Application of Dual-layer Detector Spectral Computed Tomography Virtual Non-contrast Scanning in Enhanced Chest Computed Tomography for Children
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摘要:
目的:讨论双层探测器光谱CT(DLCT)虚拟平扫(VNC)技术在儿童胸部CT增强检查中应用的可行性。方法:回顾性分析我院在双层探测器光谱CT上扫描的51例儿童增强胸部CT影像数据及临床资料。对每例原始图像采取相同方案进行处理:分别利用静脉期光谱基数据(SBI)进行投影空间光谱重建得到VNC图像,并和常规真实平扫(TNC)图像从图像质量和辐射剂量两方面进行比较:选用两位高年资影像诊断医生分别在两组影像上测量肺动脉干、胸主动脉干、竖脊肌、肺部组织、胸壁下皮下脂肪的CT值和SD值,计算相应影像的信噪比(SNR)和对比度噪声比(CNR),分别记录平扫期、动脉期、静脉期的辐射剂量;对两组图像运用5分法进行主观评分,采用Kappa检验分析两位医师对两种图像主观评价的一致性,采用Mann-Whitney U检验比较两种图像的图像质量的主观评分;运用配对样本t检验对组间图像质量和辐射剂量进行客观统计学分析。结果:图像质量客观评价中各结构的SNR、CNR及主观评分组两组之间无明显统计学差异,TNC组和VNC组的主观图像评分中位数均为4分;VNC组有效剂量长度乘积(DLP)(298.14±119.40)mGy·cm和有效辐射剂量(ED)(4.27±1.34)mSv均显著低于TNC组的DLP(437.31±178.28)mGy·cm和ED(6.26±2.00)mSv,VNC组两期扫描相比TNC组3期扫描DLP降低了31.82%,ED降低了31.79%。结论:将光谱CT虚拟平扫VNC图像用于儿童胸部增强扫描中以替代常规平扫期TNC图像,有较好的图像质量用于诊断,并能够显著降低辐射剂量。
Abstract:Objective: This study aimed to explore the feasibility of applying dual-layer detector spectral computed tomography (DLCT) virtual non-contrast (VNC) technology in pediatric enhanced chest CT examinations. Methods: Retrospective analysis was conducted on the enhanced chest CT imaging data and clinical information of 51 children who underwent DLCT scanning at Wuhan Union Hospital. The same processing protocol was applied to each original image. VNC images were obtained using projection space spectral reconstruction from the venous phase spectral base images (SBI) and compared with true non-contrast (TNC) images regarding image quality and radiation dose. Two radiologists measured the CT and SD values of the pulmonary artery trunk, aorta trunk, erector spinae, lung tissue, and subcutaneous fat of the chest wall on image sets, calculating the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). Non-contrast, arterial, and venous phase radiation doses were recorded. Subjective image quality scores were assigned using a 5-point Likert scale, and inter-observer consistency was assessed with the Kappa test. The Mann–Whitney U test compared subjective scores, while the paired t-test was used for objective image quality and radiation dose analyses. Results: Objective evaluation of image quality showed no significant statistical differences between the SNR, CNR, and subjective scores of both groups. The median subjective image scores for TNC and VNC were 4 points. The DLP and ED values of the VNC group (298.14±119.40) mGy·cm, (4.27±1.34) mSv were significantly lower than those of the TNC group (437.31±178.28) mGy·cm, (6.26±2.00) mSv. The DLP and ED of the VNC group reduced by 31.82% and 31.79%, respectively, compared to the TNC group. Conclusion: Spectral CT virtual non-contrast (VNC) images as a substitute for conventional non-contrast (TNC) images in pediatric enhanced chest scans offers satisfactory diagnostic image quality and can significantly reduce radiation dose.
