ADC值在术前评价脑胶质瘤病理级别的应用价值

胶质瘤是颅内最常见的原发肿瘤之一,临床在手术治疗、放射治疗、化学药物治疗等方面有明显进展,但胶质母细胞瘤的预后较差。用影像学方法评估胶质瘤恶性程度对指导临床治疗十分必要。国内外学者利用MR扩散加权成像(DWI)对表观扩散系数(ADC)与肿瘤细胞构成及病理级别的相关性进行了初步探讨,研究显示通过DWI能够反映肿瘤病变的组织学特性,对肿瘤病变术前评估具有一定价值。本研究证实,ADC值与胶质瘤的良恶性有很高的相关性,结合常规MRI检查可为临床术前治疗方案的制定提供可靠依据。1材料与方法1.1临床资料收集2005年2月~2006年12月我…     

Amide proton transfer imaging to discriminate between low- and high-grade gliomas: added value to apparent diffusion coefficient and relative cerebral blood volume

Objectives

To evaluate the added value of amide proton transfer (APT) imaging to the apparent diffusion coefficient (ADC) from diffusion tensor imaging (DTI) and the relative cerebral blood volume (rCBV) from perfusion magnetic resonance imaging (MRI) for discriminating between high- and low-grade gliomas.

Methods

Forty-six consecutive adult patients with diffuse gliomas who underwent preoperative APT imaging, DTI and perfusion MRI were enrolled. APT signals were compared according to the World Health Organization grade. The diagnostic ability and added value of the APT signal to the ADC and rCBV for discriminating between low- and high-grade gliomas were evaluated using receiver operating characteristic (ROC) analyses and integrated discrimination improvement.

Results

The APT signal increased as the glioma grade increased. The discrimination abilities of the APT, ADC and rCBV values were not significantly different. Using both the APT signal and ADC significantly improved discrimination vs. the ADC alone (area under the ROC curve [AUC], 0.888?vs.?0.910; P?=?0.007), whereas using both the APT signal and rCBV did not improve discrimination vs. the rCBV alone (AUC, 0.927?vs.?0.923; P?=?0.222).

Conclusions

APT imaging may be a useful imaging biomarker that adds value to the ADC for discriminating between low- and high-grade gliomas.

Key points

? Higher APT values were correlated with higher glioma grades. ? Adding the APT signal to the ADC improved glioma grading. ? Adding the APT signal to rCBV did not improve glioma grading. ? APT is a useful adjunct to the ADC for glioma grading.

     

The added value of the apparent diffusion coefficient calculation to magnetic resonance imaging in the differentiation and grading of malignant brain tumors

OBJECTIVE: ADC calculation can improve the diagnostic efficacy of MR imaging in brain tumor grading and differentiation. METHODS: Apparent diffusion coefficient (ADC) values and ratios of 33 low-grade (23 astrocytomas, 10 oligodendrogliomas) and 40 high-grade (25 metastases and 15 high-grade astrocytomas) malignant tumors were prospectively evaluated. RESULTS: Tumoral ADC values (r=-0.738, P <0.000) and ratios (r=-0.746, P < 0.000) were well correlated with higher degree of malignancy and quite effective in grading of malignant brain tumors (P < 0.000). By using cutoff values of 0.99 for tumoral ADC value and 1.22 for normalized ADC ratio, the sensitivity of MR imaging could be increased from 72.22% to 93.75% and 90.63%, the specificity from 81.08% to 92.68% and 90.24%, PPV from 78.79% to 90.91% and 87.88%, and NPV from 75.00% to 95.00% and 92.50%, respectively. CONCLUSION: ADC calculation was quite effective in grading of malignant brain tumors but not in differentiation of them and added more information to conventional contrast-enhanced MR imaging.     

