X-ray CT scanner capable of performing improved log conversion

An X-ray CT scanner comprising:

• an X-ray source generating an X-ray toward an object;
• a detector detecting the X-ray transmitted from the object;
• a processor applying logarithm conversion processing to an output signal from the detector to produce projection data, the logarithm conversion processing being based on an ideal logarithm function and a function different from the ideal logarithm function;
• and
• a reconstruction unit configured to reconstruct an image using the projection data produced by the processor,
• wherein the processor includes selection means configured to select either the ideal logarithm function or the function different from the ideal logarithm function, dependently on the output signal from the detector.

An X-ray CT scanner comprising:

• an X-ray source generating an X-ray toward an object;
• a detector detecting the X-ray transmitted from the object;
• a determining unit configured to determine if or not an output signal from the detector is low-count data;
• a conversion processing unit configured to perform a conversion of the determined low-count data on a first conversion function to produce a conversion of projection data and to perform non-low-count data on a second conversion function different from the first conversion function to produce the projection data, the non-low-count-data being determined by the determining unit as data excluded from the low-count data, and
• a reconstruction unit configured to reconstruct an image using the projection data produced by the conversion processing unit.

An X-ray CT scanner comprising:

• an X-ray source generating an X-ray toward an object;
• a detector detecting the X-ray transmitted from the object;
• a classifying unit configured to use a threshold to classify whether an output signal from the detector is either low-count data or non-low-count data;
• a conversion processing unit configured to perform a conversion of the classified low-count data on a first conversion function to produce projection data and to perform a conversion of the classified non-low-count data on a second conversion function different from the first conversion function to produce the projection data;
• and
• a reconstruction unit configured to reconstruct an image using the projection data produced by the conversion processing unit.

An X-ray CT scanner comprising:

• an X-ray source generating an X-ray toward an object;
• a detector detecting the X-ray transmitted from the object;
• a storing unit configured to store a plurality of types of conversion processing for converting the output signal from the detector on the functions;
• a setting device configured to set an imaging condition;
• a determining unit configured to determine a threshold for switching the plurality of types of conversion functions stored in the storing unit depending on the imaging condition;
• a conversion processing unit configured to perform conversion processing with an output signal from the detector to produce projection data by using a conversion function switchably determined from the plurality of types of conversion functions by the determining unit;
• and
• a reconstruction unit configured to reconstruct an image using the projection data produced by the conversion processing unit.