1. Nichols. S1, Milner. M1, Meijer. R2, Carroll. S1, Ingle. L1
Variability of carotid intima-media thickness measurements by novice operators
Nichols. S1, Milner. M1, Meijer. R2, Carroll. S1, Ingle. L1
1Department of Sport, Health & Exercise Science, University of Hull
2Julius Centre for Health Sciences and Primary Care, University Medical Centre, Utrecht
Introduction
The distance between two echogenic lines observed upon insonation of the common carotid artery (CAA) with B-mode ultrasound represent an accurate measure of the carotid intima—media thickness (c-IMT) [5]. Increased c-IMT is one of the earliest observable phenotypes of atherosclerosis, indicative of long term exposure to cardiovascular risk factors and highly predictive of cardiovascular events [3].
Carotid intima-media thickness measurements are affected by choice of protocol, inter- and intra- operator variability and operator experience. Manufacturers have developed ultrasound machines to minimise measurement variability by using boundary detection software that automatically calculates c-IMT at specified insonation angles and artery segments (Figure 1). These devices are advocated as a way in which less experienced operators can accurately measure c-IMT [6]. The variability of such devices should be assessed before they are widely used. Using novice operators, the aim of this study was to quantify the variability of c-IMT measurements taken using the fully automated Panasonic CardioHealth Station, (Panasonic Biomedical Sales, Europe BV, Leicestershire, UK).
Figure 2 – A participant positioned supine undergoing C-IMT examination with a foam gauge standardising head rotation angle to 45°.
Results
Participant characteristics are presented in Table 1. Fifty participants (60% male) aged 26.2 ± 5.0 years. Immediate inter-operator variability (Figure 3) was low across all time points (Initial scan LoA : to mm; immediate repeat scan LoA: to mm; 1-week follow-up scan LoA to mm). Longer term variability was also low; O1’s initial measurement had good agreement with O2’s 7-day measurement (LoA to mm), and O2’s initial measurement had good agreement with O1’s 7-day measurement (LoA to mm) whilst ICCs were (95% CI: to 0.857) and (95% CI to 0.856), respectively. Intra-operator ICC’s also remained good (Table 2).
Table 1 - Participant characteristics (mean ± SD and median with interquartile range
BMI = Body Mass Index; W/H = Waist to Hip Circumference Ratio; SBP = Systolic Blood Pressure; DBP = Diastolic Blood Pressure;
RHR = Resting Heart Rate; 1= paired sample t-test; 2 = Wilcoxon test;
* = Significant Difference
Table 2 – Short- (10 minute) and longer- term (one week) intra-operator variability
Figure 1 - A c-IMT investigation with angle of examination (bottom right) , region of interest (ROI) marker and vertical dotted line (centre -left). The distance between these two features measures the distance between the flow divider of the bifurcation and ROI.
Methods
Visit 1
Visit 2
Operator 1 and 2 (O1 and O2) perform initial and 10-minute repeat scan
O 1 and O2 perform one-week follow up scan
Ultrasound CCA examination order - right lateral, right anterior, left lateral and left anterior. Head rotation angle was standardised to 45° (figure 2).
Figure 3 - Bland-Altman plots showing O1 and O2’s inter-operator LoA and mean bias for initial (left), 10 minute repeat (middle) and 7 day scan (right).
Agreement calculated using Bland-Altman analysis with limits of agreement (LoA) [2] and intra-class correlations (ICC) [1]
Conclusion
Novice operators produce acceptable short-term and 1-week inter- and intra-operator C-IMT measurement variability in healthy, young to middle-aged adults using the Panasonic CardioHealth Station[4].
Immediate inter-operator variability calculated by comparing time-matched measurements; short-term by initial Vs 10 minute repeat scan and longer-term by initial Vs one week follow up
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Short -and longer-term intra-operator variability was calculated by comparing operator’s initial scan to 10-minute repeat scan and initial scan to one week follow-up scan respectively.
With thanks to Panasonic for funding this poster presentation at BASES 2014