Anisotropic diffusion in kidney: apparent diffusion coefficient measurements for clinical use

The Use of Diffusion Tensor Imaging in the Identification of Acute Rejection and Chronic Allograft Nephropathy After Renal Transplantation

BACKGROUND

Identifying the cause of renal allograft dysfunction is important for the clinical management of kidney transplant recipients.

PURPOSE

To evaluate the diagnostic efficiency of diffusion tensor imaging (DTI) for identifying allografts with acute rejection (AR) and chronic allograft nephropathy (CAN).

STUDY TYPE

Prospective.

SUBJECTS

Seventy-seven renal transplant patients (aged 42.5 ± 9.5 years), including 29 patients with well-functioning stable allografts (Control group), 25 patients diagnosed with acute rejection (AR group), and 23 patients diagnosed with chronic allograft nephropathy (CAN group).

FIELD STRENGTH/SEQUENCE

1.5 T/T2-weighted imaging and DTI.

ASSESSMENT

The serum creatinine, proteinuria, pathologic results, and fractional anisotropy (FA) values were obtained and compared among the three groups.

STATISTICAL TEST

One-way analysis of variance; correlation analysis; independent-sample t-test; intraclass correlation coefficients and receiver operating characteristic curves. Statistical significance was set to a P-value <0.05.

RESULTS

The AR and CAN groups presented with significantly elevated serum creatinine as compared with the Control group (191.8 ± 181.0 and 163.1 ± 115.8 μmol/L vs. 82.3 ± 20.9 μmol/L). FA decreased in AR group (cortical/medullary: 0.13 ± 0.02/0.31 ± 0.07) and CAN group (cortical/medullary: 0.11 ± 0.02/0.27 ± 0.06), compared with the Control group (cortical/medullary: 0.15 ± 0.02/0.35 ± 0.05). Cortical FA in the AR group was higher than in the CAN group. The area under the curve (AUC) for identifying AR from normal allografts was 0.756 and 0.744 by cortical FA and medullary FA, respectively. The AUC of cortical FA and medullary FA for differentiating CAN from normal allografts was 0.907 and 0.830, respectively. The AUC of cortical FA and medullary FA for distinguishing AR and CAN from normal allografts was 0.828 and 0.785, respectively. Cortical FA was able to distinguish between AR and CAN with an AUC of 0.728.

DATA CONCLUSION

DTI was able to detect patients with dysfunctional allografts. Cortical FA can further distinguish between AR and CAN.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

Precision of region of interest-based tri-exponential intravoxel incoherent motion quantification and the role of the Intervoxel spatial distribution of flow velocities

PURPOSE

The purpose of this work was to obtain precise tri-exponential intravoxel incoherent motion (IVIM) quantification in the liver using 2D (b-value and first-order motion moment [M1 ]) IVIM-DWI acquisitions and region of interest (ROI)-based fitting techniques.

METHODS

Diffusion MRI of the liver was performed in 10 healthy volunteers using three IVIM-DWI acquisitions: conventional monopolar, optimized monopolar, and optimized 2D (b-M1 ). For each acquisition, bi-exponential and tri-exponential full, segmented, and over-segmented ROI-based fitting and a newly proposed blood velocity SDdistribution (BVD) fitting technique were performed to obtain IVIM estimates in the right and left liver lobes. Fitting quality was evaluated using corrected Akaike information criterion. Precision metrics (test-retest repeatability, inter-reader reproducibility, and inter-lobar agreement) were evaluated using Bland-Altman analysis, repeatability/reproducibility coefficients (RPCs), and paired sample t-tests. Precision was compared across acquisitions and fitting methods.

RESULTS

High repeatability and reproducibility was observed in the estimations of the diffusion coefficient (Dtri  = [1.03 ± 0.11] × 10-3  mm2 /s; RPCs ≤ 1.34 × 10-4  mm2 /s), perfusion fractions (F1  = 3.19 ± 1.89% and F2  = 16.4 ± 2.07%; RPCs ≤ 2.51%), and blood velocity SDs (Vb,1  = 1.44 ± 0.14 mm/s and Vb,2  = 3.62 ± 0.13 mm/s; RPCs ≤ 0.41 mm/s) in the right liver lobe using the 2D (b-M1 ) acquisition in conjunction with BVD fitting. Using these methods, significantly larger (p < 0.01) estimates of Dtri and F1 were observed in the left lobe in comparison to the right lobe, while estimates of Vb,1 and Vb,2 demonstrated high interlobar agreement (RPCs ≤ 0.45 mm/s).

CONCLUSIONS

The 2D (b-M1 ) IVIM-DWI data acquisition in conjunction with BVD fitting enables highly precise tri-exponential IVIM quantification in the right liver lobe.

Diffusion-weighted magnetic resonance imaging in rat kidney using two-dimensional navigated, interleaved echo-planar imaging at 7.0 T

The purpose of this study was to investigate the feasibility of two-dimensional (2D) navigated, interleaved multishot echo-planar imaging (EPI) to enhance kidney diffusion-weighted imaging (DWI) in rats at 7.0 T. Fully sampled interleaved four-shot EPI with 2D navigators was tailored for kidney DWI (Sprague-Dawley rats, n = 7) on a 7.0-T small bore preclinical scanner. The image quality of four-shot EPI was compared with T₂ -weighted rapid acquisition with relaxation enhancement (RARE) (reference) and single-shot EPI (ss-EPI) without and with parallel imaging (PI). The contrast-to-noise ratio (CNR) was examined to assess the image quality for the EPI approaches. The Dice similarity coefficient and the Hausdorff distance were used for evaluation of image distortion. Mean diffusivity (MD) and fractional anisotropy (FA) were calculated for renal cortex and medulla for all DWI approaches. The corticomedullary difference of MD and FA were assessed by Wilcoxon signed-rank test. Four-shot EPI showed the highest CNR among the three EPI variants and lowest geometric distortion versus T₂ -weighted RARE (mean Dice: 0.77 for ss-EPI without PI, 0.88 for ss-EPI with twofold undersampling, and 0.92 for four-shot EPI). The FA map derived from four-shot EPI clearly identified a highly anisotropic region corresponding to the inner stripe of the outer medulla. Four-shot EPI successfully discerned differences in both MD and FA between renal cortex and medulla. In conclusion, 2D navigated, interleaved multishot EPI facilitates high-quality rat kidney DWI with clearly depicted intralayer and interlayer structure and substantially reduced image distortion. This approach enables the anatomic integrity of DWI-MRI in small rodents and has the potential to benefit the characterization of renal microstructure in preclinical studies.

Does diffusion-weighted magnetic resonance imaging help in the detection of renal parenchymal disease and staging/prognostication in chronic kidney disease?

Purpose

Diffusion-weighted imaging (DWI) in renal diseases is an upcoming modality, and its utility as an additional marker is yet to be proven. This study was intended to find the relationship between apparent diffusion coefficient (ADC) values with renal function tests and stages of chronic kidney disease (CKD) to assess renal dysfunction, and to label a cut-off for normal renal function and dysfunction.

Material and methods

A prospective diagnostic study was conducted on 120 patients: 60 with deranged renal function tests (RFT) and 60 with normal RFT. DWI using a 1.5-Tesla MRI (at b-values of 0 and 500 s/mm²) was done. A region of interest of size 1-2 cm² was placed on renal parenchyma in the region of medulla, one each, over the superior, mid, and lower regions of each kidney separately. ADC values were recorded for renal parenchyma and compared.

Results

In patients with renal dysfunction ADC values were significantly lower than in patients with normal function (1.75 ± 0.25 vs. 2.28 ± 0.21 of right kidney and 1.79 ± 0.17 vs. 2.29 ± 0.21 of left kidney [×10⁻³ mm²/s]; p = 0.001). ADC values of different stages of CKD showed a decreasing trend with increasing stage.

Conclusions

ADC values taken at all poles to get focal involvement of the kidney can be used to measure each kidney separately, and values can be individually correlated with the elevated renal parameters. The cut-off value of the mean ADC for individual kidneys was > 2.28 (×10⁻³ mm²/s) in normal renal function and < 2.00 (×10⁻³ mm²/s) in renal dysfunction.

