Time-dependent diffusion magnetic resonance imaging:measurement,modeling,and applications

Increasingly,attention is being directed towards time-dependent diffusion magnetic resonance imaging(TDDMRI),a method that reveals time-related changes in the diffusional behavior of water molecules in biological tissues,thereby enabling us to probe related microstructure events.With ongoing improvements in hardware and advanced pulse sequences,significant progress has been made in applying TDDMRI to clinical research.The development of accurate mathematical models and computational methods has bolstered theoretical support for TDDMRI and elevated our understanding of molecular diffusion.In this review,we introduce the concept and basic physics of TDDMRI,and then focus on the measurement strategies and modeling approaches in short-and long-diffusion-time domains.Finally,we discuss the challenges in this field,including the requirement for efficient scanning and data processing technologies,the development of more precise models depicting time-dependent molecular diffusion,and critical clinical applications.

Value of multiple models of diffusion-weighted imaging to predict hepatic lymph node metastases in colorectal liver metastases patients

BACKGROUND About 10%-31% of colorectal liver metastases(CRLM)patients would concomitantly show hepatic lymph node metastases(LNM),which was considered as sign of poor biological behavior and a relative contraindication for liver resection.Up to now,there’s still lack of reliable preoperative methods to assess the status of hepatic lymph nodes in patients with CRLM,except for pathology examination of lymph node after resection.AIM To compare the ability of mono-exponential,bi-exponential,and stretchedexponential diffusion-weighted imaging(DWI)models in distinguishing between benign and malignant hepatic lymph nodes in patients with CRLM who received neoadjuvant chemotherapy prior to surgery.METHODS In this retrospective study,97 CRLM patients with pathologically confirmed hepatic lymph node status underwent magnetic resonance imaging,including DWI with ten b values before and after chemotherapy.Various parameters,such as the apparent diffusion coefficient from the mono-exponential model,and the true diffusion coefficient,the pseudo-diffusion coefficient,and the perfusion fraction derived from the intravoxel incoherent motion model,along with distributed diffusion coefficient(DDC)andαfrom the stretched-exponential model(SEM),were measured.The parameters before and after chemotherapy were compared between positive and negative hepatic lymph node groups.A nomogram was constructed to predict the hepatic lymph node status.The reliability and agreement of the measurements were assessed using the coefficient of variation and intraclass correlation coefficient.RESULTS Multivariate analysis revealed that the pre-treatment DDC value and the short diameter of the largest lymph node after treatment were independent predictors of metastatic hepatic lymph nodes.A nomogram combining these two factors demonstrated excellent performance in distinguishing between benign and malignant lymph nodes in CRLM patients,with an area under the curve of 0.873.Furthermore,parameters from SEM showed substantial repeatability.CONCLUSION The developed nomogram,incorporating the pre-treatment DDC and the short axis of the largest lymph node,can be used to predict the presence of hepatic LNM in CRLM patients undergoing chemotherapy before surgery.This nomogram was proven to be more valuable,exhibiting superior diagnostic performance compared to quantitative parameters derived from multiple b values of DWI.The nomogram can serve as a preoperative assessment tool for determining the status of hepatic lymph nodes and aiding in the decision-making process for surgical treatment in CRLM patients.

Role of diffusion-weighted magnetic resonance imaging in the diagnosis of extrahepatic cholangiocarcinoma

