Functional MRI: evaluation of chronic kidney disease with perfusion imaging

Multiparametric Quantitative Ultrasound Imaging in Assessment of Chronic Kidney Disease

OBJECTIVES

To evaluate the value of multiparametric quantitative ultrasound imaging in assessing chronic kidney disease (CKD) using kidney biopsy pathologic findings as reference standards.

METHODS

We prospectively measured multiparametric quantitative ultrasound markers with grayscale, spectral Doppler, and acoustic radiation force impulse imaging in 25 patients with CKD before kidney biopsy and 10 healthy volunteers. Based on all pathologic (glomerulosclerosis, interstitial fibrosis/tubular atrophy, arteriosclerosis, and edema) scores, the patients with CKD were classified into mild (no grade 3 and <2 of grade 2) and moderate to severe (at least 2 of grade 2 or 1 of grade 3) CKD groups. Multiparametric quantitative ultrasound parameters included kidney length, cortical thickness, pixel intensity, parenchymal shear wave velocity, intrarenal artery peak systolic velocity (PSV), end-diastolic velocity (EDV), and resistive index. We tested the difference in quantitative ultrasound parameters among mild CKD, moderate to severe CKD, and healthy controls using analysis of variance, analyzed correlations of quantitative ultrasound parameters with pathologic scores and the estimated glomerular filtration rate (GFR) using Pearson correlation coefficients, and examined the diagnostic performance of quantitative ultrasound parameters in determining moderate CKD and an estimated GFR of less than 60 mL/min/1.73 m² using receiver operating characteristic curve analysis.

RESULTS

There were significant differences in cortical thickness, pixel intensity, PSV, and EDV among the 3 groups (all P < .01). Among quantitative ultrasound parameters, the top areas under the receiver operating characteristic curves for PSV and EDV were 0.88 and 0.97, respectively, for determining pathologic moderate to severe CKD, and 0.76 and 0.86 for estimated GFR of less than 60 mL/min/1.73 m² . Moderate to good correlations were found for PSV, EDV, and pixel intensity with pathologic scores and estimated GFR.

CONCLUSIONS

The PSV, EDV, and pixel intensity are valuable in determining moderate to severe CKD. The value of shear wave velocity in assessing CKD needs further investigation.

Is low b-factors-based apparent diffusion coefficient helpful in assessing renal dysfunction?

PURPOSE

To investigate whether low b-factors-based apparent diffusion coefficient (ADC) is helpful in assessing renal dysfunction.

MATERIALS AND METHODS

Forty-four subjects were recruited, and classified as having severe renal injury group (sRI) or not (non-sRI) according to a threshold of estimated glomerular filtration rate (eGFR) = 30 ml/min/1.73 m(2). A free-breathing DWI with 7 b-factors (0, 20, 40, 80, 200, 400, and 800 s/mm(2)) was performed. After choosing an anatomical section that covered the largest part of right kidney, the regions of interest covered the renal parenchyma. For each subject, two apparent diffusion coefficients based on all b-factors less than 400 s/mm(2) (ADC0-400) and 800 s/mm(2) (ADC0-800) were calculated by fitting the signal intensity at different b-factors to a mono-exponential decay, respectively. It was found that the examination time of the free-breathing DWI sequence in this study can be reduced from 3.27 to 2.55 min if the b-factor (800 s/mm(2)) is removed.

RESULTS

ADC0-400 was larger than ADC0-800 in each group (P < 0.05). Both ADC0-400 and ADC0-800 were smaller in the sRI group than those in the non-sRI group (P < 0.01), and they were linearly related with eGFR (P < 0.05). While a significant difference was not found between the two coefficients to differentiate sRI from non-sRI participants (P > 0.05), a strong correlation was present between ADC0-400 and ADC0-800 (r = 0.856, P < 0.001).

CONCLUSION

The low b-factors-based ADC was an economical option for reducing the examination time without sacrificing its diagnostic performance.

Correlation of histopathologic and dynamic tissue perfusion measurement findings in transplanted kidneys

Background

Cortical perfusion of the renal transplant can be non-invasively assessed by color Doppler ultrasonography. We performed the Dynamic Tissue Perfusion Measurement (DTPM) of the transplant’s renal cortex using color Doppler ultrasonography (PixelFlux technique), and compared the results with the histopathological findings of transplant biopsies.

