RESUMO
Coronary artery disease (CAD) is one of the leading causes of death globally. Currently, diagnosis and intervention in CAD are typically performed via minimally-invasive cardiac catheterization procedures. Using current diagnostic technology such as angiography and FFR, interventional cardiologists must decide which patients require intervention and which can be deferred. 10% of patients with stable CAD are incorrectly deferred using current diagnostic best practices. By developing a forward-viewing intravascular ultrasound (FV-IVUS) 2D array capable of simultaneously evaluating morphology, hemodynamics, and plaque composition, physicians would be better able to stratify risk of major adverse cardiac events in patients with intermediate stenosis. For this application, a forward-viewing, 16 MHz 2D array transducer was designed and fabricated. A 2 mm-diameter aperture consisting of 140 elements, with element dimensions of 98 µm × 98 µm × 70 µm (w × h × t) and a nominal inter-element spacing of 120 µm was designed for this application based on simulations. The acoustic stack for this array was developed with a designed center frequency of 16 MHz. A novel via-less interconnect was developed to enable electrical connections to fan out from a 140-element 2D array with 120 µm inter-element spacing. The fabricated array transducer had 96/140 functioning elements operating at a center frequency of 16 MHz with a -6 dB fractional bandwidth of 62 ± 7%. Single element SNR was 23 ± 3 dB, and the measured electrical crosstalk was -33 ± 3 dB. In imaging experiments, the measured lateral resolution was 0.231 mm and the measured axial resolution was 0.244 mm at a depth of 5 mm. Finally, the transducer was used to perform 3D B-mode imaging of a 3 mm-diameter spring and 3D B-mode and power Doppler imaging of a tissue-mimicking phantom.
RESUMO
Coronary artery disease (CAD) is a leading cause of death globally. Computed tomography coronary angiography (CTCA) is a noninvasive imaging procedure for diagnosis of CAD. However, CTCA requires cardiac gating to ensure that diagnostic-quality images are acquired in all patients. Gating reliability could be improved by utilizing ultrasound (US) to provide a direct measurement of cardiac motion; however, commercially available US transducers are not computed tomography (CT) compatible. To address this challenge, a CT-compatible 2.5-MHz cardiac phased array transducer is developed via modeling, and then, an initial prototype is fabricated and evaluated for acoustic and radiographic performance. This 92-element piezoelectric array transducer is designed with a thin acoustic backing (6.5 mm) to reduce the volume of the radiopaque acoustic backing that typically causes arrays to be incompatible with CT imaging. This thin acoustic backing contains two rows of air-filled, triangular prism-shaped voids that operate as an acoustic diode. The developed transducer has a bandwidth of 50% and a single-element SNR of 9.9 dB compared to 46% and 14.7 dB for a reference array without an acoustic diode. In addition, the acoustic diode reduces the time-averaged reflected acoustic intensity from the back wall of the acoustic backing by 69% compared to an acoustic backing of the same composition and thickness without the acoustic diode. The feasibility of real-time echocardiography using this array is demonstrated in vivo, including the ability to image the position of the interventricular septum, which has been demonstrated to effectively predict cardiac motion for prospective, low radiation CTCA gating.