Restricted diffusion MRI as a functional biomarker for the assessment of acute calcular upper urinary tract obstruction: initial experience

Background

Acute renal obstruction due to stone is a prevalent scenario. The diffusion-weighted magnetic resonance imaging (DWI) of the kidneys provides a noninvasive information on renal function. Our objective is to prospectively assess the potential role of DWI to predict the signal changes of a kidney with acute calcular obstruction.

Results

Chi-square and Fissure exact tests were used to assess the association of diffusion signal changes among patients and control groups. Cohen's Kappa test was run to determine the degree of agreement between the two radiologists. An independent sample t-test was performed to assess the significant difference among ADC values between the two groups. Restricted signals of the obstructed kidneys showed a statistically significant difference when compared with contralateral unobstructed kidney and control group with p value (0.001) and (0.01), respectively. Furthermore, there is a moderate agreement between the two radiologists K = 0.7, p = 0. 001. There is no statistically significant difference in ADC values when comparing the obstructed kidney and the contralateral unobstructed kidney of the patient group or with the control group p value (0.06) and (0.05), respectively.

Conclusion

Restricted signals of the obstructed kidney by DWI may be a helpful tool in diagnosing acute unilateral renal obstruction and can affect its management; however, it needs further validation by more studies.

Diffusion tensor imaging based multiparametric characterization of renal lesions in infants with urinary tract infections: an explorative study

Background

Conventional diffusion weighted imaging (DWI) is a promising non-invasive tool in the evaluation of infants with symptomatic urinary tract infections (UTI). The use of multiparametric diffusion tensor imaging (DTI) provides further information on renal pathology by reflecting renal microstructure. However, its potential to characterize and distinguish between renal lesions, such as acute pyelonephritic lesions, permanent renal damages or dysplastic changes has not been shown. This study aimed to evaluate the potential of multiparametric DTI for characterization of renal lesions with purpose to distinguish acute pyelonephritis from other renal lesions in young infants with their first UTI.

Methods

Nine kidneys in seven infants, age 1.0–5.6 months, with renal lesions i.e. uptake reductions, on acute scintigraphy performed after their first UTI, were included. The DTI examinations were performed during free breathing without sedation. The signal in the lesions and in normal renal tissue was measured in the following images: b0, b700, apparent diffusion coefficient (ADC), and fractional anisotropy (FA). In addition, DTI tractographies were produced for visibility.

Results

There was a difference between lesions and normal tissue in b700 signal (197 ± 52 and 164 ± 53, p = 0.011), ADC (1.22 ± 0.11 and 1.45 ± 0.15 mm²/s, p = 0.008), and FA (0.18 ± 0.03 and 0.30 ± 0.10, p = 0.008) for all nine kidneys. Six kidneys had focal lesions with increased b700 signal, decreased ADC and FA indicating acute inflammation. In three patients, the multiparametric characteristics of the lesions were diverging.

Conclusion

Multiparametric DTI has the potential to further characterize and distinguish acute pyelonephritis from other renal lesions in infants with symptomatic UTI.

R, R. S. Role of Diffusion Tensor Imaging in Functional Assessment of Transplant Kidneys at 3-Tesla MRI

Objectives The main purpose of this article is to measure the fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of cortex and medulla of renal allograft using 3-Tesla diffusion tensor imaging (DTI) in renal transplant patients with normal and graft dysfunction and to assess the correlation between diffusion tensor parameters (ADC and FA) and the estimated glomerular filtration rate (eGFR) value.

Materials and Methods Fifty renal transplant recipients who received either living or cadaveric renal allografts were included in the study. Blood samples for serum creatinine and eGFR value were taken on the same day prior to the magnetic resonance study and the patients were assigned to three groups (A, B, C) according to allograft function (eGFR levels). The mean ADC and FA values of the cortex/medulla in upper, mid, and lower poles were calculated from the DTI sequence. Statistical analysis was performed using paired sample Student’s t-test and one-way analysis of variance test.

Results The mean ADC values of the cortex were higher than the medulla that was statistically significant. However, the mean FA values were significantly higher in the medulla than the cortex. Mean ADCs and FA of the renal cortex and medulla were significantly higher in group A patients with normal renal function than in group B and C with poor renal functions. The corticomedullary difference in the FA values was more in group A. However, this difference was lower in group B and more so in group C.

Conclusion ADC and FA values in the renal cortex and medulla exhibit a good correlation with allograft function and were significantly lower in transplants with dysfunction than those with good function. FA values appear to be more sensitive than eGFR and ADC for detection of early pathological changes in the graft dysfunction.

Relationship of renal apparent diffusion coefficient and functional MR urography in children with pelvicalyceal dilation

OBJECTIVE

The aim is to evaluate the age-related changes and relationship of renal apparent diffusion coefficient (ADC) against the morphological and functional changes detected by functional magnetic resonance urography (fMRU) in children with pelvicalyceal dilation, with suspected or known ureteropelvic junction obstruction.

MATERIALS AND METHODS

We retrospectively analyzed fMRUs with diffusion-weighted imaging (DWI) of the kidney in 35 subjects (25 males; median age: 7.1 years, range: 0.3-22.7 years) with 70 kidneys (40 with pelvicalyceal dilation and 30 with no pelvicalyceal dilation). Inclusion criteria were pelvicalyceal dilation, the absence of duplex kidneys and no ureteric dilation. DWI was performed with 3 diffusion gradient directions (b values = 0, 200, 500, 800 and 1,000 s/mm2). Metrics for fMRU included calyceal and renal transit times (CTT, RTT), time-to-peak (TTP), differential renal function based on volume (vDRF), Patlak number (pDRF) and combined volume and Patlak number (vpDRF). The grades of pelvicalyceal dilation, cortical thinning and corticomedullary differentiation were evaluated. The relationship between ADC values and the fMRU parameters was analyzed.

RESULTS

ADC increases with age in kidneys without pelvicalyceal dilation (R²=0.37, P<0.001). Renal ADC does not correlate with any of the morphological or fMRU parameters (P>0.07). The median ADC of kidneys without pelvicalyceal dilation was 3.73×10^-3 mm²/s (range: 2.78-5.37×0^-3 mm²/s) and the median ADC of kidneys with pelvicalyceal dilation was 3.82×10^-3 mm²/s (range: 2.70-5.70×10^-3 mm²/s). There was no correlation between ADC and the absolute differences of vDRF or pDRF (P>0.33).

CONCLUSION

Renal ADC does not correlate with morphological and functional results of fMRU changes in children with pelvicalyceal dilation due to suspected or known ureteropelvic junction obstruction.

Perfusion-weighted and diffusion-weighted magnetic resonance imaging of the liver, spleen, and kidneys of healthy adult male cats

OBJECTIVE To describe perfusion and diffusion characteristics of the liver, spleen, and kidneys of healthy adult male cats as determined by morphological, perfusion-weighted, and diffusion-weighted MRI. ANIMALS 12 healthy adult male cats. PROCEDURES Each cat was anesthetized. Morphological, perfusion-weighted, and diffusion-weighted MRI of the cranial aspect of the abdomen was performed. A region of interest (ROI) was established on MRI images for each of the following structures: liver, spleen, cortex and medulla of both kidneys, and skeletal muscle. Signal intensity was determined, and a time-intensity curve was generated for each ROI. The apparent diffusion coefficient (ADC) was calculated for the hepatic and splenic parenchyma and kidneys on diffusion-weighted MRI images. The normalized ADC for the liver was calculated as the ratio of the ADC for the hepatic parenchyma to the ADC for the splenic parenchyma. RESULTS Perfusion-weighted MRI variables differed among the 5 ROIs. Median ADC of the hepatic parenchyma was 1.38 × 10^-3 mm²/s, and mean ± SD normalized ADC for the liver was 1.86 ± 0.18. Median ADC of the renal cortex and renal medulla was 1.65 × 10^-3 mm²/s and 1.93 × 10^-3 mm²/s, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Results provided preliminary baseline information about the diffusion and perfusion characteristics of structures in the cranial aspect of the abdomen of healthy adult male cats. Additional studies of cats of different sex and age groups as well as with and without cranial abdominal pathological conditions are necessary to validate and refine these findings.