A prospective study on the added value of pulsed arterial spin-labeling and apparent diffusion coefficients in the grading of gliomas

BACKGROUND AND PURPOSE: The purpose of this study was to determine whether qualitative and quantitative measures obtained with pulsed arterial spin-labeling (PASL) and apparent diffusion coefficients (ADC) improve glioma grading compared with conventional MR images. MATERIALS AND METHODS: We prospectively performed 2 qualitative consensus reviews in 33 suspected gliomas: 1) conventional MR images alone and 2) conventional MR images with PASL and ADC. To calculate the diagnostic performance parameters of PASL and ADC, we used a qualitative scoring system on the basis of the tumor perfusion signal intensity (sTP) and visual ADC scoring (sADC). We then analyzed quantitative regions of interest and calculated the ratio of the maximum tumor perfusion signal intensity (rTPmax) and the minimum ADC value (mADC). RESULTS: Two observers diagnosed accurate tumor grades in 23 of 33 (70%) lesions in the first review and in 29 of 33 (88%) lesions in the second review. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for determining a glioma grading by using combined sTP and sADC scoring were 90.9, 90.9, 95.2, and 83.3%, respectively. Statistical analysis gave a threshold value of 1.24 for rTPmax and 0.98 x 10(-3) mm/s(2) for mADC to provide a sensitivity, specificity, PPV, and NPV of 95.5, 81.8, 91.3, and 90.1% and 90.9, 81.8, 90.9, and 81.8%, respectively. The receiver operator characteristic curve analyses showed no significant difference between the quantitative and combined qualitative parameters. CONCLUSION: PASL and ADC significantly improve the diagnostic accuracy of glioma grading compared with conventional imaging.     

The value of apparent diffusion coefficient maps in early cerebral ischemia

BACKGROUND AND PURPOSE: Prediction of the regions of the ischemic penumbra that are likely to progress to infarction is of great clinical interest. Whether lowered apparent diffusion coefficient (ADC) values were present in the ischemic penumbra of patients presenting with acute ischemic stroke and were specific to regions of the penumbra that proceeded to infarction was investigated. METHODS: Nineteen patients with hemispheric stroke of less than 6 hours' onset and with acute scans showing a perfusion lesion greater than a diffusion lesion (ischemic penumbra) were studied. Scans also were performed subacutely (days 3 to 5) and at outcome (day 90). The outcome scan was used to identify regions of the penumbra that proceeded to infarction. RESULTS: The ADC ratios were significantly reduced (P <.00001) in regions of the penumbra that progressed to infarction on the outcome scan compared with those that remained normal. In regions that showed transition to infarction, the mean ADC ratios were typically 0.75 to 0.90. CONCLUSION: Intermediate ADC values are present in the ischemic penumbra and are indicative of tissue at risk of infarction.     

扩散系数值在脑星形细胞肿瘤病理学分级中的应用

目的探讨扩散系数值对脑星形细胞肿瘤病理学分级的应用价值。方法对56例脑星形细胞肿瘤进行扩散加权成像（DWI）检查，分别测量肿瘤实质部分、瘤周水肿区、瘤周T1WI正常表现白质区（瘤周白质区）、瘤体镜面对侧正常白质区及瘤周镜面对侧正常白质区的表观扩散系数（ADC）值和指数扩散系数（EDC）值，并计算肿瘤实质部分、瘤周水肿区、瘤周白质区的相对表观扩散系数（rADC）值和相对指数扩散系数（rEDC）值。分析各测量区的扩散系数值与肿瘤病理学分级的关系。结果56例脑星形细胞肿瘤经手术病理证实，低级星形细胞瘤35例（Ⅰ、Ⅱ级），间变性星形细胞瘤8例（Ⅲ级），胶质母细胞瘤13例（Ⅳ级）。低级星形细胞瘤、间变性星形细胞瘤和胶质母细胞瘤肿瘤实质部分的ADC值分别为（1．44±0．26）×10^-3、（0．98±0．22）×10^-3和（0．83±0．15）×10^-3mm^2／s，rADC值分别为（1．91±0．39）％、（1．34±0．33）％和（1．06±0．20）％，EDC值分别为0．26±0．11、0．39±0．09和0．44±0．07，rEDC值分别为（0．55±0．20）％、（0．81±0．19）％和（0．98±0．16）％，各指标间差异均有统计学意义（F值分别为36．189、31．756、19．623和24．760，P值均为0．000）。高级星形细胞瘤（间变性星形细胞瘤和胶质母细胞瘤）的肿瘤实质部分的ADC值和rADC值分别为（0．89±0．19）×10^-3mm^2／s和（1．17±0．28）％，明显低于低级星形细胞瘤（t值分别为8．332和7．620，P值均为0．000），EDC值和rEDC值分别为0．42±0．08和（0．91±0．18）％，明显高于低级星形细胞瘤（t值分别为-6．082和-6．776，P值均为0．000）。以低级星形细胞瘤实质部分的rADC值的下限（1．52％）作为判断低、高级别星形细胞瘤阈值的准确性为89．3％。结论肿瘤实质部分的扩散系数值对脑星形细胞肿瘤的病理学分级准确性较高，尤以rADC值为佳。     

