title: A magnetic resonance (MR) microscopy system using a microfluidically cryo-cooled planar coil.
abstract: We present the development of a microfluidically cryo-cooled planar coil for magnetic resonance (MR) microscopy. Cryogenically cooling radiofrequency (RF) coils for magnetic resonance imaging (MRI) can improve the signal to noise ratio (SNR) of the experiment. Conventional cryostats typically use a vacuum gap to keep samples to be imaged, especially biological samples, at or near room temperature during cryo-cooling. This limits how close a cryo-cooled coil can be placed to the sample. At the same time, a small coil-to-sample distance significantly improves the MR imaging capability due to the limited imaging depth of planar MR microcoils. These two conflicting requirements pose challenges to the use of cryo-cooling in MR microcoils. The use of a microfluidic based cryostat for localized cryo-cooling of MR microcoils is a step towards eliminating these constraints. The system presented here consists of planar receive-only coils with integrated cryo-cooling microfluidic channels underneath, and an imaging surface on top of the planar coils separated by a thin nitrogen gas gap. Polymer microfluidic channel structures fabricated through soft lithography processes were used to flow liquid nitrogen under the coils in order to cryo-cool the planar coils to liquid nitrogen temperature (-196 °C). Two unique features of the cryo-cooling system minimize the distance between the coil and the sample: (1) the small dimension of the polymer microfluidic channel enables localized cooling of the planar coils, while minimizing thermal effects on the nearby imaging surface. (2) The imaging surface is separated from the cryo-cooled planar coil by a thin gap through which nitrogen gas flows to thermally insulate the imaging surface, keeping it above 0 °C and preventing potential damage to biological samples. The localized cooling effect was validated by simulations, bench testing, and MR imaging experiments. Using this cryo-cooled planar coil system inside a 4.7 Tesla MR system resulted in an average image SNR enhancement of 1.47 ± 0.11 times relative to similar room-temperature coils.
authors: Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA.
authors: Chiwan
authors: C
authors: Koo
authors: Richard F
authors: RF
authors: Godley
authors: Jaewon
authors: J
authors: Park
authors: Mary P
authors: MP
authors: McDougall
authors: Steven M
authors: SM
authors: Wright
authors: Arum
authors: A
authors: Han
references: Med Phys. 1986 Jan-Feb;13(1):1-7
references: 3951399
references: Lab Chip. 2009 Jan 7;9(1):17-23
references: 19209329
references: Magn Reson Med. 1999 Nov;42(5):952-62
references: 10542355
references: Magn Reson Med. 2008 Jun;59(6):1440-7
references: 18421696
references: NMR Biomed. 2009 Nov;22(9):982-93
references: 19441080
references: Magn Reson Med. 2005 Aug;54(2):386-92
references: 16032696
references: Magn Reson Med. 2000 Feb;43(2):163-9
references: 10680678
references: Biomaterials. 1999 Dec;20(23-24):2363-76
references: 10614942
references: IEEE Trans Biomed Eng. 1994 Feb;41(2):195-7
references: 8026853
references: Magn Reson Med. 2001 Mar;45(3):376-82
references: 11241693
references: Magn Reson Med. 1994 Sep;32(3):396-400
references: 7984072