title: An evaluation of motion compensation strategies and repeatability for abdominal (1)H MR spectroscopy measurements in volunteer studies and clinical trials.
abstract: Increased expression of choline kinase has frequently been shown in tumours and is thought to be associated with disease progression. Studies using magnetic resonance spectroscopy have shown an increase in total choline-containing metabolites (tCho) in tumour compared with healthy tissue. Subsequent reductions in tCho following successful treatment support the use of tCho as a biomarker of disease and response. However, accurate measurement of tCho using MRS in abdominal tumours is complicated by respiratory motion, blurring the acquisition volume and degrading the lineshape and signal-to-noise ratio (SNR) of metabolites. Motion compensation using prospectively gated acquisitions or offline correction of phase and frequency distortions can help restore the SNR and linewidth of metabolites. Prospectively gated acquisitions have the advantage of confining the volume of acquisition to the prescribed volume but are constrained by the repetition time (TR) of the respiratory motion. In contrast, data acquired for offline correction may use a shorter repetition time and therefore yield an increased SNR per unit time. In this study abdominal spectra acquired from single-voxel 'free-breathing' measurements in liver of healthy volunteers and in abdominal tumours of cancer patients were compared with those of prospective gating and with an implementation of offline correction. The two motion compensation methodologies were assessed in terms of SNR, linewidth and repeatability. Our experiments show that prospective gating and offline correction result in a 12-22% reduction in median tCho linewidth, while offline correction also provides a significant increase in SNR. The repeatability coefficient (the expected interval for 95% of repeat measurements) for tCho/water ratio was reduced by 37% (prospective gating) and 41% (offline correction). Both methods of motion compensation substantially improved the reproducibility of the tCho/water measurement and the tCho linewidth. While offline correction also leads to a significant improvement in SNR, it may suffer more from out-of-voxel contamination.
authors.affiliation: Royal Marsden Hospital and Institute of Cancer Research, Downs Road, Sutton, Surrey, SM2 5PT, UK. michael.germuska@wolfson.ox.ac.uk
authors.forename: M
authors.initials: M
authors.lastname: Germuska
authors.forename: N
authors.initials: N
authors.lastname: Tunariu
authors.forename: M O
authors.initials: MO
authors.lastname: Leach
authors.forename: Jian
authors.initials: J
authors.lastname: Xu
authors.forename: G S
authors.initials: GS
authors.lastname: Payne
mesh_terms: D000008:Abdominal Neoplasms / Q000737:chemistry* / Q000175:diagnosis*; D016477:Artifacts; D014408:Biomarkers, Tumor / Q000032:analysis*; D002794:Choline / Q000032:analysis*; D002986:Clinical Trials as Topic; D003936:Diagnosis, Computer-Assisted / Q000379:methods; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011522:Protons; D015203:Reproducibility of Results; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods*; D012680:Sensitivity and Specificity
chemical_list: D014408:Biomarkers, Tumor; D011522:Protons; D002794:Choline