# Characterization of the previous normal-dose CT scan induced nonlocal means regularization method for low-dose CT image reconstruction

## TL;DR

This paper investigates the effectiveness and limitations of the ndiNLM regularization method for low-dose CT image reconstruction, especially when previous normal-dose images differ in structure from current low-dose images, using clinical lung nodule data.

## Contribution

The study provides a detailed characterization of the ndiNLM regularization method's performance in scenarios with structural differences between prior and current CT images.

## Key findings

- ndiNLM can improve low-dose CT reconstruction but may introduce false structures.
- Performance varies depending on structural differences between previous and current images.
- The method's limitations are characterized through clinical case simulations.

## Abstract

Repeated computed tomography (CT) scans are required in some clinical applications such as image-guided radiotherapy and follow-up observations over a time period. To optimize the radiation dose utility, a normal-dose (or full-dose) CT scan is often first performed to set up reference, followed by a series of low-dose scans. Using the previous normal-dose scan to improve follow-up low-dose scans reconstruction has drawn great interests recently, such as the previous normal-dose induced nonlocal means (ndiNLM) regularization method. However, one major concern with this method is that whether it would introduce false structures or miss true structures when the previous normal-dose image and current low-dose image have different structures (e.g., a tumor could be present, grow, shrink or absent in either image). This study aims to investigate the performance of the ndiNLM regularization method in the above mentioned situations. A patient with lung nodule for biopsy was recruited to this study. A normal-dose scan was acquired to set up biopsy operation, followed by a few low-dose scans during needle intervention toward the nodule. We used different slices to mimic different possible cases wherein the previous normal-dose image and current low-dose image have different structures. The experimental results characterize performance of our ndiNLM regularization method.

---
Source: https://tomesphere.com/paper/1702.06668