1. Field of the Invention
The invention relates generally to the field of medical and/or biomedical research imaging. More particularly, a preferred embodiment of the invention is directed to a positron emission tomography (PET) camera with individually rotatable detector modules and/or movable shielding sections. The invention thus relates to a PET camera of the type that can be termed convertible.
2. Discussion of the Related Art
Positron emission tomography, sometimes called PET, is known to those skilled in the art. For instance, a conventional PET camera typically includes a detector ring having a number of detector modules.
A problem with this technology has been that typical PET samples to be imaged are of widely varying sizes. With regard to a human patient, a whole body scan must consider a much larger sample space than a head or breast scan. The larger sample space necessitates a detector ring, and detector noise shield of large radius. A major use of PET cameras is for whole body imaging for the purpose of tumor localization. Conversely, the smaller sample space defined by a head or breast can be accommodated within a smaller detector ring. Further, biomedical research imaging can generally be performed with a detector ring of relatively small radius. A small laboratory animal (e.g., a mouse) can be imaged with a detector ring of relatively small radius.
While many samples can be imaged with a small detector ring, a clinically useful instrument should provide a large detector ring radius to accommodate the largest sample, for example the whole body of an obese patient. On the other hand, when imaging a small sample, the level of signal detected by a detector ring with a large radius will be lower due to the increased distance between the sample and the detector ring, and the level of noise in the data can be higher due to the large radius of the noise shield. A large radius shield makes the detector more wide open to receive scattered radiation noise. Therefore, what is required is an approach that permits samples of widely varying sizes to be imaged by a detector ring with a variable radius.
One technique that has been used to vary the radius of a detector ring is to subdivide the detector ring into a number of detector modules that are radially repositionable.(1-3) A limitation of this technique has been that increasing the radius of a detector ring to accommodate larger samples causes gaps to be opened up between the individual detector modules that compose the ring. Optimal imaging is performed with a fully populated detector ring. That design would form a close packed ring for small objects but form a ring with gaps for large samples. That design is optimal for small samples but sub-optimal for large samples; the detector gaps reduce detector sensitivity and they cause image artifacts. Large gaps require macro-rotation of the detector ring as a whole, thereby increasing the time required for complete imaging. Therefore, what is also required is an approach that can vary the radius of a detector ring without creating gaps between the detectors or creating only a minimum amount of gap.
Another problem with this technology has been that the mass of the sample absorbs much of the emitted radiation. Thus, an emission image, of radioisotope in a patient for example, must be corrected with data from a transmission image, of a controlled radiation source which is typically located outside the sample. The transmission image is then used to correct the emission image. The need to obtain the transmission image increases the total amount of time required to process one sample. Therefore, what is also required is an approach that can simultaneously perform both emission and transmission imaging.
Heretofore, the requirements of a variable detector ring radius, avoidance and/or minimization of gaps within the detector ring, and simultaneous emission and transmission imaging referred to above have not been fully met. What is needed is a solution that addresses these requirements, depending on the imaging situation.
A goal of the invention is to satisfy the requirements of a variable detector ring radius, avoidance and/or minimization of gaps within the detector ring, protecting a variable detector ring with a corresponding variable detector shield, increasing the axial extent of the camera in some situations, and simultaneous emission and transmission imaging which, in the case of the prior art have not been fully satisfied.
One embodiment of the invention is based on an apparatus, comprising a detector ring including a plurality of individually movable detector modules. Another embodiment of the invention is based on a method, comprising: converting a detector ring including moving at least one of a plurality of independently movable detector modules. Another embodiment of the invention is based on a computer program comprising computer program means adapted to perform the steps of converting a detector ring including moving at least one of a plurality of independently movable detector modules when said program is run on a computer. Another embodiment of the invention is based on an apparatus, comprising a radiation shield including a plurality of individually moveable shield sections. Another embodiment of the invention is based on a method, comprising: reconfiguring a radiation shield including moving at least one of a plurality of independently movable shield sections. Another embodiment of the invention is based on a computer program comprising computer program means adapted to perform the steps of reconfiguring a radiation shield including moving at least one of a plurality of independently movable shield sections when said program is run on a computer. Another embodiment of the invention is based on a method, comprising: generating an emission image of a sample; generating a transmission image of said sample while generating said emission image of said sample; and then correcting said emission image with said transmission image.
These, and other, aspects of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the invention without departing from the spirit thereof, and the invention includes all such modifications.