Dynamic contrast enhanced ultrasound in differential diagnosis of hepatocellular carcinoma: A systematic review and meta-analysis

BACKGROUND Non-invasive differential diagnosis between hepatocellular carcinoma(HCC)and other liver cancer(i.e.cholangiocarcinoma or metastasis)is highly challenging and definitive diagnosis still relies on histological exam.The patterns of enhancement and wash-out of liver nodules can be used to stratify the risk of malignancy only in cirrhotic patients and HCC frequently shows atypical features.Dynamic contrast-enhanced ultrasound(DCEUS)with standardized software could help to overcome these obstacles,providing functional and quantitative parameters and potentially improving accuracy in the evaluation of tumor perfusion.AIM To explore clinical evidence regarding the application of DCEUS in the differential diagnosis of liver nodules.METHODS A comprehensive literature search of clinical studies was performed to identify the parameters of DCEUS that could relate to histological diagnosis.In accordance with the study protocol,a qualitative and quantitative analysis of the evidence was planned.RESULTS Rise time was significantly higher in HCC patients with a standardized mean difference(SMD)of 0.83(95%CI:0.48-1.18).Similarly,other statistically significant parameters were mean transit time local with a SMD of 0.73(95%CI:0.20-1.27),peak enhancement with a SMD of 0.37(95%CI:0.03-0.70),area wash-in area under the curve with a SMD of 0.47(95%CI:0.13-0.81),wash-out area under the curve with a SMD of 0.55(95%CI:0.21-0.89)and wash-in and wash-out area under the curve with SMD of 0.51(95%CI:0.17-0.85).SMD resulted not significant in fall time and wash-in rate,but the latter presented a trend towards greater values in HCC compared to intrahepatic cholangiocarcinoma.CONCLUSION DCEUS could improve non-invasive diagnosis of HCC,leading to less liver biopsy and early treatment.This quantitative analysis needs to be applied on larger cohorts to confirm these preliminary results.

Multiphase convolutional dense network for the classification of focal liver lesions on dynamic contrast-enhanced computed tomography

BACKGROUND The accurate classification of focal liver lesions(FLLs)is essential to properly guide treatment options and predict prognosis.Dynamic contrast-enhanced computed tomography(DCE-CT)is still the cornerstone in the exact classification of FLLs due to its noninvasive nature,high scanning speed,and high-density resolution.Since their recent development,convolutional neural network-based deep learning techniques has been recognized to have high potential for image recognition tasks.AIM To develop and evaluate an automated multiphase convolutional dense network(MP-CDN)to classify FLLs on multiphase CT.METHODS A total of 517 FLLs scanned on a 320-detector CT scanner using a four-phase DCECT imaging protocol(including precontrast phase,arterial phase,portal venous phase,and delayed phase)from 2012 to 2017 were retrospectively enrolled.FLLs were classified into four categories:Category A,hepatocellular carcinoma(HCC);category B,liver metastases;category C,benign non-inflammatory FLLs including hemangiomas,focal nodular hyperplasias and adenomas;and category D,hepatic abscesses.Each category was split into a training set and test set in an approximate 8:2 ratio.An MP-CDN classifier with a sequential input of the fourphase CT images was developed to automatically classify FLLs.The classification performance of the model was evaluated on the test set;the accuracy and specificity were calculated from the confusion matrix,and the area under the receiver operating characteristic curve(AUC)was calculated from the SoftMax probability outputted from the last layer of the MP-CDN.RESULTS A total of 410 FLLs were used for training and 107 FLLs were used for testing.The mean classification accuracy of the test set was 81.3%(87/107).The accuracy/specificity of distinguishing each category from the others were 0.916/0.964,0.925/0.905,0.860/0.918,and 0.925/0.963 for HCC,metastases,benign non-inflammatory FLLs,and abscesses on the test set,respectively.The AUC(95%confidence interval)for differentiating each category from the others was 0.92(0.837-0.992),0.99(0.967-1.00),0.88(0.795-0.955)and 0.96(0.914-0.996)for HCC,metastases,benign non-inflammatory FLLs,and abscesses on the test set,respectively.CONCLUSION MP-CDN accurately classified FLLs detected on four-phase CT as HCC,metastases,benign non-inflammatory FLLs and hepatic abscesses and may assist radiologists in identifying the different types of FLLs.