The role of MR imaging in the assessment of renal allograft vasculature

Renal allograft dysfunction after transplantation is a relatively common occurrence with various potential etiologies. Vascular etiologies are of particular importance as early surgical or minimally invasive intervention can, in some cases, salvage the graft. Diagnosis of vascular pathology resulting in allograft dysfunction requires a thorough workup, of which imaging is a key component. Generally, ultrasound is the first-line imaging modality. More recently, MRI has been shown to be an effective and safe modality for diagnosis of vascular pathology after renal transplantation, particularly for diagnosis of transplant renal artery stenosis. This review will summarize imaging modalities that are most commonly used in evaluating vascular pathology after renal transplantation, with a focus on the various contrast- and non-contrast-enhanced MR techniques described in the literature and used at our institution. Of particular interest is the relatively recent utilization of the non-gadolinium containing iron-based contrast agent, ferumoxytol, in time-resolved contrast-enhanced MR angiography.

Rejection evaluation after renal transplantation using MR diffusion tensor imaging

Background Renal allograft dysfunction monitoring is mainly performed using the serum creatinine (SC) level, Doppler ultrasound (US), or renal biopsy. Recently proposed diffusion-based magnetic resonance imaging (MRI) methods have been explored as new, non-invasive tools for assessing renal function after transplantation. Purpose To investigate the value of fractional anisotropy (FA) measurements in the evaluation of acute rejection cases after renal transplant. Material and Methods Doppler US and MRI diffusion tensor imaging (DTI) were performed in 21 patients with graft dysfunction requiring graft biopsy after renal transplantation and in 21 patients with normal graft function. The MR examinations were performed on a 1.5-T MRI using two b-values (0 and 800 s/mm²). FA values were measured from the cortex and medulla of the transplanted kidney at the upper, middle, and lower poles. Results Twenty-one transplant patients diagnosed with acute rejection (Group 1) were compared to the control group of 21 transplant patients with normal graft function (Group 2). The measured FA values of the medulla were 0.19 ± 0.02 and 0.22 ± 0.05 ( P = 0.017) for Groups 1 and 2, respectively. On the other hand, the measured FA values of the renal cortex were 0.18 ± 0.04 and 0.18 ± 0.04 ( P = 0.97) for Groups 1 and 2, respectively. Conclusion The good correlation between the renal medulla FA values and allograft function shows that MR DTI has potential for non-invasive functional assessment of transplanted kidneys. On the other hand, the renal cortex FA values had no correlation with the allograft function.

REnal Flow and Microstructure AnisotroPy (REFMAP) MRI in Normal and Peritumoral Renal Tissue

BACKGROUND

Diffusion-weighted imaging (DWI) provides insight into the pathophysiology underlying renal dysfunction. Variants of DWI include intravoxel incoherent motion (IVIM), which differentiates between microstructural diffusion and vascular or tubular flow, and diffusion tensor imaging (DTI), which quantifies diffusion directionality.

PURPOSE

To investigate the reproducibility of joint IVIM-DTI and compare controls to presurgical renal mass patients.

STUDY TYPE

Prospective cross-sectional.

SUBJECTS

Thirteen healthy controls and ten presurgical renal mass patients were scanned. Ten controls were scanned twice to investigate reproducibility.

FIELD STRENGTH/SEQUENCE

Subjects were scanned on a 3T system using 10 b-values and 20 diffusion directions for IVIM-DTI in a study approved by the local Institutional Review Board.

ASSESSMENT

Retrospective coregistration and measurement of joint IVIM-DTI parameters were performed.

STATISTICAL ANALYSIS

Parameter reproducibility was defined as intraclass correlation coefficient (ICC) >0.7 and coefficient of variation (CV) <30%. Patient data were stratified by lesion side (contralateral/ipsilateral) for comparison with controls. Corticomedullary differentiation was evaluated.

RESULTS

In controls, the reproducible subset of REnal Flow and Microstructure AnisotroPy (REFMAP) parameters had average ICC = 0.82 and CV = 7.5%. In renal mass patients, medullary fractional anisotropy (FA) was significantly lower than in controls (0.227 ± 0.072 vs. 0.291 ± 0.044, P = 0.016 for the kidney contralateral to the mass and 0.228 ± 0.070 vs. 0.291 ± 0.044, P = 0.018 for the kidney ipsilateral). In the kidney ipsilateral to the mass, cortical D_p,radial was significantly higher than in controls (P = 0.012). Conversely, medullary D_p,axial was significantly lower in contralateral than ipsilateral kidneys (P = 0.027) and normal controls (P = 0.044).

DATA CONCLUSION

REFMAP-MRI parameters provide unique information regarding renal dysfunction. In presurgical renal mass patients, directional flow changes were noted that were not identified with IVIM analysis alone. Both contralateral and ipsilateral kidneys in patients show reductions in structural diffusivities and anisotropy, while flow metrics showed opposing changes in contralateral vs. ipsilateral kidneys.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018.

Computed diffusion weighted imaging (cDWI) and voxelwise-computed diffusion weighted imaging (vcDWI) for oncologic liver imaging: A pilot study

Objective

Aim of the study was to evaluate the influence of the selection of measured b-values on the precision of cDWI in the upper abdomen as well as on the lesion contrast of PET-positive liver metastases in cDWI and vcDWI.

Methods

We performed a retrospective analysis of 10 patients (4 m, 63.5 ± 12.9 y/o) with PET-positive liver metastases examined in 3 T-PET/MRI with b = 100,600,800,1000 and 1500s/mm². cDWI (cb1000/cb1500) and vcDWI were computed based on following combinations: i) b = 100/600 s/mm², ii) b = 100/800 s/mm², iii) b = 100/1000s/mm², iv) b = 100/600/1000s/mm² v) all measured b-values. Mean signal intensity (SI) and standard deviation (SD) in the liver, spleen, kidney, bone marrow and in liver lesions were acquired. The coefficient of variation (CV = SD/SI), the differences of SI between measured and calculated high b-value images and the lesion contrast (SI lesion/liver) were computed.

Results

With increasing upper measured b-values, the CV in cDWI and vcDWI decreased (CV in the liver in cb1500: 0.42 with b100/600 s/mm² and 0.28 with b100/b1000s/mm²) while the differences of measured and calculated b-value images decreased (in the liver in cb1500: 30.7% with b = 100/600 s/mm², 19.7% with b100/b1000s/mm²). In diffusion-restricted lesions, lesion contrast was at least 1.6 in cb1000 and 1.4 in cb1500, respectively, with an upper measured b-value of b = 800 s/mm² and 2.1 for vcDWI with an upper measured b-value of b = 1000s/mm². Overall, the lesion contrast was superior in cb1500 and vcDWI compared to cb1000 (15% and 11%, respectively).

Conclusion

Measuring higher upper b-values seems to lead to more precise computed high b-value images and a decrease of CV. vcDWI provides a comparable lesion contrast to b = 1500s/mm² and offers additionally the reduction of T2 shine-through effects. For vcDWI, measuring b = 1000s/mm² as upper b-value seems to be necessary to guarantee good lesion visibility in the liver based on our preliminary results.

MR urogram findings and diffusion restriction in the renal papilla and calyx in papillary necrosis-a new finding: preliminary report

Renal papillary necrosis is a clinicopathological entity where any or all of the papillae undergo selective necrosis, which can be demonstrated either radiologically or histologically. The most important causes are diabetes, pyelonephritis, obstructive uropathy, tuberculosis, analgesic abuse or overuse, sickle cell disease and renal vein thrombosis. Although this condition was first described in the 19th century the clinical diagnosis of this condition remains a problem to this day. Uncomplicated papillary necrosis may initially remain occult to imaging by ultrasound and non-contrast CT, but may later be complicated by obstructive uropathy. A few studies have described renal papillary necrosis on CT urogram. In this case series, the authors describe the finding of calyceal filling defect with diffusion restriction in the calyx and the tip of the renal pyramid on MR urogram, along with other findings that are classically seen on intravenous urogram or CT urogram. To the best of our knowledge, the finding of diffusion restriction at the tip of the renal pyramid has not been described before. Further, literature review showed only a single study describing the classical findings of papillary necrosis on an MR urogram. The early diagnosis of papillary necrosis on MR imaging equips the radiologist to suggest short-term clinical and radiological follow-up to check for the development of hydronephrosis. Additionally, such risk stratification may enable early ureteric stenting to prevent the development of obstructive uropathy.

