Temporal B0 field variation effects on MRSI of the human prostate at 7 T and feasibility of correction using an internal field probe. (12th September 2014)

• Record Type: Journal Article
• Authors: Arteaga de Castro, C. S.; Boer, V. O.; Luttje, M. P.; van der Velden, T. A.; Bhogal, A.; van Vulpen, M.; Luijten, P. R.; van der Heide, U. A.; Klomp, D. W. J.
• Is Part Of: NMR in biomedicine. Volume 27:Number 11(2014:Nov.)
• Page Start: 1353
• Page End: 1360
• Publication Date: 2014-09-12
• Subjects: Nuclear magnetic resonance -- Periodicals; Magnetic Resonance Spectroscopy -- Periodicals; 574
• DOI: 10.1002/nbm.3197
• Languages: English
• ISSNs: 0952-3480

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Spectral degradations as a result of temporal field variations are observed in MRSI of the human prostate. Moving organs generate substantial temporal and spatial field fluctuations as a result of susceptibility mismatch with the surrounding tissue (i.e. periodic breathing, cardiac motion or random bowel motion). Nine patients with prostate cancer were scanned with an endorectal coil (ERC) on a 7‐T MR scanner. Temporal <italic>B</italic><sub>0</sub> field variations were observed with fast dynamic <italic>B</italic><sub>0</sub> mapping in these patients. Simulations of dynamic <italic>B</italic><sub>0</sub> corrections were performed using zero‐ to second‐order shim terms. In addition, the temporal <italic>B</italic><sub>0</sub> variations were applied to simulated MR spectra causing, on average, 15% underestimation of the choline/citrate ratio. Linewidth distortions and frequency shifts (up to 30 and 8 Hz, respectively) were observed. To demonstrate the concept of observing local field fluctuations in real time during MRSI data acquisition, a field probe (FP) tuned and matched for the <sup>19</sup> F frequency was incorporated into the housing of the ERC. The data acquired with the FP were compared with the <italic>B</italic><sub>0</sub> field map data and used to correct the MRSI datasets retrospectively. The dynamic <italic>B</italic><sub>0</sub> mapping data showed variations of up to 30 Hz (0.1 ppm) over 72 s at 7 T. The simulated zero‐order corrections, calculated as the root mean square, reduced the standard deviation (SD) of the dynamic variations by an average of 41%. When using second‐order corrections, the reduction in the SD was, on average, 56%. The FP data showed the same variation range as the dynamic <italic>B</italic><sub>0</sub> data and the variation patterns corresponded. After retrospective correction, the MRSI data showed artifact reduction and improved spectral resolution. <italic>B</italic><sub>0</sub> variations can degrade the MRSI substantially. The simple incorporation of an FP into an ERC can improve prostate cancer MRSI without prior knowledge of the origin of the dynamic field distortions. Copyright © 2014 John Wiley & Sons, Ltd.</p> </abstract>