A case of occult insulinoma localized by pancreatic dynamic enhanced spiral CT

Insulinomas are the most common category of pancreatic endocrine tumors,with an annual incidence of 1-4 cases per million people.Most are intrapancreatic,benign and solitary.Therefore,they have an excellent prognosis after surgical resection.However,the localization diagnosis of insulinomas still poses a challenge to surgeons and radiologists.In this case,the tumor was occult and could not be found by either abdominal enhanced spiral computed tomography(CT)or ultrasonography.Therefore,we tried a new method of CT scanning and localized the tumor.

Diagnosis value of diffusion-weighted MR imaging with dynamic enhanced scanning toward pancreatic endocrine tumors

Objective： The aim of our study was to analysis the pictures of conventional magnetic resonance imaging （MR）, diffusion-weighted imaging （DWl） and dynamic enhanced magnetic resonance imaging （DEMRI） of pancreatic endocrine tumors （PETs）, and evaluate diagnostic value of MR, DWl and DEMRI for diagnosing PETs. Methods： DWl and DEMRI scanning toward 13 patients with PETs being confirmed by surgical pathology before surgery on the basis of conventional MR scanning were carried out, and MR findings was analyzed retrospectively. Results： Of 13 patients with PETs there was 11 cases with single lesion, 2 with multiple, and had 15 lesions altogether, of which there were 3 lesions in pancreatic head, 1 in its neck, 2 in its body, 4 in its body and tail, 5 in its tail. MR findings： （1） T1WI signal was low or slightly lower （9/15）, and equal ones （5/15）; （2） T2WI showed high or slightly higher signal （10/15）, and equal ones （5/15）; （3） T1WI with fat suppression： the signal was low （11/15）, mixed signal （2/15）, and equal ones （2/15）; （4） DWI： normal pancreatic tissue exhibited homogeneous intermediate signal, all 15 lesions were high or slightly higher signal, the measured ADC values of tissue of PETs was （1.124 ± 0.252） × 104 mm2/s, and the ADC value of normal pancreatic tissue （1.873 ± 0.157） × 10^3 mm2/s; （5） Enhanced （M3D/LAVA） scanning： among 13 patients with PETs there were 12 pancreatic lesions with significantly enhanced signals in the arterial phase in all 15, and significantly higher than normal pancreatic tissue, and two slight enhancement was slightly higher signal; and 1 no enhancement. Enhanced pattern： homogeneous enhancement were 6 lesions, and the heterogeneous 4, and the edge ring 5. Conclusion： MR and DWl combining with DEMRI help qualitative diagnosis of pancreatic endocrine tumors.

Mammography combined with breast dynamic contrast-enhanced-magnetic resonance imaging for the diagnosis of early breast cancer

Objective The aim of this study was to investigate the application of mammography combined with breast dynamic contrast-enhanced magnetic resonance imaging(DCE-MRI) for the diagnosis of early breast cancer. Methods Mammography and DCE-MRI were performed for 120 patients with breast cancer(malignant, 102; benign; 18). Results The sensitivity of mammography for early diagnosis of breast cancer was 66.67%, specificity was 77.78%, and accuracy was 68.33%. The sensitivity of MRI for early diagnosis of breast cancer was 94.12%, specificity was 88.89%, and accuracy was 93.33%. However, the sensitivity of mammography combined with DCE-MRI volume imaging with enhanced water signal(VIEWS) scanning for early diagnosis of breast cancer was 97.06%, specificity was 94.44%, and accuracy was 96.67%. Conclusion Mammography combined with DCE-MRI increased the sensitivity, specificity, and accuracy of diagnosing early breast cancer.

