Assessment of chronic allograft injury in renal transplantation using diffusional kurtosis imaging.

BACKGROUND: Chronic allograft injury (CAI) is a significant reason for which many grafts were lost. The study was conducted to assess the usefulness of diffusional kurtosis imaging (DKI) technology in the non-invasive assessment of CAI. METHODS: Between February 2019 and October 2019, 110 renal allograft recipients were included to analyze relevant DKI parameters. According to estimated glomerular filtration rate (eGFR) (mL/min/ 1.73 m2) level, they were divided to 3 groups: group 1, eGFR ≥ 60 (n = 10); group 2, eGFR 30-60 (n = 69); group 3, eGFR < 30 (n = 31). We performed DKI on a clinical 3T magnetic resonance imaging system. We measured the area of interest to determine the mean kurtosis (MK), mean diffusivity (MD), and apparent diffusion coefficient (ADC) of the renal cortex and medulla. We performed a Pearson correlation analysis to determine the relationship between eGFR and the DKI parameters. We used the receiver operating characteristic curve to estimate the predicted values of DKI parameters in the CAI evaluation. We randomly selected five patients from group 2 for biopsy to confirm CAI. RESULTS: With the increase of creatinine, ADC, and MD of the cortex and medulla decrease, MK of the cortex and medulla gradually increase. Among the three different eGFR groups, significant differences were found in cortical and medullary MK (P = 0.039, P < 0.001, P < 0.001, respectively). Cortical and medullary ADC and MD are negatively correlated with eGFR (r = - 0.49, - 0.44, - 0.57, - 0.57, respectively; P < 0.001), while cortical and medullary MK are positively correlated with eGFR (r = 0.42, 0.38; P < 0.001). When 0.491 was set as the cutoff value, MK's CAI assessment showed 87% sensitivity and 100% specificity. All five patients randomly selected for biopsy from the second group confirmed glomerulosclerosis and tubular atrophy/interstitial fibrosis. CONCLUSION: The DKI technique is related to eGFR as allograft injury progresses and is expected to become a potential non-invasive method for evaluating CAI.

Mechanical Anisotropy Assessment in Kidney Cortex Using ARFI Peak Displacement: Preclinical Validation and Pilot In Vivo Clinical Results in Kidney Allografts.

The kidney is an anisotropic organ, with higher elasticity along versus across nephrons. The degree of mechanical anisotropy in the kidney may be diagnostically relevant if properly exploited; however, if improperly controlled, anisotropy may confound stiffness measurements. The purpose of this study is to demonstrate the clinical feasibility of acoustic radiation force (ARF)-induced peak displacement (PD) measures for both exploiting and obviating mechanical anisotropy in the cortex of human kidney allografts, in vivo. Validation of the imaging methods is provided by preclinical studies in pig kidneys, in which ARF-induced PD values were significantly higher ( , Wilcoxon) when the transducer executing asymmetric ARF was oriented across versus along the nephrons. The ratio of these PD values obtained with the transducer oriented across versus along the nephrons strongly linearly correlated ( R2 = 0.95 ) to the ratio of shear moduli measured by shear wave elasticity imaging. On the contrary, when a symmetric ARF was implemented, no significant difference in PD was observed ( p > 0.01 ). Similar results were demonstrated in vivo in the kidney allografts of 14 patients. The symmetric ARF produced PD measures with no significant difference ( p > 0.01 ) between along versus across alignments, but the asymmetric ARF yielded PD ratios that remained constant over a six-month observation period post-transplantation, consistent with stable serum creatinine level and urine protein-to-creatinine ratio in the same patient population ( p > 0.01 ). The results of this pilot in vivo clinical study suggest the feasibility of 1) implementing symmetrical ARF to obviate mechanical anisotropy in the kidney cortex when anisotropy is a confounding factor and 2) implementing asymmetric ARF to exploit mechanical anisotropy when mechanical anisotropy is a potentially relevant biomarker.

Assessment of time-resolved renal diffusion parameters over the entire cardiac cycle.

