 in the medulla, respectively). Our results indicate that DKI is feasible in the human kidney. We have reported the preliminary DKI measurements of normal human kidney that demonstrate well the non-Gaussian behavior of water diffusion, especially in the renal medulla.

Correlativity between blood measures related to blood stasis blocking collaterals and gene expression of angiotensin-converting enzyme of renal cortex in diabetic rats and effect of stasis removing and collaterals dredging.

OBJECTIVE: To investigate the correlativity between the changes of blood measures related to blood stasis blocking collaterals and gene expression levels of angiotensin-converting enzyme (ACE) and ACE2 of renal cortex in diabetic rats with stasis blocking collaterals syndrome, as well as the effect of stasis removing and collaterals dredging. METHODS: Male Sprague-Dawley rats were divided randomly into normal control group (C group), high-carbohydrate-fat control group (H group) and streptozotocin (STZ)-injecting group. The diabeticrats were induced from rats in the STZ-injecting, group by high-carbohydrate-fat diet combined with STZ intraperitoneal injection, with sustained high-carbohydrate-fat diet fed afterwards, and were further divided into model group (M group) and Chinese medicine of stasis removing and collaterals dredging group (Z group). Rats in the Z group were fed with stasis-removing-and-collaterals-dredging herbal granule suspension intragastrically daily for 16 weeks, while drinking water of corresponding volume was administrated to the rats in other groups. At the end of the 16th week after successful establishment of models, the ultrastructures of glomeruli in different groups were detected by a transmission electron microscopy; and blood measures related to blood stasis blocking collaterals, including lipid profile and blood viscosity measures, were tested, as well as the relative gene expressions of ACE and ACE2. RESULTS: Changes in ultrastructures of glomeruli in the M group were characterized by lack of clarity in structure and occasional thickening of glomerular basement membrane and extensive fusion in foot processes. The correlation analysis showed that there were positive correlations between lipid profile, blood viscosity, and the ACE mRNA expression levels in the M group (P < 0.05), except for cholesterol. And except for triglyceride, the blood measures were in negative correlation with the ACE2 mRNA expression levels in the M group (P < 0.05). Compared with the C and H groups, the lipid profile, plasma viscosity and blood viscosity were significantly higher (P < 0.01). All the above-mentioned measures were significantly improved in the Z group rats (P < 0.05). ACE mRNA expression was significantly higher in the M group than in the C group(P < 0.05). ACE2 mRNA level was significantly lower in the M group than in the C and H groups (P < 0.01); and its level in the Z group was higher than that in the M group (P < 0.01). CONCLUSION: Blood measures related to blood stasis blocking collaterals had positive linear correlations with ACE mRNA expression and negative linear correlations with ACE2 mRNA expression in the M group. Chinese recipe of stasis removing and collaterals dredging could play a renal protecting role for diabetic rats by reducing lipid profile and blood viscosity, down-regulating ACE mRNA expression and up-regulating ACE2 mRNA expression.

Comparison of DMSA scan 99 m and EC scan 99 m in diagnosis of cortical defect and differential renal function.

INTRODUCTION: Diagnosis of renal cortical lesions by radioisotopes in nuclear medicine is one of the most common techniques and procedures can be performed by different radiotracer. However, all these materials are accurate in determining kidney function, but there are differences between them in the field. The purpose of this study was to evaluate the effectiveness of EC scans compared with DMSA scan in the detection of cortical lesions and DRF. METHODS: 65 cases, which have been referred for various reasons, for DMSA scans were enrolled. Patients 1 week after DMSA scan with the previous consent of the EC being scanned. The results were compared in terms of convergence as well as sensitivity, specificity, positive and negative predictive value of EC with respect to the results of DMSA scan. RESULTS: PPV of EC was 100%, negative predictive value of EC was 68.75%, sensitivity of EC was 90.74% and specificity of EC was 100% in the detection of cortical lesions. DMSA scan and EC convergence rates result in cortical lesions in our study was high. DISCUSSION: We suggest EC scan as an alternative to reduce the cost of therapy and radiation, but considering the benefits of DMSA scan, it could remain the gold standard method of diagnosis. 

