Semi-Automatic Graphical Tool for Measuring Coronary Artery Spatially Weighted Calcium Score from Gated Cardiac Computed Tomography Images

Summary

This video demonstrates the use of a novel graphical tool for measuring the spatially weighted calcium score (SWCS), an alternative to the Agatston score, for quantifying coronary artery calcification. The graphical tool computes SWCS based on image data from gated cardiac computed tomography and user-defined paths of the coronary arteries.

Abstract

The current standard for measuring coronary artery calcification to determine the extent of atherosclerosis is by calculating the Agatston score from computed tomography (CT). However, the Agatston score disregards pixel values less than 130 Hounsfield Units (HU) and calcium regions less than 1 mm². Due to this thresholding, the score is not sensitive to small, weakly attenuating regions of calcium deposition and may not detect nascent micro-calcification. A recently proposed metric called the spatially weighted calcium score (SWCS) also utilizes CT but does not include a threshold for HU and does not require elevated signals in contiguous pixels. Thus, the SWCS is sensitive to weakly attenuating, smaller calcium deposits and may improve the measurement of coronary heart disease risk. Currently, the SWCS is underutilized owing to the added computational complexity. To promote translation of the SWCS into clinical research and reliable, repeatable computation of the score, the aim of this study was to develop a semi-automatic graphical tool that calculates both the SWCS and the Agatston score. The program requires gated cardiac CT scans with a calcium hydroxyapatite phantom in the field of view. The phantom allows for deriving a weighting function, from which each pixel's weight is adjusted, allowing for the mitigation of signal variations and variability between scans. With all three anatomical views visible simultaneously, the user traces the course of the four main coronary arteries by placing points or regions of interest. Features such as scroll-to-zoom, double-click to delete, and brightness/contrast adjustment, along with written guidance at every step, make the program user-friendly and easy to use. Once tracing the arteries is complete, the program generates reports, which include the scores and snapshots of any visible calcium. The SWCS may reveal the presence of subclinical disease, which may be used for early intervention and lifestyle changes.

Introduction

Measuring the amount of calcium within arteries using computed tomography (CT) is an established way to assess the severity of coronary atherosclerosis. Knowing and quantifying the extent of atherosclerosis is key to determining the risk of future coronary heart disease^1,2,3,4. The most common way of measuring calcium in the coronary arteries is using the Agatston score⁵. However, part of the Agatston score calculation relies on the intensity of the chosen pixels, measured in Hounsfield Units (HU). Any pixels less tha....

Protocol

This study was conducted with approval of the Mount Sinai Institutional Review Board (HS-20-01011), and all subjects gave written informed consent.

1. Preparation before starting the protocol

1. Appropriate folder structure is necessary for this program. Start by creating a main folder for the project anywhere on the computer by right-clicking and selecting the New Folder option in the files directory. All input DICOM files and results will be stored .......

Discussion

While the protocol for this program is relatively easy to follow, there are a few critical steps that are necessary for successful use and reliable results. Before starting, it is important to make sure the patient data that will be used in this program is anonymized to ensure patient confidentiality. The initial formatting and naming of the project's main folder must be correct for the program to recognize where to pull and place data. Incorrect naming and/or placement of folders, especially the Meta_Data folder, leads .......

Materials

Name	Company	Catalog Number	Comments
Calcium Hydroxyapatite	Sigma-Aldrich	289396-100G	Suspended in EpoxAcast 690 resin for phantom creation
Clinical Cardiac CT Scanner	Siemens	SOMATOM Force Dual Source CT	Used for the source images; Any cardiac CT will be sufficient
EpoxAcast 690	Smooth-On	03641	Used for phantom creation
MATLAB	Mathworks	R2019a	Requires Image Processing Toolbox and Statistics and Machine Learning Toolbox; Any version compatible with and able to run version R2019a scripts is sufficient
Standard Computer	N/A	N/A	macOS or Windows operating system
syngo.via	Siemens	VB60A_HF04	Commercial software used for computing Agatston score for validation study