Evaluation of image quality using 1 : 1 pitch and 1.5 : 1 pitch helical CT in children: a comparative study

OBJECTIVE: The objective of this study was to compare the quality of 1 : 1 and 1.5 : 1 pitch helical contrast-enhanced thoracic and abdominal CT images in children who cannot cooperate for breath holding. MATERIALS AND METHODS: This is a retrospective study of 33 contrast-enhanced CT examinations in 11 children of 0-4 years of age. All children had an initial CT study using 1 : 1 pitch helical scanning followed over the next 6-36 months by one to four CT examinations with 1.5 : 1 pitch. Radiation dose with the two techniques was measured with a pencil ionization chamber. RESULTS: The two techniques provided comparable overall image quality. There was 33 % less radiation dose with 1.5 : 1 pitch helical scanning. CONCLUSION: The 1.5 : 1 pitch helical CT provides comparable quality images and a smaller radiation dose than 1 : 1 pitch in examining children aged 0-4 years.     

The effect of helical pitch and beam collimation on the lesion contrast and slice profile in helical CT imaging

A model is presented in this paper to describe how the contrast of a reconstructed object and slice sensitivity profile are affected by (1) the table speed or helical pitch, (2) the x-ray collimations, (3) the size of the object, (4) the alignment between the reconstructed slice and the object, (5) the distance of the object from the axis of rotation, and (6) the helical CT reconstruction algorithm employed. This contrast model is validated by both computer simulations and experiments. With this model, the contrast of a reconstructed object, slice sensitivity profile, and the longitudinal MTF can be accurately predicted. The optimal scan strategy and the point of diminishing returns can be determined prior to scanning. Several conclusions can be drawn from this model. First, overlapping reconstruction significantly improves overall scan contrast sensitivity of helical CT. Second, with a given x-ray collimation, low pitch helical scans provide better longitudinal resolutions. Third, with a given volume coverage rate (i.e., a given table speed), narrow collimation high pitch helical scans provide better longitudinal resolutions than wide collimation low pitch ones and therefore are recommended for high-contrast thin-slice applications. A lesion conspicuity model is also established.     

常规低碳钢板坯的高速连铸工艺技术

 高速连铸具有显著减少建设投资、大幅提高产量和降低物料消耗等优势。但欧、美及国内多数钢厂均使用中低拉速连铸常规厚度板坯,主要原因是高速连铸拉漏风险增加与卷渣导致的表面质量恶化。为解决上述问题,以日本JFE为代表的钢企开发了一系列关键技术,JFE福山No.5 铸机连铸厚度220 mm低碳钢板坯最大拉速达到3.0 m/min。阐述了国内外常规板坯铸机的高速连铸发展历程。基于JFE福山No.5 CCM和首钢京唐No.3 CCM低碳钢高速连铸实践,综述了高速连铸的3项关键技术,分别是强冷却能力结晶器技术、高速连铸结晶器卷渣控制技术和电磁冶金技术,为生产冷轧薄板钢种为主的钢厂提高铸机拉速提供参考。     

Dynamic helical CT of breast tumors

Expression of liver-enriched trans-acting hepatocyte nuclear factors 1alpha (HNF1alpha) and 4 (HNF4) is correlated with the hepatic phenotype in cultured rat hepatoma cells. We have used a hepatoma variant cell line, H11, that specifically lacks the HNF4 --> HNF1alpha pathway as a model to understand mechanisms controlling hepatic gene expression. We have introduced randomly marked human chromosomes into H11 cells and have isolated a number of microcell hybrids that have rescued hepatic gene expression, including HNF4, HNF1alpha, and alpha1-antitrypsin. Chromosomal analysis of cell hybrids showed that the rescued hepatic phenotype correlated closely with the presence of human chromosome 12p sequences. Although the gene encoding HNF1alpha is located on chromosome 12q24, its retention was not required to rescue the hepatic phenotype. Thus, we suggest that a locus on human chromosome 12p plays an important role in maintenance of hepatic gene expression through activation of the HNF4 --> HNF1alpha pathway.     

