Diffusion of Eu(III) in compacted bentonite—effect of pH, solution concentration and humic acid

The effect of pH, Eu(III) solution concentration and humic acid on the diffusion of Eu(III) in compacted bentonite (ρ_b=1000±30 kg/m³) was studied with “in-diffusion” method at an ionic strength of 0.1 M NaClO₄. The results (K_d values from the first slice and theoretical calculation, apparent and effective diffusion coefficients) derived from the new capillary method are in good agreement with the literature data under similar conditions, and fit the Fick's second law very well. The results suggest that the diffusion of Eu(III) is dependent on pH values and independent on solution concentration in our experimental conditions. Humic acid forms precipitation/complexation with Eu(III) at the surface of compacted bentonite and thus deduces the diffusion/transport of Eu(III) in compacted bentonite. The K_d values in compacted bentonite are in most cases lower than those in powdered bentonite obtained from batch experiments. The difference between the K_d values from powdered and compacted bentonite is a strong function of the bulk density of the bentonite. The results suggest that the content of interlaminary space plays a very important role to the diffusion, sorption and migration of Eu(III) in compacted bentonite.     

急性脑缺血及再灌注磁共振扩散加权成像的特点

目的 用改良的线栓法制作大脑中动脉阻塞（ＭＣＡＯ）动物模型,探讨急性脑缺血及再灌注的磁共振扩散加权成像（ＤＷＩ）的特点。方法 １８只Ｓｐｒａｇｕｅ－Ｄａｗｌｙ大白鼠,随机分为４组：Ａ组（６只）,非再通组;Ｂ、Ｃ、Ｄ组（各４只）,分别是于ＭＣＡＯ３０分钟、１小时、２小时后再通,于不同时间点作ＤＷＩ和Ｔ２ＷＩ,通过后处理得到表观扩散系数（ＡＤＣ）像并计算感兴趣区的ＡＤＣ、相对ＡＤＣ（ｒＡＤＣ）及ＤＷＩ     

MR扩散加权成像检查膝关节软骨早期退变的研究

目的 探讨早期关节软骨退变在3.0 T MR扩散加权成像(DWI)卜的表现及其价值.方法 选用山羊20只,20个左侧膝关节腔内注射10 ml木瓜蛋白酶溶液(5 U),建立早期关节软骨退变动物模型(试验组),20个右侧膝关节作为正常对照组,并在注药前及注药后24 h行双侧膝关节常规MRI及DWI.测昔膝关节软骨各个感兴趣区的表观扩散系数(ADC)值,比较各组问的差异.并取关节软骨组织作蛋白多糖含量测定和组织病理学检查.对骨性关节炎软骨病变组患者的100个膝关节和正常对照组20个膝关节行常规MRI及DWI,测量膝关节软骨各个感兴趣区的ADC值,比较各组间的差异.对所获数据进行配对t检验分析.结果 羊正常对照组关节软骨ADC均值(ADCav)为(14.2±2.3)×10-4mm2/s,膝关节兴趣区早期退变关节软骨ADCav为(17.5±4.2)×10-4mm2/s,早期退变关节软骨组的ADC值明显高于对照组,两组间差异有统计学意义(t=2.709;P=0.016).羊膝关节软骨蛋白多糖含量变化:对照组关节软骨蛋白多糖含量平均为4.22 ×106μg/kg,木瓜蛋白酶注射后24 h试验组关节软骨蛋白多糖含量降低至0.82 × 106μg/kg,试验组与正常对照组比较,差异有统计学意义(t=2.705,P=0.018).对照组人膝关节软骨ADCav为(7.6±2.2)×10-4mm2/s,骨性关节炎软骨病变组人膝关节软骨ADCav为(10.3±4.2)×10-4mm2/s.人骨性关节炎软骨病变组膝关节软骨的ADCav值明显高于正常组,差异有统计学意义(t=2.609;P=0.014).结论 MR DWI能发现常规MRI序列软骨信号尚未改变的更早期关节软骨退变.     

