Intravascular Ultrasonic Research Articles

Catheter-Mounted CMOS Front-Ends for Broadband Intravascular Ultrasonic Imaging.

Intravascular ultrasonic (IVUS) imaging catheters currently use ceramic piezoelectric transducers to form radial images of blood vessel walls. Further improvements in image quality may be enabled through Capacitive and Piezoelectric Micromachined Ultrasonic Transducers (CMUTs and PMUTs). Polymer PMUTs offer many benefits in imaging quality, however, the low acoustic sensitivity and high electrical impedance of polymer PMUTs prevents unbuffered use with 50-Ω IVUS cables. Here, we present the design and optimization of an integrated CMOS front-end specifically designed to be integrated on a 0.8-mm imaging catheter. A series-duplexer topology with active limiter was selected for simplicity of integration, and compatibility with conventional high-voltage IVUS pulser-receiver systems. Noise optimization of the front-end revealed that an impedance-matching optimum exists, which balances the system parasitic capacitances relative to the transducer complex impedance. Optimized design equations compared favorably to simulation results in predicting front-end bandwidth and transducer-referred SNR. Large-signal transient simulation showed that the front-end can withstand 100-V pulses while recovering in 240 ns for echo reception. The integrated front-end occupied 0.74 × 1.8 mm die area (including large solder-bump bond pads), with an estimated transducer-referred noise floor of 6.5 over a 100-MHz imaging bandwidth.

Renal Sympathetic Denervation System via Intraluminal Ultrasonic Ablation: Therapeutic Intravascular Ultrasound Design and Preclinical Evaluation

PurposeTo assess the safety and performance of a nonfocused and nonballooned ultrasonic (US) catheter–based renal sympathetic denervation (RDN) system in normotensive swine. Materials and MethodsRDN with the therapeutic intravascular US catheter was evaluated in 3 experiments: (i) therapeutic intravascular US RDN vs a control group of untreated animals with follow-up of 30, 45, and 90 days (n = 6; n = 12 renal arteries for each group); (ii) therapeutic intravascular US RDN vs radiofrequency (RF) RDN in the contralateral artery in the same animal (n = 2; n = 4 renal arteries); and (iii) therapeutic intravascular US RDN in a recently stent-implanted renal artery (n = 2; n = 4 renal arteries). ResultsIn the first experiment, therapeutic intravascular US RDN was safe, without angiographic evidence of dissection or renal artery stenosis. Neuronal tissue vacuolization, nuclei pyknosis, and perineuronal inflammation were evident after RDN, without renal artery wall damage. Norepinephrine levels were significantly lower after therapeutic intravascular US RDN after 30, 45, and 90 days compared with the control group (200.17 pg/mg ± 63.35, 184.75 pg/mg ± 44.51, and 203.43 pg/mg ± 58.54, respectively, vs 342.42 pg/mg ± 79.97). In the second experiment, deeper neuronal ablation penetrance was found with therapeutic intravascular US RDN vs RF RDN (maximal penetrance from endothelium of 7.0 mm vs 3.5 mm, respectively). There was less damage to the artery wall after therapeutic intravascular US RDN than with RF RDN, after which edema and injured endothelium were seen. In the third experiment, denervation inside the stent-implanted segments was feasible without damage to the renal artery wall or stent. ConclusionsThe therapeutic intravascular US system performed safely and reduced norepinephrine levels. Deeper penetrance and better preservation of vessel wall were observed with therapeutic intravascular US RDN vs RF RDN. Neuronal ablations were observed in stent-implanted renal arteries.

Intravascular Ultrasonic Imaging of Coronary Arterial Remodeling in Heart Transplant Recipients

The purpose of this study was to evaluate long-term changes of transplant coronary arteries, including vessel, plaque, and lumen areas. There are limited long-term data on vessel remodeling after heart transplantation. We analyzed serial intravascular ultrasound images of the left anterior descending coronary artery (LAD) in 54 heart transplantation recipients. Nine patients (16.7%) had a history of rejection. Proximal left anterior descending artery segments were matched among time points, a ≥20-mm long segment was analyzed every 1mm, and results were normalized for analysis length and reported asmm(3)/mm. During follow-up, vessel area decreased (-0.48 ± 1.3mm(3)/mm/year), and plaque area did not change (-0.01 ± 0.47mm(3)/mm/year). As a result, lumen area decreased (-0.52 ± 1.34mm(3)/mm/year). The change in mean lumen area was well correlated to the change in mean vessel area (r= 0.94, p <0.01) but not to the change in mean plaque area (r=-0.27, p= 0.05). In conclusion, lumen loss occurred during long-term follow-up of patients who underwent heart transplantation, primarily secondary to negative remodeling (decrease in vessel dimensions).

