Principles of CT: multislice CT

This article describes the principles and evolution of multislice CT (MSCT), including conceptual differences associated with slice definition, cone beam effects, helical pitch, and helical scan technique. MSCT radiation dosimetry is described, and dose issues associated with MSCT-and with CT in general-as well as techniques for reducing patient radiation dose are discussed. Factors associated with the large volume of data associated with MSCT examinations are presented.     

Principles of CT and CT technology

This article provides a review of the basic principles of CT within the context of the evolution of CT. Modern CT technology can be understood as a natural progression of improvements and innovations in response to both engineering problems and clinical requirements. Detailed discussions of multislice CT, CT image quality evaluation, and radiation doses in CT will be presented in upcoming articles in this series.     

CT扫描参数对人体组织CT值影响的研究

目的 探索不同CT扫描参数对人体同一种组织CT值的影响。方法 通过在同一台CT机上,分别改变其中1个扫描参数,如X线管电压、毫安秒和重建函数等,而保持其他扫描参数不变,多次扫描标准体模,测量和分析体模中不同物质的CT值。结果 X线管电压的改变对物质的CT值影响具有显著意义。聚乙烯、聚碳酸酯、有机玻璃的CT值与管电压成正相关;聚四氟乙烯的CT值与管电压成负相关。毫安秒和重建函数对CT值的影响差异无统计学意义。结论 同一个人体组织在不同的X线管电压条件下CT值是变化的。因此,在临床影像诊断和放疗中应该考虑图像扫描参数的设置对诊断和治疗结果的影响。     

Limitations of CT during PET/CT.

Our aim was to determine the diagnostic limitations of low-dose, unenhanced CT scans performed for anatomic reference and attenuation correction during PET/CT. METHODS: The Radiology Information System at our oncologic hospital was queried during the 9-mo period from July 2002 to April 2003 for patients with PET/CT scans and diagnostic enhanced CT within 2 wk of each other. One radiologist interpreted the CT portion of the PET/CT (CT(p)) unaware of the PET results and the associated enhanced diagnostic CT (CT(d)). A medical student compared this interpretation with the official report of the CT(d) and listed all discrepancies between reports. A separate radiologist compared CT(p) and CT(d) images and classified true discrepant findings as due to lack of intravenous contrast, arm-position artifact, lack of enteric contrast, low milliamperage (mA), and quality of lung images. RESULTS: Among 100 patients, the most common malignancies were lymphoma (n = 37), cancer of the colorectum (n = 31), and esophageal cancer (n = 15). Among 194 true discrepancies in which findings were missed at CT(p), causes were as follows: (a) lack of intravenous contrast (128/194, 66%), (b) arm-down artifact (17/194, 9%), (c) quality of lung images (26/194, 13%), (d) lack of enteric contrast (15/194, 8%), and (e) low mA (8/194, 4%). Discrepancies were seen most commonly in detecting lymphadenopathy and visceral metastases. CONCLUSION: Most missed findings on the unenhanced CT portion of the PET/CT scans were due to technical factors that could be altered. Discrepant findings would have led to altered management in only 2 patients, suggesting a role for limited repeat imaging to reduce radiation and use of valuable resources.     

多层螺旋CT对周围肺动脉显示能力的研究

目的比较多层螺旋CT肺动脉造影不同层厚重建对周围肺动脉的显示能力. 资料与方法 21例无肺部疾患和血栓病史的患者行CT肺动脉造影检查,均用0.75 mm准直扫描,分别用0.75 mm/0.5 mm（层厚/层间距）（A组）、1.0 mm/0.6 mm（B组）、1.5 mm/1.0 mm（C组）重建,记录每例患者3种不同重建层厚对段肺动脉、亚段肺动脉、5级和6级肺动脉的显示情况及血管不能显示的原因. 结果 3组人均肺段动脉的显示率均为96.45%（19.29/20）;人均亚段动脉显示率分别为94.42%、93.44%、91.13%,3组间均无显著性差异;A、B、C组对第5级肺动脉的人均显示率分别为80.44%、73.47%、59.02%,A组与C组有显著性差异（P＜0.01）,B组与C组间有显著性差异（P＜0.05）;6级肺动脉3组人均显示率分别为33.75%、31.69%、23.56%,A组与C组有显著性差异（P＜0.01）.段肺动脉不能分析的主要原因是解剖变异（53.33%）和心脏搏动伪影（40%）;A、B组亚段肺动脉不能分析的主要原因是解剖变异和心脏搏动伪影,C组的主要原因是部分容积效应（43.84%）与A组比较有显著性差异（10.87%）（P=0.015）;3组对5级和6级肺动脉不能分析的主要原因均为部分容积效应. 结论多层螺旋CT肺动脉造影0.75 mm、1.0 mm、1.5 mm重建层厚对段肺动脉和亚段肺动脉均有很好的显示率,A、B组对5级肺动脉的显示率也较好.影响亚段肺动脉显示的主要原因是解剖变异和心脏搏动伪影.1.0 mm重建层厚可满足肺动脉的观察和图像处理的需要.     

