Histogram Analysis of Intravoxel Incoherent Motion for Differentiating Recurrent Tumor from Treatment Effect in Patients with Glioblastoma: Initial Clinical Experience

BACKGROUND AND PURPOSE:Intravoxel incoherent motion can simultaneously measure diffusion and perfusion characteristics. Our aim was to determine whether the perfusion and diffusion parameters derived from intravoxel incoherent motion could act as imaging biomarkers for distinguishing recurrent tumor from treatment effect in patients with glioblastoma.MATERIALS AND METHODS:Fifty-one patients with pathologically confirmed recurrent tumor (n = 31) or treatment effect (n = 20) were assessed by means of intravoxel incoherent motion MR imaging. The histogram cutoffs of the 90th percentiles for perfusion and normalized CBV and the 10th percentiles for diffusion and ADC were calculated and correlated with the final pathology results. A leave-one-out cross-validation was used to evaluate the diagnostic performance of our classifiers.RESULTS:The mean 90th percentile for perfusion was significantly higher in the recurrent tumor group (0.084 ± 0.020) than in the treatment effect group (0.040 ± 0.010) (P < .001). The 90th percentile for perfusion provided a smaller number of patients within an overlap zone in which misclassifications can occur, compared with the 90th percentile for normalized CBV. The mean 10th percentile for diffusion was significantly lower in the recurrent tumor group than in the treatment effect group (P = .006). Receiver operating characteristic curve analyses showed the 90th percentile for perfusion to be a significant predictor for differentiation, with a sensitivity of 87.1% and a specificity of 95.0%. There was a significant positive correlation between the 90th percentiles for perfusion and normalized CBV (r = 0.674; P < .001).CONCLUSIONS:A histogram analysis of intravoxel incoherent motion parameters can be used as a noninvasive imaging biomarker for differentiating recurrent tumor from treatment effect in patients with glioblastoma.

In clinical practice, it is often difficult to determine whether a progressively enhancing lesion occurring after concurrent chemoradiotherapy is caused by a recurrent tumor or by treatment effect.¹ Several studies have used physiologic imaging techniques, such as T2*-weighted dynamic susceptibility-weighted contrast-enhanced perfusion MR imaging, to differentiate recurrent tumor from treatment effect.^1,2 Intravoxel incoherent motion (IVIM) was introduced by Le Bihan et al^3,4 as a method for simultaneously measuring perfusion and diffusion. Le Bihan et al⁴ defined IVIM as the microscopic translational motions that occur in each image voxel in MR imaging. In biologic tissues, these incoherent motions include molecular diffusion of water and microcirculation of blood in the capillary network, called “perfusion.” These 2 phenomena account for the bi-exponential decay of the signal intensity on DWI when different diffusion b-values are applied. With the use of IVIM theory, both true molecular diffusion and water molecule motion in the capillary network can be estimated by means of a single diffusion imaging acquisition technique. The major advantages of IVIM MR imaging are as follows: it allows the simultaneous acquisition of diffusion and perfusion parameters, which can provide perfusion measures within corresponding solid lesions on ADC or the D-map without the requirement for a co-registration processing step; intravenous contrast injection is not required; and it allows processing and image analysis to be performed within a reasonable timeframe.In the present study, we attempted to validate IVIM-derived perfusion and diffusion parameters through the use of both the pathologic correlation and normalized CBV (nCBV) derived from DSC MR perfusion imaging, which has been commonly used as a perfusion parameter for assessing the glioblastoma treatment response. For pathologic correlation, we used IVIM MR imaging in patients with pathologically confirmed recurrent tumor or treatment effect.Our first hypothesis was that the difference in vascularity between recurrent tumor and treatment effect can be assessed by means of an IVIM-derived perfusion fraction (f), and it would correlate with the value of nCBV derived from DSC MR perfusion imaging. Our second hypothesis was that the true diffusion parameter (D), derived from a biexponential model that separates perfusion effects, may be more significantly different between the recurrent tumor and the treatment effect groups than ADC. The purpose of this study was to determine whether the perfusion (f) and diffusion (D) parameters derived from IVIM can act as imaging biomarkers for distinguishing recurrent tumor from treatment effect in patients with glioblastoma.     

