SAFAIR联合双能量单能谱及非线性优化对比技术提高颈根部图像质量的应用

目的 探讨原始数据迭代重建（SAFIRE）-3联合双能CT单能谱或优化对比技术在去除颈根部伪影、提高图像质量中的应用价值。方法 选择CT双能量增强扫描颈根部有明显伪影的30例患者图像,均采用线性融合SAFAIR-3重建、获得A组图像（SAFAIR-3重建组）,之后加行单能谱分析、获得B组图像（重建+单能谱组）,或加行双能量非线性优化对比处理、获得C组图像（重建+优化对比组）。分别对A、B、C组图像SD、SNR、CNR及图像质量对比分析。结果 A、B、C组伪影区SD、SNR及CNR差异有统计学意义（P<0.05）。B、C组伪影区SNR、CNR高于A组,噪声低于A组（P均<0.05）。B组与C组的SD、SNR及CNR比较差异无统计学意义（P均>0.05）。A、B、C组图像主观评分差异有统计学意义（P<0.05）,A组3分及以上的图像少于B组及C组（P均<0.05）;B组与C组图像主观评分差异无统计学意义（P>0.05）。结论 采用SAFIRE技术联合单能谱或非线性优化对比技术可减轻颈根部硬化伪影、提高颈根部图像质量。单能谱与优化对比技术在提高颈根部图像质量方面无差异。     

基于12和16 bit CT图像的金属伪影校正对放疗剂量分布的影响

目的 利用金属伪影去除技术去除基于12 bit和16 bit CT图像中金属植入物伪影,分析其对图像CT值分布和放疗剂量分布的影响。方法 将金属棒插入模体中,CT扫描得到12和16 bit原始CT图像,运用归一化伪影去除法（NMAR）分别对所得到的原始CT图像进行去伪影处理,得到NMAR修正后图像。临床中选取人工股骨头患者CT图像,对其进行同样处理。比较分析各图像伪影去除前后CT值分布。在放疗计划系统中,基于各图像设计放射治疗计划,计算剂量分布,比较分析各图像的剂量分布差异。结果 12 bit图像中金属CT值为3 071 HU,远小于金属实际CT值11 080 HU;16 bit图像中金属CT值为11 098 HU,与实际值很接近。原始CT图像在金属周围含有大量伪影,CT值与参考图像CT值偏差很大;NMAR校正后图像伪影显著减少,CT值与参考图像较接近。NMAR修正后16 bit图像的剂量分布与参考图像最接近,中心轴上最大剂量偏差为1.8%;12 bit图像与参考图像在金属后方剂量差异很大,最大剂量偏差为81.6%。射线穿过原始图像伪影区域后导致剂量分布与参考图像有明显差异,引起最大剂量偏差达21.6%。结论 含有金属植入物时,基于16 bit图像进行NMAR伪影校正可以得到准确的CT值分布,从而得到准确的剂量分布。     

Effects of premedication with Pronase for endoscopic ultrasound of the stomach: A randomized controlled trial

AIM To analyze the effects of premedication with Pronase for endoscopic ultrasound(EUS) examination of the stomach.METHODS This was a prospective, randomized and controlled clinical study. All patients were randomly assigned to either the Pronase group or placebo group. The pretreatment solution was a mixed solution of 20000 U of Pronase and 60 m L sodium bicarbonate solution in the Pronase group, while an equal amount of sodium bicarbonate solution was administered to the placebo group. All operators, image evaluators and experimental recorders in EUS did not participate in the preparation and allocation of pretreatment solution. Two blinded investigators assessed the obscurity scores for the EUS images according to the size of artifacts(including ultrasound images of the gastric cavity and the gastric wall). Differences in imaging quality, the duration of examination and the usage of physiological saline during the examination process between the Pronase group and the control group were compared.RESULTS No differences existed in patient demographics between the two groups. For the gastric cavity, the Pronase group had significantly lower mean obscurity scores than the placebo group(1.0476 ± 0.77 vs 1.6129 ± 0.96, respectively, P = 0.000). The mean obscurity scores for the gastric mucosal surface were significantly lower in the Pronase group than the placebo group(1.2063 ± 0.90 vs 1.7581 ± 0.84, respectively, P = 0.001). The average EUS procedure duration for the Pronase group was 11.60 ± 3.32 min, which was significantly shorter than that of the placebo group(13.13 ± 3.81 min, P = 0.007). Less saline was used in the Pronase group than the placebo group, and the difference was significant(417.94 ± 121.38 m L vs 467.42 ± 104.52 mL, respectively, P = 0.016).CONCLUSION The group that had Pronase premedication prior to the EUS examination had clearer images than the placebo group. With Pronase premedication, the examination time was shorter, and the amount of saline used during the EUS examination was less.     