CT of fundoplication

To determine the CT findings postfundoplication, we retrospectively compared CT in 22 postfundoplication patients with CT in 22 patients with unrepaired hiatal hernias and gastroesophageal (GE) junction abnormalities and 24 patients with gastric or esophageal carcinoma involving the GE junction. Seventeen of the 22 postfundoplication patients had undergone a Nissen procedure. Of the 22 patients, 11 had esophageal dilatation, 14 had GE junction masses, 4 had esophageal wall thickening, 7 had surgical clips, and none had hepatic metastases or upper abdominal lymphadenopathy. Statistically, on CT, postfundoplication patients are more likely to have a GE junction mass (p = 0.023) and least likely to have wall thickening (p = 0.021). Nonetheless, because the findings occur frequently in each group, they are not diagnostic in the individual patient. However, 11 of 12 post-Nissen masses had the unique finding of an oval or linear central fat density within the mass. This finding was absent in the other postfundoplication masses and in those patients with repaired hiatal hernia or tumor. We conclude that pseudomasses occur on CT postfundoplication and can be indistinguishable from hiatal hernias and GE junction neoplasms unless a central fat density is present.     

CT of pheochromocytoma

The computed tomographic (CT) findings in 10 patients with pheochromocytoma are presented. Three of 10 patients had multiple endocrine adenomatosis, all with bilateral adrenal masses. One other patient had bilateral adrenal masses, four had right, and one had left sided adrenal masses. One tumor was extraadrenal. CT, when used as the initial imaging study, correctly identified nine of nine pheochromocytomas in six patients. In another four patients, recurrent or metastatic disease was identified. CT findings of use in diagnosis were mass lesions, some with areas of decreased attenuation indicating hemorrhage, and metastases identified in liver, mediastinum, lung, and spine. CT differentiation of benign from malignant lesions is facilitated by demonstration of local invasion or metastasis. CT is recommended as the initial radiographic procedure in the evaluation of patients with clinical or biochemical suspicion of pheochromocytoma, and for follow-up examination in patients with evidence of recurrent disease.     

PET/CT in malignant melanoma: contrast-enhanced CT versus plain low-dose CT

Purpose  

The aim of this study was to evaluate the diagnostic value of contrast-enhanced CT (CECT) versus non-enhanced low-dose CT (NECT) in the staging of advanced malignant melanoma with ¹⁸F-fluordeoxyglucose (FDG) positron emission tomography (PET)/CT.     

CT of emphysema

This article focuses on three main topics: (1) the importance of emphysema as a serious respiratory disease, (2) qualitative assessment of emphysema using CT, and (3) the emerging importance of quantitative CT in the evaluation of patients with emphysema for surgery and drug therapy. CT also can identify the major anatomic subtypes of emphysema. CT is critical in the assessment of patients with the potential for lung volume reduction surgery. CT may well be superior to pulmonary function tests in the longitudinal assessment of current and proposed drug therapies for the treatment of emphysema.     