表观扩散系数值评价直肠癌术前放化疗疗效的价值

目的 探讨ADC值对直肠癌术前放化疗疗效的早期监测的可行性及应用价值.方法 搜集2004年12月到2006年10月26例经病理证实的原发性直肠癌患者,术前行常规MRI和DWI检查.测量放化疗过程中不同监测时间点(包括治疗前、治疗后第1周、治疗后第2周、手术前)肿瘤ADC值.以放化疗前肿瘤的临床T分期与术后病理T分期比较,以T分期是否降低为标准,分为治疗效果较好的T-降期组和治疗效果较差的T-未降期组.应用随机区组设计的方差分析比较肿瘤ADC值变化情况.结果 26例中,T-降期组和T-未降期组分别为12和14例.T-降期组治疗前、治疗后第1周、治疗后第2周、手术前ADC值分别为(1.10±0.13)×10~(-3)、(1.32±0.19)×10~(-3)、(1.35±0.13)×10~(-3)和(1.32±1.00)×10~(-3) mm~2/s,差异有统计学意义(F=16.420,P＜0.01).T-未降期组在治疗后第1周ADC值由(1.16±0.16)×10~(-3) mm~2/g升高至(1.23±0.13)×10-3 mm~2/s,升高不明显(P＞0.05),在治疗后第2周ADC值继续升高至(1.30±0.16)×10-3 mm~2/s,差异有统计学意义(F=5.023,P＜0.01).用治疗后第1周肿瘤平均ADC值升高程度11.6%作为诊断直肠癌T分期是否出现降期的指标,诊断敏感性为75.O%,特异性为78.6%,阳性预测值为75.0%,阴性预测值为78.6%.ROC曲线下面积为0.774(95%可信区间为0.583～0.964),具有中等诊断价值.结论 ADC值具有作为早期监测直肠癌放化疗疗效影像学指标的可能性.治疗第1周肿瘤平均ADC值变化对于区分放化疗反应性较为敏感,可以作为有效的时间监测点.     

Diagnostic value of minimum apparent diffusion coefficient values in prediction of neuroepithelial tumor grading

Purpose:

To retrospectively evaluate the diagnostic accuracy of diffusion weighted image (DWI) in the prediction of neuroepithelial tumors grading, and to appraise the apparent diffusion coefficient (ADC) value of neuroepithelial tumors with histologic findings as a reference standard.

Materials and Methods:

ADC values in 110 patients with pathologically proved neuroepithelial tumors, including 77 astrocytic tumors, 16 oligodendroglial tumors, 11 oligoastrocytic tumors, and 6 ependymal tumors, were investigated retrospectively. The minimum ADC (MinADC) value of tumors was measured postoperatively on ADC maps, avoiding cystic, necrotic, or hemorrhagic components. The Ki‐67 Labeling Index (Ki‐67 LI) was determined by immunohistochemistry. The patients were classified into low (WHO II) and high (WHO III or IV) grade groups. Correlation analysis, Student t‐test, Welch test, receiver operating characteristic (ROC) analysis, and analysis of variance were used for statistical evaluation.

Results:

There was a negative correlation between MinADC value and Ki‐67 LI (P < 0.001). The mean MinADC value (1.057 × 10^?3 mm²/s) of low grade group was higher than that (0.773 × 10^?3 mm²/s) of high grade group. The area under the ROC curve (AUC) was 0.809, and the cutoff MinADC value of 0.900 × 10^?3 mm²/s for the differentiation between high and low grade neuroepithelial tumors provided the best combination of sensitivity (85.4%) and specificity (71.0%).

Conclusion:

MinADC value may be a simple and effective optional tool for the prediction of neuroepithelial tumor grading. J. Magn. Reson. Imaging 2010;31:1331–1338. © 2010 Wiley‐Liss, Inc.