3 Tesla-Diffusion Tensor Imaging in Autosomal Dominant Polycystic Kidney Disease: The Nephrologist's Point of View

BACKGROUND/AIMS

CT, MRI and ultrasound are currently used for screening and follow-up of individuals affected by autosomal dominant polycystic kidney disease (ADPKD). Dynamic contrast-enhanced MRI studies renal perfusion after gadolinium administration, with possible side effects, such as nephrogenic systemic fibrosis. The aim of our study was to evaluate the clinical application of 3 Tesla (3T)-diffusion tensor image (DTI) in ADPKD patients, correlating its parameters, such as fractional anisotropy (FA), and apparent diffusion coefficient (ADC) with kidney function tests.

METHODS

Eight ADPKD patients and 6 healthy volunteers (HS) were enrolled. FA and ADC mean values were calculated. And correlations between DTI-parameters, creatinine and estimated glomerular filtration rate (eGFR) were evaluated.

RESULTS

Parenchymal FA was significantly lower in ADPKD than HS (FA: 0.17 ± 0.03 vs. 0.22 ± 0.01; p = 0.02), whereas parenchymal ADC was higher in patients than controls (2.48 (×10-3) ± 0.16 vs. 2.28 (×10-3) ± 0.09), but a statistically significant difference was not achieved (p = 0.27). Direct correlations were revealed between eGFR and FA (r = 0.82; p = 0.0003), whereas an inverse correlation was found with creatinine (r = -0.77; p = 0.001). Similarly, ADC closely correlated with creatinine (r = 0.79; p = 0.0006) and eGFR (r = -0.620; p = 0.01).

CONCLUSION

3T-DTI is a promising radiological tool that could be used by nephrologists to evaluate ADPKD patients, highlighting early micro-structure alterations, without side effects and contrast agent administration.

Functional Magnetic Resonance Imaging in Acute Kidney Injury: Present Status

Acute kidney injury (AKI) is a common complication of hospitalization that is characterized by a sudden loss of renal excretory function and associated with the subsequent development of chronic kidney disease, poor prognosis, and increased mortality. Although the pathophysiology of renal functional impairment in the setting of AKI remains poorly understood, previous studies have identified changes in renal hemodynamics, perfusion, and oxygenation as key factors in the development and progression of AKI. The early assessment of these changes remains a challenge. Many established approaches are not applicable to humans because of their invasiveness. Functional renal magnetic resonance (MR) imaging offers an alternative assessment tool that could be used to evaluate renal morphology and function noninvasively and simultaneously. Thus, the purpose of this review is to illustrate the principle, application, and role of the techniques of functional renal MR imaging, including blood oxygen level-dependent imaging, arterial spin labeling, and diffusion-weighted MR imaging, in the management of AKI. The use of gadolinium in MR imaging may exacerbate renal impairment and cause nephrogenic systemic fibrosis. Therefore, dynamic contrast-enhanced MR imaging will not be discussed in this paper.

Functional evaluation of secondary renal amyloidosis with diffusion-weighted MR imaging

OBJECTIVES

This study evaluated whether diffusion-weighted magnetic resonance imaging (DW-MRI) can be used to diagnose secondary renal amyloidosis looking specifically at the diagnostic efficacy of two apparent diffusion coefficient (ADC) measurement methods as they were used with DW-MRI.

METHODS

The study included 24 amyloid nephropathy (AN) patients, 20 chronic kidney disease (CKD) patients, and 20 healthy volunteers (HV). ADC values were measured using two different methods: 1) the method of the region of interest indicators (ROIs) and 2) the method of drawing whole renal parenchyma (WP). The correlation between the two methods was evaluated.

RESULTS

ROIs could differentiate AN-CKD (p = 0.007). ROIs and WP could differentiate AN-HV (p < 0.05). However, none of the methods could differentiate CKD-HV (p > 0.05). The sensitivity and specificity of the ROIs method in differentiating AN from CKD patients for 1.8 × 10(-3) cutoff ADC values were 79% and 60% and for AN-HV patients 79% and 70%. ADC values of AN patients with GFR > 60 mL/min were lower than that of HV (p < 0.01).

CONCLUSION

DW-MRI is a useful and non-invasive diagnostic tool in diagnosing secondary renal amyloidosis and differentiating renal amyloidosis from other CKDs. ROIs had the highest sensitivity and specificity for assessing the involvement of renal amyloidosis. MRI diagnosis of AN may obviate a renal biopsy for diagnosis.

Renal Apparent Diffusion Coefficient Values in Patients with Obstructive Uropathy and High Values of Creatinine

Purpose: Diffusion weighted magnetic resonance imaging (DW-MRI) of the kidneys provides noninvasive information on renal function in healthy volunteers, and it is feasible in severely ill patients. It may provide information on the degree of kidney dysfunction.

The purpose of this study is to evaluate apparent diffusion coefficient (ADC) values using DW-MRI in patients with obstructive uropathy and elevated serum creatinine levels.

Methods: Fifty patients with high serum creatinine levels and diagnoses of chronic urinary obstruction detected by ultrasonography were included in this study.

DW-MRIs were obtained from 50 patients with hydronephrotic kidneys and 26 healthy volunteers using a 1.5T whole-body MR scanner.

Results: ADC measurements of renal parenchyma in hydronephrotic kidneys were significantly lower compared to normal kidneys (p < 001).

Conclusion: The measurement of ADC values has potential value in the evaluation of the functional status of hydronephrotic kidneys.

Relationship between renal apparent diffusion coefficient values and glomerular filtration rate in infants with congenital hydronephrosis

The aim was to investigate the relationship between apparent diffusion coefficient (ADC) values measured by diffusion-weighted magnetic resonance imaging (DW MRI) and the split glomerular filtration rate (GFR) in infants with congenital hydronephrosis. Diffusion-weighted imaging (DWI) (b = 0 and 700 seconds/mm(2)) was performed with a General Electric Company (GE) Signa 1.5T MR unit in 46 infants suffering single congenital hydronephrosis and in 30 healthy infants as normal control group. The ADCs were calculated with regions of interest (ROIs) positioned in the renal parenchyma. The 46 obstructed kidneys were classified into four groups according to the GFR level: renal dysfunction compensated group, renal dysfunction decompensated group, renal failure group, and uremia group. The renal ADCs in six groups (normal kidneys in control group, contralateral kidneys, and four groups of hydronephrotic kidneys) were compared statistically using analysis of variance (ANOVA), and the correlative relationship between ADCs and GFR was examined by Pearson's correlation test. There were statistically significant differences in renal ADCs among the six groups. The ADCs of hydronephrotic kidneys were lower than that of the normal kidneys. There was a moderate positive correlation between the ADCs of hydronephrotic kidneys and split GFR (r = 0.744). This study indicated that the ADCs of congenital hydronephrotic kidneys were lower than that of normal renal parenchyma, and there was a positive correlation between the ADCs and split renal GFR, which demonstrates that the ADCs can reflect the filtration function of hydronephrotic kidneys and may provide some reference to help clinical physician to explore a novel noninvasive approach to evaluate the single renal function.

Diffusion weighted imaging and diffusion tensor imaging in the evaluation of transplanted kidneys

OBJECTIVE

The aim of this study is to investigate the relation between renal indexes and functional MRI in a population of kidney transplant recipients who underwent MR with diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) of the transplanted graft.

METHOD

Study population included 40 patients with single kidney transplant. The patients were divided into 3 groups, on the basis of creatinine clearance (CrCl) values calculated using Cockcroft-Gault formula: group A, including patients with normal renal function (CrCl ≥ 60 mL/min); group B, which refers to patients with moderate renal impairment (CrCl > 30 but <60 mL/min); and, finally, group C, which means severe renal deterioration (CrCl ≤ 30 mL/min). All patients were investigated with a 1.5 Tesla MRI scanner, acquiring DWI and DTI sequences. A Mann-Whitney U test was adopted to compare apparent diffusion coefficients (ADCs) and fractional anisotropy (FA) measurements between groups. Receiver operating characteristic (ROC) curves were created for prediction of normal renal function (group A) and renal failure (group C). Pearson correlation was performed between renal clearance and functional imaging parameter (ADC and FA), obtained for cortical and medullar regions.