High-resolution diffusion tensor imaging of the human kidneys using a free-breathing, multi-slice, targeted field of view approach.

Fractional anisotropy (FA) obtained by diffusion tensor imaging (DTI) can be used to image the kidneys without any contrast media. FA of the medulla has been shown to correlate with kidney function. It is expected that higher spatial resolution would improve the depiction of small structures within the kidney. However, the achievement of high spatial resolution in renal DTI remains challenging as a result of respiratory motion and susceptibility to diffusion imaging artefacts. In this study, a targeted field of view (TFOV) method was used to obtain high-resolution FA maps and colour-coded diffusion tensor orientations, together with measures of the medullary and cortical FA, in 12 healthy subjects. Subjects were scanned with two implementations (dual and single kidney) of a TFOV DTI method. DTI scans were performed during free breathing with a navigator-triggered sequence. Results showed high consistency in the greyscale FA, colour-coded FA and diffusion tensors across subjects and between dual- and single-kidney scans, which have in-plane voxel sizes of 2 × 2 mm(2) and 1.2 × 1.2 mm(2) , respectively. The ability to acquire multiple contiguous slices allowed the medulla and cortical FA to be quantified over the entire kidney volume. The mean medulla and cortical FA values were 0.38 ± 0.017 and 0.21 ± 0.019, respectively, for the dual-kidney scan, and 0.35 ± 0.032 and 0.20 ± 0.014, respectively, for the single-kidney scan. The mean FA between the medulla and cortex was significantly different (p < 0.001) for both dual- and single-kidney implementations. High-spatial-resolution DTI shows promise for improving the characterization and non-invasive assessment of kidney function.

MR diffusion tensor imaging of normal kidneys.

PURPOSE: To assess the feasibility of diffusion tensor imaging (DTI) of normal kidneys and the influence of hydration state. MATERIALS AND METHODS: Ten healthy volunteers underwent renal DTI after fasting for 12 hours and 4 hours, without fasting, and following water diuresis. Medullary and cortical apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured and compared in the four different states of hydration. DTI was performed with a 3T magnetic resonance imaging (MRI) system using fat-saturated single-shot spin-echo echo planar imaging sequence. RESULTS: ADC of normal cortex (2.387 ± 0.081 × 10(-3) mm(2) /s) was significantly higher (t = 20.126, P = 0) than that of medulla (1.990 ± 0.063 × 10(-3) mm(2) /s). The FA value of normal cortex (0.282 ± 0.017) was significantly lower (t = -42.713, P = 0) than that of medulla (0.447 ± 0.022). The ADC and FA values of the left renal cortex (2.404 ± 0.082 × 10(-3) mm(2) /s, 0.282 ± 0.017) and medulla (2.002 ± 0.081 × 10(-3) mm(2) /s, 0.452 ± 0.024) were not significantly different (P > 0.05) from those of right renal cortex (2.369 ± 0.080 × 10(-3) mm(2) /s, 0.283 ± 0.018) and medulla (1.978 ± 0.039 × 10(-3) mm(2) /s, 0.443 ± 0.019). Values for ADC (×10(-3) mm(2) /s) and FA in the 12-hour fasting, 4-hour fasting, nonfasting, and water diuresis states were 2.372 ± 0.095 and 0.278 ± 0.018, 2.387 ± 0.081 and 0.282 ± 0.017, 2.416 ± 0.051 and 0.279 ± 0.023, 2.421 ± 0.068, and 0.270 ± 0.021, respectively, in cortex, 1.972 ± 0.084 and 0.438 ± 0.014, 1.990 ± 0.063 and 0.447 ± 0.022, 2.021 ± 0.081 and 0.450 ± 0.031, 2.016 ± 0.076 and 0.449 ± 0.028, respectively, in medulla. The ADC and FA values in different hydration states were not significantly different (P > 0.05). CONCLUSION: DTI of normal kidneys is feasible with reproducible ADC and FA values independent of hydration states.

