## 2 Methods  
In this retrospective cross-sectional study, data from 62 patients who had undergone percutaneous transluminal angioplasty (PTA) of long femoro-popliteal arteries lesions and intraoperative Doppler ultrasound (DUS) were retrieved. The procedures were performed by highly skilled operators, at two referral hospitals for peripheral interventions, in 2018 and 2019. All patients signed an informed consent form for the procedure. The study diagram and patients' eligibility criteria are described in Figure 1.  
The aim of this study was to evaluate whether an intraoperative DUS assessment allows for a more accurate definition of technical success compared to angiography. This was assessed through the identification of intermediate residual stenosis or grade C dissections that, despite fulfilling the angiographic criteria for technical success, have a functional relevance at DUS assessment and therefore might benefit from further treatment, such as balloon post-dilatation or stenting. The decision to optimize the PTA result by single or multiple post-dilatations or stenting, and also the balloon size and inflation pressure, were entirely left to the operator's discretion. In all cases, a DUS was also performed at the end of the procedure to assess any changes in PSNR or any spectral Doppler abnormality within or distally to the treated segment, respectively. Out of the 62 patients enrolled, 51 (82%) completed a 1-year clinical follow-up, which also included a DUS evaluation to assess any target lesion restenosis. Figure 1: A study flow diagram illustrating patients’ eligibility criteria and how the study population was selected. DUS = Doppler ultrasound. PTA = percutaneous transluminal angioplasty. (*) residual stenosis of the treated lesion by visual estimate >50% and/or presence of flow-limiting dissection. The patients' data were anonymized and managed according to the data safety protocols of the two centers. This study was approved by the institutional review board of each center and performed in accordance with the Declaration of Helsinki. Intraoperative Doppler ultrasound procedure. DUS examination was performed using a 7.5 MHz linear transducer. The treated segment was visualized using B-mode and color-Doppler ultrasound images. The Doppler signal was acquired at an angle of \(\leq\)60 degrees. Peak systolic velocity (PSV) proximal within and distal to the residual stenosis were evaluated, respectively. PSVR was calculated using the ratio between the highest PSV within TL and PSV at the level of a normal proximal segment. Consistent with previous studies, residual stenosis was judged as significant in case of PSVR > 2.4 m/s (Figure 2). Similarly, any lumen reduction within the dissection responsible for a PSV > 2.4 m/s or any abnormal spectral flow distally to the dissection were judged as a sub-optimal result [5,13] (Figure 3). Furthermore, a DUS assessment of residual dissections also included a bi-dimensional color-coded evaluation in both the long- and short-axis views, respectively. **Definitions**. Technical success was defined as the completion of the endovascular procedure with \(<\)50% residual stenosis of the treated lesion by visual estimate and the absence of flow-limiting dissection. DUS-integrated technical success was defined as the completion of endovascular procedure with angiographic technical success plus a PSVR < 2.4 within the treated segment. Primary patency was defined as freedom from the  
Figure 2: Example of intraoperative DUS assessment of residual stenosis that occurred after PTA of calcified stenosis. (**A**). Digital subtraction angiography showed intermediate residual stenosis < 50% (white arrow). (**B**) Intraoperative DUS showed abnormal PSVR within treated segment. (**C**) Result after bailout stenting that was necessary to fix persistent lesion recoil despite multiple post-dilatation (white asterisk). DUS = Doppler ultrasound. PSV = peak systolic velocity. PTA = percutaneous transluminal angioplasty.