AIM: To determine the clinical value of diffusion-weight- ed imaging (DWI) for the diagnosis of extrahepatic cholangiocarcinoma (EHCC) by comparing the diagnostic sensitivity of DWI and magnetic resonance cholan-giopancreatography (MRCP). METHODS: Magnetic resonance imaging examination was performed in 56 patients with suspected EHCC. T1- weighted imaging, T2-weighted imaging, MRCP and DWI sequence, DWI using single-shot spin-echo echoplanar imaging sequence with different b values (100, 300, 500, 800 and 1000 s/mm2), were performed. All cases were further confirmed by surgery or histopathological diagnosis. Two radiologists jointly performed the analysis of the DWI and MRCP images. Apparent diffusion coefficient (ADC) value and signal-noise ratio were calculated for EHCC. Sensitivity, specificity, accuracy, positive predictive value and negative predictive value were tested using DWI with a b value of 500 s/mm2 and MRCP images, respectively. RESULTS: Histopathological diagnosis confirmed that among the 56 cases, 35 were EHCC (20 hilar and 15 distal extrahepatic), 16 were cholangitis, and 5 were cal-culus of bile duct. Thirty-three out of the 35 EHCC cases were detected by DWI. EHCC exhibited differential levels of high signal intensity in DWI and low signal intensity in the ADC map. The mean value for ADC was (1.31 ± 0.29) × 10-3 mm2/s. The detection rate of EHCC was significantly higher by DWI (94.3%) than by MRCP (74.3%) (P < 0.05). There was a significant difference in sensitivity (94.3% vs 74.3%), specificity (100% vs 71.4%), accu- racy (96.4% vs 73.2%), positive predictive value (100% vs 81.3%), and negative predictive value (91.3% vs 62.5%) between DWI and MRCP in diagnosing EHCC. CONCLUSION: DWI has a high sensitivity for the detection of EHCC as it shows the EHCC lesion more unambiguously than MRCP does. DWI can also provide additional clinically important information in EHCC patients when added to routine bile duct MR imaging protocols.

Diffusion-weighted magnetic resonance imaging in management of bladder cancer, particularly with multimodal bladder-sparing strategy

Bladder-sparing strategy for muscle-invasive bladdercancer(MIBC) is increasingly demanded instead ofradical cystectomy plus urinary diversion. Multimodaltherapeutic approaches consisting of transurethralresection, chemotherapy, radiotherapy and/or partialcystectomy improve patients' quality of life by preserv-ing their native bladder and sexual function withoutcompromising oncological outcomes. Because a favor-able response to chemoradiotherapy(CRT) is a prereq-uisite for successful bladder preservation, predictingand monitoring therapeutic response is an essentialpart of this approach. Diffusion-weighted magneticresonance imaging(DW-MRI) is a functional imagingtechnique increasingly applied to various types of can-cers. Contrast in this imaging technique derives fromdifferences in the motion of water molecules among tissues and this information is useful in assessing the biological behavior of cancers. Promising results in pre-dicting and monitoring the response to CRT have been reported in several types of cancers. Recently, growing evidence has emerged showing that DW-MRI can serve as an imaging biomarker in the management of blad-der cancer. The qualitative analysis of DW-MRI can be applied to detecting cancerous lesion and monitoring the response to CRT. Furthermore, the potential role of quantitative analysis by evaluating apparent diffu-sion coefficient values has been shown in character-izing bladder cancer for biological aggressiveness and sensitivity to CRT. DW-MRI is a potentially useful tool for the management of bladder cancer, particularly in multimodal bladder-sparing approaches for MIBC.

Clinical Value of Whole-body Magnetic Resonance Diffusion Weighted Imaging on Detection of Malignant Metastases

Objective To evaluate the value of whole-body diffusion weighted imaging （WB-DWI） on detection of malignant metastasis. Methods Forty-six patients with malignant tumors underwent WB-DWI examinations between April 2007 and August 2007 in our hospital. Before WB-DWI examination, the primary cancers of all the patients were confirmed by pathology, and the TNM-stage was assessed with conventional magnetic resonance imaging （MRI） or computed tomography （CT）. WB-DWI was performed using short TI inversion recovery echo-planar imaging （STIR-EPI） sequence. Abnormal high signal intensities on WB-DWI were considered as metastases. The results of WB-DWI were compared with other imaging modalities. For the assessment of the diagnostic capability of WB-DWI, WB-DWI were compared with CT for demonstrating mediastinal lymph node metastases and lung metastases, and with conventional MRI for demonstrating metastases in other locations. Results WB-DWI demonstrated 143 focuses, 14 routine imaging. The number of bone metastases depicted of which were diagnosed to be benign lesions in on WB-DWI and routine imaging was 85 and 86; lymph node metastases was 17 and 18; liver metastases was 14 and 14; lung metastases was 4 and 8; and brain metastases was 6 and 8, respectively. WB-DWI failed to detect 12 metastatic lesions including 3 osteoplastic bone metastases, 4 lung metastases, 3 mediastinal lymph node metastases, and 2 brain metastases Four metastatic lesions including 2 deltopectoral lymph nodes and 2 rib metastases were detected with WB-DWI alone, all of which evolved greatly during clinical follow-up for more than 6 months. WB-DWI had higher detection rates for metastatic lesions in liver, bone, and lymph nodes than those in lung and brain （ X^2=30, P〈0.001）. Conclusions WB-DWI could detect most of metastatic lesions that were diagnosed with conventional MRI and CT. The limitations of WB-DWI might be had high false-positive rate and low efficiency in detecting mecliastinal lymph node, brain, and lung metastases.