Renal intraspecific variation along an aridity gradient detected by new renal indices in a desert herbivorous rodent.

Mammals that live in arid and semi-arid environments in South America present physiological mechanisms that enable them to conserve water. Body water is lost through the kidneys, lungs, skin, and intestines. Regarding renal adaptation for water conservation, several indices have been used to estimate the capacity of the kidneys to produce a maximum urine concentration. Most studies were conducted at an inter-specific level, with only few performed at the intraspecific level. In this work, we compare renal function and morphology among five populations of Southern mountain cavy, Microcavia australis, present along an aridity gradient. We hypothesized that individuals from drier zones would present morphological and functional renal modifications that imply a greater capability to conserve body water. These features were studied considering the classical indices (RMT, PMT, PMA, and RMA) and three new indices that consider area measurements; the latter showed to be more adequate to reflect intraspecific differences. Our results suggest that the morphological modifications of kidneys, that is, the greater areas of renal inner medulla, would be related to the aridity gradient where populations of Southern mountain cavy occur.

Structure, not just function.

Although kidney size can be important in the evaluation of renal disease, it has not been carefully studied and true volume is rarely measured, and good normative data are lacking. Wang et al. measured both cortical and medullary volumes in potential transplant donors and correlate these with physiologic, morphometric, and metabolic parameters. The results reveal interesting and potentially important correlations and differential responses between the two compartments, providing a framework for future investigation.

High-resolution mechanical imaging of the kidney.

The objective of this study was to test the feasibility and reproducibility of in vivo high-resolution mechanical imaging of the asymptomatic human kidney. Hereby nine volunteers were examined at three different physiological states of urinary bladder filling (a normal state, urinary urgency, and immediately after urinary relief). Mechanical imaging was performed of the in vivo kidney using three-dimensional multifrequency magnetic resonance elastography combined with multifrequency dual elastovisco inversion. Other than in classical elastography, where the storage and loss shear moduli are evaluated, we analyzed the magnitude |G(⁎)| and the phase angle φ of the complex shear modulus reconstructed by simultaneous inversion of full wave field data corresponding to 7 harmonic drive frequencies from 30 to 60Hz and a resolution of 2.5mm cubic voxel size. Mechanical parameter maps were derived with a spatial resolution superior to that in previous work. The group-averaged values of |G(⁎)| were 2.67±0.52kPa in the renal medulla, 1.64±0.17kPa in the cortex, and 1.17±0.21kPa in the hilus. The phase angle φ (in radians) was 0.89±0.12 in the medulla, 0.83±0.09 in the cortex, and 0.72±0.06 in the hilus. All regional differences were significant (P<0.001), while no significant variation was found in relation to different stages of bladder filling. In summary our study provides first high-resolution maps of viscoelastic parameters of the three anatomical regions of the kidney. |G(⁎)| and φ provide novel information on the viscoelastic properties of the kidney, which is potentially useful for the detection of renal lesions or fibrosis.

In vivo sodium (23Na) imaging of the human kidneys at 7 T: preliminary results.

