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Ultrasound settings significantly alter arterial lumen and wall thickness measurements.

Potter K, Reed CJ, Green DJ, Hankey GJ, Arnolda LF - Cardiovasc Ultrasound (2008)

Bottom Line: For a given gain level, a 5 dB increase in DR reduced the measured lumen diameter by 0.02 +/- 0.004 mm (p < 0.001).For a given DR level, a 5 dB increase in gain reduced measured lumen diameter by 0.04 +/- 0.004 mm (p < 0.001).DR, gain and probe distance significantly alter lumen diameter and CIMT measurements made using image analysis software.

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: Flow-mediated dilation (FMD) and carotid intima-medial thickness (CIMT), measured by ultrasound, are widely used to test the efficacy of cardioprotective interventions. Although assessment methods vary, automated edge-detecting image analysis software is routinely used to measure changes in FMD and CIMT. We aimed to quantify the effect that commonly adjusted ultrasound settings have on arterial lumen and wall thickness measurements made with CIMT measurement software.

Methods: We constructed phantom arteries from a tissue-mimicking agar compound and scanned them in a water bath with a 10 MHz multi-frequency linear-array probe attached to a high-resolution ultrasound machine. B-mode images of the phantoms were recorded with dynamic range (DR) and gain set at five decibel (dB) increments from 40 dB to 60 dB and -10 dB to +10 dB respectively. Lumen diameter and wall-thickness were measured off-line using CIMT measurement software.

Results: Lumen measurements: there was a strong linear relationship between DR and gain and measured lumen diameter. For a given gain level, a 5 dB increase in DR reduced the measured lumen diameter by 0.02 +/- 0.004 mm (p < 0.001). For a given DR level, a 5 dB increase in gain reduced measured lumen diameter by 0.04 +/- 0.004 mm (p < 0.001). A 5 mm increase in distance between the ultrasound probe and the artery reduced measured lumen diameter by 0.04 +/- 0.03 mm (p < 0.001)CIMT measurements: For a fixed gain level, a 5 dB increase in DR increased measured wall thickness by 0.003 +/- 0.002 mm (p < 0.001). The effects of increasing gain were not consistent and appeared to vary depending on the distance between the artery and the ultrasound probe and the thickness of the artery wall.

Conclusion: DR, gain and probe distance significantly alter lumen diameter and CIMT measurements made using image analysis software. When CIMT and FMD are used to test the efficacy of cardioprotective interventions, the DR, gain and probe position used to record baseline scans should be documented and replicated in post-treatment scans in individual trial subjects. If more than one sonographer or imaging centre is used to collect data, the study protocol should document specific DR and gain settings to be used in all subjects.

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Scanning set-up for recording phantom images. Phantom and probe held in fixed position with stereotactic clamps in a water bath at approximately 37°C.
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Figure 2: Scanning set-up for recording phantom images. Phantom and probe held in fixed position with stereotactic clamps in a water bath at approximately 37°C.

Mentions: The phantom arteries were scanned in an insulated container of water at approximately 37°C. The phantom and the ultrasound probe were held in place with stereotactic clamps (Figure 2). The exam and image presets (persistence, edge-tracking and pre- and post-processing) used for human vascular imaging were used for the phantom scans. Early results showed that the distance between the probe and the phantom influenced lumen measurements, so we recorded scans with the probe set at 10 mm, 15 mm, 20 mm and 25 mm from the phantom. At each distance setting, the transmit zone (focal zone) was set as close as possible to the far wall of the artery. Depth gain compensation (DGC, also known as time gain compensation) was adjusted with the image at DR 50 dB and gain 0 dB to ensure that the near and far walls of the artery were of similar brightness and that the lumen was dark. The DGC was not altered again during the scan. For each distance setting, we adjusted the DR in 5 dB increments from 40 to 60 dB. For each DR setting, we adjusted the overall gain in 5 dB increments from -10 to +10 dB and recorded each image for approximately 2 seconds. Early results suggested that the phantoms were not completely symmetrical, so we repeated these sets of scans four times for each phantom, rotating the phantom a quarter-turn for each set of recordings. Final values were averaged from the results from each of these four positions.