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Keywords:
- spectral CT /
- VNC /
- low dose /
- children /
- enhanced CT
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基底细胞癌(basal cell carcinoma,BCC)与睑板腺癌(sebaceous carcinoma of eyelid,SC)是中老年人最常见的眼睑恶性肿瘤,发病率分别位于第1和第2位,但是因两者恶性程度和侵袭性的不同,患者的治疗方法和预后有很大不同[1-2]。术前对BCC和SC进行定性评估,对手术方法的选择、提高治愈率和降低转移率尤为重要。
本文回顾性分析我院2015年1月至2020年9月经手术病理证实的14例SC及7例BCC的影像学资料,对两种疾病的一般资料与CT、MRI表现做比较和总结,以提高对眼睑部疾病的认识和诊断准确率。
1. 资料和方法
1.1 一般资料
本组SC患者14例,男性1例,女性13例,年龄54~86岁,平均年龄(73.07±10.87)岁。BCC患者7例,男性3例,女性4例,年龄57~84岁,平均年龄(70.71±9.46)岁。临床症状均为发现眼睑部肿物或有异物感,2例既往有眼眶手术史。所有病例最终诊断均由手术病理证实。
1.2 检查方法
14例SC患者术前6例行CT平扫检查,7例行MRI平扫检查,1例行CT与MRI检查。7例BCC患者1例行CT平扫检查,5例行MRI平扫检查,1例行CT与MRI检查。
CT检查采用GE Light speed 16排CT扫描机。扫描参数:120 kV,200 mA,常规扫描层厚3 mm,薄层重建层厚1 mm,螺距1.0;MRI检查采用Philips 3.0 T扫描仪及GE 1.5 T MRI扫描仪,使用眼眶专用线圈,扫描序列包括T1 WI、T2 WI、T2抑脂,DWI,扫描方位包括横断位、冠状位、矢状位,扫描层厚4 mm。
1.3 图像分析
所有患者CT和MRI图像由两位具有5年以上头颈部影像诊断工作经验的放射诊断医师共同阅片,如有意见分歧,两位医师共同协商达成一致意见。分析内容包括病变部位、形态、大小、密度及信号特征、病灶与邻近结构的关系、有无钙化、气体、囊变等。
2. 结果
2.1 睑板腺癌
14例SC患者影像学表现。①发病部位:右眼睑6例,其中4例位于上睑,1例位于下睑,1例病变侵犯眶内;左眼睑8例,3例位于上睑,5例位于下睑。②形态及大小:14例肿瘤长径范围1.1~3.8 cm,平均长径(1.84±0.81)cm;5例肿瘤呈环条状及斑块状附着于眼环前方,可见“弧形征”(图1),8例肿瘤表现为眼睑部软组织结节,其中1例呈“菜花状”向外凸起(图2);1例肿瘤呈团块状向眼眶内生长;7例病灶边界不清晰,7例边界清晰。③病灶密度及信号特征:7例行CT检查的患者表现为等密度软组织影,病灶较大时密度不均匀,未见囊变坏死区;4例内部见气体密度影,均未见钙化影;8例行MRI检查的患者表现为T1 WI等或低信号,T2 WI呈稍高信号,脂肪抑制序列为高信号,DWI呈高或稍高信号。④病灶与邻近结构的关系:14例中13例局限于眶隔前区,11例表皮受累,2例仅位于皮下未侵及眼睑皮肤(图3),1例肿瘤范围较大,侵犯球内及球后,累及眼外肌、泪腺及视神经。
2.2 基底细胞癌
7例BCC患者影像学表现。①发病部位:右眼睑4例,左眼睑3例,均位于下睑。②形态及大小:1例呈环条状肿块,3例呈结节状,1例呈扁丘状,边界均较清晰;肿瘤长径范围0.6~4.4 cm,平均长径(1.60±1.58) cm;1例呈边界不清晰的团片状混杂信号影;1例仅见皮肤表面略不光整,未见明显肿块;仅1例见“弧形征”。③病灶密度及信号特征:2例行CT检查的患者表现为密度均匀的软组织影,1例病灶内见点状钙化(图4);6例行MRI检查的患者表现为T1 WI等或低信号,T2 WI呈稍高或高信号,DWI呈稍高信号。④病灶与邻近结构的关系:7例肿瘤均局限于眶隔前区,2例仅局限在皮肤,未侵犯皮下脂肪组织(图5)。
2.3 SC与BCC的鉴别诊断
SC与BCC的一般资料对比(表1)显示,女性患者比例SC(92.9%)高于BCC(57.1%)。
表 1 SC与BCC一般资料对比Table 1. The comparison of general information of SC and BCC肿瘤类型 例数 平均年龄/岁 性别 男 女 SC 14 73.07±10.87 1 13 BCC 7 70.71± 9.46 3 4 SC与BCC发病部位与病灶范围对比(表2)显示,SC上睑发病率高于下睑,BCC则均发生于下睑。SC病例中有1例侵犯眶内,其余病灶均局限于眶隔前区,BCC病例中病灶均局限于眶隔前区。
