Jan Honkoop

Temporal correlation of blood scattering signals in vivo from radiofrequency intravascular ultrasound

One limitation encountered using high frequency intravascular ultrasound (IVUS) is the echogenicity of blood, which increases dramatically at frequencies of 20-40 MHz. Because of the higher velocity of moving blood particles, the echo pattern of flowing blood shows more variations in time than that of the wall. To investigate the time-varying characteristics of the blood scattering measurements were performed on the radiofrequency (RF) data collected in vivo from five pig experiments. After positioning the echo catheter inside the iliac artery, an M-mode sequence of 30 RF traces was acquired at a high pulse repetition rate (5 kHz). The RF correlation time was measured on the regions of blood and the arterial wall. Two processing techniques, temporal averaging and correlation, were tested for suppression of the blood echo intensity. The correlation time Tc measured in the blood region was approximately 1 ms, which was shorter than that measured in the wall region (Tc >> 6 ms). The correlation values calculated in a small window showed a large variation in the blood region while the wall region produced a constant high output. After processing eight consecutive RF traces (delta T = 200 microseconds), the temporal averaging method results in a 50% intensity reduction in the blood region. Using the correlation output as a weighting function, the blood echo intensity can be further reduced to only 10% of its original value. Application of the RF correlation processing to a cross-sectional image data demonstrates the feasibility of this technique to remove most of the blood echoes and enhance the image contrast of the luminal interface.

Displacement Sensing Device Enabling Accurate Documentation of Catheter Tip Position

The need for reproducible positioning of an intravascular ultrasound catheter tip before and after intervention in relation to the angiographic records, resulted in the development of a dedicated displacement sensing device that provides instantaneous information about the catheter tip position on the videoscreen. The relative distance information can be displayed together with the ultrasound image. The accuracy of this device was tested in vitro.

Reproducibility of volumetric quantification in intravascular ultrasound images

The reproducibility of volume measurements in intravascular ultrasound (IVUS) images derived from separate pull-back manoeuvres remains to be elucidated. Patients (n = 23) were imaged with IVUS prior to (first series) and following percutaneous transluminal angioplasty (PTA) (second series). In 15 patients, one matched vascular segment (3-4 cm in length), not subjected to PTA, was used for analysis of lumen, vessel and plaque volume using an automated contour analysis system. Volume measurements assessed by two independent observers and in the two separate series were compared. Interobserver differences in volume measurements were small (< or =0.4%), with low coefficients of variation (< or =1.7%) and high correlation coefficients (r = 1.00). Differences in volume measurements obtained in the two separate series were small (< or =2.6%), with low coefficients of variation (< or = 8.6%) and high correlation coefficients (r = 0.97-0.99). In conclusion, volume measurements derived from IVUS images are highly reproducible. Therefore, IVUS may be used to monitor the progression/regression of atherosclerotic plaque volume in a longitudinal study.

Plaque area increase and vascular remodeling contribute to lumen area change after percutaneous transluminal angioplasty of the femoropopliteal artery: An intravascular ultrasound study☆☆☆

OBJECTIVE The aim of the study was to assess the change in lumen area (LA), plaque area (PLA), and vessel area (VA) after percutaneous transluminal angioplasty (PTA) of the femoropopliteal artery. METHODS This was a prospective study. Twenty patients were studied with intravascular ultrasound (IVUS) immediately after PTA and at follow-up examination. Multiple corresponding IVUS cross-sections were analyzed at the segments that were dilated by PTA (ie, treated sites; n = 168), including the most stenotic site (n = 20) and the nondilated segments (ie, reference sites; n = 77). RESULTS At follow-up examination, both the PLA increase (13%) and the VA decrease (9%) resulted in a significant LA decrease (43%) at the most stenotic sites (P =.001). At the treated sites, the LA decrease (15%) was smaller and was caused by the PLA increase (15%). At the reference sites, the PLA increase (15%) and the VA increase (6%) resulted in a slight LA decrease (3%). An analysis of the IVUS cross-sections that were grouped according to LA change (difference >/=10%) revealed a similar PLA increase in all the groups: the type of vascular remodeling (VA decrease, no change, or increase) determined the LA change. At the treated sites, the LA change and the VA change correlated closely (r = 0.77, P <.001). At the treated sites, significantly more PLA increase was seen in the IVUS cross-sections that showed hard lesion or media rupture (P <.05). No relationship was found between the presence of dissection and the quantitative changes. CONCLUSION At the most stenotic sites, lumen narrowing was caused by plaque increase and vessel shrinkage. Both the treated sites and the reference sites showed a significant PLA increase: the type of vascular remodeling determined the LA change at follow-up examination. The extent of the PLA increase was significantly larger in the IVUS cross-sections that showed hard lesion or media rupture.

