Definition of common carotid wall thickness affects risk classification in relation to degree of internal carotid artery stenosis: the Plaque At RISK (PARISK) study.

BACKGROUND: Mean or maximal intima-media thickness (IMT) is commonly used as surrogate endpoint in intervention studies. However, the effect of normalization by surrounding or median IMT or by diameter is unknown. In addition, it is unclear whether IMT inhomogeneity is a useful predictor beyond common wall parameters like maximal wall thickness, either absolute or normalized to IMT or lumen size. We investigated the interrelationship of common carotid artery (CCA) thickness parameters and their association with the ipsilateral internal carotid artery (ICA) stenosis degree. METHODS: CCA thickness parameters were extracted by edge detection applied to ultrasound B-mode recordings of 240 patients. Degree of ICA stenosis was determined from CT angiography. RESULTS: Normalization of maximal CCA wall thickness to median IMT leads to large variations. Higher CCA thickness parameter values are associated with a higher degree of ipsilateral ICA stenosis (p < 0.001), though IMT inhomogeneity does not provide extra information. When the ratio of wall thickness and diameter instead of absolute maximal wall thickness is used as risk marker for having moderate ipsilateral ICA stenosis (>50%), 55 arteries (15%) are reclassified to another risk category. CONCLUSIONS: It is more reasonable to normalize maximal wall thickness to end-diastolic diameter rather than to IMT, affecting risk classification and suggesting modification of the Mannheim criteria. TRIAL REGISTRATION: Clinical trials.gov NCT01208025 .

Test signal injection for Doppler systems.

Objective: To evaluate the performance of continuous and pulsed Doppler systems a test signal generator has been developed, simulating an ultrasound radio frequency signal, to be injected by induction into the front-end of an ultrasound Doppler system. Unlike for flow rigs the characteristics of the simulated signal are exactly known and under full control of the user, allowing for an objective interpretation of the test results. Methods: Under software control specific signal characteristics, e.g. ultrasound carrier frequency, clutter frequency, amplitude of clutter signal with respect to Doppler signal amplitude, Doppler signal-to-noise ratio, mean Doppler frequency, shape and width of the Doppler spectral distribution, and its time-dependent behavior can be set and varied. Results: A software package was developed to manipulate the relevant characteristics of the radio frequency signal and to drive a PC compatible plug-in card for signal generation. To illustrate the applicability of the Doppler signal generator some specific examples will be discussed. Conclusion: The proposed test signal generator allows for a variety of Doppler test procedures under controlled and realistic conditions. Copyright 1997 Elsevier Science Ireland Ltd.