表 2 SC与BCC发病部位与病灶范围对比Table 2. The comparison of pathogenic sites and lesion range of SC and BCC肿瘤类型 例数 发病部位 病灶范围 上睑 下睑 仅限眶隔前区 向眶内侵犯 SC 14 7 6 13 1 BCC 7 0 7 7 0 SC与BCC影像学特征对比(表3)显示,SC病灶长径大于BCC,形态上28.6% 的病灶呈环条状,高于BCC(14.3%),SC 14 例病例中有50% 病灶边界不清晰,高于BCC(14.3%)。病灶出现弧形征、气体征比例SC(35.7%,57.1%)高于BCC(14.3%,0%)。
表 3 SC与BCC影像学特征对比Table 3. The comparison of imaging findings of SC and BCC肿瘤类型 例数 平均长径/cm 形态 边界 弧形征 气体征 环条状 结节状 清晰 不清晰 SC 14 1.84±0.81 4 8 7 7 5 4 BCC 7 1.60±1.58 1 3 6 1 1 0 3. 讨论
3.1 概述
BCC与SC是中老年眼睑常见的两类恶性肿瘤,发病率分别位于第1和第2位,但是因两者恶性程度不同,致使治疗方法和预后有很大不同[1-2]。BCC是最常见的皮肤恶性肿瘤,起源于表皮基底层,男性患者比例稍多于女性,大部分发生在下眼睑[3],侵袭邻近结构及发生转移概率较低,患者一般预后较好,紫外线照射是其重要的危险因素[4-5]。SC发生于眼睑Meibomian腺或Zeis腺[6],在我国眼睑恶性肿瘤中,位居第2位,约占31.7%[7],女性较男性多见,易发生于上睑[8],而在西方人种中较为罕见[9]。
SC恶性程度较高,可侵犯临近组织结构并发生淋巴结及血行转移,患者预后不良,死亡率可高达50% 以上,临床上表现为眼睑弥漫性增厚,部分可触及眼睑肿块。目前该疾病主要依靠活检进行组织病理学诊断[10]。
3.2 SC影像学特征
病灶在CT表现为软组织密度影[9],密度较均匀,囊变及钙化少见,形态多呈环条状、结节状软组织影像。本研究中14例SC中12例呈结节状、环条状,与文献相符[11]。MRI表现为T1 WI等或低信号,T2 WI呈稍高信号,DWI呈高或稍高信号,这可能与SC肿瘤细胞较密集造成扩散受限有关。SC特征性影像学改变为病灶后方被眼环阻挡呈“弧形征”,以及病灶内部因继发坏死感染形成的气体征[11-12],本研究发生率分别为35.7%(5/14)和57.1%(4/7)。晚期肿瘤可侵犯眶内及球内,并可发生淋巴结转移和远处转移[13]。
3.3 BCC的影像学特征
肿瘤病理学最常见的类型有结节型和浅表型,影像学结节型表现为眼睑部皮肤及皮下软组织结节,浅表型表现为扁丘状及鳞片状软组织斑块[4-5]。本研究中两种病理类型BCC比例分别为42.9%(3/7)和28.6%(2/7)。BCC在MRI中病灶内常有T2 WI高信号区,这与BCC瘤体中含有充满粘液的囊腔有关,此信号特点与本研究病例的MRI特征相符。侵犯皮下组织较少见,本研究7例BCC患者中有2例局限在皮肤,未侵犯皮下,与文献报道[3]稍不符,需要更大样本量加以印证。BCC如果不及时治疗或术后复发也可侵犯至球内及球后,此外CT、MRI检查可评估BCC的淋巴结转移、远处脏器转移及骨骼受累情况[3]。
3.4 SC与BCC的相似点
SC与BCC作为眼睑常见的恶性肿瘤,好发于中老年,均发生于眶隔前区,影像学均表现为眼睑部软组织肿块。CT密度较均匀,病灶内少见囊变、液化坏死,MRI信号相似,均为T1 WI等或低信号,T2 WI呈稍高或高信号,DWI呈稍高信号。
3.5 SC与BCC鉴别诊断要点
结合本组对比研究结果及文献资料,总结SC与BCC鉴别诊断要点如下:
①发病性别和发病部位:SC好发于老年女性,肿瘤多位于上眼睑;BCC患者男女性患者比例相近,肿瘤多位于下眼睑。②病灶起源位置、形态及边界:SC起源于皮下睑板,向表皮层生长,形态多呈环条状和结节状,病灶边界清晰或不清晰;而BCC起源于皮肤,向皮下生长,形态多呈结节状或扁丘状,有时仅见皮肤破损改变,病灶边界较清晰。③影像学特殊征象:弧形征、气体征多见于SC,病灶内钙化可能更多见于BCC,需要更多行CT检查的BCC病例证实。
3.6 本研究的局限性
①本研究为回顾性研究,患者检查设备和扫描方案不完全一致,大部分患者未同时行CT、MRI检查,对分析病灶内部成分造成困难。②入组患者未行增强检查,无法获取肿瘤的血供、强化曲线等信息。③样本量较少,分析结果可能存在一定偏差,需要在今后的工作中进一步收集病例。