Ultrasound settings significantly alter arterial lumen and wall thickness measurements.

Potter K, Reed CJ, Green DJ, Hankey GJ, Arnolda LF - Cardiovasc Ultrasound (2008)

Scanning set-up for recording phantom images. Phantom and probe held in fixed position with stereotactic clamps in a water bath at approximately 37°C.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2254584&req=5

Figure 2: Scanning set-up for recording phantom images. Phantom and probe held in fixed position with stereotactic clamps in a water bath at approximately 37°C.
Mentions: The phantom arteries were scanned in an insulated container of water at approximately 37°C. The phantom and the ultrasound probe were held in place with stereotactic clamps (Figure 2). The exam and image presets (persistence, edge-tracking and pre- and post-processing) used for human vascular imaging were used for the phantom scans. Early results showed that the distance between the probe and the phantom influenced lumen measurements, so we recorded scans with the probe set at 10 mm, 15 mm, 20 mm and 25 mm from the phantom. At each distance setting, the transmit zone (focal zone) was set as close as possible to the far wall of the artery. Depth gain compensation (DGC, also known as time gain compensation) was adjusted with the image at DR 50 dB and gain 0 dB to ensure that the near and far walls of the artery were of similar brightness and that the lumen was dark. The DGC was not altered again during the scan. For each distance setting, we adjusted the DR in 5 dB increments from 40 to 60 dB. For each DR setting, we adjusted the overall gain in 5 dB increments from -10 to +10 dB and recorded each image for approximately 2 seconds. Early results suggested that the phantoms were not completely symmetrical, so we repeated these sets of scans four times for each phantom, rotating the phantom a quarter-turn for each set of recordings. Final values were averaged from the results from each of these four positions.

Bottom Line: For a given gain level, a 5 dB increase in DR reduced the measured lumen diameter by 0.02 +/- 0.004 mm (p < 0.001).For a given DR level, a 5 dB increase in gain reduced measured lumen diameter by 0.04 +/- 0.004 mm (p < 0.001).DR, gain and probe distance significantly alter lumen diameter and CIMT measurements made using image analysis software.

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: Flow-mediated dilation (FMD) and carotid intima-medial thickness (CIMT), measured by ultrasound, are widely used to test the efficacy of cardioprotective interventions. Although assessment methods vary, automated edge-detecting image analysis software is routinely used to measure changes in FMD and CIMT. We aimed to quantify the effect that commonly adjusted ultrasound settings have on arterial lumen and wall thickness measurements made with CIMT measurement software.

Methods: We constructed phantom arteries from a tissue-mimicking agar compound and scanned them in a water bath with a 10 MHz multi-frequency linear-array probe attached to a high-resolution ultrasound machine. B-mode images of the phantoms were recorded with dynamic range (DR) and gain set at five decibel (dB) increments from 40 dB to 60 dB and -10 dB to +10 dB respectively. Lumen diameter and wall-thickness were measured off-line using CIMT measurement software.

Results: Lumen measurements: there was a strong linear relationship between DR and gain and measured lumen diameter. For a given gain level, a 5 dB increase in DR reduced the measured lumen diameter by 0.02 +/- 0.004 mm (p < 0.001). For a given DR level, a 5 dB increase in gain reduced measured lumen diameter by 0.04 +/- 0.004 mm (p < 0.001). A 5 mm increase in distance between the ultrasound probe and the artery reduced measured lumen diameter by 0.04 +/- 0.03 mm (p < 0.001)CIMT measurements: For a fixed gain level, a 5 dB increase in DR increased measured wall thickness by 0.003 +/- 0.002 mm (p < 0.001). The effects of increasing gain were not consistent and appeared to vary depending on the distance between the artery and the ultrasound probe and the thickness of the artery wall.

Conclusion: DR, gain and probe distance significantly alter lumen diameter and CIMT measurements made using image analysis software. When CIMT and FMD are used to test the efficacy of cardioprotective interventions, the DR, gain and probe position used to record baseline scans should be documented and replicated in post-treatment scans in individual trial subjects. If more than one sonographer or imaging centre is used to collect data, the study protocol should document specific DR and gain settings to be used in all subjects.

Show MeSH
Related in: MedlinePlus