Clinical Application Of Amide Proton Transfer Imaging In Head And Neck Tumors And Ischemic Stroke

Part 1 Preliminary Study of Amide Proton Transfer Imaging Technique in Head and Neck TumorsBackground and Purpose:Amide proton transfer(APT)imaging is an important part of chemical exchange saturation transfer(CEST)imaging and can characterize the tissue by detecting mobile proteins and peptides in tissues.Few reports evaluated head and neck tumors by APT imaging.The selection of region of interest(ROI)in APT imaging studies mainly includes extreme value method and whole value method.The purpose of this study was to prospectively evaluate the value of APT imaging technique for the differential diagnosis of head and neck tumors and to compare the difference of the two ROI selection methods.Materials and methods:Twenty-nine patients with head and neck tumors(13 benign tumors and 16 malignant tumors)were enrolled in this study.All patients underwent 3.0T MR scanning,including conventional sequences and APT imaging.Magnetization transfer ratio asymmetry at 3.5ppm(MTRasym)of the lesions were measured using extreme value method(APTmax,APTmin)and whole value method(APTwhole).The differences of APTmax,APTmin and APTwhole between the malignant and benign tumors were compared by using the independent sample t-test.Receiver operating characteristic(ROC)analysis was used to determine the value of APTmax,APTmin and APTwhole for the differentiation of malignant tumors from benign tumors.The area under curve(AUC)of APTmax,APTmin,APTwhole were compared by Z test.Results:APTmax,APTmin and APTwhole of the malignant tumors were significantly higher than that of benign ones((4.11 ± 1.35)%vs(2.35 ± 0.92)%,P<0.001,(3.01 ±0.89)%vs(1.72 ± 0.74)%,P<0.001,(3.66 ± 1.15)%vs(1.94 ± 0.93)%,P<0.001,respectively).AUC of APTmax,APTmin and APTwhole was 0.865,0.846 and 0.899,respectively.The differences of the AUC of APTmax and APTmin,APTmax and APTwhole,APTmin and APTwhole were not significant(Z value was 0.267,0.717 and 0.991 respectively and P value was 0.79,0.47,0.32 respectively).Conclusion:APT imaging technique can differentiate benign and malignant tumors in the head and neck and provide a noninvasive method for head and neck tumors without radiation.The two ROI selection methods have similar differential diagnosis value.Part 2 Clinical Application of Amide Proton Transfer Imaging Technique in Evaluating the Effect of Non-thrombolytic Therapy in Ischemic StrokeBackground and Purpose:Amide proton transfer(APT)imaging is sensitive to pH changes and shows promise in evaluating tissue acidosis in ischemic stroke.But few studies focused on the evaluation of therapeutic effects by APT imaging.The purpose of this study was to prospectively assess the therapeutic effect of non-thrombolytic treatment in ischemic stroke patients using the APT imaging technique and to evaluate the correlation between diffusion weighted imaging(DWI)and APT imaging.Materials and Methods:Forty-three patients with ischemic stroke were recruited and scanned on a 3T MR scanner before treatment.The follow-up and MRI scan were underwent during and after therapeutic process.The sequences included T1WI,T2WI,T2FLAIR,DWI and APT imaging.The magnetization-transfer-ratio asymmetry(MTRasym)at 3.5 ppm of the ischemic lesions,usually called the APT value,was measured.APT value of the contralateral normal white matter(CNAWM)was also acquired.APT contrast was defined as APT value difference between an ischemic lesion and the CNAWM.Apparent diffusion coefficient(ADC)of the ischemic lesion was measured.The extreme value method(APTmax and APTmin)and whole value method(APTwhole)were used to select region of interest(ROI).The National Institutes of Health Stroke Scale(NIHSS)was assessed before MR scan.Pearson correlation analysis was performed to assess NIHSS and the baseline APTmax,APTmin,APTwhole before treatment.All patients were divided into four groups(S 96 hours,47 days,8～21 days and≥22 days)according to the treatment time and the APT changes following treatment(among pre-treatment group,≤96 hours,4～7 days,8～21 days and≥22 days)were analyzed by using one-way ANOVA.The patients were divided into four groups(≤96 hours,4～7 days,8～21 days and≥22 days)according to the onset time and APT value differences between stroke patients with and without treatment at the same onset time were analyzed by independent sample t-test.Pearson correlation analysis was used to compare the correlation between APT value and ADC.Results:Twenty-six patients underwent follow-up and MRI scan(once to three times at different time points)and the other 17 patients didn’t undergo follow-up.Baseline APTmax,APTmin,APTwhole of the ischemic lesions inversely correlated with NIHSS scale.Twenty-four cases(92.3%)with follow-up showed clinical symptom improvements and NIHSS scale decreased.APTmax and corresponding APTmax contrast,APTwhole of ischemic lesions at two post-treatment times of 8～21 days and≥22 days group increased significantly compared with pre-treatment group.APTmin and APTmin contrast of the ischemic lesions at the four post-treatment times(≤96 hours,4～7 days,8～21 days and≥22 days)increased significantly compared with pre-treatment group.APTmin and APTmin contrast of the ischemic lesions at two post-onset times of≤96 hours and 4～7 days with treatment increased significantly compared with those without treatment and NIHSS scale decreased.APTmax and APTwhole of the ischemic lesions at two post-onset times of<96 hours and 4～7 days with treatment didn’t show significant differences compared with those without treatment.Before treatment,APTmin of the ischemic lesions showed no correlation with ADC(r=-0.002,P=0.988).After treatment,APTmin was correlated with ADC(r=0.523,P<0.001).Two cases(7.7%)showed further decreased APT value in the follow-up scan,accompanied by clinical symptom aggravation.Conclusion:APT value can be used as an imaging biomarker to assess the effect of non-thrombolytic therapy of ischemic stroke quantitatively.APT imaging provides a non-invasive and objective method to evaluate therapeutic effect without radiation.