RESULTS

Mann-Whitney U test revealed a highly significant difference (p < 0.01) between patients with low CrCl (group C) and normal CrCl (group A) considering both medullar ADC and FA and cortical ADC. Regarding contiguous groups, the difference between group B and C was highly significant (p < 0.01) for medullar ADC and significant (p < 0.05) for cortical ADC and medullar FA. No difference between these groups was found considering cortical FA. Analyzing groups A and B, we found a significant difference (p < 0.05) for medullar both ADC and FA, while no difference was found for cortical ADC and FA. Strongest Pearson correlation was found between CrCl and medullar ADC (r = 0.65). For predicting normal renal function or severe renal impairment, highest values of AUC were observed using medullar ADC cut-off values (respectively 0.885 and 0.871); medullar FA showed also high accuracy (respectively 0.831 and 0.853).

CONCLUSIONS

DWI and DTI are promising tools for non-invasive monitoring of renal function; medullar ADC proved to be the best parameter for renal function assessment.

Renal water molecular diffusion characteristics in healthy native kidneys: assessment with diffusion tensor MR imaging

Background

To explore the characteristics of diffusion tensor imaging (DTI) and magnetic resonance (MR) imaging in healthy native kidneys.

Methods

Seventy-three patients without chronic kidney disease underwent DTI-MRI with spin echo-echo planar (SE-EPI) sequences accompanied by an array spatial sensitivity encoding technique (ASSET). Cortical and medullary mean, axial and radial diffusivity (MD, AD and RD), fractional anisotropy (FA) and primary, secondary and tertiary eigenvalues (λ₁, λ₂, λ₃) were analysed in both kidneys and in different genders.

Results

Cortical MD, λ₂, λ₃, and RD values were higher than corresponding medullary values. The cortical FA value was lower than the medullary FA value. Medullary λ₁ and RD values in the left kidney were lower than in the right kidney. Medullary λ₂, and λ₃ values in women were higher than those in men. Medullary FA values in women were lower than those in men. Medullary FA (r = 0.351, P = 0.002) and λ₁ (r = 0.277, P = 0.018) positively correlated with eGFR. Medullary FA (r = −0.25, P = 0.033) negatively correlated with age.

Conclusions

Renal water molecular diffusion differences exist in human kidneys and genders. Age and eGFR correlate with medullary FA and primary eigenvalue.

Chronic kidney disease: pathological and functional assessment with diffusion tensor imaging at 3T MR

OBJECTIVE

Our objective was to evaluate pathological and functional changes in chronic kidney disease (CKD) using diffusion tensor imaging (DTI) at 3 T.

METHODS

There were fifty-one patients with CKD who required biopsy and 19 healthy volunteers who were examined using DTI at 3 T. The mean values of fractional anisotropy (FA) and the apparent diffusion coefficient (ADC) were obtained from the renal parenchyma (cortex and medulla). Correlations between imaging results and the estimated glomerular filtration rate (eGFR), as well as pathological damage (glomerular lesion and tubulointerstitial injury), were evaluated.

RESULTS

The renal cortical FA was significantly lower than the medullary in both normal and affected kidneys (p < 0.001). The parenchymal FA was significantly lower in patients than healthy controls, regardless of whether eGFR was reduced. There were positive correlations between eGFR and FA (cortex, r = 0.689, p = 0.000; and medulla, r = 0.696, p = 0.000), and between eGFR and ADC (cortex, r = 0.310, p = 0.017; and medulla, r = 0.356, p = 0.010). Negative correlations were found between FA and the glomerular lesion (cortex, r = -0.499, p = 0.000; and medulla, r = -0.530, p = 0.000), and between FA and tubulointerstitial injury (cortex, r = -0.631, p = 0.000; and medulla, r = -0.724, p = 0.000).

CONCLUSION

DTI is valuable for noninvasive assessment of renal function and pathology in patients with CKD. A decrease in FA could identify the glomerular lesions, tubulointerstitial injuries, and eGFR.

Diffusion-weighted magnetic resonance imaging findings of kidneys with obstructive uropathy: differentiation between benign and malignant etiology

PURPOSE

In this study, we aimed to evaluate the capability of diffusion-weighted magnetic resonance imaging (DWI) in differentiation between benign and malignant etiology of obstructive uropathy.

MATERIALS AND METHODS

DWI was performed in 41 patients with hydronephrotic kidneys and 26 healthy volunteers. MR imaging was performed using a 1.5 T whole-body superconducting MR scanner. The signal intensities of the renal parenchyma on DWI and apparent diffusion coefficient (ADC) maps were noted. DWI was performed with the following diffusion gradient b values: 100, 600, and 1000 s/mm(2). A large circular region of interest was placed in the corticomedullary junction of the kidneys. For statistical analysis, the independent-samples t test was used.

RESULTS

The mean renal ADC values for b100, b600, and b1000 in hydronephrosis patients with benign and malignant etiology and the healthy volunteers of the control group were analysed. ADC measurements of renal parenchyma in all hydronephrotic kidneys with benign and malignant etiology were found to be statistically low compared to those of normal kidneys (P < 0.05).

CONCLUSIONS

There were significant differences in the ADC values of obstructed kidneys compared to those of normal kidneys. Obstructed kidneys with malignant etiology had lower ADC values for b1000 compared to obstructed kidneys with benign etiology, but these alterations were statistically insignificant.

Diffusion tensor imaging and tractography of the kidney in children: feasibility and preliminary experience

BACKGROUND

Functional magnetic resonance urography (fMRU) provides morphological and functional information based on perfusion. Diffusion tensor imaging (DTI) complements fMRU by measuring renal microstructure and provides insight into the relationship between renal structure and function.

OBJECTIVE

To evaluate the feasibility and utility of renal DTI and tractography in the setting of fMRU in children.

MATERIALS AND METHODS

We prospectively enrolled 9 children (6 boys, 3 girls) with a mean age of 4.3 years (range 6 months to 14.8 years). All children were examined with MRI at 3.0 tesla. DTI was acquired with an echo-planar sequence (TR/TE = 2,300/69 ms, b = 300 s/mm2) with 12 non-collinear directions and 3 signal averages. Functional MRU results were used to group the moieties as normal or abnormal. Regions of interest were placed in the medulla and cortex to measure DTI parameters of microstructure. DTI tractography measures of parenchymal volume were compared to fMRU-derived volumes.

RESULTS

We analyzed 19 moieties (13 normal; 6 abnormal). Tractography of normal moieties showed numerous tracks with a radial arrangement and convergence into pyramids. Abnormal moieties did not show the radial arrangement or converging architecture and had tracks that were loosely arranged and left hollow spaces. Tractography volume correlated with MRU parenchymal volume (r 2 = 0.93, P < 0.005) and abnormal moieties exhibited greater tractography volume than normal moieties (P < 0.005). Tractography volume also correlated with age of the child (P < 0.001). In normal moieties, the medulla had higher fractional anisotropy (0.401 +/−0.05) than the cortex (0.183 +/− 0.03) (P < 0.001); fractional anisotropy in these regions did not change with age (P > 0.1). There were no differences in apparent diffusion coefficient values between the cortex and medulla (P > 0.5). We observed a trend of increasing apparent diffusion coefficient values with age in the cortex and medulla, which did not reach statistical significance (cortex: r2 = 0.21, P > 0.1; medulla: r2 = 0.135, P > 0.1).

CONCLUSION

DTI with tractography is feasible in children and can complement the functional information obtained from fMRU.

Diffusion weighted magnetic resonance imaging of kidneys in children with vesicoureteral reflux

PURPOSE

The apparent diffusion coefficient (ADC) which obtain from diffusion-weighted magnetic resonance imaging (DWI), is a quantitative parameter representing the renal function and parenchymal damage in some renal disorders. The primary aim of this study was to investigate whether renal tissue alterations associated with vesicoureteral reflux (VUR) can be displayed by DWI. The secondary aim was to assess how ADC values change with age in kidneys with and without VUR.

