Chemical exchange saturation transfer effect in blood

Relationship between multi-pool model-based chemical exchange saturation transfer imaging, intravoxel incoherent motion MRI, and 11C-methionine uptake on PET/CT in patients with gliomas

PURPOSE

Magnetization transfer ratio asymmetry (MTRasym) analysis is used for chemical exchange saturation transfer (CEST) in patients with gliomas; however, this approach has limitations. CEST imaging using a multi-pool model (MPM) may allow a more detailed assessment of gliomas; however, its mechanism remains unknown. This study aimed to assess the relationship between CEST imaging by MPM, intravoxel incoherent motion (IVIM), and 11C-methionine (11C-MET) uptake on positron emission tomography/computed tomography (PET/CT) to clarify the clinical significance of CEST imaging using MPM in gliomas.

METHODS

This retrospective study included 17 patients with gliomas who underwent 11C-MET PET/CT at our institution between January 2020 and January 2022. Two-dimensional axial CEST imaging was conducted using single-shot fast-spin echo acquisition at 3 T. The apparent diffusion coefficient (ADC), true diffusion coefficient (D), pseudo-diffusion coefficient (D*), f, MTRasym (3.5 ppm), parameters of MPM-based CEST imaging, and tumor-to-contralateral normal brain tissue (T/N) ratio were calculated using a region-of-interest analysis. Shapiro-Wilk test, weighted kappa coefficient, and Spearman's rank correlation coefficients were used for statistical analysis.

RESULTS

Significant correlations were found between APT_T1 and T/N ratio (ρ = 0.87, p < 0.001), APT_T2 and T/N ratio (ρ = 0.47, p < 0.05), MTRasym and T/N ratio (ρ = 0.55, p < 0.01), and T2/T1 and T/N ratio (ρ = -0.36, p < 0.05). Furthermore, significant correlations were observed between APT_T1 and ADC (ρ = -0.67, p < 0.001), APT_T1 and D (ρ = -0.70, p < 0.001), APT_T2 and D* (ρ = -0.45, p < 0.05), and T2/T1 and D (ρ = 0.39, p < 0.05).

CONCLUSION

These preliminary findings indicate that MPM-based CEST imaging parameters correlate with IVIM and 11C-MET uptake on PET/CT in patients with gliomas. In particular, the new parameter APT_T1 correlated more strongly with 11C-MET uptake compared to the traditional CEST parameter MTRasym.

Amide Proton Transfer-Weighted Imaging in Assessing the Aggressive and Proliferative Potential of Bladder Cancer

BACKGROUND

Ki-67 and human epidermal growth factor receptor 2 (HER2) are known oncogenes involved in bladder cancer (BCa) patient risk stratification. Preoperative assessment of their expression level can assist in clinical treatment decision-making. Recently, amide proton transfer-weighted (APTw) MRI has shown promising potential in the diagnosis of several malignancies. However, few studies reported the value of APTw imaging in evaluating Ki-67 and HER2 status of BCa.

PURPOSE

To investigate the feasibility of APTw MRI in assessing the aggressive and proliferative potential regarding the expression levels of Ki-67 and HER2 in BCa.

STUDY TYPE

Retrospective.

SUBJECTS

114 patients (mean age, 64.78 ± 11.93 [SD] years; 97 men) were studied.

FIELD STRENGTH/SEQUENCE

APTw MRI acquired by a three-dimensional fast-spin-echo sequence at 3.0 T MRI system.

ASSESSMENT

Patient pathologic findings, included histologic grade and the expression status of Ki-67 and HER2, were reviewed by one uropathologist. The APTw values of BCa were independently measured by two radiologists and were compared between high-/low-tumor grade group, high-/low-Ki-67 expression group, and high-/low-HER2 expression group.

STATISTICAL TESTS

The interclass correlation coefficient, independent sample t-test, Mann-Whitney U test, Spearman's rank correlation, and receiver operating characteristic curve (ROC) analysis were used. P < 0.05 was considered statistically significant.

RESULTS

Significantly higher APTw values were found in high-grade BCa patients (7.72% vs. 4.29%, P < 0.001), high-Ki-67 expression BCa patients (8.40% vs. 3.25%, P < 0.001) and HER2 positive BCa patients (8.24% vs. 5.40%, P = 0.001). APTw values were positively correlated with Ki-67 (r = 0.769) and HER2 (r = 0. 356) expression status. The area under the ROC curve of the APTw values for detecting Ki-67 and HER2 expression status were 0.883 (95% CI: 0.790-0.945) and 0.713 (95% CI: 0.592-0.816), respectively.

DATA CONCLUSIONS

APTw MRI is a potential method to assess the biological and proliferation potential of BCa.

LEVEL OF EVIDENCE: 4

TECHNICAL EFFICACY

Stage 2.

Amide proton transfer-weighted MRI in predicting pathological types of brain metastases in lung Cancer

Most brain metastases originate from lung cancer. The majority of cases of lung cancer can be categorized into squamous carcinoma and adenocarcinoma,necessitating distinct clinical treatments and yielding diverse prognoses.Therefore,accurate preoperative evaluation of pathological types through imaging techniques is essential. The objective of this study is to assess the capability of amide proton transfer-weighted(APTw) MRI in predicting the pathological types of brain metastases in lung cancer.Additionally,it seeks to evaluate whether APTw MRI can provide additional value to diffusion-weighted imaging(DWI) at MRI·In this study,a total of 32 participants(mean age,60 ± 9 years;14 men) underwent evaluation,comprising 9 with squamous carcinoma and 23 with adenocarcinoma.Interestingly,adenocarcinoma demonstrated elevated APTw values(2.70 ± 0.81% vs 1.82 ± 0.47%;P = 0.001) and a higher apparent diffusion coefficient(ADC) value(1.00 ± 0.40 × 10-3 mm2/s vs 0.77 ± 0.13 × 10-3 mm2/s;P<0.05) in comparison to squamous carcinoma. The area under the receiver operating characteristic curve(AUC) of APTw and ADC in distinguishing between squamous carcinoma and adenocarcinoma were found to be 0.84 and 0.63,respectively.Moreover,the combined area under the receiver operating characteristic curve of the two techniques is 0.84. Amide proton transfer-weighted has the potential to predict the pathological types of brain metastases in lung cancer.