BLOOD FLOW PATTERN AND QUANTITATIVE STUDY IN SOLITARY PULMONARY NODULES WITH DYNAMIC CONTRAST-ENHANCED MRI

Objective To evaluate the efficacy of contrast enhanced dynamic MRI in differentiating solitary pulmonary nodules（SPNs）. Methods Eighty-three patients with SPNs undertaken contrast enhanced dynamic MRI. Time-signal intensity curve （T-SI Curve） was made. Peak height （PH） , steepest slope （SS）, maximum enhancement （ Emax ） and the enhancement rates of signal intensity were recorded at the frst （ E1 ）, second （ E2 ）, third （ E3 ） , fourth （ E4 ） , fifth （E5）, and sixth （ E6 ） minute after injection. Results Malignant nodules and inflammatory nodules enhanced significantly higher than benign nodules, and malignant nodules and inflammatory nodules showed obviously higher PH, SS, Emax, El-E6 values than benign nodules （ P 〈 0. 01 ）. There were no sig- nificant differences in PH, SS, Emax, E1-E6 values between malignant nodules and inflammatory nodules （P 〉 0. 05）. Conclusion Contrast enhanced dynamic MR imaging can provide SPNs＇ hemodynamic information and is helpful in differentiating SPNs.

Relationship between dynamic contrast-enhanced MRI parameters and angiogenesis in peripheral pulmonary adenocarcinoma

Objective:To investigate the relationship between dynamic contrast-enhanced MRI parameters and tumor angiogenesis in peripheral pulmonary adenocarcinoma.Methods:Thirty-seven patients with pathologic proved pulmonary adenocarcinoma underwent dynamic contrast-enhanced MR Imaging. Microvessel density(MVD) was counted and vascular endothelial growth factor(VEGF) expression was assessed with immunohistochemical method. Dynamic contrast-enhanced MRI-derived parameters, such as peak height(PH), steepest slope(SS), maximum enhancement rate(E max),enhancement rate at 1-6 minutes(E 1-6), were calculated and compared with MVD in pulmonary adenocarcinoma. And the parameters were also compared between VEGF-positive and VEGF-negative pulmonary adenocarcinoma. Results:The microvessel density was 68.31±19.84 in 37 pulmonary adenocarcinoma. The PH, SS, E max, E 1-6 correlated positively with MVD respectively(P<0.001). The strongest relationship was found between SS and MVD(r=0.827,P<0.001). There was a significant difference between MVD of VEGF-positive pulmonary adenocarcinoma (79.47±21.35) and MVD of VEGF-negative pulmonary adenocarcinoma (43.16±17.85)(P<0.001). All the parameters in VEGF-positive pulmonary adenocarcinoma were higher than those in VEGF-negative pulmonary adenocarcinao(P<0.001). Conclusion: Dynamic contrast-enhanced MRI-derived parameters of pulmonary adenocarcinoma correlated positively with MVD. The parameters in VEGF-positive pulmonary adenocarcinoma were higher than those in VEGF-negative pulmonary adenocarcinoma(P<0.001).

Correlation between CT dynamic enhanced scanning parameters and serum tumor markers before and after radiofrequency ablation in patients with lung cancer

Objective:To study the correlation between CT dynamic enhanced scanning parameters and serum tumor markers before and after radiofrequency ablation in patients with lung cancer.Methods:60 patients with advanced non-small cell lung cancer who were treated in this hospital between January 2015 and January 2017 were divided into control group(n=30)and observation group(n=30)by random number table method.Control group received conventional intravenous chemotherapy,and observation group received intravenous chemotherapy combined with radiofrequency ablation.The differences in CT dynamic enhanced scanning parameter levels and serum tumor marker contents were compared between the two groups of patients before and after treatment.Pearson test was used to evaluate the correlation between CT dynamic enhanced scanning parameters and serum tumor marker contents in patients with advanced non-small cell lung cancer.Results:Before treatment,the differences in CT dynamic enhanced scanning parameter levels,non-organ-specific tumor marker contents and vascular tumor marker contents were not statistically significant between the two groups of patients(P>0.05).After treatment,CT dynamic enhanced scanning parameters PH and perfusion value levels of observation group were lower than those of control group(P<0.05);serum non-organ specific tumor markers CA125,CA153,CEA and CYFRA21-1 contents of observation group were lower than those of control group;serum vascular tumor markers VEGF,Ang-2,HIF-1 and MMP-9 contents were lower than those of control group(P<0.05).Pearson test showed that CT dynamic enhanced scanning parameters PH and perfusion value levels in patients with non-small cell lung cancer were positively correlated with serum non-organ specific tumor marker and vascular tumor marker contents.Conclusion:Adjuvant radiofrequency ablation can significantly reduce the tumor malignancy of patients with advanced non-small cell lung cancer.

