Microcomputed tomography (micro-CT) is a noninvasive imaging tool commonly used to probe the internal structures of small animals for biomedical research and for the inspection of microelectronics. Here we report the development of a micro-CT scanner with a carbon nanotube- (CNT-) based microfocus x-ray source. The performance of the CNT x-ray source and the imaging capability of the micro-CT scanner were characterized.

A nanotube-based field emission x-ray source for microcomputed tomography

The fundamental studies of a repetitive soft flash x‐ray generator having a high‐durability diode for high‐speed radiography in biomedical and technological fields are described. This generator consisted of the following essential components: a constant negative high‐voltage power supply, a line‐type high‐voltage pulser with two 10 m coaxial‐cable condensers, each with a capacity of 1.0 nF, a thyratron pulser as a trigger device, an oil‐diffusion pump, and a flash x‐ray tube. The x‐ray tube was of a diode type which was evacuated by an oil‐diffusion pump with a pressure of approximately 6.7×10−3 Pa and was composed of a planar tungsten anode, a planar ferrite cathode, and a polymethylmethacrylate tube body. The space between the anode and cathode electrodes (AC space) could be regulated from the outside of the tube. The two cable condensers were charged from −40 to −60 kV by a power supply, and the output voltage was about −1.5 times the charged voltage. Both the first peak voltage and current increased a...

Repetitive flash x‐ray generator having a high‐durability diode driven by a two‐cable‐type line pulser

Fundamental studies on a long-duration flash X-ray generator are described. This generator consisted of the following components: a high-voltage power supply with a maximum voltage of 100 kV, an energy-storage condenser of 500 nF, a main discharge condenser of 10 nF, a turbo molecular pump, a thyratron pulser as a trigger device, and a surface-discharge triode. The effective pulse width was less than 30 µs, and the X-ray intensity approximately had a value of 0.6 µC/kg at 1.0 m per pulse with a charged voltage of 60 kV. The maximum tube voltage was equivalent to the initial charged voltage of the condenser, and the peak tube current was less than 40 A. With this generator, we could obtain stable X-ray intensity maximized by preventing damped oscillations of the tube voltage and current.

Fundamental study on a long-duration flash X-ray generator with a surface-discharge triode

The cerium target x-ray generator is useful in order to perform enhanced K-edge angiography using a cone beam because K-series characteristic x rays from the cerium target are absorbed effectively by iodine-based contrast mediums. The x-ray generator consists of a main controller, a unit with a Cockcroft-Walton circuit and a fixed anode x-ray tube, and a personal computer. The tube is a glass-enclosed diode with a cerium target and a 0.5−mm-thick beryllium window. The maximum tube voltage and current were 65kV and 0.4mA, respectively, and the focal-spot sizes were 1.0×1.3mm. Cerium Kα lines were left using a barium sulfate filter, and the x-ray intensity was 0.48μC/kg at 1.0m from the source with a tube voltage of 60kV, a current of 0.40mA, and an exposure time of 1.0s. Angiography was performed with a computed radiography system using iodine-based microspheres. In coronary angiography of nonliving animals, we observed fine blood vessels of approximately 100μm with high contrasts.

Demonstration of enhanced K-edge angiography using a cerium target x-ray generator.

In the plasma flash x-ray generator, a 200 nF condenser is charged up to 50 kV by a power supply, and flash x rays are produced by the discharging. The x-ray tube is a demountable triode with a trigger electrode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of weakly ionized linear plasma, consisting of copper ions and electrons, around the fine target, and intense characteristic x rays are produced. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 20 kA. When the charging voltage was increased, the linear plasma formed, and the K-series characteristic x-ray intensities increased. The K lines were quite sharp and intense, and hardly any bremsstrahlung rays were detected at all. The x-ray pulse widths were approximately 700 ns, and the time-integrated x-ray intensity had a value of approximately 30 μC/kg at 1.0 m from the x-ray source with a charging voltage of 50 kV.

