Joerg Pintaske, Presenter: Nothing to Disclose

Petros Martirosian MS, Abstract Co-Author: Nothing to Disclose

Claus Detlef Claussen MD, Abstract Co-Author: Nothing to Disclose

Fritz Schick MD, PhD, Abstract Co-Author: Nothing to Disclose

In MRI magnetically labeled cells (MLC) cause local field inhomogeneities within the single voxels as well as on a macroscopic scale. The related Larmor frequency shift near MLC was exploited to obtain bright visualization and improvements in MR imaging contrast applying spectral selective saturation (SSS).

SK-Mel28 cells were labeled with superparamagnetic contrast agent SHU 555A. Low cell concentrations (0, 5, 20, 30, 50, 75, and 150 MLC/μl) and high cell concentrations (1.000, 3.000, 6.000, and 10.000 MLC/μl)were examined at 3 Tesla. Shimming and frequency adjustment to ν0 was performed with the built in routine of the scanner. A 2D spin echo (SE) sequence with broadband excitation and refocusing pulses was used (BWex = 1.000 Hz). Prior to each TR, a non-selective saturation sinc pulse centred at ν0 was applied. Bandwidth (BWsat) of this pulse was varied from 100 Hz to 800 Hz in logarithmic steps.

Without SSS highest value of Crel (i.e. relative MR contrast of labeled to unlabeled volume) was found for 150 MLC/μl with 10%. Applying SSS pulses led to hyperintensity of the complete labeled volume for concentrations ≥20 MLC/μl and to remarkable improvements in Crel.With increasing cell concentrations Crel raised to maximum, that was given by 52% (BWsat=100 Hz) and 28% (BWsat = 200 Hz) found for 75 MLC/μl. For 150 MLC/μl Crel decreased, but was significantly higher than value without SSS. Signal could be detected near cell aggregations (high cell concentrations) despite saturation. For low / high cell concentrations the entire sample was signalfree at BW ≥400 Hz.

Positive MR contrast can be considered as a function depending on concentration of MLC inside the voxel, TE, BWsat, and BWex. In our experiments we showed that positive MR contrast of voxels containing concentrations ≥ 20 - 150 MLC / μl can be achieved by SSS with BWsat 100 Hz and BWsat 200 Hz. This led to excellent improvements in imaging contrast and hence higher probability to detect MLC as compared to MR strategies focusing on MLC induced signal reductions. According experimental conditions Crel was optimized for 75 MLC / μl.

In MRI magnetically labeled cells (MLC) cause local field inhomogeneities within the single voxels as well as on a macroscopic scale. The related Larmor frequency shift near MLC was exploited to obtain bright visualization and improvements in MR imaging contrast applying spectral selective saturation (SSS).

SK-Mel28 cells were labeled with superparamagnetic contrast agent SHU 555A. Low cell concentrations (0, 5, 20, 30, 50, 75, and 150 MLC/μl) and high cell concentrations (1.000, 3.000, 6.000, and 10.000 MLC/μl)were examined at 3 Tesla. Shimming and frequency adjustment to ν0 was performed with the built in routine of the scanner. A 2D spin echo (SE) sequence with broadband excitation and refocusing pulses was used (BWex = 1.000 Hz). Prior to each TR, a non-selective saturation sinc pulse centred at ν0 was applied. Bandwidth (BWsat) of this pulse was varied from 100 Hz to 800 Hz in logarithmic steps.

Without SSS highest value of Crel (i.e. relative MR contrast of labeled to unlabeled volume) was found for 150 MLC/μl with 10%. Applying SSS pulses led to hyperintensity of the complete labeled volume for concentrations ≥20 MLC/μl and to remarkable improvements in Crel.With increasing cell concentrations Crel raised to maximum, that was given by 52% (BWsat=100 Hz) and 28% (BWsat = 200 Hz) found for 75 MLC/μl. For 150 MLC/μl Crel decreased, but was significantly higher than value without SSS. Signal could be detected near cell aggregations (high cell concentrations) despite saturation. For low / high cell concentrations the entire sample was signalfree at BW ≥400 Hz.

Positive MR contrast can be considered as a function depending on concentration of MLC inside the voxel, TE, BWsat, and BWex. In our experiments we showed that positive MR contrast of voxels containing concentrations ≥ 20 - 150 MLC / μl can be achieved by SSS with BWsat 100 Hz and BWsat 200 Hz. This led to excellent improvements in imaging contrast and hence higher probability to detect MLC as compared to MR strategies focusing on MLC induced signal reductions. According experimental conditions Crel was optimized for 75 MLC / μl.

Pintaske, J, Martirosian, P, Claussen, C, Schick, F, Enhancement of MR Sensitivity to Detect SPIO-labeled Cells by Means of Spectral Selective Saturation.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4407532.html