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Comparing different analysis methods for quantifying the MRI amide proton transfer (APT) effect in hyperacute stroke patients.

ABSTRACT: Amide proton transfer (APT) imaging is a pH mapping method based on the chemical exchange saturation transfer phenomenon that has potential for penumbra identification following stroke. The majority of the literature thus far has focused on generating pH-weighted contrast using magnetization transfer ratio asymmetry analysis instead of quantitative pH mapping. In this study, the widely used asymmetry analysis and a model-based analysis were both assessed on APT data collected from healthy subjects (n = 2) and hyperacute stroke patients (n = 6, median imaging time after onset = 2 hours 59 minutes). It was found that the model-based approach was able to quantify the APT effect with the lowest variation in grey and white matter (? 13.8 %) and the smallest average contrast between these two tissue types (3.48 %) in the healthy volunteers. The model-based approach also performed quantitatively better than the other measures in the hyperacute stroke patient APT data, where the quantified APT effect in the infarct core was consistently lower than in the contralateral normal appearing tissue for all the patients recruited, with the group average of the quantified APT effect being 1.5 ± 0.3 % (infarct core) and 1.9 ± 0.4 % (contralateral). Based on the fitted parameters from the model-based analysis and a previously published pH and amide proton exchange rate relationship, quantitative pH maps for hyperacute stroke patients were generated, for the first time, using APT imaging.

SUBMITTER: Tee YK

PROVIDER: S-EPMC4737232 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature

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Comparing different analysis methods for quantifying the MRI amide proton transfer (APT) effect in hyperacute stroke patients.

Tee Y K YK Harston G W J GW Blockley N N Okell Thomas W TW Levman J J Sheerin F F Cellerini M M Jezzard P P Kennedy J J Payne S J SJ Chappell M A MA

NMR in biomedicine 20140610 9

Amide proton transfer (APT) imaging is a pH mapping method based on the chemical exchange saturation transfer phenomenon that has potential for penumbra identification following stroke. The majority of the literature thus far has focused on generating pH-weighted contrast using magnetization transfer ratio asymmetry analysis instead of quantitative pH mapping. In this study, the widely used asymmetry analysis and a model-based analysis were both assessed on APT data collected from healthy subjec ...[more]

PMID: 24913989

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Project description:Amide proton transfer (APT) imaging is a variation of chemical exchange saturation transfer MRI that has shown promise in diagnosing tumors, ischemic stroke, multiple sclerosis, traumatic brain injury, etc. Specific quantification of the APT effect is crucial for the interpretation of APT contrast in pathologies. Conventionally, magnetization transfer ratio with asymmetric analysis (MTRasym ) has been used to quantify the APT effect. However, some studies indicate that MTRasym is contaminated by water longitudinal relaxation time (T1w ), and thus it is necessary to normalize T1w in MTRasym to obtain specific quantification of the APT effect. So far, whether to use MTRasym or the T1w -normalized MTRasym is still under debate in the field. In this paper, the influence of T1w on the quantification of APT was evaluated through theoretical analysis, numerical simulations, and phantom studies for different experimental conditions. Results indicate that there are two types of T1w effect (T1w recovery and T1w -related saturation), which have inverse influences on the steady-state MTRasym . In situations with no or weak direct water saturation (DS) effect, there is only the T1w recovery effect, and MTRasym linearly depends on T1w . In contrast, in situations with significant DS effects, the dependence of MTRasym on T1w is complex, and is dictated by the competition of these two T1w effects. Therefore, by choosing appropriate irradiation powers, MTRasym could be roughly insensitive to T1w . Moreover, in non-steady-state acquisitions with very short irradiation time, MTRasym is also roughly insensitive to T1w . Therefore, for steady-state APT imaging at high fields or with very low irradiation powers, where there are no significant DS effects, it is necessary to normalize T1w to improve the specificity of MTRasym . However, in clinical MRI systems (usually low fields or non-steady-state acquisitions), T1w normalization may not be necessary when appropriate sequence parameters are chosen.

Project description:BackgroundThe three-dimensional chemical exchange saturation transfer (3D CEST) technique is a novel and promising magnetic resonance sequence; however, its application in nasopharyngeal carcinoma (NPC) lacks sufficient evaluation. This study aimed to assess the feasibility of the 3D CEST technique in predicting the short-term treatment outcomes for chemoradiotherapy (CRT) in NPC patients.MethodsForty NPC patients and fourteen healthy volunteers were enrolled and underwent the pre-treatment 3D CEST magnetic resonance imaging and diffusion-weighted imaging (DWI). The reliability of 3D CEST was assessed in healthy volunteers by calculating the intra- and inter-observer correlation coefficient (ICC) for amide proton transfer weighted-signal intensity (APTw-SI) and magnetization transfer ratio (MTR) values. NPC patients were divided into residual and non-residual groups based on short-term treatment outcomes after CRT. Whole-tumor regions of interest (ROIs) were manually drawn to measure APTw-SI, MTR and apparent diffusion coefficient (ADC) values. Multivariate analysis and the receiver operating characteristic curve (ROC) were used to evaluate the prediction performance of clinical characteristics, APTw-SI, MTR, ADC values, and combined models in predicting short-term treatment outcomes in NPC patients.ResultsFor the healthy volunteer group, all APTw-SI and MTR values exhibited good to excellent intra- and inter-observer agreements (0.736-0.910, 0.895-0.981, all P > 0.05). For NPC patients, MTR values showed a significant difference between the non-residual and residual groups (31.24 ± 5.21% vs. 34.74 ± 1.54%, P = 0.003) while no significant differences were observed for APTw-SI and ADC values (P > 0.05). Moreover, the diagnostic power of MTR value was superior to APTw-SI (AUC: 0.818 vs. 0.521, P = 0.017) and comparable to ADC values (AUC: 0.818 vs. 0.649, P > 0.05) in predicting short-term treatment outcomes for NPC patients. The prediction performance did not improve even when combining MTR values with APTw-SI and/or ADC values (P > 0.05).ConclusionsThe pre-treatment MTR value acquired through 3D CEST demonstrated superior predictive performance for short-term treatment outcomes compared to APTw-SI and ADC values in NPC patients after CRT.

Dataset Information

Comparing different analysis methods for quantifying the MRI amide proton transfer (APT) effect in hyperacute stroke patients.

Publications

Comparing different analysis methods for quantifying the MRI amide proton transfer (APT) effect in hyperacute stroke patients.

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