Research progress on super-resolution X-ray single pixel imaging

[ Instrument R & D of Instrument Network ] X-ray transmission imaging / CT, as a non-invasive diagnostic method, is currently the most important clinical detection method in the medical field. However, due to ionizing effect X-rays will cause a considerable degree of radiation damage to proteins, cells, etc. According to the International Radiological Society research report, the annual medical diagnosis of X-rays will cause a considerable number of cancer and leukemia patients, so how to reduce the diagnosis The dosage is critical. Since the discovery of X-rays by Roentgen in 1895, the imaging method has not changed fundamentally. They all use a technique of directly projecting onto a surface detector and displaying a certain gray distribution by accumulating photons with object information, so this The imaging efficiency of this method is very low. Not only is it difficult to significantly reduce the dose required for imaging, but the resolution is limited by the size of the light source and the resolution of the detection device, which becomes the two major bottleneck problems that restrict the traditional imaging method.

The concept of dose is related to the dose of medicine and refers to the amount of medicine taken by the patient at one time. Later, it also generally refers to the amount of medicine given to patients or given in other ways. But radiation is not a "medicine" in the general sense, and it is difficult to use the word "give", but depends on the "received" or "absorbed" radiation energy. Therefore, the so-called "dose" just borrowed the word, which is very different from the original meaning. Even in the field of ionizing radiation the interpretation of the term dose has many divergences. On the one hand, many scientists think that this term cannot be counted as a scientific term because he does not have a precise definition; on the other hand, he has to use this term, which is not a term, because it is difficult to describe what we are facing without him. Subject. In view of this, one or more definitions of the word dose have to be defined below.

In response to the bottleneck problem of radiation dose, Wu Lingan and Chen Liming, researchers from the Key Laboratory of Photophysics of the Institute of Physics of the Chinese Academy of Sciences / Beijing National Research Center for Condensed Matter Physics in 2018, for the first time realized a tabletop X-ray "ghost" "Imaging, this indirect imaging method is based on the second-order correlation of the light field, and the imaging quality depends on the fluctuation of the detection signal rather than the absolute value of the intensity. Based on this, the team completed single-photon-level ultra-low-dose imaging, and the results received widespread attention after being published in Optica and reported by Science in the depth column. In the Science report, experts in the same field gave a high evaluation: "If it is applied in the field of medical imaging, this will be a revolutionary progress", and at the same time, it also hopes for the work: "Improve the resolution of imaging With quality to suit the requirements of medical imaging. " Based on the above actual needs, Wu Lingan, a researcher at the Institute of Physics, and Chen Liming, a professor at Shanghai Jiaotong University, once again cooperated to start the exploration of solving the bottleneck of imaging resolution.

The pixel detector is a particle track detector using silicon as a detection material, and is a kind of semiconductor detector. The characteristic of the pixel detector is its excellent spatial resolution and rapid time response capability. Among the ATLAS detectors in LHC in European Nuclear, the sub-detector closest to the beam is the pixel detector. In a 2cm × 6cm area module, there are 47,268 pixel units, and particles passing through any pixel will be recorded.

The recent Ph.D. students He Yuhang and Zhang Aixin (a co-author) used the independently developed Hadamard gold mask amplitude modulation plate to realize the incoherent X-ray ghost imaging based on a true single pixel detector for the first time. Compared with the random modulation scheme, this method utilizes the orthogonal completeness of Hadamard matrix, so it can reconstruct a better image even under sparse sampling. On this basis, the original algorithm was upgraded by introducing compressed sensing and convolutional neural networks, and finally using a 37 μm source-sized X-ray source, an imaging result with a resolution of 10 μm was obtained at a sampling rate of only 18.75%. , Super resolution imaging that breaks through the source size limitation is realized, which is enough to directly judge the cancerous tissue, and meet the resolution requirements of clinical medical fine imaging. Under the framework of computing ghost imaging, high-performance algorithms and the fine structure of the modulation board ensure better image quality in super-resolution, and a lower sampling rate means shorter exposure time and lower dose, so it is expected Use this technique to further reduce the dose. The whole experiment layout is simple and easy to use. The application of single pixel detector can also greatly reduce the cost. On the other hand, the application of this method greatly reduces the spatial coherence and intensity requirements of the radioactive source, which can greatly advance the practical process of X-ray ghost imaging.

Source: Encyclopedia, Institute of Physics