SYSTEM AND METHOD FOR REDUCING ANGULAR GEOMETRIC DISTORTION IN AN IMAGING DEVICE

A system and method are provided for significantly reducing or substantially eliminating angular geometric distortions in devices designed for imaging and/or inspection of an interior portion or surface of a cavity. A series of processing steps or methods may be employed to eliminate Non-Uniform Rotational Distortion (NURD) in such devices, for example, unidirectional and bi-directional intravascular ultrasonic (IVUS) imaging systems. The system may include a processor and an electronic module which control operation of a transducer assembly provided at a distal end of a catheter assembly. The system invokes a first processing step or method to collect and store raw angle and line data, as well as one or more of second and third processing steps or methods which adjust for NURD experienced during backlash of a bi-directional imaging system and a fourth processing step or method which performs a line-to-line correlation function.

Comparison of Clinical Characteristics and Arterial Remodeling by Intravascular Ultrasonic Imaging in Three Age Groups (≤55, 56 to 69 and ≥70 Years) of Japanese Patients With Acute Myocardial Infarction

Recent epidemiologic, pathologic, and intravascular ultrasound (IVUS) studies have shown that there are differences in coronary risk factors or plaque morphology between younger and older patients with acute myocardial infarctions (AMIs). This study examined clinical background and plaque morphology using IVUS in younger and older adults with AMIs in Japan. The study population consisted of 96 patients with AMIs, for whom preinterventional IVUS images were obtained. Patients were classified into 3 groups: a young group (aged < or =55 years), a middle-aged group (aged 56 to 69 years), and an old group (aged > or =70 years). The remodeling index was defined as the ratio of the external elastic membrane area at the culprit lesion to the external elastic membrane area at the proximal reference site. Expansive remodeling was defined as a remodeling index >1.05 and constrictive remodeling as a remodeling index <0.95. The frequency of hypercholesterolemia was significantly different among the 3 age groups. Total cholesterol (p <0.001), low-density lipoprotein cholesterol (p <0.005), and triglyceride (p <0.05) levels and body mass index (p <0.001) in the young group were significantly higher than in the old group. On IVUS images, constrictive remodeling was most common in the young group, whereas expansive remodeling occurred most commonly in the middle-aged and old groups. In conclusion, this study demonstrated that patients with AMIs in the young group had higher levels of hypercholesterolemia, obesity, and constrictive remodeling compared with those in the old group. The differences in arterial remodeling of the culprit lesions between younger and older patients with AMIs may reflect different biologic mechanisms of plaque activation and destabilization.

The Editor’s Roundtable: Intravascular Ultrasonic Imaging of the Coronary Arteries

r. Friedewald has no relevant financial relationships to dislose. Dr. Marso has received honoraria for consulting and rants for research from Volcano Therapeutics, Rancho Corova, California. Dr. Roberts has received honoraria for speakng from Merck, Fort Washington, Pennsylvania; Scheringlough, North Wales, New Jersey; Pfizer, Inc., New York, ew York; AstraZeneca Pharmaceuticals, Wilmington, elaware; and Novartis, East Hanover, New Jersey. Dr. Tuzcu has received honoraria for speaking from erck, Fort Washington, Pennsylvania; and Pfizer, Inc., ew York, New York. Dr. Weissman has received honoaria for consulting from Boston Scientific, Natick, Massahusetts; Merck, Fort Washington, Pennsylvania; Takeda, eerfield, Illinois; and grant support from Boston Scientific, atick, Massachusetts; and Lipid Sciences, Inc, Pleasanton, alifornia.

Relation of Plaque Size to Necrotic Core in the Three Major Coronary Arteries in Patients With Acute Coronary Syndrome as Determined by Intravascular Ultrasonic Imaging Radiofrequency

According to pathologic studies, the content of a necrotic core increases in a "linear fashion" as plaque enlarges. In addition, these 2 plaque characteristics have been associated with plaque vulnerability. This study assessed the relation between plaque cross-sectional area (CSA) and content of necrotic core (NC). Twenty-five patients (75 arteries) with acute coronary syndrome were studied. In total, 7,834 CSAs were analyzed. An analysis of plaque CSA in percentiles was performed (median 5.5 mm(2), interquartile range 3.7 to 7.8); subsequently, plaque CSA values were categorized as small (< or = 3.7 mm(2)), medium (>3.7 to < or = 7.8 mm(2)), and large (>7.8 mm(2)). There was a difference in content of the NC between arteries within each plaque CSA category. This observation was confirmed in a multivariate analysis in which only 2 variables remained statistically significant, plaque CSA (estimate 1.34, SE 0.05, p <0.0001) and studied artery (left anterior descending coronary artery, estimate 0.29, SE 0.08, p = 0.0003; left circumflex coronary artery, estimate 0.23, SE 0.07, p = 0.0014; and these vs the right coronary artery). In conclusion, the NC and plaque increase in patients with acute coronary syndromes.