OBJECT: To assess changes diffusion properties of renal cortex over the entire cardiac cycle using electrocardiogram-gated respiratory-triggered dynamic diffusion-weighted imaging (DWI). MATERIALS AND METHODS: 20 healthy volunteers were investigated on a 1.5 T MR scanner. Blood flow velocity within the renal arteries was determined by electrocardiogram-gated phase-contrast measurements. For dynamic renal DWI, an electrocardiogram-gated respiratory-triggered coronal single-slice EPI sequence was acquired at 14 times at 20, 70, 120, 170, …, 570, 620, 720 ms after the R-wave over the cardiac cycle. ROI measurements were performed by two authors in the renal cortex on apparent diffusion coefficient (ADC) maps. A pulsatility index was calculated for ADC as maximal percentage change. Five subjects were measured twice to assess scan-rescan reproducibility. RESULTS: Flow measurements exhibited a minimum velocity of 15.7 ±â€¯4.3 cm/s during the R-wave and a maximum of 43.2 ±â€¯10.4 cm/s at 182.5 ±â€¯48.3 ms after the R-wave. A minimal mean ADC of 2.19 ±â€¯0.09 × 10-3 mm2/s was observed during the R-wave. A maximum mean ADC of 2.85 ±â€¯0.20 × 10-3 mm2/s was measured 193 ±â€¯57 ms after the R-wave. The mean ADC pulsatility index in the renal cortex was 29.9 ±â€¯5.8%. ADC variation exhibited a significant correlation with pulsatile blood flow velocity. The scan-rescan reproducibility in this study had a low deviation of 0.3 ±â€¯0.1%. The inter-reader reproducibility was 2.9 ±â€¯0.6%. CONCLUSION: Renal ADCs exhibit pulsatile characteristics. Due to the significant difference of systolic and diastolic ADCs, the pulsatility index can be calculated.

Dynamic tissue perfusion assessment reflects associations between antihypertensive treatment and renal cortical perfusion in patients with chronic kidney disease and hypertension.

PURPOSE: Renal cortical perfusion measured in noninvasive, dynamic ultrasonic method is connected with the hemodynamic cardiac properties and renal function. Antihypertensive drugs affect the functioning of the heart and kidneys. The aim of the study was to evaluate the effect of a chronic use of antihypertensive drugs on ultrasound parameters of renal cortical perfusion. METHODS: The study included 56 consecutive patients (49 M + 7 F, age 54.0 ± 13.3) with stable chronic kidney disease and hypertension. Color Doppler dynamic tissue perfusion measurement was used to assess renal cortical perfusion. RESULTS: Patients were treated with a mean of 2.7 ± 1.4 antihypertensive drugs, of which diuretics accounted for 25%, angiotensin-converting enzyme inhibitors (ACE-I) together with angiotensin receptor blockers (ARB) 24%, beta-blockers (BB) 23%, calcium channel blockers 16%, alpha-1 blockers (α1B) 9% and centrally acting drugs 3%. All investigated groups of drugs correlated significantly with parameters of renal perfusion. In multivariable regression analyses adjusted to age, diuretics were connected with the decrease (r = - 0.473) and ACE-I + ARB (r = 0.390) with the improvement of proximal and whole renal cortex perfusion (R2 = 0.28; p < 0.001), whereas BB (r = - 0.372) and α1B (r = - 0.280) independently correlated with worsened perfusion of renal distal cortex (R2 = 0.21, p < 0.01). CONCLUSIONS: The type of antihypertensive therapy had a significant influence on the ultrasound parameters of renal cortical perfusion. Noninvasive, ultrasonic dynamic tissue perfusion measurement method appears to be an adequate tool to assess the impact of drugs on renal cortical perfusion.

A rapid T1 mapping method for assessment of murine kidney viability using dynamic manganese-enhanced magnetic resonance imaging.

