IntroductionThe introduction of spiral CT and the advent of faster and more powerful scanners designed for volume CT scanning in spiral mode led to a renaissance of CT. The range of CT applications and the frequency of examinations still show a continuous upward trend. In parallel to the positive technical and clinical trends, an increasing awareness ± sometimes even an irrational fear ± of the dose associated with X-rays developed; these trends are particularly strong in Europe, especially in Scandinavia, the United Kingdom and Germany. A number of activities at the European level are under way. In particular, the European Union (EU) sponsored initiatives to limit dose and mandated the establishment of reference dose levels for CT examinations [1]. The recently introduced Council Directive 97/43/ Euratom of 30 June 1997 on the health protection of individuals against the dangers of ionizing radiation in relation to medical exposure [2] demands special attention to CT as an examination associated with a high patient dose. In addition, it requires the evaluation of patient dose values for all CT examinations. This topical background added to the motivation to limit the dose in CT or, better, to achieve the required level of image quality with a reduced dose.It was the purpose of this study to investigate approaches and to develop technical means for a dose reduction in CT that are not associated with a loss or compromise of image quality. This means in particular that simple approaches, such as a general reduction of tube current, measured in milliamperes (mA), are not the optimal solution. Lower mA values can be selected by the CT user at any time, but this will increase pixel noise. We assume here that the optimal mA value and the mAs product (tube current multiplied by scan time per 360 rotation) have been selected; i. e. noise is as high as is tolerable and the dose thereby chosen as low as achievable for the given diagnostic task.We strove to reduce the total mAs without increasing pixel noise. The principal idea, as will be outlined below, Abstract. We investigated approaches to reducing the dose in CT without impairing image quality. Dose can be reduced for non-circular object cross-sections without a significant increase in noise if X-ray tube current is reduced at angular tube positions where the X-ray attenuation by the patients is small. We investigated different schemes of current modulation during tube rotation by simulation and phantom measurements. Both pre-programmed sinusoidal modulation functions and attenuation-based on-line control of the tube current were evaluated. All relevant scan parameters were varied, including constraints such as the maximum modulation amplitude. A circular, an elliptical and two oval water phantoms were used. Results were validated on six cadavers. Dose reduction of 10±45 % was obtained both in simulations and in measurements for the different non-circular phantom geometries and current modulation algorithms without an increase in pixel noise values. On-line attenuatio...

This study investigated the potential of attenuation-based on-line modulation of tube current to reduce the dose of computed tomography (in milliamperes) without loss in image quality. The dose can be reduced for non-circular patient cross-sections by reducing the tube current at the angular positions at which the diameter through the patient diameter is smallest. We investigated a new technical approach with attenuation-based on-line modulation of tube current. Computed tomographic projection data were analyzed to determine the optimal milliampere values for each projection angle in real time, instead of performing prior measurements with localizer radiographs. We compared image quality, noise pattern, and dose for standard scans and for scans with attenuation-based on-line modulation of tube current in a group of 30 radiation therapy patients. Six different anatomical regions were examined: head, shoulder, thorax, abdomen, pelvis, and extremities (knee). Image quality was evaluated by four radiologists in a blinded fashion. We found the dose to be reduced typically by 15-50 %. In general, no deterioration in image quality was observed. Thus the dose in computed tomography be reduced substantially by technical measures without sacrificing image quality. Attenuation-based on-line modulation of tube current is an efficient and practical means for this.

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In a controlled patient study we investigated the potential of attenuation-based on-line modulation of the tube current to reduce milliampere values (mAs) in CT examinations of children without loss of image quality. mAs can be reduced for non-circular patient cross sections without an increase in noise if tube current is reduced at those angular positions where the patient diameter and, consequently, attenuation are small. We investigated a technical approach with an attenuation-based on-line control for the tube current realised as a workinprogress implementation. The CT projection data are analysed in real time to determine optimal mAs values for each projection angle. We evaluated mAs reduction for 100 spiral CT examinations with attenuation-based on-line modulation of the tube current in a group of children. Two radiologists evaluated image quality by visual interpretation in consensus. We compared the mAs values read from the CT scanner with preset mAs of a standard protocol. Four different scan regions were examined in spiral technique (neck, thorax, abdomen, thorax and abdomen). We found the mAs product to be reduced typically by 10-60% depending on patient geometry and anatomical regions. The mean reduction was 22.3% (neck 20%, thorax 23%, abdomen 23%, thorax and abdomen 22%). In general, no deterioration of image quality was observed. There was no correlation between the age and the mean mAs reduction in the different anatomical regions. By classifying the children respectively to their weight, there is a positive trend between increasing weight and mAs reduction. We conclude that mAs in spiral CT examinations of children can be reduced substantially by attenuation-based on-line modulation of the tube current without deterioration of image quality. Attenuation-based on-line modulation of tube current is efficient and practical for reducing dose exposure to children.

Although contrast medium analysis provided statistical criteria, these, however, do not possess the ability to improve the diagnostic prediction of tumor histology. Neither the morphologic classification nor contrast medium analysis was able to identify a malignant lesion sufficiently.

The potential of online tube current modulation in subsecond multislice spiral CT (MSCT) examinations of children to reduce the dose without a loss in image quality is investigated in a controlled patient study. The dose can be reduced for oval patient sectional view without an increase in noise if the tube current is reduced where the patient diameter and, consequently, attenuation are small. We investigated a product version of an online control for tube current in a SOMATOM Sensation 4 (Siemens, Forchheim). We evaluated image quality, noise and dose reduction for examinations with online tube current modulation in 30 MSCT of thorax/abdomen and abdomen and compared mA s for tube current modulation to the mA s in standard weight-adapted children protocols. Image quality was rated as "very good," "good," "diagnostic" and "poor" in a consensus by three radiologists. Noise was assessed in comparison to 24 MSCT examinations without tube current modulation measured as SD in ROIs. The dose was reduced from 26 to 43% (mean 36%), depending on the patient's geometry and weight. In general, no loss of image quality was observed. Measured noise showed a decrease up to 26% and an increase up to 36%, although there was no decrease of image quality. Online tube current modulation is now used as a standard in MSCT at our institution. Dose in MSCT examinations of children can be reduced substantially in routine examinations by online tube current modulation without a loss of image quality.

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an 8.5-year-old boy presented with signs of precocious puberty. Laboratory analyses (suppressed gonadotropins, elevated testosterone) and thoracic CT demonstrated a beta-human chorionic gonadotropin (beta-hCG) and alpha(1)-feto protein (alpha-FP) secreting mediastinal tumor. Histological analysis showed a mixed germ cell tumor comprising choriocarcinoma (CH), embryonal carcinoma (EC), mature teratoma (MT), and yolk sac tumor (YS). He was successfully treated by surgery and adjuvant chemotherapy. Epianalysis of published cases: all KS patients (n = 12), age 4-9 years, presented with precocious sexual development (PP), whereas the older ones showed thorax-associated symptoms, mainly chest pain, dyspnea, and cough. The histological distribution was also age-dependent with mixed germ cell tumors predominantly in younger patients. Thus, M-GCTs are strongly associated with precocious puberty in young boys with KS. Therefore, a karyotype analysis should be included in the clinical work-up of boys with precocious puberty and M-GCT. There is still no convincing explanation for the association of M-GCTs and KS.