Multiple helical scans and the reconstruction of over FOV-sized objects in cone-beam CT

In cone-beam computed tomography （CBCT）, there are often cases where the size of the specimen is larger than the field of view （FOV） （referred to as over FOV-sized （OFS））. To acquire the complete projection data for OFS objects, some scan modes have been developed for long objects and short but over-wide objects. However, these modes still cannot meet the requirements for both longitudinally long and transversely wide objects. In this paper, we propose a multiple helical scan mode and a corresponding reconstruction algorithm for both longitudinally long and transversely wide objects. The simulation results show that our model can deal with the problem and that the results are acceptable, while the OFS object is twice as long compared with the FOV in the same latitude.

Derivative-Hilbert-Backprojection based image reconstruction from truncated projections in helical cone-beam CT

In helical cone-beam computed tomography(CT), Feldkamp-Davis-Kress(FDK) based image reconstruction algorithms are by far the most popular. However, artifacts are commonly met in the presence of lateral projection truncation. The reason is that the ramp filter is global. To restrain the truncation artifacts, an approximate reconstruction formula is proposed based on the Derivative-Hilbert-Backprojection(DHB) framework. In the method, the first order derivative filter is followed by the Hilbert transform. Since the filtered projection values are almost zero by the first order derivative filter, the following Hilbert transform has little influence on the projection values, even though the projections are laterally truncated. The proposed method has two main advantages. First, it has comparable computational efficiency and image quality as well as the conventional helical FDK algorithm for non-truncated projections. The second advantage is that images can be reconstructed with acceptable quality and much lower computational cost in comparison to the Laplace operator based algorithm in cases with truncated projections. To point out the advantages of our method, simulations on the computer and real data experiments on our laboratory industrial cone-beam CT are conducted. The simulated and experimental results demonstrate that the method is feasible for image reconstruction in the case of projection truncation.

Cone-beam computed tomography noise reduction method based on U-Net with convolutional block attention module in proton therapy

Cone-beam computed tomography(CBCT) is mostly used for position verification during the treatment process. However,severe image artifacts in CBCT hinder its direct use in dose calculation and adaptive radiation therapy re-planning for proton therapy. In this study, an improved U-Net neural network named CBAM-U-Net was proposed for CBCT noise reduction in proton therapy, which is a CBCT denoised U-Net network with convolutional block attention modules. The datasets contained 20 groups of head and neck images. The CT images were registered to CBCT images as ground truth. The original CBCT denoised U-Net network, sCTU-Net, was trained for model performance comparison. The synthetic CT(SCT) images generated by CBAM-U-Net and the original sCTU-Net are called CBAM-SCT and U-Net-SCT images, respectively. The HU accuracies of the CT, CBCT, and SCT images were compared using four metrics: mean absolute error(MAE), root mean square error(RMSE), peak signal-to-noise ratio(PSNR), and structure similarity index measure(SSIM). The mean values of the MAE, RMSE, PSNR, and SSIM of CBAM-SCT images were 23.80 HU, 64.63 HU, 52.27 dB, and 0.9919, respectively,which were superior to those of the U-Net-SCT images. To evaluate dosimetric accuracy, the range accuracy was compared for a single-energy proton beam. The γ-index pass rates of a 4 cm × 4 cm scanned field and simple plan were calculated to compare the effects of the noise reduction capabilities of the original U-Net and CBAM-U-Net on the dose calculation results. CBAM-U-Net reduced noise more effectively than sCTU-Net, particularly in high-density tissues. We proposed a CBAM-U-Net model for CBCT noise reduction in proton therapy. Owing to the excellent noise reduction capabilities of CBAM-U-Net, the proposed model provided relatively explicit information regarding patient tissues. Moreover, it maybe be used in dose calculation and adaptive treatment planning in the future.

Application of two-phase helical CT in liver neoplasms

Objective: To assess the value of helical CT in the di- agnosis of liver diseases. Methods: 59 patients with different liver diseases were examined by two-phase or multi-phase dynamic helical CT. Results: Small hepatocellular carcinoma showed a higher density in the arterial phase, and a lower den- sity in the portal vein phase. Large hepatic carcino- ma showed a mixed pattern of higher-density in the arterial phase, and a lower density in the portal vein phase. Metastasis carcinoma showed an 'oxeye sign' in the portal vein phase. Hemangioma was not obvi- ously enhanced in the early arterial phase, marginal- ly enhanced in the arterial phase, and equally-densed in the balanced phase. Conclusion: Two-phase helical CT is of value in im- proving the detection rate of or determining the fea- tures of hepatic diseases by two-phase helical dyna- mic scan (2.0-3.0 ml/s speed, and delay time 25- 30 s and 70-85 s).