PURPOSE: Dynamic manganese-enhanced MRI (MEMRI) allows assessment of tissue viability by tracing manganese uptake. We aimed to develop a rapid T1 mapping method for dynamic MEMRI to facilitate assessments of murine kidney viability. METHODS: A multi-slice saturation recovery fast spin echo (MSRFSE) was developed, validated, and subsequently applied in dynamic MEMRI at 16.4T on ischemic mouse kidneys after 4 weeks of unilateral renal artery stenosis (RAS). Baseline T1 values and post-contrast R1 (1/T1 ) changes were measured in cortex (CO), outer (OSOM), inner (ISOM) strips of outer medulla, and inner medulla (IM). RESULTS: Validation studies showed strong agreement between MSRFSE and an established saturation recovery Look-Locker method. Baseline T1 (s) increased in the stenotic kidney CO (2.10 [1.95-2.56] vs. 1.88 [1.81-2.00], P = 0.0317) and OSOM (2.17 [2.05-2.33] vs. 1.96 [1.87-2.00], P = 0.0075) but remained unchanged in ISOM and IM. This method allowed a temporal resolution of 1.43 min in dynamic MEMRI. Mn2+ uptake and retention decreased in stenotic kidneys, particularly in the OSOM (ΔR1 : 0.48 [0.38-0.56] vs. 0.64 [0.61-0.69] s-1 , P < 0.0001). CONCLUSION: Dynamic MEMRI by MSRFSE detected decreased cellular viability and discerned the regional responses to RAS. This technique may provide a valuable tool for noninvasive evaluation of renal viability. Magn Reson Med 80:190-199, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Assessment of unilateral ureter obstruction with multi-parametric MRI.

PURPOSE: Quantitative multi-parametric MRI (mpMRI) methods may allow the assessment of renal injury and function in a sensitive and objective manner. This study aimed to evaluate an array of MRI methods that exploit endogenous contrasts including relaxation rates, pool size ratio (PSR) derived from quantitative magnetization transfer (qMT), chemical exchange saturation transfer (CEST), nuclear Overhauser enhancement (NOE), and apparent diffusion coefficient (ADC) for their sensitivity and specificity in detecting abnormal features associated with kidney disease in a murine model of unilateral ureter obstruction (UUO). METHODS: MRI scans were performed in anesthetized C57BL/6N mice 1, 3, or 6 days after UUO at 7T. Paraffin tissue sections were stained with Masson trichrome following MRI. RESULTS: Compared to contralateral kidneys, the cortices of UUO kidneys showed decreases of relaxation rates R1 and R2 , PSR, NOE, and ADC. No significant changes in CEST effects were observed for the cortical region of UUO kidneys. The MRI parametric changes in renal cortex are related to tubular cell death, tubular atrophy, tubular dilation, urine retention, and interstitial fibrosis in the cortex of UUO kidneys. CONCLUSION: Measurements of multiple MRI parameters provide comprehensive information about the molecular and cellular changes produced by UUO. Magn Reson Med 79:2216-2227, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

The assessment of renal cortex and parenchymal volume using automated CT volumetry for predicting renal function after donor nephrectomy.

BACKGROUND: Contrast-enhanced CT is necessary before donor nephrectomy and is usually combined with a Tc-99m-mercapto-acetyltriglycine (MAG3) scan to check split renal function (SRF). However, all transplant programs do not use MAG3 because of its high cost and exposure to radiation. We examined whether CT volumetry of the kidney can be a new tool for evaluating SRF. METHODS: Sixty-three patients underwent live donor nephrectomy. Patients without a 1.0 mm slice CT or follow-up for <12 months were excluded leaving 34 patients' data being analyzed. SRF was measured by MAG3. Split renal volume (SRV) was calculated automatically using volume analyzer software. The correlation between SRF and SRV was examined. The association between the donor's postoperative estimated glomerular filtration rate (eGFR) and predicted eGFR calculated by MAG3 or CT volumetry was analyzed at 1, 3, and 12 months post nephrectomy. RESULTS: Strong correlations were observed preoperatively in a Bland-Altman plot between SRF measured by MAG3 and either CT cortex or parenchymal volumetry. In addition, eGFR after donation correlated with SRF measured by MAG3 or CT volumetry. The correlation coefficients (R) for eGFR Mag3 split were 0.755, 0.615, and 0.763 at 1, 3 and 12 months, respectively. The corresponding R values for cortex volume split were 0.679, 0.638, and 0.747. Those for parenchymal volume split were 0.806, 0.592, and 0.764. CONCLUSION: Measuring kidney by CT volumetry is a cost-effective alternative to MAG3 for evaluating SRF and predicting postoperative donor renal function. Both cortex and parenchymal volumetry were similarly effective.

A non-invasive magnetic resonance imaging approach for assessment of real-time microcirculation dynamics.

