E³ 126b - Functional MRI of the kidneys: ready for prime time?
1. To learn about the technical issues of DWI.
2. To understand the physiological determinants of diffusion measurements.
3. To assess the role of DWI in clinical practice.
Diffusion-weighted MRI of the kidney has multiple applications in morphological renal imaging. Its applications in the functional field of parenchymal renal diseases are still to be defined. For morphological applications such as renal tumours or infections, 3 b-values are enough with calculation of an ADC-map based on a mono-exponential fit. For functional applications, the tendency goes toward more sophisticated approaches such as the IVIM technique with more b-values and a bi-exponential fit or characterisation of the diffusion tensor, based on acquisition of at least 6 directions, of diffusion encoding. All functional and tissue changes decreasing water movements or increasing the cell density in renal parenchyma can decrease diffusion coefficients. Renal ADC decrease is correlated with the degree of renal dysfunction in parenchymal diseases. Urinary obstruction and parenchymal processes such as inflammation or fibrosis also decrease the diffusion coefficients. In chronic diseases, tissue changes and fibrosis induce changes of the microarchitecture responsible for a decrease of renal anisotropy shown by diffusion tensor imaging.
1. To learn about the clinical indications for kidney perfusion imaging.
2. To become familiar with perfusion protocols for kidney perfusion imaging.
3. To learn about difficulties in kidney perfusion imaging.
Because of its high spatial resolution, magnetic resonance urography has demonstrated high accuracy in the morphologic assessment of urinary tract. More recently, functional MRU (fMRU) has shown feasibility in adults and children, using dynamic pulse sequences performed after injection of an intravenous bolus of gadolinium chelates (DCE-MRU), which allow calculating the split renal function (SRF) from time-intensity curves, where the Patlak method should be preferred to the area under the curve method. Using MRU to obtain both anatomical and functional information in a single examination without radiation would be beneficial, especially for follow-up in young patients. Complementary medico-economic analysis confirms the interest of a potential substitution of nuclear renal scintigraphy by fMRU as an adjunct to morphological MRU.
1. To understand the physiological and technical basis of blood oxygen level-dependent (BOLD) imaging of the kidneys.
2. To learn typical findings of BOLD-MRI in patients with kidney disease.
3. To review the physics and technique of arterial spin labelling (ASL) perfusion measurements of the kidneys.
4. To see typical findings of ASL measurements in patients with kidney diseases.
In functional renal magnetic resonance imaging (MRI) advanced techniques are used to obtain functional and molecular information from the state of the kidney. In blood oxygenation level-dependent (BOLD) MRI, the susceptibility difference between oxyhaemoglobin (diamagnetic) and deoxyhaemoglobin (paramagnetic) is used to extract information on tissue oxygenation, which is interesting because of the physiological hypoxia in the renal medulla. BOLD MRI, therefore, may be applied to non-invasively assess renal oxygenation and the oxygen metabolism of the kidneys. Arterial spin labelling (ASL) is a non-invasive technique, which uses radiofrequency-labelled blood water as endogenous tracer to visualize and quantify renal perfusion. Using the extended Bloch equations, quantitative perfusion values in ml/100 g/min can be calculated.