     

Usefulness of apparent diffusion coefficient value and proton magnetic resonance spectroscopy as a noninvasive techniques in recurrent cerebral gliomas

Objective

Conventional MRI does not provide sufficient information to differentiate post-radiotherapy necrosis from brain tumor recurrence, recent studies have investigated the use of more advanced imaging modalities that are able to differentiate between the two entities.

评价ADC值对橄榄桥小脑萎缩的诊断价值

目的 评价表现扩散系数(ADC)值对橄榄桥小脑萎缩(OPCA)的诊断价值.方法 (1)选取经临床诊断为OPCA的52例患者及25列年龄匹配的正常人作为对照组,行常规MRI检查(T1 WI、T2 WI、DWI).根据MRI表现将患者分为轻度组和重度组.轻度组:小脑脑沟增多、脑干稍变细,桥脑无明显改变;重度组:小脑脑沟增多,桥脑、延髓橄榄萎缩,第四脑室、脑干基底池扩大.(2)选取桥脑、小脑中脚和小脑半球为感兴趣区(ROI)并测量其ADC值.运用单因素方差对3组ROI的ADC值进行统计分析.结果 3组ROI的ADC值差异有统计学意义(P＜0.05).OPCA患者组(轻度组及重度组)ROI的ADC值较对照组明显升高,差异有统计学意义(P＜0.05).OPCA重度组ROI的ADC值较轻度组升高,且重度组病程长于轻度组,差异均有统计学意义(P＜0.05).结论 桥脑、小脑中脚、小脑半球的ADC值对OPCA有重要的诊断价值,尤其对于MRI表现不明显的OPCA轻度组患者具有重要的诊断意义.     

Survival analysis in patients with glioblastoma multiforme: predictive value of choline-to-N-acetylaspartate index, apparent diffusion coefficient, and relative cerebral blood volume

Purpose

To investigate the potential value of pre‐external‐beam radiation therapy (XRT) choline‐to‐NAA (N‐acetylaspartate) index (CNI), apparent diffusion coefficient (ADC), and relative cerebral blood volume (rCBV) for predicting survival in newly diagnosed patients with glioblastoma multiforme (GBM).

Materials and Methods

Twenty‐eight patients with GBM were studied using in vivo proton magnetic resonance spectroscopic imaging (¹H MRSI) and diffusion‐ and perfusion‐weighted imaging after surgery but prior to XRT. Patients were categorized on the basis of their volumes of morphologic and metabolic abnormalities (volume of CNI ≥ 2 and CNI values), normalized ADC (nADC), or rCBV values within the T1 contrast‐enhancing and T2 regions. The median survival time was compared.

Results

A significantly shorter median survival time was observed for patients with a large volume of metabolic abnormality than for those with a small abnormality (12.0 and 17.1 months, respectively, P = 0.002). A similar pattern was observed for patients with a low mean nADC value compared to those with high mean nADC value within the T2 region (11.2 and 21.7 months, respectively, P = 0.004). A shorter median survival time was also observed for patients with contrast‐enhancing residual disease than for those without the presence of contrast enhancement with marginal significance.

Conclusion

The pre‐XRT volume of the metabolic abnormality and the nADC value within the T2 region may be valuable in predicting outcome for patients with GBM. J. Magn. Reson. Imaging 2004;19:546–554. © 2004 Wiley‐Liss, Inc.

     

Measurements of diagnostic examination performance using quantitative apparent diffusion coefficient and proton MR spectroscopic imaging in the preoperative evaluation of tumor grade in cerebral gliomas

Purpose

Tumor grading is very important both in treatment decision and evaluation of prognosis. While tissue samples are obtained as part of most therapeutic approaches, factors that may result in inaccurate grading due to sampling error (namely, heterogeneity in tissue sampling, as well as tumor-grade heterogeneity within the same tumor specimen), have led to a desire to use imaging better to ascertain tumor grade. The purpose in our study was to evaluate the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), area under the curve (AUC), and accuracy of diffusion-weighted MR imaging (DWI), proton MR spectroscopic imaging (MRSI) or both in grading primary cerebral gliomas.

