Measurement and correction of microscopic head motion during magnetic resonance imaging of the brain.

Magnetic resonance imaging (MRI) is a widely used method for non-invasive study of the structure and function of the human brain. Increasing magnetic field strengths enable higher resolution imaging; however, long scan times and high motion sensitivity mean that image quality is often limited by the involuntary motion of the subject. Prospective motion correction is a technique that addresses this problem by tracking head motion and continuously updating the imaging pulse sequence, locking the imaging volume position and orientation relative to the moving brain. The accuracy and precision of current MR-compatible tracking systems and navigator methods allows the quantification and correction of large-scale motion, but not the correction of very small involuntary movements in six degrees of freedom. In this work, we present an MR-compatible tracking system comprising a single camera and a single 15 mm marker that provides tracking precision in the order of 10 m and 0.01 degrees. We show preliminary results, which indicate that when used for prospective motion correction, the system enables improvement in image quality at both 3 T and 7 T, even in experienced and cooperative subjects trained to remain motionless during imaging. We also report direct observation and quantification of the mechanical ballistocardiogram (BCG) during simultaneous MR imaging. This is particularly apparent in the head-feet direction, with a peak-to-peak displacement of 140 m.

Proton magnetic resonance spectroscopy of brain in obstructive sleep apnoea in north Indian Asian subjects.

BACKGROUND & OBJECTIVES: Repeated apnoeic/hypoapnoeic episodes during sleep may produce cerebral damage in patients with obstructive sleep apnoea (OSA). The aim of this study was to determine the absolute concentration of cerebral metabolites in apnoeic and non-apnoeic subjects from different regions of the brain to monitor the regional variation of cerebral metabolites. METHODS: Absolute concentration of cerebral metabolites was determined by using early morning proton magnetic resonance spectroscopy ((1)H MRS) in 18 apnoeic patients with OSA (apnoeics) having apnoea/hypopnoea index (AHI) >5/h, while 32 were non-apnoeic subjects with AHI< 5/h. RESULTS: The absolute concentration of tNAA [(N-acetylaspartate (NAA)+N-acetylaspartylglutamate (NAAG)] was observed to be statistically significantly lower (P<0.05) in apnoeics in the left temporal and left frontal gray regions compared to non-apnoeics. The Glx (glutamine, Gln + glutamate, Glu) resonance showed higher concentration (but not statistically significant) in the left temporal and left frontal regions of the brain in apnoeics compared to non-apnoeics. The absolute concentration of myo-inositol (mI) was significantly high (P<0.03) in apnoeics in the occipital region compared to non-apnoeics. INTERPRETATION & CONCLUSIONS: Reduction in the absolute concentration of tNAA in apnoeics is suggestive of neuronal damage, probably caused by repeated apnoeic episodes in these patients. NAA showed negative correlation with AHI in the left frontal region, while Cho and mI were positively correlated in the occipital region and Glx showed positive correlation in the left temporal region of the brain. Overall, our results demonstrate that the variation in metabolites concentrations is not uniform across various regions of the brain studied in patients with OSA. Further studies with a large cohort of patients to substantiate these observations are required.

Investigation of hepatic gluconeogenesis pathway in non-diabetic Asian Indians with non-alcoholic fatty liver disease using in vivo ((31)P) phosphorus magnetic resonance spectroscopy.

OBJECTIVE: To study hepatic gluconeogenesis pathway in non-diabetic Asian Indian males having non-alcoholic fatty liver disease (NAFLD) using in vivo ((31)P) phosphorous magnetic resonance spectroscopy (MRS) and correlate these data with anthropometry and insulin resistance. RESEARCH DESIGN AND METHODS: Forty non-diabetic patients with NAFLD and 20 healthy controls were divided into (i) obese with NAFLD (group I, n=20), (ii) non-obese with NAFLD (group II, n=20) and (iii) non-obese without NAFLD (group III, n=20). Anthropometric and biochemical profiles, short insulin tolerance test (SITT), liver ultrasound, and (31)P MRS (to determine hepatic gluconeogenesis metabolite; phosphomonoesters (PMEs), inorganic phosphate (Pi) and their ratios with respect to ATP) were done. RESULTS: Insulin resistance (Kitt value) was highest in group I (p<0.05; compared to other two groups), but was also higher in group II as compared to group III (p=ns). The values of PME/Pi, PME/gammaATP, PME/betaATP, PME/tATP ratios were higher (p<0.05) in group I compared to other two groups. Interestingly, non-obese subjects with NAFLD also showed more derangements of hepatic gluconeogenesis metabolites than non-obese subjects without NAFLD. Positive correlation was observed between PME and other ratios in relation to body mass index, waist circumference, body fat percentage and fasting serum insulin levels in all the three groups. CONCLUSIONS: Derangements in hepatic gluconeogenesis as assessed non-invasively using (31)P MRS, was observed in obese and non-obese, non-diabetic Asian Indians with NAFLD. Further research is warranted whether this investigation in NAFLD subjects could be developed as a non-invasive tool to assess those predisposed to develop hyperglycemia.