Three-dimensional intravascular ultrasound assessment of abdominal aortic aneurysm necks.

Purpose: To document the accuracy of an automated analysis system for measuring lumen diameter and neck lengths of abdominal aortic aneurysms (AAAs) from intravascular ultrasound (IVUS) images and to describe additional features associated with 3-dimensional (3D) IVUS imaging. Methods: Twenty-two aortic aneurysms were studied with IVUS. Lumen diameters obtained using the automated analysis system were compared with manual measurements from axial IVUS scans, as were neck lengths obtained using automated analysis versus those measured with the aid of a displacement sensing device. Automated analyses were repeated by a second observer. Agreement was expressed as the coefficient of variation (CV). Results: Twenty proximal aortic, 6 distal aortic, and 3 iliac necks were available for analysis. Comparison between automated analysis and manual measurements for lumen diameter revealed a difference of 0.45 ± 0.42 mm (mean ± SD, Pearsons r = 0.99, p < 0.001, CV = 2.1%) and a difference of 0.05 ± 0.12 cm (r = 0.99, p = 0.04, CV = 4.1%) for neck length. Interobserver difference for lumen diameter was 0.13 ± 0.66 mm (r = 0.99, p < 0.001, CV = 3.4%) and 0.05 ± 0.11 cm for length measurements (r = 0.99, p = 0.02, CV = 3.5%). The 3D IVUS imaging facilitated the identification of neck configuration. Conclusions: Automated analysis of IVUS images allows accurate measurement of the lumen diameter of proximal and distal AAA necks and gives length measurements comparable to those of manual analysis. Longitudinal display of IVUS images aids in the elucidation of neck anatomy.

Temporal correlation of blood scattering signals from intravascular ultrasound

The time-varying characteristics of blood scattering on high frequency intravascular ultrasound were investigated in vivo in 5 pig experiments. The RF correlation time T/sub c/ was measured on an M-mode sequence acquired at a high pulse repetition rate. Results showed that T/sub c/ measured in blood was approximately 1 ms which was significantly shorter than that measured in wall (T/sub c//spl Gt/6 ms). Using the correlation output as a weighting function, most of the blood scattering echoes can be removed for contrast enhancement of the lumen interface.

Femorodistal venous bypass evaluated with intravascular ultrasound

OBJECTIVE To evaluate the feasibility of intravascular ultrasound imaging during femorodistal venous bypass procedures to assess qualitative and quantitative parameters of the greater saphenous vein and to detect potential causes for (re)stenosis and/or occlusion. METHODS Intravascular ultrasound data obtained from 15 patients were reviewed and compared with angiographic data. RESULTS Intravascular ultrasound enabled differentiation between normal and thickened vein wall. Venous side-branches could be located. Intact valves could be differentiated from valves disrupted by valve cutting. Patent anastomoses could be distinguished from anastomoses with some degree of obstruction. Intravascular ultrasound imaging of the inflow and outflow tracts revealed obstructive lesions, not evidenced angiographically. Quantitative analysis revealed that the median normal vein wall thickness (tunica intima and tunica media) was 0.25 mm (range 0.17-0.40 mm). The distinct vein wall thickening encountered in three patients measured 0.82, 0.95 and 1.06 mm, respectively, and was associated with narrowing in two patients. In five of 15 patients intravascular ultrasound findings altered surgical management. CONCLUSION Intravascular ultrasound is able to assess qualitative and quantitative parameters of the venous bypass and has the potential to influence surgical management based on morphologic and quantitative data.

