Separating changes in the intra- and extracellular water apparent diffusion coefficient following focal cerebral ischemia in the rat brain.

Selective intracellular (IC) and extracellular (EC) brain water apparent diffusion coefficient (ADC) values were measured in normal and ischemic rat brain. Selective T(1)-relaxation enhancement of the EC water, using intracerebroventricular (ICV) infusion of an NMR contrast reagent (CR), was used to separate the IC and EC signal contributions. In the CR-infused, normal brain (n = 4), T(1) = 235 +/- 10 ms and T(2) = 46 +/- 2 ms for IC water (85%) and T(1) = 48 +/- 8 ms and T(2) = 6 +/- 2 ms for EC water (15%). Volume-localized ADC(z) (z-gradient axis) values were 0.90 +/- 0.02 (EC+IC), 0.81 +/- 0.05 (IC), 0.51 +/- 0.02 (EC+IC), and 0.53 +/- 0.07 (IC), for normal, CR-infused, ischemic, and ischemic/CR-infused groups, respectively (ADC values are x10(-3) mm(2)/s; n = 5 for each group). Imaging ADC(z) values were 0.81 +/- 0.03 (EC+IC), 0.75 +/- 0.05 (IC), 0.51 +/- 0.04 (EC+IC), and 0.52 +/- 0.05 (IC), respectively, for the same groups. Imaging ADC(av) (average diffusivity) values for the same groups were 0.70 +/- 0.05 (EC+IC), 0.69 +/- 0.06 (IC), 0.45 +/- 0.06 (EC+IC), and 0.44 +/- 0.06 (IC), respectively. These results suggest that the IC water ADC determines the overall water ADC value in normal and ischemic rat brain.     

Diffusion weighted imaging and estimation of prognosis using apparent diffusion coefficient measurements in ischemic stroke

Objective

Estimation of the prognosis of infarction by using diffusion weighted imaging (DWI) and quantitative apparent diffusion coefficient (ADC) measurements.

Methods

23 patients having acute stroke symptoms with verified infarction in magnetic resonance imaging (MRI) were included in this study. Their MRI studies were performed between 6 and 12 h after the onset of their symptoms and were repeated on the fifth day. The infarction volumes were calculated by using DWI and the patients were divided into two groups as the ones having an expansion in the infarction area (group 1, n = 16) and the others having no expansion in the infarction area (group 2, n = 7). Quantitative ADC values were estimated. The groups were compared in terms of the ADC values on ADC maps obtained from DWI, performed during the between 6 and 12 h from the onset of the symptoms, referring to the core of the infarction (ADC_IC), ischemic penumbra (ADC_P) and the nonischemic parenchymal tissue (ADC_N). P values < 0.05 were accepted to be statistically significant.

Results

During the between 6 and 12 h mean infarction volume calculated by DWI was 23.3 cm³ for group 1 patients (ranging from 1.1 to 68.6) and this was found to be 40.3 cm³ (ranging from 1.8 to 91.5) on the fifth day. For the group 2 patients these values were found to be 42.1 cm³ (ranging from 1 to 94.7) and 41.9 (ranging from 1 to 94.7) for the same intervals respectively. A significant statistical result was failed to be demonstrated between the mean ADC_IC and ADC_N values (p = 0.350 and p = 0.229 respectively). However the comparison of the ADC_P values between the groups was found to be highly significant (p < 0.001). When the differences between the ADC_P and ADC_IC and ADC_N and ADC_P were compared the results proved to be statistically significant (p = 0.038 and p < 0.001 respectively).

Conclusions

We believe that ADC results that would be obtained from the core and the penumbra of the infarction area will be beneficial in the estimation of the infarction prognosis and in the planning of a treatment protocol.     

Feasibility of single‐voxel MRS measurement of apparent diffusion coefficient of water in breast tumors

We report initial results with single voxel spectroscopy (SVS) using diffusion weighting and localization by adiabatic selective refocusing (LASER) in breast tumors to measure the apparent diffusion coefficient of water (ADCw). This is a quick (30 s) and relatively easy method to implement compared with image‐based diffusion measurements, and is insensitive to lipid signal contamination. The ADCw and concentration of total choline containing compounds [tCho] were evaluated for associations with each other and final pathologic diagnosis in 25 subjects. The average (± SD) ADCw in benign and malignant lesions was 1.96 ± 0.47 mm²/s and 1.26 ± 0.29 × 10^?3 mm²/s, respectively, P< 0.001. Receiver operating characteristic curve analysis showed an area under the curve of 0.92. Analysis of the single voxel (SV) ADCw and [tCho] showed significant correlation with a R² of 0.56, P< 0.001. Compared with more commonly used image‐based methods of measuring water ADC, SV‐ADCw is faster, more robust, insensitive to fat, and potentially easier to implement on standard clinical systems. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Role of the apparent diffusion coefficient in the differential diagnosis of gastric wall thickening

Purpose:

To evaluate the role of the apparent diffusion coefficient (ADC) measurement made using diffusion‐weighted magnetic resonance imaging (DWMRI) in the differential diagnosis of benign and malignant gastric wall thickening.

