Oilfield nuclear magnetic resonance (NMR) applications are widely accepted for characterizing reservoir rocks and fluids. All of the downhole applications, and most oilfield NMR lab work, are carried out assuming that the results are independent of the operating frequency. The assumption is generally warranted, since most NMR logging tools and lab devices operate in the 0.5 to 2 MHz range. However, two strong motivations exist for investigating the frequency dependence (that is, dispersion) of NMR of crude oil samples: 1) introduction and acceptance of lower frequency logging while drilling (LWD) and multi- frequency wireline NMR tools, and 2) sensitivity of NMR dispersion to the interaction and dynamics of molecules of varying size in complex fluids. We report here on a versatile frequency-dependent lab NMR measurement known as fast field cycling (FFC) NMR. The results clearly demonstrate a frequency dependence of the longitudinal relaxation time, T1, for crude oils between 10 kHz and 40 MHz. The study investigates the full T1 distributions for crude oils containing significant amounts of all the SARA (saturates, aromatics, resins, asphaltene) fractions, including a broad range of concentrations for the heavier fractions. For crude oils containing minimal asphaltene and resin fractions, the dispersion is minimal. In contrast, crude oils containing larger concentrations of asphaltene and resins show a clear shift of the T1 distribution to longer times at higher frequencies. We will discuss the implications and benefits of NMR dispersion for oilfield application. We suggest how the dispersion can be understood in terms of the molecular dynamics of asphaltenes with the rest the oil. Finally, we will provide an overview of the experimental challenges in making these measurements, including the hardware design and the specialized pulse sequences required for acquiring multi-frequency data.
Background: Near-infrared spectroscopy (NIRS) has been applied for cerebral oxygen saturation (rSO2) monitoring in neonates. There is a paucity of data from low-middle income countries (LMIC) setting of cerebral rSO2 in neonates with encephalopathy of diverse etiologies. This study aimed to monitor cerebral rSO2 using NIRS in encephalopathic neonates aiming to maintain the rSO2 between 55 to 85%, in the first 72 hours of admission in order to improve short-term neurodevelopmental outcomes (NDO). Materials and Methods: This was a prospective cohort study enrolling encephalopathic neonates with hypoxic ischemic encephalopathy (HIE) and non-HIE etiologies into 8 clinical categories. Monitoring and targeting the cerebral rSO2 between 55 to 85% employing predefined actions and management alterations was done over 72 hours. The neurodevelopmental assessment was conducted at 3, 6 and 9-12 months corrected age. Motor and mental developmental quotients (MoDQ) (MeDQ) were recorded and compared to historical control. Results: A total of 120 neonates were enrolled and assessed for NDO. The MoDQ (mean ± SD) was 92.55 ± 14.85, 93.80 ± 13.20, 91.02 ± 12.69 and MeDQ (mean ± SD) was 91.80 ± 12.98, 91.80 ± 13.69, 88.41 ± 11.60 at 3, 6 and 9-12 months. The MoDQ and MeDQ scores of the historic cohort at 12 months were 86.35 ± 20.34 and 86.58 ± 18.27. The mean difference [MD (95%CI)] for MoDQ was - 4.670 (- 8.48 to - 0.85) (p=0.0165) and for MeDQ was - 1.83 (- 5.26 to 1.6) (p=0.29). There was a negative correlation between the composite developmental quotient (CoDQ) with mean rSO2 and a positive correlation with cerebral fractional tissue oxygen extraction (CFTOE). Neonates with HIE and neonatal encephalopathy (NE) (n=37/120) had the lowest motor and mental DQ on neurodevelopmental assessment. Clinical categories neonatal meningitis (NM) and intraventricular hemorrhage (IVH) showed improvement in DQ scores over the study period. Conclusion: In neonates with encephalopathy resulting from varied etiologies monitoring and maintaining cerebral rSO2 between 55-85% by appropriate management changes resulted in improved neurodevelopmental scores at 12 month follow-up.
9-year-old boy presented with frequent falls, tremors, and slurring of speech over the past 2 months. There was no history of seizures, jaundice, or viral illness in early childhood. He was born to nonconsanguineous parents and there was no other affected family member. On examination, he had an expressionless face, Kayser-Fleischer rings (bilateral cornea; Figure, A), dysarthria, drooling, axial and appendicular tremors, generalized dystonia, and rigidity. A clinical diagnosis of Wilson disease was considered.Investigation showed normal liver function tests, markedly decreased serum ceruloplasmin levels (5.7 mg/dL; normal, 20-35 mg/dL), and increased urinary copper excretion (1200 mg/24 h; normal, <40 mg/24 h). Magnetic resonance imaging of the brain (Figure, B and D) showed signal changes in basal ganglia, mid brain and pons suggestive of
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