Constant Tube Current Research Articles

撮影条件自動適正化機能を用いたルーチン化への検討

Auto mA is a function that automatically controls tube current so as to stabilize image quality. To determine the applicability of this function to routine inspection work, an evaluation was carried out by two doctors in the department of radiology and five technicians in the department of diagnostic radiology using home-made phantoms and phantoms for low contrast resolution determination. The phantom experiment provided an almost constant level of SD values in each Auto mA mode tested, independent of scanning type, slice thickness, and phantom shape. In addition, nearly stable low contrast resolution was attained independent of phantom shape, e.g., circle and ellipse. The results suggest that stable image quality is available in the clinical stage for individual patients and regions, independent of the size and shape of targets. As for the evaluation of clinical images, the image quality requested by clinical operations at our hospital was attained even in the low dose mode that provides the lowest dose level. In addition, for variations in tube current values for photographing in individual regions, both sustained image uniformity and exposure reduction were found to be satisfactory in comparison with constant tube current.

Dosisreduktion bei der Spiral-CT: Detektion von Lungenrundherden mit und ohne anatomisch angepasster Röhrenstrommodulation

To investigate the potential of projection angle-dependent anatomical adaptation of tube current to reduce dose in spiral CT examinations of the thorax without loss in detectability of pulmonary nodules and image quality. Dose can be reduced for non-circular patient cross-sections without an increase in noise if the tube current is reduced at those angular positions where the patient diameter and, consequently, attenuation are small. The examinations were dose with SOMATOM Plus 4 (Siemens AG). CT projection data were analysed to determine the optimum tube current for each projection angle in real time. We compared image quality, done, and detection rates of pulmonary nodules for thoracic spiral CT examinations with and without online anatomically adapted tube current control in a group of 38 patients. Three radiologists counted all intrapulmonary nodules in consensus separated in three different groups (< 5 mm, 5-10 mm, > 10 mm). Image quality was evaluated in a scale from 1-3 (1 = very good, 2 = good, 3 = worse). On average, the dose was reduced by 21% (15-34%). With a constant tube current, 704 pulmonary nodules were detected, with tube current modulation 707 pulmonary nodules. For three patients we saw more pulmonary nodules (five) with tube current modulation, for two patients we saw less pulmonary nodules (two). In a direct comparison, the missed intrapulmonary nodules were also detected in the respective method. Thus, the detection rate of intrapulmonary nodules was uninfluenced. In general, no deterioration of image quality was observed. On average, 21% dose reduction was achieved by an anatomically adapted tube current modulation in spiral CT examinations of the thorax without a loss in detectability of pulmonary nodules and image quality. This method is an important contribution to dose reduction in spiral CT.

System performance of multislice spiral computed tomography.

Multislice spiral CT offers many new possibilities for clinical CT imaging. Drastically increased scan speeds and z-resolution, respectively, as well as applications such as cardiac CT that have become feasible for the first time in routine clinical use. The concept of multiple simultaneously acquired slices yields image quality equivalent or better than single-slice spiral CT. Especially, there is no dependence on spiral pitch, neither with regard to noise nor to slice sensitivity. The reconstructed slice width can be chosen freely and retrospectively, which offers additional flexibility when evaluating optimal protocols for various kinds of examinations. Three-dimensional isotropic resolution can be achieved routinely with examinations fast enough to scan in a single breath hold (Fig. 9). Without any drawbacks in image quality, MSCT in combination with online tube current modulation can reduce patient dose. In some body regions, dose is decreased to 50% compared to a scan with constant tube current. One of the most promising new applications is the dedicated ECG-gated cardiac interpolation 180 degrees MCI, which allows four-dimensional (4-D) imaging of the heart. The complete beating heart can be reconstructed in well-defined phases of the heart cycle, thereby adding high temporal resolution to isotropic 3-D spatial resolution (for more examples refer to http://www.imp.uni-erlangen.de/e/research/cardio/).

Anatomisch adaptierte Variation des Röhrenstroms bei der CT

To assess the impact of a method for anatomically adapted tube current variation. The resulting CT image quality was evaluated quantitatively and qualitatively. CT scans of 100 patients were performed with a constant tube current (Group 1) and another 100 patients with an anatomically adapted tube current (Group 2). The CT tube current was varied during a 360 degrees tube rotation reflecting the measured density values extracted from two perpendicular scout views. The standard deviation of densities of defined regions was measured. The image quality was ranked (1 = non-diagnostic-5 = excellent) by three radiologists. The effective tube current could be reduced by an average of 8.9% (0-20.4%). The mean tube current reduction depended on the body region: pelvis (13.2%), abdomen (8.4%) and thorax (3.3%). The image quality was not significantly reduced in Group 2. The method for anatomically adapted tube current variation leads especially in the pelvis to a significant mAs reduction without considerable loss of image quality.

Experiments with Fluorescent X Rays in the 10- to 50-Å Wavelength Region

Apparatus for the production, dispersion, and detection of soft fluorescent x-rays (10 to 50 Å) is described. The apparatus includes a new type of gaseous discharge x-ray tube capable of operating at 3000 v and 200 ma, a servo-type vacuum controller for maintaining constant x-ray tube current, and built-up films of heavy-metal soaps for use as analyzing crystals. Photographs are included of fluorescent spectral lines of carbon from graphite (Kα, λ=44.5 Å) and of copper (Lα, λ=13.3 Å) obtained, respectively, in 2 and in 4½ hr.

A Practical Method for the Routine Determination of the Quantity and Quality of X-rays

THE intensity or effective wave length output of our present high tension X-ray transformers and X-ray tubes does not appear to be either scientifically or practically uniform and constant; at least, not sufficiently accurate to permit the desired exact duplication of dosages, even though the determinations are made under the most favorable conditions of constant voltage and tube current. A review of the many careful recent researches of the physicists studying these problems more or less substantiates our practical experiences and observations in the administration of X-ray dosages in our daily clinical routine treatments, and the results observed in our biological researches at the Barnard Free Skin and Cancer Hospital. Duane has recently stated that “Variations of 40 per cent and more in the intensity of the X-ray projected through the same filter and at the same distance from the tube with different machines are not uncommon, and in the extreme cases one machine may project twice as much X-radiation as another.” Many physicists and investigators, including Glasser, Mutscheller, Erskine, Kelly, and Fricke, have predicted that spark gap estimation and energy input valuation will become obsolete, since the presence of so many variables almost necessitates measuring the output of the tube rather than the intake. In the past the usual standard sphere gap measurements and milliamperemeter readings have been erroneously considered the basis or indications of the quality and quantity of the filtered X-rays employed in the treatment of benign and malignant disease. It seems to us, however, that uniform results can neither be expected nor duplicated under the above conditions. It is becoming more and more self-evident that perhaps the great irregularity in results reported at meetings in the past are traceable to our present inaccurate method of defining and measuring the X-ray dose. Failla recently stated that the present radiation technic is due almost entirely to chance. We use whatever amount of radiation is available, or the voltage and current our machine can deliver, and then we adjust the treatment accordingly. If we have obtained some good results it is perhaps by mere accidental coincidence. That is indeed a most serious indictment. If the above deductions are partly correct, then even the study of the unknown biological phenomena must be considered secondary to the physical standardization of our X-ray beam. The biological phenomena of radiated cellular tissues as a whole cannot be interpreted and duplicated with precision, and, therefore, such changes are not of practical value unless considered in terms of a known physical agent producing such an effect. It would seem most logical and opportune to, first of all, continue our efforts in the latter direction, provided we do not ultimately find the many variable factors and physical obstacles too difficult of elimination in the production of our X-rays.