Magnetic resonance-based total liver volume and magnetic resonance-diffusion weighted imaging for staging liver fibrosis in mini-pigs

AIM:To determine whether and how magnetic resonance imaging(MRI)-based total liver volume(TLV) and diffusion weighted imaging(DWI) could predict liver fibrosis.METHODS:Sixteen experimental mature mini-pigs(6 males,10 females),weighing between 20.0 and 24.0 kg were prospectively used to model liver fibrosis induced by intraperitoneal injection of 40% CCl4 dissolved in fat emulsion twice a week for 16 wk,and by feeding 40% CCl4 mixed with maize flour twice daily for the subsequent 5 wk.All the survival animals underwent percutaneous liver biopsy and DWI using b = 300,500 and 800 s/mm2 followed by abdominal gadolinium-enhanced MRI at the 0,5th,9th,16th and 21st weekend after beginning of the modeling.TLV was obtained on enhanced MRI,and apparent diffusion coefficient(ADC) was obtained on DWI.Hepatic tissue specimens were stained with hematoxylin and Masson' s trichrome staining for staging liver fibrosis.Pathological specimens were scored using the human METAVIR classification system.Statistical analyses were performed to determine whether and how the TLV and ADC could be used to predict the stage of liver fibrosis.RESULTS:TLV increased from stage 0 to 2 and decreased from stage 3(r = 0.211;P < 0.001).There was a difference in TLV between stage 0-1 and 2-4(P = 0.03) whereas no difference between stage 0-2 and 3-4(P = 0.71).TLV could predict stage ≥ 2 [area under receiver operating characteristic curve(AUC) = 0.682].There was a decrease in ADC values with increasing stage of fibrosis for b = 300,500 and 800 s/mm2(r =-0.418,-0.535 and-0.622,respectively;all P < 0.001).Differences were found between stage 0-1 and 2-4 in ADC values for b = 300,500 and 800 s/mm2,and between stage 0-2 and 3-4 for b = 500 or 800 s/mm2(all P < 0.05).For predicting stage ≥ 2 and ≥ 3,AUC was 0.803 and 0.847 for b = 500 s/mm2,and 0.848 and 0.887 for b = 800 s/mm2,respectively.CONCLUSION:ADC for b = 500 or 800 s/mm2 could be better than TLV and ADC for b = 300 s/mm2 to pre-dict fibrosis stage ≥ 2 or ≥ 3.

Cerebellum and neurodegenerative diseases:Beyond conventional magnetic resonance imaging

The cerebellum plays a key role in movement control and in cognition and cerebellar involvement is described in several neurodegenerative diseases.While conventional magnetic resonance imaging(MRI) is widely used for brain and cerebellar morphologic evaluation,advanced MRI techniques allow the investigation of cerebellar microstructural and functional characteristics.Volumetry,voxel-based morphometry,diffusion MRI based fiber tractography,resting state and task related functional MRI,perfusion,and proton MR spectroscopy are among the most common techniques applied to the study of cerebellum.In the present review,after providing a brief description of each technique's advantages and limitations,we focus on their application to the study of cerebellar injury in major neurodegenerative diseases,such as multiple sclerosis,Parkinson's and Alzheimer's disease and hereditary ataxia.A brief introduction to the pathological substrate of cerebellar involvement is provided for each disease,followed by the review of MRI studies exploring structural and functional cerebellar abnormalities and by a discussion of the clinical relevance of MRI measures of cerebellar damage in terms of both clinical status and cognitive performance.

