Ex-vivo cellular MRI with b-SSFP: quantitative benefits of 3T over 1.5 T.
BACKGROUND
The use of MRI with iron-based magnetic nanoparticles for imaging cells is a rapidly growing field of research. We have recently reported that single iron-labeled cells could be detected, as signal voids, in vivo in mouse brains using a balanced steady-state free precession imaging sequence (b-SSFP) and a customized microimaging system at 1.5 T.


METHODS
In the current study we assess the benefits, and challenges, of using a higher magnetic field strength for imaging iron-labeled cells with b-SSFP, using ex vivo mouse brain specimens imaged with near identical systems at 1.5 and 3.0 T.


RESULTS
The substantial banding artifact that appears in 3 T b-SSFP images was readily minimized with RF phase cycling, allowing for banding-free b-SSFP images to be compared between the two field strengths. This study revealed that with an optimal 3 T b-SSFP imaging protocol, more than twice as many signal voids were detected as with 1.5 T.


CONCLUSIONS
There are several factors that contributed to this important result. First, a greater-than-linear SNR gain was achieved in mouse brain images at 3 T. Second, a reduction in the bandwidth, and the associated increase in repetition time and SNR, produced a dramatic increase in the contrast generated by iron-labeled cells.
Ramadan
Soha Said
SS
Imaging Research Laboratories, Robarts Research Institute, London, ON, Canada. sramadan@imaging.robarts.ca
Heyn
Chris
C
Mackenzie
Lisa T
LT
Chambers
Ann F
AF
Rutt
Brian K
BK
Foster
Paula J
PJ
D000818:Animals; D016477:Artifacts; D001921:Brain / Q000166:cytology*; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D007501:Iron / Q000737:chemistry*; D008279:Magnetic Resonance Imaging / Q000379:methods; D053768:Metal Nanoparticles; D051379:Mice; D008819:Mice, Nude
D007501:Iron