Prediction of the treatment outcome using intravoxel incoherent motion and diffusional kurtosis imaging in nasal or sinonasal squamous cell carcinoma patients

Objectives

To evaluate the diagnostic value of intravoxel incoherent motion (IVIM) and diffusional kurtosis imaging (DKI) parameters in nasal or sinonasal squamous cell carcinoma (SCC) patients to determine local control/failure.

Methods

Twenty-eight patients were evaluated. MR acquisition used single-shot spin-echo EPI with 12 b-values. Quantitative parameters (mean value, 25th, 50th and 75th percentiles) of IVIM (perfusion fraction f, pseudo-diffusion coefficient D*, and true-diffusion coefficient D), DKI (kurtosis value K, kurtosis corrected diffusion coefficient D_k) and apparent diffusion coefficient (ADC) were calculated. Parameter values at both the pretreatment and early-treatment period, and the percentage change between these two periods were obtained.

Results

Multivariate logistic regression analysis: the percentage changes of D (mean, 25th, 50th, 75th), K (mean, 50th, 75th), Dk (mean, 25th, 50th), and ADC (mean, 25th, 50th) were predictors of local control. ROC curve analysis: the parameter with the highest accuracy = the percentage change of D value with the histogram 25th percentile (0.93 diagnostic accuracy). Multivariate Cox regression analyses: the percentage changes of D (mean, 25th, 50th), K (mean, 50th, 75th), Dk (mean, 25th, 50th) and ADC (mean, 25th, 50th) are predictors.

Conclusions

IVIM and DKI parameters, especially the D-value’s histogram 25th percentile, are useful for predicting local control.

Key Points

? Noninvasive assessment of treatment outcome in SCC patients was achieved using IVIM/DKI.? Several IVIM and DKI parameters can predict the local control.? Especially, the D-value’s histogram 25th percentile has high diagnostic accuracy.

     

Can the IVIM model be used for renal perfusion imaging?

Objective: Renal perfusion imaging may provide information about the hemodynamic significance of a renal artery stenosis and could improve noninvasive characterization when combined with angiography. It was proposed previously that diffusion sequences could provide useful perfusion indices based on the intravoxel incoherent motion (IVIM) model. Owing to motion artifacts, diffusion imaging has been restricted to relatively immobile organs like the brain. With the availability of single-shot echo-planar imaging (EPI) our purpose was to evaluate the IVIM model in renal perfusion. Methods and material: Eight volunteers underwent diffusion-sensitive magnetic resonance (MR) imaging of the kidneys using a spin echo (SE) EPI sequence. The diffusion coefficients determined by a linear regression analysis and fits to the IVIM function were calculated. Results and conclusion: Our preliminary experience does not support the possibility of obtaining perfusion information using the IVIM model in the kidneys.     

Head and neck tumours: combined MRI assessment based on IVIM and TIC analyses for the differentiation of tumors of different histological types

Objectives

We evaluated the combined use of intravoxel incoherent motion (IVIM) and time-signal intensity curve (TIC) analyses to diagnose head and neck tumours.

Methods

We compared perfusion-related parameters (PP) and molecular diffusion values (D) determined from IVIM theory and TIC profiles among 92 tumours with different histologies.

Results

IVIM parameters (f and D values) and TIC profiles in combination were distinct among the different types of head and neck tumours, including squamous cell carcinomas (SCCs), lymphomas, malignant salivary gland tumours, Warthin’s tumours, pleomorphic adenomas and schwannomas. A multiparametric approach using both IVIM parameters and TIC profiles differentiated between benign and malignant tumours with 97 % accuracy and diagnosed different tumour types with 89 % accuracy.

Conclusions

Combined use of IVIM parameters and TIC profiles has high efficacy in diagnosing head and neck tumours.

Key points

? Head and neck tumours have wide MR perfusion/diffusion properties. ? Dynamic contrast-enhanced (DCE) MR imaging can characterise tumour perfusion (TIC analysis). ? Intravoxel incoherent motion (IVIM) imaging can provide diffusion and perfusion properties. ? However, IVIM or DCE imaging alone is insufficient for diagnosing head/neck tumours. ? Multiparametric approach using both IVIM and TIC profiles can facilitate the diagnosis.     