低浓度沥青烟的净化处理

该主要论述在碳素生产过程和相关沥青加工行业中，排放的无组织、弥漫性低浓度沥青烟净化的综合净化治理的设计条件及处理方式，并引入多层吸附，解吸再生，再吸附的循环过程。充分利用有效介质，减轻工人的劳动强度。通过工业实践。达到最佳的设计指标，该净化系统在国内较为领先，对同行业具有借鉴作用。     

Detection of hepatocellular carcinoma in patients with cirrhosis: MR imaging versus angiographically assisted helical CT

OBJECTIVE: The purpose of our study was to compare the combination of conventional spin-echo, phase-shift gradient-recalled echo (GRE), and triple-phasic dynamic GRE MR imaging with the combination of helical CT hepatic arteriography (CTA) and CT performed during arterial portography (CTAP) in the preoperative detection of hepatocellular carcinoma (HCC). MATERIALS AND METHODS: Thirty-seven patients with cirrhosis underwent MR imaging and angiographically assisted CT imaging. Paired T1- and T2-weighted spin-echo images, paired in-phase and out-of-phase GRE images, triple-phasic dynamic GRE images, the combined MR images, and the paired CTA and CTAP images were retrospectively and independently reviewed by three radiologists. Image review was done on a segment-by-segment basis. Of the 280 liver segments, 58 segments contained 79 HCCs that were 0.5-8.0 cm (mean, 2.0 cm) in diameter. The diagnostic value of each pair of images was rated by means of receiver operating characteristic curve analysis. RESULTS: The diagnostic accuracy of combined CTA and CTAP (mean area under the receiver operating characteristic curve [Az] = 0.94) was significantly better than that of spin-echo (Az = 0.86, p < .0001), phase-shift GRE (Az = 0.83, p < .0001), dynamic GRE (Az = 0.85, p < .0001), and all combined (Az = 0.91, p < .001) MR imaging. The relative sensitivity of combined CTA and CTAP (89%) was also significantly (p < .0005) better than that of the combined MR imaging (75%). CONCLUSION: Angiographically assisted helical CT imaging was superior to MR imaging combined with conventional spin-echo, phase-shift GRE, and triple-phasic dynamic GRE techniques in the detection of HCC in patients with cirrhosis. The noninvasive dedicated combined MR imaging could not obviate invasive angiographically assisted CT imaging. Combined CTA and CTAP is recommended, especially in the preoperative examination of patients with HCC.     

Ghosting of pulmonary nodules with respiratory motion: comparison of helical and conventional CT using an in vitro pediatric model

OBJECTIVE: The study was designed to compare helical CT with varying pitch and reconstruction intervals and conventional CT for revealing pulmonary nodules in a model that simulates respiratory motion in children. MATERIALS AND METHODS: CT scans were obtained in an experimental model with one nodule (3 or 10 mm) in each scan. One-second scans were obtained at rates of 10, 20, and 30 respirations per minute using conventional CT with 4-mm collimation and table incrementation and helical CT with 4-mm collimation and either 4-mm/sec (pitch, 1:1) or 8-mm/sec (pitch, 2:1) table speed. Reconstructions were at 1-, 2-, and 4-mm intervals for scans obtained using 4-mm/sec table speed and at 1- and 4-mm intervals for scans obtained using 8-mm/sec table speed. Images were independently reviewed by three radiologists who estimated the number of nodules on each image. RESULTS: Ghosting (depiction of more than one nodule in a study) was seen in 79%, 80%, and 75% of helical CT scans obtained with a 1:1 pitch using 1-, 2-, and 4-mm reconstruction intervals, respectively. By comparison, ghosting was seen in only 54% and 58% of helical CT scans with a 2:1 pitch using 1-mm reconstruction intervals and 4-mm reconstruction intervals, respectively, and in 56% of conventional CT scans (p < .0001). A single nodule was detected on all other scans, and at least one nodule was seen on all scans. CONCLUSION: Ghosting of nodules is common in this model. Ghosting was seen less often on conventional scans and helical scans with 2:1 pitch than it was on helical scans with 1:1 pitch. Nonetheless, ghosting was seen on more than 50% of all scans with each technique.     

CT imaging of abdominal hernias

Most abdominal hernias can be diagnosed on the basis of findings on physical examination or plain films and barium studies. However, diagnostic dilemmas can arise when patients are obese or have had surgery. Cross-sectional CT scans can show hernias and the contents of the peritoneal sac. More important, CT findings can be used to diagnose unsuspected hernias and to distinguish hernias from masses of the abdominal wall, such as tumors, hematomas, abscesses, undescended testes, and aneurysms. This essay illustrates the CT findings in diaphragmatic hernias, internal hernias, and abdominal wall hernias.     