Materials and methods

We performed conventional MR imaging (MR), DWI, and MRSI in 74 patients with newly diagnosed brain gliomas: 59 patients had histologically verified high-grade gliomas: 37 glioblastomas multiform (GBM) and 22 anaplastic astrocytomas (AA), and 15 patients had low-grade gliomas. Apparent diffusion coefficient (ADC) values of tumor and peritumoral edema, and ADC ratios (ADC in tumor or peritumoral edema to ADC of contralateral white matter, as well as ADC in tumor to ADC in peritumoral edema) were determined from three regions of interest. The average of the mean, maximum, and minimum for ADC variables was calculated for each patient. The metabolite ratios of Cho/Cr and Cho/NAA at intermediate TE were assessed from spectral maps in the solid portion of tumor, peritumoral edema and contralateral normal-appearing white matter. Tumor grade determined with the two methods was then compared with that from histopathologic grading. Logistic regression and receiver operating characteristic (ROC) curve analysis were performed to determine optimum thresholds for tumor grading. Measures of diagnostic examination performance, such as sensitivity, specificity, PPV, NPV, AUC, and accuracy for identifying high-grade gliomas were also calculated.

Results

Statistical analysis demonstrated a threshold minimum ADC tumor value of 1.07 to provide sensitivity, specificity, PPV, and NPV of 79.7%, 60.0%, 88.7%, and 42.9% respectively, in determining high-grade gliomas. Threshold values of 1.35 and 1.78 for peritumoral Cho/Cr and Cho/NAA metabolite ratios resulted in sensitivity, specificity, PPV, and NPV of 83.3%, 85.1%, 41.7%, 97.6%, and 100%, 57.4%, 23.1% and 100% respectively for determining high-grade gliomas. Significant differences were noted in the ADC tumor values and ratios, peritumoral Cho/Cr and Cho/NAA metabolite ratios, and tumoral Cho/NAA ratio between low- and high-grade gliomas. The combination of mean ADC tumor value, maximum ADC tumor ratio, peritumoral Cho/Cr and Cho/NAA metabolite ratios resulted in sensitivity, specificity, PPV, and NPV of 91.5%, 100%, 100% and 60% respectively.

Conclusion

Combining DWI and MRSI increases the accuracy of preoperative imaging in the determination of glioma grade. MRSI had superior diagnostic performance in predicting glioma grade compared with DWI alone. The predictive values are helpful in the clinical decision-making process to evaluate the histologic grade of tumors, and provide a means of guiding treatment.     

表观弥散系数在高级别胶质瘤与急性期脑梗死鉴别诊断中的应用

目的探讨表观弥散系数(ADC值)在高级别胶质瘤与急性期脑梗死鉴别诊断中的应用。方法回顾性分析经手术和病理证实的18例高级别胶质瘤及正规及时溶栓治疗的28例急性期脑梗死的常规磁共振表现和弥散加权成像(DWI)表现,对照分析高级别胶质瘤实性部分、急性期脑梗死灶中心部分及对侧正常脑组织ADC值。结果 18例高级别胶质瘤患者共发现20个病灶,其中11例病灶内合并有出血、坏死和囊变,肿瘤实质部分呈稍高信号,囊变坏死区呈明显低信号,肿瘤实质部分平均ADC值为(0.92±0.12)×10-3mm2/s,对侧相应正常部位平均ADC值为(0.79±0.09)×10-3mm2/s,差异有统计学意义(P<0.05),急性期脑梗死在DWI上表现为高或稍高信号,其ADC值明显低于对侧相应区域,平均ADC值为(0.69±0.10)×10-3mm2/s,高级别胶质瘤实性部分与急性期脑梗死平均ADC值差异有统计学意义(P<0.05)。结论 DWI表现及ADC值对高级别胶质瘤与急性期脑梗死磁共振鉴别诊断具有重要价值。     

The value of apparent diffusion coefficient in the assessment of cervical cancer

Objectives

To evaluate the potential value of apparent diffusion coefficient (ADC) measurement in the assessment of cervical cancer.

Methods

One hundred twelve patients with cervical cancer and 67 control subjects underwent diffusion-weighted imaging (DWI) in addition to routine MR imaging at 3.0-T MRI before therapy. All ADCs were calculated from b?=?0, 600 s/mm² and b?=?0, 1,000 s/mm².

Results

The ADCs of cervical cancer were significantly lower than those of normal cervix for both ADC maps. There was a statistically significant difference between the ADCs of well-/moderately differentiated (G1/2) tumours and poorly differentiated (G3) tumours, between the ADCs of squamous cell carcinoma and adenocarcinoma, between the pretherapy ADCs of tumour recurrence or metastasis and tumour free patients after radical hysterectomy for both ADC maps. There was no significant difference among the ADCs of cervical cancer when divided by other features (FIGO, lymph node status, tumour size and age groups) for both ADC maps.