EFFECT OF POSITIVE-INDEFINITE MATRIX ON MAGNETIC RESONANCE DIFFUSION TENSOR-DERIVED PARAMETERS

To evaluate the effect of the positive-indefinite matrix on the diffusion tensor-derived parameters, a modified algorithm is proposed for calculating these parameters. Magnetic resonance （MR） diffusion tensor images of five healthy volunteers are collected. The diffusion sensitive gradient magnetic fields are applied along 25 directions and the diffusion weighting value is 1 000 s/mm^2. Many positive-indefinite diffusion tensors can be found in the white matter area, such as the genu and the splenium of corpus callosum. Due to the positive-indefinite matrix, the mean diffusivity （MD） and the fractional anisotropy （FA） are under-estimated and over-estimated by using the conventional algorithm. Thus, the conventional algorithm is modified by using the absolute values of all eigenvalues. Results show that both the robustness and the reliability for deriving these parameters are improved by the modified algorithm.

APPLICATION OF WHOLE BODY DIFFUSION WEIGHTED MR IMAGING FOR DIAGNOSIS AND STAGING OF MALIGNANT LYMPHOMA

Objective To evaluate the clinical impact of whole body diffusion weighted imaging （WB-DWI） on diagnosis and staging of malignant lymphoma. Methods Thirty-one patients with suspected lymphadenopathy were enrolled. WB-DWI was performed by using short TI inversion recovery echo-planar imaging sequence with free breathing and built-in body coil. Axial T2- weighted imaging images of the same location were used as reference. The results of WB-DWI were compared with pathological results and other imaging modalities. The mean apparent diffusion coefficient （ADC） values of different kinds of lymph nodes were compared. Results WB-DWI was positive in all 18 cases with lymphoma, 5 cases with metastatic lymph nodes and 4 of 8 eases with benign lymphadenopathy. The mean ADC value of lymphomatous, metastatic and benign lymph nodes was （0.87 ± 0.17） × 10^3, （0.98± 0.09） × 10^3 and （1.20 ± 0.10） × 10^3 mm^2/s. There was significant difference in ADC value between benign lymph nodes and other two groups （P 〈 0.01）. The sensitivity, specificity and accuracy of WB-DWI in diagnosis of lymphoma were 100% （18/18）, 30.8% （4/13） and 71.0% （22/31）. When an ADC value of 1.08 × 10^-3 mm^2/s was used as the threshold value for differentiating malignant from benign lymph nodes, the best results were obtained with sensitivity of 87.8% and specificity of 91.3%. Sixteen of eighteen cases （88.9%） of lymphoma were accurately staged in accordance with clinical staging. Conclusions WB-DWI is a sensitive, but less specific technique for diagnosis of lymphoma. It is difficult to differentiate lymphnmatous from metastatic lymph nodes using WB-DWI. However, it is a valuable imaging modality for staging of patients with malignant lymphoma.

