1. A method for improving image reconstruction speed, comprising: acquiring scanning data and extracting an image-construction parameter from the scanning data; generating thread configurations, each comprising information indicating the numbers of threads used for respective steps of image reconstruction, and obtaining image reconstruction speeds corresponding to the thread configurations by performing image reconstruction on the scanning data with the thread configurations; and obtaining image reconstruction speeds meeting a preset condition, grouping the thread configurations, which correspond to the image reconstruction speeds meeting the preset condition, into a candidate set of thread configurations, and extracting a thread configuration from the candidate set as an optimal thread configuration to be used in image reconstruction of the scanning data having the image-construction parameter.