Value of helical CT volume rendering technique in post-operative evaluation of screw in screw fixation of axis fractures

To explore the value of helical CT volume rendering technique (VRT) in post-operative evaluation of screw fixation of axis fractures.Methods There were 21 cases of screw fixation of axis fractures between February 2002 and May 2004 in the study including six cases with fractures on axis body,five on odontoid process and 10 on axis body and odontoid process.All cases received X-ray plain film,helical CT scanning,multi-planar reformatting(MPR) and VRT.Results Screw fixation through axis body and massa lateralis atlantis was performed in 10 cases and that through axis body and odontoid process in 11.VRT could clearly display full aperture of screw orbit,location of screw and angle of fixation and hence was superior to X-ray plain film and MPR.Multi-angle VRT displayed asymmetrical space of odontoid process and massa lateralis atlantis in four cases and medial deviation of 2～5 mm of half screw in screw fixation through axis body and massa lateralis atlantis in six.Conclusion VRT can eliminate false shadow of fixation screw,clearly display full aperture of screw orbit and hence supply improtant imaging evidence for post-operative evaluation of screw fixation of axis fractures.7 refs,1 fig,1 tab.

利用Cone-Beam CT探讨支抗微螺钉周围骨密度与其稳定性的关系

目的:利用Cone-Beam CT测量支抗微螺钉周围骨密度值,探讨其与微螺钉稳定性的关系。方法:选取颌骨左右对称植入微螺钉后一侧松动而另一侧稳固的7名(共18枚微螺钉)正畸患者。拍摄CBCT,所得三维影像重建后用OnDemand 3DApplication软件对微螺钉骨内部分周围2mm范围内骨密度(以Hounsfield Unit表示)进行测量,自身对照比较分析双侧对称部位所植入微螺钉周围骨密度测量值间的差异。结果:松动微螺钉与稳定微螺钉骨内部分周围2mm范围内骨密度无统计学差异,两侧微螺钉钉尖部1/3、钉中部1/3及钉颈部1/3周围骨密度均无统计学差异。结论:微螺钉种植支抗的稳定性与其周围骨密度间未发现明显相关性。

The Association between Lower Incisal Inclination and Morphology of the Supporting Alveolar Bone—A Cone-Beam CT Study

Aim To investigate the relationship between the positioning of the lower central incisor and physical morphology of the surrounding alveolar bone. Methodology Thirty-eight patients （18 males, 20 females）, with mean age of 13.4 years, were included in this study. As part of orthodontic treatment planning the patients were required to take dental Cone-beam CT （CBCT） covering the region of lower incisors, the sur- rounding alveolar bone and the mandibular symphysis. The cephalometric parameters were designed and measured to indicate the inclination of lower central incisor and physical morphology of the adjacent alveolar bone. Computer-aided descriptive statistical analysis was performed using SPSS 15.0 software package for Windows. A correlation analysis and a linear regression analysis between the incisor inclination and the alveolar bone morphology were performed. Results Significant positive correlations were found between the lower central incisor inclination and the morphological contour of the alveolar bone （P〈0.05）. The lower central incisor root apex was closer to the lingual alveolar crest when it was buccally inclined. Conclusion The morphology of the alveolar bone may be affected by incisal inclination.

Slice-wise reconstruction for low-dose cone-beam CT using a deep residual convolutional neural network

Because of the growing concern over the radiation dose delivered to patients, X-ray cone-beam CT(CBCT) imaging of low dose is of great interest. It is difficult for traditional reconstruction methods such as Feldkamp to reduce noise and keep resolution at low doses. A typical method to solve this problem is using optimizationbased methods with careful modeling of physics and additional constraints. However, it is computationally expensive and very time-consuming to reach an optimal solution. Recently, some pioneering work applying deep neural networks had some success in characterizing and removing artifacts from a low-dose data set. In this study,we incorporate imaging physics for a cone-beam CT into a residual convolutional neural network and propose a new end-to-end deep learning-based method for slice-wise reconstruction. By transferring 3D projection to a 2D problem with a noise reduction property, we can not only obtain reconstructions of high image quality, but also lower the computational complexity. The proposed network is composed of three serially connected sub-networks: a cone-to-fan transformation sub-network, a 2D analytical inversion sub-network, and an image refinement sub-network. This provides a comprehensive solution for end-to-end reconstruction for CBCT. The advantages of our method are that the network can simplify a 3D reconstruction problem to a 2D slice-wise reconstruction problem and can complete reconstruction in an end-to-end manner with the system matrix integrated into the network design. Furthermore, reconstruction can be less computationally expensive and easily parallelizable compared with iterative reconstruction methods.