Conclusion

ADC values were reliable for differentiating cervical cancer from normal cervix with high diagnostic accuracy. The ADCs can be used to indicate the degree and histological type of cervical cancer, although there is some overlap. G3 tumours and lower ADCs may indicate poor prognosis. The diagnostic accuracy was equal for both ADC maps.

Key Points

? Diffusion-weighted magnetic resonance imaging provides new information about cervical cancer ? Apparent diffusion coefficient values can differentiate cervical cancer from normal cervical tissue ? Pretherapy ADCs can also predict the prognosis for patients who have undergone radical hysterectomy ? ADCs can help indicate the degree and histological type of cervical cancer ? Patients with G3 tumours and lower ADCs may benefit from preoperative chemoradiation     

Relationship between choline and apparent diffusion coefficient in patients with gliomas

PURPOSE: To examine the relationship between apparent diffusion coefficients (ADC) from diffusion weighted imaging (DWI) and choline levels from proton magnetic resonance spectroscopic imaging (MRSI) in newly diagnosed Grade II and IV gliomas within distinct anatomic regions. MATERIALS AND METHODS: A total of 37 patients with Grade II and 28 patients with Grade IV glioma were scanned on a 1.5T system with 3D MRSI and DWI. Region level analysis included Spearman rank correlation between median normalized ADC and choline for each patient per grade within each distinct abnormal anatomical region. Voxel level analysis calculated a Spearman rank correlation per region, per patient. RESULTS: Grade II lesions showed no evidence of a correlation between normalized ADC and choline using either the region or voxel level analysis. Region level analysis of Grade IV lesions did not appear to correlate in the contrast enhancement or necrotic core, but did suggest a significant negative correlation in the more heterogeneous nonenhancing and combined regions. CONCLUSION: There appears to be differences in the relationship between ADC and choline levels in Grade II and Grade IV gliomas. Correlation within these regions in Grade IV lesions was strongest when all regions were included, suggesting heterogeneity may be driving the relationship.     

不同类型正常乳腺表观扩散系数值差异的研究

目的 研究不同类型正常乳腺表观扩散系数（ADC）值的差异，探讨ADC值与组织学分型之间的关系。方法 采用单次激发平面回波（EPI）技术，扩散敏感因子（b）值分别为0、500、1000s／mm^2，对62个正常乳腺（包括42例乳腺病变患者的对侧正常乳腺及10名健康志愿者20个乳腺）进行MR扫描及MR扩散加权成像（DWI）检查，计算62个正常乳腺分别在不同b值时的ADC值。将62个正常乳腺分为3型，比较3型之间ADC值的差异及不同b值时ADC值的差异。结果 42例乳腺病变患者对侧正常乳腺的DWI及ADC图与组织切片对比，不同类型乳腺组织学结构不同，其DWI及ADC图表现亦有差异。62个正常乳腺分为致密型10个，分叶斑点型42个及退化型10个。致密型和分叶斑点型乳腺随b值降低ADC值升高，而退化型乳腺随b值降低ADC值变化不明显。b=1000—0s／mm^2时，致密型、分叶斑点型、退化型乳腺ADC值分别为（1．70±0．37）、（1．93±0．46）、（1．18±0．65）×10^-3mm^2／s，3组间比较差异有统计学意义（F=12．998，P=0．000）。不同b值时每2种类型间进行单因素方差分析，致密型和分叶斑点型之间差异无统计学意义（F=2．167，P=0．147）；致密型和退化型之间、分叶斑点型和退化型之间差异均有统计学意义（F值分别为5．593、19．128，P值分别为0．029、0．000）。结论 3型正常乳腺ADC值受乳腺组织学结构的影响，致密型和分叶斑点型乳腺ADC值受b值高低的影响。     

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.     

