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spin spin relaxation time (
) heterogeneity of hyperpolarized [
C,
N
]urea in the rat kidney was investigated. Selective quenching of the vascular hyperpolarized
C signal with a macromolecular relaxation agent revealed that a long-
component of the [
C,
N
]urea signal originated from the renal extravascular space, thus allowing the vascular and renal filtrate contrast agent pools of the [
C,
N
]urea to be distinguished via multi-exponential analysis. The
response to induced diuresis and antidiuresis was performed with two imaging agents: hyperpolarized [
C,
N
]urea and a control agent hyperpolarized bis-1,1-(hydroxymethyl)-1-
C-cyclopropane-
H
. Large
increases in the inner-medullar and papilla were observed with the former agent and not the latter during antidiuresis. Therefore, [
C,
N
]urea relaxometry is sensitive to two steps of the renal urea handling process: glomerular filtration and the inner-medullary urea transporter (UT)-A1 and UT-A3 mediated urea concentrating process. Simple motion correction and subspace denoising algorithms are presented to aid in the multi exponential data analysis. Furthermore, a
-edited, ultra long echo time sequence was developed for sub-2 mm
resolution 3D encoding of urea by exploiting relaxation differences in the vascular and filtrate pools.