Usefulness of on-line three-dimensional reconstruction of intracoronary ultrasound for guidance of stent deployment

Freehand 3-D Ultrasound Imaging: A Systematic Review

Two-dimensional ultrasound (US) imaging has been successfully used in clinical applications as a low-cost, portable and non-invasive image modality for more than three decades. Recent advances in computer science and technology illustrate the promise of the 3-D US modality as a medical imaging technique that is comparable to other prevalent modalities and that overcomes certain drawbacks of 2-D US. This systematic review covers freehand 3-D US imaging between 1970 and 2017, highlighting the current trends in research fields, the research methods, the main limitations, the leading researchers, standard assessment criteria and clinical applications. Freehand 3-D US systems are more prevalent in the academic environment, whereas in clinical applications and industrial research, most studies have focused on 3-D US transducers and improvement of hardware performance. This topic is still an interesting active area for researchers, and there remain many unsolved problems to be addressed.

Detection of cardiac cycle from intracoronary ultrasound

In this paper, we describe a method automatically to determine the phase of a cardiac cycle for each video frame of an intravascular ultrasound (IVUS) video recorded in vivo. We first review the principle of IVUS video and demonstrate the general applicability of our method. We show that the pulsating heart leads to phasic changes in image content of an IVUS video. With an image processing method, we can reverse this process and reliably extract the heart-beat phase directly from IVUS video. With the phase information, we demonstrate that we can build 3-D (3D) time-variant shapes and measure lumen volume changes within a cardiac cycle. We may also measure the changes of IVUS imaging probe off-center vector within a cardiac cycle, which serves as an indicator of vessel center-line curvature. The cardiac cycle extraction algorithm requires one scan of the IVUS video frames and takes O(n) time to complete, n being the total number of the video frames. The advantage of this method is that it requires no user interaction and no hardware set-up and can be applied to coronary scans of live beating hearts. The extracted heart-beat rate, compared with clinical recordings, has less than 1% error.

Two dimensional arrays for real time 3D intravascular ultrasound

We have previously described 2D arrays operating at up to 10.0 MHz consisting of several thousand elements for transthoracic cardiac imaging and over a hundred elements for intracardiac imaging using 7 Fr to 12 Fr catheters. We have begun to explore forward viewing real time 3D phased array intravascular ultrasound, which may require imaging depths of a few centimeters to look down the axis of a vessel to view vulnerable atherosclerotic plaque. We used a noncoaxial based cable technology that allowed 100 signal wires to be placed inside a4.8 French IVUS lumen with an inner diameter of 1.3 mm. We pursued two different fabrication technologies for the building of the transducers. Each transducer was constructed in the forward viewing configuration to allow simultaneous real time B-scans, C-scans and volumetric rendering of vessels and vascular stents distal to the catheter tip. In order to obtain the desired penetration depth, each transducer was constructed to operate at 10.0 MHz. The first method included an ordered array of 11 x 11 = 121 elements. In order to conform to the round aperture of the IVUS lumen, the comers were cut off, resulting in a total of 97 signal channels. Real time images include a 4 mm diameter vessel in a tissue mimicking phantom, an expanded stent and a stent in an excised sheep aorta. The second method is based upon a laser dicing technique that cuts the individual elements in a random pattern. This resulted in 61 signal channels. Real time 3D images of the AIUM test object were made with this transducer.

Ultrasonographic Modalities to Assess Vascular Anatomy and Disease

Medical ultrasound (US) encompasses a family of imaging techniques linked by the use of high-frequency sound waves, typically 2.5-10 million cycles per second (MHz), to interrogate tissue. Although similar, each imaging technique has relatively distinct features and may provide unique information. This review is designed to provide vascular and interventional radiologists with an in-depth understanding of each US imaging technique and relevant physics principles to assist in optimizing the US examination so that the specific vascular anatomy and disease states in question can be comprehensively understood. This review will be limited to principles of transcutaneous US and will not include specific techniques for assessment of individual vessels (except for illustrative purposes) or methods to optimize US scan parameters.

