title: Validating a robust double-quantum-filtered (1) H MRS lactate measurement method in high-grade brain tumours.
abstract: (1) H MRS measurements of lactate are often confounded by overlapping lipid signals. Double-quantum (DQ) filtering eliminates lipid signals and permits single-shot measurements, which avoid subtraction artefacts in moving tissues. This study evaluated a single-voxel-localized DQ filtering method qualitatively and quantitatively for measuring lactate concentrations in the presence of lipid, using high-grade brain tumours in which the results could be compared with standard acquisition as a reference. Paired standard acquisition and DQ-filtered (1) H MR spectra were acquired at 3T from patients receiving treatment for glioblastoma, using fLASER (localization by adiabatic selective refocusing using frequency offset corrected inversion pulses) single-voxel localization. Data were acquired from 2 × 2 × 2 cm(3) voxels, with a repetition time of 1 s and 128 averages (standard acquisition) or 256 averages (DQ-filtered acquisition), requiring 2.15 and 4.3 min respectively. Of 37 evaluated data pairs, 20 cases (54%) had measureable lactate (fitted Cramér-Rao lower bounds ≤ 20%) in either the DQ-filtered or the standard acquisition spectra. The measured DQ-filtered lactate signal was consistently downfield of lipid (1.33 ± 0.03 ppm vs 1.22 ± 0.08 ppm; p = 0.002), showing that it was not caused by lipid breakthrough, and that it matched the lactate signal seen in standard measurements (1.36 ± 0.02 ppm). In the absence of lipid, similar lactate concentrations were measured by the two methods (mean ratio DQ filtered/standard acquisition = 1.10 ± 0.21). In 7/20 cases with measurable lactate, signal was not measureable in the standard acquisition owing to lipid overlap but was quantified in the DQ-filtered acquisition. Conversely, lactate was undetected in seven DQ-filtered acquisitions but visible using the standard acquisition. In conclusion, the DQ filtering method has proven robust in eliminating lipid and permits uncontaminated measurement of lactate. This is important validation prior to use in tissues outside the brain, which contain large amounts of lipid and which are often susceptible to motion.
authors: MRI Unit, Royal Marsden Hospital, Sutton, Surrey, UK. gsp@icr.ac.uk.
authors: G S
authors: GS
authors: Payne
authors: MRI Unit, Royal Marsden Hospital, Sutton, Surrey, UK.
authors: L M
authors: LM
authors: Harris
authors: MRI Unit, Royal Marsden Hospital, Sutton, Surrey, UK.
authors: G S
authors: GS
authors: Cairns
authors: MRI Unit, Royal Marsden Hospital, Sutton, Surrey, UK.
authors: C
authors: C
authors: Messiou
authors: MRI Unit, Royal Marsden Hospital, Sutton, Surrey, UK.
authors: N M
authors: NM
authors: deSouza
authors: MRI Unit, Royal Marsden Hospital, Sutton, Surrey, UK.
authors: A
authors: A
authors: Macdonald
authors: MRI Unit, Royal Marsden Hospital, Sutton, Surrey, UK.
authors: F
authors: F
authors: Saran
authors: MRI Unit, Royal Marsden Hospital, Sutton, Surrey, UK.
authors: M O
authors: MO
authors: Leach
mesh_terms: D000465:Algorithms; D014408:Biomarkers, Tumor / Q000378:metabolism*; D001932:Brain Neoplasms / Q000378:metabolism* / Q000473:pathology*; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism*; D008279:Magnetic Resonance Imaging / Q000379:methods; D057054:Molecular Imaging / Q000379:methods*; D060787:Neoplasm Grading; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted
chemical_list: D014408:Biomarkers, Tumor; D019344:Lactic Acid
keywords: MRS; brain; double-quantum filter; glioblastoma; lactate; single voxel