Technicare Corporation

Ohio Nuclear, Inc.

Roland W Carlson

Edward A Blaskis

John Covic

Dominic J Heuscher

Ronald G Walters

Carl T Jagatich

Glen Leininger

An all metal and ceramic high vacuum rotary anode x-ray tube adapted for mounting on a gantry of a rotational type CT scanner. The evacuated region where x-rays are generated is maintained at about 10.sup.-7 Torr. Vacuum sealing about the rotating shaft of the anode is provided by a magnetic fluid. No bearings are utilized within the evacuated region. Large, long wearing ball bearings that transmit rotation through the vacuum seal are provided about the shaft outside of the high vacuum region where conventional lubricants may be applied. Circulating coolant is applied internally through the anode assuring continual operation of the tube without the need for frequent cool-down waits. A preferred embodiment discloses a modified path in the rotor for the coolant designed to disturb the conventional laminar type of flow which is heat transfer inefficient to one characterized by high turbulence resulting in approximately an order of magnitude improvement in the coefficient of heat transfer.

High vacuum rotating anode x-ray tube

An all metal and ceramic high vacuum rotary anode X-ray tube adapted for mounting on a gantry of a rotational type CT scanner. The evacuated region where X-rays are generated is maintained at about 10.sup.-7 Torr. Vacuum sealing about the rotating shaft of the anode is provided by a magnetic fluid. No bearings are utilized within the evacuated region. Large, long wearing ball bearings that transmit rotation through the vacuum seal are provided about the shaft outside of the high vacuum region where conventional lubricants may be applied. Circulating coolant is applied internally through the anode assuring continual operation of the tube without the need for frequent cool-down waits.

High vacuum rotating anode X-ray tube

A method of vacuum assembling a rotating anode X-ray tube of the type having a rotor and a shaft extending therefrom with a magnetic fluid for vacuum sealing about the shaft. The tube is subjected to a high temperature bake-out whereby gases are sufficiently evolved from exposed metal parts that a stable low pressure region is created. A static seal is used to temporarily seal the region during bake-out with the anode temporarily rendered non-rotatable and the permanent magnetic vacuum seal protected from the high temperature. The system is then allowed to cool off before the permanent magnetic vacuum seal is moved into its operational position within the high vacuum. Assembly tooling is provided ensuring that the high vacuum is maintained throughout the installation. Bearings are installed external to the region of high vacuum to transmit rotary motion of the shaft through the permanent seal. Finally, the tube is rendered operational by displacing the static seal thereby permitting the anode to be rotated.

Method for assembling a high vacuum rotating anode X-ray tube

In a rotating fan beam tomographic scanner there is included a variable detector aperture housed within a radiation scatter shield. The scanner includes a diverging source of penetrating radiation which is directed toward a patient receiving section for passing a fan shaped beam of radiation through a planar section of the patient. The incident radition beam is attenuated during its passage through the patient receiving section and the transmitted beam passes from the patient receiving section until it impinges on a plurality of detectors for eventual reconstruction into a visible image. The variable detector aperture controls the thickness of the fan shaped beam and hence limits the amount of radiation impinging on the detectors. The aperture includes a pair of elongated beam thickness defining members having an opening therebetween and rotatable relative to the scanning plane. The opening between the two members in a direction transverse to the scanning plane defines the thickness of the attenuated fan beam passing therethrough.

Variable detector aperture

A radiation detector or detector array which has a non-constant spatial response individually and in combination with a tomographic scanner. The detector has a first dimension which is oriented parallel to the plane of the scan circle in the scanner. Along the first dimension, the detector is most responsive to radiation received along a centered segment of the dimension and less responsive to radiation received along edge segments. This non-constant spatial response can be achieved in a detector comprised of a scintillation crystal and a photoelectric transducer. The scintillation crystal in one embodiment is composed of three crystals arranged in layers, with the center crystal having the greatest light conversion efficiency. In a preferred embodiment, the non-constant spatial response is achieved in a detector comprised of a single scintillation crystal whose response is shaped by inducing along said first dimension a scintillation conversion efficiency gradient. In the single crystal embodiment, the gradient is chosen so that the crystal has greater conversion efficiency centrally than peripherally.