Coronary intravascular ultrasound: implications for understanding the development and potential regression of atherosclerosis

The incremental value of intravascular ultrasound (IVUS), compared with angiographic analysis of coronary atherosclerosis, originates principally from 2 key features-its tomographic perspective and the ability to image coronary atheroma directly. Whereas angiography depicts the cross-sectional coronary anatomy as a planar silhouette of the lumen, ultrasound directly images the atheroma within the vessel wall, allowing measurement of atheroma size, distribution, and to some extent, composition. Although angiography remains the principal method to assess the extent of coronary atherosclerosis and to guide percutaneous coronary interventions, IVUS is rapidly altering conventional paradigms in the diagnosis and therapy of coronary artery disease. Thus, IVUS has become a vital adjunctive imaging modality for the aggressive coronary interventional cardiologist. As such, ultrasound has earned a role as a viable complementary technique relative to angiography, rather than an alternative to conventional angiographic methods. This article reviews the rationale, technical advantages and limitations, and interpretation of intravascular ultrasonography from the perspective of the general and invasive cardiologist. We emphasize the impact that IVUS studies have had on our understanding of the atherosclerotic coronary artery disease process, because these findings have important implications for all cardiologists. We then review several trials that are currently using intravascular ultrasonography for the study of coronary artery disease regression.

The use of mechanical devices as adjuncts to intracoronary stenting

A number of mechanical adjuncts to intracoronary stenting are now available to the interventional cardiologist. These devices have assisted in the development of a safer and more effective stenting practice. Intravascular ultrasound-guided stenting has been shown to reduce the rate of subacute thrombosis and subsequent restenosis. It allows a greater appreciation of lesion structure and severity so that an appropriate intervention strategy can be devised. Debulking techniques may allow the optimal deployment of stents so that restenosis is reduced; however, the results of large randomized studies are still awaited. The use of thrombectomy and distal embolization protection devices is emerging as a safer alternate to stenting alone in difficult patient subsets, such as those with thrombus-laden lesions and degenerated vein grafts. Doppler and pressure wires may be useful in determining optimal stent deployment and predict subsequent patient outcomes. An understanding of the indications and limitations of these devices is of increasing importance to the interventional cardiologist as the coming decade threatens to yield an impressive array of high-tech innovations.

Resource utilization and clinical outcomes of coronary stenting: a comparison of intravascular ultrasound and angiographical guided stent implantation

BACKGROUND

Intravascular ultrasound (IVUS) guided stent implantation studies have demonstrated that inadequate stent implantation can occur despite achieving an optimal angiographic result. Furthermore, IVUS-guided stent implantation has been shown to improve lesional acute gain. However, it is unknown whether the use of IVUS guidance during stent implantation is associated with improved acute and long-term clinical outcomes. Moreover, the additional procedural cost and time incurred with the use of IVUS-directed stent implantation has not been evaluated. Thus the purpose of this study was to determine whether IVUS-guided stent implantation is associated with improved clinical outcomes compared with angiographically guided stent implantation and to evaluate the difference in resource utilization between these respective stent deployment strategies.

METHODS

Data were collected on 278 consecutive patients in whom 455 stents were deployed in native coronary arteries. High-pressure (> or = 12 atm) balloon inflations were performed until an optimal angiographic result was obtained. In the angiographically guided group, no IVUS imaging was performed. In the IVUS-guided group, IVUS imaging and additional interventions were performed attempting to achieve full apposition, absence of edge tear, and acute gain (lesion lumen area: distal reference lumen area) > or = 0.8 in subsequent IVUS imaging. Total procedure time, fluoroscopy time, contrast media volume, number of balloons, stents, guidewires, guide catheters, and procedural cost were calculated. In hospital abrupt closure rate and 6-month major adverse cardiovascular events (cardiac death, myocardial infarction, target vessel revascularization) rate were obtained.