14例Abernethy畸形患者多层螺旋CT及MRI影像学表现分析

目的分析Abernethy畸形患者多层螺旋CT(multislice helical CT,MSCT)及MRI影像资料,以提高对该类疾病的认识。方法选取2015年1月至2022年1月中山大学附属第一医院及韶州人民医院符合诊断标准的l4例具有完整MSCT或MRI影像资料的Abernethy畸形患者作为研究对象,分析其影像学表现。结果14例患者中,4例Ⅰ型Abernethy畸形患者影像学表现为肝门静脉缺如,1例Ⅰa型门静脉缺如脾静脉-左肾静脉,肠系膜上静脉-腔静脉,3例Ⅰb型Abernethy畸形患者中,肠系膜上静脉及脾静脉-左肾静脉2例,门脉缺如,肠系膜上静脉及脾静脉-腔静脉;肝动脉增粗1例;10例Ⅱ型Abernethy畸形患者影像学特点为门静脉主干或分支细小,部分分支缺如,其中肠系膜上静脉及脾静脉-左肾静脉7例,肠系膜上静脉及脾静脉汇入肠系膜下静脉再分支并与双侧髂内静脉沟通1例,门脉右支-腔静脉2例。结论Abernethy畸形是较罕见的先天性疾病,MSCT及MRI增强扫描是诊断本病的主要影像学手段,对疾病的分型及确定门体分流途径起到重要作用,提高对该病的认识是实现准确诊断的关键。

多层螺旋CT及其后处理技术对隐匿性骨折的诊断价值

目的 探讨多层螺旋CT(MSCT)二维(MPR、MIP)和三维(VRT、SSD)重建技术对复杂结构的隐匿性骨折的诊断价值。资料与方法 对4 2例外伤患者普通X线平片中未显示而临床怀疑有骨折的患者进行MSCT扫描后,通过特殊的CT图像处理软件包在工作站上进行后处理(MPR、MIP、VRT及SSD) ,得到外伤部位骨骼高清晰度的二维和三维图像后,由两位有经验的放射科医师共同阅片,以共同意见为准。结果 4 2例X线平片中未显示骨折的患者经MSCT重建后,18例显示有骨折,其中枕骨骨折2例,肩胛骨骨折2例,肋骨骨折4例,脊椎骨折3例,骨盆骨折3例,股骨颈骨折3例,跟骨骨折1例。结论 MSCT二维和三维重建对临床怀疑骨折而普通X线不能确诊为骨折的病例能准确地作出诊断,并对治疗方案的选择及预后的估计有重要价值。

胆管癌螺旋CT强化特征与病理学对照研究

目的 探讨胆管癌的螺旋CT增强扫描表现与病理学的关系 ,以及螺旋CT的诊断价值。资料与方法 2 8例经手术及病理证实的肝门区胆管癌的螺旋CT平扫及多期增强扫描资料 ,重点观察肿块相对于肝脏的密度变化。结果 肝门区胆管癌CT主要表现为肝门区不规则低或略低密度软组织肿块 ,在动态扫描过程中相对于肝脏密度的变化趋势为高、低、高。 75 % (2 1/ 2 8)的病变于门脉期 (10例 )和延迟期 (11例 )显示最清楚 ,19例有延迟强化 ,延迟强化率为 6 7.9% (19/ 2 8) ;此外螺旋CT还清楚地显示了胆管扩张 ,肝叶萎缩 ,病变周围的异常强化区等间接征象。结论 肝门区胆管癌的CT表现与病理密切相关 。