Role of pulmonary perfusion magnetic resonance imaging for the diagnosis of pulmonary hypertension:A review

Among five types of pulmonary hypertension,chronic thromboembolic pulmonary hypertension(CTEPH)is the only curable form,but prompt and accurate diagnosis can be challenging.Computed tomography and nuclear medicine-based techniques are standard imaging modalities to non-invasively diagnose CTEPH,however these are limited by radiation exposure,subjective qualitative bias,and lack of cardiac functional assessment.This review aims to assess the methodology,diagnostic accuracy of pulmonary perfusion imaging in the current literature and discuss its advantages,limitations and future research scope.

Differential study of DCE-MRI parameters in spinal metastatic tumors, brucellar spondylitis and spinal tuberculosis

Objective： In the present study, spinal metastatic tumors, brucellar spondylitis and spinal tuberculosis werequantitatively analyzed using dynamic contrast-enhanced magnetic resonance imaging （DCE-MRI） to assess thevalue of DCE-MRI in the differential diagnosis of these diseases.Methods： Patients with brucellar spondylitis, spinal tuberculosis or a spinal metastatic tumor （30 cases of each）received conventional MRI and DCE-MRI examination. The volume transfer constant （Ktrans）, rate constant （Kep）,extravascular extracellular volume fraction （Ve） and plasma volume fraction （Vp） of the diseased vertebral bodieswere measured on the perfusion parameter map, and the differences in these parameters between the patients werecompared.Results： For pathological vertebrae in cases of spinal metastatic tumor, brucellar spondylitis and spinaltuberculosis, respectively, the Ktrans values （median ＋ quartile pitch） were 0.989±0.014, 0.720±0.011 and0.317±0.005 min-1; the Kep values were 2.898±0.055, 1.327±0.017 and 0.748±0.006 min-1; the Ve values were0.339±0.008, 0.542±0.013 and 0.428±0.018; the Vp values were 0.048±0.008, 0.035±0.004 and 0.028±0.009; thecorresponding H values were 50.25 （for Ktrans）, 52.47 （for Kep）, 48.33 （for Ve） and 46.56 （for Vp）, and all differenceswere statistically significant （two-sided P〈0.05）.Conclusions： The quantitative analysis of DCE-MRI has a certain value in the differential diagnosis of spinalmetastatic tumor, brucellar spondylitis and spinal tuberculosis.

The application of breast DCE-MRI combined with time signal curve in diagnosing early breast cancer

Objective： The aim of this study was to investigate the application value of breast dynamic contrast-enhanced magnetic resonance imaging combined with time signal curve in diagnosis of early breast cancer. Methods： Conducted dynamic contrast-enhanced MRI and drew the time signal curves of breast lesions in 60 patients with breast disease （malignant 46, benign 14）. Results： Morphological features of malignant tumors mostly showed blurred or thin spiculate outlines, irregular shape or Iobular signs, signal heterogeneity or peripheral enhancement in dynamic contrast-enhanced MRI. Time signal curve showed type III or II. Morphologic features of benign tumors mostly showed clear edge, regular shape and homogeneous signal, or diffuse spot enhancement. Time signal curve showed type I or II. Conclusion： breast dynamic contrast enhanced scan in MRI can provide morphology and functional diagnosis information of the breast tissues. Dynamic contrast-enhanced MRI combined with time signal curve can further improve the accuracy of diagnosis of early breast cancer.