Perfusion Measurement in Brain Gliomas with Intravoxel Incoherent Motion MRI

BACKGROUND AND PURPOSE:Intravoxel incoherent motion MRI has been proposed as an alternative method to measure brain perfusion. Our aim was to evaluate the utility of intravoxel incoherent motion perfusion parameters (the perfusion fraction, the pseudodiffusion coefficient, and the flow-related parameter) to differentiate high- and low-grade brain gliomas.MATERIALS AND METHODS:The intravoxel incoherent motion perfusion parameters were assessed in 21 brain gliomas (16 high-grade, 5 low-grade). Images were acquired by using a Stejskal-Tanner diffusion pulse sequence, with 16 values of b (0–900 s/mm²) in 3 orthogonal directions on 3T systems equipped with 32 multichannel receiver head coils. The intravoxel incoherent motion perfusion parameters were derived by fitting the intravoxel incoherent motion biexponential model. Regions of interest were drawn in regions of maximum intravoxel incoherent motion perfusion fraction and contralateral control regions. Statistical significance was assessed by using the Student t test. In addition, regions of interest were drawn around all whole tumors and were evaluated with the help of histograms.RESULTS:In the regions of maximum perfusion fraction, perfusion fraction was significantly higher in the high-grade group (0.127 ± 0.031) than in the low-grade group (0.084 ± 0.016, P < .001) and in the contralateral control region (0.061 ± 0.011, P < .001). No statistically significant difference was observed for the pseudodiffusion coefficient. The perfusion fraction correlated moderately with dynamic susceptibility contrast relative CBV (r = 0.59). The histograms of the perfusion fraction showed a “heavy-tailed” distribution for high-grade but not low-grade gliomas.CONCLUSIONS:The intravoxel incoherent motion perfusion fraction is helpful for differentiating high- from low-grade brain gliomas.

An estimated 69,720 new cases of primary central nervous system tumors are expected to be diagnosed in the United States in 2013, of which an estimated 24,620 new cases will be malignant (13,630 in males and 10,990 in females).¹ The 5-year relative survival rate following diagnosis of primary malignant CNS tumors, mostly gliomas, is poor, with an average of 33.8%, but it is age-dependent, decreasing monotonically from 73% for 0–19 years of age to 10% for 65–74 years of age (data from 1995–2009).²The assessment of perfusion characteristics of those lesions by using dynamic susceptibility MR imaging has become an important part of the initial evaluation and follow-up because cerebral blood volume has been shown to correlate with the degree of neovascularization³ and increased local perfusion has been shown to correlate with tumor grading⁴ and prognosis.⁵ Histologically, the assessment of microvascularity is important for the grading of a primary brain tumor⁶ because high-grade neoplasms produce a pathologic microvascular network through neoangiogenesis to satisfy a growing need for nutriments and oxygen.Le Bihan et al⁷ have proposed measuring microvascular perfusion with an MR imaging–based method called intravoxel incoherent motion (IVIM) imaging. The incoherent motion of spins, which can be understood as the spatial “mixing” of spins during the time of measurement, reduces exponentially the signal amplitude obtained from a diffusion-weighted sequence such as the Stejskal-Tanner sequence.⁸ This incoherent motion arises inevitably from the thermal diffusion characterized by diffusion coefficient (D) and, in biologic perfused tissue, from movements of blood in the microvasculature, called by analogy pseudodiffusion and characterized by pseudodiffusion coefficient (D*).Therefore, an IVIM biexponential signal equation⁷ has been proposed to model incoherent motion in biologic tissue, with the perfusion fraction (f) describing the fraction of incoherent signal arising from the vascular compartment in each voxel over the total incoherent signal. Furthermore, under the assumption of an isotropic, randomly laid microvascular network, a linear relationship were derived⁹ between D* and fD* (the scalar multiplication of f and D*, referred to as the flow-related parameter) and CBV, MTT⁻¹, and CBF, respectively.Recently, IVIM showed promising results in helping discriminate high- and low-grade tumors, for example in the salivary gland, among Warthin tumors, pleomorphic adenomas, and malignant tumors¹⁰; in the pancreas between healthy pancreas and pancreatic cancer¹¹; or between renal¹² and breast tumor subtypes.¹³ In the brain, where initial reports were made,^7,14–19 IVIM perfusion parameters showed recently a gradual increase in response to gradual increase of hypercapnia.²⁰The purpose of this study was to evaluate the utility of IVIM perfusion parameters (f, D*, and fD*) to differentiate high- and low-grade brain gliomas.     