RESULTS

A total of 178 patients underwent IVUS-guided stent placement and 100 patients underwent angiographically guided stent implantation. There was no significant difference in procedure time (107 +/- 49 vs 100 +/- 50 minutes, P = .22), fluoroscopy time (33 +/- 24 vs 30 +/- 18 minutes, P = .36), contrast volume (411 +/- 157 vs 386 +/- 181 mL, P = .23), guide catheters (1.3 +/- 0.8 vs 1.3 +/- 0.6, P = .69), guidewires (1.6 +/- 1.2 vs 1.6 +/- 1.0, P = .99), balloons (2.4 +/- 1.0 vs 2.3 +/- 1.3, P = .58), and stents (1.7 +/- 0.9 vs 1.6 +/- 0.9, P = .42). Intraprocedural cost was significantly higher in the IVUS-guided group, $4142 +/- 1547 verus $3635 +/- 1949 (P = .03), which was primarily related to the cost of the IVUS catheter. However, the in-hospital acute vessel closure rate was significantly lower in the IVUS-guided group, 0.6% versus 4% (P = .04). There was a trend toward lower target vessel revascularization rate in the IVUS-guided group (11% vs 19%, P = .08). By multivariate analysis IVUS use was demonstrated to be an independent negative predictor of cardiac death, myocardial infarction, repeat revascularization, and abrupt stent closure with a relative risk of 0.49 (95% confidence interval of 0.25 to 0.98), and P = .04.

CONCLUSIONS

The use of IVUS guidance during stent implantation does not significantly increase procedure time, fluoroscopy exposure, contrast volume, or device utilization. Furthermore, despite the increase in procedural cost, IVUS-guided stent implantation is associated with a significant decrease in the in-hospital abrupt closure rate and a trend toward a lower 6-month target vessel revascularization.

Evaluation of three-dimensional segmentation algorithms for the identification of luminal and medial-adventitial borders in intravascular ultrasound images

Intravascular ultrasound (IVUS) provides direct depiction of coronary artery anatomy, including plaque and vessel area, which is important in quantitative studies on the progression or regression of coronary artery disease. Traditionally, these studies have relied on manual evaluation, which is laborious, time consuming, and subject to large interobserver and intraobserver variability. A new technique, called active surface segmentation, alleviates these limitations and makes strides toward routine analyses. However, for three-dimensional (3-D) plaque assessment or 3-D reconstruction to become a clinical reality, methods must be developed which can analyze many images quickly. Presented is a comparison between two active surface techniques for three-dimensional segmentation of luminal and medial-adventitial borders. The force-acceleration technique and the neighborhood-search technique accurately detected both borders in vivo (r2 = 0.95 and 0.99, Williams' index = 0.67 and 0.65, and r2 = 0.95 and 0.99, WI = 0.67 and 0.70, respectively). However, the neighborhood-search technique was significantly faster and required less computation. Volume calculations for both techniques (r2 = 0.99 and r2 = 0.99) also agreed with a known-volume phantom. Active surface segmentation allows 3-D assessment of coronary morphology and further developments with this technology will provide clinical analysis tools.

Role of intracoronary ultrasound after high-pressure stent implantation

BACKGROUND

Poststent high-pressure balloon inflation has been shown to improve clinical outcomes. However, it is unknown whether intracoronary ultrasound (ICUS) provides additional clinical guidance after initial high-pressure balloon inflation is used during stent placement. Thus the purpose of this study was to determine if stent deployment techniques are improved with ICUS imaging despite an optimal angiographic result achieved with high-pressure balloon inflation.

