Value of diffusion-weighted MR imaging for the detection of nephritis

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.

Diffusion weighted imaging is a promising method to detect acute pyelonephritis in non-sedated free breathing infants

INTRODUCTION

Urinary tract infection (UTI) is a common disease in infants. The initial evaluation includes imaging to identify risk factors for permanent renal damage, such as malformation and renal parenchymal involvement of the infection i.e. pyelonephritis. 99mTc-Dimercaptosuccinic acid (DMSA) scintigraphy is a well-established method for detection of pyelonephritis and renal damage, but has limitations in availability, spatial resolution, and detection of congenital malformations. Diffusion weighted magnetic resonance imaging (DWI) has been shown to have a high sensitivity for detection of pyelonephritis in children without the use of invasive procedures, contrast agents or ionizing radiation. How this method performs in young infants during non-sedated free breathing remains, however, to be investigated.

OBJECTIVE

To prospectively assess the feasibility and performance of DWI for detection of pyelonephritis in non-sedated free breathing infants.

METHODS

32 children <6 months of age with first-time symptomatic UTI were examined with DWI and DMSA scintigraphy. The DWI examination was performed using a free breathing protocol without the use of sedation. Pyelonephritic lesions were registered for both methods by independent observers. Agreement between DWI and DMSA was evaluated. Consensus diagnosis was determined and compared to the DWI findings.

RESULTS

The MRI and DMSA examinations were completed in 25 infants, with a median age of 1.7 (0.7-5.5) months. Focal uptake reductions were detected on the DMSA images in 12 (24%) of the 50 kidneys. The DWI method demonstrated a fair to good agreement with DMSA, k = 0.50 (p < 0.0001). The consensus diagnosis was pyelonephritis in eight (16%) of the 50 kidneys. DWI detected seven of the eight kidneys with pyelonephritis. No false positive findings were detected with DWI compared to consensus diagnosis.

DISCUSSION

This study has shown an agreement between DWI and DMSA scintigraphy in the detection of pyelonephritis. Further validation of the performance of DWI, using a consensus diagnosis as a reference, confirmed the potential of the method. This feasibility study included a limited number of patients and the results need to be confirmed in a prospective study of a larger cohort.

CONCLUSION

Free breathing DWI is a promising method for detection of pyelonephritic lesions in non-sedated infants.

Validity of diffusion-weighted magnetic resonance imaging in the evaluation of acute pyelonephritis in comparison with contrast-enhanced computed tomography

Purpose

Applications of diffusion-weighted magnetic resonance imaging outside the brain have gained increasing importance in recent years, and recent studies have shown the usage of diffusion-weighted (DW) imaging in diagnosing pyelonephritis based on renal cortical and medullary apparent diffusion coefficient (ADC) values. The aim of this study was to assess the validity of DW magnetic resonance (MR) imaging in comparison with contrast-enhanced computed tomography (CECT) in diagnosing pyelonephritis.

Material and methods

A cross-sectional observational study was conducted for a period of six months in a tertiary hospital in Coimbatore. All patients with clinical and laboratory diagnosis of acute pyelonephritis, who were referred for radiological imaging (CECT), were taken into the study. Out of 112 patients with a clinical and laboratorial diagnosis of acute pyelonephritis (APN), who underwent both DW MR and CECT, diagnosis of APN was made in 100 patients based on CECT, while in 12 cases the investigation (CECT) was negative. Finally, these 100 patients were included in the study. The validity of DW MR imaging in diagnosing APN was assessed by deriving sensitivity, specificity, and positive and negative predictive value in comparison with CECT findings.

Results

The validity report of DW MR imaging in the detection of APN showed a very high sensitivity (96-100%) and specificity (86-90%) and very low false positives (6-10%) and negatives (< 5%), and it also showed that in the areas of affected renal parenchyma ADC values were consistently lower compared to unaffected renal parenchyma.

Conclusion

Based on the generated hypothesis, DW MR imaging of the kidneys seems to be highly sensitive and specific for the detection of focal or diffuse infections within the kidney in comparison with CECT.

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.

[Functional magnetic resonance imaging of the kidneys]

Interest in functional renal magnetic resonance imaging (MRI) has significantly increased in recent years. This review article provides an overview of the most important functional imaging techniques and their potential clinical applications for assessment of native and transplanted kidneys, with special emphasis on the clarification of renal tumors.