We present a novel, non-invasive magnetic resonance imaging (MRI) technique to assess real-time dynamic vasomodulation of the microvascular bed. Unlike existing perfusion imaging techniques, our method is sensitive only to blood volume and not flow velocity. Using graded gas challenges and a long-life, blood-pool T 1-reducing agent gadofosveset, we can sensitively assess microvascular volume response in the liver, kidney cortex, and paraspinal muscle to vasoactive stimuli (i.e. hypercapnia, hypoxia, and hypercapnic hypoxia). Healthy adult rats were imaged on a 3 Tesla scanner and cycled through 10-minute gas intervals to elicit vasoconstriction followed by vasodilatation. Quantitative T 1 relaxation time mapping was performed dynamically; heart rate and blood oxygen saturation were continuously monitored. Laser Doppler perfusion measurements confirmed MRI findings: dynamic changes in T 1 corresponded with perfusion changes to graded gas challenges. Our new technique uncovered differential microvascular response to gas stimuli in different organs: for example, mild hypercapnia vasodilates the kidney cortex but constricts muscle vasculature. Finally, we present a gas challenge protocol that produces a consistent vasoactive response and can be used to assess vasomodulatory capacity. Our imaging approach to monitor real-time vasomodulation may be extended to other imaging modalities and is valuable for investigating diseases where microvascular health is compromised.

Ultrasound Strain Relaxation Time Ratio: A Quantitative Marker for the Assessment of Cortical Inflammation/Edema in Renal Allografts.

Purpose: To evaluate the ability of ultrasound strain relaxation time ratio to assess cortical inflammation/edema in renal allografts. Materials and Methods: We prospectively assessed renal allograft cortical inflammation/edema in 16 renal transplants using ultrasound elasticity imaging and correlated the findings with kidney biopsy. Strain relaxation times in the renal cortex and reference soft tissue were produced by free-hand compression with the ultrasound transducer and estimated with 2 D speckle tracking. Compression was performed in 3-second compression-relaxation cycles (push for 1 second, constant pressure for 1 second, and release for 1 second). We propose a strain relaxation time ratio (time of cortical strain to return to zero/time of the reference strain return to zero) to assess the relationship of compression-induced time-dependent strain relaxation in the cortex and reference tissue. 16 patients were divided into a group with ≤ 25 % (n = 8) and a group with > 26 % (n = 8) cortical inflammation/edema based on the Banff score. A t-test was used to examine the difference in the strain relaxation time ratio between the two groups. The diagnostic accuracy, inter-rater reliability, and reproducibility of this technique in discriminating between the groups were tested. Results: The strain relaxation time ratio of cortex/reference tissue was significantly higher in patients with > 26 % than in patients with ≤ 25 % cortical inflammation/edema (1.15 ±â€Š0.10 vs. 0.91 ±â€Š0.08, P = 0.0002). The strain relaxation time ratio has high reliability (Pearson correlation coefficient, R²â€Š= 0.93), reproducibility (intraclass correlation coefficient = 0.98, P = 0.000), and accuracy (area under curve = 1) in determining > 26 % renal cortical inflammation/edema. Conclusion: The strain relaxation time ratio of cortex/reference tissue can be used as a quantitative marker for the assessment of cortical inflammation/edema in renal allografts.

Computed Tomography Volumetry in Preoperative Living Kidney Donor Assessment for Prediction of Split Renal Function.

BACKGROUND: Transplant centers commonly evaluate split renal function (SRF) with Tc-99m-mercapto-acetyltriglycin (MAG3) scintigraphy in living kidney donation. Alternatively, the kidney volume can be measured based on predonation CT scans. The aim of this study was to identify the most accurate CT volumetry technique for SRF and the prediction of postdonation kidney function (PDKF). METHODS: Three CT volumetry techniques (modified ellipsoid volume [MELV], smart region of interest [ROI] volume, renal cortex volume [RCV]) were performed in 101 living kidney donors. Preoperation CT volumetric SRF was determined and compared with MAG3-SRF, postoperation donor kidney function, and graft function. RESULTS: The correlation between donors predonation total kidney volume and predonation kidney function was the highest for RCV (0.58 with creatine clearance, 0.54 with estimated glomerular filtration rate-Cockcroft-Gault). The predonation volume of the preserved kidney was (ROI, MELV, RCV) 148.0 ± 29.1 cm, 151.2 ± 35.4 and 93.9 ± 25.2 (P < 0.005 MELV vs RCV and ROI vs RCV). Bland-Altman analysis showed agreement between CT volumetry SRF and MAG3-SRF (bias, 95% limits of agreement: ROI vs MAG3 0.4%, -7.7% to 8.6%; MELV vs MAG3 0.4%, -8.9% to 9.7%; RCV vs MAG3 0.8%, -9.1% to 10.7%). The correlation between predonation CT volumetric SRF of the preserved kidney and PDKF at day 3 was r = 0.85 to 0.88, between MAG3-SRF and PDKF (r = 0.84). The difference of predonation SRF between preserved and donated kidney was the lowest for ROI and RCV (median, 3% and 4%; 95th percentile, 9% and 13%). CONCLUSIONS: Overall renal cortex volumetry seems to be the most accurate technique for the evaluation of predonation SRF and allows a reliable prediction of donor's PDKF.