急性阑尾炎的CT表现

目的 探讨急性阑尾炎的CT表现。方法 对 68例手术、病理证实为急性阑尾炎病人的腹部CT资料进行回顾性分析 ,对阑尾大小、有无阑尾结石、阑尾周围及盲肠末端的改变作了观察、分析。结果 68例中 61例CT诊断为急性阑尾炎 ,7例假阴性 ,CT诊断急性阑尾炎的敏感性为 89.7%。急性阑尾炎的CT表现主要有阑尾增粗 ( 76.5 % ) ,阑尾结石( 2 9.4% ) ,阑尾周围炎性改变 ( 66.2 % ) ,阑尾脓肿 ( 13 .2 % ) ,蜂窝织炎 ( 10 .3 % ) ,盲肠末端肠壁增厚 ( 7.4% )和局部淋巴结肿大 ( 5 .9% )。结论 急性阑尾炎可出现多种CT表现 ,熟悉这些表现有助于提高CT诊断阑尾炎的准确性。

螺旋CT对胃癌浸润及转移的诊断价值

目的 评价螺旋CT三期增强扫描对胃癌浸润及转移的准确性,并探讨影像学与病理学的内在联系。资料与方法 对46例胃癌患者行螺旋CT三期增强扫描并与术后病理对照。结果 (1)螺旋CT诊断浆膜受侵、淋巴结转移和远处转移的准确性分别为84.8％、87.0％和100％。(2)螺旋CT征象中浆膜侵犯、淋巴结转移和远处转移均与其病理特征密切相关(P<0.05)。结论 螺旋CT三期增强扫描能较全面、准确地反映胃癌病理特征,是诊断胃癌浸润及转移的可靠影像学方法。

实时灰阶超声造影和螺旋CT诊断肝肿瘤的比较研究

目的 比较实时超声造影和螺旋CT显示肝肿瘤血流信号的特点。方法 对 2 9例肝肿瘤 (原发性肝癌 16例 ,转移性肝癌 2例 ,血管瘤 6例和肝局灶性结节增生 5例 )分别进行超声造影和CT检查。结果 超声造影显示肝恶性肿瘤的整体型、血管瘤的周边型及局灶性结节增生的中央型出现率显著高于其他病变 (P <0 .0 1)。CT示恶性肿瘤中 94.4%( 17/ 18)动脉期强化、门脉期低密度 ;血管瘤中 83 .3 % ( 5 / 6)呈结节状强化 ;肝局灶性结节增生动脉期均明显强化。超声造影和CT鉴别肝肿瘤的能力无显著差异。结论 超声造影和CT都能敏感地显示不同肝肿瘤的血供特征。

非增强螺旋CT扫描对急性阑尾炎的诊断价值

目的 评价非增强螺旋CT扫描对急性阑尾炎的诊断价值。资料与方法 对 115例临床怀疑急性阑尾炎患者作非增强螺旋CT扫描 ,不口服或结肠内灌注对比剂 ,层厚 10mm ,Pitch 1,扫描范围从L3 椎体至耻骨联合。CT诊断急性阑尾炎的标准包括阑尾增粗横径超过 6mm ,或阑尾结石同时伴有阑尾周围的炎性改变。CT诊断结果与手术、病理或临床随访结果进行对照。结果 CT发现 5 6例真阳性 ,49例真阴性 ,7例假阴性和 3例假阳性。CT诊断急性阑尾炎的敏感性为 89%,特异性为 94%,准确性为 91%,阳性预测值为 95 %,阴性预测值为 88%。 49例无阑尾炎患者中 ,CT发现其他病变 2 2例 (45 %)。结论 非增强螺旋CT扫描 ,能快速、准确地诊断有无急性阑尾炎 ,而且还能发现除阑尾炎以外的其他各种病变。

周围性肺栓塞螺旋CT强化扫描肺密度测量的研究

目的 探讨螺旋CT平扫与强化扫描肺实质密度测量在周围性肺栓塞诊断中的作用。方法 8只犬于DSA下复制为单侧周围性肺栓塞动物模型后进行螺旋CT平扫和强化扫描 ,根据DSA发现的栓塞肺动脉的位置 ,于螺旋CT平扫和强化扫描图像上分别测量栓塞区与对侧肺正常肺实质的CT值 ,比较双肺的CT值差异与净增CT值差异。结果 螺旋CT平扫栓塞区的CT值与对侧正常肺实质的CT值之间无明显差异 (P >0 .0 5 ) ;螺旋CT强化扫描显示栓塞区的CT值明显低于正常肺实质的CT值 (P <0 .0 1) ,而且栓塞区的净增CT值也明显低于正常肺实质的净增CT值 (P <0 .0 1)。结论 螺旋CT强化扫描可以发现周围性肺栓塞所致的低灌注区 。

