Pulsed magnetic field gradients generated by gradient coils are widely used in signal location in magnetic resonance imaging (MRI). However, gradient coils can also induce eddy currents in final magnetic field in the nearby conducting structures which lead to distortion and artifact in images, misguiding clinical diagnosis. We tried in our laboratory to measure the magnetic field of gradient-induced eddy current in 1.5 T superconducting magnetic resonance imaging device; and extracted key parameters including amplitude and time constant of exponential terms according to inductance-resistance series mathematical module. These parameters of both self-induced component and crossing component are useful to design digital filters to implement pulse pre-emphasize to reshape the waveform. A measure device that is a basement equipped with phantoms and receiving coils was designed and placed in the isocenter of the magnetic field. By applying testing sequence, contrast experiments were carried out in a superconducting magnet before and after eddy current compensation. Sets of one dimension signal were obtained as raw data to calculate gradient-induced eddy currents. Curve fitting by least squares method was also done to match inductance-resistance series module. The results also illustrated that pulse pre-emphasize measurement with digital filter was correct and effective in reducing eddy current effect. Pre-emphasize waveform was developed based on system function. The usefulness of pre-emphasize measurement in reducing eddy current was confirmed and the improvement was also presented. All these are valuable for reducing artifact in magnetic resonance imaging device.
ObjectiveTo help junior radiologists and surgeons better interpret MRI images of rectal cancer.MethodThe guidelines, expert consensus and research progress on the application of MR imaging in rectal cancer in recent years were reviewed.ResultsRectal MR had the ability to accurately evaluate a number of important findings that may impact patient’ management, including distance of the tumor to the mesorectal fascia, presence of extramural vascular invasion, and presence of lymph nodes.ConclusionsRectal MRI is an important basis for clinical staging and multidisciplinary diagnosis and treatment of rectal cancer. Surgeons and radiologists must master the key imaging anatomical basis and clinical practice points in order to accurately interpret the image information of MRI in rectal cancer.
ObjectiveTo explore the value of magnetic resonance diffusion weighted imaging (DWI) in preoperative Bismuth-Corlette classification of hilar cholangiocarcinoma (HCCA). MethodsA total of 53 HCCA patients confirmed by postoperative pathology were retrospectively included. The accuracy of two sequence combinations, namely dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) + magnetic resonance cholangiopancreatography (MRCP) and DCE-MRI + MRCP + DWI, in evaluating the longitudinally involved bile duct segments and Bismuth-Corlette classification of HCCA was compared. Additionally, the correlation between apparent diffusion coefficient (ADC) values and tumor Bismuth-Corlette classification as well as degree of differentiation was analyzed. ResultsThere were 318 bile duct segments in 53 HCCA patients. The accuracy rate of DCE-MRI + MRCP was 93.7% (298/318), the sensitivity was 91.5% (161/176), and the specificity was 96.5% (137/142). The accuracy rate of DCE-MRI + MRCP + DWI was 96.5% (307/318), the sensitivity was 96.0% (169/176), and the specificity was 97.2% (138/142). Receiver operating characteristic (ROC) curve analysis showed that the area under the ROC curve (AUC) of DCE-MRI + MRCP + DWI was 0.966 [95%CI (0.940, 0.983), P＜0.001], and its diagnostic efficacy was superior to that of DCE-MRI + MRCP [AUC=0.940, 95%CI (0.908, 0.963), P＜0.001]. The DeLong test indicated a statistically significant difference in AUC between the two sequences (Z=2.633, P＜0.01). The accuracy rates of preoperative Bismuth-Corlette classification of HCCA evaluated by DCE-MRI + MRCP and DCE-MRI + MRCP + DWI were 86.8% (46/53) and 94.3% (50/53), respectively. After adding the DWI sequence, the consistency between Bismuth-Corlette classification results and surgical pathological classification results (Kappa=0.922, P<0.001) was higher than that of DCE-MRI + MRCP sequence (Kappa=0.820, P<0.001), with a statistically significant difference (χ2=160.370, P<0.001). In addition, the ADC value of HCCA was negatively correlated with tumordegree of differentiation (rs=–0.524, P<0.001), but had no significant correlation with its Bismuth-Corlette classification (rs=–0.058, P=0.682). ConclusionsDCE-MRI + MRCP + DWI sequence can effectively improve the accuracy in preoperative evaluation of the involvement of bile duct segments and Bismuth-Corlette classification of HCCA, which provides guidance for precise preoperative surgical planning in clinical practice. In addition, the ADC value can provide additional information required for non-invasive preoperative prediction of the prognosis of HCCA patients.
