from Section 1 - Physiological MR techniques
Published online by Cambridge University Press: 05 March 2013
Introduction
In general, proton MRS, as implemented on modern clinical MR machines, provides a reliable adjunct to the growing cadre of imaging methods. Pitfalls can be minimized using automation and standard protocols.[1] Given that the spectral patterns are well known, minor artifacts are relatively easy to identify and read through, at least for the large signals in the spectrum, such as choline (Cho), creatine (Cr) and N-acetyl aspartate (NAA). However, the current trend is toward the incorporation of second tier markers, such as lactate (Lac), glutamate (Glu), glutamine (Gln) and myo-inositol (mI), as well as a demand for longitudinal studies with narrow repeatability requirements. These applications require an understanding of potential artifacts, and the limits of the existing remedies. To achieve repeatability at the limit of biological variation may, in fact, require the development of new artifact reduction algorithms. This chapter details artifacts, remedies, and trade-offs that impact the quantitative use of in vivo MRS. The focus is on proton spectroscopy and spectroscopic imaging (SI) of cerebral metabolites, but the basic principles can be applied to other nuclei, and other parts of the body. With a few notable exceptions, most of the advances in MRS artifact reduction were developed for proton neurological applications at 1.5 T using orthogonal-slice localization methods, most notably stimulated echo acquisition mode (STEAM) and double spin echo (SE) point resolved spectroscopy (PRESS).
Pre-scan
Pre-scan operations, including prescription, sequence, variable selection, shimming, transmit gain and water suppression, all impact the limits of detection and repeatability of the examination. Even with automation and reproducible, predefined protocols, attention to the details of the pre-scan may improve repeatability. Some applications still benefit from manual pre-scan operations. Routine maintenance and quality-control checks using a standard MRS phantom will also reduce the chance for system contributions to variance.
To save this book to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.