Bootstrap quantification of cardiac pulsation artifact in DTI

While several studies have shown the benefit of cardiac gating in diffusion MRI with single-shot EPI acquisition, cardiac gating is still not commonly used. This is probably because it requires additional time and many investigators may not be convinced that cardiac gating is worth the extra effort. Here, we tested a clinically feasible protocol with a minimal increase in scan time, and quantified the effect of cardiac gating under partial or full Fourier acquisition. Eight volunteers were scanned on a 3 T scanner with a SENSE 8-channel head coil. Diffusion-weighted, single-shot spin-echo EPI images were acquired along 32 gradient directions, with or without cardiac gating and with partial or full Fourier acquisition. Vectorcardiography (VCG) was used to trigger acquisition at a minimum delay (30 ms). The uncertainties of DTI derived parameters were estimated using residual bootstrap. With partial Fourier, cardiac gating reduced the uncertainties, and better efficiency in reducing DTI parameter variability was also achieved even allowing for the increase in total scan time. For full Fourier acquisition, minimum time gating slightly decreased the uncertainties but the efficiency was worse. A minimum trigger delay might not be the optimal scheme to avoid the majority of systole but it allows clinically acceptable scan times. We have demonstrated that cardiac gating, especially of partial Fourier acquisitions, can reduce the uncertainties of DTI derived parameters in a time-efficient manner.     

Abolition of Respiratory-Motion Artifact in Computed Tomography Coronary Angiography with Ultrafast Examinations: A Comparison Between 64-row and 320-row Multidetector Scanners

Purpose

To compare the incidence of respiratory artifact in computed tomography (CT) coronary angiography performed with 64-row and 320-row multidetector scanners and to assess its effect on coronary evaluability.

Methods

A retrospective review of consecutive coronary angiograms performed on a 64-row multidetector CT from March to April 2007 (group 1: 115 patients, 63 men; mean age [standard deviation] 59.6 ± 12.8 years) and on a 320-row multidetector CT from March to April 2008 (group 2: 169 patients, 89 men; mean [SD] age 57.9 ± 11.6 years). Two cardiac radiologists assessed the occurrence of respiratory artifact and coronary evaluability in studies with respiratory artifacts. Unevaluable coronary segments because of motion at the same anatomical level of the respiratory artifact were considered unevaluable because of this artifact. The association between the occurrence of respiratory artifact and patient biometrics, medication, and scan parameters was examined.

Results

Respiratory artifacts were detected in 9 of the 115 patients from group 1 (7.8%) and in none of the 169 patients from group 2 (P < .001). Group 1 had longer scan times (median, 9.3 seconds; range, 7.5−14.4 seconds) compared with group 2 (median, 1.5 seconds; range, 1.1−3.5 seconds; P < .001). In group 1, 4 patients (3.5%) showed unevaluable coronary segments because of respiratory artifacts, and the CT coronary angiography was repeated in 1 patient (0.9%).

Conclusions

Respiratory artifacts are important in CT coronary angiography performed with 64-row multidetector scanners and impair the diagnostic utility of the examination in up to 3.5% of the studies. These artifacts can be virtually eliminated with a faster scan time provided by 320-row multidetector CT.     

