Carotid intima-medial thickness measured on multiple ultrasound frames: evaluation of a DICOM-based software system

doi:10.1186/1476-7120-5-29

Cardiovascular Ultrasound
Volume 5

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Potter K
Green DJ
Reed CJ
Woodman RJ
Watts GF
McQuillan BM
Burke V
Hankey GJ
Arnolda LF

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Green DJ
Reed CJ
Woodman RJ
Watts GF
McQuillan BM
Burke V
Hankey GJ
Arnolda LF
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Research

Carotid intima-medial thickness measured on multiple ultrasound frames: evaluation of a DICOM-based software system

Kathleen Potter¹ , Daniel J Green²^,3 , Christopher J Reed⁴ , Richard J Woodman¹ , Gerald F Watts¹ , Brendan M McQuillan¹^,5 , Valerie Burke¹ , Graeme J Hankey¹^,6 and Leonard F Arnolda¹^,7

¹School of Medicine and Pharmacology, University of Western Australia, Perth, Australia

²School of Human Movement and Exercise Science, University of Western Australia, Perth, Australia

³Cardiac Transplant Unit, Royal Perth Hospital, Perth, Australia

⁴Department of Medical Engineering and Physics, Royal Perth Hospital, Perth, Australia

⁵Department of Medicine, Sir Charles Gairdner Hospital, Perth, Australia

⁶Department of Neurology, Royal Perth Hospital, Perth, Australia

⁷Department of Cardiology, Royal Perth Hospital, Perth, Australia

author email corresponding author email

Cardiovascular Ultrasound 2007, 5:29doi:10.1186/1476-7120-5-29


Published:	24 September 2007

Abstract

Background

Carotid intima-media thickness (CIMT) measured by B-mode ultrasonography is a marker of atherosclerosis and is commonly used as an outcome in intervention trials. We have developed DICOM-based software that measures CIMT rapidly on multiple end-diastolic image frames. The aims of this study were to compare the performance of our new software with older bitmap-based CIMT measurement software and to determine whether a ten-fold increase in the number of measurements used to calculate mean CIMT would improve reproducibility.

Methods

Two independent sonographers recorded replicate carotid scans in thirty volunteers and two blinded observers measured CIMT off-line using the new DICOM-based software and older bitmap-based software. A Bland-Altman plot was used to compare CIMT results from the two software programs and t-tests were used to compare analysis times. F-tests were used to compare the co-efficients of variation (CVs) from a standard six-frame measurement protocol with CVs from a sixty-frame measurement protocol. Ordinary least products (OLP) regression was used to test for sonographer and observer biases.

Results

The new DICOM-based software was much faster than older bitmap-based software (average measurement time for one scan 3.4 ± 0.6 minutes versus 8.4 ± 1.8 minutes, p < 0.0001) but CIMT measurements were larger than those made using the alternative software (+0.02 mm, 95%CI 0.01–0.03 mm). The sixty-frame measurement protocol had worse reproducibility than the six-frame protocol (inter-observer CV 5.1% vs 3.5%, p = 0.004) and inter and intra-observer biases were more pronounced in the sixty-frame than the six-frame results.

Conclusion

While the use of DICOM-based software significantly reduced analysis time, a ten-fold increase in the number of measurements used to calculate CIMT did not improve reproducibility. In addition, we found that observer biases caused differences in mean CIMT of a magnitude commonly reported as significant in intervention trials. Our results highlight the importance of good study design with concurrent controls and the need to ensure that no observer drift occurs between baseline and follow-up measurements when CIMT is used to monitor the effect of an intervention.