Ultrasound clutter and noise improvements applied to echocardiographic left atrial appendage visualization

Summary
Ultrasonic imaging is the most widely used advanced imaging modality in the United States, and excluding
planar radiography, it represents 44% of all imaging studies. Unfortunately, ultrasound images are often subopti-
mal, and some echocardiography studies show degradation in up to 98% of patients. This rate of degradation and
the freehand nature of clinical ultrasound means that image quality is more dependent on operator skill than other
advanced modalities, but even with the most skilled practitioners, ultrasound completely fails in 11-64% of clinical
tasks. Our overall goal for this application is to fundamentally decrease ultrasound failure rates. Low-quality
ultrasound is particularly problematic in echocardiography because of its role as a first-line tool for diagnosing
and monitoring cardiac disease. When transthoracic echo is inadequate more costly and time-consuming exams
like transesophageal echo or MRI are required. To (1) facilitate the high volumes of transthoracic echo, (2) im-
prove patient comfort and safety (i.e. reduce transesophageal echo), (3) reduce cost and procedure time, and (4)
maximize physician efficiency, it is crucial to have consistently high quality transthoracic echo. To provide this, we
introduce new acquisition and reconstruction solutions for ultrasound imaging.
Echocardiographic imaging of the left atrial appendage is growing in importance in lockstep with the rising
incidence of atrial fibrillation, which currently effects as many as 2-6 million Americans and is expected to grow
to 6-12 million by 2050. In patients with atrial fibrillation, thrombus may appear in as many as 12-26% of left
atria with most appearing in the appendage. Therefore, in patients with current atrial fibrillation the left atrial
appendage must be screened with echocardiography for thrombus before cardioversion can be performed to
return the heart to sinus rhythm. Further, patients receiving a left atrial appendage closure device due to chronic
atrial fibrillation require annual transesophageal echo follow ups to monitor the device. For both cases, the gold-
standard and standard-of-care is transesophageal echocardiography, and while the left atrial appendage can be
visualized transthoracically, is is rarely used because the image quality is considered too unreliable.
Ultrasound image quality is degraded by both clutter and thermal noise, so to make clinically transforma-
tional improvements to ultrasound–and echocardiography specifically–it is necessary to address both the clutter
problem and the noise problem. Addressing both of these issues is becoming increasingly important because
recent developments in beamforming have focused on non-linear algorithms (including deep networks), and the
performance of these methods are more strongly linked to the noise level compared to conventional beamforming
methods. To this end, we introduce both a solution enhancing signal-to-noise ratio using coded excitation and a
comprehensive solution for clutter reduction using deep network beamforming.

Grant Number: 5R01HL156034-04
NIH Institute/Center: NIH
Principal Investigator: Brett Byram