C.T. Lancee

Intravascular optical coherence tomography imaging at 3200 frames per second

We demonstrate intravascular optical coherence tomography (OCT) imaging with frame rate up to 3.2 kHz (192,000 rpm scanning). This was achieved by using a custom-built catheter in which the circumferential scanning was actuated by a 1.0 mm diameter synchronous motor. The OCT system, with an imaging depth of 3.7 mm (in air), is based on a Fourier domain mode locked laser operating at an A-line rate of 1.6 MHz. The diameter of the catheter is 1.1 mm at the tip. Ex vivo images of human coronary artery (78.4 mm length) were acquired at a pullback speed of 100 mm/s. True 3D volumetric imaging of the entire artery, with dense and isotropic sampling in all dimensions, was performed in <1 second acquisition time.

Heartbeat OCT: In vivo intravascular megahertz-optical coherence tomography

Cardiac motion artifacts, non-uniform rotational distortion and undersampling affect the image quality and the diagnostic impact of intravascular optical coherence tomography (IV-OCT). In this study we demonstrate how these limitations of IV-OCT can be addressed by using an imaging system that we called Heartbeat OCT, combining a fast Fourier Domain Mode Locked laser, fast pullback, and a micromotor actuated catheter, designed to examine a coronary vessel in less than one cardiac cycle. We acquired in vivo data sets of two coronary arteries in a porcine heart with both Heartbeat OCT, working at 2.88 MHz A-line rate, 4000 frames/s and 100 mm/s pullback speed, and with a commercial system. The in vivo results show that Heartbeat OCT provides faithfully rendered, motion-artifact free, fully sampled vessel wall architecture, unlike the conventional IV-OCT data. We present the Heartbeat OCT system in full technical detail and discuss the steps needed for clinical translation of the technology.

Design of a Multilayer Transducer for Acoustic Bladder Volume Assessment

Catheterization remains the gold standard for bladder volume assessment, but it is invasive and introduces the risk of infections and traumas. Therefore, noninvasive bladder volume measurement methods have gained interest. In a preceding study a new technique to measure the bladder volume on the basis of nonlinear ultrasound wave propagation was validated. This paper describes a first prototype of a dedicated multilayer transducer to implement this approach. It is composed of a PZT transducer for transmission and a PVDF layer for reception. Acoustical measurements in a water tank and phantom measurements showed that there is a relation between bladder volume and the harmonic contents of the echo obtained from a region of interest behind the bladder. Simulations with an equivalent transducer model on the basis of KLM-circuit modeling closely matched with the results from the acoustical measurements. The results demonstrated the feasibility of the multilayer transducer design for bladder volume assessment on the basis of nonlinear wave propagation

Novel developments in intravascular imaging

In the development of intravascular ultrasound (IVUS), a serious emphasis has been given to the improvement of the image quality in terms of resolution. The image quality is indeed a very important issue, but there is lot more information hidden in the ultrasound signals than is currently exploited by commercially available IVUS equipment. Over the past few years, at the Thorax centre we have been exploring the possibilities of analysing sequences of radiofrequency (RF) traces. This could provide a significant extension of the functionality of the IVUS machines. It gives possibilities for local elasticity assessment, flow estimation and enhanced lumen detection. This paper is an up to date impression of where RF-data analysis has taken us.

Harmonic 3-d echocardiography with a fast-rotating ultrasound transducer

Although the advantages of three-dimensional (3-D) echocardiography have been acknowledged, its application for routine diagnosis is still very limited. This is mainly due to the relatively long acquisition time. Only recently has this problem been addressed with the introduction of new real-time 3-D echo systems. This paper describes the design, characteristics, and capabilities of an alternative concept for rapid 3-D echocardiographic recordings. The presented fast-rotating ultrasound (FRU) transducer is based on a 64-element phased array that rotates with a maximum speed of 8 Hz (480 rpm). The large bandwidth of the FRU-transducer makes it highly suitable for tissue and contrast harmonic imaging. The transducer presents itself as a conventional phased-array transducer; therefore, it is easily implemented on existing 2-D echo systems, without additional interfacing. The capabilities of the FRU-transducer are illustrated with in-vitro volume measurements, harmonic imaging in combination with a contrast agent, and a preliminary clinical study

A new transducer for 3D harmonic imaging

We developed a fast rotating ultrasound transducer for 3D-echocardiography containing a broadband linear array. In the harmonic mode the tissue to clutter ratio was measured as function of frequency. This resulted in an optimal harmonic transmit frequency of 2.0 MHz. In-vitro evaluation, using the optimal frequency, showed an average volume error, for 5 reconstructed agar phantoms, of approximately 1%. Further, a clinical case study proved the feasibility of dynamic left ventricular volume measurements for the transducer.

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.

Improved spatiotemporal voxel space interpolation for 3D echocardiography with irregular sampling and multibeat fusion

We developed a novel multi-beat image fusion technique using a special spatiotemporal interpolation for sparse, irregularly sampled data (ISI). It is applied to irregularly distributed 3D cardiac ultrasound data acquired with the fast rotating ultrasound (FRU) transducer developed in our laboratory, a phased array rotating mechanically at very high speed (240-480rpm). High-quality 2D images are acquired at ~100 frames/s over 5-10 seconds. ISI was compared quantitatively to spatiotemporal nearest neighbor interpolation (STNI) on synthetic data and compared qualitatively to classical trilinear voxel interpolation on 10 in-vivo cardiac image sets. ISI showed considerably lower absolute distance errors than STNI. For in-vivo images, ISI voxel sets showed reduced motion artifacts, suppression of noise and interpolation artifacts and better delineation of endocardium. In conclusion, ISI improves the quality of 3D+T images acquired with a fast rotating transducer in simulated and in-vivo data.

Image artifacts in intravascular elastography

Intravascular ultrasound is being investigated as a tool for imaging the local elasticity of atherosclerotic vessels: the ultimate goal is to obtain images of the (compression or shear) modulus of elasticity. In practice, radial strain images are used to depict local hardness. The approximate nature of this technique can result in image artifacts that must be understood and corrected for. Several artifacts are described and characterized using phantom studies and finite element modelling. In simple morphologies compensation for the artifacts may be possible, but complex morphologies require complex compensations. In these cases, the finite element method can assist in a correct interpretation of local tissue hardness from strain images.

Quantitative harmonic 3D echocardiography with a fast rotating ultrasound transducer

Left ventricular (LV) volume and function measurement is the most common clinical referral question in the echocardiography laboratory. A fast, practical and accurate method would facilitate access to this important diagnostic information. We developed a fast rotating phased array transducer for 3D harmonic imaging of the heart, which makes fast and accurate LV volume and function measurement feasible. In this manuscript the implementation and validation of the data processing is described.