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PubMed2006

Compatibility of interventional x-ray and magnetic resonance imaging: feasibility of a closed bore XMR (CBXMR) system.

A next-generation interventional guidance system is proposed that will enable intraprocedural access to both x-ray and magnetic resonance imaging (MRI) modalities. This closed bore XMR (CBXMR) system is comprised of a conventional radiographic rotating anode x-ray tube and a direct conversion flat panel detector on a rotating gantry positioned adjacent to the bore of a 1.5 T MRI. To assess the feasibility of such a system, we have investigated the degree of compatibility between the x-ray components and the MRI. For /-->B(ext)/ < 200 G the effect on the radiographic tube motor was negligible regardless of the orientation of -->B(ext) with respect to the motor axis of rotation--the frequency of anode rotation remained within 6% of the 3400 rpm frequency measured at 0 G. For /-->B(ext)/ >2400 G the anode slowed down to below 2400 rpm at all orientations. At intermediate B(ext), the frequency of rotation varied between 2400 and 3200 rpm, showing a strong dependence on orientation, with -->B(ext) perpendicular to the tube axis having a much stronger effect on the rotation frequency than -->B(ext) parallel to the tube axis. In contrast to the effect of -->B(ext) on the induction motor, parallel -->B(ext) had a stronger detrimental effect on the cathode-anode electron beam, whose path was at 16 degrees to the tube axis, than the perpendicular -->B(ext). Parallel -->B(ext) of several hundred Gauss had a defocusing effect on the x-ray focal spot. -->B(ext) perpendicular to the electron beam shifted the beam without significant defocusing. We have determined that the direct conversion flat panel detector (FPD) technology is not intrinsically sensitive to -->B(ext), and that the modifications required to make the proposed FPDs MRI compatible are minimal. The homogeneity of the MRI signal in the normal field of view was not significantly degraded by the presence of these x-ray components in the vicinity of the MRI bore entrance.

Equipment Design↗
PubMed2005

[CR-mammography with pixel size of 50 microm and dual-sided reading system: effect of the oblique incident of the X-ray beam on imaging properties and detection].

In mammography units, the X-ray tube focal spot is located directly above the chest wall edge of the detector. Therefore, the X-ray beam is incident at a different angle along the cathode-anode axis. When the X-ray beam is incident on the imaging plate (IP) at a relatively large angle, the resolution property of a new imaging plate with dual-sided reading system would be degraded compared with the conventional imaging plate because of the parallax effect, which produces a shift in the image on two sides of the imaging plate. To evaluate the oblique incidence effect of the X-ray beam on the degradation of resolution properties and detection of simulated microcalcifications of a new CR system with a pixel size of 50 microm, its basic imaging properties and observer performance tests were compared with those of a conventional CR system. The resolution properties were evaluated by measuring modulation transfer functions (MTFs). Observer performance tests were conducted to compare the detectability of simulated microcalcifications of CR systems. Degradation of presampling MTFs for the new system is greater than that of the conventional CR system when the X-ray beam was incident at the same angle on the imaging plate. We found that the degradation of the area under the ROC curve (Az) for the new CR system was greater than that of the conventional CR system when the X-ray beam was incident at the same angle on the imaging plate.

Calcinosis↗
PubMed2005

Prototype heel effect compensation filter for cone-beam CT.

The prototype cone-beam CT (CBCT) has a larger beam width than the conventional multi-detector row CT (MDCT). This causes a non-uniform angular distribution of the x-ray beam intensity known as the heel effect. Scan conditions for CBCT tube current are adjusted on the anode side to obtain an acceptable clinical image quality. However, as the dose is greater on the cathode side than on the anode side, the signal-to-noise ratio on the cathode side is excessively high, resulting in an unnecessary dose amount. To compensate for the heel effect, we developed a heel effect compensation (HEC) filter. The HEC filter rendered the dose distribution uniform and reduced the dose by an average of 25% for free air and by 20% for CTDI phantoms compared to doses with the conventional filter. In addition, its effect in rendering the effective energy uniform resulted in an improvement in image quality. This new HEC filter may be useful in cone-beam CT studies.

Equipment Design↗
PubMed1980

An investigation and explanation of the fall-off of x-ray tube current during an exposure.

It was observed that the radiation output of x-ray tubes falls off exponentially during an exposure with a time constant of about 120 ms. The equilibrium value is approximately 15% lower than that at the beginning of the exposure. The clinically noticeable consequences are discrepancies in x-ray generator calibration, the loss of the strict mA s (tube current X exposure time) linearity, and, in scanning devices, the possibility of artefact generation. A systematic investigation of the phenomenon revealed that it is caused by the cooling of the cathode due to evaporation of electrons. Theoretical expressions for the magnitude and time constant of the fall-off derived from basic thermodynamics are in good agreement with the observations. A simple mA stabilisation circuit which prevents the fall-off is described.

Technology, Radiologic↗
PubMed1995

Effects of induced charge in the kinestatic charge detector.

