Transcatheter interventions for structural heart disease demand real-time visualization of catheter devices and their relationship to cardiac anatomy. Co-registration of x-ray fluoroscopy with echocardiography has been proposed to provide the necessary device and soft tissue visualization for these procedures. Development of real-time 3D x-ray/echo registration systems with device tracking has been hampered by the lack of a suitable test model. This study presents a phantom that is compatible with x-ray, CT, transthoracic (TTE), and transesophageal echo (TEE) for testing the feasibility and accuracy of new registration solutions. The phantom consists of a 20.3-cm diameter, 15-cm tall cylindrical shell with acoustic windows for TTE and an access port for a TEE probe. The interior contains 24 dual-modality targets, 5-mm in diameter, suspended in a three-turn helix occupying a volume that is similar to an adult heart. An ultrasound-compatible, tissue-mimicking slurry medium fills the remainder of the phantom. The dual-modality targets are agar based with barium sulfate (BaSO4) powder and glass beads added to generate contrast in both x-ray and ultrasound. Appropriate concentrations of these additives were determined experimentally with contrast measurements in x-ray, CT, and ultrasound. Selected concentrations were 150 mg/mL BaSO4 and 100 mg/mL of 53-63 mu m diameter glass beads. Average target contrast (+/- SD) was 16% +/- 2% in x-ray fluoroscopy (90 kV) and 1805 +/- 99 HU in CT (100 kV). In ultrasound, target CNR was 4.30 +/- 0.62 in 2D B-mode and 4.03 +/- 1.06 in 4D-mode images acquired at a center frequency of 2.8 MHz.

Fluoroscopic imaging provides good visibility of prosthetic valve stent frames during transcatheter aortic valve replacement (TAVR) procedures. Recently, efforts have been made to perform 3D tracking of valve frames based on biplane fluoroscopic imaging; however, x-ray-based imaging lacks contrast in the soft tissue structures of the heart. The purpose of this work was to develop a system for real-time 3D visualization of transcatheter prosthetic valve frames and cardiac soft tissue anatomy using the fusion of biplane fluoroscopy and echocardiography. The system is a workstation that accepts real-time image streams from commercial biplane x-ray and echocardiography systems. The image datasets can be registered based on an x-ray visible fiducial apparatus attached to the echocardiography probe, or alternatively, manually registered. During the procedure, a real-time display shows the 3D valve representation together with adjustable cut-planes through the real time 3D ultrasound data. To validate the system, a phantom with cylindrical cavities was created using an agar-graphite mixture. Dual-modality fiducials were attached to the phantom for manual registration and evaluation of registration error. At maximum speed, the frame rate of the fusion system was 24.6 fps. The fiducial registration error between the ultrasound and x-ray imaging systems was 1.3 mm. The target registration error between the 3D prosthetic valve model reconstructed from biplane x-ray and a reference CT acquisition was 1.2 mm. The proposed system works with commercially available angiography and ultrasound systems and provides a novel 3D visualization of the prosthetic valve within the ultrasound image space in real-time.

Cyanobacteria are attractive hosts for converting carbon dioxide and sunlight into desirable chemical products. To engineer these organisms and manipulate their metabolic pathways, the biotechnology community has developed genetic tools to control gene expression. Many native cyanobacterial promoters and related sequence elements have been used to regulate genes of interest, and heterologous tools that use non-native small molecules to induce gene expression have been demonstrated. Overall, IPTG-based induction systems seem to be leaky and initially demonstrate small dynamic ranges in cyanobacteria. Consequently, a variety of other induction systems have been optimized to enable tighter control of gene expression. Tools require significant optimization because they function quite differently in cyanobacteria when compared to analogous use in model heterotrophs. We hypothesize that these differences are due to fundamental differences in physiology between organisms. This review is not intended to summarize all known products made in cyanobacteria nor the performance (titer, rate, yield) of individual strains, but instead will focus on the genetic tools and the inherent aspects of cellular physiology that influence gene expression in cyanobacteria.