不同定量测量参数对子宫肌瘤IVIM扩散和灌注特点显示的差异

目的 研究用直方图计算的不同定量测量参数对子宫肌瘤体素内不相干运动(IVIM)扩散和灌注特点显示的差异.方法 63例患者80个子宫肌瘤,进行了MR 3D T2WI和IVIM成像,根据肌瘤T2WI信号将肌瘤分为Funaki 1型、2型、3型.分别用直方图计算3种类型肌瘤的IVIM扩散系数(D)、灌注系数(D*)和灌注分数(f)的平均值、位于直方图左侧第25%(D25、D*25、f25)、50%(D50、D*50、f50)、75%(D75、D*75、f75)位置的数值.使用方差分析对3种肌瘤的IVIM定量测量参数进行比较.结果 80个肌瘤中Funaki分型1型肌瘤44个,2型肌瘤24个,3型肌瘤12个,3种肌瘤间D的直方图计算值和均值都有显著性差异(P<0.05),但灌注参数只有D*75有显著性差异(P<0.05).3种肌瘤的f不论是直方图计算值还是均值都无显著性差异.结论 用直方图计算子宫肌瘤IVIM的扩散参数没有比均值提供更多的信息,但直方图计算灌注参数D*75较均值更能反映不同类型肌瘤的灌注特点.     

Intravoxel Incoherent Motion in Normal Pituitary Gland: Initial Study with Turbo Spin-Echo Diffusion-Weighted Imaging

BACKGROUND AND PURPOSE:DWI with conventional single-shot EPI of the pituitary gland is hampered by strong susceptibility artifacts. Our purpose was to evaluate the feasibility of intravoxel incoherent motion assessment by using DWI based on TSE of the normal anterior pituitary lobe.MATERIALS AND METHODS:The intravoxel incoherent motion parameters, including the true diffusion coefficient (D), the perfusion fraction (f), and the pseudo-diffusion coefficient (D*), were obtained with TSE-DWI in 5 brain regions (the pons, the WM and GM of the vermis, and the genu and splenium of the corpus callosum) in 8 healthy volunteers, and their agreement with those obtained with EPI-DWI was evaluated by using the intraclass correlation coefficient. The 3 intravoxel incoherent motion parameters in the anterior pituitary lobe were compared with those in the brain regions by using the Dunnett test.RESULTS:The agreement between TSE-DWI and EPI-DWI was moderate (intraclass correlation coefficient = 0.571) for D, substantial (0.699) for f'', but fair (0.405) for D*. D in the anterior pituitary lobe was significantly higher than in the 5 brain regions (P < .001). The f in the anterior pituitary lobe was significantly higher than in the 5 brain regions (P < .001), except for the vermian GM. The pituitary D* was not significantly different from that in the 5 brain regions.CONCLUSIONS:Our results demonstrated the feasibility of intravoxel incoherent motion assessment of the normal anterior pituitary lobe by using TSE-DWI. High D and f values in the anterior pituitary lobe were thought to reflect its microstructural and perfusion characteristics.

Intravoxel incoherent motion (IVIM) imaging is an advanced DWI technique that allows a separate quantitative evaluation of all the microscopic random motion that contributes to DWI, which is essentially represented by molecular diffusion and blood microcirculation (perfusion).¹ Currently, DWI based on single-shot EPI is most commonly used for IVIM imaging.^2,3 However, EPI-DWI is associated with strong susceptibility artifacts, which cause image degradation in the skull base,⁴ making it difficult, if not impossible, to accurately measure the IVIM parameters in the anterior pituitary lobe. DWI based on TSE has been reported to mitigate such problems in the skull base.⁵ To our knowledge, perfusion of the normal pituitary gland has not yet been evaluated by imaging modalities. Therefore, the purpose of this study was to evaluate the feasibility of IVIM assessment based on TSE-DWI in the normal pituitary gland.     

Ultrafast MR imaging of water mobility: animal models of altered cerebral perfusion.