CT arthrography of the glenohumeral joint: CT fluoroscopy versus conventional CT and fluoroscopy--comparison of image-guidance techniques

PURPOSE: To compare examination time with radiologist time and to measure radiation dose of computed tomographic (CT) fluoroscopy, conventional CT, and conventional fluoroscopy as guiding modalities for shoulder CT arthrography. MATERIALS AND METHODS: Glenohumeral injection of contrast material for CT arthrography was performed in 64 consecutive patients (mean age, 32 years; age range, 16-74 years) and was guided with CT fluoroscopy (n = 28), conventional CT (n = 14), or conventional fluoroscopy (n = 22). Room times (arthrography, room change, CT, and total examination times) and radiologist times (time the radiologist spent in the fluoroscopy or CT room) were measured. One-way analysis of variance and Bonferroni-Dunn posthoc tests were performed for comparison of mean times. Mean effective radiation dose was calculated for each method with examination data, phantom measurements, and standard software. RESULTS: Mean total examination time was 28.0 minutes for CT fluoroscopy, 28.6 minutes for conventional CT, and 29.4 minutes for conventional fluoroscopy; mean radiologist time was 9.9 minutes, 10.5 minutes, and 9.0 minutes, respectively. These differences were not statistically significant. Mean effective radiation dose was 0.0015 mSv for conventional fluoroscopy (mean, nine sections), 0.22 mSv for CT fluoroscopy (120 kV; 50 mA; mean, 15 sections), and 0.96 mSv for conventional CT (140 kV; 240 mA; mean, six sections). Effective radiation dose can be reduced to 0.18 mSv for conventional CT by changing imaging parameters to 120 kV and 100 mA. Mean effective radiation dose of the diagnostic CT arthrographic examination (140 kV; 240 mA; mean, 25 sections) was 2.4 mSv. CONCLUSION: CT fluoroscopy and conventional CT are valuable alternative modalities for glenohumeral CT arthrography, as examination and radiologist times are not significantly different. CT guidance requires a greater radiation dose than does conventional fluoroscopy, but with adequate parameters CT guidance constitutes approximately 8% of the radiation dose.     

Spiral CT vs incremental CT: Is spiral CT superior in imaging of the brain?

The aim of this study was to evaluate image quality of spiral CT of the brain as compared with incremental CT using identical scanning parameters. Incremental or spiral cranial CT was performed on 46 consecutive, randomized patients with non-traumatic disease of the brain on a Siemens (Erlangen, Germany) Somatom Plus 4. Evaluation was done in a randomized blinded way by two experienced radiologists. Different anatomical structures, image noise, and artifacts were scaled 1 (bad) to 4 (very good). Statistical analysis was done using the F-test of variance for partial sums of squares as well as Student's t-test. Incremental CT was superior to spiral CT for evaluation of the internal capsule, supratentorial artifacts, gray/white matter differentiation, and image noise. No statistically significant differences were seen for evaluation of the pons, infratentorial artifacts, and eye muscles. With identical scanning parameters incremental CT is superior to spiral CT in the assessment of small, complex structures in a low-contrast setting. No differences are seen for larger structures or small structures in a medium-contrast range. Artifacts localized close to the skull in spiral CT can easily mimic hemorrhage in traumatized patients. Spiral CT should therefore only be used for CT angiography and if 3D reconstructions are needed. Received 19 June 1997; Accepted 6 August 1997     

肝脏16层螺旋CT增强多期相扫描及血管成像的综合应用

目的:探索16层螺旋CT在肝脏多期相扫描设置的优化及血管成像的综合应用技术,以期提高肝脏疾病的诊断准确率.方法:参照肝脏增强时间密度曲线,选择兼顾肝动脉、门静脉成像及肝内病变检出的最佳时间段设置扫描期相.采用此期相设置对40例经B超发现肝脏有病变的患者进行16层CT增强检查.将所得双期血管成像与其中12例行数字减影血管造影(DSA)检查的患者进行比较,作出前瞻性诊断后追踪病理及临床综合资料并作比较.结果:在注射对比剂后40例患者病变均能检出,且前瞻性诊断符合率达95%,双期血管成像与DSA比较有较好的相似性.结论:肝脏16层CT多期相设置及血管成像的综合技术有较高的临床应用价值.     

CT of appendicitis

The CT findings of 38 consecutive patients with acute appendicitis are analyzed, described, and illustrated. CT showed intraabdominal disease in 92% of patients and made a specific diagnosis of appendicitis in 79% of cases. The most common CT findings were pericecal inflammation (68%), abscess (55%), calcified appendicolith (23%), and an abnormal appendix (18%). CT had a sensitivity similar to that of contrast enema examinations, but it correlated much better with the surgical findings in detecting the precise nature, extent, and location of the disease process. Normal CT does not exclude appendicitis, since mild forms without periappendiceal disease may escape detection.     

