Quantitative Evaluation and Comparison of In-Stent Target Lumen Reduction by Ultrasound Modalities and Angiography

Background: Detection of restenosis by morphologic differentiation of perfused lumen from plaque is an unresolved issue for ultrasonography (US). Therefore in large trials for evaluation of target lumen reduction (TLR) mostly indirect US-parameters like peak velocity ratios are used in addition to angiographic lumen measurement.

Aim: To quantitatively assess TLR as a marker of sonographic morphometry by bidirectional power doppler (BPD) as compared to conventional Color-Doppler (CCD), hemodynamic changes in flow-velocity and angiography.

Methods: US was performed with a IU 22 (Philips Germany, Hamburg) using a linear 4–8 Mhz probe. For B-mode imaging XRES and Sono-CT was employed. For CCD and BPD dynamic range, persistence, line density and priority were adjusted to maximum sensitivity and used as a standard setting. Gain control and repetition frequency was individually optimized according to hemodynamics and tissue characteristics. Prospective evaluation was off-line by two blinded readers based on raw-dicom data using QLab software (Philips Deutschland, Hamburg). Angiography was performed by planes corresponding to longitudinal US-sections (LUSS) and evaluated off-line by standard QCA software.

Results: postinterventional LUSS, cross US-sections (CUSS) and katheter angiography were performed in 30 patients with stenting of superficial femoral artery (SFA, n=25) and popliteal artery (PA, n=5). When using BPD, LUSS and CUSS axial resolution correlated better with angiographic measurements than with CCD-US. Most adequate In-Stent measurements were achieved with BPD, whereas CCD-US mostly overestimated angiographic values. Interestingly, most stents with postdilatation and angiographically sufficient wall adaptation were found to show narrowing compared to proximal segments mostly within submillimeter range and correspondingly statistically significant flow acceleration (dVm=12cm/s, p<0,05).

Discussion: BPD showed improved delineation of perfused lumen to plaque structure pre- and in stent as compared to CCD. Reduced blooming and overpainting artifacts by BPD may be the reason for better correlation with angiographic results. CCD favourably detects turbulent flow phenomena after stenosis for exact velocity measurements in sample volumes. Therefore BPD is suggested to be suitable for analysis of in-stent stenosis and morphologic assessment after stent angioplasty at least in a combined approach with CCD.

Keywords: Bidirectional Power Doppler Ultrasonography, Color Power Angiography, Quantitative Morphometry, Angiography, Target Lumen Reduction, Stent Angioplasty, Vascular Imaging