Dataset Information

Observation of true and pseudo NOE signals using CEST-MRI and CEST-MRS sequences with and without lipid suppression.

ABSTRACT: To investigate the characteristics of nuclear Overhauser enhancement (NOE) imaging signals in the brain at 7T.Fresh hen eggs, as well as six healthy, and six C6 glioma-bearing Wistar rats were scanned using chemical exchange saturation transfer-magnetic resonance imaging (CEST-MRI) and chemical exchange saturation transfer-magnetic resonance spectroscopy (CEST-MRS) sequences (saturation duration 3 s, power 1.47 µT) with and without lipid suppression. CEST data were acquired over an offset range of -6 to +6 ppm relative to the water resonance in 0.5 ppm steps.The water signals were not disrupted by other protons during the CEST-MRS sequences, and true NOE signals could be observed. Using the CEST-MRI sequence without lipid suppression, pseudo NOE imaging signals were observed in the lipid-containing regions (egg yolk, scalp, and even white matter). These pseudo NOE signals were almost (but incompletely) removed with the lipid suppression. Egg yolk results indicated the presence of the NOE to olefinic protons overlapping with the water signal. In vivo experiments showed that the amide proton transfer signal was larger in the tumor, whereas the NOE signal was larger in the normal white matter.True NOE signals can be detected using MRS sequences, and considerable pseudo NOE imaging signals may be observed using MRI sequences.

SUBMITTER: Lu J

PROVIDER: S-EPMC4223020 | biostudies-literature | 2015 Apr

REPOSITORIES: biostudies-literature

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Observation of true and pseudo NOE signals using CEST-MRI and CEST-MRS sequences with and without lipid suppression.

Lu Jianhua J Zhou Jinyuan J Cai Congbo C Cai Shuhui S Chen Zhong Z

Magnetic resonance in medicine 20140506 4

<h4>Purpose</h4>To investigate the characteristics of nuclear Overhauser enhancement (NOE) imaging signals in the brain at 7T.<h4>Methods</h4>Fresh hen eggs, as well as six healthy, and six C6 glioma-bearing Wistar rats were scanned using chemical exchange saturation transfer-magnetic resonance imaging (CEST-MRI) and chemical exchange saturation transfer-magnetic resonance spectroscopy (CEST-MRS) sequences (saturation duration 3 s, power 1.47 µT) with and without lipid suppression. CEST data wer ...[more]

PMID: 24803172

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Project description:PurposeThe sensitivity and accuracy of chemical exchange saturation transfer (CEST) and nuclear Overhauser enhancement (NOE) effects for assessing injury-associated changes in cervical spinal cords were evaluated in squirrel monkeys. Multiple interacting pools of protons, including one identified by an NOE at -1.6 ppm relative to water (NOE(-1.6)), were derived and quantified from fitting proton Z-spectra. The effects of down-sampled data acquisitions and corrections for non-specific factors including T1, semi-solid magnetization transfer, and direct saturation of free water (DS), were investigated. The overall goal is to develop a protocol for rapid data acquisition for assessing the molecular signatures of the injured spinal cord and its surrounding regions.MethodsMRI scans were recorded of anesthetized squirrel monkeys at 9.4 T, before and after a unilateral dorsal column sectioning of the cervical spinal cord. Z-spectral images at 51 different RF offsets were acquired. The amplitudes of CEST and NOE effects from multiple proton pools were quantified using a six-pool Lorenzian fitting of each Z-spectrum (MTRmfit). In addition, down-sampled data using reduced selections of RF offsets were analyzed and compared. An apparent exchange-dependent relaxation (AREXmfit) method was also used to correct for non-specific factors in quantifying regional spectra around lesion sites.ResultsThe parametric maps from multi-pool fitting using the complete sampling data (P51e) detected unilateral changes at and around the injury. The maps derived from selected twofold down-sampled data with appropriate interpolation (P26sI51) revealed quite similar spatial distributions of different pools as those obtained using P51e at each resonance shift. Across 10 subjects, both data acquisition schemes detected significant decreases in NOE(-3.5) and NOE(-1.6) and increases in DS(0.0) and CEST(3.5) at the lesion site relative to measures of the normal tissues before injury. AREXmfit of cysts and other abnormal tissues at and around the lesion site also exhibited significant changes, especially at 3.5, -1.6 and -3.5 ppm RF offsets.ConclusionThese results confirm that a reduced set of RF offsets and down sampling are adequate for CEST imaging of injured spinal cord and allow shorter imaging times and/or permit additional signal averaging. AREXmfit correction improved the accuracy of CEST and NOE measures. The results provide a rapid (~13 mins), sensitive, and accurate protocol for deriving multiple NOE and CEST effects simultaneously in spinal cord imaging at high field.

Project description:BackgroundVessel-wall enhancement (VWE) on black-blood MRI (BB MRI) has been proposed as an imaging marker for a higher risk of rupture and associated with wall inflammation. Whether VWE is causally linked to inflammation or rather induced by flow phenomena has been a subject of debate.PurposeTo study the effects of slow flow, spatial resolution, and motion-sensitized driven equilibrium (MSDE) preparation on signal intensities in BB MRI of patient-specific aneurysm flow models.Study typeProspective.Subjects/flow aneurysm model/virtual vesselsAneurysm flow models based on 3D rotational angiography datasets of three patients with intracranial aneurysms were 3D printed and perfused at two different flow rates, with and without Gd-containing contrast agent.Field strength/sequenceVariable refocusing flip angle 3D fast-spin echo sequence at 3 T with and without MSDE with three voxel sizes ((0.5 mm)3 , (0.7 mm)3 , and (0.9 mm)3 ); time-resolved with phase-contrast velocity-encoding 3D spoiled gradient echo sequence (4D flow MRI).AssessmentThree independent observers performed a qualitative visual assessment of flow patterns and signal enhancement. Quantitative analysis included voxel-wise evaluation of signal intensities and magnitude velocity distributions in the aneurysm.Statistical testsKruskal-Wallis test, potential regressions.ResultsA hyperintense signal in the lumen and adjacent to the aneurysm walls on BB MRI was colocalized with slow flow. Signal intensities increased by a factor of 2.56 ± 0.68 (P < 0.01) after administering Gd contrast. After Gd contrast administration, the signal was suppressed most in conjunction with high flows and with MSDE (2.41 ± 2.07 for slow flow without MSDE, and 0.87 ± 0.99 for high flow with MSDE). A clear result was not achieved by modifying the spatial resolution .Data conclusionsSlow-flow phenomena contribute substantially to aneurysm enhancement and vary with MRI parameters. This should be considered in the clinical setting when assessing VWE in patients with an unruptured aneurysm.Evidence level2 TECHNICAL EFFICACY: Stage 2.

Dataset Information

Observation of true and pseudo NOE signals using CEST-MRI and CEST-MRS sequences with and without lipid suppression.

Publications

Observation of true and pseudo NOE signals using CEST-MRI and CEST-MRS sequences with and without lipid suppression.

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