MATERIALS AND METHODS

This prospective study included 46 patients (8 boys, 38 girls; mean age 7.3 ± 4.2; range 1-15 years) with VUR and 54 control subjects (21 boys, 33 girls; mean age 7.7 ± 5.2; range 1-17 years). All subjects underwent DWI of the kidneys using b value of 600s/mm(2) in addition to MR urography. The ADC values of 71 kidneys with VUR were compared with those of 81 kidneys without VUR.

RESULTS

The mean ADC values were (1.93 ± 0.36)×10(-3)mm(2)/s, (1.97 ± 0.24)× 10(-3)mm(2)/s, (1.83 ± 0.37)× 10(-3)mm(2)/s, (1.98 ± 0.20)×10(-3)mm(2)/s and (2.08 ± 0.42)× 10(-3)mm(2)/s in normal kidneys, and in those with grade 1, grade 2, grade 3 and grade 4 VUR, respectively. There was no significant difference in ADC values between kidneys with and without VUR. There was a significant positive correlation between the age and ADC values both in kidneys with and without VUR (r=0.79, p<0.001 and r=0.82; p<0.001, respectively).

CONCLUSION

DWI does not reveal probable parenchymal alterations in reflux nephropathy. ADC values increase with age during childhood not only in normal kidneys but also in kidneys with VUR.

Diffusion-weighted MRI in assessment of renal dysfunction

Background:

Diffusion-weighted magnetic resonance imaging (DW-MRI) in renal diseases is an evolving field and its potential is yet to be fully realized.

Purpose:

To study the relationship between apparent diffusion coefficient (ADC) values of renal parenchyma and serum markers of renal function and stage of chronic kidney disease (CKD).

Materials and Methods:

A retrospective review was performed of all adult patients who underwent DW-MRI (at b-values of 0 and 500 s/mm²) for renal lesions from January 2009 to September 2010 and revealed 88 patients, of which 22 patients had renal dysfunction and 66 had normal renal function. Of these 22, 15 patients were known cases of CKD and were staged depending on disease severity. ADC values were determined for renal parenchyma and compared. Receiver operating characteristic (ROC) curves were drawn to establish cut-off ADC values. Pearson's correlation coefficient (R) was calculated between ADC and renal function parameters.

Results:

ADC values in patients with renal dysfunction were significantly lower than in patients with normal renal function (2.1133 ± 0.2851 vs. 2.3198 ± 0.1246 (×10^-3 mm²/s)). ADC values lower than 2.0354 (×10^-3 mm²/s) were seen only with renal dysfunction and higher than 2.4516 (×10^-3 mm² /s) were seen only with normal function. There was significant inverse correlation between ADC and serum creatinine (R = -0.530), blood urea (R= -0.502), and significant linear correlation (R = 0.784) with estimated glomerular filtration rate (eGFR). ADC values showed a statistically significant decreasing trend with increasing stage of CKD.

Conclusion:

ADC values may serve as an additional marker for the presence and degree of renal dysfunction.

Diffusion-weighted MRI in the assessment of split renal function: comparison of navigator-triggered prospective acquisition correction and breath-hold acquisition

OBJECTIVE

The purpose of this study was to ascertain whether prospective acquisition correction (PACE) diffusion-weighted MRI (DWI) is superior to conventional breath-hold DWI in assessment of split renal function.

SUBJECTS AND METHODS

Fifty-four subjects underwent coronal breath-hold DWI and PACE DWI with the b value set at 0 and 800 s/mm(2). Isotope renographic glomerular filtration rate (GFR) was used as the reference standard for assessing split renal function. A GFR of 40 mL/min or greater indicated normal and a GFR less than 40 mL/min indicated reduced split renal function. Reduced split renal function was further divided into a mild reduction group (GFR ≥ 20 mL/min) and a moderate-to-severe reduction group (GFR < 20 mL/min). Various comparisons between the imaging methods were conducted.

RESULTS

The signal-to-noise and contrast-to-noise ratios of the PACE DW images were greater than those of the breath-hold DW images (p < 0.001). The correlation between the apparent diffusion coefficient (ADC) value and GFR was stronger when the ADC was measured with PACE DWI than with breath-hold DWI (p = 0.033). Area under the receiver operator curve (AUC) analysis revealed that PACE DWI (AUC, 0.790 ± 0.045; p < 0.001) but not breath-hold DWI (AUC, 0.616 ± 0.060; p = 0.053) had diagnostic value in predicting a reduction in split renal function. ADC value assessed with PACE DWI was lower in the groups with mild and moderate-to-severe reduction in split renal function than in the group with normal function (p < 0.01).

CONCLUSION

Preliminary results imply that PACE DWI is superior to breath-hold DWI in the assessment of split renal function.

Diffusion tensor imaging and tractography of the kidneys: assessment of chronic parenchymal diseases

OBJECTIVE

To assess renal dysfunction in chronic kidney diseases using diffusion tensor imaging (DTI).

METHODS

Forty-seven patients with impaired renal function (study group) and 17 patients without renal diseases (control group) were examined using DTI sequences. Cortical and medullary regions of interest (ROIs) were located to obtain the corresponding values of the apparent diffusion coefficient (ADC) and the fractional anisotropy (FA). The mean values of the ADC and FA, for each ROI site, were obtained in each group and were compared. Furthermore, the correlations between the diffusion parameters and the estimated glomerular filtration rate (eGFR) were determined.

RESULTS

In both the normal and affected kidneys, we obtained the cortico-medullary difference of the ADC and the FA values. The FA value in the medulla was significantly lower (P = 0.0149) in patients with renal function impairment as compared to patients with normal renal function. A direct correlation between DTI parameters and the eGFR was not found. Tractography visualised disruption of the regular arrangement of the tracts in patient with renal function alteration.

CONCLUSION

DTI could be a useful tool in the evaluation of chronic kidney disease and, in particular, the medullary FA value seems to be the main parameter for assessing renal damage.

KEY POINTS

• Magnetic resonance diffusion tensor imaging (MRDTI) provides new information about renal problems. • DTI allows non-invasive repeatable evaluation of the renal parenchyma, without contrast media. • DTI could become useful in the management of chronic parenchymal disease. • DTI seems more appropriate for renal evaluation than diffusion-weighted imaging.

Gadolinium-induced fibrosis testing by protein targeting assay and superparamagnetic iron oxide nanoparticle-based magnetic resonance microscopy of skin and kidneys

Gadolinium-based magnetic resonance imaging (MRI) contrast agents cause undefined fibrosis in kidneys and skin damage. Magnetic resonance microimaging of rat skin and kidney was used first time to identify the physical factors modulating the gadolinium Omniscan®-induced fibrosis by protein targeting. A 500-MHz MR imaging was done to visualize fibrosis in gadolinium-treated animals. Cationic superparamagnetic iron oxide magnetoferritin (SPIOM) was injected in rat to target basement membrane (in rat kidney and different skin structures including epidermis glycolipids and dermis proteins. After MR imaging, excised rat skin and kidneys tissues were imaged by ex vivo 900 MHz MR microimaging to confirm renal fibrosis and skin epidermis thickening. The proton density-weighted images visualized micro details of skin structures and nephron territories while T2-weighted images showed better contrast of tissue structures in both skin and kidney. The gadolinium further enhanced the image contrast and targeted the proteins in renal basement membrane and viable proteins in epidermis. SPIOM enhanced the tissue contrast due to dephasing effect caused by SPIOM on structural changes in nephron and epidermis. Conclusion: Tissue membrane protein and chelate ligand group binding with gadolinium biophysical interaction at molecular level may develop fibrosis. SPIOM injection improved the dephased image contrast of different structures in both skin and nephrons. The epidermis thickening and nephrofibrosis changes may be associated with nephrogenic systemic fibrosis or fibrosing dermatopathy.

Intravoxel incoherent motion and diffusion-tensor imaging in renal tissue under hydration and furosemide flow challenges

PURPOSE

To assess the reproducibility and the distribution of intravoxel incoherent motion (IVIM) and diffusion-tensor (DT) imaging parameters in healthy renal cortex and medulla at baseline and after hydration or furosemide challenges.