不同b值和扩散张量成像导出量的定量关系研究

目的　探索不同b值和扩散张量成像参数的定量关系。方法　对 12例正常成人进行扩散张量磁共振扫描 ,测量多个灰白质感兴趣区的表观扩散系数 (ADC)、指数表观扩散系数 (EADC)、最大特征值、各向异性比率 (FA)、各向异性指数 (AI)和相对各向异性 (RA)等参数 ,分析这些参数随着b值的变化趋势。结果　FA和RA的平均值、中位数、标准差以及变异系数都不随b值变化 (P >0 5 ) ;而ADC、EADC及最大特征值受b值的影响 (P <0 0 1) ,随b值的增加而降低 ;AI的平均值、中位数、标准差及变异系数在不同被试者间差异存在显著性意义 (P <0 0 5 )。结论　b值确实影响多个扩散张量成像的导出量。在临床应用中当比较不同被试者 ,或者不同组织结构时 ,应尽量选择同样的成像参数 ,特别是b值 ,同时选择不受b值影响的参数 ,如FA和RA。     

MR线性扫描扩散加权技术在猪股骨头骨骺缺血模型中的初步应用研究

目的 采用MR线性扫描扩散加权成像(LSDWI)技术,观察乳猪股骨头骨骺缺血不同时期的DWI表现特征及变化过程,以期提供骨骺缺血性损害的时间及程度信息.方法 25只1周龄大小的乳猪,手术结扎一侧股骨颈处全部供血动脉,引起股骨头骨骺缺血,另一侧作为健康对照侧.分别在术前(25只)及术后3 h(25只)、72 h(20只)、1周(15只)、3周(10只)、6周(5只)进行LSDWI,计算股骨头骨骺表观扩散系数(ADC)值,采用配对t检验比较缺血侧和对照侧ADC值的差异,观察不同时期ADC值的变化.各时间点LSDWI扫描完成后分别处死5只,行解剖学及组织学研究.结果 术后3 h,缺血性股骨头的ADC值[(1.22±0.37)×10-3mm2/s]较正常对照侧[(1.73±0.33)×10-3mm2/s]显著下降(t=3.914,P＜0.01),术后72 h ADC值[(2.15±0.32)×10-3mm2/s]较正常对照侧[(1.70±0.22)×10-3mm2/s]升高(t=3.348,P＜0.01),其后一直保持上升趋势至术后第6周[缺血侧为(1.61±0.27)×10-2mm2/s,对照侧为(1.11±0.45)×10-3mm2/s](t=4.136,P＜0.01).除术后第3周和第6周2个时间点ADC值的变化百分之间差异无统计学意义外(t=2.29,P＞0.05),在整个实验过程中,每2个连续时间点之间ADC值的变化百分差异均有统计学意义(P值均＜0.01).组织学研究显示,在缺血性股骨头骨骺,首先是软骨细胞和骨细胞死亡,血管塌陷.随时间的变化,出现不同程度的缺血性股骨头骨骺软骨的异常增厚、二次骨化中心内出现软骨岛和局限性的生长板组织结构破坏.结论 股骨头骨骺的LSDWI表现特征随缺血时间的延长而变化,通过LSDWI技术能获得股骨头骨骺的ADC值,其作为股骨头缺血和坏死的一个指标,可用于评估缺血性骨骺组织受损时间性信息及程度.     

正常人颈髓MR扩散张量成像的初步研究

目的探讨颈髓扩散张量成像(DTI)的方法,获取正常人颈髓DTI的参数值,为颈髓病变的DTI研究提供依据。方法使用单次激发自旋回波平面回波(SE-EPI)序列对36例健康志愿者行颈髓扩散张量成像检查。在颈髓各节段分别测量其表观扩散系数(ADC)值、各向异性分数(FA)值、第1本征值(λ1)、第2本征值(λ2)以及第3本征值(λ3)。结果所有志愿者均完成该项检查,后处理图像上颈髓显示清晰,没有明显图像失真。颈髓ADC值为(914.44±82.61)×10-6mm2/s,FA值为(593.84±52.22)×10-3,λ1、λ2、λ3分别为(1585.10±130.07)×10-6mm2/s、(559.84±66.49)×10-6mm2/s、(613.28±128.71)×10-6mm2/s。λ1与λ2、λ3值比较,λ1值明显大于λ2及λ3,差异有统计学意义(P<0.05),λ2与λ3之间差异无统计学意义(P>0.05)。2λ1/(λ2+λ3)的比值为2.74±0.32。结论使用SE-EPI序列行颈髓DTI的检查能够获得比较满意的图像,测得的各项张量参数值稳定。平行于脊髓长轴方向的水分子扩散活动明显强于垂直于脊髓长轴方向的扩散,从而提示脊髓具有圆柱状的扩散特点。     