METHODS AND RESULTS

Prospective data were collected on 96 consecutive patients in whom 151 stents were deployed. Stents and high-pressure balloons were angiographically sized 1:1 by visual estimation. High-pressure (> or =12 atm in all cases) balloon inflations were continued until angiographic completion (<10% residual stenosis), after which index ICUS imaging was performed. Stent apposition, symmetry, and lumen dimensions were evaluated. An optimal ICUS result was defined as full apposition of the stent, symmetry ratio > or =0.80, and acute gain > or =0.80 of the reference lumen area. If inadequate ICUS results were found, further dilations with higher pressures or larger balloons and subsequent stent reevaluation with ICUS were performed. Sixty-nine (46%) stents required additional balloon inflations. Of these stents, 35 (23%) had initial acute gains that were <80% of the reference lumen area. Forty-six (30%) stents were found to have unapposed struts and 24 (16%) had a symmetry ratio <0.80. In patients requiring additional inflations, minimum stent area increased from 7.6 +/- 2.2 mm(2) to 9.2 +/- 2.4 mm(2) (P <.0001). Similarly, complete stent apposition improved from 33% to 68% of total stents (P <.0001). After initial ICUS, higher-pressure dilations were performed in 40 patients, whereas larger balloons greater than or equal to ICUS reference vessel diameter were used in 33 patients. Follow-up was obtained in 95 (99%) patients. The overall major adverse cardiac event rate at 6 months was 9.3%, which consisted of 8 target vessel revascularizations and 1 abrupt closure requiring repeat intervention.

CONCLUSIONS

Even when poststent high-pressure balloon inflation achieves an optimal angiographic result, ICUS assists in optimizing acute gain, symmetry, and apposition of intracoronary stents in approximately 50% of patients. Moreover, ICUS guidance is associated with low rates for target vessel revascularization and major adverse cardiac events at 6-month follow-up.

Axial movement of the intravascular ultrasound probe during the cardiac cycle: implications for three-dimensional reconstruction and measurements of coronary dimensions

BACKGROUND

Motion of the intravascular ultrasound (IVUS) probe within the coronary artery from cardiac contraction may result in artifacts during 3-dimensional ultrasound image reconstruction and inaccurate measurements of coronary compliance. The purpose of this study was to establish whether longitudinal movement of the IVUS transducer in the coronary artery occurs and to quantify such motion.

METHODS

In 31 patients we positioned IVUS transducers at 59 coronary branch points: 41 in the left anterior descending coronary artery, 11 in the left circumflex coronary artery, and 7 in the right coronary artery. In each image sequence the branching vessel oscillated in and out of the imaging plane during the cardiac cycle, confirming longitudinal transducer movement. The extent of movement was estimated by IVUS from the dimension of the branch vessel traversed. In addition, angiographic visualization and measurement of IVUS probe motion was performed at 17 branch points in 12 patients.

RESULTS

Average longitudinal transducer movement as measured by IVUS was 1.50 +/- 0.80 mm (n = 46, range 0.5 to 5.5 mm). Because IVUS could not account for probe motion that exceeded the vessel branch diameter, the values obtained represent minimum movement. Average probe motion as assessed by cineangiography in a subset of 12 patients was 2.43 +/- 1.42 mm (range 0.57 to 6.56 mm).

CONCLUSIONS

This study establishes that longitudinal movement of IVUS transducers within coronary vessels occurs during the cardiac cycle. Because documented extent of motion may be sufficient to influence analysis, IVUS images are best obtained with electrocardiographic gating.

Reference chart derived from post-stent-implantation intravascular ultrasound predictors of 6-month expected restenosis on quantitative coronary angiography

BACKGROUND

Intravascular ultrasound (IVUS)-guided stent implantation and the availability of a reference chart to predict the expected in-stent restenosis rate based on operator-dependent IVUS parameters may interactively facilitate optimal stent placement. The use of IVUS guidance protects against undue risks of dissection or rupture.