MATERIALS AND METHODS

Using an institutional review board-approved HIPAA-compliant protocol with written informed consent, IVIM and DT imaging were performed at 3 T in 10 volunteers before and after water loading or furosemide administration. IVIM (apparent diffusion coefficient [ADC], tissue diffusivity [D(t)], perfusion fraction [f(p)], pseudodiffusivity [D(p)]) and DT (mean diffusivity [MD], fractional anisotropy [FA], eigenvalues [λ(i)]) imaging parameters and urine output from serial bladder volumes were calculated. (a)Reproducibility was quantified with coefficient of variation, intraclass correlation coefficient, and Bland-Altman limits of agreement; (b) contrast and challenge response were quantified with analysis of variance; and (c) Pearson correlations were quantified with urine output.

RESULTS

Good reproducibility was found for ADC, D(t), MD, FA, and λ(i) (average coefficient of variation, 3.7% [cortex] and 5.0% [medulla]), and moderate reproducibility was found for D(p), f(p), and f(p) · D(p) (average coefficient of variation, 18.7% [cortex] and 25.9% [medulla]). Baseline cortical diffusivities significantly exceeded medullary values except D(p), for which medullary values significantly exceeded cortical values, and λ(1,) which showed no contrast. ADC, D(t), MD, and λ(i) increased significantly for both challenges. Medullary diffusivity increases were dominated by transverse diffusion (1.72 ± 0.09 [baseline] to 1.79 ± 0.10 [hydration] μm(2)/msec, P = .0059; or 1.86 ± 0.07 [furosemide] μm(2)/msec, P = .0094). Urine output correlated with cortical ADC with furosemide (r = 0.7, P = .034) and with medullary λ(1) (r = 0.83, P = .0418), λ(2) (r = 0.85, P = .0301), and MD (r = 0.82, P = .045) with hydration.

CONCLUSION

Diffusion MR metrics are sensitive to flow changes in kidney induced by diuretic challenges. The results of this study suggest that vascular flow, tubular dilation, water reabsorption, and intratubular flow all play important roles in diffusion-weighted imaging contrast.

Measuring anisotropic diffusion in kidney using MRI

RATIONALE AND OBJECTIVES

To measure the anisotropic diffusion in kidney and to demonstrate the feasibility of renal tractography.

MATERIALS AND METHODS

Diffusion tensor imaging was acquired in kidney from 10 healthy volunteers and 5 patients with chronic kidney disease. Diffusion indices were calculated from the tensor, including fractional anisotropy, intervoxel diffusion coherence, and mean/axial/radial diffusivity.

RESULTS

Acquisitions with respiratory triggering could provide improved image quality in all diffusion indices, as compared to that by breathhold. It is sufficient to use five to seven scan averages when the measured diffusion indices converge to a steady state in medulla, which reduced the acquisition time in a triggered measurement down to a clinically tolerable limit. Second, the measured diffusion indices can be affected by the diffusion weighting. An increased diffusion weighting will lead to an underestimation in all diffusion indices. Finally the direction of water diffusion is consistent in the kidney cortex, which was properly reflected in intervoxel diffusion coherence. In a feasibility study in healthy volunteers and patients, renal tractography was performed that visualized the organized renal structure and as it declined with the progress of chronic kidney disease.

CONCLUSION

When compared to conventional breath hold technique, the significant improvement in image quality compensated for the prolonged acquisition time. Therefore, triggered acquisition is preferred in a clinical setting because it required less from patient cooperation.

Diffusion tensor imaging and tractography for assessment of renal allograft dysfunction-initial results

OBJECTIVES

To evaluate MR diffusion tensor imaging (DTI) as non-invasive diagnostic tool for detection of acute and chronic allograft dysfunction and changes of organ microstructure.

METHODS

15 kidney transplanted patients with allograft dysfunction and 14 healthy volunteers were examined using a fat-saturated echo-planar DTI-sequence at 1.5 T (6 diffusion directions, b = 0, 600 s/mm²). Mean apparent diffusion coefficient (ADC) and mean fractional anisotropy (FA) were calculated separately for the cortex and for the medulla and compared between healthy and transplanted kidneys. Furthermore, the correlation between diffusion parameters and estimated GFR was determined.

RESULTS

The ADC in the cortex and in the medulla were lower in transplanted than in healthy kidneys (p < 0.01). Differences were more distinct for FA, especially in the renal medulla, with a significant reduction in allografts (p < 0.001). Furthermore, in transplanted patients a correlation between mean FA in the medulla and estimated GFR was observed (r = 0.72, p < 0.01). Tractography visualized changes in renal microstructure in patients with impaired allograft function.

CONCLUSIONS

Changes in allograft function and microstructure can be detected and quantified using DTI. However, to prove the value of DTI for standard clinical application especially correlation of imaging findings and biopsy results is necessary.

Diffusion-weighted MR imaging of native and transplanted kidneys

Applications of diffusion-weighted (DW) magnetic resonance (MR) imaging outside the brain have gained increasing importance in recent years. Owing to technical improvements in MR imaging units and faster sequences, the need for noninvasive imaging without contrast medium administration, mainly in patients with renal insufficiency, can be met successfully by applying this technique. DW MR imaging is quantified by the apparent diffusion coefficient (ADC), which provides information on diffusion and perfusion simultaneously. By using a biexponential fitting process of the DW MR imaging data, these two entities can be separated, because this type of fitting process can serve as an estimate of both the perfusion fraction and the true diffusion coefficient. DW MR imaging can be applied for functional evaluation of the kidneys in patients with acute or chronic renal failure. Impairment of renal function is accompanied by a decreased ADC. Acute ureteral obstruction leads to perfusion and diffusion changes in the affected kidney, and renal artery stenosis results in a decreased ADC. In patients with pyelonephritis, diffuse or focal changes in signal intensity are seen on the high-b-value images, with increased signal intensity corresponding to low signal intensity on the ADC map. The feasibility and reproducibility of DW MR imaging in patients with transplanted kidneys have already been demonstrated, and initial results seem to be promising for the assessment of allograft deterioration. Overall, performance of renal DW MR imaging, presuming that measurements are of high quality, will further boost this modality, particularly for early detection of diffuse renal conditions, as well as more accurate characterization of focal renal lesions.

Renal diffusion tensor imaging: is it possible to define the tubular pathway? A case report

The authors report a case of unilateral xanthogranulomatous pyelonephritis, associated with chronic lithiasis studied by standard clinical magnetic resonance imaging protocol and diffusion tensor imaging (DTI). Maps of apparent diffusion coefficient (ADC) and fractional anisotropy (FA) and tractography were reconstructed on both healthy and pathologic kidney. ADC and FA values are in agreement with the literature. Tractography reconstruction of tubular renal architecture was confirmed by histology. This result suggests the potential ability of DTI to detect structural alterations in the architecture of the kidney, as noninvasive tool, preceding the onset of clinical-laboratory alterations.

Diffusion-weighted magnetic resonance imaging in the upper abdomen: technical issues and clinical applications

Recent technological achievements have enabled the transposition of diffusion-weighted imaging (DWI) with good diagnostic quality into other body regions, especially the abdomen and pelvis. Many emerging and established applications are now being evaluated on the upper abdomen, the liver being the most studied organ. This article discusses imaging strategies for DWI on the upper abdomen, describes the clinical protocol, and reviews the most common clinical applications of DWI on solid abdominal organs.

Diffusion-weighted MRI with parallel imaging technique: apparent diffusion coefficient determination in normal kidneys and in nonmalignant renal diseases

The purpose of the study was to assess the capability and the reliability of apparent diffusion coefficient (ADC) measurements in the evaluation of different benign renal abnormalities. Twenty-five healthy volunteers and 31 patients, divided into seven different groups (A-G) according to pathology, underwent diffusion-weighted magnetic resonance imaging (DW MRI) of the kidneys using 1.5-T system. DW images were obtained in the axial plane with a spin-echo echo planar imaging single-shot sequence with three b values (0, 300, and 600 s/mm²). Before acquisition of DW sequences, we performed in each patient a morphological study of the kidneys. ADC was 2.40±0.20×10⁻³ mm² s⁻¹ in volunteers. A significant difference was found between Groups A (cysts=3.39±0.51×10⁻³ mm² s⁻¹) and B (acute/chronic renal failure=1.38±0.40×10⁻³ mm² s⁻¹) and between Groups A and C (chronic pyelonephritis=1.53±0.21×10⁻³ mm² s⁻¹) (P<.05). An important difference was also observed among Group D (hydronephrosis=4.82±0.35×10⁻³ mm² s⁻¹) and Groups A, B, and C (P<.05), whereas no differences were found between Groups B and C (P>.05). A considerable correlation between glomerular filtration rate and ADC was found (P=.04). In conclusion, significant differences were detected among different patient groups, and this suggests that ADC measurements can be useful in differentiating normal renal parenchyma from most commonly encountered nonmalignant renal lesions.