综上所述,SC与BCC是中老年眼睑最常见的两种恶性肿瘤,在流行病学、发病部位、影像学特征等方面均有一定的差异,对于老年女性发生于上眼睑的环条状病灶,CT及MRI发现弧形征、气体征的影像学特征,边界不清晰,应首先考虑为SC;如果病灶发生于下眼睑,呈结节状或扁丘状,边界较清晰,病变仅局限于皮肤未侵及皮下,则首先考虑为BCC。掌握以上鉴别要点,可提高眼睑恶性肿瘤术前诊断的准确性,降低误诊率。
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表 1 TNC和VNC两组图像的客观测量指标比较(n=51,
$\bar x\pm s $ )Table 1 Comparison of Objective Measurement Metrics between TNC and VNC Image Groups (n=51,
$\bar x\pm s $ )观测指标 区域 组别 统计检验 TNC VNC t p CT值 竖脊肌 50.31 ± 6.82 51.47 ± 6.84 -1.052 0.298 肺动脉干 38.98 ± 21.89 40.24 ± 11.58 -0.364 0.717 主动脉干 40.07 ± 20.86 44.63 ± 13.09 -1.453 0.152 胸部皮下脂肪 -103.81 ± 20.88 -95.26 ± 24.15 -3.846 0.000 空白处 -995.24 ± 14.21 -995.38 ± 15.37 0.152 0.880 肺组织 -803.13 ± 80.74 -796.22 ± 80.22 -0.676 0.502 SD值 竖脊肌 13.58 ± 4.78 13.66 ± 7.11 -0.082 0.935 肺动脉干 9.91 ± 3.13 11.31 ± 3.63 -4.091 0.000 主动脉干 11.67 ± 3.88 12.17 ± 4.082 -1.153 0.254 胸部皮下脂肪 14.38 ± 8.04 17.62 ± 24.54 -0.949 0.347 空白处 15.91 ± 21.27 15.83 ± 15.69 0.050 0.960 肺组织 47.03 ± 41.05 50.09 ± 40.91 -0.389 0.699 SNR 竖脊肌 4.16±1.50 4.44±1.84 -1.088 0.282 肺动脉干 4.28±2.29 3.92±1.74 1.034 0.306 主动脉干 3.68±1.71 3.99±1.68 -1.043 0.302 胸部皮下脂肪 -9.22±4.69 -8.41±5.45 -1.448 0.154 空白处 -106.43±54.42 -89.25±35.07 -2.922 0.005 肺组织 -31.03±21.68 -28.74±21.29 -0.682 0.499 CNR 竖脊肌 - - - - 肺动脉干 0.98±1.34 1.03±1.62 0.234 0.816 主动脉干 0.92±1.43 0.72±1.65 -0.712 0.479 胸部皮下脂肪 13.43±6.15 12.82±8.03 -0.725 0.472 空白处 - - - - 肺组织 72.48±29.82 72.10±39.17 0.088 0.930 注:TNC 为真实平扫图像;VNC 为虚拟平扫图像;SD 为背景噪声;SNR 为信噪比;CNR 为对比度噪声比。 表 2 主观评价一致性kappa分析表
Table 2 Kappa analysis for subjective evaluation consistency
组别 评分标准 评分 统计检验 医师A 医师B k P TNC组 3 1 1 4 37 36 0.859 0.00 5 13 14 VNC组 3 1 1 4 35 33 0.829 0.00 5 15 17 表 3 两组图像评分差异
Table 3 Differences in image scores between the two groups
TNC组(n=51) VNC组(n=51) Z P 图像质量评分 4(4,5) 4(4,5) -0.460 0.645 表 4 虚拟平扫组和常规平扫组剂量的差异(n=51,
$\bar x\pm s $ )Table 4 Differences in dose between the two groups (n=51,
$\bar x\pm s $ )项目 组别 统计检验 TNC组 VNC组 t p DLP/(mGy·cm) 437.31±178.28 298.14±119.40 15.95 0.00 ED/mSv 6.26±2.00 4.27±1.34 19.85 0.00 -
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