Materials and Methods:

Axial T2‐weighted and DWMRI at b 600 and b 1000 s/mm² gradients were performed in 94 patients (44 patients with gastric malignancy and 50 patients with benign gastric diseases) with gastric wall thickening which was detected by multidetector computed tomography (MDCT). The ADC values of the gastric lesions and healthy gastric walls in patients with gastric malignancies and in patients with benign gastric diseases were used in the differential diagnosis of benign and malignant lesions of the stomach.

Results:

The mean ADC values were lower in patients with gastric malignancies (1.62 ± 0.57 and 1.40 ± 0.33 at b 600 and b 1000, respectively) compared to those with healthy gastric walls (2.95 ± 0.59 and 2.18 ± 0.48) and benign gastric diseases (3.08 ± 0.52 and 2.34 ± 0.42) at b 600 and b 1000 gradients (P < 0.0001).

Conclusion:

The ADC measurement on DWMRI may be used to differentiate between benign and malignant gastric diseases. J. Magn. Reson. Imaging 2012;36:672–677. © 2012 Wiley Periodicals, Inc.     

Diagnostic value of apparent diffusion coefficient (ADC) in assessment of pituitary macroadenoma consistency

Background

Pre-operative assessment of macroadenoma consistency is helpful for proper surgical planning. DWI correlated with ADC value adding information about the tumor consistency that cannot be obtained with cMRI.

Patients and methods

Thirty patients with pituitary adenomas were examined by MRI including cMRI (conventional magnetic resonance) and DWI (diffusion weighted imaging) with ADC value measurement. Diagnosis was correlated with intra-operative finding and histopathology.

Results

According to ADC values, we classified our cases into three groups of macroadenoma consistency; Group A (Soft tumors = 22/30) had mean ADC value of 0.482 × 10⁻³ mm²/s, Group B (intermediate consistency = 5/30) had mean ADC value of 0.730 × 10⁻³ mm²/s and Group C (Firm adenomas = 3/30) with mean ADC value of 0.992 × 10⁻³ mm²/s. Diagnostic overlap was detected in one case of group A and 2 cases of group B. The sensitivity, specificity, PPV, NPD and accuracy of ADC values were 80%, 88%, 57.1% and 95.7% at ADC 0.7 × 10⁻³ mm²/s and 100%, 88%, 62.5% and 100% at ADC 0.6 × 10⁻³ mm²/s respectively.

Conclusion

DWI that correlated with ADC value should be included in routine pre-operative assessment of macroadenoma consistency. We recommend a cut off value of 0.6 × 10⁻³ mm²/s, for accurate discrimination of the intermediate/soft macroadenomas from firm adenomas.     

Comparison of the return-to-the-origin probability and the apparent diffusion coefficient of water as indicators of necrosis in RIF-1 tumors.

Two model-independent measures of diffusion, the apparent diffusion coefficient (ADC) and return-to-the-origin probability enhancement (R) were compared for their ability to detect tissue necrosis in RIF-1 murine tumors. Both reflect the degree of restriction experienced by the endogenous water molecules; however, the ADC is calculated from the initial linear slope of the diffusion attenuation curve, while R is calculated from data that includes the non-monoexponential part of the curve. In spectroscopic studies (n = 9), neither the ADC nor R showed a strong correlation with tumor volume. In imaging studies (n = 14), ADC, R, and T(2) were calculated on a pixel-by-pixel basis. There, the mean ADC and mean R for the entire imaging slice showed reasonable correlation with necrotic tumor fraction (r(2) = 0.679 and -0.665, respectively). The mean T(2) value yielded a poor correlation (r(2) = 0.436). Regions-of-interest were chosen from areas identified as either necrotic or viable and the resulting sets of ADC and R-values were subjected to discriminant analysis to determine the identification error rate. The error was greater for R than for the ADC (P < 0.001). Therefore, in this application, the use of the non-monoexponential part of the diffusion attenuation curve does not provide additional identification power.     