Post-Surgical Depositions of Blood Products Are No Major Confounder for the Diagnostic and Prognostic Performance of CEST MRI in Patients with Glioma

Amide proton transfer (APT) and semi-solid magnetization transfer (ssMT) imaging can predict clinical outcomes in patients with glioma. However, the treatment of brain tumors is accompanied by the deposition of blood products within the tumor area in most cases. For this reason, the objective was to assess whether the diagnostic interpretation of the APT and ssMT is affected by methemoglobin (mHb) and hemosiderin (Hs) depositions at the first follow-up MRI 4 to 6 weeks after the completion of radiotherapy. A total of 34 participants underwent APT and ssMT imaging by applying reconstruction methods described by Zhou et al. (APTwasym), Goerke et al. (MTRRexAPT and MTRRexMT) and Mehrabian et al. (MTconst). Contrast-enhancing tumor (CE), whole tumor (WT), mHb and Hs were segmented on contrast-enhanced T1wCE, T2w-FLAIR, T1w and T2*w images. ROC-analysis, Kaplan-Meier analysis and the log rank test were used to test for the association of mean contrast values with therapy response and overall survival (OS) before (WT and CE) and after correcting tumor volumes for mHb and Hs (CEC and WTC). CEC showed higher associations of the MTRRexMT with therapy response (CE: AUC = 0.677, p = 0.081; CEC: AUC = 0.705, p = 0.044) and of the APTwasym with OS (CE: HR = 2.634, p = 0.040; CEC: HR = 2.240, p = 0.095). In contrast, WTC showed a lower association of the APTwasym with survival (WT: HR = 2.304, p = 0.0849; WTC: HR = 2.990, p = 0.020). Overall, a sophisticated correction for blood products did not substantially influence the clinical performance of APT and ssMT imaging in patients with glioma early after radiotherapy.

Amide proton transfer imaging in stroke

Amide proton transfer (APT) imaging, a variant of chemical exchange saturation transfer MRI, has shown promise in detecting ischemic tissue acidosis following impaired aerobic metabolism in animal models and in human stroke patients due to the sensitivity of the amide proton exchange rate to changes in pH within the physiological range. Recent studies have demonstrated the possibility of using APT-MRI to detect acidosis of the ischemic penumbra, enabling the assessment of stroke severity and risk of progression, monitoring of treatment progress, and prognostication of clinical outcome. This paper reviews current APT imaging methods actively used in ischemic stroke research and explores the clinical aspects of ischemic stroke and future applications for these methods.

Conventional and Advanced Magnetic Resonance Imaging Assessment of Non-Enhancing Peritumoral Area in Brain Tumor

The non-enhancing peritumoral area (NEPA) is defined as the hyperintense region in T2-weighted and fluid-attenuated inversion recovery (FLAIR) images surrounding a brain tumor. The NEPA corresponds to different pathological processes, including vasogenic edema and infiltrative edema. The analysis of the NEPA with conventional and advanced magnetic resonance imaging (MRI) was proposed in the differential diagnosis of solid brain tumors, showing higher accuracy than MRI evaluation of the enhancing part of the tumor. In particular, MRI assessment of the NEPA was demonstrated to be a promising tool for distinguishing high-grade gliomas from primary lymphoma and brain metastases. Additionally, the MRI characteristics of the NEPA were found to correlate with prognosis and treatment response. The purpose of this narrative review was to describe MRI features of the NEPA obtained with conventional and advanced MRI techniques to better understand their potential in identifying the different characteristics of high-grade gliomas, primary lymphoma and brain metastases and in predicting clinical outcome and response to surgery and chemo-irradiation. Diffusion and perfusion techniques, such as diffusion tensor imaging (DTI), diffusional kurtosis imaging (DKI), dynamic susceptibility contrast-enhanced (DSC) perfusion imaging, dynamic contrast-enhanced (DCE) perfusion imaging, arterial spin labeling (ASL), spectroscopy and amide proton transfer (APT), were the advanced MRI procedures we reviewed.

Identification of ovarian endometriotic cysts in cystic lesions of the ovary by amide proton transfer-weighted imaging and R2∗ mapping

AIM

To investigate the value of amide proton transfer weighted (APTw) imaging and R2∗ mapping of cystic fluid in differentiating ovarian endometriotic cysts (OE) from other ovarian cystic (OOC) lesions.

MATERIALS AND METHODS

A total of 42 patients who underwent 3 T pelvic magnetic resonance imaging (MRI) were enrolled. Nineteen lesions were OE and 27 lesions were OOC. The APTw imaging and R2∗ values of the cystic fluid were measured and compared between the two groups using the independent sample t-test or Mann-Whitney U-test. Receiver operating characteristic (ROC) curves were used to evaluate the diagnostic efficacy of different parameters. The area under ROC curves (AUCs) was compared using the Delong test. Spearman's correlation analysis was used to assess the correlation between APTw imaging and R2∗ values.

RESULTS

APTw imaging values of OE were lower, while R2∗ values were higher in OE than those in OOC (p=0.001 and < 0.001). The AUCs of APTw imaging and R2∗ values to identify OE from OOC were 0.910 and 0.975. The AUC increased to 0.990 when combining APTw imaging and R2∗ values, yet without a significant difference to the APTw imaging or R2∗ value alone (p=0.229 and 0.082, respectively). APTw imaging values were negatively correlated with R2∗ values (r=-0.522, p<0.001).

CONCLUSION

Both APTw imaging and R2∗ values of OE are significantly different from other ovarian cystic lesions. APTw imaging combined with R2∗ values show excellent diagnostic efficacy to differentiate between OE and OOC.

Whole-tumor amide proton transfer-weighted imaging histogram analysis to predict pathological extramural venous invasion in rectal adenocarcinoma: a preliminary study

OBJECTIVES

To evaluate amide proton transfer-weighted (APTw)-derived whole-tumor histogram analysis parameters in predicting pathological extramural venous invasion (pEMVI) positive status of rectal adenocarcinoma (RA).

METHODS

Preoperative MR including APTw imaging of 125 patients with RA (mean 61.4 ± 11.6 years) were retrospectively analyzed. Two radiologists reviewed each case's EMVI status based on the MR-based modified 5-point scale system with conventional MR images. The APTw histogram parameters of primary tumors were obtained automatically using whole-tumor volume histogram analysis. The independent risk factors markedly correlated with pEMVI-positive status were assessed using univariate and multivariate logistic regression analyses. Diagnosis performance was assessed by receiver operating characteristic curve (ROC) analysis. The AUCs were compared using the Delong method.

RESULTS

Univariate analysis demonstrated that MR-tumor (T) stage, MR-lymph node (N) stage, APTw-10%, APTw-90%, interquartile range, APTw-minimum, APTw-maximum, APTw-mean, APTw-median, entropy, kurtosis, mean absolute deviation (MAD), and robust MAD were significantly related to pEMVI-positive status (all p < 0.05). Multivariate analysis demonstrated that MR-T stage (OR = 4.864, p = 0.018), MR-N stage (OR = 4.967, p = 0.029), interquartile range (OR = 0.892, p = 0.037), APT-minimum (OR = 1.046, p = 0.031), entropy (OR = 11.604, p = 0.006), and kurtosis (OR = 1.505, p = 0.007) were the independent risk factors enabling prediction of pEMVI-positive status. The AUCs for diagnostic ability of conventional MRI assessment, the APTw histogram model, and the combined model (including APTw histogram and clinical variables) were 0.785, 0.853, and 0.918, respectively. The combined model outperformed the APTw histogram model (p = 0.013) and the conventional MRI assessment (p = 0.006).

CONCLUSIONS

Whole-tumor histogram analysis of APTw images combined with clinical factors showed better diagnosis efficiency in predicting EMVI involvement in RA.