Three-dimensional display of the bronchi using helical CT

The purpose of this study was to evaluate the clinical usefulness of three-dimensional (3D) images of the bronchi obtained using helical CT. Thirteen patients with lung cancer, one with tracheal diverticulum, and one with bronchial amyloidosis were examined. The CT scanner employed was the Toshiba Xforce. The helical CT scan cycle consisted of 20 continuous rotations, each requiring 1.5 sec, for a total scanning time of 30 sec. Scans were obtained using a 5-mm X-ray beam width, a 5-mm/1.5 sec couchtop sliding speed, and a 2-mm reconstruction interval. 3D images were reconstructed using a CEMAX VIPstation. The optimal lower and upper threshold CT values for 3D images of the bronchi were -650 and -100 HU, respectively, and 3D images clearly depicted endobronchial lesions. Cartilage crescents were also demonstrated, but longitudinal and circular mucosal folds could not be visualized. In conclusion, 3D images of the bronchi acquired using helical CT were useful in evaluating endobronchial lesions.     

Developmental versus conventional care: a comparison of clinical outcomes for very low birth weight infants

The purpose of this research was to describe the clinical profile of very low birth weight (VLBW) infants receiving conventional versus developmental care during their hospitalization and to determine the appropriateness of developmental-care interventions. A phase-lag study with 124 preterm infants indicated that although there were no significant differences in individual clinical outcomes, developmental care had a significant effect on the physiologic stability of the infant over time. Developmental interventions were used for all infants receiving the developmental-care intervention, with varying frequency.     

Slice thickness of spiral CT images as function of pitch

Latex is a ubiquitous part of life today. It is a constituent of many household products and medical devices, although not always obvious on examination. The increase in incidence of potentially life-threatening allergic reactions to latex has been a cause for mounting concern over recent years. Although there have been recent reviews of the general problem of latex allergy, there is little advice available to anaesthetists on how to develop an effective strategy to implement within their own hospitals. The aim of this article is to improve awareness of latex allergy and by describing the development of our strategy to identify and safely manage those at risk in the peri-operative period, facilitate the process for other departments.     

CT of abdominal wall implantation metastases after abdominal percutaneous procedures

PURPOSE: Our goal was to report the CT manifestations of abdominal wall implantation metastases occurring after abdominal percutaneous procedure. METHOD: CT scans and clinical data of six patients with abdominal wall implantation metastases at the puncture site following abdominal percutaneous procedure were reviewed. The abdominal percutaneous procedures included drainage of intraperitoneal abscess in patients with colon or gastric cancer (n = 2), transhepatic biliary drainage in a patient with hilar cholangiocarcinoma (n = 1), biopsy of intrahepatic hepatocellular carcinoma (n = 1), biopsy of a metastatic left adrenal gland (n = 1), and laparoscopic cholecystectomy in a patient with unsuspected gallbladder cancer (n = 1). RESULTS: CT enabled the diagnosis of abdominal wall implantation metastasis in all six patients and showed coexisting intraabdominal tumor sites in five patients. All abdominal wall implantation metastases were homogeneous before intravenous administration of iodinated contrast material and became moderately heterogeneous on contrast-enhanced CT scan with marked enhancement relative to adjacent tissues. CONCLUSION: Abdominal wall implantation metastases are moderately heterogeneous on contrast-enhanced CT scan with marked enhancement relative to adjacent tissues. In most cases of abdominal wall implantation metastasis following abdominal percutaneous procedure, CT shows additional intraabdominal tumor sites. This complication may occur following a variety of abdominal percutaneous procedures (either radiological or surgical).     

CT angiography of the abdominal arteries

The aims of this study were to investigate if low-frequency fatigue (LFF) dependent on the duration of repeated muscle contractions and to compare LFF in voluntary and electrically induced exercise. Male subjects performed three 9-min periods of repeated isometric knee extensions at 40% maximal voluntary contraction with contraction plus relaxation periods of 30 plus 60 s, 15 plus 30 s and 5 plus 10 s in protocols 1, 2 and 3, respectively. The same exercise protocols were repeated using feedback-controlled electrical stimulation at 40% maximal tetanic torque. Before and 15 min after each exercise period, knee extension torque at 1, 7, 10, 15, 20, 50 and 100 Hz was assessed. During voluntary exercise, electromyogram root mean square (EMGrms) of the vastus lateralis muscle was evaluated. The 20-Hz torque:100-Hz torque (20:100 Hz torque) ratio was reduced more after electrically induced than after voluntary exercise (P < 0.05). During electrically induced exercise, the decrease in 20:100 Hz torque ratio was gradually (P < 0.05) reduced as the individual contractions shortened. During voluntary exercise, the decrease in 20:100 Hz torque ratio and the increase in EMGrms were greater in protocol 1 (P < 0.01) than in protocols 2 and 3, which did not differ from each other. In conclusion, our results showed that LFF is dependent on the duration of individual muscle contractions during repetitive isometric exercise and that the electrically induced exercise produced a more pronounced LFF compared to voluntary exercise of submaximal intensity. It is suggested that compensatory recruitment of faster-contracting motor units is an additional factor affecting the severity of LFF during voluntary exercise.     