Gd-EOB-DTPA对多b值肝脏DWI中表观弥散系数值的影响

目的 通过行肝脏多b值弥散加权成像（DWI）,观察注射钆塞酸二钠（Gd-EOB-DTPA）前、后不同时相表观弥散系数（ADC）值的变化,探讨增强后行DWI的可行性。方法 收集行Gd-EOB-DTPA肝脏增强的受检者126例,其中,例行体检的健康志愿者30名,肝脏病变患者96例（原发性肝癌25例、转移性肝癌20例、肝血管瘤28例、肝囊肿23例）,均经临床或病理证实。在Philips Achieva 1.5T双梯度超导MR成像系统上,行同相与正反相T1加权像闭气轴位平扫及轴位呼吸门控DWI。通过肘静脉向受检者注射0.025 mmol/kg Gd-EOB-DTPA,行动脉期、静脉期、3 min期、10 min期、20 min期、30 min期闭气轴位T1加权高分辨率各向同性容积激发序列（THRIVE）扫描,在5 min期,行轴位T2加权像脂肪抑制呼吸门控扫描,在15 min期,行轴位呼吸门控DWI后,接着行冠状位T2加权闭气扫描,在25 min期,行轴位呼吸门控DWI。平扫期、15 min期、25 min期的DWI参数完全一致,为单次激发自旋回波-平面回波成像（SE-EPI）序列,b值依次取0、50、300、600 s/mm2,扫描时间196 s。在EWS工作站上,通过ADC分析函数生成平扫期、15 min期、25 min期在b=50、300、600 s/mm2时的ADC图,测出正常肝脏、原发性肝癌、转移性肝癌、肝血管瘤、肝囊肿的ADC值,对同一b值下同一疾病在平扫期、15 min期及25 min期的ADC值进行t检验,分析是否存在统计学差异。结果 同一b值下同一疾病的ADC值在平扫期时最大,随着Gd-EOB-DTPA的注入,ADC值开始下降,然后上升,到了25 min期,ADC值与平扫期时基本一致,15 min期的ADC值最低,平扫期、15 min期、25 min期的ADC值差异无统计学意义（t=0.25~1.29,P均>0.05）。同一疾病同一时相的DWI中,随着b值的增加,ADC值不断下降,b值越小,ADC值越大。结论 静脉注射Gd-EOB-DTPA后,肝脏ADC值下降十分有限,增强后行DWI是可行的。     

DWIBS和全脊柱MR成像对脊柱恶性肿瘤的诊断研究

目的 探讨磁共振背景抑制弥散加权成像(DWIBS)在脊柱恶性肿瘤早期诊断中临床应用价值.方法 60例临床证实为恶性肿瘤患者行全身弥散加权成像检查,并于同一时间对可疑部位行常规磁共振成像检查,必要时增强扫描,诊断结果与临床综合评价结果进行比较,分别比较DWIBS和常规磁共振成像所显示的病例数.结果 60例患者中55例经临床综合评价为脊柱转移瘤.常规MRI联合DWIBS检查的敏感性、特异性、阳性预测值、阴性预测值分别为98.8％、99.4％、95.4％、99.8％.与常规MRI及DWIBS比较,P＜0.05有统计学意义.结论 DWIBS在恶性肿瘤脊柱转移瘤早期诊断中具有一定的应用价值,结合常规MRI检查可进一步明确诊断.     

MR扩散张量成像对健康成人视放射纤维束的初步研究

分别为(43.5±8.1)、(43.2±7.5)mm,FA分别为0.53±0.10、0.53±0.07,差异均无统计学意义(t值分别为0.12、0.00,P值分别为0.91、1.00).结论 视放射Meyer袢MT值变异较大,可以作为预测颞叶切除术后视野缺损的重要指标.     