Automatic prediction of infarct growth in acute ischemic stroke from MR apparent diffusion coefficient maps

RATIONALE AND OBJECTIVES: We introduce a new approach to the prediction of final infarct growth in human acute ischemic stroke based on image analysis of the apparent diffusion coefficient (ADC) maps obtained from magnetic resonance imaging. Evidence from multiple previous studies indicate that ADC maps are likely to reveal brain regions belonging to the ischemic penumbra, that is, areas that may be at risk of infarction in the few hours following stroke onset. MATERIALS AND METHODS: In a context where "time is brain," and contrarily to the alternative-and still-debated-perfusion-diffusion weighted image (PWI/DWI) mismatch approach, the DWI magnetic resonance sequences are standardized, fast to acquire, and do not necessitate injection of a contrast agent. The image analysis approach presented here consists of the segmentation of the ischemic penumbra using a fast three-dimensional region-growing technique that mimics the growth of the infarct lesion during acute stroke. RESULTS: The method was evaluated with both numerical simulations and on two groups of 20 ischemic stroke patients (40 patients total). The first group of patient data was used to adjust the parameters of the model ruling the region-growing procedure. The second group of patient data was dedicated to evaluation purposes only, with no subsequent adjustment of the free parameters of the image-analysis procedure. Results indicate that the predicted final infarct volumes are significantly correlated with the true final lesion volumes as revealed by follow-up measurements from DWI sequences. CONCLUSION: The DWI-ADC mismatch method is an encouraging fast alternative to the PWI-DWI mismatch approach to evaluate the likeliness of infarct growth during the acute stage of ischemic stroke.     

The role of apparent diffusion coefficient (ADC) value in the differentiation between the most common pediatric posterior fossa tumors

Background

Diffusion weighted imaging (DWI) and apparent diffusion coefficient (ADC) map provide information on MRI about the cellularity of the tumor and have an important role in the pre-operative differentiation of different tumor types.

Aim

Is to evaluate the role of ADC value measurement in the differentiation between the most common pediatric posterior fossa tumors which include juvenile pilocytic astrocytoma, ependymoma and medulloblastoma.

Patients & methods

Thirty patients were retrospectively included in this study. They were referred from the Neurosurgery Department and all of them suspected to have posterior fossa SOL according to the contrast enhanced CT. All patients were subjected to conventional MRI followed by diffusion MR imaging and calculation of the ADC values.

Results

In JPA (group 1, n = 14), ADC values ranged between 2.4 and 1.3 × 10⁻³ mm²/s, ependymoma (group 2, n = 9), ADC values ranged between 1 and 1.3 × 10⁻³ mm²/s and medulloblastoma (group 3, n = 7), ADC values ranged between 0.5 and 0.9 × 10⁻³ mm²/s. Statistically significant difference in ADC value was detected between group1, group 2 and group 3, while no statistically significant difference was detected between group 1 and group 2.

Conclusion

The calculation of ADC value in the solid enhancing portion of a tumor is a simple and reliable technique for preoperative differentiation of the most common posterior fossa.     

Time course of the apparent diffusion coefficient after cerebral infarction

The purpose of this study was to evaluate quantitative apparent diffusion changes in the center of infarction by measurement of the apparent diffusion coefficient (ADC), and to investigate the influence of ischemia on the contralateral hemisphere. By diffusion echo-planar imaging (EPI) 52 patients showing cerebral infarction were studied within 5 h to >12 months after onset of clinical symptoms. Using three diffusion gradient strengths (b1=30 s/mm(2); b2=300 s/mm(2), b3=1100 s/mm(2)) ADC maps were generated. After onset of ischemia, ADC in the center of infarction was lower than in the contralateral regions of human brain. At first ADC declined for approximately 28 h to a minimum of approximately 150x10(-8) cm(2)/s. Then the ADC reincreased and reached a "pseudonormalization" after approximately 5 days. Chronic infarctions did show much higher ADC values (2000x10(-8) cm(2)/s) than unaffected areas. Neither localization nor size of infarctions showed a significant influence on this time course. In the center of infarction diffusion is isotropic. Even brain regions of the contralateral hemisphere are influenced by cerebral ischemia. In these regions ADC is higher than for physiological conditions. The ADC also declines especially for the first 2-3 days after onset of symptoms, also followed by reincrease. The ADC calculation enables determination of the onset of infarction more exactly than is possible using only diffusion-weighted imaging. Diffusion in the center of infarction is isotropic; hence, orientation of the diffusion gradients has no significant influence on sensitivity of measurements. The calculation of the ADC ratio based on data derived from the center of infarction and the contralateral hemisphere seems to be critical because the ADC in the unaffected contralateral hemisphere also changes.     

