Arterial Spin Labeling (ASL) is a technique allowing for perfusion imaging without the application of gadolinium-based contrast-agents. In ASL, magnetically labeled blood water is used as an endogeneous tracer. In pulsed ASL, two images of the same slice with different spin preparations are recorded using an inversion pre-pulse: one image with slice selective inversion and one image with global inversion. The perfusion image is generated by subtraction of these two images due to the difference in magnetization resulting from inflowing spins of tissue perfusion.

If the T1 relaxation time of the tissue and the tissue equilibrium magnetization (measured with a PDw image) is known, the quantitative tissue perfusion in units of ml/100g tissue/min can be calculated from the extended Bloch equations. Regarding the intended imaging region, a suitable image readout technique has to be chosen. For perfusion quantification of brain tissue, echo-planar imaging (EPI) data readout strategies are most commonly applied as they provide fast single-shot image acquisition and high signal-to-noise ratio. However, EPI is susceptible to magnetic field inhomogeneities. One major focus of our research is the development of strategies for compensation of magnetic field inhomogeneities allowing the application of ASL for body imaging.

Selected contributions
Rossi C, Artunc F, Schlemmer HP, Schick F, Boss A. Histogram Analysis of Renal Arterial Spin Labeling Perfusion Data Reveals Differences between Volunteers and Patients with mild Chronic Kidney Disease. Investigative Radiology (in press)

Schraml C, Schwenzer NF, Martirosian P, Boss A, Schick F, Schäfer S, Stern M, Claussen CD, Schäfer JF. Non-invasive pulmonary perfusion assessment in young patients with cystic fibrosis using an arterial spin labeling MR technique at 1.5 T. MAGMA. 2011 Jul 24. [Epub ahead of print]

Martirosian P, Boss A, Schraml C, Schwenzer NF, Graf H, Claussen CD, Schick F. Magnetic resonance perfusion imaging without contrast media. Eur J Nucl Med Mol Imaging. 2010 Aug;37(Suppl 1):S52-64. Boss A, Martirosian P, Fritz J, Kötter I, Henes JC, Claussen CD, Schick F, Horger M. Magnetic resonance spin-labeling perfusion imaging of synovitis in inflammatory arthritis at 3.0 T. MAGMA 22(3):175-80. (2009)

Schwenzer N, Schraml C, Martirosian P, Boss A, Claussen CD, Schick F MR measurement of blood flow in the parotid gland without contrast medium: a functional study before and after gustatory stimulation NMR Biomed 21 (6): 598 - 605 (2008)

Boss A, Martirosian P, Klose U, Nägele T, Claussen CD, Schick F FAIR-TrueFISP imaging of cerebral perfusion in areas of high magnetic susceptibility differences at 1.5 and 3 Tesla J Magn Reson Imaging 25 (5): 924 - 931 (2007)

Schraml C, Boss A, Martirosian P, Schwenzer N, Claussen CD, Schick F FAIR true-FISP perfusion imaging of the thyroid gland J Magn Reson Imaging 26 (1): 66 - 71 (2007)

Boss A, Martirosian P, Schraml C, Clasen S, Fenchel M, Anastasiadis A Claussen CD, Pereira PL, Schick F Morphological, contrast-enhanced and spin labeling perfusion imaging for monitoring of relapse after RF ablation of renal cell carcinomas Eur Radiol 16 (6): 1226 - 1236 (2006)

Boss A, Martirosian P, Claussen CD, Schick F Quantitative ASL Muscle perfusion imaging using a Fair-TrueFISP technique at 3.0 T NMR Biomed 19 (1): 125 - 132 (2006)

Boss A, Martirosian P, Graf H, Claussen CD, Schlemmer H, Schick F High Resolution MR Perfusion Imaging of the Kidneys at 3 Tesla without Administration of Contrast Media Fortschr Röntgenstr 177: 1625 - 1630 (2005)