astra重建时利用循环语句对多张图片进行投影，并对投影后的数据进行三维重建

Astra是一款用于CT重建的开源软件，可以利用循环语句对多张图片进行投影，并对投影后的数据进行三维重建。下面是一些基本的代码示例：

1. 循环读取多张图片并投影

import astra
import numpy as np

# 创建一个2D扫描几何体
vol_geom = astra.create_vol_geom(512, 512)
proj_geom = astra.create_proj_geom('parallel', 1.0, 512, np.linspace(0, np.pi, 180, False))

# 创建一个投影矩阵
proj_id = astra.create_projector('linear', proj_geom, vol_geom)

# 循环读取图片并投影
for i in range(100):
    img = np.loadtxt(f"image_{i}.txt")
    sinogram_id, sinogram = astra.create_sino(img, proj_id)
    astra.data2d.delete(sinogram_id)

2. 循环读取多张投影并重建

import astra
import numpy as np

# 创建一个2D扫描几何体
vol_geom = astra.create_vol_geom(512, 512)
proj_geom = astra.create_proj_geom('parallel', 1.0, 512, np.linspace(0, np.pi, 180, False))

# 创建一个投影矩阵
proj_id = astra.create_projector('linear', proj_geom, vol_geom)

# 创建一个重建矩阵
recon_id = astra.create_reconstruction(vol_geom)

# 循环读取投影并重建
for i in range(100):
    sinogram = np.loadtxt(f"sinogram_{i}.txt")
    sinogram_id = astra.data2d.create('-sino', proj_geom, data=sinogram)
    astra.reconstruct(sinogram_id, recon_id)
    recon = astra.data2d.get(recon_id)
    np.savetxt(f"recon_{i}.txt", recon)
    astra.data2d.delete(sinogram_id)