Comparison of Ultrasound Corticomedullary Strain with Doppler Parameters in Assessment of Renal Allograft Interstitial Fibrosis/Tubular Atrophy.

To compare the capability of ultrasound strain and Doppler parameters in the assessment of renal allograft interstitial fibrosis/tubular atrophy (IF/TA), we prospectively measured ultrasound corticomedullary strain (strain) and intra-renal artery Doppler end-diastolic velocity (EDV), peak systolic velocity (PSV) and resistive index (RI) in 45 renal transplant recipients before their kidney biopsies. We used 2-D speckle tracking to estimate strain, the deformation ratio of renal cortex to medulla produced by external compression using the ultrasound transducer. We also measured Doppler EDV, PSV and RI at the renal allograft inter-lobar artery. Using the Banff scoring system for renal allograft IF/TA, 45 patients were divided into the following groups: group 1 with ≤5% (n = 12) cortical IF/TA; group 2 with 6%-25% (n = 12); group 3 with 26%-50% (n = 11); and group 4 with >50% (n = 10). We performed receiver operating characteristic curve analysis to test the accuracy of these ultrasound parameters and duration of transplantation in determining >26% cortical IF/TA. In our results, strain was statistically significant in all paired groups (all p < 0.005) and inversely correlated with the grade of cortical IF/TA (p < 0.001). However, the difference in PSV and EDV was significant only between high-grade (>26%, including 26%-50% and >50%) and low-grade (≤25%, including <5% and 6%-25%) cortical IF/TA (p < 0.001). RI did not significantly differ in any paired group (all p > 0.05). The areas under the receiver operating characteristic curve for strain, EDV, PSV, RI and duration of transplantation in determining >26% cortical IF/TA were 0.99, 0.94, 0.88, 0.52 and 0.92, respectively. Our results suggest that corticomedullary strain seems to be superior to Doppler parameters and duration of transplantation in assessment of renal allograft cortical IF/TA.

Development and evaluation of convergent and accelerated penalized SPECT image reconstruction methods for improved dose-volume histogram estimation in radiopharmaceutical therapy.

PURPOSE: Three-dimensional (3D) dosimetry has the potential to provide better prediction of response of normal tissues and tumors and is based on 3D estimates of the activity distribution in the patient obtained from emission tomography. Dose-volume histograms (DVHs) are an important summary measure of 3D dosimetry and a widely used tool for treatment planning in radiation therapy. Accurate estimates of the radioactivity distribution in space and time are desirable for accurate 3D dosimetry. The purpose of this work was to develop and demonstrate the potential of penalized SPECT image reconstruction methods to improve DVHs estimates obtained from 3D dosimetry methods. METHODS: The authors developed penalized image reconstruction methods, using maximum a posteriori (MAP) formalism, which intrinsically incorporate regularization in order to control noise and, unlike linear filters, are designed to retain sharp edges. Two priors were studied: one is a 3D hyperbolic prior, termed single-time MAP (STMAP), and the second is a 4D hyperbolic prior, termed cross-time MAP (CTMAP), using both the spatial and temporal information to control noise. The CTMAP method assumed perfect registration between the estimated activity distributions and projection datasets from the different time points. Accelerated and convergent algorithms were derived and implemented. A modified NURBS-based cardiac-torso phantom with a multicompartment kidney model and organ activities and parameters derived from clinical studies were used in a Monte Carlo simulation study to evaluate the methods. Cumulative dose-rate volume histograms (CDRVHs) and cumulative DVHs (CDVHs) obtained from the phantom and from SPECT images reconstructed with both the penalized algorithms and OS-EM were calculated and compared both qualitatively and quantitatively. The STMAP method was applied to patient data and CDRVHs obtained with STMAP and OS-EM were compared qualitatively. RESULTS: The results showed that the penalized algorithms substantially improved the CDRVH and CDVH estimates for large organs such as the liver compared to optimally postfiltered OS-EM. For example, the mean squared errors (MSEs) of the CDRVHs for the liver at 5 h postinjection obtained with CTMAP and STMAP were about 15% and 17%, respectively, of the MSEs obtained with optimally filtered OS-EM. For the CDVH estimates, the MSEs obtained with CTMAP and STMAP were about 16% and 19%, respectively, of the MSEs from OS-EM. For the kidneys and renal cortices, larger residual errors were observed for all algorithms, likely due to partial volume effects. The STMAP method showed promising qualitative results when applied to patient data. CONCLUSIONS: Penalized image reconstruction methods were developed and evaluated through a simulation study. The study showed that the MAP algorithms substantially improved CDVH estimates for large organs such as the liver compared to optimally postfiltered OS-EM reconstructions. For small organs with fine structural detail such as the kidneys, a large residual error was observed for both MAP algorithms and OS-EM. While CTMAP provided marginally better MSEs than STMAP, given the extra effort needed to handle misregistration of images at different time points in the algorithm and the potential impact of residual misregistration, 3D regularization methods, such as that used in STMAP, appear to be a more practical choice.

