ALGORITMA INTERPOLASI PADA DATA SINOGRAM UNTUK REKONSTRUKSI TOMOGRAFI DARI PROYEKSI CACAH TERBATAS; INTERPOLATION ALGORITHM OF THE SINOGRAM DATA FOR TOMOGRAPHIC RECONSTRUCTION OF A LIMITED NUMBER OF PROJECTION

Widodo, Catur Edi, Kusminarto

2015 | Tesis | FMIPA

In tomography, the number of projections determines the quality of the reconstructed image. The more the number of projections, which is closer to the sampling criteria, the higher the quality of the image produced. But in the medical field, for tomographic system that uses X-rays, it is important to consider the radiation dose received by the patient. The more the number of projections, the greater the radiation dose received by the patient, so that the greater the risk of tissue damage and cancer risk. Therefore, to decrease the radiation dose received by the patient, the number of projection has to be reduced. This will decline the image quality produced. In the industrial field, to reconstruct moving objects, it is required rows of source - detector active simultaneously, which can only be done if the rows of source - detector are few. If the rows source – detector is few, then the number of projections obtained few too. On the other case, the few number of projections can also occur when around the object to be reconstructed is obstructed, so that at this range of angle the row of source – detector can not be placed. This situation will cause the image produced deteriorated. To overcome this problem, in this research an algorithm for interpolating the projection data has been developed to get projections with enough number to fulfill the minimum requirement. Sinogram interpolation is performed by estimating new raysums between two projections. Estimation has been done by defining the position and gray level based on selected raysums of three projections in series. Selected raysums are raysums which have minimum gray level variance. By doing interpolation process on the whole raysums at each projection, new projection could be obtained as much as required. If the new projections are arranged, we get the complete sinogram which fulfill the sampling criteria. Sinogram interpolation algorithm that was developed is then applied to the sinogram data with a limited number of projections of the artificial Shepp-Logan object, concrete object, and glass-bit object. The sinogram data with a limited number of projections are the sinogram with a fixed wide angle of projection (sparse projection), the sinogram with varied wide angle of projections, and the sinogram with an obstructed field of view. Visually, the results of tomographic image reconstructed from interpolated sinogram could eliminate the streak artifact and quantitatively decreased errors (rmsd) from 18.94 % to 6.41 % at artificial Shepp-Logan object, from 15.98 % to 2.73 % concrete object, and from 21.06 % to 5.47 % at glassbit object.

Kata Kunci : tomography; sinogram; projection; interpolation; reconstruction