MR-DWI的ADC与rADC在乳腺疾病良恶性鉴别诊断中的比较

目的：探讨磁共振扩散加权成像（DWI）的表观扩散系数（ADC）、相对表观扩散系数（rADC）的定量分析在确定乳腺病变良恶性中的诊断价值。方法：2013年1月-2014年1月220例符合研究纳入标准：①临床拟诊良、恶性肿瘤的患者;②乳腺 MRI 检查后在本院进行手术或粗针穿刺活检取得病理结果的患者;③乳腺 MRI 检查前未进行活检及各种干预性措施的患者;④病灶截面积≥25 mm2者;⑤患者乳腺纤维腺体组织为 ACR 分型中Ⅱ～Ⅳ型（即纤维腺体体积≥25％者）等的病例进行乳腺 MRI 的扩散成像（DWI）序列诊断价值的前瞻性研究。所有病例术前均接受 MRI 检查,包括 DWI （b＝800 s/mm2）。测量患者的病灶、对侧胸肌、同侧及对侧正常纤维腺体的 ADC 值,并计算2个相对表观扩散系数值,即rADC1＝病灶 ADC 值/对侧正常纤维腺体 ADC 值和 rADC2＝病灶 ADC 值/对侧胸大肌 ADC 值,比较 ADC 与 rADC 值对乳腺良恶性病变的诊断价值。结果：220例病灶中良性病变105例,恶性病变115例。当病灶 ADC 值的良恶性诊断阈值为1．20×10-3 mm 2/s 时,曲线下面积为0．923,其敏感度为88．7％,特异度为87．6％,诊断准确率达88．2％。当rADC1值的诊断阈值为0．70时,曲线下面积为0．834,其敏感度为82．6％,特异度为79．0％,诊断准确率达80．9％。当rADC2值的诊断阈值为0．81时,曲线下面积为0．873,其敏感度为83．5％,特异度为78．1％,诊断准确率达81．0％。结论：DWI 表观扩散系数（ADC）与相对表观扩散系数（rADC）的定量分析在确定乳腺良恶性病变性质中的具有较高诊断价值。当 b 值相同时,病灶表观扩散系数（ADC 值）对于乳腺疾病良恶性的鉴别诊断特异性高于相对表观扩散系数（rADC值）;其敏感性两者之间无明显统计学差异。胸大肌作为参照,其诊断价值与正常纤维腺体相当。     

兔脑缺血区扩散、灌注成像及细胞内钙的对照研究

目的　本实验预通过制作兔大脑中动脉持久性闭塞 (MCAo)模型 ,采用MR扩散和灌注加权成像 (DWI和PWI)确认半暗带 ,并与病理脑片水平不同缺血区域的细胞内钙离子浓度的变化进行对照研究 ,试图了解脑缺血早期半暗带MR特征及其与细胞内钙超载的关系。方法　 2 8只新西兰兔按MCAo后 0 5～ 3 6h间不同时间分为 7组 ,在既定时间行DWI及PWI,最后 1次MR检查完后立即处死动物 ,并迅速取脑 ,制作病理脑片及钙离子荧光探剂标记。将制备好的脑片置于激光共聚焦显微镜下观察兴趣区荧光强度。将缺血侧尾壳核区 (Ⅰ区 )、额顶叶皮质区 (Ⅱ区 )的MR各项参数及钙离子荧光强度进行配对t检验及方差分析。结果　MR结果显示MCAo后 ,缺血侧Ⅰ区、Ⅱ区脑血流量(CBF)、脑血容量 (CBV)较对侧有明显的降低 ,MCAo后 0 5～ 6h ,Ⅰ区的相对表观扩散系数 (rADC)明显低于Ⅱ区 (t=2 6 3 3 ,P <0 0 0 1)。 12h后差异无显著性意义 (F =1 60 ,P >0 0 5)。细胞内钙荧光检测结果显示MCAo后 0 5h ,Ⅰ区的荧光强度 (FI)即较对侧增强 3 18± 0 14倍 (t =5 2 7,P <0 0 5) ,而Ⅱ区与对侧相应区域在缺血后 1 5h以内FI差异无显著性意义 (F =3 2 1,P >0 0 5) ,3h后缺血侧Ⅱ区FI较对侧相应区域升高 (F =10 3 8,P <0 0 1)。Ⅰ区缺血 3h以内rA     