KEY POINTS

• Rectal adenocarcinomas with pEMVI-positive status are typically associated with higher APTw-SI values. • APTw-minimum, interquartile range, entropy, kurtosis, MR-T stage, and MR-N stage are the independent risk factors for EMVI involvement. • The best prediction for EMVI involvement was obtained with a combined model of APTw histogram and clinical variables (area under the curve, 0.918).

Predicting treatment response to concurrent chemoradiotherapy in squamous cell carcinoma of the cervix using amide proton transfer imaging and intravoxel incoherent motion imaging

PURPOSE

The purpose of this study was to investigate whether amide proton transfer (APT) imaging and intravoxel incoherent motion (IVIM) imaging can predict tumor response to concurrent chemoradiotherapy (CCRT) in patients with squamous cell carcinoma of the cervix (SCCC).

MATERIAL AND METHODS

Fifty-nine women (mean age, 54 years ± 10 [standard deviation] years; age range: 32-81 years) with pathologically confirmed SCCC underwent magnetic resonance imaging examination of the pelvis including APT and IVIM before concurrent chemoradiotherapy. They were divided into complete remission (CR) and non-CR groups according to therapeutic effect. APT values and IVIM-derived parameters were measured. Intra- and interobserver agreement for IVIM and APT parameters was assessed using intraclass correlation coefficient (ICC) The independent samples t-test was performed to compare the evaluated parameters between the two groups. Predictive performance for treatment response was evaluated by receiver operator characteristic (ROC) curve analysis.

RESULTS

There were 38 and 21 patients in the non-CR and CR groups, respectively. Excellent interobserver and intraobserver agreement were obtained for all IVIM and APT parameters, with ICCs ranging from 0.844 to 0.962. Perfusion fraction (f) and APT values were lower in the CR group compared with the non-CR group (both P < 0.05). The combination of f and APT values showed good diagnostic performances in predicting response to concurrent chemoradiotherapy, with an area under the ROC curve of 0.852 (95% CI: 0.744-0.961), 79% sensitivity (95% CI: 63-90%), 90% specificity (95% CI: 70-99%) and 83% accuracy (95% CI: 71-92%).

CONCLUSION

APT and IVIM imaging may serve as noninvasive tools for predicting response to concurrent chemoradiotherapy in patients with SCCC.

Differentiation of hemangioblastoma from brain metastasis using MR amide proton transfer imaging

BACKGROUND AND PURPOSE

Differentiation between hemangioblastoma and brain metastasis remains a challenge in neuroradiology using conventional MRI. Amide proton transfer (APT) imaging can provide unique molecular information. This study aimed to evaluate the usefulness of APT imaging in differentiating hemangioblastomas from brain metastases and compare APT imaging with diffusion-weighted imaging and dynamic susceptibility contrast perfusion-weighted imaging.

METHODS

This retrospective study included 11 patients with hemangioblastoma and 20 patients with brain metastases. Region-of-interest analyses were employed to obtain the mean, minimum, and maximum values of APT signal intensity, apparent diffusion coefficient (ADC), and relative cerebral blood volume (rCBV), and these indices were compared between hemangioblastomas and brain metastases using the unpaired t-test and Mann-Whitney U test. Their diagnostic performances were evaluated using receiver operating characteristic (ROC) analysis and area under the ROC curve (AUC). AUCs were compared using DeLong's method.

RESULTS

All MRI-derived indices were significantly higher in hemangioblastoma than in brain metastasis. ROC analysis revealed the best performance with APT-related indices (AUC = 1.000), although pairwise comparisons showed no significant difference between the mean ADC and mean rCBV.

CONCLUSIONS

APT imaging is a useful and robust imaging tool for differentiating hemangioblastoma from metastasis.

Evaluation of Amide Proton Transfer-Weighted Imaging for Risk Factors in Stage I Endometrial Cancer: A Comparison With Diffusion-Weighted Imaging and Diffusion Kurtosis Imaging

Background

Endometrial cancer (EC) is one of the most common gynecologic malignancies in clinical practice. This study aimed to compare the value of diffusion-weighted imaging (DWI), diffusion kurtosis imaging (DKI), and amide proton transfer-weighted imaging (APTWI) in the assessment of risk stratification factors for stage I EC including histological subtype, grade, stage, and lymphovascular space invasion (LVSI).

Methods

A total of 72 patients with stage I EC underwent pelvic MRI. The apparent diffusion coefficient (ADC), mean diffusivity (MD), mean kurtosis (MK), and magnetization transfer ratio asymmetry (MTRasym at 3.5 ppm) were calculated and compared in risk groups with the Mann–Whitney U test or independent samples t-test. Spearman’s rank correlation was applied to depict the correlation of each parameter with risk stratification. The diagnostic efficacy was evaluated with receiver operating characteristic (ROC) curve analysis and compared using the DeLong test. A multivariate logistic regression was conducted to explore the optimal model for risk prediction.

Results

There were significantly greater MTRasym (3.5 ppm) and MK and significantly lower ADC and MD in the non-adenocarcinoma, stage IB, LVSI-positive, high-grade, and non-low-risk groups (all p < 0.05). The MK and MTRasym (3.5 ppm) were moderately positively correlated with risk stratification as assessed by the European Society for Medical Oncology (EMSO) clinical practice guidelines (r = 0.640 and 0.502, respectively), while ADC and MD were mildly negatively correlated with risk stratification (r = −0.358 and −0.438, respectively). MTRasym (3.5 ppm), MD, and MK were identified as independent risk predictors in stage I EC, and optimal predictive performance was obtained with their combinations (AUC = 0.906, sensitivity = 70.97%, specificity = 92.68%). The results of the validation model were consistent with the above results, and the calibration curve showed good accuracy and consistency.

Conclusions

Although similar performance was obtained with each individual parameter of APTWI, DWI, and DKI for the noninvasive assessment of aggressive behavior in stage I EC, the combination of MD, MK, and MTRasym (3.5 ppm) provided improved predictive power for non-low-risk stage I EC and may serve as a superior imaging marker.

Identification of histological features of endometrioid adenocarcinoma based on amide proton transfer-weighted imaging and multimodel diffusion-weighted imaging

BACKGROUND

Noninvasive identification of the histological features of endometrioid adenocarcinoma is necessary. This study aimed to investigate whether amide proton transfer-weighted imaging (APTWI) and multimodel (monoexponential, biexponential, and stretched exponential) diffusion-weighted imaging (DWI) could predict the histological grade of endometrial adenocarcinoma (EA). In addition, we analyzed the correlation between each parameter and the Ki-67 index.

METHODS

A total of 90 EA patients who received pelvic magnetic resonance imaging (MRI) were enrolled. The magnetization transfer ratio asymmetry [MTRasym (3.5 ppm)], apparent diffusion coefficient (ADC), diffusion coefficient (D), pseudo-diffusion coefficient (D*), perfusion fraction (f), distributed diffusion coefficient (DDC), and water molecular diffusion heterogeneity index (α) were measured and compared. Correlation coefficients between each parameter and histological grade and the Ki-67 index were calculated. Statistical methods included the independent samples t test, Spearman's correlation, and logistic regression.