Ultrasound strain zero-crossing elasticity measurement in assessment of renal allograft cortical hardness: a preliminary observation.

To determine whether ultrasound strain zero-crossing elasticity measurement can be used to discriminate moderate cortical fibrosis or inflammation in renal allografts, we prospectively assessed cortical hardness with quasi-static ultrasound elastography in 38 renal transplant patients who underwent kidney biopsy from January 2013 to June 2013. With the Banff score criteria for renal cortical fibrosis as gold standard, 38 subjects were divided into two groups: group 1 (n = 18) with ≤25% cortical fibrosis and group 2 (n = 20) with >26% cortical fibrosis. We then divided this population again into group 3 (n = 20) with ≤ 25% inflammation and group 4 (n = 18) with >26% inflammation based on the Banff score for renal parenchyma inflammation. To estimate renal cortical hardness in both population divisions, we propose an ultrasound strain relative zero-crossing elasticity measurement (ZC) method. In this technique, the relative return to baseline, that is zero strain, of strain in the renal cortex is compared with that of strain in reference soft tissue (between the abdominal wall and pelvic muscles). Using the ZC point on the reference strain decompression slope as standard, we determined when cortical strain crossed zero during decompression. ZC was negative when cortical strain did not return or returned after the reference, whereas ZC was positive when cortical strain returned ahead of the reference. Fisher's exact test was used to examine the significance of differences in ZC between groups 1 and 2 and between groups 3 and 4. The accuracy of ZC in determining moderate cortical fibrosis and moderate inflammation was examined by receiver operating characteristic analysis. The intra-class correlation coefficient and analysis of variance were used to test inter-rater reliability and reproducibility. ZC had good inter-observer agreement (ICC = 0.912) and reproducibility (p = 0.979). ZCs were negative in 18 of 18 cases in group 1 and positive in 19 of 20 cases in group 2 (p ≪ 0.001), and were positive in 18 of 20 cases in group 3 and negative in 17 of 18 cases in group 4 (p ≪ 0.001). The area under the receiver operating characteristic curve was 0.992 ± 0.010 for fibrosis and 0.988 ± 0.021 for inflammation. ZC had 100% sensitivity and 95% specificity when zero strain was used as the cutoff value to determine moderate cortical fibrosis and 94% sensitivity and 90% specificity for inflammation. ZC is a new strain marker that could be straightforward to interpret and perform, making it a potentially practical approach for monitoring progression of cortical fibrosis or inflammation in renal allografts.

Corticomedullary strain ratio: a quantitative marker for assessment of renal allograft cortical fibrosis.