The principle of the kinestatic charge detector (KCD) for digital radiography depends on the synchronization of the scan velocity of a parallel plate drift chamber with the cation drift velocity. Compared with line-beam scanners, this motion-compensated imaging technique makes better use of the x-ray tube output. A Frisch grid traditionally has been used within the KCD to minimize unwanted signal contributions from both cations and negative charge carriers during irradiation. In this work the charge induction process in a parallel plate geometry was investigated for the special case of the KCD. In the limit of infinite plates, the cathode charge density due to both cations and negative charge carriers increases quadratically in time for a kinestatically scanned narrow slit. In the KCD the cathode is segmented into an array of narrow electrodes, each aligned with the incident x-ray beam. Our conformal mapping computation determined that the shape of the induced charge signal depends critically on delta x/w, the ratio of electrode width to drift gap. Our conclusion introduces the possibility of eliminating the Frisch grid from the KCD design because the value of delta x/w required for transverse sampling in the KCD is sufficiently low as to allow "self-gridding" to take effect.

Humans↗
PubMed1981

Quantitative and qualitative comparison of two microfocus-tube imaging systems.

Two microfocus-tube magnification systems were compared: one used an RSI tube (stationary anode, Pierce-gun cathode) and the other used a GE tube (rotating anode, biased cathode). Imaging parameters for body parts of three thicknesses, the hand (low), knee (medium), and hip (high), were considered at a magnification of 2. The focal-spot MTF was measured on and off the central ray of the beam, as well as beam quality and the intensity of scatter in the image plane. Patient exposures were also determined. While both systems gave high-quality images at acceptable exposure levels, the RSI unit was judged superior for body parts up to 15 cm thick. For thicker parts, scatter degraded contrast with the RSI unit, making the GE unit superior.

Humans↗
PubMed1983

Percutaneous treatment of pulmonary tumors by electrolysis.

Five lung tumors in four patients were treated with electrolysis. One of the tumors was probably primary, while the others were metastases. Under local anesthesia, two or three platinum electrodes (diameter 3 mm) were introduced through the thoracic wall into the lung tumor using biplane fluoroscopy. The patient was sedated before the procedure and a chest tube was inserted into the pleural cavity. Between anode and cathode a direct current of 80 mA and 10 V was passed during 2-4 h, creating substantial electrolytic destruction mainly through chlorine liberation. Observations at autopsy, surgery, chest X-ray, and CT showed that 60%-80% of the tumor mass was destroyed. No tumor was completely destroyed. The patients tolerated the procedure well.

Adenocarcinoma↗
PubMed1994

10 kHz microsecond pulsed X-ray generator utilising a hot-cathode triode with variable durations for biomedical radiography.

A 10 kHz pulsed X-ray generator utilising a hot-cathode triode in conjunction with a new type of grid control device for controlling X-ray duration is described. The energy-storage condenser was charged up to 70 kV by a power supply, and the electric charges in the condenser were discharged to the X-ray tube repetitively by the grid control device. The maximum values of the grid voltage (negative value), the tube voltage, and the tube current were -1.5 kV, 70 kV, and 0.4 A, respectively. The duration of the flash X-ray pulse was primarily determined by the time constant of the grid control device and the cut-off voltage of thermoelectrons. The X-ray duration was controlled within a region of less than 1 ms; the X-ray intensity with a pulse width of 0.27 ms, a charged voltage of 70 kV, and a peak tube current of 0.4 A was 0.92 microC kg-1 at 0.5 m per pulse. The maximum repetition rate was about 10 kHz, and the size of the focal spot was about 3.5 x 3.5 mm.

Animals↗
PubMedDate not supplied

[Portable microfocal radiographic devices for medical diagnosis].

The paper outlines two portable microfocal X-ray medical diagnostic devices which have a designing principle in common. The basic features of the devices are as follows: a thin long fight-path tube at whose end there is a massive or shooting target, a three-electrode electron gun, a private-line tungsten loop-shaped cathode, and a magnetic focusing system.

Humans↗
PubMedDate not supplied

[X-ray tubes with ionic indemnification of negative space electronic charge].

How to increase anode current in the fine-focus diagnostic X-ray tubes (XTs) is analyzed. It has been found that there are new three-class XTs that have advantages of both ionic and electronic tubes. The specific feature of the new class XTs is the gaseous atmosphere available in the working volume. Ionizing the gaseous atmosphere with a emission electron flow in the path from the cathode to the anode yields a dot volumetric positively charged ion grid that closely approaches the cathode and can pay a big bonus in anode current output.

Humans↗
PubMed2002

A practical design of a cylindrical tissue-equivalent proportional counter for microdosimetry.

