First In Vivo Potassium-39 (^K) MRI at 9.4 T Using Conventional Copper Radio Frequency Surface Coil Cooled to 77 K

• Published in: IEEE transactions on biomedical engineering 2014-02, Vol.61 (2), p.334-345
• Main Authors: Elabyad, Ibrahim A., Kalayciyan, Raffi, Shanbhag, Nagesh C., Schad, Lothar R.
• Format: Article
• Language: English
• Subjects: 77 K; Aerogel; Animals; Brain - anatomy & histology; Brain - physiology; Coils; Cold Temperature; Computer Simulation; cryogenic cooling; Cryogenics; electromagnetic (EM)-simulations; Equipment Design; In vivo; in vivo ^{39} K-MRI; liquid nitrogen (LN _{2} ) cryostat; Magnetic resonance imaging; magnetic resonance imaging (MRI); Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; Male; middle cerebral artery occlusion (MCAO); Phantoms, Imaging; Potassium; potassium-39; Radio frequency; radio frequency (RF) surface resonator; Rats; Rats, Sprague-Dawley; Signal to noise ratio
• ISSN: 0018-9294; 1558-2531
• DOI: 10.1109/TBME.2013.2294277

Potassium-39 ( 39 K) magnetic resonance imaging (MRI) is a noninvasive technique which could potentially allow for detecting intracellular physiological variations in common human pathologies such as stroke and cancer. However, the low signal-to-noise ratio (SNR) achieved in 39 K-MR images hampered data acquisition with sufficiently high spatial and temporal resolution in animal models so far. Full wave electromagnetic (EM) simulations were performed for a single-loop copper (Cu) radio frequency (RF) surface resonator with a diameter of 30 mm optimized for rat brain imaging at room temperature (RT) and at liquid nitrogen (LN 2 ) with a temperature of 77 K. A novel cryogenic Cu RF surface resonator with home-built LN 2 nonmagnetic G10 fiberglass cryostat system for small animal scanner at 9.4 T was designed, built and tested in phantom and in in vivo MR measurements. Aerogel was used for thermal insulation in the developed LN 2 cryostat. In this paper, we present the first in vivo 39 K-MR images at 9.4 T for both healthy and stroke-induced rats using the developed cryogenic coil at 77 K. In good agreement with EM-simulations and bench-top measurements, the developed cryogenic coil improved the SNR by factor of 2.7 ± 0.2 in both phantom and in in vivo MR imaging compared with the same coil at RT.