RESULTS

MTRasym (3.5 ppm) [(3.72%±0.31%) vs. (3.27%±0.48%)], f [(3.15%±0.36%) vs. (2.69%±0.83%)], and α [(0.89±0.05) vs. (0.81±0.09)] were higher and ADC [(0.82±0.08) vs. (0.89±0.10) ×10^-3 mm²/s], D [(0.67±0.09) vs. (0.81±0.11) ×10^-3 mm²/s], and DDC [(1.04±0.09) vs. (1.13±0.13) ×10^-3 mm²/s] were lower in high-grade EA than in low-grade EA (P<0.05). MTRasym (3.5 ppm) and D were independent predictors for the histological grade of EA. The combination of MTRasym (3.5 ppm) and D were better able to identify high- and low-grade EA than was each parameter. MTRasym (3.5 ppm) and α were moderately and weakly positively correlated, respectively, with histological grade and the Ki-67 index (r=0.528, r=0.514, r=0.395, and r=0.367; P<0.05). D was moderately negatively correlated with histological grade and the Ki-67 index (r=-0.540 and r=-0.529; P<0.05). DDC was weakly and moderately negatively correlated with histological grade and the Ki-67 index, respectively (r=-0.473 and r=-0.515; P<0.05). ADC was weakly negatively correlated with histological grade and the Ki-67 index (r=-0.417 and r=-0.427; P<0.05). f was weakly positively correlated with histological grade and the Ki-67 index (r=0.294 and r=0.355; P<0.05).

CONCLUSIONS

Our study found that both multimodel DWI and APTWI could be used to estimate the histological grade and Ki-67 index of EA, and the combination of high MTRasym (3.5 ppm) and low D may be an effective imaging marker for predicting the grade of EA.

Correlation between amide proton transfer-related signal intensity and diffusion and perfusion magnetic resonance imaging parameters in high-grade glioma

Amide proton transfer (APT) imaging is a magnetic resonance (MR) molecular imaging technique that is sensitive to mobile proteins and peptides in living tissue. Studies have shown that APT-related signal intensity (APTSI) parallels with the malignancy grade of gliomas, allowing the preoperative assessment of tumor grades. An increased APTSI in malignant gliomas has been attributed to cytosolic proteins and peptides in proliferating tumor cells; however, the exact underlying mechanism is poorly understood. To get an insight into the mechanism of high APTSI in malignant gliomas, we investigated the correlations between APTSI and several MR imaging parameters including apparent diffusion coefficient (ADC), relative cerebral blood volume and pharmacokinetic parameters obtained in the same regions-of-interest in 22 high-grade gliomas. We found a significant positive correlation between APTSI and ADC (ρ = 0.625 and 0.490 for observers 1 and 2, respectively; p < 0.001 for both), which is known to be inversely correlated with cell density. Multiple regression analysis revealed that ADC was significantly associated with APTSI (p < 0.001 for both observers). Our results suggest possible roles of extracellular proteins and peptides in high APTSI in malignant gliomas.

Amide Proton Transfer-Weighted Imaging and Multiple Models Diffusion-Weighted Imaging Facilitates Preoperative Risk Stratification of Early-Stage Endometrial Carcinoma

BACKGROUND

Endometrial carcinoma (EC) risk stratification is generally based on histological assessment. It would be beneficial to perform risk stratification noninvasively by MRI.

PURPOSE

To investigate the application of amide proton transfer-weighted imaging (APTWI), monoexponential, biexponential, and stretched exponential intravoxel incoherent motion (IVIM), and diffusion kurtosis imaging (DKI) for the evaluation of risk stratification in early-stage EC.

STUDY TYPE

Prospective.

POPULATION

Eighty patients with early-stage EC (47 classified as low risk, 20 as medium risk, and 13 as high risk by histological grade and International Federation of Gynecology and Obstetrics stage).

FIELD STRENGTH/SEQUENCE

T1-weighted imaging, T2-weighted imaging, IVIM, APTWI, and DKI MRI at 3 T.

ASSESSMENT

The magnetization transfer ratio asymmetry (MTRasym [3.5 ppm]), apparent diffusion coefficient (ADC), diffusion coefficient (D), pseudo diffusion coefficient (D*), perfusion fraction (f), distributed diffusion coefficient (DDC), water molecular diffusion heterogeneity index (α), mean kurtosis (MK), and mean diffusivity (MD) were calculated and compared between low-risk and non-low-risk groups.

STATISTICAL TESTS

Individual sample t test, analysis of variance, and logistic regression. A P-value <0.05 was considered statistically significant.

RESULTS

The α, ADC, D, DDC, and MD were significantly higher and the f, MK, and MTRasym (3.5 ppm) were significantly lower in the low-risk group than in the non-low-risk group. The difference in D* between the two groups was not significant (P = 0.289). MTRasym (3.5 ppm), D, and MK were independent predictors of risk stratification. The combination of these three parameters was better able to identify low- and non-low-risk groups than each individual parameter.

DATA CONCLUSION

The IVIM, DKI, and APTWI parameters have potential as imaging markers for risk stratification in early-stage EC.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 3.

Evaluation of amide proton transfer-weighted imaging for endometrial carcinoma histological features: a comparative study with diffusion kurtosis imaging

OBJECTIVES

To investigate whether amide proton transfer-weighted imaging (APTWI) and diffusion kurtosis imaging (DKI) can be used to evaluate endometrial carcinoma (EC) in terms of clinical type, histological grade, subtype, and Ki-67 index.

METHODS

Eighty-eight patients with EC underwent pelvic DKI and APTWI. The non-Gaussian diffusion coefficient (D_app), apparent kurtosis coefficient (K_app), and magnetization transfer ratio asymmetry (MTRasym (3.5 ppm)) were calculated and compared based on the clinical type (type I, II), histological grade (high- and low-grade), and subtype (endometrioid adenocarcinoma (EA) and non-EA). Correlation coefficients were calculated for each parameter with histological grades and the Ki-67 index.

RESULTS

The MTRasym (3.5 ppm) and K_app values were higher in the type II group and high-grade group than in the type I and low-grade groups, respectively, while the D_app values were lower in the type I and low-grade groups, respectively (all p < 0.05). The K_app value was higher in the EA group than in the non-EA group (p = 0.022). The K_app value was the only independent predictor for the histological grade of EA and the clinical type of EC. The AUC (DKI) was higher than the AUC (APTWI) in the identification of type I and II EC and high- and low-grade EA (Z = 2.042, 2.013, p = 0.041, 0.044), while in the identification of EA and non-EA, only the difference in K_app was statistically significant. Moreover, the K_app and MTRasym (3.5 ppm) values and D_app values correlated positively and negatively, respectively, with histological grade (r = 0.759, 0.555, 0.624, and 0.462, all p < 0.05) and Ki-67 index (r = -0.704, -0.507, all p < 0.05).

CONCLUSION

Both DKI- and APTWI-related parameters have potential as imaging markers in estimating the histological features of EC, while DKI shows better performance than APTWI in this study.

KEY POINTS

• DKI and APTWI can be used to preliminarily evaluate the histological characteristics of endometrial carcinoma (EC). • The K_app was the only independent predictor for the histological grade of EA and the clinical type of EC. • The K_app, MTRasym (3.5 ppm), and D_app correlated positively and negatively, respectively, with histological grade and Ki-67 index.