Shaped detector

A method of minimizing a streaking effect found in reconstructed images obtained from high resolution CT scanning of a small scan circle that corresponds to a limited region of interest, such as portions of the spinal cord of a patient, particularly in scans that include concentrated high density material, such as bone, situated outside the small scan circle. The approximate range of view angles that will project bone from outside the limited region of interest is determined. Detectors corresponding to the determined region are selected out. The projection data acquired by the selected detectors is filtered. The filtering is accomplished by convolving the projection data with a preselected filter function or in machine implemented form by passing the electrical signal representing the projection data through a low pass filter.

Method of high resolution partial area scan involving concentrated high

A radiation detector or detector array which has a non-constant spatial response, is disclosed individually and in combination with a tomographic scanner. The detector has a first dimension which is oriented parallel to the plane of the scan circle in the scanner. Along the first dimension, the detector is most responsive to radiation received along a centered segment of the dimension and less responsive to radiation received along edge segments. This non-constant spatial response can be achieved in a detector comprised of a scintillation crystal and a photoelectric transducer. The scintillation crystal in one embodiment is composed of three crystals arranged in layers, with the center crystal having the greatest light conversion efficiency. In another embodiment, the crystal is covered with a reflective substance around the center segment and a less reflective substance around the remainder. In another embodiment, an optical coupling which transmits light from adjacent the center segment with the greatest intensity couples the scintillation crystal and the photoelectric transducer. In yet another embodiment, the photoelectric transducer comprises three photodiodes, one receiving light produced adjacent the central segment and the other two receiving light produced adjacent the edge segments. The outputs of the three photodiodes are combined with a differential amplifier.

The invention comprises a shaped filter and a filter correction circuitry for computerized tomographic scanners. The shaped filter is a generally U-shaped block of filter material which is adapted to be mounted between the source of radiation and the scan circle. The U-shaped block has a parabolic recess. The filter material may be beryllium, aluminum, sulphur, calcium, titanium, erbium, copper, and compounds including oxides and alloys thereof. The filter correction circuit comprises a first filter correction profile adding circuit for adding a first scaler valve to each intensity valve in a data line. The data line is operated on by a beam hardness correction polynomial. After the beam hardness polynomial correction operation, a second filter correction circuit adds a second filter correction profile consisting of a table of scalor values, one corresponding to each intensity reading in the data line.

Computerized tomographic scanner with shaped radiation filter

In a rotating fan beam tomographic scanner there is included an adjustable collimator and shutter assembly. The assembly includes a fan angle collimation cylinder having a plurality of different length slots through which the beam may pass for adjusting the fan angle of the beam. It also includes a beam thickness cylinder having a plurality of slots of different widths for adjusting the thickness of the beam. Further, some of the slots have filter materials mounted therein so that the operator may select from a plurality of filters. Also disclosed is a servo motor system which allows the operator to select the desired fan angle, beam thickness and filter from a remote location. An additional feature is a failsafe shutter assembly which includes a spring biased shutter cylinder mounted in the collimation cylinders. The servo motor control circuit checks several system conditions before the shutter is rendered openable. Further, the circuit cuts off the radiation if the shutter fails to open or close properly. A still further feature is a reference radiation intensity monitor which includes a tuning-fork shaped light conducting element having a scintillation crystal mounted on each tine. The monitor is placed adjacent the collimator between it and the source with the pair of crystals to either side of the fan beam.

Adjustable collimator

A radiation detector suitable for use in tomographic scanners comprising at least one cadmium tungstate scintillation crystal optically coupled with a silicon photodiode or other photoelectric transducers. A plurality of cadmium tungstate crystals may be coupled to one silicon photodiode with fiber optic light guides. In a tomographic scanner, radiation passing through the scan circle impinges on the cadmium tungstate crystals causing them to scintillate. The light scintillated strikes the area of the p-n junction of the photodiode causing the photoelectric effect to be manifested. The intensity of radiation striking the crystal is determined by measuring the photoconductive conductance, photoemissive current or photovoltaic potential. From these intensities an image is computed of the radiation attenuation in the examined scan circle.

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Lyndhurst, OH, United States of America

Roland W Carlson