MR DIFFUSION WEIGHTED IMAGING FOR EVALUATION OF RADIOTHERAPEUTIC EFFECTS ON RABBIT VX2 TUMOR MODEL

Objective To investigate the feasibility of magnetic resonance （MR） diffusion weighted imaging （DWI） for evaluation of radiotherapeutic effects on rabbit VX2 tumor model. Methods Sixteen New Zealand white rabbits received a subcutaneous implantation of VX2 tumor cell suspension 0.5 mL （4× 10^7 ceUs/mL） in their right thighs to set up tumor model. And 2 weeks later they were randomly divided into therapy group （Group T, n = 10） and control group （Group C, n = 6）. Group T received radiotherapy at a single dose of 10 Gy. MR imaging （MRI） scan including short TI inversion recovery echo-planar imaging DWI, T1-weighted imaging （T1WI） and T2-weighted imaging （T2WI） sequences were performed 1 day prior to as well as 1 day, 2 days, 3 days and 7 days after radiotherapy. Group C received only MRI scan at the same time points without any treatment. MRI appearance on T2WI, TlWI, and DWI images was compared and tumor volume was calculated. Apparent diffusion coefficient （ADC） values of the tumor were evaluated in all cases. HE staining was used for pathological study. Results Necrosis （n = 8） and hemorrhage （n = 2） were seen gradually on T2WI and T1WI images of Group T after time point of day 2 after irradiation. In Group C, no obvious necrosis was found until day 7. There was no significant difference in tumor volume between the two groups before radiotherapy. After radiotherapy, tumors in Group T showed a gradual growth but not as obvious as Group C. There was a significant difference in tumor volume between the two groups from day 2 on （P 〈 0.05）. ADC value changed dramatically fight from the 1st day after radiotherapy in Group T [（0.99 ± 0.15） ×10^-3 mm^2/s for 1 day before radiotherapy, （1.23 ± 0.08） ×10^-3 , （1.45 ± 0.07） ×10^-3 , （1.63 ± 0.06） ×10^-3 , and （2.02 ± 0.18） ×10^-3 mm^2 for day 1, 2, 3, and 7]; and ADC value had no significant changes after radiotherapy in Group C except day 7 [（1.07±0.08） ×10^-3 mm^2 for 1 day before radiotherapy, （1.03 ± 0.04）×10^-3 , （1.05 ± 0.02）×10^-3 , （1.05 ± 0.05） ×10^-3 , and （0.95 ± 0.07） ×10^-3 mm^2 for day 1, 2, 3, and 7]. There was significant difference in ADC value between the two groups for each time point after radiotherapy （P 〈 0.01）. Pathological study showed that the number of viable tumor cells in Group T decreased 1 day after radiotherapy, and the inflammatory cell infiltration was marked and almost all viable tumor cells disappeared by day 7 after radiotherapy. Conclusions DWI is a new promising technique for monitoring radiotherapy outcomes. ADC value may give a prior clue on physiological changes of radiotherapy before routine MRI could tell.

Progress of intravoxel incoherent motion diffusion-weighted imaging in liver diseases

Traditional magnetic resonance(MR)diffusion-weighted imaging(DWI)uses a single exponential model to obtain the apparent diffusion coefficient to quantitatively reflect the diffusion motion of water molecules in living tissues,but it is affected by blood perfusion.Intravoxel incoherent motion(IVIM)-DWI utilizes a double-exponential model to obtain information on pure water molecule diffusion and microcirculatory perfusion-related diffusion,which compensates for the insufficiency of traditional DWI.In recent years,research on the application of IVIM-DWI in the diagnosis and treatment of hepatic diseases has gradually increased and has achieved considerable progress.This study mainly reviews the basic principles of IVIM-DWI and related research progress in the diagnosis and treatment of hepatic diseases.

Verifying the hypothesis of disconnection syndrome in patients with conduction aphasia using diffusion tensor imaging