CT衰减校正对IQ-SPECT/CT和LEHR-SPECT/CT心肌灌注显像的影响

目的 探讨CT衰减校正（CTAC）对智能（IQ）-SPECT/CT和低能高分辨率（LEHR）-SPECT/CT心肌血流灌注显像（MPI）图像的影响。 方法 收集2018年5月至10月在山西医科大学第一医院行静息心肌灌注显像（MPI）的31例确诊或者可疑的冠心病患者,其中男性21例、女性10例,年龄（49.4±12.01）岁。所有患者同日分别行IQ-SPECT/CT+CTAC及LEHR-SPECT/CT+CTAC。视觉分析IQ-SPECT/CT CTAC前后图像及手动配位后图像、LEHR-SPECT/CT CTAC前后断层图像;同时比较左心室各个室壁（心尖、前壁、侧壁、间壁、下壁）IQ-SPECT/CT和LEHR-SPECT/CT CTAC前后与重新配位后的放射性摄取值（%）。两组间比较采用配对t检验,率的比较采用卡方检验,一致性分析采用Kappa检验。 结果 ①视觉分析:IQ-SPECT/CT与LEHR-SPECT/CT CTAC前图像比较,具有很高的一致性（Kappa值=0.795,P<0.001）。IQ-SPECT/CT CTAC后心肌节段出现放射性分布明显稀疏的比例为77%（24/31）,远高于LEHR- SPECT/CT CTAC后的23%（7/31）,差异有统计学意义（χ2=16.52,P<0.001）。将MPI与CT图像手动重新配位后,IQ-SPECT/CT左心室心尖的放射性分布为16%（5/31）,与LEHR-SPECT/CT的23%（7/31）相比,差异无统计学意义（χ2=0.103,P=0.748）。②放射性摄取值（%）:IQ-SPECT/CT CTAC前后比较,左心室心尖[（65.71±25.69）%对（58.68±20.39）%]、前壁[（204.23±43.24）%对（184.66±41.22）%]及间壁[（316.19±47.43）%对（270.03±65.33）% ] 的放射性摄取值明显降低,且差异均有统计学意义（t=4.014、4.232、5.473,均P<0.05）;LEHR-SPECT/CT CTAC前后比较,左心室前壁[（204.68±41.14）%对[（211.81±35.04）%]、间壁[（319.13±44.90）%对（350.87±44.24）%]及下壁[（185.48±31.06）%对（228.67±29.45）% ]的放射性摄取值显著增高,且差异均有统计学意义（t=?2.471,P =0.019;t=?5.968,P<0.001;t=?11.311,P<0.001）。IQ-SPECT/CT CTAC配位后与IQ-SPECT/CT CTAC前比较,左心室前壁[（212.06±33.59）%对（204.23±43.24）%]、侧壁[（372.84±39.37）%对（355.81±46.79）%]、下壁[（219.13±25.10）%对（191.58±33.06）%]和间壁[（335.00±36.84）%对（316.19±47.43）%]的放射性摄取值均明显增高,且差异均有统计学意义（t=?2.497,P=0.018;t=?2.672,P=0.012;t=?7.632,P<0.001;t=?3.557,P<0.001） 。 结论 LEHR-SPECT/CT CTAC后左心室间壁及下壁的放射性分布得到补偿;而IQ-SPECT/CT CTAC后左心室心尖、前壁及间壁的放射性分布却更加稀疏。在IQ-SPECT/CT采集模式下,CTAC后容易出现矫枉过正,重新手动配位后这种情况将得到明显改善。     

CT scout view as an essential part of CT reading

Computed tomography scout view is a mode of operating a CT system. It is generally used to prescribe CT slices and to display slice locations rather than for direct diagnosis. However, we found that a careful study of CT scout view can contribute significantly to the diagnosis. We show seven abdominal, two chest and two head CT, where the study of CT scout view allowed diagnoses to be made that were not readily apparent from the axial slices.