Evaluation and Validation of clinical 4.23 T sodium MRI in animals and human: Application of oblique multi-slice spin-echo pulse sequence

Objective: Application of high-field 4.23 T MRI clinical imager was demonstrated for sodium magnetic resonance imaging (MRI) data acquisition. of multislice spin echo (MSSE) pulse sequence at selected scan parameters can sufficiently visualize the total sodium signal as indicator of sub-clinical activity. Material and Methods: MSSE pulse sequence technique was used to simulate sodium images of human brain.. For validation purpose, inversion recovery pulse sequence was validated by optimization of scan inversion time (TI). Phantom of sodium and rat brain were imaged. Sodium images were validated and compared with proton MRI images. Results: MSSE pulse technique enabled to visualize the sodium signal at optimized scan parameters. Specifically, MSSE pulse technique enabled the identification of different sodium rich areas due to their subphysiological activity in the brain, comparable with proton MRI images. Reconstruction images of brain further enhanced the power to classify the brain tissue. Intracellular sodium images of agarose-saline solution filled-tube phantom were generated by use of inversion recovery pulse sequence. Conclusion: Using MSSE pulse sequence at 4.23 T, in vivo sodium images can be generated within acceptable scan time for routine clinical brain examination for achieving better sub-physiological information as obtained from proton MRI. 3 Introduction Integrated approach of Proton MRI with in vivo sodium magnetic resonance imaging seems promising to detect sub-physiological abnormalities. Sodium nuclei inside the brain exist in free and bound forms as extracellular and intracellular sodium populations exhibiting longer and shorter relaxation times respectively reported[1]. Sodium moves in free form or also bound with proteins, glycosides via a site localized on the exterior surface of cell membranes. Most of the Na nuclei undergo substantial relaxation before their signals can be acquired. Sodium has a spin of 3/2 and a quadruple moment. So, sodium exhibits many energy transitions and two transverse relaxation times, a long T2 = 16-30 ms and a short T2 = 0.7-3.0 ms depending upon magnetic field strength[2]. To acquire sodium images in experimental animals and human, multiple quantum (MQF), single quantum (SQF), triple quantum (TQF) filter methods have been used highlighting the need of high magnetic field at 4.23 Tesla imager as reported [3-7]. Several 2D and 3D spin echo and gradient echo pulse sequences have been in use. Sodium brain images in clinical set up at higher magnetic fields such as 4.23 T have not been reported perhaps due to two reasons: less sodium abundance and less sensitive intracellular sodium nuclei …