BACKGROUND： It is thought in disconnection theory that connection of anterior and posterior language function areas, i.e. the lesion of arcuate fasciculus causes conduction aphasia. OBJECTIVE： To verify the theory of disconnection elicited by repetition disorder in patients with conduction aphasia by comparing the characteristics of diffusion tensor imaging between healthy persons and patients with conduction aphasia. DESIGN： Case-control observation. SETTING： Department of Neurology, Hongqi Hospital Affiliated to Mudanjiang Medical College. PARTICIPANTS： Five male patients with cerebral infarction-involved arcuate fasciculus conduction aphasia, averaged （43±2） years, who hospitalized in the Department of Neurology, Hongqi Hospital Affiliated to Mudanjiang Medical College from February 2004 to February 2005 were involved in this experiment. The involved patients were all confirmed as cerebral infarction by skull CT and MRI, and met the diagnosis criteria revised in 1995 4^th Cerebrovascular Conference. They were examined by the method of Aphasia Battery of Chinese （ABC） edited by Surong Gao. The results were poorer than auditory comprehension disproportionately, and consistented with the mode of conduction aphasia. Another 5 male healthy persons, averaged （43 ± 1 ） years, who were physicians receiving further training in the Department of Neurology, Beijing Tiantan Hospital were also involved in this experiment. Informed consents of detected items were obtained from all the subjects. METHODS： All the subjects were performed handedness assessment with assessment criteria of handedness formulated by Department of Neurology, First Hospital Affiliated to Beijing Medical University. Arcuate fasciculus of involved patients and health controls were analyzed with diffusion tensor imaging （DTI） and divided into 3 parts （anterior, middle and posterior segments） for determining FA value （mean value was obtained after three times of measurements）, and a comparison of FA value was made between two sides. MAIN OUTCOME MEASURES： Analysis results of arcuate fasciculus DTI of healthy controls and patients with conduction aphasia. RESULTS： Five patients with conduction aphasia and 5 healthy controls participated in the final analysis. ①All the subjects were right-handedness.② The left FA value of anterior, middle and posterior segments of arcuate fasciculus was larger than the right one in most normal volunteers, i.e. arcuate fasciculus with normal function on the left side was more than that on the right side. Because the amount of healthy controls was small, so positive conclusion has not been obtained, and only above-mentioned tendency was demonstrated. Healthy controls had good bilateral arcuate fasciculus; Three patients with conduction aphasia presented left FA value of anterior segment of arcuate fasciculus smaller than the right one, and two patients presented the left FA value larger than the right one. Four patients presented the left FA value of middle segment of arcuate fasciculus smaller than the right one, and one patient presented the left FA value larger than the right one, i.e. middle segment of arcuate fasciculus of 5 patients with conduction aphasia was all involved in at different degrees. Four patients with conduction aphasia presented the left FA value of posterior segment of arcuate fasciculus smaller than the right one, and one patient presented the left FA value larger than the right one, i.e. posterior segment of arcuate fasciculus of 5 patients was all injured at different degrees. CONCLUSION： Arcuate fasciculus of patients with conduction aphasia all is involved in at different degrees, which verifies the theory of disconnection of repetition disorder in patients with conduction aphasia.

COMPARISON OF OPTICAL POLARIMETRY AND DIFFUSION TENSOR MR IMAGING FOR ASSESSING MYOCARDIAL ANISOTROPY

We have recently proposed an optical method for assessing heart structure that uses polarized light measurement of birefringence as an indicator of tissue anisotropy.The highly aligned nature of healthy cardiac muscle tissue has a detectable effect on the polarization of light,resulting in a measurable phase shift(“retardance”).When this organized tissue structure is perturbed,for example after cardiac infarction(heart attack),scar tissue containing disorganized collagen is formed,causing a decrease in the measured retardance values.However,these are dependent not only on tissue anisotropy,but also on the angle between the tissue’s optical anisotropy direction and the beam interrogating the sample.To remove this experimental ambiguity,we present a method that interrogates the sample at two different incident beam angles,thus yielding enough information to uniquely determine the true magnitude and orientation of the tissue optical anisotropy.We use an infarcted porcine heart model to compare these polarimetryderived anisotropy metrics with those obtained with diffusion tensor magnetic resonance imaging(DT-MRI).The latter yields the anisotropy and the direction of tissue water diffusivity,providing an independent measure of tissue anisotropy.The optical and MR results are thus directly compared in a common ex vivo biological model of interest,yielding reasonable agreement but also highlighting some technique-specific differences.

Evaluating transcatheter arterial chemoembolization for primary hepatic cancer by magnetic resonance diffusion-weighted imaging

Hepatic cancer is associated with very high mortality and morbidity, and the world＇s highest morbidity and mortality rates for this malignant tumor are found in China. Each year, the number of people who die of hepatic cancer in China amounts for 53% of the world total. Although resection is the first-choice treatment for hepatic cancer, only 20%-30% of patients have the opportunity to undergo resection. Transcatheter arterial chemoembolization （TACE） is a typical intervention therapy. Its advantages include minimal trauma, precise efficacy,

Neurite Orientation Dispersion and Density Imaging of Rat Brain Microstructural Changes due to Middle Cerebral Artery Occlusion at a 3T MRI