OBJECTIVE: To evaluate the feasibility of in vivo (23)Na imaging of the corticomedullary (23)Na gradient and to measure (23)Na transverse relaxation times (T2*) in human kidneys. METHODS: In this prospective, IRB-approved study, eight healthy volunteers (4 female, 4 male; mean age 29.4 ± 3.6 years) were examined on a 7-T whole-body MR system using a (23)Na-only spine-array coil. For morphological (23)Na-MRI, a 3D gradient echo (GRE) sequence with a variable echo time scheme (vTE) was used. T2* times were calculated using a multiecho 3D vTE-GRE approach. (23)Na signal-to-noise ratios (SNR) were given on a pixel-by-pixel basis for a 20-mm section from the cortex in the direction of the medulla. T2* maps were calculated by fitting the (23)Na signal decay monoexponentially on a pixel-by-pixel basis, using least squares fit. RESULTS: Mean corticomedullary (23)Na-SNR increased from the cortex (32.2 ± 5.6) towards the medulla (85.7 ± 16.0). The SNR increase ranged interindividually from 57.2% to 66.3%. Mean (23)Na-T2* relaxation times differed statistically significantly (P < 0.001) between the cortex (17.9 ± 0.8 ms) and medulla (20.6 ± 1.0 ms). CONCLUSION: The aim of this study was to evaluate the feasibility of in vivo (23)Na MRI of the corticomedullary (23)Na gradient and to measure the (23)Na T2* relaxation times of human kidneys at 7 T. KEY POINTS: • High field MR offers new insights into renal anatomy and physiology. • (23) Na MRI of healthy human kidneys is feasible at ultra-high field. • Renal (23) Na concentration increases from the cortex in the medullary pyramid direction. • In vivo measurements of renal (23) Na-T2* times are demonstrated at 7.0 T.

Age-related change in renal corticomedullary differentiation: evaluation with noncontrast-enhanced steady-state free precession (SSFP) MRI with spatially selective inversion pulse using variable inversion time.

PURPOSE: To evaluate age-related change in renal corticomedullary differentiation and renal cortical thickness by means of noncontrast-enhanced steady-state free precession (SSFP) magnetic resonance imaging (MRI) with spatially selective inversion recovery (IR) pulse. MATERIALS AND METHODS: The Institutional Review Board of our hospital approved this retrospective study and patient informed consent was waived. This study included 48 patients without renal diseases who underwent noncontrast-enhanced SSFP MRI with spatially selective IR pulse using variable inversion times (TIs) (700-1500 msec). The signal intensity of renal cortex and medulla were measured to calculate renal corticomedullary contrast ratio. Additionally, renal cortical thickness was measured. RESULTS: The renal corticomedullary junction was clearly depicted in all patients. The mean cortical thickness was 3.9 ± 0.83 mm. The mean corticomedullary contrast ratio was 4.7 ± 1.4. There was a negative correlation between optimal TI for the best visualization of renal corticomedullary differentiation and age (r = -0.378; P = 0.001). However, there was no significant correlation between renal corticomedullary contrast ratio and age (r = 0.187; P = 0.20). Similarly, no significant correlation was observed between renal cortical thickness and age (r = 0.054; P = 0.712). CONCLUSION: In the normal kidney, noncontrast-enhanced SSFP MRI with spatially selective IR pulse can be used to assess renal corticomedullary differentiation and cortical thickness without the influence of aging, although optimal TI values for the best visualization of renal corticomedullary junction were shortened with aging.

Age, kidney function, and risk factors associate differently with cortical and medullary volumes of the kidney.

The kidney atrophies in patients with advanced chronic kidney disease (CKD) but factors influencing kidney size in normal adults are less clear. To help define this, we measured kidney volumes on contrast-enhanced computed tomographic images from 1344 potential kidney donors (aged 18-75 years). Cortical volume per body surface area progressively declined in both genders with increased age. Statistically, this was primarily dependent on the age-related decline in glomerular filtration rate (GFR). Independent predictors of increased cortical volume per body surface area were male gender, increased GFR, increased 24-h urine albumin, current smoker, and decreased high-density lipid cholesterol. Medullary volume per body surface area increased with age in men, while it increased with age in women until the age of 50 years followed by a subsequent decline. Independent predictors of increased medullary volume per body surface area were older age, male gender, increased GFR, increased 24-h urine albumin, increased serum glucose, and decreased serum uric acid. Thus, while cortical volume declines with age along the same biological pathway as the age-related decline in GFR, albuminuria and some risk factors are actually associated with increased cortical or medullary volume among relatively healthy adults. Underlying hypertrophy or atrophy of different nephron regions may explain these findings.