Enhancement patterns of small hepatocellular carcinoma shown by dynamic MRI and CT

Objectives: To study prospectively the enhancement features of small hepatocellular carcinoma (SHCC) with multi-phase scanning of dynamic MRI and spi- ral CT, and discuss the superiority of dynamic MRI to spiral CT. Methods: Multi-phase dynamic contrast scanning of high field MRI and spiral CT were performed in 53 patients with SHCC. The arterial phase, portal ve- nous phase and delayed phase scanning of spiral CT was done after the pre-contrast scanning of the entire liver. MRI was performed with SE sequence and fast multiplanar spoiled gradient-recalled sequence dy- namic multi-phase contrast scanning. Results: Seventy-six lesions were found in all 53 pa- tients. Sixty-nine and 54 of the 76 lesions enhanced obviously in MRI and spiral CT arterial phase scan- ning respectively. The typical enhancement patterns of SHCC in the arterial phase, portal venous phase and delayed phase scanning of MRI and spiral CT were hyper-hypo-hypointense (dense) and hyper-iso- hypointense (dense). Atypical enhancement patterns were hyper-hyper-hyperintense (dense), hyper-iso- isointense (dense) and hypo-hypo-hypointense (dense). Conclusions: Both MRI and spiral CT multi-phase dynamic contrast-enhanced scanning could demon- strate the enhancement features of SHCC, and arte- rial phase scan of MRI was superior to spiral CT in reflecting the hypervascular characterization of SHCC. In addition, MRI was better than spiral CT in characterization of hepatic lesions combined with SE sequence.

Blood flow patterns of solitary pulmonary nodules with enhancement

Objective： To evaluate the efficacy of dynamic multi-slice spiral computed tomography （MSCT） for providing quantitative information about blood flow patterns of solitary pulmonary nodules （SPNs）. Methods： Seventy-eight patients with SPNs （diameter 〈 4 cm; 68 malignant; 10 active inflammatory） were underwent multi-location dynamic contrast material-enhanced serial CT （nonionic contrast material was administrated via the antecubital vein at a rate of 4 mLJs by using an autoinjector, 4 × 5 mm or 4 × 2.5 mm transverse scanning mode with stable table were performed）. Sixteen series CT scans （16 scans each for the first and second series and one scan each for the rest series） were obtained during 9 min scanning period. Precontrast and postcontrast attenuation on every scan was recorded. Perfusion, peak height and ratio of peak height of the SPN to that of the aorta were calculated. Perfusion was calculated from the maximum gradient of the time-attenuation curve and the peak height of the aorta. Results： No statistically significant difference in the peak height was found between malignant （35.79 ± 10.76 Hu） and active inflammatory （39.76 ± 4.59 Hu） （t = 1.148, P = 0.255 〉 0.05）. SPN-to-aorta ratio （14.27% ± 4.37） and perfusion value （30.18 mL/min/100 g ± 9.58） in malignant SPNs were significantly lower than those of active inflammatory （18.51% ± 2.71, 63.44 mL/min/100 g ± 43.87） （t = 2.978, P = 0.004 〈 0.05; t = 5.590, P 〈 0.0001）. Conclusion： The quantitative information about blood flow patterns of malignant and active inflammatory SPNs is different. SPN-to-aorta ratio and perfusion value are helpful in differentiating malignant nodules from active inflammatory.

Diagnostic Value of Quantitative Parameters of DCE-MRI in Endometrial Carcinoma and Its Correlation with Clinicopathological Factors

In the study,108 patients with endometrial cancer were selected as the observation group,and 105 patients with benign endometrial lesions were selected as the control group.After DCE-MRI examination,it was found that the volume transfer constant(K^(trans)),rate constant(K_(e))and extracellular space volume ratio(V_(e))in the observation group were higher than those in the control group(P<0.05).The area under curve(AUC)of combined K^(trans),K_(e) and V_(e) values in the diagnosis of endometrial cancer was 0.841.The values of K^(trans),K_(e )and V_(e) were positively correlated with the clinical stage and the degree of muscular invasion,but negatively correlated with the degree of differentiation(P<0.05).The results of the study suggested that DCE-MRI quantitative parameters have a certain value in the differential diagnosis of endometrial cancer,which helped to further distinguish the degree of muscular invasion,clinical stage,and differentiation of endometrial cancer patients.