Test-retest reliability and repeatability of renal diffusion tensor MRI in healthy subjects

PURPOSE

This study assessed test-retest reliability and repeatability of diffusion tensor imaging (DTI) in the kidneys.

MATERIALS AND METHODS

Seven healthy volunteers (age range, 19-31 years), were imaged three consecutive times on the same day (short-term reliability) and the same imaging protocol was repeated after a month (long-term reliability). Diffusion-weighted magnetic resonance imaging scans in the coronal-oblique projection of the kidney were acquired on a 1.5 T scanner using a multi-section echo-planar sequence; six contiguous slices each 5 mm thick, diffusion sensitisation along 20 non-collinear directions, TR=730 ms, TE=73 ms and 2 b-values (0 and 400 s mm(-2)). Volunteers were asked to hold their breath throughout each data acquisition (approx. 20 s). The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were obtained from maps generated using dedicated software MIStar (Apollo Medical Imaging, Melbourne, Australia).

RESULTS

Statistical analyses of both short- and long-term repeats were carried out from which the within-subject coefficient of variation (wsCV) was calculated. The wsCV obtained for both the ADC and FA values were less than 10% in all the analyses carried out. In addition, paired (repeated measures) t-test was used to measure the variation between the diffusion parameters collected from the two scanning sessions a month apart. It showed no significant difference and the wsCV obtained after comparing the first and second scans were found to be smaller than 15% for both ADC and FA.

CONCLUSION

Renal DTI produces reliable and repeatable results which make longitudinal investigation of patients viable.

The direct tensor solution and higher-order acquisition schemes for generalized diffusion tensor imaging

Both in diffusion tensor imaging (DTI) and in generalized diffusion tensor imaging (GDTI) the relation between the diffusion tensor and the measured apparent diffusion coefficients is given by a tensorial equation, which needs to be inverted in order to solve the diffusion tensor. The traditional way to do this does not preserve the tensorial structure of the equation, which we consider a weakness in the method. For a physically correct measurement procedure, the condition number of the acquisition scheme, which is a determinant of the noise behavior, needs to be rotationally invariant. The method which traditionally is used to find such schemes, however, is cumbersome and mathematically unsatisfactory. This is considered a second weakness, closely connected to the first. In this paper we present an alternative inversion of the diffusion tensor equation, which does preserve the tensor form, for arbitrary order, and which is named the direct tensor solution (DTS). The DTS is derived under the assumption that the apparent diffusion coefficient in any direction is known, i.e. in the infinite acquisition scheme. Whenever the DTS is valid for a given finite acquisition scheme and for a given order, the condition number is rotationally invariant. The DTS provides a compact, algebraic procedure to check this rotational invariance. We also present a method to construct acquisition schemes, for which the DTS is valid for the measurement of higher-order diffusion tensors. Furthermore, the DTS leads to other mathematical insights, such as tensorial relationships between diffusion tensors of different orders, and a more general understanding of the Platonic Variance Method, which we published before.

Diffusion and perfusion of the kidney

MRI of the kidney currently makes the transition from depiction of morphology to assessment of function. Functional renal imaging methods provide information on diffusion and perfusion on a microstructural level. This review article presents the current status of functional renal imaging with focus on DWI (diffusion-weighted imaging) and DCE-MRI (dynamic contrast-enhanced MRI), as well as BOLD (blood-oxygenation level dependent) MRI, DTI (diffusion tensor imaging) and arterial spin labeling (ASL). Technical background of these techniques is explained and clinical assessment of renal function, parenchymal disease, transplant function and solid masses is discussed.

Assessment of renal fibrosis with diffusion-weighted MR imaging: study with murine model of unilateral ureteral obstruction

PURPOSE

To test, in a murine model of unilateral ureteral obstruction (UUO), whether the magnetic resonance (MR) imaging-derived apparent diffusion coefficient (ADC) changes during the progression of renal fibrosis and correlates with the histopathologic changes observed in renal fibrogenesis.

MATERIALS AND METHODS

This study was approved by the institutional animal care and use committee. A UUO was created in each of 14 mice. In five mice, longitudinal diffusion-weighted (DW) imaging was performed before the UUO (day 0) and on days 3 and 7 after the UUO and was followed by histopathologic analysis. The nine remaining mice were examined with cross-sectional studies on days 0 (n = 4) and 3 (n = 5). ADCs were measured with a spin-echo echo-planar sequence at five b values ranging from 350 to 1200 sec/mm(2). Differences in ADC among the time points and between the sides were assessed by using Tukey-Kramer and Student t tests, respectively. ADC was correlated with cell density and alpha-smooth muscle actin (alpha-SMA, a marker of myofibroblasts) expression at linear regression analysis.

RESULTS

Histopathologic examination revealed typical renal fibrosis on the side with UUO. The ADC decreased over time on the UUO side, from (1.02 +/- 0.06 [standard deviation]) x 10(-3) mm(2)/sec on day 0 to (0.70 +/- 0.08) x 10(-3) mm(2)/sec on day 3 (P < .001) and (0.57 +/- 0.10) x 10(-3) mm(2)/sec on day 7 (P < .001). The percentage change in ADC was greater on the UUO side than on the contralateral side on days 3 (29% +/- 9, P = .05) and 7 (44% +/- 11, P < .01). ADC correlated with both increased cell density and increased alpha-SMA expression (P < .001 for both correlations).

CONCLUSION

An ADC decrease in renal fibrosis is associated with an increased number of cells, including fibroblasts. ADC has the potential to serve as a sensitive noninvasive biomarker of renal fibrosis.

Diffusion-weighted imaging of the renal and adrenal lesions

OBJECTIVES

The purpose of this study was to calculate the apparent diffusion coefficient (ADC) values of different renal and adrenal lesions to evaluate the ability of diffusion-weighted imaging in characterizing masses and determining malignancy.

METHODS

A total of 52 patients consisting of 67 renal lesions and 28 patients with 33 adrenal lesions in addition to 50 healthy controls with normal kidneys were enrolled in the study. Diffusion-weighted imaging was performed with b factors of 0, 500, and 1000 s/mm2, and the ADCs of the normal kidney and renal and adrenal lesions were calculated.

RESULTS

The mean (SD) ADCs of the renal cortex and medulla of the control group were 2.08 (0.22) x 10(-3) and 1.94 (0.18) x 10(-3) mm2/s, respectively. Focal renal lesions were as follows: simple cysts (2.94 [0.20] x 10(-3) mm2/s), hemorrhagic cysts (1.71 [0.38] x 10(-3) mm2/s), angiomyolipomas (1.40 [0.21] x 10(-3) mm2/s), renal cell carcinomas (1.06 [0.39] x 10(-3) mm2/s), metastases (1.50 [0.13] x 10(-3) mm2/s), and hydronephrosis (1.54 [0.25] x 10(-3) mm2/s). The mean ADCs of all these pathologies were significantly different when compared with normal parenchyma. Diffusion-weighted imaging was also able to differentiate angiomyolipomas and hemorrhagic cysts from renal cell carcinomas. Adrenal lesions were subgrouped as adenomas (1.41 [0.27] x M10(-3) mm2/s), nonadenomatous solid masses (1.08 [0.28] x 10(-3) mm2/s), and cysts (2.82 [0.24] x 10(-3) mm2/s). The mean ADCs of adenomas were significantly different when compared with nonadenomatous solid masses and cysts.

CONCLUSIONS

Our findings show that ADC measurement has a potential ability to differentiate benign and malignant focal renal and adrenal lesions with the guidance of conventional sequences. When used alone, diffusion-weighted imaging may lead to misdiagnoses due to overlapping ADCs of the lesions.