A transesophageal phased array transducer for ultrasonic imaging of the heart

In this thesis the development of a miniaturized phased array ultrasound transducer is described. The application of this transducer in the field of echocardiology is devoted to transesophageal cross-sectional scanning of the heart and its great vessels. The enormous increase in diagnostic applications of ultrasound over the last three decades is particularly due to the non-invasive character of this technique. Consequently the developments of transcutaneous scanning techniques have outnumbered all other possibilities, but researchers have continuously been investigating the alternatives of scanning organs from within the human body. In those patients in whom inhibiting factors preclude adequate diagnostic information to be obtained transcutaneously, alternative scanning techniques still may-provide vital information. For cardiac imaging two possibilities exist to enter the human body, invasively by means of a catheter or 'non-invasively' by means of an endoscope. In Chapter I, the introduction, our early experiences with a catheter-mounted scanning system are described. The limited possibilities of such a system combined with the inherent technological complications, as well as the invasive character of such a technique favoured the search for a different approach. The idea to advance in the catheter direction was never left but first the experience gained has been applied to transesophageal scanning with an endoscope-mounted transducer as described in this thesis

The relative contributions of myocardial wall thickness and ischemia to ultrasonic myocardial integrated backscatter during experimental ischemia

Abstract The purpose of this study was to assess the empirical relationship between myocardial integrated backscatter (IB) and myocardial wall thickness (WT) in normal myocardium. A second object was to estimate the additional contribution to acute ischemic integrated backscatter levels given this relationship. Myocardial IB measurements and simultaneous myocardial WT measurements were made in 16 open-chested pigs with intact coronary circulation (normal myocardium) and 10 min after the flow in the left anterior descending coronary artery had been reduced to 20% of its baseline value (ischemic myocardium). Measurements were made 50 times during one cardiac cycle and averaged over 10 cardiac cycles. IB and WT measurements were normalized with respect to the nonischemic end-diastolic values. The relationship between IB and WT in normal myocardium was estimated in every individual pig by simple linear regression. Estimates of IB during ischemia were calculated on the basis of this relationship and the ischemic WT measurements. Differences of the estimator and the actual measurement made during ischemia depict the actual contribution of the state of acute ischemia, without the influence of WT. The slope of the relationship between IB and WT during normal myocardial contraction ranged from −0.16 to 0.03 dB/% (mean = −0.036 dB/%, SD = 0.06 dB/%). The additional contribution of ischemia ranged from −3.84 to 5.56 dB (mean = 0.31 dB, SD = 2.72 dB). It was concluded that the average contribution of ischemia to IB measurements is insignificant if the IB dependency on WT is removed from the data and that the higher level of ischemic IB measurements can be explained by the decrease in wall thickness during ischemia and not by the ischemia itself

Development of a high-speed synchronous micro motor and its application in intravascular imaging

In this study, we demonstrate the design, fabrication and characterization of a synchronous micro motor. The micro motor consists of flex print coils and a permanent magnet rotor. The size of the motor is 2.0 mm length and 1.0 mm outer diameter. With 1.0 A effective driving current, the motor can rotate a 0.3 mm mirror at a maximum speed of 3640 revolutions per second. The uniformity and accuracy of the motor was characterized at 50 Hz, 200 Hz and 3200 Hz driving frequencies. The performance improved by increasing the driving frequency, which was represented as better speed uniformity and lower angular error. The torque of the motor was estimated to be 0.25-0.27 μN m with 1.0 A current by fitting the measured speed based on the equation of motion. We describe the application of the micro motor as a distal actuator for intravascular imaging. We constructed optical and ultrasonic imaging catheters and show the intravascular images of coronary arteries obtained with these catheters

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

Guiding and optimization of resynchronization therapy with dynamic three-dimensional echocardiography and segmental volume-time curves: A feasibility study

Objective: To assess a new approach for guiding and hemodynamic optimization of resynchronization therapy, using three-dimensional (3D) transthoracic echocardiography. Background: Resynchronization therapy for heart failure provides the greatest hemodynamic benefit when applied to the most delayed left ventricular (LV) site. Currently, the ideal LV pacing site is selected according to acute invasive hemodynamic assessment and/or tissue Doppler imaging. Methods: A total of 16 patients with advanced heart failure and an implanted biventricular pacemaker were included in this study. Transthoracic apical LV images at equidistant intervals were obtained using a prototype, fast-rotating second harmonic transducer to reconstruct 3D LV datasets during sinus rhythm (SR), right ventricular (RV) apical and biventricular pacing mode. A semi-automated contour analysis system (4D LV analysis, TomTec, Germany) was used for segmental wall motion analysis and identification of the most delayed contracting segment and calculation of global LV function. Results: Data acquisition duration was 10 s and analyzable 3D images were obtained in 12 patients. Of these patients, data during SR were available i

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 de