The purpose of this work was to demonstrate the feasibility of neurite orientation dispersion and density imaging(NODDI)in characterizing the brain tissue microstructural changes of middle cerebral artery occlusion(MCAO)in rats at 3T MRI,and to validate NODDI metrics with histology.A multi-shell diffusion MRI protocol was performed on 11 MCAO rats and 10 control rats at different post-operation time points of 0.5,2,6,12,24 and 72 h.NODDI orientation dispersion index(ODI)and intracellular volume fraction(V_(ic))metrics were compared between MCAO group and control group.The evolution of NODDI metrics was characterized and validated by histology.Infarction was consistent with significantly increased ODI and V_(ic)in comparison to control tissues at all time points(P<0.001).Lesion ODI increased gradually from 0.5 to 72 h,while its V_(ic)showed a more complicated and fluctuated evolution.ODI and V_(ic)were significantly different between hyperacute and acute stroke periods(P<0.001).The NODDI metrics were found to be consistent with the histological findings.In conclusion,NODDI can reflect microstructural changes of brain tissues in MCAO rats at 3T MRI and the metrics are consistent with histology.This study helps to prepare NODDI for the diagnosis and management of ischemic stroke in translational research and clinical practice.

Magnetic resonance diffusion-weighted imaging in the diagnosis of diffuse liver diseases in rats

Background The diagnosis of diffuse hepatic lesions in early stage is a tough task at any time for clinical conventional imaging. Magnetic resonance diffusion-weighted imaging (MR DWI) can detect the changes of tissue structure at molecular level. This study was designed to determine the value of DWI in the diagnosis of diffuse liver lesions in early stage. Methods Diffuse liver lesions were induced by diethylnitrosamine in 42 rats of test group. Fourteen rats in control group were fed with pure water. Dynamic changes of MR DWI were observed every week in both groups during the early stage of diffuse liver lesions (1 to 12 weeks after drug administration in the test group). Apparent diffusion coefficient (ADC) values of liver parenchyma in different stages and pathologic changes were analyzed. Results The process of diffuse hepatic lesions in the test group was classified into three stages according to pathological changes, namely hepatitis, hepatic fibrosis and cirrhosis. No obvious morphological changes were shown by conventional imaging in both groups during this stage. But MR DWI demonstrated heterogeneous signal changes in early stage of hepatic cirrhosis in the test group. No significant change of ADC values was found in the control group between different weeks ( P >0.05). The ADC values of the test group declined from the fifth week, and after the tenth week the ADC values were significantly different between the test and control groups at gradient factor (b) value 300 sec/mm 2 ( P <0.05). At b value 600 and 1000 sec/mm 2, significant difference was seen between the two groups from the sixth week onward. The range of ADC value of the groups was (1.7-0.9)±(0.40-0.04) mm 2/sec (b=600) and (1.38-0.75)±(0.07-0.35) mm 2/sec (b=1000), respectively. Dominant pathological changes included swelled hepatocytes within 1 to 4 weeks after the administration of diethylnitrosamine in the test group, hyperplasia of fibrous tissues in 5-8 weeks and formation of cirrhotic nodules in 9-12 weeks. Conclusions MR functional DWI could detect diffuse liver lesions earlier than conventional morphological imaging. ADC value as a marker for early diagnosis of diffuse liver lesions could also be used to inspect changes of the lesions

Diffusion-weighted MRI in abdominal oncology:Clinical applications

Diffusion-weighted magnetic resonance imaging(DWI) provides image contrast that is different from that obtained by conventional magnetic resonance techniques.Although previously,DWI has been used to evaluate various diseases of the central nervous system,several technical advances have expanded the clinical applications of DWI beyond the central nervous system.As a result,many reports have been published on the use of DWI in abdominal diseases.Particularly,abdominal DWI has now being focused on evaluation of patients with abdominal cancer.DWI can be used for pretreatment tumor detection,characterization including predicting tumor response to therapy,monitoring tumor response during therapy,and follow-up study after treatment to detect possible tumor recurrence.