ObjectiveTo evaluate the diagnostic value of CT, MRI, and magnetic resonance cholangiopancreatography (MRCP) in the localization and qualitative diagnosis of biliary obstruction.MethodsA total of 80 patients with biliary obstruction in our hospital from January 2018 to June 2020 were retrospectively collected. The patients were all examined by CT, MRI, and MRCP. The imaging images of all patients were interpreted by two radiologists with more than 5 years of working experience. Taking the results of operation and histopathology as the gold standard, the diagnostic value of CT, MRI+MRCP, CT+MRI+MRCP in the localization and qualitative diagnosis of biliary obstruction lesions were evaluated.ResultsCompared with the location results of surgery and histopathology, the coincidence rates of CT+MRI+MRCP and MRI+MRCP were higher than that of CT (P<0.05), but there was no significant difference between CT+MRI+MRCP and MRI+MRCP (P>0.05); compared with the benign and malignant results of surgery and histopathology, the coincidence rates of CT, CT+MRI+MRCP and MRI+MRCP were close, and there was no statistical significance among them (P>0.05).ConclusionsMRI+MRCP and CT+MRI+MRCP have the same value in the localization and qualitative diagnosis of biliary obstruction. However, MRI+MRCP have the advantages ofnon-radiation or contrast media, it is more suitable for patients who are worried about the impact of radiation, have contrast media allergy or renal insufficiency.
ObjectiveTo summarize the value of imaging in the evaluation of non-surgical therapy for pancreatic cancer.MethodThe relevant literatures about imaging evaluation of non-surgical therapy for pancreatic cancer were collected to make an review.ResultsAt present, most of the imaging evaluation of non-surgical therapy for pancreatic cancer were based on the assessment of morphological characteristics of tumors, such as contrast-enhanced CT and MRI. However, only morphological changes of tumors could not accurately evaluate the response of pancreatic cancer after non-surgical treatment. A few studies had explored the value of functional imaging and artificial intelligence.ConclusionsNon-surgical therapy provides new treatment opportunities for unresectable pancreatic cancer, especially the proposed of neoadjuvant therapy, which provides the possibility of operation for patients with advanced pancreatic cancer. More imaging indicators with stronger objectivity, higher accuracy, and wider universality need to be improved and developed in the future.
ObjectiveTo explore performances of functional magnetic resonance imaging (MRI) in evaluation of hepatic warm ischemia-reperfusion injury.MethodThe relative references about the principle of functional MRI and its application in the assessment of hepatic warm ischemia-reperfusion injury were reviewed and summarized.ResultsThe main functional MRI techniques for the assessment of hepatic warm ischemia-reperfusion injury included the diffusion weighted imaging (DWI), intravoxel incoherent motion (IVIM), diffusion tensor imaging (DTI), blood oxygen level dependent (BOLD), dynamic contrast enhancement MRI (DCE-MRI), and T2 mapping, etc.. These techniques mainly used in the animal model with hepatic warm ischemia-reperfusion injury currently.ConclusionsFrom current results of researches of animal models, functional MRI is a non-invasive tool to accurately and quantitatively evaluate microscopic information changes of liver tissue in vivo. It can provide a useful information on further understanding of mechanism and prognosis of hepatic warm ischemia-reperfusion injury. With development of donation after cardiac death, functional MRI will play a more important role in evaluation of hepatic warm ischemia-reperfusion injury.
