Magnetic resonance perfusion imaging
The Magnetresonanzperfusionsbildgebung ( MR perfusion imaging , perfusion MRI ) is an imaging method for diagnostic display and quantification of blood flow (perfusion) of biological organs and tissues using the methods of magnetic resonance imaging (MRI). Various techniques can be used for this purpose, some of which are completely non-invasive (that is, they do not require surgical interventions or injections) or are based on the administration of MRI contrast media . Perfusion MRI is a procedure that competes with nuclear medicine methods (perfusion PET , perfusion SPECT or perfusion scintigraphy ) and CT perfusion imaging .
Indications
Typical indications for a perfusion MRI are, for example, the suspicion of circulatory disorders and ischemia (due to vascular occlusions ( embolisms ) or arterial stenoses ) in the brain ( stroke ), heart ( myocardial infarction , coronary heart disease ) or in the lungs ( pulmonary embolism ), as well as the presentation of Blood flow in tumors .
techniques
There are different techniques to use magnetic resonance imaging to visualize and quantify blood flow. The two main approaches are:
Dynamic contrast medium perfusion imaging
Dynamic contrast agent-based perfusion MRT is based on measuring the contrast agent passage through the tissue of interest. The MRI contrast agent is injected intravenously as a bolus . Either the signal increase caused by the contrast agent is recorded in T1-weighted images ( dynamic contrast-enhanced MRI , DCE-MRI) or - especially for perfusion measurements in the brain - the signal decrease in T2 * -weighted images ( dynamic susceptibility contrast MRI , DSC-MRI). MRT pulse sequences that enable a high temporal resolution of up to 1 second per data set and the recording of several slices or a three-dimensional volume are desirable for this .
Essential steps in data post-processing include the calculation of the contrast agent concentration in the blood from the measured signal of the MRI recordings, as well as the calculation of the hemodynamic parameters (based on the indicator dilution theory) from the contrast agent concentration in the tissue and in a supplying artery (arterial input function, AIF) . Quantifiable parameters are the (regional) blood volume, the (regional) blood flow, the mean transit time (MTT) of the blood through the tissue; More complex models allow the calculation of further parameters such as the contrast medium leakage from the vascular system.
Arterial spin labeling (ASL)
MRT perfusion imaging using arterial spin labeling (ASL) is based on the preparation of the nuclear spin magnetization of the inflowing blood into the tissue of interest using high-frequency pulses. The blood serves here as the body's own marker for measuring perfusion; this technique does not therefore require the administration of contrast media. In comparison with contrast-enhanced perfusion MRI, longer examination times are generally required and the signal-to-noise ratio achieved is often poor.
Presentation of the perfusion MRI data
The results of the MR perfusion imaging can be displayed as parameter maps which (often color-coded) visualize the hemodynamic parameters in each recorded slice, such as the blood flow or the blood volume and the mean transit time.
Individual evidence
- ↑ Maximilian Reiser , Wolfhard Semmler (ed.): Magnetic resonance tomography . 3. Edition. Springer-Verlag, Berlin Heidelberg New York, ISBN 3-540-66668-0 , pp. 260-261 . ( limited preview in Google Book search)
- ↑ Jürgen Freyschmidt (Ed.): Handbook diagnostic radiology. Thorax . Springer-Verlag, Berlin Heidelberg New York 2003, ISBN 3-540-41421-5 , pp. 25 . ( limited preview in Google Book search)
- ↑ Dominik Weishaupt, Victor D. Köchli, Borut Marincek: How does MRI work ?: An introduction to the physics and functionality of magnetic resonance imaging . 6th edition. Springer Medizin Verlag, Heidelberg 2009, ISBN 978-3-540-89572-5 , p. 77-78 . ( limited preview in Google Book search)