Three-dimension amide proton transfer MRI of rectal adenocarcinoma: correlation with pathologic prognostic factors and comparison with diffusion kurtosis imaging

OBJECTIVES

To investigate the utility of 3D amide proton transfer (APT) MRI in predicting pathologic factors for rectal adenocarcinoma, in comparison with diffusion kurtosis imaging.

METHODS

Sixty-one patients with rectal adenocarcinoma were enrolled in this prospective study. 3D APT and diffusion kurtosis imaging (DKI) were performed. Mean APT-weighted signal intensity (APTw SI), mean kurtosis (MK), mean diffusivity (MD), and ADC values of tumors were calculated on these maps. Pathological analysis included WHO grades, pT stages, pN stages, and extramural venous invasion (EMVI) status. Student's t test, Spearman correlation, and receiver operating characteristics (ROC) analysis were used for statistical analysis.

RESULTS

High-grade rectal adenocarcinoma showed significantly higher mean APTw SI and MK values (2.771 ± 0.384 vs 2.108 ± 0.409, 1.167 ± 0.216 vs 1.045 ± 0.175, respectively; p < 0.05). T3 rectal adenocarcinoma demonstrated higher mean APTw SI and MK than T2 tumors (2.433 ± 0.467 vs 1.900 ± 0.302, p < 0.05). No kurtosis, diffusivity, and ADC differences were found between T2 and T3 tumors. Tumors with lymph node metastasis and EMVI involvement showed significantly higher mean APTw SI, MK. No difference was found in diffusivity and ADC between pN0 and pN1-2 groups, and EMVI-negative and EMVI-positive statuses. Mean APTw SI exhibited a significantly high positive correlation with WHO grades, demonstrating 92.31% sensitivity and 79.17% specificity for distinguishing low- from high-grade rectal adenocarcinoma, providing a better diagnostic capacity than MK, MD, and mean ADC values.

CONCLUSION

3D-APT could serve as a non-invasive biomarker for evaluating prognostic factors of rectal adenocarcinoma.

KEY POINTS

• Mean APTw SI was significantly higher in high-grade compared to low-grade rectal adenocarcinoma. • Mean APTw SI was significantly higher in T3 stage rectal adenocarcinoma, with lymph node metastasis, or in EMVI-positive status. • APTw SI exhibited greater diagnostic capability in discriminating low-grade from high-grade rectal adenocarcinoma, compared with kurtosis, diffusivity, and ADC.

Glymphatic System Visualized by Chemical-Exchange-Saturation-Transfer Magnetic Resonance Imaging

Dysfunction of the glymphatic system may play a significant role in the development of neurodegenerative diseases. However, in vivo imaging of the glymphatic system is challenging. In this study, we describe an unconventional MRI method for imaging the glymphatic system based on chemical exchange saturation transfer, which we tested in an in vivo porcine model of impaired glymphatic function. The blood, lymph, and cerebrospinal fluid (CSF) from one pig were used for testing the MRI effect in vitro at 7 Tesla (T). Unilateral deep cervical lymph node ligation models were then performed in 20 adult male Sprague-Dawley rats. The brains were scanned in vivo dynamically after surgery using the new MRI method. Behavioral tests were performed after each scanning session and the results were tested for correlations with the MRI signal intensity. Finally, the pathological assessment was conducted in the same brain slices. The special MRI effect in the lymph was evident at about 1.0 ppm in water and was distinguishable from those of blood and CSF. In the model group, the intensity of this MRI signal was significantly higher in the ipsilateral than in the contralateral hippocampus. The correlation between the signal abnormality and the behavioral score was significant (Pearson's, R² = 0.9154, p < 0.005). We conclude that the novel MRI method can visualize the glymphatic system in vivo.

Comparative Analysis of Amide Proton Transfer MRI and Diffusion-Weighted Imaging in Assessing p53 and Ki-67 Expression of Rectal Adenocarcinoma

BACKGROUND

The evaluation of prognostic factors in rectal carcinoma patients has important clinical significance. P53 status and the Ki-67 index have served as prognostic factors in rectal carcinoma. Amide proton transfer (APT) imaging has shown great potential in tumor diagnosis. However, few studies reported the value of APT imaging in evaluating p53 and Ki-67 status of rectal carcinoma.

PURPOSE

To investigate the feasibility of amide proton transfer MRI in assessing p53 and Ki-67 expression of rectal adenocarcinoma, and compare it with conventional diffusion-weighted imaging (DWI).

STUDY TYPE

Retrospective.

POPULATION

Forty-three patients with rectal adenocarcinoma (age: 34-85 years).

FIELD STRENGTH/SEQUENCE

3T/APT imaging using a 3D turbo spin echo (TSE)-Dixon pulse sequence with chemical shift-selective fat suppression, 2D DWI, and 2D T₂ -weighted TSE.

ASSESSMENT

Mean tumor APT signal intensity (SI_mean ) and apparent diffusion coefficient (ADC_mean ) were measured. Traditional tumor pathological analysis included WHO grades, pT (pathologic tumor) stages, and pN (pathologic node) stages. Expression levels of p53 and Ki-67 were determined by immunohistochemical assay.

STATISTICAL TESTS

One-way analysis of variance (ANOVA); Student's t-test; Spearman's correlation coefficient; receiver operating characteristic (ROC) curve analysis.

RESULTS

High-grade tumors, more advanced stage tumors, and tumors with lymph node involvement had higher APT SI_mean values: high grade (n = 15) vs. low-grade (n = 28), P < 0.001; pT2 (n = 10) vs. pT3 (n = 20) vs. pT4 (N = 13), P = 0.021; pN0 (n = 24) vs. pN1-2 (n = 19), P = 0.019. ADC_mean differences were found in tumors with different pT stage: pT2 (n = 10) vs. pT3 (n = 20) vs. pT4 (N = 13), P = 0.013, but not in tumors with different histologic grade: high grade (n = 15) vs. low-grade (n = 28), P = 0.3536; or pN stage: pN0 (n = 24) vs. pN1-2 (n = 19), P = 0.624. Tumor with p53 positive status had higher APT SI_mean than tumor with negative p53 status (2.363 ± 0.457 vs. 2.0150 ± 0.3552, P = 0.014). There was no difference in ADC_mean with p53 status (1.058 ± 0.1163 10^-3  mm² /s vs. 1.055 ± 0.128 10^-3  mm² /s, P = 0.935). APT SI_mean and ADC_mean were significantly different in tumors with low and high Ki-67 status (1.7882 ± 0.11386 vs. 2.3975 ± 0.41586, P < 0.001; 1.1741 ± 0.093 10^-3  mm² /s vs. 1.0157 ± 0.10459 10^-3  mm² /s, P < 0.001, respectively). APT SI_mean exhibited a positive correlation with p53 labeling index and Ki-67 labeling index (r = 0.3741, P = 0.0135; r = 0.7048; P < 0.001, respectively). ADC_mean showed no correlation with p53 labeling index, but a negative correlation with Ki-67 labeling index (r = -0.5543, P < 0.0001). ROC curves demonstrated that APT SI_mean had significantly higher diagnostic ability for differentiation of high Ki-67 expression of rectal adenocarcinoma than ADC_mean (81.2% vs. 78.12%, 90.91% vs. 63.64; P < 0.001 vs. P = 0.017), while no difference was found in predicting p53 status (92.86% vs. 71.4%, 53.33% vs. 66.7%; P < 0.001 vs. P = 0.0471).