The effect of low versus high approach-motivated positive affect on memory for peripherally versus centrally presented information.

Emotions influence attention and processes involved in memory. Although some research has suggested that positive affect categorically influences these processes differently than neutral affect, recent research suggests that motivational intensity of positive affective states influences these processes. The present experiments examined memory for centrally or peripherally presented information after the evocation of approach-motivated positive affect. Experiment 1 found that, relative to neutral conditions, pregoal, approach-motivated positive affect (caused by a monetary incentives task) enhanced memory for centrally presented information, whereas postgoal, low approach-motivated positive affect enhanced memory for peripherally presented information. Experiment 2 found that, relative to a neutral condition, high approach-motivated positive affect (caused by appetitive pictures) enhanced memory for centrally presented information but hindered memory for peripheral information. These results suggest a more complex relationship between positive affect and memory processes and highlight the importance of considering the motivational intensity of positive affects in cognitive processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quantitative evaluation of pancreatic enhancement during dual-phase helical CT

PURPOSE: To determine the improvement in pancreatic enhancement at helical computed tomography (CT) performed with an early delay after administration of contrast material compared with that performed with a standard delay. MATERIALS AND METHODS: Dual-phase helical CT of the abdomen was performed in 120 patients with a 150-mL bolus of contrast material infused at 5 mL/sec. Early and standard delayed scanning was performed beginning at 20 seconds and 49-71 seconds, respectively. Regions of interest were measured in the head, body, and tail of the pancreas in 92 patients. The difference in enhancement between early and standard delayed scanning was calculated. RESULTS: Mean pancreatic enhancement was 82 HU +/- 3 (standard error) with an early delay, whereas enhancement on standard delay scans was 62 HU +/- 2 (P < .001). An improvement in enhancement greater than 10 HU was attained in 66 of 92 cases (72%). CONCLUSION: Pancreatic enhancement at helical CT with an early delay after contrast material administration is often significantly greater than the enhancement seen with a standard delay when a monophasic, rapidly infused bolus of contrast material is used.     

Acute pulmonary embolism: assessment of helical CT for diagnosis

Male pigeons, Columba livia, employ intense mate guarding and frequent copulation apparently as strategies to ensure their paternity. The aim of this study was to investigate the benefits to females of mate guarding by males and frequent copulation. Field observations showed that females initiated the majority of copulations and females that solicited copulations more frequently were guarded more closely by their partner. Experimental removal of guarding male partners showed that: (1) unguarded, fertile females suffered increased harassment from extrapair males which reduced their foraging efficiency; and (2) unguarded, fertile females did not seek copulations with extrapair males. Various explanations for frequent pair copulation initiated by females are discussed and we conclude that female pigeons trade pair copulations for protection (mate guarding) against sexual harassment from other males. Copyright 1998 The Association for the Study of Animal Behaviour.     

The evaluation of three dimensional image distortion of helical scanning CT

We developed a computer algorithm to simulate distortion in the three-dimensional (3D) displays obtained by helical scanning. The algorithm constitutes calculation of the image profile in the longitudinal direction, which is assumed to be a convolution of the object function with the slice sensitivity profile (SSP) of helical scanning. Experiments were performed to examine the algorithm for its validity with the use of a K2HPO4 phantom. Simulated results and measurements was in a good agreement. The distortion was investigated by the computer simulation. The model simulated was a high density object (Ol) surrounded by low density tissue (Os). The helical interpolation used was 360-degree linear interpolation. Two parameters were defined: delta Lz, which is the difference in length between the 3D image and the actual object Ol in the longitudinal direction, and the cut level index (CLI), which is defined as CLI = (Cut Level CT Number-CT Number of Os)/(CT Number of OI-CT Number of Os). We found that magnitude of delta Lz increased depending on the table feed distance per 360-degree scan (Dt). When Ol was twice as long as Dt, delta Lz directly depended on CLI, but was independent of Ol length. When Ol length was longer than Dt, delta Lz was shown to be 0 at CLI not equal to 0.5 at every Dt. When Ol was shorter than Dt, delta Lz decreased remarkably depending on the length of Ol in higher CLI. The simulations, with the use of a newly developed algorithm, were demonstrated to be useful for evaluating the amount of distortion and for better understanding the characteristics of 3D displays of helical scanning.