"Single shot" magnetic resonance (MR) diffusion imaging was used to study the details of signal decay curves in experimental perturbations of cerebral perfusion induced by hypercapnia or death. Despite large perfusion increases observed with dynamic susceptibility-contrast MR imaging, no correlation with these changes was seen in either the diffusion coefficient or any other intravoxel incoherent motion (IVIM) model parameters in dog gray matter as arterial carbon dioxide pressure increased. Non-monoexponential signal decay in cat gray matter was seen both before and after death. In addition, cat gray matter demonstrated a steady decrease in the diffusion coefficient after death. These data are strong evidence that the fast component of the non-monoexponential diffusion-related signal decay is not due solely to perfusion. The authors believe that a second compartment of nonexchanging spins, most likely cerebrospinal fluid, accounts for the non-monoexponential decay.     

Intravoxel incoherent motion imaging using steady-state free precession

IVIM MR imaging is a method which generates images of diffusion and perfusion in vivo. Until now, intravoxel incoherent motion (IVIM) images have been obtained using spin-echo sequences with extragradient pulses, resulting in long acquisition times (typically 2 x 8 min 32 s). A new method is proposed here, using steady-state free precession (SSFP), which allows IVIM images to be obtained in a couple of minutes. Phantom studies showed that the sensitivity of SSFP to IVIMs is much greater than that of spin echoes. In vivo images are shown.     

IVIM双指数、拉伸指数模型对子宫内膜癌分型的价值

目的 探讨体素内不相干运动（IVIM）双指数、拉伸指数模型各参数在Ⅰ型与Ⅱ型子宫内膜癌（EC）中的鉴别诊断价值。 方法 回顾性分析51例经手术病理证实的Ⅰ型（31例）与Ⅱ型（20例）EC病人的IVIM成像资料。由2名医师在IVIM各参数伪彩图上分别测量慢速表观扩散系数（ADC-slow）、快速表观扩散系数（ADC-fast）、灌注分数（f）、扩散分布指数（DDC）和扩散异质性指数（α）。采用组内相关系数（ICC）评价2名医师测量参数的一致性。采用Fisher确切概率法比较Ⅰ型与Ⅱ型EC的病理类型及分级分期。绘制受试者操作特征（ROC）曲线,分析2组间有统计学差异的参数及其诊断效能。 结果 2名医师所测数据的一致性较好（均ICC≥0.75）。Ⅰ型组的ADC-slow、DDC值均高于Ⅱ型组,ADC-fast值低于Ⅱ型组（均P<0.05）。ADC-slow值为0.500×10^-3 mm²/s时,鉴别Ⅰ型和Ⅱ型EC的AUC为0.926,敏感度、特异度、准确度分别为80.0%、90.3%、86.3%。 结论 双指数模型的参数ADC-slow、ADC-fast值和拉伸指数模型的参数DDC值均有助于鉴别Ⅰ型与Ⅱ型EC,其中ADC-slow值鉴别诊断效能更大。     

Magnetic resonance: perfusion and diffusion imaging

Summary The use of magnetic resonance imaging to detect normal and pathological problems of perfusion and diffusion is reviewed. Motion sensitised spin-echo images can be used to detect changes in slow flow velocity within a voxel (intravoxel coherent motion (IVCM) as well as intravoxel incoherent motion (IVIM) effects attributable to both diffusion and perfusion. Changes have been identified in a variety of brain diseases in the absence of changes in conventional images but the techniques are very vulnerable to motion artefact of all types. More rapid and more sensitive approaches using steady state free precision and echo-planer imaging are being investigated. Anisotropic diffusion imaging enables white matter tracts to be demonstrated within the brain and spinal cord as a function of their direction because diffusion of water across axons is much more restricted than it is along them. This technique provides a unique method for localisation of lesions and displays obvious changes in disease in which diffusion becomes less restricted.     

Echo-planar imaging of intravoxel incoherent motion

The recently established single-shot technique of echo-planar imaging of intravoxel incoherent motion (IVIM) for determining and imaging the variations of microscopic motions of water has been applied to studies of water perfusion in phantoms and to in vivo studies of diffusion and perfusion in cat and human brains. The phantom results demonstrate that perfusion levels comparable with those found in vivo have easily observable and reproducible effects on signal amplitude that are consistent with previous IVIM theory. Reliable measurements of the diffusion coefficient in various types of brain tissue have been obtained. The results for white matter are consistent with the existence of anisotropic diffusion in oriented bundles of myelinated nerve fibers. The results for gray matter can be fitted to the IVIM theory and suggest a value of up to 14% for the fraction of the signal contributed by randomly perfusing fluid in normal cerebral cortex.     