DATA CONCLUSION

APT SI_mean was related to p53 and Ki-67 expression levels in rectal adenocarcinoma. APT imaging may serve as a noninvasive biomarker for assessing genetic prognostic factors of rectal adenocarcinoma.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY STAGE: 2.

Amide proton transfer imaging for differentiating benign ovarian cystic lesions: Potential of first time right

PURPOSE

To investigate whether amide proton transfer (APT) imaging is useful to differentiate benign ovarian cystic lesions.

MATERIALS AND METHODS

This prospective study enrolled a total of 19 lesions in 18 patients with benign ovarian cystic lesion: serous cystadenoma (SCA), n = 4; mucinous cystadenoma (MCA), n = 9; or functional cyst (FC), n = 6. APT imaging was performed with three different presaturation pulse durations: 0.5, 1.0 and 2.0 s. APT signal was defined as magnetization transfer ratio asymmetry at 3.5 ppm. The SI ratios of cyst to muscle calculated on T1- and T2-weighted images were defined as T1- and T2-ratios. Apparent diffusion coefficient (ADC) maps were also generated. We compared the three cystic lesion groups' APT signals, T1-ratio, T2-ratio, and ADC.

RESULTS

When using 2.0 s of presaturation, the APT signals were 1.41 ± 0.71% in SCA, 5.15 ± 1.92% in MCA and 8.52 ± 1.17% in FC. Significant differences were observed between SCA and MCA (p < .01) and MCA and FC (p < .05), as well as between SCA and FC (P <  .0001). When 1.0 s presaturation pulse was used, similar results were obtained. On the other hand, ADC value shows significance only between SCA (2.91±0.03×10-3 mm2/s) and MCA (2.59 ± 0.49 × 10-3 mm2/s, p < .05). Further, there was no significant difference in the T1-ratio, T2-ratio among the three groups.

CONCLUSIONS

APT imaging might be useful for the non-invasive diagnosis of benign ovarian cystic lesions. With the use of the longer presaturation pulse as possible, APT imaging may provide an early and correct diagnosis of ovarian cystic lesions without additional follow-up studies.

Amide proton transfer imaging of glioblastoma, neuroblastoma, and breast cancer cells on a 11.7 T magnetic resonance imaging system

PURPOSE

The purpose of this study was (i) to determine the optimal magnetization transfer (MT) pulse parameter for amide proton transfer (APT) chemical exchange saturation transfer (CEST) imaging on an ultra-high-field magnetic resonance imaging (MRI) system and (ii) to use APT CEST imaging to noninvasively assess brain orthotopic and ectopic tumor cells transplanted into the mouse brain.

METHODS

To evaluate APT without the influence of other metabolites, we prepared egg white phantoms. Next, we used 7-11-week-old nude female mice and the following cell lines to establish tumors after injection into the left striatum of mice: C6 (rat glioma, n = 8) as primary tumors and Neuro-2A (mouse neuroblastoma, n = 11) and MDA-MB231 (human breast cancer, n = 8) as metastatic tumors. All MRI experiments were performed on an 11.7 T vertical-bore scanner. CEST imaging was performed at 1 week after injection of Neuro-2A cells and at 2 weeks after injection of C6 and MDA-MB231 cells. The MT pulse amplitude was set at 2.2 μT or 4.4 μT. We calculated and compared the magnetization transfer ratio (MTR) and difference of MTR asymmetry between normal tissue and tumor (ΔMTR asymmetry) on APT CEST images between mouse models of brain tumors. Then, we performed hematoxylin and eosin (HE) staining and Ki-67 immunohistochemical staining to compare the APT CEST effect on tumor tissues and the pathological findings.

RESULTS

Phantom study of the amide proton phantom containing chicken egg white, z-spectra obtained at a pulse length of 500 ms showed smaller peaks, whereas those obtained at a pulse length of 2000 ms showed slightly higher peaks. The APT CEST effect on tumor tissues was clearer at a pulse amplitude of 2.2 μT than at 4.4 μT. For all mouse models of brain tumors, ΔMTR asymmetry was higher at 2.2 μT than at 4.4 μT. ΔMTR asymmetry was significantly higher for the Neuro-2A model than for the MDA-MB231 model. HE staining revealed light bleeding in Neuro-2A tumors. Immunohistochemical staining revealed that the density of Ki-67-positive cells was higher in Neuro-2A tumors than in C6 or MDA-MB231 tumors.

CONCLUSION

The MTR was higher at 4.4 μT than at 2.2 μT for each concentration of egg white at a pulse length of 500 ms or 2000 ms. High-resolution APT CEST imaging on an ultra-high-field MRI system was able to provide tumor information such as proliferative potential and intratumoral bleeding, noninvasively.

Protein aggregation linked to Alzheimer's disease revealed by saturation transfer MRI

The goal of this study was to develop a molecular biomarker for the detection of protein aggregation involved in Alzheimer's disease (AD) by exploiting the features of the water saturation transfer spectrum (Z-spectrum), the CEST signal of which is sensitive to the molecular configuration of proteins. A radial-sampling steady-state sequence based ultrashort echo time (UTE) readout was implemented to image the Z-spectrum in the mouse brain, especially the contributions from mobile proteins at the frequency offsets for the composite protein amide proton (+3.6 ppm) and aliphatic proton (-3.6 ppm) signals. Using a relatively weak radiofrequency (RF) saturation amplitude, contributions due to strong magnetization transfer contrast (MTC) from solid-like macromolecules and direct water saturation (DS) were minimized. For practical measure of the changes in the mobile protein configuration, we defined a saturation transfer difference (ΔST) by subtracting the Z-spectral signals at ±3.6 ppm from a control signal at 8 ppm. Phantom studies of glutamate solution, protein (egg white) and hair conditioner show the capability of the proposed scheme to minimize the contributions from amine protons, DS, and MTC, respectively. The ST signal at ±3.6 ppm of the cross-linked bovine serum albumin (BSA) solutions demonstrated that the ΔST signal can be used to monitor the aggregation process of the mobile proteins. High-resolution ΔST images of AD mouse brains at ±3.6 ppm of mouse brains showed significantly reduced ΔST (-3.6) signal compared to the age-matched wild-type (WT) mice. Thus, this signal has potential to serve as a molecular biomarker for monitoring protein aggregation in AD.