Quasi-monochromatic flash x-ray generator utilizing weakly ionized linear copper plasma

The construction and the fundamental studies of a repetitive flash x‐ray generator having a simple diode with an energy‐selective function are described. This generator consisted of the following components: a constant high‐voltage power supply, a high‐voltage pulser, a repetitive high‐energy impulse switching system, a turbo molecular pump, and a flash x‐ray tube. The circuit of this pulser employed a modified two‐stage surge Marx generator with a capacity during main discharge of 425pF. The x‐ray tube was of the demountable‐diode type which was connected to the turbo molecular pump and consisted of the following major devices: a rod‐shaped anode tip made of tungsten, a disk cathode made of graphite, an aluminum filter, and a tube body made of glass. Two condensers inside of the pulser were charged from 40 to 60 kV, and the output voltage was about 1.9 times the charging voltage. The peak tube voltage was primarily determined by the anode‐cathode (A‐C) space, and the peak tube current was less than 0.6 kA. The peak tube voltage slightly increased when the charging voltage was increased, but the amount of change rate was small. Thus, the maximum photon energy could be easily controlled by varying the A‐C space. The pulse width ranged from 40 to 100 ns, and the x‐ray intensity was less than 1.0 μC/kg at 0.3 m per pulse. The repetitive frequency was less than 50 Hz, and the effective focal spot size was determined by the diameter of the anode tip and ranged from 0.5 to 3.0 mm in diameter.

Repetitive flash x‐ray generator utilizing a simple diode with a new type of energy‐selective function

The construction and fundamental studies are described for a sub-kilohertz X-ray generator for producing low-dose rate flash X-rays. The X-ray tube was a glass-enclosed cold-cathode triode, composed of a tungsten plate target, a rod-shaped graphite cathode, a mesh-type trigger electrode made of tungsten wires, and a glass tube body. The coaxial condenser was charged up to 60 kV by a power supply, and the electric charges in the condenser were discharged to the X-ray tube repetitively when a negative high-voltage pulse was applied to the trigger electrode. The maximum tube voltage before the discharging was equivalent to the initial charged voltage of the condenser, and the maximum tube current was about 0.3 kA with a charged voltage of 60 kV. The X-ray durations were about 1 microsecond, and the X-ray intensity was about 0.47 microC kg-1 at 0.5 m per pulse with a charged voltage of 60 kV. The maximum repetition rate of the X-rays was about 0.4 kHz, and high-speed radiography was performed.

Sub-kilohertz flash X-ray generator utilising a glass-enclosed cold-cathode triode.

The construction and the fundamental studies of a kilohertz‐range flash x‐ray generator having a triode in conjunction with an extremely hot cathode are described. This generator consisted of the following components: a constant‐high voltage power supply, an energy storage condenser of 100 nF, a constant high‐voltage power supply for regulating an initial grid voltage of −1.6 kV, a grid pulser, and an x‐ray tube. The x‐ray tube was of an enclosed‐triode type and consisted of the following major parts: an anode rod made of copper, a plane anode tip (target) made of tungsten, a focusing electrode made of iron, a hot cathode (filament) made of tungsten, a grid made from tungsten wire, and a glass tube body. The energy storage condenser was charged from 50 to 70 kV, and the electric charges in the condenser were discharged repetitively to the x‐ray tube by the grid electrode driven by the grid pulser. The temperature of the filament was about 2000 K, and the cathode current was primarily controlled by the gri...

Kilohertz‐range flash x‐ray generator utilizing a triode in conjunction with an extremely hot cathode

The construction and the fundamental studies for the repetitive flash x-ray generators designed by Japan Impulse Laboratory in Iwate Medical University are described. These generators are classified to the following two major types: (1) generators having diodes, and (2) generators having triodes. In order to generate high-voltage impulses, we employed the following transmission lines (pulsers): (a) high-voltage-inversion type with a maximum output voltage V om of about 80 kV, (b) high-voltage- inversion type having a coaxial cable (V om equals 130 kV), (c) two-stage Marx pulser (V om equals 150 kV), (d) two-cable-type Blumlein (V om equals 120 kV), (e) modified Blumlein (V om equals 120 kV), (f) fundamental transmission line for triode (V om equals 100 kV), and (g) transmission line for an enclosed triode (V om equals 100 kV). Using these generators we succeeded in performing high-speed radiography as follows: (a) delayed radiography; (b) multiple-shot radiography; and (c) cineradiography.

Kei Takahashi

Papers

Repetitive flash x‐ray generator utilizing a simple diode with a new type of energy‐selective function

Fundamental study on a long-duration flash X-ray generator with a surface-discharge triode

Sub-kilohertz flash X-ray generator utilising a glass-enclosed cold-cathode triode.

Kilohertz‐range flash x‐ray generator utilizing a triode in conjunction with an extremely hot cathode

Repetitive compact flash x-ray generators for soft radiography