Preoperative grading of presumptive low-grade astrocytomas on MR imaging: diagnostic value of minimum apparent diffusion coefficient

BACKGROUND AND PURPOSE: Histopathologic grade of glial tumors is inversely correlated with the minimum apparent diffusion coefficient (ADC). We assessed the diagnostic values of minimum ADC for preoperative grading of supratentorial astrocytomas that were diagnosed as low-grade astrocytomas on conventional MR imaging.MATERIALS AND METHODS: Among 118 patients with astrocytomas (WHO grades II–IV), 16 who showed typical MR imaging findings of low-grade supratentorial astrocytomas on conventional MR imaging were included. All 16 patients underwent preoperative MR imaging and diffusion-weighted imaging. The minimum ADC value of each tumor was determined from several regions of interest in the tumor on ADC maps. To assess the relationship between the minimum ADC and tumor grade, we performed the Mann-Whitney U test. A receiver operating characteristic (ROC) analysis was used to determine the cutoff value of the minimum ADC that had the best combination of sensitivity and specificity for distinguishing low- and high-grade astrocytomas.RESULTS: Eight of the 16 patients (50%) were confirmed as having high-grade astrocytomas (WHO grades III and IV), and the other 8 patients were confirmed as having low-grade astrocytomas (WHO grade II). The median minimum ADC of the high-grade astrocytoma (1.035 × 10⁻³ mm² · sec⁻¹) group was significantly lower than that of the low-grade astrocytoma group (1.19 × 10⁻³ mm² · sec⁻¹) (P = .021). According to the ROC analysis, the cutoff value of 1.055 × 10⁻³ mm² · sec⁻¹ for the minimum ADC generated the best combination of sensitivity (87.5%) and specificity (79%) (P = .021).CONCLUSION: Measuring minimum ADC can provide valuable diagnostic information for the preoperative grading of presumptive low-grade supratentorial astrocytomas.

Despite aggressive treatments, overall prognosis of high-grade astrocytomas, especially glioblastomas, is still poor, mainly due to their infiltrative nature and high relapse rate compared with those of low-grade astrocytomas.^1–4 Accurate preoperative grading of a brain tumor is thus pivotal in choosing the treatment strategy and in the assessment of prognosis.On conventional MR imaging, malignant gliomas usually show strong contrast enhancement, peritumoral edema, mass effects, heterogeneity, central necrosis, and intratumoral hemorrhage. The typical MR imaging features of low-grade astrocytomas include a relatively well-defined usually homogeneous mass that displays little or no mass effect, with minimal or no vasogenic edema and little or no enhancement after contrast administration.^5–7 Nevertheless, it is not always easy to differentiate low-grade astrocytomas from high-grade ones on the basis of conventional MR imaging findings. It has been reported that high-grade and low-grade astrocytomas can have overlapping features on MR imaging.^2,8–12 Recently, it was shown that the histopathologic grade of glial tumors is inversely correlated with the minimum apparent diffusion coefficient (ADC).^1,3,9,13,14 Thus, we hypothesized that a high-grade astrocytoma may demonstrate a lower minimum ADC value even though it shows the typical MR imaging features of low-grade gliomas.The purpose of this study was to evaluate the diagnostic value of the minimum ADC for preoperative histopathologic grading in supratentorial astrocytomas that showed typical features of low-grade astrocytomas on conventional MR imaging.     

Isotropic apparent diffusion coefficient mapping of postnatal cerebral development

Diffusion-weighted imaging (DWI) allows us to image the motion of tissue water. This has been used to demonstrate acute ischaemia. Diffusion imaging is also sensitive to water movement along neuronal tracts. Our objective was to map brain maturation in vivo using maps of apparent diffusion coefficient (ADC). We studied 22 children without neurological disease aged between 2 and 720 days. MRI was performed at 1.5 tesla. Multislice single-shot echoplanar DWI was performed at b 0 and 1000 s/mm(2). ADC maps were generated automatically and measurements were performed in the basal ganglia, frontal and temporal white matter and the pons. There was a decrease over time in water diffusion in the areas examined, most marked in the frontal (0.887-1.898 x 10(-3) mm(2)/s) and temporal (1.077-1.748 x 10(-3) mm(2)/s)lobes. There was little change, after an initial decrease, in the basal ganglia (0.690-1.336 x 10(-3) mm(2)/s). There was a difference in water diffusion between the anterior (0.687-1.581 x 10(-3) mm(2)/s) and posterior (0.533-1.393 x 10(-3) mm(2)/s) pons. These changes correlate well with those observed in progressive myelination: the increased water content probably reflects incomplete myelination and the decrease with time in water motion reflects the increase in myelinated brain.