Vaskuläre und parenchymale Erkrankungen der Nieren

Susceptibility weighted imaging (SWI) of the kidney at 3T--initial results

Susceptibility weighted imaging provides diagnostic information in strokes, hemorrhages, and cerebral tumors and has proven to be a valuable tool in imaging venous vessels in the cerebrum. The SWI principle is based on the weighting of T(2)* weighted magnitude images with a phase mask, therewith improving image contrast of veins or neighbouring structures of different susceptibility, in general. T(2)* weighted MRI is already used for assessment of kidney function. In this paper, the feasibility of SWI on kidneys was investigated. Translation of SWI from the brain to the kidneys comes along with two main challenges: (i) organ motion due to breathing and (ii) a higher oxygenation level of renal veins compared to the brain. To handle these problems, the acquisition time has been cut down to allow for breath-hold examinations, and different post-processing methods including a new phase mask were investigated to visualize renal veins. Results showed that by a new post-processing strategy SWI contrast was enhanced on average by a factor of 1.33 compared to the standard phase mask. In summary, initial experiences of SWI on the kidneys demonstrated the feasibility. However, further technical developments have to be performed to make this technology applicable in clinical abdominal MRI.

[Hypertension in patients with renal artery stenosis]

Renal artery stenosis (RAS) is often present in patients with severe hypertension and atherosclerotic vascular disease. In this setting it is important to screen patients for renovascular disease, e.g. with Duplex-ultrasound, CT- or MR-angiography. The challenge of treating these patients is to find the evidence proving that the RAS is responsible for hypertension and/or renal dysfunction. Measurement of the intra-arterial pressure gradient is necessary in order to determine hemodynamic relevance. On the other side, in these patients hypertension is often of primary and/or renoparenchymatous origin and is aggravated by a renovascular disease. This explains why hypertension cannot be cured even if a high grade stenosis has been removed. In addition, thromb- and cholesterol-embolic material is often mobilized during an invasive procedure and leads to renaparenchymatous ischemia which sustains hypertension after intervention. An individual evaluation of profit versus risk is important for the decision for or against an invasive procedure, especially since there is no sufficient evidence for a decrease of mortality after interventions of RAS. The optimal conservative treatment, including the treatment of atherosclerotic risk factors is recommended.