On Possible Pitfalls in Working on SPIO Labelled Cells with 2D UTE Sequences

Introduction In the past years many strategies for the in-vivo detection of cells have been proposed. Many of these approaches are based on superparamagnetic iron oxide (SPIO) nanoparticles to overcome the inherent low sensitivity of MRI to common T1 based contrast agents [1]. In addition new pulse sequences were introduced to gain positive contrast out of the native dark T2* contrast of SPIO particles [2]. One promising method is the use of ultra short echo time sequences (UTE) [4,5] either to acquire the T1 signature of SPIO particles or to gain positive contrast through double echo with subtraction. Latter method obtains the first image from the free induction decay and the second some 100μs later. Within this study we would like to outline some crucial points concerning the use of 2D UTE sequences for this purpose. We show that especially in regions of high iron density many artefacts caused by the pulse sequence could yield to misinterpretations or wrong quantitative results. On the basis of an ectopic labelled cell population we discuss the artefacts caused by a common 2D UTE acquisition strategy with half-pulse excitation.