Technicare Corporation

Other

Ronald G Walters

Robert H Wake

Joseph B Richey

Roland W Carlson

Willard F Hunt

Steven L Cool

The present invention includes a back projector (44) suitable for assisting in the reconstruction of computerized tomography projection data. In particular it provides a fast and universal back projection system which can accomodate virtually any scanner geometry. The back projector (44) is based on an algorithm which involves the scaling of an image matrix pixel location to determine a pointer into a projection data memory (114). A linearization memory (112) contains pointers into a projection data memory (114). The location of the pixel is used to determine the proper location within the linearization memory (112) preferably using a linear interpolation process. The projection data contained in memory (114) is also preferably extracted using a similar interpolation process.

Method and apparatus for back projecting image data into an image matrix

A dual energy method for CT scanning. Scanning is carried out at low and high energy levels, S.sub.2 and S.sub.1 respectively, each at a preselected dose level. Detected electronic signals (I.sub.2,I.sub.1) are digitized. A look up table is used to generate a pair of values from each pair of signals, one a photoelectric component and the other a Compton component. Each of these values are subjected to spatial filtering by a convolution filter function for each signal specially designed to increase the signal to noise ratio in the resultant combined image by exploiting the correlation in noise in the two values.

Dual energy computerized tomography system

The invention relates to a method for processing attenuation data to produce a tomographic image which requires only that each point within the scan circle be viewed from 180.degree. in order to produce a full set of data. Data from views beyond 180.degree. are redundant and do not improve the picture quality. The invention further relates to an X-ray source and detector arrangement in which the X-ray source is a fan-shaped beam of X-rays and the detectors are arranged about the scan circle for 180.degree. plus approximately the angle of the fan beam. The invention further relates to method and apparatus for back projecting data from a polar coordinate system into a rectangular coordinate system in which the matrix points in the rectangular coordinate system can be loaded sequentially with the appropriate density value from the data line expressed in the polar coordinate system.

X-ray tomographic apparatus

The patient's ECG signal is employed in a traverse-and-rotate type CT scanner as a time base for triggering the beginning of a traverse such that the traveling beam reaches the heart at a desired phase of the cardiac cycle. For a purely-rotational-type CT scanner, continuously generated scan data is only stored for corresponding phases of successive cardiac cycles. Alternatively, gating of the beams themselves can be controlled by the ECG signal. The use of a pacemaker to stabilize the cardiac period is described along with a system for recognizing unacceptable variations in the cardiac period. In a traverse-and-rotate-type fan-beam CT scanner, the effective beam width is narrowed to hasten the traverse of the heart.

Cardiac imaging with CT scanner

The invention relates to the method for constructing a representation of the variation of attenuation of penetrating radiation in a planar slice of a patient positioned in a scan circle. The patient is irradiated with a fan shaped swath of radiation which is rotated about the patient for 180.degree. plus approximately the angle of the fan. Radiation passing through the scan circle is converted to sets of data, each set representing a radiation attenuation across a fan. The sets of data are filtered with a window function to remove data from some of the sets which represent radiation passing through a point in the scan circle by more than 180.degree. relative to radiation paths through the same point. The sets of data are serially convolved and back-projected into an image memory for display on a video monitor. The back projector addresses each set of data by generating subsequent addresses from the previous address and the incremental displacement between adjacent pixels of the image memory using pixel driven algorithms.

Tomographic apparatus

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.

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Aurora, OH, United States of America

Ronald G Walters