A 12 mm tissue-equivalent proportional counter (TEPC) was designed, constructed and successfully tested. This detector achieves features common to others TEPCs, but it does not use field shaping electrodes and it is able to work at higher bias voltages which makes it capable of measuring the whole range of energy deposition events for gamma rays. The following approach was used to design the detector: first of all the use of a cylindrical shape detector featured as simple as possible but keeping its performance as well, the next point is to avoid the use of field shaping tubes and the last one is to make the preamplifier small and as close as possible to the detector. Its construction is based on a cylindrical proportional counter with A-150 tissue-equivalent material as cathode, TE-methane gas as a proportional gas and a 20 microns diameter wire as anode.

Cesium Radioisotopes↗
PubMedDate not supplied

Clinical application and dosimetric calibration procedure of the superficial and orthovoltage therapy unit Therapax DXT300.

AIMS AND BACKGROUND: The aim of this study was to configure a new superficial and orthovoltage therapy unit for clinical use and discuss the clinical indications for this kind of energy. There is renewed interest in radiotherapy using photon beams in the range from 40 to 300 kVp, in particular for the treatment of non-neoplastic diseases and superficial lesions. This is due to the fact that the latest units are of good quality, relatively cheap and reliable in comparison with alternative equipment. It is therefore necessary to document the steps involved in the clinical application of this therapeutic equipment. METHODS: The calibration procedure for a new superficial/orthovoltage therapy unit, Therapax DXT300 (Pantak, USA), installed at the Radiotherapy Department of the Mauriziano Hospital in Turin, was carried out by measurement of beam quality (half-value layer, HVL), percentage depth dose (PDD), profiles, internal dosimetry system, dose rate calibration and output factors. The Therapax DXT300 can be programmed to stop treatment either by time or dose, like a linear accelerator. It is equipped with one adjustable collimator (2 x 2 divided by 20 x 20 cm2) for orthovoltage therapy (focus skin distance, FSD = 50 cm) and six fixed applicators for superficial and orthovoltage therapy (FSD = 30 and 50 cm, respectively). Up to eight combinations of generating potential, tube current and added beam filter can be set. RESULTS: In the range of accelerating potentials from 40 to 300 kVp the Therapax provides beams with HVL ranging from 1.48 mm Al to 3.68 mm Cu. As regards the PDD curves, a slight difference between PDD values has been observed with potentials ranging from 200 to 300 kVp. The beam symmetry and flatness are almost the same in Y and X plane directions for accelerating potentials of less than 200 kVp. At higher kVp values these parameters are significantly worse in the anode-cathode axis direction, because the useful X-ray beam is extracted perpendicular to the anode-cathode axis direction: as the energy increases, the bremsstrahlung becomes more forward directed, resulting in a higher dose rate on the anode side. CONCLUSION: The present paper suggests a methodological approach for the clinical application of an orthovoltage/superficial therapy unit and discusses its current indications. It is necessary to maintain the performance of the equipment within predefined limits in order to meet the requirements of an efficient quality assurance program. This unit is particularly useful in the treatment of superficial lesions and non-neoplastic diseases and in palliative care (eg for bone metastases).

Calibration↗
PubMed2006

Characterization of Pt nanoparticles deposited onto carbon nanotubes grown on carbon paper and evaluation of this electrode for the reduction of oxygen.

Multiwalled carbon nanotubes (MWCNTs) were grown on the fibers of a commercial porous carbon paper used as carbon-collecting electrodes in fuel cells. The tubes were then covered with Pt nanoparticles in order to test these gas diffusion electrodes (GDEs) for oxygen reduction in H2SO4 solution and in H2/O2 fuel cells. The Pt nanoparticles were characterized by cyclic voltammetry, transmission electron microscopy, and X-ray photoelectron spectroscopy. The majority of the Pt particles are 3 nm in size with a mean size of 4.1 nm. They have an electrochemically active surface area of 60 m2/g Pt for Pt loadings of 0.1-0.45 mg Pt/cm2. Although the electroactive Pt surface area is larger for commercial electrodes of similar loadings, Pt/MWCNT electrodes largely outperform the commercial electrode for the oxygen reduction reaction in GDE experiments using H2SO4 at pH 1. On the other hand, when the same electrodes are used as the cathode in a H2/O2 fuel cell, they perform only slightly better than the commercial electrodes in the potential range going from approximately 0.9 to approximately 0.7 V and have a lower performance at lower voltages.

Journal Article↗
PubMed2006

In situ electrochemical and photo-electrochemical generation of the fenton reagent: a potentially important new water treatment technology.

In this work, the design and construction of an annular tube reactor for the electrochemical and photo-electrochemical in situ generation of H2O2 are described. By cathodic reduction of dissolved oxygen and the coupled oxidation of water at a UV-illuminated nanocrystalline-TiO2 semiconductor anode, it was found that the electrochemically generated H2O2 can be employed to readily oxidize the model compound Direct Yellow-52 in dilute acidic solution at high rates in the presence of small quantities of dissolved iron(II). Although, the model organic compound is chemically stable under UV radiation, its electrochemical oxidation rate increases substantially when the semiconductor anode is illuminated as compared to the same processes carried out in the dark.

Carbon↗