New perspectives on imaging of urinary tract infections in infants

Abstract: Background: Urinary tract infection (UTI) is a common disease in infants that may lead to renal damage with an increased risk of long term complications. The diagnostic imaging aims to identify risk factors as underlying urinary tract abnormalities and renal involvement of the infection for prevention of long term adverse outcome. There is a need for alternative methods to the ones presently used for investigation and follow-up of this patient group without the use of invasive procedures, contrast agents or ionizing radiation. The aim of this thesis was to evaluate the potential of ultrasound (US), diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) in the initial evaluation of the urinary tract in infants with their first UTI. Methods: Infants with their first symptomatic UTI were included in four prospective studies. The infants were examined with US, magnetic resonance imaging (MRI) including DWI and DTI, and 99mTc-dimercaptosuccinic acid (DMSA) scintigraphy during the acute phase of the infection. Inflammatory parameters, C-reactive protein and body temperature, were registered. Follow-up examinations included US after 1 month and scintigraphy after one year. Results: Renal size measured at early US determined renal swelling in infants with a UTI. The renal swelling correlated with inflammatory parameters and was associated with renal damage at acute and follow-up DMSA scintigraphy. There was an agreement between DWI and DMSA scintigraphy in the detection of pyelonephritis. With the use of DTI, differences were found in quantitative and qualitative parameters in lesions compared to normal tissue and further lesion characterization patterns were recognised. Conclusion: The results show that US, DWI and DTI are valuable non-invasive, nonradiating tools in the initial evaluation of infants with their first UTI. Renal length US measurements adds value to the early US examination by helping to identify patients at risk for renal damage even though it cannot replace DMSA scintigraphy. DWI and DTI have the potential to be advantageous alternatives to DMSA scintigraphy. However, studies of larger cohorts are needed to verify the results.

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