APT-weighted MRI: Techniques, current neuro applications, and challenging issues

Amide proton transfer-weighted (APTw) imaging is a molecular MRI technique that generates image contrast based predominantly on the amide protons in mobile cellular proteins and peptides that are endogenous in tissue. This technique, the most studied type of chemical exchange saturation transfer imaging, has been used successfully for imaging of protein content and pH, the latter being possible due to the strong dependence of the amide proton exchange rate on pH. In this article we briefly review the basic principles and recent technical advances of APTw imaging, which is showing promise clinically, especially for characterizing brain tumors and distinguishing recurrent tumor from treatment effects. Early applications of this approach to stroke, Alzheimer's disease, Parkinson's disease, multiple sclerosis, and traumatic brain injury are also illustrated. Finally, we outline the technical challenges for clinical APT-based imaging and discuss several controversies regarding the origin of APTw imaging signals in vivo. Level of Evidence: 3 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2019;50:347-364.

CEST MRI of sepsis-induced acute kidney injury

Sepsis-induced acute kidney injury (SAKI) is a major complication of kidney disease associated with increased mortality and faster progression. Therefore, the development of imaging biomarkers to detect septic AKI is of great clinical interest. In this study, we aimed to characterize the endogenous chemical exchange saturation transfer (CEST) MRI contrast in the lipopolysaccharide (LPS)-induced SAKI mouse model and to investigate the use of CEST MRI for detecting such injury. We used a SAKI mouse model that was generated by i.p. injection of 10 mg/kg LPS. The resulting kidney injury was confirmed by the elevation of serum creatinine and histology. MRI assessments were performed 24 h after LPS injection, including CEST MRI at different B₁ strengths (1, 1.8 and 3 μT), T₁ mapping, T₂ mapping and conventional magnetization transfer contrast (MTC) MRI. The CEST MRI results were analyzed using Z-spectra, in which the normalized water signal saturation (S_sat /S₀ ) is measured as a function of saturation frequency. Substantial decreases in CEST contrast were observed at both 3.5 and - 3.5 ppm frequency offset from water at all B₁ powers, with the most significant difference obtained at a B₁ of 1.8 μT. The average S_sat /S₀ differences between injured and normal kidneys were 0.07 (0.55 ± 0.04 versus 0.62 ± 0.04, P = 0.0028) and 0.07 (0.50 ± 0.04 versus 0.57 ± 0.03, P = 0.0008) for 3.5 and - 3.5 ppm, respectively. In contrast, the T₁ and T₂ relaxation times and MTC contrast in the injured kidneys did not show a significant change compared with the normal control. Our results showed that CEST MRI is more sensitive to the pathological changes in injured kidneys than the changes in T₁ , T₂ and MTC effect, indicating its potential clinical utility for molecular imaging of renal diseases.

The z-spectrum from human blood at 7T

Chemical Exchange Saturation Transfer (CEST) has been used to assess healthy and pathological tissue in both animals and humans. However, the CEST signal from blood has not been fully assessed. This paper presents the CEST and nuclear Overhauser enhancement (NOE) signals detected in human blood measured via z-spectrum analysis. We assessed the effects of blood oxygenation levels, haematocrit, cell structure and pH upon the z-spectrum in ex vivo human blood for different saturation powers at 7T. The data were analysed using Lorentzian difference (LD) model fitting and AREX (to compensate for changes in T₁), which have been successfully used to study CEST effects in vivo. Full Bloch-McConnell fitting was also performed to provide an initial estimate of exchange rates and transverse relaxation rates of the various pools. CEST and NOE signals were observed at 3.5 ppm, −1.7 ppm and −3.5 ppm and were found to originate primarily from the red blood cells (RBCs), although the amide proton transfer (APT) CEST effect, and NOEs showed no dependence upon oxygenation levels. Upon lysing, the APT and NOE signals fell significantly. Different pH levels in blood resulted in changes in both the APT and NOE (at −3.5 ppm), which suggests that this NOE signal is in part an exchange relayed process. These results will be important for assessing in vivo z-spectra.

Amide proton transfer-weighted MRI detection of traumatic brain injury in rats

The purpose of this study was to explore the capability and uniqueness of amide proton transfer-weighted (APTw) imaging in the detection of primary and secondary injury after controlled cortical impact (CCI)-induced traumatic brain injury (TBI) in rats. Eleven adult rats had craniotomy plus CCI surgery under isoflurane anesthesia. Multi-parameter MRI data were acquired at 4.7 T, at eight time points (1, 6 h, and 1, 2, 3, 7, 14, and 28 days after TBI). At one and six hours post-injury, average APTw signal intensities decreased significantly in the impacted and peri-lesional areas due to tissue acidosis. A slightly high APTw signal was seen in the core lesion area with respect to the peri-lesional area, which was due to hemorrhage, as shown by T₂*w. After the initial drop, the APTw signals dramatically increased in some peri-lesional areas at two and three days post-injury, likely due to the secondary inflammatory response. The use of APTw MRI has the potential to introduce a novel molecular neuroimaging approach for the simultaneous detection of ischemia, hemorrhage, and neuroinflammation in TBI.

Improving the detection sensitivity of pH-weighted amide proton transfer MRI in acute stroke patients using extrapolated semisolid magnetization transfer reference signals

PURPOSE

To quantify amide protein transfer (APT) effects in acidic ischemic lesions and assess the spatial-temporal relationship among diffusion, perfusion, and pH deficits in acute stroke patients.

METHODS

Thirty acute stroke patients were scanned at 3 T. Quantitative APT (APT^# ) effects in acidic ischemic lesions were measured using an extrapolated semisolid magnetization transfer reference signal technique and compared with commonly used MTR_asym (3.5ppm) or APT-weighted parameters.

RESULTS

The APT^# images showed clear pH deficits in the ischemic lesion, whereas the MTR_asym (3.5ppm) signals were slightly hypointense. The APT^# contrast between acidic ischemic lesions and normal tissue in acute stroke patients was more than three times larger than MTR_asym (3.5ppm) contrast (-1.45 ± 0.40% for APT^# versus -0.39 ± 0.52% for MTR_asym (3.5ppm), P < 4.6 × 10^-4 ). Hypoperfused and acidic areas without an apparent diffusion coefficient abnormality were observed and assigned to an ischemic acidosis penumbra. Hypoperfused areas at normal pH were also observed and assigned to benign oligemia. Hyperintense APT signals were observed in a hemorrhage area in one case.

CONCLUSIONS

The quantitative APT study using the extrapolated semisolid magnetization transfer reference signal approach enhances APT MRI sensitivity to pH compared with conventional APT-weighted MRI, allowing more reliable delineation of an ischemic acidosis in the penumbra. Magn Reson Med 78:871-880, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Characterizing amide proton transfer imaging in haemorrhage brain lesions using 3T MRI

OBJECTIVES

The aim of this study was to characterize amide proton transfer (APT)-weighted signals in acute and subacute haemorrhage brain lesions of various underlying aetiologies.

METHODS

Twenty-three patients with symptomatic haemorrhage brain lesions including tumorous (n = 16) and non-tumorous lesions (n = 7) were evaluated. APT imaging was performed and analyzed with magnetization transfer ratio asymmetry (MTR asym ). Regions of interest were defined as the enhancing portion (when present), acute or subacute haemorrhage, and normal-appearing white matter based on anatomical MRI. MTR asym values were compared among groups and components using a linear mixed model.