Magnetic resonance diffusion tensor imaging with fluorescein sodium dyeing for surgery of gliomas in brain motor functional areas

Background Tumor surgery in brain motor functional areas remains challenging. Novel techniques are being developed to gain maximal and safe resection for brain tumor surgery. Herein, we assessed the magnetic resonance diffusion tensor imaging （MR-DTI） and fluorescein sodium dyeing （FLS） guiding technique for surgery of glioma located in brain motor functional areas. Methods Totally 83 patients were enrolled according to our inclusion and exclusion criteria （56 patients in experimental group, 27 patients in control group）. In the experimental group, the surgical approach was designed by DTI imaging, which showed the relationship between the tumor and motor tract. The range of resection in the operation was determined using the FLS-stained area, which recognized the tumor and its infiltrated tissue. The traditional routine method was used in the control group. Postoperatively, all patients underwent enhanced brain MRI within 72 hours to ascertain the extent of resection. Patients were followed in our outpatient clinic over 6-24 months. Neurological deficits and Karnofsky scoring （KPS） were evaluated. Results There were no significant differences in balance test indexes of preoperative data （sex, age, lesion location and volume, and neurological deficits before operation） and diagnosis of histopathology between the two groups. There was a trend in the experimental group for greater rates of gross total resection （80.4% vs. 40.7%）, and the paralysis rate caused by surgery was lower in experimental （25.0%） vs. control （66.7%） groups （P 〈0.05）. The 6-month KPS in the low-grade and high-grade gliomas was 91＋11 and 73＋26, respectively, in the experimental group vs. 82＋9 and 43＋27, respectively, in the control group （P 〈0.05 for both）. Conclusions MR-DTI and FLS dye guiding for surgery of glioma located in brain motor functional areas can increase the gross total resection rate, decrease the paralysis rate caused by surgery, and improve patient quality of life compared with traditional glioma surgery.

Tissue Microstructure Estimation of SANDI Based on Deep Network

Diffusion magnetic resonance imaging(dMRI)is a noninvasive method to capture the anisotropic pattern of water displacement in the neuronal tissue.The soma and neurite density imaging(SANDI)model introduced soma size and density to biophysical model for the first time.In addition to neurite density,it can achieve their joint estimation non-invasively using dMRI.In the traditional method,parameters of the SANDI are estimated in a maximum likelihood frame-work,where the nonlinear model fitting is computationally intensive.Also,the present methods require a large number of diffusion gradients.Efficient and accurate algorithms for tissue microstructure estimation of SANDI is still a challenge currently.Consequently,we introduce deep learning method for tissue microstructure estimation of the SANDI model.The model comprises two functional components.The first component produces the sparse representation of diffusion sig-nals of input patches.The second component computes tissue microstructure from the sparse repre-sentation given by the first component.The deep network can produce not only tissue microstruc-ture estimates but also the uncertainty of the estimates with a reduced number of diffusion gradi-ents.Then,multiple deep networks are trained and their results are fused for the final prediction of tissue microstructure and uncertainty quantification.The deep network was evaluated on the MGH Connectome Diffusion Microstructure Dataset.Results indicate that our approach outperforms the traditional methods in terms of estimation accuracy.

Value of diffusion-weighted imaging in distinguishing pancreatic carcinoma from mass-forming chronic pancreatitis： a meta-analysis

Background Several previous studies have shown that diffusion-weighted imaging （DWl） can provide additional information for focal pancreatic lesions by demonstrating more restricted diffusion in solid malignant tumors than in chronic pancreatitis, which can be indicated by a decreased apparent diffusion coefficient （ADC）. However, these studies have a modest sample size and convey inconclusive results. The aim of this study was to determine, in a meta-analysis, the diagnostic performance of quantitative diffusion-weighted magnetic resonance imaging in distinguishing pancreatic carcinoma from mass-forming chronic pancreatitis. Methods We determined the sensitivities and specificities across studies. A summary receiver operator characteristic （sROC） curve was constructed to calculate the area under the curve （AUC）. Results The pooled sensitivity of DWI was 0.86 （95% Cl： 0.80-0.91） and the pooled specificity was 0.82 （95% CI： 0.72- 0.89）. The AUC of the sROC was 0.91 （95% CI： 0.88-0.93）. Conclusions DWl may be a potentially technically feasible tool for differentiating pancreatic carcinoma from mass- forming chronic pancreatitis. However, large-scale randomized control trials are necessary to assess its clinical value.