Perfusion-related parameters in intravoxel incoherent motion MR imaging compared with CBV and CBF measured by dynamic susceptibility-contrast MR technique

OBJECTIVE: Perfusion-related parameters obtained by intravoxel incoherent motion (IVIM) MR imaging (MRI) were compared with cerebral blood volume and flow (CBV and CBF), retrieved by dynamic susceptibility-contrast (DSC) MRI. MATERIAL AND METHODS: Twenty-eight volunteers (average age 68.5 years) were investigated. Spin-echo echo-planar imaging with IVIM-encoding gradients was employed (36 different b values, 0-1200 s/mm2). The perfusion fraction and the pseudo-diffusion coefficient were calculated for regions in thalamus gray matter and frontal white matter, using asymptotic and full fitting. In DSC-MRI, a Gd-DTPA-BMA contrast-agent bolus was monitored using simultaneous-dual FLASH. Deconvolution of the measured tissue concentration-versus-time curve with an arterial input function from the carotid artery was applied, and maps of CBV and CBF were calculated. RESULTS: The correlation between the perfusion fraction and CBV was r=0.56 (p<0.0000006) using asymptotic fitting, and r=0.35 (p<0.0004) when full fitting was applied. Average CBF was 41.5 ml/(min 100 g), to be compared with the IVIM-based value of 63.6 ml/(min 100 g), obtained from the median value of the pseudo-diffusion coefficient in combination with assumptions about capillary network structure. CONCLUSION: The IVIM concept provided results that agreed reasonably with conventional CBV and CBF. The non-linear fitting to noisy signal data was problematic, in accordance with previously presented simulations.     

MRI在肝外胆管癌诊断中的应用

胆管癌是一种少见的恶性肿瘤,预后不良,大多数发生于肝外胆管。肝外胆管癌（EHCC）的定位诊断常依赖于影像检查,MRI为目前诊断EHCC常用的影像检查方法之一。随着MR技术的发展,越来越多的序列如扩散加权成像（DWI）、体素内不相干运动（IVIM）、扩散峰度成像（DKI）等应用于EHCC的诊断,并且可以对肿瘤的病理级别进行预测和评估,对判断病人的预后及肿瘤的复发具有重要意义。就不同MR成像序列在EHCC诊断中的应用予以综述。     

Evaluation of breast cancer using intravoxel incoherent motion (IVIM) histogram analysis: comparison with malignant status,histological subtype,and molecular prognostic factors

Purpose

To examine heterogeneous breast cancer through intravoxel incoherent motion (IVIM) histogram analysis.

Materials and methods

This HIPAA-compliant, IRB-approved retrospective study included 62 patients (age 48.44?±?11.14 years, 50 malignant lesions and 12 benign) who underwent contrast-enhanced 3 T breast MRI and diffusion-weighted imaging. Apparent diffusion coefficient (ADC) and IVIM biomarkers of tissue diffusivity (D_t), perfusion fraction (f_p), and pseudo-diffusivity (D_p) were calculated using voxel-based analysis for the whole lesion volume. Histogram analysis was performed to quantify tumour heterogeneity. Comparisons were made using Mann–Whitney tests between benign/malignant status, histological subtype, and molecular prognostic factor status while Spearman’s rank correlation was used to characterize the association between imaging biomarkers and prognostic factor expression.

Results

The average values of the ADC and IVIM biomarkers, D_t and f_p, showed significant differences between benign and malignant lesions. Additional significant differences were found in the histogram parameters among tumour subtypes and molecular prognostic factor status. IVIM histogram metrics, particularly f_p and D_p, showed significant correlation with hormonal factor expression.

Conclusion

Advanced diffusion imaging biomarkers show relationships with molecular prognostic factors and breast cancer malignancy. This analysis reveals novel diagnostic metrics that may explain some of the observed variability in treatment response among breast cancer patients.

Key Points

? Novel IVIM biomarkers characterize heterogeneous breast cancer.? Histogram analysis enables quantification of tumour heterogeneity.? IVIM biomarkers show relationships with breast cancer malignancy and molecular prognostic factors.