Methods

Ninety-six DTPM studies of the renal transplant’s cortex followed by transplant biopsies were performed in 78 patients. The cortical perfusion data were compared with the parameter of peritubular inflammatory cell accumulation (PTC 0 to 3) based on Banff-classification system.

Results

A significant decrease of cortical perfusion could be demonstrated as the inflammatory cells accumulation in peritubular capillaries increased. Increasing peritubulitis caused a perfusion loss from central to distal layers of 79% in PTC 0, of 85% in PTC 1, of 94% in PTC 2, and of 94% in PTC 3. Furthermore, the perfusion loss due to peritubular inflammation was more prominent in the distal cortical layer. The extent of perfusion decline with increasing peritubulitis (from PTC 0 to PTC 3) was 64% in proximal 20% cortical layer (p20), 63% in proximal 50% cortical layer (p50), increased to 76% in distal 50% cortical layer (d50), and peaked at 90% in the distal 20% cortical layer (d20). For those without peritubulitis (PTC 0), the increase in the the Interstitial Fibrosis/Tubular Atrophy (IF/TA) score was accompanied by a significantly increased cortical perfusion. A Polyomavirus infection was associated with an increased cortical perfusion.

Conclusions

Our study demonstrated that the perfusion of the renal transplant is associated with certain pathological changes within the graft. DTPM showed a significant reduction of cortical perfusion in the transplant renal cortex related to peritubular capillary inflammation.

Dynamic MR imaging of kidneys perfused with EOB-Gd-DTPA

Gandolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) is a hepatobiliary contrast agent for MRI. It was reported that Gd-EOB-DTPA is useful to detect liver tumors and differentially diagnose benign and malignant pathologies in the liver. Since Gd-EOB-DTPA partially accumulates in the hepatocytes and bile via various transporters after intravenous injection, signal intensity in the liver increases on T1-weighted images. The signal intensity of the liver after Gd-EOB-DTPA injection depends on the Gd-EOB-DTPA uptake by hepatocytes and bile excretion. It is known tha the Gd-EOB-DTPA accumulating in the kidney is excreted to the urine through glomerular filtration. Because Gd-DTPA is concentrated in the renal tubules after being filtered at the Bowman's capsule, and since it is neither secreted nor reabsorbed the concentrating and diluting function of the renal tubules can be studied by imaging techniques. since renal function can be evaluated with Gd-EOB-DTPA can also be used to evaluate renal function. Eith the development of MRI equipment and rapid imaging techniques, temporal resolution had improved greatly. However, no previous study has been carried out on renal function using Gd-EOB-DTPA dynamic MR study that was correlated with estimated glomerular filtration rate (eGFR) and stage of chronic kidney disease (CKD) in the Japan Association of chronic kidney disease initiative.

Distinct patterns of kidney and liver cyst growth in pkd2(WS25/-) mice

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disease that results in the development of cystic kidneys and liver. Pkd2(WS25/-) mice are a key genetic mouse model of human ADPKD that recapitulate the 'molecular recessive' nature of human ADPKD. Providing the foundation for future long-term studies, the present work documents distinct patterns of long-term cyst growth in the kidneys and liver of male and female pkd2(WS25/-) mice.

METHODS

Gravimetric measurements documented the progression of kidney and liver growth in male and female pkd2(WS25/-) mice over 12 months. A fast imaging with steady-state precision-magnetic resonance imaging (FISP-MRI) technique to measure kidney and liver organ and cyst volumes was optimized and validated. Longitudinal FISP-MRI analyses of changes in cyst volumes were performed in pkd2(WS25/-) mice over 15 months.

RESULTS

Male and female pkd2(WS25/-) mice had significant increases in kidney weights after 4 months of age. The progression of kidney growth was minimal after 4 months of age. Liver cyst growth in male pkd2(WS25/-) mice was minimal after 4 months of age but showed an accelerated rate of growth after 8 months of age. Female pkd2(WS25/-) mice also showed accelerated growth but this was delayed in time when compared with male pkd2(WS25/-) mice.

CONCLUSIONS

Pkd2(WS25/-) mice are a genetic mouse model that recapitulates the early phenotypic characteristics of human ADPKD kidney cystogenesis. Male pkd2(WS25/-) mice consistently display a late progression in liver growth that is seen in clinically impacted livers of human ADPKD patients.