RESULTS

MTR asym values were 3.68 % in acute haemorrhage, 1.6 % in subacute haemorrhage, 2.65 % in the enhancing portion, and 0.38 % in normal white matter. According to the linear mixed model, the distribution of MTR asym values among components was not significantly different between tumour and non-tumour groups. MTR asym in acute haemorrhage was significantly higher than those in the other regions regardless of underlying pathology.

CONCLUSIONS

Acute haemorrhages showed high MTR asym regardless of the underlying pathology, whereas subacute haemorrhages showed lower MTR asym than acute haemorrhages. These results can aid in the interpretation of APT imaging in haemorrhage brain lesions.

KEY POINTS

• Acute haemorrhages show significantly higher MTR asym values than subacute haemorrhages. • MTR asym is higher in acute haemorrhage than in enhancing tumour tissue. • MTR asym in haemorrhage does not differ between tumorous and non-tumorous lesions.

Perfusion has no effect on the in vivo CEST effect from Cr (CrCEST) in skeletal muscle

Creatine, a key component of muscle energy metabolism, exhibits a chemical exchange saturation transfer (CEST) effect between its amine group and bulk water, which has been exploited to spatially and temporally map creatine changes in skeletal muscle before and after exercise. In addition, exercise leads to an increase in muscle perfusion. In this work, we determined the effects of perfused blood on the CEST effects from creatine in skeletal muscle. Experiments were performed on healthy human subjects (n = 5) on a whole-body Siemens 7T magnetic resonance imaging (MRI) scanner with a 28-channel radiofrequency (RF) coil. Reactive hyperemia, induced by inflation and subsequent deflation of a pressure cuff secured around the thigh, was used to increase tissue perfusion whilst maintaining the levels of creatine kinase metabolites. CEST, arterial spin labeling (ASL) and 31 P MRS data were acquired at baseline and for 6 min after cuff deflation. Reactive hyperemia resulted in substantial increases in perfusion in human skeletal muscle of the lower leg as measured by the ASL mean percentage difference. However, no significant changes in CrCEST asymmetry (CrCESTasym ) or 31 P MRS-derived PCr levels of skeletal muscle were observed following cuff deflation. This work demonstrates that perfusion changes do not have a major confounding effect on CrCEST measurements.

UCEPR: Ultrafast localized CEST-spectroscopy with PRESS in phantoms and in vivo

PURPOSE

Chemical exchange saturation transfer (CEST) is a contrast mechanism enhancing low-concentration molecules through saturation transfer from their exchangeable protons to bulk water. Often many scans are acquired to form a Z-spectrum, making the CEST method time-consuming. Here, an ultrafast localized CEST-spectroscopy with PRESS (UCEPR) is proposed to obtain the entire Z-spectrum of a voxel using only two scans, significantly accelerating CEST.

THEORY AND METHODS

The approach combines ultrafast nonlocalized CEST spectroscopy with localization using PRESS. A field gradient is applied concurrently with the saturation pulse producing simultaneous saturation of all Z-spectrum frequencies that are also spatially encoded. A readout gradient during data acquisition resolves the spatial dependence of the CEST responses into frequency. UCEPR was tested on a 3T scanner both in phantoms and in vivo.

RESULTS

In phantoms, a fast Z-spectroscopy acquisition of multiple pH-variant iopamidol samples was achieved with four- to seven-fold acceleration as compared to the conventional CEST methods. In vivo, amide proton transfer (APT) in white matter of healthy human brain was measured rapidly in 48 s and with high frequency resolution (≤ 0.2 ppm).

CONCLUSION

Compared with conventional CEST methods, UCEPR has the advantage of rapidly acquiring high-resolution Z-spectra. Potential in vivo applications include ultrafast localized Z-spectroscopy, quantitative, or dynamic CEST studies.

Simultaneous detection and separation of hyperacute intracerebral hemorrhage and cerebral ischemia using amide proton transfer MRI

PURPOSE

To explore the capability of amide proton transfer (APT) imaging in the detection of hemorrhagic and ischemic strokes using preclinical rat models.

METHODS

The rat intracerebral hemorrhage (ICH) model (n = 10) was induced by injecting bacterial collagenase VII-S into the caudate nucleus, and the permanent ischemic stroke model (n = 10) was induced by using a 4-0 nylon suture to occlude the origin of the middle cerebral artery. APT-weighted (APTw) MRI was acquired on a 4.7T animal imager and quantified using the magnetization transfer-ratio asymmetry at 3.5 ppm from water.

RESULTS

There was a consistently high APTw MRI signal in hyperacute ICH during the initial 12 h after injection of collagenase compared with the contralateral brain tissue. When hemorrhagic and ischemic stroke were compared, hyperacute ICH and cerebral ischemia demonstrated opposite APTw MRI contrasts-namely, hyperintense versus hypointense compared with contralateral brain tissue, respectively. There was a stark contrast in APTw signal intensity between these two lesions.

CONCLUSION

APT-MRI could accurately detect hyperacute ICH and distinctly differentiate hyperacute ICH from cerebral ischemia, thus opening up the possibility of introducing to the clinic a single MRI scan for the simultaneous visualization and separation of hemorrhagic and ischemic strokes at the hyperacute stage. Magn Reson Med 74:42-50, 2015. © 2014 Wiley Periodicals, Inc.

Oxidation-responsive Eu(2+/3+)-liposomal contrast agent for dual-mode magnetic resonance imaging

An oxidation-responsive contrast agent for magnetic resonance imaging was synthesized using Eu(2+) and liposomes. Positive contrast enhancement was observed with Eu(2+), and chemical exchange saturation transfer was observed before and after oxidation of Eu(2+). Orthogonal detection modes render the concentration of Eu inconsequential to molecular information provided through imaging.

Amide proton transfer-weighted imaging of the head and neck at 3 T: a feasibility study on healthy human subjects and patients with head and neck cancer

The aim of this study was to explore the feasibility and repeatability of amide proton transfer-weighted (APTw) MRI for the head and neck on clinical MRI scanners. Six healthy volunteers and four patients with head and neck tumors underwent APTw MRI scanning at 3 T. The APTw signal was quantified by the asymmetric magnetization transfer ratio (MTRasym) at 3.5 ppm. Z spectra of normal tissues in the head and neck (masseter muscle, parotid glands, submandibular glands and thyroid glands) were analyzed in healthy volunteers. Inter-scan repeatability of APTw MRI was evaluated in six healthy volunteers. Z spectra of patients with head and neck tumors were produced and APTw signals in these tumors were analyzed. APTw MRI scanning was successful for all 10 subjects. The parotid glands showed the highest APTw signal (~7.6% average), whereas the APTw signals in other tissues were relatively moderate. The repeatability of APTw signals from the masseter muscle, parotid gland, submandibular gland and thyroid gland of healthy volunteers was established. Four head and neck tumors showed positive mean APTw ranging from 1.2% to 3.2%, distinguishable from surrounding normal tissues. APTw MRI was feasible for use in the head and neck regions at 3 T. The preliminary results on patients with head and neck tumors indicated the potential of APTw MRI for clinical applications.