     

体素内不相干运动扩散加权成像在良性脑膜瘤中的初步研究

目的 探讨多b值体素内不相干运动扩散加权磁共振成像（introvoxel incoherent motion MR imaging,IVIM MRI）的单、双指数模型在良性脑膜瘤中的应用价值.方法 纳入22例手术病理证实为良性脑膜瘤并术前行常规MR序列及IVIM序列扫描的患者.多b值IVIM序列包括14个b值（0～1 000s/mm2）,所得IVIM序列原始数据经单、双指数模型处理,得到单、双指数模型衰减曲线,并生成对应参数图,测量肿瘤实质区及正常脑白质的单指数模型的扩散系数ADC值和双指数模型的扩散系数D值、灌注分数f值、灌注系数D＊值,采用配对样本t检验进行统计学分析.结果 单、双指数模型衰减曲线显示肿瘤实质区信号强度随b值的增大而衰减.肿瘤实质区ADC值、D值、D＊值、f值分别为（0.87±0.13）μm2/ms、（0.79±0.10）μm2/ms、（58.68±27.52）μm2/ms、（7.68±3.59）％;正常脑白质的ADC值、D值、D＊值、f值分别为（0.74±0.06）μm2/ms、（0.69±0.04）μm2/ms、（93.43±31.64）μm2/ms、（4.48±2.39）％.单指数模型中肿瘤实质区ADC值较正常脑白质ADC值两者比较差异有统计学意义（t=5.793,P＜0.05）;双指数模型中,肿瘤实质与正常脑白质D、f、D＊值分别进行比较,肿瘤实质的D、f值均较正常脑白质增高（t=4.384,P＜0.05和t=3.349,P＜0.05）;而肿瘤实质D＊值较正常脑白质D＊值减低（t=-3.559,P＜0.05）.肿瘤实质区单指数模型ADC值与双指数模型D值两者差异有统计学意义,且单指数ADC值显著较双指数模型D高（t=6.492,P＜0.05）.结论 基于棠规DWI序列的多b值IVIM双指数模型可以更准确地描述良性脑膜瘤的扩散信息,同时非侵入性地获得肿瘤灌注信息.     

Renal artery stenosis: in vivo perfusion MR imaging

The intravoxel incoherent motion (IVIM) model of perfusion and diffusion imaging was applied to an in vivo canine model of unilateral renal artery stenosis and was compared with relative renal blood flow determination with radioactive microspheres. The percentage relative renal blood flow as determined with radioactive microspheres correlated closely with the percentage apparent diffusion coefficient. If this method can be adapted to human imaging, it may provide a noninvasive means for detecting renal artery stenosis.     

Assessment of microvessel perfusion of pituitary adenomas: a feasibility study using turbo spin-echo-based intravoxel incoherent motion imaging

European Radiology - To evaluate the feasibility of assessment of microvessel perfusion of pituitary adenomas with intravoxel incoherent motion (IVIM) imaging using single-shot turbo...     

Intravoxel incoherent motion imaging using spin echoes

The purpose of this paper is to review the basic principles of diffusion measurement with spin echoes. These principles can be combined with those of MR imaging to generate maps of diffusion coefficients. Diffusion imaging can be extended to imaging of other intravoxel incoherent motions (IVIM), such as blood microcirculation. Some of the technical problems encountered when implementing IVIM imaging are presented.     

Diffusion-weighted MR imaging of the brain: value of differentiating between extraaxial cysts and epidermoid tumors

This study demonstrates the use of diffusion-weighted MR imaging in improving the specificity of the diagnosis of extraaxial brain tumors. Three surgically proved lesions (one arachnoid cyst and two epidermoid tumors) and two nonsurgically proved lesions (arachnoid and ependymal cysts) were evaluated with T1- and T2-weighted spin-echo studies followed by intravoxel incoherent motion (IVIM) MR imaging. The IVIM images of the lesions were displayed as an apparent diffusion coefficient (ADC) image obtained at 0.65 G/cm (maximum gradient b value = 100 sec/mm2) and compared with external oil and water phantoms. The ADC of arachnoid cysts was similar to stationary water whereas the ADC of epidermoid tumors was similar to brain parenchyma, indicating the solid nature and the slower diffusion rate of the epidermoid tumors. Cisternal CSF demonstrated uniformly high ADC, primarily because of bulk flow, which enhanced image contrast. Improved delineation of postsurgical changes was also possible. Our preliminary results show that diffusion-weighted MR imaging can be useful in distinguishing between arachnoid cysts and epidermoid tumors.