**2.2. Main iterative algorithms**

There are many algorithms that have been developed that used the iterative method for tomographic reconstruction (see practical example 1). Among these algorithms, the main ones are: the Algebraic Reconstruction Technique (ART), the Simultaneous Iterative Reconstruction Technique (SIRT), and the Iterative Least Squared Technique (ILST). Currently, the most commonly used algorithms are: the Expectation Maximization algorithm (EM) and the Conjugate Gradient algorithm (CG).