The application of DCE-MRI in diagnosing breast cancer

Objective The aim of the study was to further explore the diagnostic value of breast dynamic contrast enhancement (DCE), and improve specificity of breast cancer diagnosis.

Classification of breast lesions based on a dual S-shaped logistic model in dynamic contrast enhanced magnetic resonance imaging

This study proposes a novel dual S-shaped logistic model for automatically quantifying the characteristic kinetic curves of breast lesions and for distinguishing malignant from benign breast tumors on dynamic contrast enhanced (DCE) magnetic resonance (MR) images.D(,) is the diagnostic parameter derived from the logistic model.Significant differences were found in D(,) between the malignant benign groups.Fisher's Linear Discriminant analysis correctly classified more than 90% of the benign and malignant kinetic breast data using the derived diagnostic parameter (D(,)).Receiver operating characteristic curve analysis of the derived diagnostic parameter (D(,)) indicated high sensitivity and specificity to differentiate malignancy from benignancy.The dual S-shaped logistic model was effectively used to fit the kinetic curves of breast lesions in DCE-MR.Separation between benign and malignant breast lesions was achieved with sufficient accuracy by using the derived diagnostic parameter D(,) as the lesion's feature.The proposed method therefore has the potential for computer-aided diagnosis in breast tumors.

Intra-individual comparison of different gadolinium-based contrast agents in the quantitative evaluation of C6 glioma with dynamic contrast-enhanced magnetic resonance imaging

This experiment aimed to compare the ionic （Gadodiamide, Gd-DTPA-BMA） and non-ionic （Gadopentetate dimeglumine, Gd-DTPA） gadolinium-based contrast agents （GBCA） in the quantitative evaluation of C6 glioma with dynamic contrast-enhanced magnetic resonance imaging （DCE-MRI）. A C6 glioma model was established in 12 Wistar rats, and magnetic resonance （MR） scans were performed six days after tumor implantation. Imaging was performed using a 3.0-T MR scanner with a 7-inch handmade circular coil. Pre-contrast T1 mapping and dynamic contrast-enhanced T1WI after a bolus injection （0.2 mL s 1） of GBCA at 0.4 mmol kg-1 were performed. Each rat received two DCE-MRI scans, 24 h apart. The first and second scans were performed using Gd-DTPA-BMA and Gd-DTPA, respectively. Image data were processed using the Patlak model. Both Kns and Vp maps were generated. Tumors were manually segmented on all 3D K and Vp maps. Pixel counts and mean values were recorded for use in a paired t-test. Three radiologists independently performed the tumor segmentation and value calculation. The agreements from different observers were subjective to the intra-class correlation coefficient （ICC）. Readers demonstrated that the pixel counts of tumors in/Crns maps were higher with Gd-DTPA-BMA than with Gd-DTPA （P〈0.001, all readers）. Although the/（r,,s values were higher with Gd-DTPA-BMA than with Gd-DTPA, there was no statistical significance （P〉0.05, all readers）. The pixel counts of tumors in Vp maps, as well as Vp values, showed no obvious difference between the two agents （P〉0.05, all readers）. Excellent interobserver measurement reproducibility and reliability were demonstrated in the ICC tests. The Gd-DTPA-BMA contrast agent had significantly higher pixel counts of glioma in the maps, and an increased tendency for average/Us values, indicating that DCE-MRI with Gd-DTPA-BMA may be more suitable and sensitive for the evaluation of glioma.

Tumor infiltration of bone marrow in patients with hemato-logical malignancies: dynamic contrast-enhanced magnetic resonance imaging

