BACKGROUND

In molecular medical imaging, sometimes known as nuclear medicine, images representing radiopharmaceutical distributions may be generated for medical diagnosis. Prior to imaging, radiopharmaceuticals are injected into an imaging subject such as a patient. The radiopharmaceuticals emit radioactive photons, which can penetrate through the body to be detected by a photon detector. Based on information from the received photons, the photon detector may then determine the distribution of the radiopharmaceuticals inside the patient. Their distribution represents the physiological function of the patient, and therefore images of their distribution provide valuable clinical information for diagnosis of a variety of diseases and conditions such as those in cardiology, oncology, neurology, etc.

A collimator is a device that guides photon path. In molecular imaging, photons may originate from unknown locations inside a subject, unlike in X-ray or CT where photons are emitted from a known source (or sources) position. Without collimators, photons from all directions may be recorded by gamma detectors, and image reconstruction may become difficult. Therefore, collimators are employed to guide possible photon paths so that images can be reconstructed, similar to the role of lens in a photography camera. Although existing collimator and detector imaging systems have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects. For example, existing imaging systems are often limited by background noise and nonuniformity artifacts. Therefore, improvement on image reconstruction methods is desired to increase imaging sensitivity or resolution for collimator and detector based medical imaging systems.

SUMMARY

According to various embodiments, the present disclosure provide a method of imaging reconstruction, including providing a target object, a detector, and a mask disposed between the target object and the detector; acquiring a measured image of the target object by the detector; providing an estimated image of the target object; partitioning the mask into multiple regions; for each of the regions, deriving a forward projection from the estimated image of the target object and the respective region, thereby acquiring multiple forward projections; comparing the measured image of the target object with the forward projections; and updating the estimated image of the target object based on a result of the comparing. In some embodiments, the method further includes repeating the steps of deriving, comparing, and updating. In some embodiments, the method further includes on condition that a difference of the estimated images of the target object in consecutive two steps is less than a predetermined threshold, storing one of the estimated images of the target object as a reconstructed image of the target object. In some embodiments, the method further includes on condition that the step of updating the estimated image of the target object is repeated for a predetermined number of times, storing the estimated image of the target object as a reconstructed image of the target object. In some embodiments, the method further includes repeating the steps of partitioning, deriving, comparing, and updating, wherein a number of the regions increases during the repeating of the steps. In some embodiments, the deriving of the forward projection includes a convolution operation. In some embodiments, the deriving of the forward projection includes for each of the regions calculating a respective angular effect correction factor. In some embodiments, the angular effect correction factor includes a cos3(θ) term, θ being an incident angle. In some embodiments, the mask has multiple through holes, and wherein each of the regions has at least one through hole. In some embodiments, the mask has at least two regions having different numbers of through holes. In some embodiments, each of the regions has a convex shape. In some embodiments, updating the estimated image includes for each of the regions calculating a backward projection based on applying a respective forward projection to a correlation operation.

According to various embodiments, the present disclosure also provides a method of imaging processing, including providing a target object and a mask partially blocking a radiation from the target object; providing an estimated image of the target object; partitioning the mask into multiple regions; for each of the regions, deriving a forward projection from the estimated image of the target object and the respective region, thereby acquiring multiple forward projections, wherein the deriving of the forward projection includes for each of the regions calculating a respective angular effect correction factor. In some embodiments, the angular effect correction factor includes a cos3(θ) term, θ being an incident angle. In some embodiments, the method further includes acquiring a measured image of the target object by a detector; comparing the measured image of the target object with the forward projections; and updating the estimated image of the target object based on a result of the comparing.

According to various embodiments, the present disclosure also provides a medical imaging system, including a collimator configured to filter radiation emitted from a target object; a detector configured to acquire a measured image of the target object by detecting the radiation that has passed through the collimator; and a controller operable to execute computer-readable codes to perform following operations: receiving the measured image from the detector; providing an estimated image of the target object; partitioning the collimator into multiple regions; for each of the regions, deriving a forward projection, thereby acquiring multiple forward projections; and updating the estimated image based on a result of comparing the measured image and the forward projections. In some embodiments, the initial estimated image is acquired from a CT scan. In some embodiments, steps of deriving the forward projection and updating the estimated image are part of an iteration operation. In some embodiments, the step of partitioning the collimator is also part of the iteration operation, and wherein a number of the regions increases during the iteration operation. In some embodiments, for each of the regions, there is one or more through holes forming a coded aperture pattern.

According to various embodiments, the present disclosure also provides a collimating apparatus for medical imaging, including a perforated plate with a top surface and a bottom surface; and a plurality of holes, wherein each of the plurality of holes extends from the top surface to the bottom surface, wherein: the plurality of holes is grouped into two or more regions of the perforated plate; and each of the two or more regions includes a coded aperture pattern formed by a portion of the plurality of holes. In some embodiments, the coded aperture pattern is one of a URA array, a MURA array, a random array, and a pseudo random array. In some embodiments, the coded aperture pattern in each of the two or more regions is different from each other.