OBJECTIVES: To quantitatively assess the correlation between the corticomedullary strain ratio and cortical fibrosis in renal transplants. METHODS: Using quasistatic ultrasound elasticity imaging, we prospectively assessed the corticomedullary strain ratio in renal allografts of 33 patients who underwent renal transplant sonography and biopsy. Based on Banff score criteria for renal cortical fibrosis, 33 allografts were divided into 2 groups: group 1 (n = 19), with mild (<25%) fibrosis; and group 2 (n = 14), with moderate (>26%) fibrosis. We used 2-dimensional speckle-tracking software to perform offline analysis of cortical and medullary strain induced by external compression by the ultrasound transducer. We then calculated the corticomedullary strain ratio (cortical normalized strain/medullary normalized strain; normalized strain = developed strain/applied strain [deformation from the abdominal wall to the pelvic muscles]). An unpaired 2-tailed t test was used to determine differences in normalized strain and the strain ratio between the groups. Receiver operating characteristic curve analysis was performed to determine the best strain ratio cutoff value for identifying moderate fibrosis. RESULTS: Normalized strain differed between the cortex and medulla (mean ± SD: group 1, 4.58 ± 2.02 versus 2.58 ± 1.38; P = .002; group 2, 1.71 ± 0.42 versus 2.60 ± 0.87; P = .0011). The strain ratio in group 1 was higher than in group 2 (2.06 ± 1.33 versus 0.70 ± 0.20; P = .0007). The area under the receiver operating characteristic curve was 0.964. The sensitivity and specificity of a strain ratio cutoff value of 0.975 for determining moderate fibrosis were 92.9% and 94.7%, respectively. CONCLUSIONS: Strain values vary in different compartments of the kidney. The corticomedullary strain ratio on ultrasound elasticity imaging decreases with increasing renal cortical fibrosis, which makes it potentially useful as a noninvasive quantitative marker for monitoring the progression of fibrosis in renal transplants.

Assessment of a new mathematical model for the computation of numerical parameters related to renal cortical blood flow and fractional blood volume by contrast-enhanced ultrasound.

We analyzed the value of a new mathematical model for the quantification of renal cortical blood flow and fractional blood volume by contrast-enhanced ultrasound after the injection of sulfur hexafluoride-filled microbubbles. A vessel-mimicking phantom experiment was preliminarily performed which showed that the effect of microbubble diffusion is negligible compared with the effect of liquid drag. Twelve healthy volunteers (7 male, 5 female; 27 to 48 years [n = 6; group 1], and 61 to 80 years [n = 6; group 2], respectively), with normal renal and cardiac function and not undergoing any pharmacologic treatment, were examined. In each volunteer, both kidneys were scanned after intravenous injection of sulfur hexafluoride-filled microbubbles at a slow rate (4.8 mL at a flow of 4.0 mL/min), and the refill kinetics of the renal cortex after microbubble destruction was evaluated by echo-signal intensity quantification. The progressive replenishment of the renal vessels was approximated both by standard negative exponential function and by the piecewise linear function resulting from our mathematical model. A better dataset approximation was provided by piecewise linear versus standard negative exponential function (overall mean square error: 0.44 vs. 0.51; p < 0.05, Wilcoxon test). The piecewise linear function provided a curve composed of four linear tracts (n = 3 volunteers; 2 from group 1 and 1 from group 2), three linear tracts (n = 6 volunteers; 3 from group 1 and 3 from group 2) or two linear tracts (n = 3 volunteers; 1 from group 1 and 2 from group 2). The piecewise linear function versus standard negative exponential function improved data approximation for the computation of numerical values related to renal cortical blood flow velocity and fractional blood volume.

Quantitative assessment of renal cortical echogenicity in clinically normal cats.

In this study, we assessed the renal cortical echogenicity of clinically normal adult cats by histogram analysis to obtain basic ultrasonographic data. Ultrasound images were taken under the following sets of conditions: (1) high contrast and low gain setting using a convex probe, (2) low contrast and high gain setting using a convex probe, (3) high contrast and low gain setting using a linear probe and (4) low contrast and high gain setting using a linear probe. Echogenicity of the region of interest (ROI) in the right and left renal cortices, liver and spleen was determined by histogram analysis; kidney/spleen (Kid/Sp) and kidney/liver (Kid/Liv) echogenicity ratios were calculated. Kid/Sp and Kid/Liv values varied among different ROI sites in the kidney when obtained using the convex probe, but were constant when obtained using the linear probe. Kid/Sp measured in the middle sites of the kidney showed similar values for the different settings; however, Kid/Liv differed between probes. The present findings suggest that determination of Kid/Sp using a linear probe is a feasible method for quantitative evaluation of renal cortical echogenicity in cats.