METHODS AND RESULTS

IVUS-determined post-stent-implantation predictors of 6-month in-stent restenosis on quantitative coronary angiography (QCA) were identified by logistic regression analysis. These predictors were used to construct a reference chart that predicts the expected 6-month QCA restenosis rate. IVUS and QCA data were obtained from 3 registries (MUSIC [Multicenter Ultrasound Stenting in Coronaries study], WEST-II [West European Stent Trial II], and ESSEX [European Scimed Stent EXperience]) and 2 randomized in-stent restenosis trials (ERASER [Evaluation of ReoPro And Stenting to Eliminate Restenosis] and TRAPIST [TRApidil vs placebo to Prevent In-STent intimal hyperplasia]). In-stent restenosis was defined as luminal diameter stenosis >50% by QCA. IVUS predictors were minimum and mean in-stent area, stent length, and in-stent diameter. Multiple models were constructed with multivariate logistic regression analysis. The model containing minimum in-stent area and stent length best fit the Hosmer-Lemeshow goodness-of-fit test. This model was used to construct a reference chart to calculate the expected 6-month restenosis rate.

CONCLUSIONS

The expected 6-month in-stent restenosis rate after stent implantation for short lesions in relatively large vessels can be predicted by use of in-stent minimal area (which is inversely related to restenosis) and stent length (which is directly related to restenosis), both of which can be read from a simple reference chart.

Dynamic imaging of coronary stent structures: an ECG-gated three-dimensional intracoronary ultrasound study in humans

Three-dimensional (3D) intracoronary ultrasound (ICUS) systems allow dynamic 3D reconstruction of coronary segments after stent deployment, but motion artifacts are frequently present. The use of an electrocardiographic-gated ICUS image acquisition workstation and a dedicated pullback device may overcome this problem. In the present study, we evaluated the potential of dynamic 3D reconstruction of intracoronary stents in 51 patients. Two different types of stent designs were investigated: (1) the Wallstent (mesh type; n = 36) and (2) the Cordis Coronary stent (coil type; n = 15). There was a tendency for imaging of the mesh stent type to be better than imaging of coil type stents (p = 0.06). Differences in the orientation of the stent struts (mesh:longitudinal; coil:transversal) most likely explain this difference. These in vivo observations were tested and confirmed in in vitro experiments. In conclusion, dynamic 3D ICUS reconstruction of the entire stent architecture in vivo was feasible for stents of mesh type, while stents of coil type were incompletely visualized.

Ultrasound-guided stent placement

IVUS imaging has dramatically increased understanding of the process of coronary stent placement. Preintervention or diagnostic IVUS has been shown to be of value before stent placement to assess lesion severity and length as well as the degree and location of calcification. Before stent placement, ultrasound dimensions may also be used to select the appropriate type and size of device. Although studies are in progress to define the role of prestent ultrasound imaging, much interest centers around the use of IVUS to detect significant superficial coronary calcium and direct rotational atherectomy before stent placement. Clinical trials have demonstrated the feasibility and safety of IVUS-guided coronary stent placement without postprocedure warfarin anticoagulation. Although it has been established subsequently that reduced anticoagulation may be administered to low-risk patients without IVUS guidance, three important points have been established by these trials. First, IVUS is superior to angiography for assessment of adequate stent expansion and apposition. As noted in several studies, angiography frequently overestimates lumen dimensions after stent placement. Second, IVUS-guided stent implantation yields larger acute stent dimensions. Third, IVUS-guided therapy in the form of additional stent placement or use of a larger balloon does not increase stent procedure complication rates when appropriate criteria for optimal stent placement are used. A randomized clinical trial (AVID) of angiography-directed versus IVUS-directed coronary stent placement is in progress (with a second soon to begin enrollment). In this trial, ultrasound guidance has been shown to improve acute procedural results, providing larger lumen dimensions without an increase in complication rates. IVUS guidance, however does not appear to affect the incidence of stent thrombosis within 30 days in the present era of high-pressure balloon inflations and aggressive antiplatelet therapy. Results concerning the effect of ultrasound-guided therapy on long-term target lesion revascularization rates are pending. To date, IVUS imaging has greatly contributed to advancements in coronary stent placement techniques. The future of IVUS-guided coronary stent placement will, of course, depend on the results of several ongoing clinical trials.