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

Potter K, Green DJ, Reed CJ, Woodman RJ, Watts GF, McQuillan BM, Burke V, Hankey GJ, Arnolda LF - Cardiovasc Ultrasound (2007)

Bottom Line: A Bland-Altman plot was used to compare CIMT results from the two software programs and t-tests were used to compare analysis times.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).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.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Medicine and Pharmacology, University of Western Australia, Perth, Australia. pottek04@cyllene.uwa.edu.au

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.

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Related in: MedlinePlus

Bland-Altman plot of the differences between the CIMT measured with our new DICOM-based software and the alternative bitmap-based software. Differences are calculated as our software minus the alternative software and are plotted against the mean CIMT (mm) from both software programs. Dashed lines show mean ± 2SD for estimated difference between software programs.
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Figure 2: Bland-Altman plot of the differences between the CIMT measured with our new DICOM-based software and the alternative bitmap-based software. Differences are calculated as our software minus the alternative software and are plotted against the mean CIMT (mm) from both software programs. Dashed lines show mean ± 2SD for estimated difference between software programs.

Mentions: Figure 2 shows the differences between the CIMT measurements made using our software and the alternative software program plotted against the mean CIMT from both programs. The mean difference was 0.019 mm (95%CI 0.012 to 0.025 mm). The upper limit of agreement was 0.060 mm (95%CI 0.049 to 0.072 mm) and the lower limit was -0.023 mm (95%CI -0.033 to -0.011 mm). On the recorded images, one pixel represents approximately 0.05 mm. It took 3 minutes and 22 seconds (SD 34 seconds) to measure CIMT on six frames using our software and 8 minutes and 24 seconds (SD 109 seconds) with the alternative software (t = -8.31, df = 80, p < 0.0001).


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

Potter K, Green DJ, Reed CJ, Woodman RJ, Watts GF, McQuillan BM, Burke V, Hankey GJ, Arnolda LF - Cardiovasc Ultrasound (2007)

Bland-Altman plot of the differences between the CIMT measured with our new DICOM-based software and the alternative bitmap-based software. Differences are calculated as our software minus the alternative software and are plotted against the mean CIMT (mm) from both software programs. Dashed lines show mean ± 2SD for estimated difference between software programs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2100042&req=5

Figure 2: Bland-Altman plot of the differences between the CIMT measured with our new DICOM-based software and the alternative bitmap-based software. Differences are calculated as our software minus the alternative software and are plotted against the mean CIMT (mm) from both software programs. Dashed lines show mean ± 2SD for estimated difference between software programs.
Mentions: Figure 2 shows the differences between the CIMT measurements made using our software and the alternative software program plotted against the mean CIMT from both programs. The mean difference was 0.019 mm (95%CI 0.012 to 0.025 mm). The upper limit of agreement was 0.060 mm (95%CI 0.049 to 0.072 mm) and the lower limit was -0.023 mm (95%CI -0.033 to -0.011 mm). On the recorded images, one pixel represents approximately 0.05 mm. It took 3 minutes and 22 seconds (SD 34 seconds) to measure CIMT on six frames using our software and 8 minutes and 24 seconds (SD 109 seconds) with the alternative software (t = -8.31, df = 80, p < 0.0001).

Bottom Line: A Bland-Altman plot was used to compare CIMT results from the two software programs and t-tests were used to compare analysis times.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).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.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Medicine and Pharmacology, University of Western Australia, Perth, Australia. pottek04@cyllene.uwa.edu.au

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.

Show MeSH
Related in: MedlinePlus