A measurement setup for direct ¹⁷O MRI at 7 T

Abstract

An efficient breathing system was designed for direct 17 O MRI to perform oxygen metabolism studies of the human brain. The breathing system consists of a demand oxygen delivery device for 17 O 2 supply and a custom-built rebreathing circuit with pneumatic switching valve. To efficiently deliver the 17 O gas to the alveoli of the lungs, the system applies short gas pulses upon an inspiration trigger via a nasal cannula. During and after 17 O 2 administration, the exhaled gas volumes are stored and filtered in the re-breathing section to make the most efficient use of the rare 17 O gas. In an inhalation experiment, 2.2 6 0.

Quantification of oxygen metabolic rates in Human brain with dynamic 17O MRI: Profile likelihood analysis

“…Thus, it is of high clinical interest to map oxygen metabolism in clinical routine. With the recent implementation of 17 O MRI (26,27,(30)(31)(32)(33), clinical CMRO 2 quantification and oxygen metabolism mapping might become feasible; however, the different parameters in the numerical description of the oxygen uptake are often not identifiable from time-resolved measurements alone. In this study, the PL method was used to identify those parameters in the CMRO 2 quantification model that require prior knowledge for a unique identification.…”

“…If CMRO 2 was non-identifiable, a DODS was fixed to 0.27/ 0.31 (for Exp1/Exp2) based on the estimated amount of 17 O 2 inhaled with a single DODS pulse as in (27,32) 2 , which include the optimum CMRO 2 value, were calculated using Equation [5] for the confidence level CL ¼ 0.33 and were used to present the calculated CMRO 2 values. It is worth noting that in this study the CMRO 2 values were presented for each dataset separately, and not as the range among several MR examinations.…”

“…Initially, the RB system was proposed in (27), where a potential 17 O signal during RB phase was excluded from the data analysis due to complexity of the analytical solution of Equation [7]. Later, it was solved for constant a values (33); in this study, a numerical integration was used instead of solving the ODEs analytically.…”

“…To calculate metabolic rates of oxygen consumption in humans, the 17 O MRI signal changes from H 2 17 O molecules are observed during and after inhalation of isotope-enriched 17 O gas (26)(27)(28)(29)(30)(31)(32)(33). Direct 17 O MRI and MR spectroscopy has been predominantly performed at ultra-high magnetic fields (UHFs) of 7T and 9.4T (26)(27)(28)(29)(32)(33)(34)(35)(36). UHFs are advantageous for 17 O MRI because they partly compensate for the low MR sensitivity of the 17 O isotope which is only about 1.1 Á 10 À5 of 1 H due to the low natural abundance of 17 O nucleus of 0.037% and the approximately sevenfold lower gyromagnetic ratio.…”

“…Recently, feasibility of direct 17 O MRI in human brain and heart at clinical field strengths of 3T has been reported (37), which has the ultimate goal of implementing CMRO 2 quantification at clinical MR systems. In the previous studies, a rebreathing (RB) system was implemented for efficient usage of rare and expensive 17 O 2 gas by re-inhalation of the stored 17 O 2 gas in subsequent inhalation cycles (27,33). Unfortunately, this delivery method leads to uncertainties in the determination of the 17 O enrichment fraction of the inhaled gas, which in turn can lead to systematic errors in the quantities derived from this enrichment fraction.…”