Comparison of mathematic models for assessment of glomerular filtration rate with electron-beam CT in pigs.

PURPOSE: To prospectively compare in pigs three mathematic models for assessment of glomerular filtration rate (GFR) on electron-beam (EB) computed tomographic (CT) images, with concurrent inulin clearance serving as the reference standard. MATERIALS AND METHODS: This study was approved by the institutional animal care and use committee. Inulin clearance was measured in nine pigs (18 kidneys) and compared with single-kidney GFR assessed from renal time-attenuation curves (TACs) obtained with EB CT before and after infusion of the vasodilator acetylcholine. CT-derived GFR was calculated with the original and modified Patlak methods and with previously validated extended gamma variate modeling of first-pass cortical TACs. Statistical analysis was performed to assess correlation between CT methods and inulin clearance for estimation of GFR with least-squares regression analysis and Bland-Altman graphical representation. Comparisons within groups were performed with a paired t test. RESULTS: GFR assessed with the original Patlak method indicated poor correlation with inulin clearance, whereas GFR assessed with the modified Patlak method (P < .001, r = 0.75) and with gamma variate modeling (P < .001, r = 0.79) correlated significantly with inulin clearance and indicated an increase in response to acetylcholine. CONCLUSION: CT-derived estimates of GFR can be significantly improved by modifications in image analysis methods (eg, use of a cortical region of interest).

Risk assessment of renal cortical scarring with urinary tract infection by clinical features and ultrasonography.

AIMS: To address some of the issues in the ongoing debate over the optimal diagnostic imaging following childhood urinary tract infection (UTI), by determining the risk of missing renal cortical scarring which would be detected on a technetium-99m dimercaptosuccinic acid (DMSA) gold standard if ultrasound alone were used, factoring for clinical features (upper or lower tract), UTI recurrence, and age group (infants, preschool, or school age). METHODS: Details of UTI clinical features and recurrence were recorded for 990 children with a proven UTI, and their DMSA and ultrasound results were compared for each kidney. RESULTS: The risks of missing DMSA scarring varied between 0.4% (school age children with solitary lower tract UTI) and 11.1% (infants with recurrent upper tract UTI). CONCLUSIONS: UTI clinical features are important in assessing the need for DMSA imaging. Current UK imaging guidelines are endorsed, although preschool children with solitary lower tract UTI remain a controversial group and more attention needs to focused on children with recurrent UTI.

Economic issue in pediatric nuclear medicine: cortical scanning of acute pyelonephritis.

Pediatric nuclear medicine, in order to survive, must be innovative in finding ways of competing with other pediatric imaging subspecialties for the health care dollars. Newer radiopharmaceuticals and imaging methods that are time-effective in answering clinical problems and cost-effective in attracting the health care providers are ways of accomplishing this difficult task. Renal cortical scanning for the diagnosis of acute pyelonephritis is presented as an example of an existing nuclear medicine study that is accurate and cost-effective, but has not yet taken a major place in the imaging armamentarium. In this discussion, the cortical scan is endorsed as the primary imaging tool for children presenting with acute urinary infection.

Assessment of the cortical rim sign in posttraumatic renal infarction.

PURPOSE: The cortical rim sign has frequently been described as a sign of renal infarction. It is reported to be present in approximately 50% of focal or global infarcts and is thought to be due to an intact renal collateral circulation. This study evaluates the incidence and temporal development of the cortical rim sign in posttraumatic renal vascular compromise. METHOD: This retrospective study included 20 patients who were diagnosed by contrast-enhanced CT to have posttraumatic focal or global infarcts. The CT scans were reviewed to evaluate the size of infarcts and the presence and appearance of the rim sign. Medical records were reviewed to identify the timing of trauma in relation to the CT examination. RESULTS: Eight patients had multiple CT examinations and 12 had a single CT study. For all cases that demonstrated a rim sign (n = 14, 8 of which had more than one CT), the earliest appearance of the rim sing was 8 h (median time to appearance was 7 days). All cases with no rim sign (n = 6) were evaluated within 10 h of trauma, with a median time of 4 h. CONCLUSION: This study suggests that in spite of the presence of renal collateral circulation, it takes a minimum period of 8 h after trauma for this circulation to expand and become apparent on CT. CT demonstrated a rim sign in all cases performed after 1 week.