Effects of intracellular organelles on the apparent diffusion coefficient of water molecules in cultured human embryonic kidney cells

The apparent diffusion coefficient (ADC) of water in tissues is dependent on the size and spacing of structures in the cellular environment and has been used to characterize pathological changes in stroke and cancer. However, the factors that affect ADC values remain incompletely understood. Measurements of ADC are usually made using relatively long diffusion times; so they reflect the integrated effects of cellular structures over a broad range of spatial scales. We used temporal diffusion spectroscopy to study diffusion in packed cultured human embryonic kidney cells over a range of effective diffusion times following microtubule and actin/cytoskeleton depolymerization and disassembly of the Golgi complex. While Golgi disruption did not change ADC, depolymerization of the microtubule and the actin filament networks caused small decreases in ADC at short diffusion times only. Temporal diffusion spectroscopy provided a novel way to assess intracellular influences on the diffusion properties of tissue water. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Correction for distortion of echo-planar images used to calculate the apparent diffusion coefficient

An algorithm for correcting the distortions that occur in diffusion-weighted echo-planar images due to the strong diffusion-sensitizing gradients is presented. The dominant distortions may be considered to be only changes of scale coupled with a shear and linear translation in the phase-encoding direction. It is then possible to correct for them by using an algorithm in which each line of the image in the phase-encoding direction is considered in turn, with only one parameter (the scale) to be found by searching.     

ADC在急性缺血性卒中缺血半暗带判定中的价值

目的:探讨ADC对确定急性缺血性卒中缺血半暗带的价值。方法:选择33例超急性、急性脑梗死患者,采用全自动图像分析系统,以DWI图像计算得到的ADC图作为输入数据,来判断缺血半暗带的存在(简称为ADC方法),并在2～30d内复查T2WI确定最终梗死范围,测量梗死中心区、缺血半暗带及对侧镜像区的扩散变化。结果:梗死中心区与缺血半暗带ADC平均值分别为4.38×10-4 mm2/s、6.81×10-4 mm2/s,rADC平均值分别为0.56及0.85,梗死中心区ADC及rADC均明显降低,缺血半暗带ADC及rADC轻度下降,二者之间差异有统计学意义。结论:ADC方法对确定缺血半暗带具有潜在的临床实用价值,有望成为一种简便易行的确定缺血半暗带的方法。     

Water diffusion and acute stroke

The occlusion of the middle cerebral artery was used as an experimental acute stroke model in 30 cats. The diffusion of water was followed by diffusion-sensitized MRI between 1 and 15 h after induction of stroke. It is demonstrated that images representing the trace of the diffusion tensor provide a much more accurate delineation of affected area than images representing the diffusion in one direction only. The reason is that the strong contrast caused by the anisotropy and orientation of myelin fibers is completely removed in the trace of the diffusion tensor. The trace images show a small contrast between white and gray matter. The diffusion coefficient of white matter is decreased in acute stroke to approximately the same extent as gray matter. It is further shown that the average lifetime of water in extra and intracellular space is shorter than 20 ms both for healthy and ischemic tissue indicating that myelin fibers are permeable to water. The anisotropy contrast did not change before or after induction of stroke, nor after sacrifice. Together, these observations are consistent with the view that the changes in water diffusion during acute stroke are directly related to cytotoxic oedema, i.e., to the change in relative volume of intra- and extracellular spaces. Changes in membrane permeability do not appear to contribute significantly to the changes in diffusion.     

Relationship between bone marrow cellularity and apparent diffusion coefficient

This study was performed to determine if there is a relationship between apparent diffusion coefficient (ADC) and cellularity of bone marrow of the posterior ilium. Four groups of various marrow cellularity underwent diffusion-weighted echo-planar imaging: 1) adults with normal hypocellularity (21 patients); 2) adults with normal normocellularity (13 patients); 3) young children with normal hypercellularity (5 patients); and 4) adults with lymphoma-related hypercellularity (3 patients). In all adults, marrow cellularity was confirmed by uni-or bilateral bone marrow biopsies. In children, the iliac marrow was presumed hypercellular because of their ages. A total of 66 ADC values of bone marrow calculated from diffusion-weighted images with b-values of 30 and 300 seconds/mm(2) was evaluated. Hypercellular marrow (normal and lymphoma-related) showed the highest mean ADC, and hypocellular the lowest ADC. Statistically significant differences were found between three groups of normal marrow: hypocellular, normocellular, and hypercellular. There is a positive correlation between ADC and cellularity of bone marrow. J. Magn. Reson. Imaging 2001;13:757-760.     