颈髓MR扩散加权成像优化b值初步研究

目的：探讨1.5T磁共振颈髓扩散加权成像（DWI）b值的选择及获取正常脊髓表观扩散系数（ADC值）。方法：50例健康志愿者进行颈髄DWI检查,采用单次激发平面回波（SSH-EPI-DWI）序列,扩散梯度因子b值分别取300、500和1000 s/mm^2,分3组进行扫描,测量正常人颈髓ADC值并分析各组DWI图像及ADC图像质量,对比不同b值对成像效果的影响。结果：50例受检者均获得较满意的DWI和ADC图像并测得正常人颈髓ADC值。随着b值由300 s/mm^2升高到1000 s/mm^2,图像信号强度逐渐降低。以b值为500 s/mm^2时成像效果较好,信噪比和对比度较高,伪影较少。在500s/mm^2时测得的50例正常颈髓的平均ADC值为（95.70±11.01）×10-5mm^2/s。结论：利用SSH-EPI-DWI序列,正常人颈髓在b值为500 s/mm^2时可获得颈髓较满意的DWI和ADC图像。     

Effect of gadolinium chelate contrast agents on diffusion weighted MR imaging of the liver, spleen, pancreas and kidney at 3 T

Purpose

To retrospectively test the null hypotheses that the qualitative appearance of DWI and the signal intensity values in DWI and corresponding ADC values of the liver, spleen, pancreas and kidneys are identical before and after the administration of gadolinium.

Materials and methods

Following IRB approval, DWI was acquired in 50 patients (25 male; mean age 54.9 years) prior to and after contrast administration, using single-shot echo planar imaging with b-values of 50 s/mm² and 800 s/mm² at 3 T. Binomial analysis was used to determine which image set was more significantly preferred in conveying the diffusion information. Pre- and post-gadolinium DWI and ADC values of corresponding regions of each organ were analyzed using standardized signal intensity measurements.

Results

Pre-contrast DWI images of the liver, spleen, and pancreas were preferred 52%, 49%, and 58%, respectively, with none of the differences being statistically significant. DWI of the kidneys was preferred on pre-contrast images in 83% (p < 0.001). In the liver and spleen, contrast caused a significant increase in the post-contrast DWI signal intensity values at b = 50 (p < 0.02) and b = 800 (p < 0.05) but had no statistically significant effect on the ADC value (p > 0.40). Pancreatic DWI signal intensity and ADC values pre- and post-contrast were also not significantly different (p = 0.489). In the renal parenchyma, significant decrease in the values of DWI at b = 50 (p < 0.01) and b = 800 (p < 0.01) as well as ADC (p < 0.02) was demonstrated following gadolinium administration.

Conclusion

Intravenous gadolinium administration does not make a statistically significant difference in the qualitative appearance or ADC measurements of the liver, spleen, or pancreas when comparing pre-contrast to post-contrast DWI. In the kidneys, however, ADC values are significantly lower post-contrast with the pre-contrast diffusion weighted images also being qualitatively preferred.     

Comparison of the diagnostic performances of diffusion parameters in diffusion weighted imaging and diffusion tensor imaging of breast lesions

Purpose

To evaluate the diagnostic efficiency of the diffusion parameters measured by conventional diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) for discrimination of malignant breast lesions from benign lesions and the normal breast.

Materials and methods

The study included 52 women with 55 breast lesions (30 malignant, 25 benign). DTI and DWI were performed complementary to dynamic contrast MRI at 3T. Apparent diffusion coefficient (ADC) of DWI, mean diffusivity (MD) and fractional anisotropy (FA) values of DTI were measured for lesions and contralateral breast parenchyma in each patient. We used b factors of 0, 50, 850, 1000 and 1500 s/mm² for DWI and b 0 and 1000 s/mm² for DTI. ADC, MD and FA values were compared between malignant and benign lesions, and the normal parenchyma by univariate and multivariate analyses.