16层螺旋CT结肠三维成像与仿真内镜的临床应用研究

目的 探讨 16层螺旋CT三维成像与仿真内镜在结肠肿瘤诊断中的应用价值。资料与方法 应用Lightspeed 16CT对 2 6例纤维结肠镜活检证实的结肠癌 (19例 )和结肠息肉 (7例 )进行容积扫描 ,在AW4 .2工作站进行三维成像和仿真内镜观察 ,并与纤维结肠镜结果相比较。结果 2 5例三维成像效果良好 ,仿真内镜与纤维结肠镜显示基本一致 ,1例因肠道准备不彻底 ,成像效果欠佳 ,但不影响诊断 ;CT仿真结肠镜 (CTVC)结合 2D多平面重建(MPR)和透明显示 (RaySum)图像 ,可以提供更多信息 ,有助于病变的准确定位、定性。结论 16层螺旋CT仿真内镜结合三维成像能达到与纤维结肠镜同样的敏感性和特异性 ,加上MPR。

肺腺鳞癌的螺旋CT表现与病理对照研究

目的 探讨肺腺鳞癌的螺旋CT表现与组织病理所见的相关性。资料与方法 搜集经手术病理证实的肺腺鳞癌 15例 ,男 10例 ,女 5例 ,年龄 42～ 73岁 ,平均 6 0 .8岁。均采用螺旋CT扫描。结合组织病理所见 ,观察和评价肿瘤内部结构、密度分布、边缘特征及周围肺组织改变等CT表现。结果 15例肺腺鳞癌中 ,周围型 12例 ,中央型 3例 ;肿块直径为 3.8± 1.1cm ;均匀密度肿块 2例 (13%) ,不均匀密度肿块 13例 (87%) ;常见CT征象包括分叶征 14例 (93%) ,胸膜凹陷征 12例 (80 %) ,肿块内坏死 11例 (73%) ,血管集束征 10例 (6 7%)和毛刺征 8例 (5 3%)。不常见征象包括空洞和支气管气相各 1例。病理上肿瘤呈灰白色 ,边界清楚 ,分叶 ,肿瘤呈实体性生长 ,腺癌与鳞癌成分并存。结论 肺腺鳞癌以周围型多见 ,螺旋CT像上呈软组织肿块 ,常伴有坏死 ,这与肿瘤呈实体性生长的组织病理学特征有关。

主动脉壁内血肿的多层面螺旋CT诊断

目的:评价多层面螺旋CT诊断主动脉壁内血肿的价值。材料和方法:对23例怀疑主动脉病变的患者进行多层面螺旋CT扫描并诊断为主动脉壁内血肿。两名有经验的心血管放射医师按照CT标准做出诊断。使用16排多层面螺旋CT获得1.25mm层厚(1mm重建间隔)图像,应用多平面重建、曲面重建、最大密度投影和容积重建等方法显示壁内血肿及穿透溃疡。结果:23例主动脉壁内血肿中,1例A型,22例B型;B型壁内血肿中,仅累及降主动脉的8例,胸腹主动脉受累11例,局限于腹主动脉3例;11例壁内血肿伴主动脉穿透溃疡,其中2例行带膜内支架治疗。结论:多层面螺旋CT能为主动脉壁内血肿的诊断、鉴别诊断和治疗提供重要信息。

螺旋CT对膀胱癌侵袭性及局部侵袭范围的研究

目的 探讨螺旋CT增强扫描对膀胱癌侵袭性及局部侵袭范围判断的价值。方法 5 0例膀胱癌患者术前一周内行盆腔CT平扫与螺旋CT增强扫描 ,CT所见与手术病理对照。结果 绝大多数膀胱癌出现不同程度强化。I级、I～Ⅱ级癌灶的强化均值为 13Hu、17.8Hu ,Ⅱ级、Ⅱ～Ⅲ级、Ⅲ级癌灶强化均值大于 3 0Hu。螺旋CT增强早期 ,癌组织未侵犯肌层时 ,病变处增厚的膀胱壁见 2～ 3层结构 ,对癌组织局部侵犯范围 (T分期 )分为Tis～T1、T2 、T3a、T3b、T4组 ,总准确率为 85 .7%。结论 膀胱癌的强化程度与其病理组织分级有一定关联。