TABLE 5.

Recommendations for ¹H MRS of acetylcarnitine

Acquisition	Large voxel still must be placed in one muscle group to avoid inclusion of different fiber composition and acetylcarnitine content.
	Long TE‐protocols (e.g., 350 ms) allows detection of acetylcarnitine at rest (without the need of exercise) and irrespective of the field strength.
	Strong lipid signals can be reduced by the application of longitudinal relaxation time editing.
	Long TE spectra require a relatively large voxel (min. 20 mL, preferably using PRESS or sLASER) and a sufficient number of acquisitions (64‐256) to achieve optimal SNR.
	Sufficiently long TR (≥6000 ms) should be used to avoid T1 saturation.
Processing and /Quantitation	The singlet signal at 2.13 ppm is better suited for acetylcarnitine detection and quantification than the 3.17 ppm peak.
	While absolute concentration of acetylcarnitine can be based on either water or total creatine (tCr, 3.03 ppm), it is preferable to use tCr during exercise studies.
	Caveats for quantitation: small variations of water relaxation times have a strong effect and tCr must be corrected for residual dipolar effects.
Physiology and /Preconditioning	Studies of resting acetylcarnitine levels require a standardized preconditioning: 2 days omitting strenuous exercise and at least 1 day defined diet without large variations in macronutrient composition.
	MR examinations should be planned at the same time during the day to avoid effects of diurnal variations.
	Volunteers must rest for half an hour before the measurement.
	Intensity, duration, muscle investigated and fed/fasted state must be standardized and documented in exercise protocols.
	High‐intensity exercise protocols (in combination with glucose intake) are recommended to maximize acetylcarnitine concentrations.