Early experience with intravascular ultrasound in evaluating the effect of statins on femoropopliteal arterial disease: hypothesis-generating observations in humans.

The purpose of this study was to compare the vascular response seen with intravascular ultrasound (IVUS) at 1-year follow-up between statin-treated and non–statin-treated patients. Patients (n=10) undergoing percutaneous transluminal angioplasty (PTA) of the femoropopliteal artery were studied with IVUS immediately after PTA and at 1-year follow-up. In nondilated matched vascular segments, the change in lumen, vessel, and plaque volume was assessed. In balloon-dilated matched vascular segments, the change in lumen, vessel, and plaque area was assessed. A comparison was made between statin-treated (n=5) and non–statin-treated patients (n=5) in lumen, vessel, and plaque changes. At follow-up, both statin-treated and non–statin-treated patients showed a similar increase in plaque volume at the nondilated segment (+4% and +2%, respectively). In statin-treated patients the plaque volume increase was compensated by an increase in vessel volume (+2%), resulting in an increase in lumen volume (+1%). In non–statin-treated patients, on the other hand, the increase in plaque volume was associated with a decrease in vessel volume (−2%), resulting in a decrease in lumen volume (−4%). At the balloon-dilated segment a similar trend in changes of lumen, vessel, and plaque was encountered. Differences between both groups of patients were not statistically significant. Despite the nonsignificant nature of the observation, this small retrospective IVUS study may generate the hypothesis that statin therapy may contribute to superior long-term lumen dimensions by inducing positive vascular remodeling both in nondilated and balloon-dilated vascular segments.

Intravascular ultrasound in endovascular stent-grafts for peripheral aneurysm: a clinical study.

Purpose: To evaluate the potential diagnostic information of intraprocedural intravascular ultrasound (IVUS) in patients undergoing endovascular stent-grafting for peripheral aneurysm. Methods: IVUS was used in 17 patients preprocedurally to measure the diameter of the proximal and distal neck and the length of the aneurysm. Balloon and stent-graft sizes were selected based on these measurements. Following stent-graft deployment, angiography and IVUS were used to document stent apposition and the configuration and diameter of the stent-graft. Results: Stent-graft insertion was considered successful in 8 patients based on angiography and IVUS images. In 9 others, both imaging modalities showed inadequate results, necessitating 12 additional procedures: balloon angioplasty for stent-graft stenosis (2) and inadequate stent-graft apposition (1); an additional stent-graft (4); an extra stent (1); thrombectomy (2); and conversion (2) for inadequate stent-graft position and a graft rupture. In these patients, intraprocedural IVUS was superior to angiography in contributing vital information to aid in the selection of the additional interventions. Conclusions: During management of peripheral aneurysms with endovascular stent-grafts, IVUS monitoring was a useful adjunct when the initial procedure was unsatisfactory and/or when intraprocedural angiographic studies were inconclusive.

Discrepancy between stent deployment and balloon size used assessed by intravascular ultrasound

OBJECTIVES This study was designed to assess the discrepancy in stent deployment seen on intravascular ultrasound and its relation to the balloon size selected for stent delivery. DESIGN Prospective study. MATERIALS AND METHODS The study group comprised 27 patients treated using a stent (n = 18) or stent-graft combination (n = 9). Following angiographically optimal stent deployment (< 10% residual stenosis) intravascular ultrasound was used to compare the smallest intra-stent lumen area with measurements at both stent edges and the lumen area of the proximal and distal reference sites. RESULTS In 14 of the 27 stents the intra-stent dimension was the same as the dimension of the stent edge (difference < or = +/- 10%). Of the remaining stents the intra-stent dimension was smaller (difference > 10%) than the proximal stent edge in seven stents (range 11-39%), smaller than the distal stent edge in three stents (range 11-20%) and smaller than both stent edges in three stents (range 12-37%). Both in patients treated with a stent or stent-graft combination, the resulting smallest intra-stent lumen area was smaller than the balloon size used (mean difference 32% and 42%, respectively) and smaller than the mean lumen area of the reference sites (mean difference 25% and 23%, respectively). CONCLUSION This intravascular ultrasound study shows a discrepancy between intra-stent lumen area, the area of the stent edges and the balloon size used.