能谱CT单能量成像去除CT尿路成像排泄期对比剂硬化伪影--临床应用研究

目的 探讨能谱CT单能量(85、90 keV)成像技术去除CT尿路成像(CTU)排泄期对比剂硬化伪影(BHA)的价值.方法 对15例成年患者于CTU排泄期应用能谱CT行尿路区能谱模式(GSI)扫描,在工作站以GSI viewer浏览器重建66、85和90 keV三组单能量图像.用66 keV图像代替传统120 kVp混合能量图像进行对比分析.由2名放射科医师在固定窗宽(350 HU)、窗位(40 HU)下对重建的1.25mm薄层轴位图像及重组VR图像质量进行主观目测评分,并测量图像指定区域(肾盂、肾盏旁BHA最明显处肾实质)的噪声值(以SD值表示),以腹壁下脂肪的噪声值为图像背景噪声(Nb),BHA(BHA)值为No与Nb平方差的平方根.结果 66、85和90 keV三组单能量图像的BHA分别为(28.12±8.89)HU、(16.75±8.05)HU及(16.05±7.78) HU,Nb分别为(13.01±1.96) HU、(19.83±2.84) HU及(20.13±2.83)HU.与66 keV组图像比较,85 keV和90 keV组图像的BHA分别降低了约40.43％和42.92％(P均＜0.001),Nb分别增加了约52.42％及54.72％(P均＜0.001),但85 keV和90 keV两组单能量图像间的BHA及Nb差异均无统计学意义(P=0.682、0.516).对图像的BHA面积、肾小盏边缘显示的锐利程度及重组VR图像质量进行主观评分,85和90 keV组图像的评分分别较66 keV组提高约100.75％、105.26％和94.49％(x2=26.82、28.71、24.88,P均＜0.001);而85和90 keV两组图像间各主观评分差异均无统计学意义(P=1.00).结论 与相当于传统120 kVp混合能量模式的66 keV组图像相比,能谱CT可在85和90 keV单能量水平显著降低CTU排泄期肾盂肾盏内高浓度对比剂产生的BHA,提高图像质量.     

探讨数字断层融合技术层中心与图像变形的相关性

目的通过模型评价数字断层融合(DTS)技术层中心与图像变形的相关性。方法按左右(L-R)方向和头尾(C-C)方向均相距6cm将11个直径为13.5mm钢球排在同一平面。将实验模型固定在距检查床120mm高度处,变化Height值;变化实验模型高度,同时变化对应Height值;分别测量各钢球在L-R和C-C两个方向上的直径及C-C方向上的成像范围。结果采用Thickness++重建后,各钢球L-R方向上的直径无明显变形,C-C方向上的直径均变小,最大变形度约为2.96%,位于层中心的钢球变形度最小。在C-C方向上存在金属伪影,采用Thickness++(Metal)重建后金属伪影不明显,但钢球在L-R和C-C两个方向的直径均变小。实验模型越靠近床面,C-C方向上的成像范围越大。结论 DTS偏中心成像时,ROI图像会发生变形;采用Thickness++(Metal)重建能有效去除金属伪影。     

能谱成像技术减除脊柱金属植入物伪影的临床应用价值

目的评价宝石CT能谱成像技术在减除脊柱金属植入物伪影方面的临床应用价值。方法对20例带有脊柱金属植入物的患者行宝石CT能谱扫描,扫描后获得(120Kvp)混合能量图像。用能谱分析软件(GSI viewer)进行分析,在40-140Kev(间距10Kev)重建11种单能量图像。然后选取最佳单能量图像行金属伪影消除重建(Metal-Artifacts Reduction System,MARs),获得MARs能谱图像(110Kev单能量+MARs图像)。由3名放射科医师采用4分量表对图像质量进行主观目测评分,测量椎弓根螺钉前端的放射状伪影长度以评价其伪影程度。对所获得数据采用SPSS17.0进行配对t检验分析。结果在11种单能量图像组中,110Kev单能量图像组的放射状金属伪影长度最短,主观评分最高,因此所有20例患者的图像均于110Kev行MARs重建。MARs能谱图像组(110Kev单能量+MARS图像)与混合能量图像组的主观评分及伪影长度之间均存在显著性差异(P=0.000<0.05),即MARs能谱图像组的金属伪影明显降低,图像质量明显优于混合能量图像组。结论在脊柱金属植入物患者的单能量图像组中,110Kev为图像质量最佳的单能量成像点。宝石CT能谱成像技术能够显著减少脊柱金属植入物的伪影,使CT图像的质量明显提高,具有较高的临床应用价值。     

Diagnostic problems in two-dimensional shear wave elastography of the liver

Two-dimensional shear wave elastography (2D-SWE) is used in the clinical setting for observation of the liver. Unfortunately, a wide spectrum of artifactual images are frequently encountered in 2D-SWE, the precise mechanisms of which remain incompletely understood. This review was designed to present many of the artifactual images seen in 2D-SWE of the liver and to analyze them by computer simulation models that support clinical observations. Our computer simulations yielded the following suggestions: (1) When performing 2D-SWE in patients with chronic hepatic disease, especially liver cirrhosis, it is recommended to measure shear wave values through the least irregular hepatic surface; (2) The most useful 2D-SWE in patients with focal lesion will detect lesions that are poorly visible on B-mode ultrasound and will differentiate true tumors from pseudo-tumors (e.g., irregular fatty change); and (3) Measurement of shear wave values in the area posterior to a focal lesion must be avoided.