Robust estimation of the apparent diffusion coefficient (ADC) in heterogeneous solid tumors

The least‐squares algorithm is known to bias apparent diffusion coefficient (ADC) values estimated from magnitude MR data, although this effect is commonly assumed to be negligible. In this study the effect of this bias on tumor ADC estimates was evaluated in vivo and was shown to introduce a consistent and significant underestimation of ADC, relative to those given by a robust maximum likelihood approach (on average, a 23.4 ± 12% underestimation). Monte Carlo simulations revealed that the magnitude of the bias increased with ADC and decreasing signal‐to‐noise ratio (SNR). In vivo, this resulted in a much‐reduced ability to resolve necrotic regions from surrounding viable tumor tissue compared with a maximum likelihood approach. This has significant implications for the evaluation of diffusion MR data in vivo, in particular in heterogeneous tumor tissue, when evaluating bi‐ and multiexponential tumor diffusion models for the modeling of data acquired with larger b‐values (b > 1000 s/mm²) and for data with modest SNR. Use of a robust approach to modeling magnitude MR data from tumors is therefore recommended over the least‐squares approach when evaluating data from heterogeneous tumors. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Diagnostic utility of diffusion‐weighted MR imaging and apparent diffusion coefficient value for the diagnosis of adrenal tumors

Purpose

To determine the utility of diffusion‐weighted MR imaging (DWI) for the diagnosis of adrenal tumors.

Materials and Methods

Forty‐two patients (24 men and 18 women; age, 61.5 ± 12.7 years old; range, 34–86 years) with 43 adrenal tumors (11 functioning cortical adenomas, 20 nonfunctioning cortical adenomas, 7 metastatic tumors, and 5 pheochromocytomas) were retrospectively investigated. DWIs were obtained by single‐shot spin‐echo type echo‐planar imaging sequence (1.5 Tesla [T]; TR = 8000 ms, TE = 72, b‐factor = 0 and 1000 s/mm²), and apparent diffusion coefficient (ADC) value was calculated. Chemical shift images were obtained by gradient echo sequence (TR = 161, TE = 2.38 [out‐of‐phase, OP] and 4.76 [in‐phase, IP], FA = 60), and the signal intensity index (SII; [IP‐OP]/IP *100%) was calculated.

Results

There was no difference in ADC values between adenomas (1.09 ± 0.29*10^?3 mm²/s; range, 0.52–1.64) and metastatic tumors (0.85 ± 0.26*10^?3; 0.51–1.23; p = 0.14). Pheochromocytomas showed the higher mean ADC value (1.59 ± 0.34*10^?3; 1.04–1.96) compared with those of adenomas or metastatic tumors (P < 0.05 and P < 0.005, respectively). The mean SII of adenomas (62.1 ± 17.9%; 14.5–88.4) was significantly higher than those of pheochromocytomas (4.0 ± 10.0%; ?19.6–3.3; P < 0.005) or metastatic tumors (?1.5 ± 11.7%; ?18.3–8.2; P < 0.01). There was no correlation between ADC values and SII.

Conclusion

Although pheochromocytomas showed higher ADC values, we did not find that ADC value had diagnostic utility for differentiating adenomas and metastatic tumors. J. Magn. Reson. Imaging 2009;29:112–117. © 2008 Wiley‐Liss, Inc.

     

Evaluation of extra- and intracellular apparent diffusion coefficient of sodium in rat skeletal muscle: effects of prolonged ischemia.

The mechanism of water and sodium apparent diffusion coefficient (ADC) changes in rat skeletal muscle during global ischemia was examined by in vivo 1H and 23Na magnetic resonance spectroscopy (MRS). The ADCs of Na+ and water are expected to have similar characteristics because sodium is present as an aqua-cation in tissue. The shift reagent, TmDOTP5(-), was used to separate intra- and extracellular sodium (Na+i and Na+e, respectively) signals. Water, total tissue sodium (Na+t), Na+i, and Na+e ADCs were measured before and 1, 2, 3, and 4 hr after ischemia. Contrary to the general perception, Na+i and Na+e ADCs were identical before ischemia. Thus, ischemia-induced changes in Na+e ADC cannot be explained by a simple change in the size of relative intracellular or extracellular space. Na+t and Na+e ADCs decreased after 2-4 hr of ischemia, while water and Na+i ADC remained unchanged. The correlation between Na+t and Na+e ADCs was observed because of high Na+e concentration. Similarly, the correlation between water and Na+i ADCs was observed because cells occupy 80% of the tissue space in the skeletal muscle. Ischemia also caused an increase in the Na+i and an equal decrease in Na+e signal intensity due to cessation of Na+/K+-ATPase function.