Results

Diffusion parameters showed no difference according to menopausal status in the normal breast. ADC and MD values of the malignant lesions were significantly lower than benign lesions and normal parenchyma (p = 0.001). The FA showed no statistical significance. With the cut-off values of ≤1.23 × 10⁻³ mm²/s (b 0–1000 s/mm²) and ≤1.12 × 10⁻³ mm²/s (b 0–1500 s/mm²), ADC showed 92.85% and 96.15% sensitivity; 72.22% and 73.52% PPV, respectively. With a cut-off value of ≤1.27 × 10⁻³ mm²/s (b 1000 s/mm²), MD was 100% sensitive with a PPV of 65.90%. Comparing the diagnostic performance of the parameters in DTI with DWI, we obtained similar efficiency of ADC with b values of 0,1000 and 0,1500 s/mm² and MD with a b value of 0, 1000 s/mm² (AUC = 0.82 ± 0.07).

Conclusion

ADC of DWI and MD of DTI values provide significant discriminative factors for benign and malignant breast lesions. FA measurement was not discriminative. Supported with clinical and dynamic contrast MRI findings, DWI and DTI findings provide significant contribution to the final radiologic decision.     

DTI在腰椎间盘退行性改变中的应用初探

目的:探讨扩散张量成像(DTI)定量指标ADC及FA值与腰椎间盘退行性改变Pfirrmann分级的相关性.方法:将105例腰腿痛患者纳入研究,所有患者行椎间盘常规MRI及矢状面DTI扫描,根据T2 WI上椎间盘的特点对525个腰椎椎间盘进行Pfirrmann(Pm)分级,观察邻近终板的退变情况,测量椎间盘髓核区的ADC值及FA值并比较各级椎间盘之间的差异,采用Spearman等级相关检验分析ADC和FA值与Pm分级的相关性,并计算2个指标对椎间盘退变(PmⅣ～Ⅴ级)的诊断效能.结果:105例共525个腰椎椎间盘中PmⅠ～Ⅴ级分别有41、112、164、141和67个.经方差分析,Pm Ⅰ和Ⅱ级椎间盘间ADC值、PmⅣ及Ⅴ级椎间盘间ADC值和FA值的差异无统计学意义(P＞0.05),其余各分级之间2个指标的差异有统计学意义(P＜0.05).经ROC分析,ADC值及FA值对PmⅣ、Ⅴ级椎间盘的诊断效能分别为0.846和0.932,两者间差异有统计学意义(P＜0.05).Spearman秩相关分析显示,椎间盘退变Pm分级与ADC值呈负相关(rs=-0.66,P＜0.05),与FA值呈正相关(rs=0.805,P＜0.05).结论:DTI作为定量MRI的一种特殊检查技术,其测量参数与Pfirrmann分级之间具有很好的相关性,可作为一种无创性的检查方法应用于椎间盘退变的研究.     

表观扩散系数预测乳腺癌新辅助化疗反应初探

目的 探讨乳腺癌患者新辅助化疗前肿瘤表观扩散系数(ADC)及化疗第1周期后ADC的变化,预测新辅助化疗反应的价值.方法 20例21个病灶经穿刺活检证实为乳腺癌的患者分别于阿霉素类和紫杉类抗肿瘤新辅助化疗前1周之内、第1周期化疗后(18～21 d之内)、术前1周之内进行MR扩散加权成像(DWI)和增强扫描,根据增强MRI肿瘤的变化,将其分为反应组及相对无反应组,对2组肿瘤初始ADC及化疗第1周期后ADC的变化进行分析.结果 反应组15个病灶化疗前初始ADC为(0.98±0.15)×10-3 mm2/s,化疗第1周期后升高到(1.22±0.23)x 10-3 mm2/s,差异具有统计学意义(P<0.05);相对无反应组6个病灶化疗前初始ADC为(1.09±0.08)×10-3mm 2/s,第1周期后为(1.11±0.07)×10-3 mm2/s,差异无统计学意义(P>0.05);反应组初始ADC低于相对无反应组(P<0.05);肿瘤初始ADC与化疗第1周期后ADC的变化值呈负相关关系(r=-0.51,P<0.05).结论 初步研究结果表明,乳腺癌肿瘤初始ADC值及新辅助化疗第1周期后ADC值变化有可能成为预测乳腺癌新辅助化疗疗效的指标之一.     