ObjectiveTo investigate the imaging characteristics of gallium-68 labeled fibroblast activation protein inhibitor (68Ga-FAPI)-positron emission tomography/magnetic resonance (PET/MR) imaging in patients with liver fibrosis or liver tumor. MethodsThirteen patients with suspected liver tumor who underwent 68Ga-FAPI-PET/MR examination from May 2020 to April 2021 were retrospectively analyzed. Maximum standard uptake value (SUVmax) was investigated. All patients underwent liver surgery or biopsy. Scheuer scoring system was used to evaluate the liver fibrosis. The imaging characteristics of liver fibrosis or liver tumor were analyzed. ResultsThe liver fibrosis was confirmed in 6 patients, including 1 case of S2, 2 cases of S3, and 3 cases of S4. Among them, 4 patients had increased uptake of 68Ga-FAPI, with patchy or diffuse abnormal concentration of liver, and the SUVmax was 7.9±3.1. The liver imaging of the other 2 patients with liver fibrosis showed no obvious radioactive concentration. In addition, 2 patients were diagnosed with hepatocellular carcinoma, its SUVmax was 7.2 and 6.1; 1 patient was diagnosed with hepatobiliary duct carcinoma and its SUVmax was 13.8. Moreover, increased uptake of 68Ga-FAPI was observed in 4 patients with metastatic liver cancer, with SUVmax of 6.7±2.7. ConclusionBoth liver fibrosis and liver tumor are suitable for 68Ga-FAPI-PET/MR examination, which have different imaging characteristics.
Dilated cardiomyopathy (DCM) is a highly prevalent disease which has multiple clinical manifestations and pathological features. With the characteristics of multi-sequence and multi-parameter, cardiac magnetic resonance imaging (MRI) can accurately assess the morphology, function and tissue characterization of heart, and provide comprehensive information for diagnosis of DCM. This review focuses on the sequences and clinical applications of MRI evaluation in DCM in order to provide additional information for clinical diagnosis, treatment and prognosis.
Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) may provide more information in diagnosis of malignant tumor compared to conventional magnetic resonance imaging (MRI). Nowadays, in order to utilize the information expediently and efficiently, many researchers are aiming at the development of computer-aided diagnosis (CAD) of malignant tumor based on DCE-MRI. In this review, we survey the research in this field and summarize the literature in four parts, i.e. ① image preprocessing——noise reduction and image registration; ② region of interests (ROI) segmentation; ③ feature extraction——exploring the image characteristics by analyzing the ROI quantitatively; ④ tumor lesion recognition and classification——distinguishing and classifying tumor lesions by learning the features of ROI. We summarize the application of CAD techniques of DCE-MRI for cancer diagnosis and, finally, give some discussion on how to improve the efficiency of CAD in the future research.
Objective To summarize manifestation, imaging characteristics, and treatment of hepatic focal nodular hyperplasia (FNH). Methods From January 2007 to December 2016, the patients pathologically confirmed hepatic FNH were included in this study. The clinical features and imaging characteristics were analyzed retrospectively. Results Twenty-two cases were pathologically diagnosed as hepatic FNH with an age of (36.8±11.2) years (range from 20 to 61 years). Ten were males and 12 were females. Three patients had abdominal pain and 19 patients had no symptoms. The diameter of the lesions was (4.16±1.92) cm (range from 1.0 to 7.8 cm) and approximately 9 (40.9%) lesions were more than 5.0 cm. The diagnosis rates of CT and MRI were 64.70% (11/17) and 84.21% (16/19), respectively. All the patients underwent hepatectomy successfully and recovered without severe complications. No recurrence and metastasis happened during following-up of 1–103 months. Conclusions Hepatic FNH is more common in young patients and has no typical symptoms. MRI is useful in diagnosis of hepatic FNH.