Iterative Reconstruction in Computed Tomography Equipments

Iterative Reconstruction in CT

• Iterative reconstruction is a technique used in CT scans to estimate the x-ray photon counts in each projection.
• The process involves repeated calculations of the estimated x-ray photon counts and comparisons with the actual measured counts.
• The ratio of estimated to actual x-ray counts is used to formulate a correction factor to create the next estimate.

How Iterative Reconstruction Works

• The process starts with an initial assumption (e.g., all points in the matrix have the same value).
• The assumed values are compared with the measured values, and corrections are made to bring the two into agreement.
• The process is repeated over and over until the assumed and measured values are the same or within acceptable limits.

Numeric Illustration

• Initial estimate: Calculate the average of four elements and assign it to each pixel (e.g., 1 + 2 + 3 + 4 = 10; 10/4 = 2.5).
• First correction for error: Calculate the difference between original and new horizontal ray sums divided by 2 (e.g., (3 5)/2 and (7 5)/2 = 2/2 and 2/2 = 1.0).
• Second correction for error: Calculate the difference between original and new vertical ray sums divided by 2 (e.g., (4 5)/2 and (6 5)/2 = 1.0/2 and +1.0/2 = 0.5 and +0.5 = 0.5).

Advantages of Iterative Reconstruction

• Reduces image noise
• Minimizes the higher radiation dose inherent in the filtered back-projection algorithm

Resurgence of Iterative Reconstruction

• Iterative reconstruction algorithms have resurfaced due to the availability of high-speed computing.

This quiz covers the topic of iterative reconstruction in computed tomography equipments, specifically in the Radiological Techniques Department at Middle Technical University College of Health and Medical Techniques in Baghdad. Learn about the iterative techniques used for image reconstruction in CT equipments.