Theoretical and experimental evaluation of phase-dispersion effects caused by brain motion in diffusion and perfusion MR imaging

We investigated intravoxel phase dispersion caused by pulsatile brain motion in diffusion spin-echo pulse sequences. Mathematical models were used to describe the spatial and temporal velocity distributions of human brain motion. The spatial distribution of brain-tissue velocity introduces a phase spread over one voxel, leading to signal loss. This signal loss was estimated theoretically, and effects on observed diffusion coefficient and perfused capillary fraction were assessed. When parameters from a diffusion pulse sequence without motion compensation were used, and ECG triggering with inappropriate delay times was assumed, the maximal signal loss caused by brain-motion-induced phase dispersion was predicted to be 21%. This corresponds to a 95% overestimation of the diffusion coefficient, and the perfusion-fraction error was small. Corresponding calculations for motion-compensated pulse sequences predicted a 1% to 1.5% signal loss due to undesired phase dispersion, whereas experimental results indicated a signal loss related to brain motion of 4%.     

Diffusion as a mechanism of postmortem drug redistribution: An experimental study in rats

Summary In some cases of drug overdose there is a reservoir of unabsorbed drug in the stomach and gut. Furthermore, agonal aspiration might establish a second reservoir in the lungs. Two experimental rat models were used to study if diffusion from these reservoirs could contribute to the phenomenon of postmortem drug redistribution. Overnight fasted rats were sacrificed by CO₂ and 75 mg of amitriptyline (AMI) was administered by a gastric tube. In the first series (n = 19), the tubes were removed after AMI administration. In the second series (n = 17), the trachea was ligated and cut prior to drug administration to prevent airways contamination. The rats were left at room temperature on their back for a period of 5, 10, 24, 48, 96 up to 192 h and samples of heart blood, blood from the inferior vena cava, tissue samples from heart, lungs, different liver lobes, kidney and psoas muscle were taken. In both series of rats we observed that as early as 5 h postmortem increasing concentrations of amitriptyline were found in the liver lobes lying closest to the stomach. In rats where the trachea was not ligated, drug contamination of the lungs also resulted in an increase in drug concentration within 5 h in heart blood and heart muscle. In rats where the trachea had been ligated, amitriptyline was found in the lungs after 96 h postmortem. The main metabolite nortriptyline was also detected. We concluded that postmortem diffusion from the gastrointestinal tract could be a major mechanism behind the phenomenon of postmortem redistribution of drugs in human case material, and that agonal aspiration may be followed by a rapid increase in postmortem drug concentration in autopsy samples.      

Role of PROPELLER diffusion weighted imaging and apparent diffusion coefficient in the diagnosis of sellar and parasellar lesions

Objective

To evaluate the role of the apparent diffusion coefficient (ADC) using periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) diffusion weighted imaging (DWI) in the differentiation between sellar and parasellar mass lesions.

Materials and methods

The study protocol was approved by our institutional review board. We retrospectively studied 60 patients with sellar and parasellar lesions who had undergone PROPELLER DWI on a 3-T MR imager. Conventional MRI findings were expressed as the ratio of signal intensity (SI) in the lesions to the normal white matter and the degree of contrast enhancement. ADC values were calculated as the minimum (ADC-MIN), mean (ADC-MEAN), and maximum (ADC-MAX). All patients underwent surgery and all specimens were examined histologically. Logistic discriminant analysis was performed by using the SI ratios on T1- and T2-weighted images (T1-WI, T2-WI), the degree of enhancement, and absolute ADC values as independent variables.

Results

ADC-MIN of hemorrhagic pituitary adenomas was lower than of the other lesions with similar appearance on conventional MRI (non-hemorrhagic pituitary adenomas, craniopharyngiomas, Rathke's cleft cysts; accuracy 100%); the useful cut-off value was 0.700 × 10⁻³ mm²/s. ADC-MAX of meningiomas was lower than of non-hemorrhagic pituitary adenomas (accuracy 90.3%; p < 0.01). ADC-MIN of craniopharyngiomas was lower than of Rathke's cleft cysts (accuracy 100%; p < 0.05).

Conclusion

As PROPELLER DWI is less sensitive to susceptibility artifacts than single-shot echoplanar DWI, it is more useful in the examination of sellar and parasellar lesions. Calculation of the ADC values helps to differentiate between various sellar and parasellar lesions.