Manual B-mode versus automated radio-frequency carotid intima-media thickness measurements.
BACKGROUND
Carotid intima-media thickness (CIMT) serves as an indicator of atherosclerosis and cardiovascular risk. Manual measurements of B-mode ultrasound images are the most applied method. Automated measurements with radiofrequency (RF) ultrasound have been suggested as an alternative. The aim of this study was to compare these methods in terms of risk-factor relations and associations with future events.


METHODS
Data from participants of the Second Manifestations of Arterial Disease (SMART) study were used. Far wall common CIMT was measured online with manual B-mode and automated RF ultrasound. Measurements were performed by a group of 6 sonographers. Risk-factor information was obtained. All participants were followed for the occurrence of vascular events (mean follow-up, 2.1 years). CIMT was related to risk factors with linear regression models and to future events with Cox proportional-hazards models.


RESULTS
Data were available for 2,146 participants. Agreement between the methods was modest (intraclass correlation coefficient = 0.34). Risk-factor relations with age and systolic blood pressure were stronger for B-mode than for RF ultrasound. Association with future events was better for B-mode than for RF ultrasound (vascular death, 1.27 vs 1.00; ischemic stroke, 1.45 vs 1.03). In participants with CIMT < 0.9 mm (without plaque), the intraclass correlation between the measures was 0.50. In addition, in that subgroup, RF ultrasound showed a stronger association with future events than B-mode ultrasound (all events, 1.59 vs 1.09; vascular death, 1.72 vs 0.93; coronary ischemic events, 1.65 vs 1.05).


CONCLUSIONS
The preference for either B-mode or RF measurements may be driven by the type of study population, the expected presence of local atherosclerotic abnormalities, and the main aim of the study (assessing risk factors or events). However, in this study, as in many others, the B-mode approach was shown to be robust in risk-factor relations and the prediction of events.
Dogan
Soner
S
Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, The Netherlands.
Plantinga
Yvonne
Y
Dijk
Joke M
JM
van der Graaf
Yolanda
Y
Grobbee
Diederick E
DE
Bots
Michiel L
ML
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002339:Carotid Arteries / Q000000981:diagnostic imaging*; D002340:Carotid Artery Diseases / Q000000981:diagnostic imaging*; D004452:Echocardiography / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011846:Radio Waves; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D017539:Tunica Intima / Q000000981:diagnostic imaging*; D055815:Young Adult