Ongoing dual‐angle measurements for the correction of partial saturation in ³¹P MR spectroscopy

Abstract

Use of a repetition time similar to, or shorter than, metabolite T 1 s is common in NMR spectroscopy of biological samples to improve the signal-to-noise ratio. Conventionally, the partial saturation that results from this is corrected using saturation factors. However, this can lead to erroneous results in the presence of chemical exchange or nonconstant T 1 s. We describe an alternative approach to correction for saturation, based on ongoing dual-angle T 1 measurement. Using 31 P magnetic resonance spectroscopy of the perfused rat heart undergoing ischemia-reperfusion, we demonstrate that signal alternations in the data acquired by the dual-angle approach are eliminated by the ongoing dual-angle T 1 measurement correction scheme, meaning that metabolite concentration and T 1 measurement can be made throughout the course of the ischemia-reperfusion protocol. Simulations, based on parameters pertinent to the perfused rat heart, demonstrate that accurate saturation correction is possible with this method except at times of rapid concentration change. Additionally, compared to the conventional saturation factor correction method, the ongoing dual-angle T 1 measurement correction scheme results in improved accuracy in determining the [phosphocreatine] recovery time constant. Thus, the ongoing dual-angle T 1 measurements procedure permits accurate monitoring of metabolite concentrations even in the setting of chemical exchange and T 1 changes and allows more accurate analysis of bioenergetic status. Magn Reson Med 64:957-966,

Hyperpolarized butyrate: A metabolic probe of short chain fatty acid metabolism in the heart

“…The lack of any metabolic alteration between the fed and fasted states may also be related to the fact that the metabolism of short‐chain fatty acids lies outside of the normal regulatory mechanisms of fatty acid oxidation . Oxidation of long‐chain fatty acids is controlled at the point of mitochondrial uptake, via inhibition of carnitine palmitoyltransferase I by malonyl‐CoA, whereas SCFAs do not require this mitochondrial transport mechanism and are therefore not regulated in the same way .…”

“…The hearts were then excised and briefly washed in ice‐cold Krebs Henseleit (KH) buffer, followed by dissection to reveal the aorta. The aorta was cannulated, tied off with 3/0 suture (Pearsalls, UK), and the heart perfused in the Langendorff mode at 85 mmHg pressure, using KH buffer at a temperature of 37°C and oxygenated with 95%O 2 /5%CO 2 gas .…”

A Mouse Model of Creatine Transporter Deficiency Reveals Impaired Motor Function and Muscle Energy Metabolism

“…From the PCr/ATP and P i /ATP signal ratios we estimated tissue levels of PCr and P i after correction for T1 saturation. For P i a T1 of 1.95 s was applied ( Nabuurs et al, 2010 ; Tyler et al, 2010 ). T1 values, for PCr and βATP, derived from skeletal muscle of 3 CT1 +/y mice at 11.7T using inversion recovery, were 2.25 ± 0.118 and 0.656 ± 0.07 s, respectively.…”

Hyperpolarized ketone body metabolism in the rat heart

“…Hearts were then excised and rapidly washed in ice‐cold Krebs–Henseleit (KH) buffer, followed by dissection to reveal the aorta. The aorta was cannulated, tied off with monofilament 3/0 (0.3 mm in diameter) silk suture (Pearsalls, Taunton, Somerset, UK) and the heart was perfused in the Langendorff mode at constant pressure (85 mmHg/11.3 kPa, corresponding to an approximate flow rate of 15 mL/min) using KH buffer at a temperature of 37°C and oxygenated with 95% O 2 /5% CO 2 gas . A polyethylene tube was inserted into the left ventricle and through the apex of the heart in order to drain Thebesian flow.…”

“…The aorta was cannulated, tied off with monofilament 3/0 (0.3 mm in diameter) silk suture (Pearsalls, Taunton, Somerset, UK) and the heart was perfused in the Langendorff mode at constant pressure (85 mmHg/11.3 kPa, corresponding to an approximate flow rate of 15 mL/min) using KH buffer at a temperature of 37°C and oxygenated with 95% O 2 /5% CO 2 gas. [27][28][29][30] A polyethylene tube was inserted into the left ventricle and through the apex of the heart in order to drain Thebesian flow. A polypropylene balloon connected to a pressure transducer and a PowerLab system (AD Instruments, Abingdon, Oxfordshire, UK) was then inserted into the left ventricle to monitor contractile function, and the heart was subsequently placed inside a 20-mm NMR test tube, which was inserted into the bore of the 11.7-T magnet described above.…”