Joseph A. Heanue

Scanning-beam digital x-ray (SBDX) system for cardiac angiography

An advanced Scanning-Beam Digital X-ray (SBDX) system for cardiac angiography has been constructed. The 15-kW source operates at 70 - 120 kVp and has an electron beam that is electromagnetically scanned across a 23-cm X 23-cm transmission target. The target is directly liquid cooled for continuous full-power operation and is located behind a focused source collimator. The collimator is a rectangular grid of 100 X 100 apertures whose axes are aligned with the center of the detector array. X-ray beam divergence through the collimator apertures is matched to the 5.4-cm X 5.4 cm detector, which is 150 cm from the source. The detector is a 48 X 48 element CdZnTe direct-conversion photon-counting detector. A narrow x-ray beam scans the full field of view at up to 30 frames per second. A custom digital processor simultaneously reconstructs sixteen 1,0002 pixel tomographic images in real time. The slices are spaced 1.2 cm apart and cover the entire cardiac anatomy. The small detector area and large patient-detector distance result in negligible detected x-ray scatter. Image signal-to-noise ratio is calculated to be equal to conventional fluoroscopic systems at only 12% of the patient exposure and 25% of the staff exposure. Exposure reduction is achieved by elimination of detected scatter, elimination of the anti-scatter grid, increased detector DQE, and increased patient entrance area.

CdZnTe detector array for a scanning-beam digital x-ray system

The Scanning-Beam Digital X-ray (SBDX) system promises low- dose cardiac fluoroscopy and angiography with excellent image quality. The system demands a detector capable of high count rates and excellent detection efficiency. Cadmium zinc telluride (CdZnTe) is well suited to these requirements. The SBDX detector comprises sixteen 3-mm-thick, 13.5 mm X 13.5 mm tiles arranged in a 4 X 4 array. Each tile has 144 imaging elements. Thus, the entire detector measures 54.0 mm X 54.0 mm and includes 2,304 imaging elements on a 1.125 mm pitch. Because the SBDX system has a geometric magnification of 3.3, the imaging-element size is consistent with a system spatial-resolution of 2.2 lp/mm. The 3-mm thickness is chosen to guarantee a stopping efficiency of more than 90% at 120 kVp. Each detector tile is flip-chip mounted to a custom- designed integrated circuit (IC) using indium bump bonding techniques. Fabricated in a 1.2-micrometer CMOS process, the IC includes high-speed photon-counting circuitry that operates at rates up to 5 X 106 counts/s(DOT)mm2. The circuitry is designed both to maximize the achievable count- rate and to minimize false double counts due to charge sharing between elements. Testing confirms that the detector performs with minimum cross talk between elements at count rates in excess of 2 X 106 counts/s(DOT)mm2. Measurements of the detective quantum efficiency (DQE) are presented. The relationship between material properties and detector performance is also discussed. The circuit design and device fabrication techniques are applicable to a variety of imaging applications.

Frame-by-frame 3D catheter tracking methods for an inverse geometry cardiac interventional system

The Scanning-Beam Digital X-ray (SBDX) system performs rapid scanning of a narrow x-ray beam using an electronically scanned focal spot and inverse beam geometry. SBDXs ability to perform real-time multi-plane tomosynthesis with high dose efficiency is well-suited to interventional procedures such as left atrial ablation, where precise knowledge of catheter positioning is desired and imaging times are long. We describe and evaluate techniques for frame-by-frame 3D localization of multiple catheter electrodes from the stacks of tomosynthetic images generated by SBDX. The localization algorithms operate on gradient-filtered versions of the tomosynthetic planes. Small high contrast objects are identified by thresholding the stack of images and applying connected component analysis. The 3D coordinate of each object is the center-of-mass of each connected component. Simulated scans of phantoms containing 1-mm platinum spheres were used to evaluate localization performance with the SBDX prototype (5.5 × 5.5 cm detector, 3° tomographic angle) and a with new SBDX detector under design (10-cm wide × 6 cm, 6° × 3°). Z-coordinate error with the SBDX prototype was -0.6 +/- 0.7 mm (mean+/-standard deviation) with 28 cm acrylic, 24.3 kWp source operation, and 12-mm plane spacing. Localization improved to -0.3 +/- 0.3 mm using the wider SBDX detector and a 3-mm plane spacing. The effects of tomographic angle, plane-to-plane spacing, and object velocity are evaluated, and a simulation demonstrating ablation catheter localization within a real anatomic background is presented. Results indicate that SBDX is capable of precise real-time 3D tracking of high contrast objects.

CdZnTe detector arrays for low-dose x-ray fluoroscopy

The Scanning-Beam Digital X-ray (SBDX) system promises low- dose cardiac fluoroscopy and angiography with excellent image quality. The system demands a detector capable of high count rates and excellent detection efficiency. Cadmium zinc telluride (CdZnTe) is well suited to these requirements. The SBDX detector comprises sixteen 3-mm-thick, 13.5 mm X 13.5 mm tiles arranged in a 4 X 4 array. Each tile has 144 imaging elements. Thus, the entire detector measures 54.0 mm X 54.0 mm and includes 2,304 imaging elements on a 1.125 mm pitch. Because the SBDX system has a geometric magnification of 3.3, the imaging-element size is consistent with a system spatial-resolution of 2.2 lp/mm. The 3-mm thickness is chosen to guarantee a stopping efficiency of more than 90% at 120 kVp. Each detector tile is flip-chip mounted to a custom-designed integrated circuit using indium bump bonding techniques. Fabricated in a 1.2-micrometers CMOS process, the IC includes high-speed photon-counting circuitry that operates at rates up to 5 X 106 counts/s(DOT)mm2. The circuitry is designed both to maximize the achievable count-rate and to minimize false double counts due to charge sharing between elements. Testing confirms that the detector performs with minimum cross talk between elements at count rates in excess of 2 X 106 counts/s(DOT)mm2. Measurements of the detective quantum efficiency are presented. The relationship between material properties and detector performance is also discussed.