Abstract

Background. Heart disease affects millions of Americans each year. In order to improve primary prevention, early risk identification is essential. B-mode ultrasound of the common carotid artery (CCA) intima-media thickness (IMT) assesses risk of a coronary event early in the process of plaque development. Because IMT changes are so small over time, in order to determine clinically significant versus clinically insignificant changes in IMT over a 12 month time period, a protocol is needed which can detect the least significant difference (LSD) of at least 0.030 mm.

Purpose. The purpose of this study was to develop and test a well-defined protocol for CCA IMT testing, using an edge detection software program, in order to reach this LSD goal.

Methodology. Using a repeated measures study design, 26 subjects were scanned over four weeks, one session a week for a total of four separate sessions. Three operators performed scanning at the first session and two operators at the following three sessions on each subject. Operators obtained far wall measurements of a 10 mm section of IMT, centered at five mm proximal to the bulb. Images were recorded from two angles of both the right and left CCA. Six measures (three with EKG gating and three without), were recorded per angle for a total of 24 per subject or 2,400 total images.

Analysis. Analysis of data using generalizability theory was performed to determine the optimal number of sessions, measurements, operators and machines and to assess whether a LSD of at least 0.030 mm can be detected. Data were also analyzed to determine whether the max or the mean IMT has a higher repeatability estimate and whether EKG gating is a significant factor in repeatability of IMT images. Generalizability coefficients were computed using seven facets [session, replication (one measure-three were taken per angle), angle, machine (instrument), readings (measurements), operator, and reader] and interactions of each. Four more generalizability coefficients were computed based on EKG gating and whether max or mean IMT values were used.

Significance to Preventive Care. IMT scanning is useful in the identification of subclinical atherosclerotic disease risk. The ability to track and assess the efficacy of prescribed measures intended to reduce cardiovascular disease risk can also be accomplished with IMT scanning.

Results. The percentage of error variance for mean, non-gated IMT values showed results of the 16 variance components comprised of the seven facets and their interactions. The greatest contributors to measurement error were machine (16.79%), and the following interactions: subject*operator (13.29%), subject*session (11.2%), and subject*machine (6.95%). If one operator uses only one model machine to acquire three images from each of two specific angles (both left and right sides, 12 images), and the same operator scans the same subject in the same way the next time (within 4 weeks), then the same reader measures the IMT images twice, one can expect IMT results will be within 96.5% of the first IMT value, 90% of the time. At maximal standardization, non-EKG gating provides consistently superior LSD and reproducibility over EKG gating. In this study, a LSD of 0.030mm was detected. There was a significant difference when using two different model ultrasound scanners for serial tracking of individuals; one consistent model of machine is recommended.

Conclusion. Based on results of this study, when performing serial carotid ultrasounds, it is important to use a consistent model of ultrasound machine. EKG gating does not improve repeatability. Use of IMT promises to be a useful noninvasive measurement which will allow practitioners to identify subclinical atherosclerotic disease risk and to track and assess the efficacy of prescribed measures aimed at reducing the amount of cardiovascular disease risk in those who are at high risk.

School

School of Public Health

First Advisor

Helen Hopp Marshak

Second Advisor

Helmuth Fritz

Third Advisor

Brenda Rea

Degree Name

Doctor of Public Health (DrPH)

Degree Level

Ph.D.

Year Degree Awarded

2007

Date (Title Page)

4-2007

Language

English

Library of Congress/MESH Subject Headings

Carotid Artery, Common -- ultrasonography. Carotid Artery, Internal -- ultrasonography: Predictive Value of Tests: Reproducibility of Results; Image Processing, Computer, Assisted; Atherosclerosis -- diagnosis; Risk Assessment -- methods.

Type

Dissertation

Page Count

viii; 114

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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