Background Conventional magnetic resonance （MR） scanning techniques can identify bone marrow （BM） containing mostly fat cells. But they are not able to differentiate BM tumor infiltration, BM fibrosis and normal red BM. This is particularly problematic in assessment of recurrent or refractory hematological malignancy. This pilot study used dynamic contrast-enhanced MR imaging （DCE-MRI） to evaluate the bone marrow status and to determine whether several calculated parameters derived from the DCE-MRI correlate with histological characteristics of marrow, especially with the tumor fraction （TF）. Methods DCE-MRI scans were performed in 25 patients with proven or known hematological malignancy who were about to undergo bone marrow biopsy of the posterior iliac crest. The location chosen for biopsy was examined with MRI approximately one hour prior to the biopsy. Time-signal intensity curves （TIC） were generated from the region of the iliac crest corresponding to the planned biopsy site. Enhancement parameters were calculated, including peak enhancement ratio （PER）, maximum enhancement slope （S1opemax）, time to peak （TTP） and mean time （MT）. The biopsy specimen was reported synoptically, with relevant reported parameters including cellularity and tumor fraction （TF）. Results PER values were significantly higher for the bone marrow tumor infiltration group than for the normal bone marrow group （P〈0.05）. A significant positive correlation was found between PER and TF as well as S1opemax and TF. A negative correlation was found between TTP and TF. There was no significant difference in the mean TTP and MT values between the BM tumor infiltration group and the normal bone marrow group. Conclusions The presence of diffuse bone marrow infiltration in patients with haematological malignancies could be verified using DCE-MRI.

Cutting of Graphite at Atomic and Close-to-Atomic Scale Using Flexible Enhanced Molecular Dynamics

Atomic and close-to-atomic scale manufacturing is the key technology for the production of next-generation devices with atomic precision.As an important approach of mechanical processing,cutting has evolved as a potential candidate to generate an atomically smooth surface;thus,exploring its ultimate capability is significant.In this paper,single-crystal graphite,whose lattice structure and chemical bond property are of representation for demonstration,is selected to study the mechanism of atomic layer removal using molecular dynamics.A localized workpiece,which is dynamically updated on the basis of the tool position,is used to improve the computation efficiency.The principle and bullet points of this modeling method are first introduced,followed by a series of simulations under various undeformed chip thicknesses and tool edge radi.In addition,different potentials for the tool-workpiece interaction are tested,and the effect on the material response is presented.Based on the analysis of deformation,the number of carbon layers removed,and cutting forces,the chip formation mechanism and further understanding of the controllability of cutting at atomic and close-to-atomic scale can be achieved.

Feasibility and value of quantitative dynamic contrast enhancement MR imaging in the evaluation of sinonasal tumors

Background Quantitative dynamic contrast enhancement MR imaging （DCE-MRI）,used to measure properties of tissue microvasculature and tumor angiogenesis,is a promising method for distinguishing benign and malignant tumors and characterizing tumor response to antiangiogenic treatment.The aim of this study was to assess the feasibility of quantitative parameters derived from clinically used DCE-MRI for distinguishing benign from malignant tumors in the sinonasal area,which may be potentially useful for prediction and monitoring of treatment response to chemoradiotherapy of sinonasal tumors.Methods One hundred and forty-three patients with sinonasal tumors,including 78 malignant tumors and 65 benign tumors and tumor-like lesions,underwent clinically used DCE-MRI.Parametric maps were obtained for quantitative parameters including Ktrans,kep and ve.Two radiologists reviewed these maps and measured Ktrans,kep and ve in the tumor tissue.Data were analyzed using independent T-test or Mann-Whitney U test analysis and receiver operating characteristic curves.Results Ktrans,kep and ve showed significant differences between benign and malignant tumors in the sinonasal area （P=-0.000 1）.The accuracy of Ktrans,kep and ve in differentiation between benign and malignant sinonasal tumors were 72.0％,76.2％ and 67.1％,respectively.There were significant differences in kep and ve between malignant epithelial sinonasal tumors and lymphomas （P ＜0.05）.Using a ve value of 0.213 as the threshold value differentiated malignant epithelial tumors from lymphomas with an accuracy of 78.3％,sensitivity of 88.2％,specificity of 68.0％,positive predictive value of 66.7％,and negative predictive value of 90.9％.However,no significant difference in Ktrans and kep was found between malignant epithelial and non-epithelial tumors in the sinonasal area （P ＞0.05）.Conclusions It is feasible that quantitative parameters of tumors can be derived from clinically used DCE-MRI in the sinonasal region.Preliminary findings suggest an increased value for quantitative DCE-MRI in the evaluation of sinonasal tumors in clinical practice.