Comparison of Diagnostic and Therapeutic Value of Transesophageal Echocardiography, Intravascular Ultrasonic Imaging, and Intraluminal Phased-Array Imaging in Aortic Dissection With Tear in the Descending Thoracic Aorta (Type B)

Transesophageal echocardiography (TEE) and conventional intravascular ultrasound (IVUS) have limited capabilities in type B aortic dissection. To evaluate its diagnostic value, intraluminal phased-array imaging (IPAI) was compared with IVUS and TEE. In 23 patients with type B aortic dissection, IPAI was tested with respect to its ability to depict true lumen (TL) and false lumen (FL), to localize which abdominal arteries originate from the TL and FL, and to identify all entries and reentries. After the completion of TEE, 2 additional examiners performed angiography and positioned an AcuNav catheter inside the TL. An IVUS catheter was then introduced into the TL by a fourth examiner. All examiners were blinded to one another. Four additional patients with type B aortic dissection developed peripheral malperfusion due to TL collapse. Transvenous IPAI was used to guide emergency fenestration of the intimal flap. TL and FL could be equally well identified by all diagnostic methods. IPAI detected more entries than IVUS (3.0 +/- 1.2 vs 0.8 +/- 0.5, p <0.001), and thoracic IPAI depicted more entries than TEE (1.8 +/- 1.0 vs 1.2 +/- 0.5, p <0.001). IPAI and IVUS showed >90% of the abdominal side branches. In all patients with peripheral malperfusion, successful emergency intimal flap fenestration was safely guided by IPAI. In conclusion, in the detailed diagnostic evaluation of type B aortic dissection, IPAI is superior to IVUS and TEE in detecting communications between the TL and FL. IPAI is also highly useful as a guiding tool for emergency intimal flap fenestration.

Alteplase Stability and Bioactivity after Low-Power Ultrasonic Energy Delivery with the OmniSonics Resolution System

Low-power ultrasonic (US) energy is capable of clot dissolution in vivo. The combination of US energy plus alteplase may further accelerate clot lysis; however, the effects of cavitation could potentially denature and inactivate the lytic protein. The purpose of this study was to determine the bioactivity and stability of alteplase when exposed to US energy with use of a novel intravascular US wire in an in vitro model. The model consisted of a 6.4-mm-diameter silicone tube closed at one end and filled with alteplase (1 mg/mL) in a water bath (37 degrees C). A 95-cm US wire (0.025-inch diameter, 20 kHz) was inserted into the tube and connected to a variable power generator. The wire delivers low-power acoustic energy 360 degrees around its 20-cm active length and was irrigated by a continuous infusion of purified water. Fresh 6-mL alteplase aliquots were exposed to US energy and tested in duplicates. Zero (control), 1 W, or 2 W of energy was delivered to individual test samples for zero (control), 0.5, 3, or 6 minutes. Alteplase samples were assayed for optical clarity and protein concentration with use of UV spectrophotometry, for percent protein monomer with use of high-performance size-exclusion chromatography, and for in vitro clot lysis activity. In the control samples, optical clarity was clear or colorless in all samples; protein concentration was 1.02 mg/mL +/- 0; protein monomer was 98%; and clot lysis activity was 108% per mg +/- 1. In the test samples, optical clarity was clear or colorless in all samples; protein concentrations at 0.5, 3, and 6 minutes were 0.98 mg/mL +/- 0.02, 0.93 mg/mL +/- 0.01, and 0.86 mg/mL +/- 0.02, respectively, at 1 W, and 1.00 mg/mL +/- 0.03, 0.94 mg/mL +/- 0.10, and 0.84 mg/mL +/- 0.17, respectively, at 2 W. Protein monomer was 98% for all samples. Clot lysis activity levels at 0.5, 3, and 6 minutes were 111% per mg +/- 1, 110% per mg +/- 1, and 115% per mg +/- 1, respectively, at 1 W, and 110% per mg +/- 0, 111% per mg +/- 1, and 116% per mg +/- 2, respectively, at 2 W. Alteplase solutions exposed to low-power US energy for as long as 6 minutes remained fully active and stable as determined by protein assays. Further investigation is warranted with use of combinations of US energy and alteplase.

Stent-graft entry closure and balloon fenestration for a case of aortic dissection accompanied by organ malperfusion

J Thorac Cardiovasc Surg 2001;121:1216-8

Intravascular Ultrasonic Imaging with a Micromotor

This paper reports a new intravascular imaging system with a micromotor, revolution characteristics of the micromotor and experimental results using a plastic tube. In this system, an ultrasonic beam is scanned radially by the micromotor instead of a scanning wire. The experimental results show that a cross-sectional image of the tube is reconstructed and that this system has a possibility of application to the observation of the inside of a blood vessel.