Joerg Pintaske, Presenter: Nothing to Disclose

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

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

High concentrations of magnetically labeled cells (MLC) cause signal voids in MR images. A detailed investigation of MLC induced relaxation enhancement in dependence on both cell concentration and field strength have not been performed so far. This work aims to show our efforts to investigate relaxation rate enhancement ΔR2(SE) and ΔR2(GRE) in spin-echo (SE) and gradient-recalled-echo (GRE) sequences. We experimentally assessed ΔR2(SE) and ΔR2(GRE) for various cell concentrations and field strengths.

Incubation of SK-Mel28 cells in a medium containing SHU 555A (400 µg Fe/ml) resulted in an average iron-content of 50 pg Fe/cell. Agargel was mixed with various cell concentrations N=0,1,5,10,20,40,and 80 MLC/µl-1 and filled into tubes. Measurements were performed at clinical MR systems, operating at 0.2T, 1.5T, and 3T. Relaxation rates were assessed using 3D SE- and GRE-sequences with voxel size 1µl, TR 4.000ms, flip-angle 90°, TE 12-250ms (SE), and TE 10-100ms (GRE).ΔR2(SE) and ΔR2(GRE) were considered as increases in transverse relaxation of samples with N≥1 µl-1 as compared to samples with N=0 µl-1.

For N=1 μl-1 ΔR2(SE) and ΔR2(GRE) were 1.1s-1 (+27% to N=0) and 2.3s-1 (+52%)for 0.2T, 1.4s-1 (+34%) and 3.1s-1 (+72%) for 1.5T, 1.5s-1 (+36%)and 3.2s-1 (+72%) for 3T, respectively. For N=1 μl-1 the values of ΔR2(GRE) were 109% (0.2T), 121% (1.5T) and 113% (3T) higher as compared to ΔR2(SE). Linear increases in ΔR2(SE) and ΔR2(GRE) with respect to cell concentration was found for all field strengths. ΔR2(SE) and ΔR2(GRE) at 1.5T were about 30% higher as compared to 0.2T. Minimal increases (5%)in ΔR2(SE) and ΔR2(GRE)were found for 3T as compared to 1.5 T.

A sample concentration of a single MLC per voxel of 1μl cause relaxation enhancement in MRI for 0.2T, 1.5T, and 3T, and can be expected to provide sufficient MR contrast even in-vivo. Sensitivity to detect MLC is maximized for GRE-sequences for high fields. ΔR2(SE) and ΔR2(GRE) remain nearly unchanged at fields ≥1.5T indicating saturation of particle magnetic moments.

High concentrations of magnetically labeled cells (MLC) cause signal voids in MR images. A detailed investigation of MLC induced relaxation enhancement in dependence on both cell concentration and field strength have not been performed so far. This work aims to show our efforts to investigate relaxation rate enhancement ΔR2(SE) and ΔR2(GRE) in spin-echo (SE) and gradient-recalled-echo (GRE) sequences. We experimentally assessed ΔR2(SE) and ΔR2(GRE) for various cell concentrations and field strengths.

Incubation of SK-Mel28 cells in a medium containing SHU 555A (400 µg Fe/ml) resulted in an average iron-content of 50 pg Fe/cell. Agargel was mixed with various cell concentrations N=0,1,5,10,20,40,and 80 MLC/µl-1 and filled into tubes. Measurements were performed at clinical MR systems, operating at 0.2T, 1.5T, and 3T. Relaxation rates were assessed using 3D SE- and GRE-sequences with voxel size 1µl, TR 4.000ms, flip-angle 90°, TE 12-250ms (SE), and TE 10-100ms (GRE).ΔR2(SE) and ΔR2(GRE) were considered as increases in transverse relaxation of samples with N≥1 µl-1 as compared to samples with N=0 µl-1.

For N=1 μl-1 ΔR2(SE) and ΔR2(GRE) were 1.1s-1 (+27% to N=0) and 2.3s-1 (+52%)for 0.2T, 1.4s-1 (+34%) and 3.1s-1 (+72%) for 1.5T, 1.5s-1 (+36%)and 3.2s-1 (+72%) for 3T, respectively. For N=1 μl-1 the values of ΔR2(GRE) were 109% (0.2T), 121% (1.5T) and 113% (3T) higher as compared to ΔR2(SE). Linear increases in ΔR2(SE) and ΔR2(GRE) with respect to cell concentration was found for all field strengths. ΔR2(SE) and ΔR2(GRE) at 1.5T were about 30% higher as compared to 0.2T. Minimal increases (5%)in ΔR2(SE) and ΔR2(GRE)were found for 3T as compared to 1.5 T.

A sample concentration of a single MLC per voxel of 1μl cause relaxation enhancement in MRI for 0.2T, 1.5T, and 3T, and can be expected to provide sufficient MR contrast even in-vivo. Sensitivity to detect MLC is maximized for GRE-sequences for high fields. ΔR2(SE) and ΔR2(GRE) remain nearly unchanged at fields ≥1.5T indicating saturation of particle magnetic moments.

Pintaske, J, Claussen, C, Schick, F, MR Contrast Due to a Single SPIO-labeled Cell per Imaging Voxel: Experiments at 0.2 T, 1.5 T, and 3 T.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4409086.html