PneumaOCT: Pneumatic optical coherence tomography endoscopy for targeted distortion-free imaging in tortuous and narrow internal lumens

Abstract

The complex anatomy of internal luminal organs, like bronchioles, poses challenges for endoscopic optical coherence tomography (OCT). These challenges include limited steerability for targeted imaging and nonuniform rotation distortion (NURD) with proximal scanning. Using rotary micromotors for distal scanning could address NURD but raises concerns about electrical safety and costs. We present pneumaOCT, the first pneumatic OCT endoscope, comprising a steerable catheter with a soft pneumatic actuator and an imaging probe with a miniature pneumatic turbine. With a diameter of 2.8 mm, pneumaOCT allows for a bending angle of up to 237°, facilitating navigation through narrow turns. The pneumatic turbine enables adjustable imaging speeds from 51 to 446 revolutions per second. We demonstrate the pneumaOCT in vivo imaging of mouse esophagus and colon, as well as targeted and distortion-free imaging of peripheral bronchioles in a bronchial phantom and a porcine lung. This advancement substantially improves endoscopic OCT for navigational imaging in curved and narrow lumens.

Fig. 1.. An example application of pneumaOCT for targeted distortion-free imaging in the peripheral lung.

(A) PneumaOCT passes through tortuous tracts. (B) The distal end allows for large deflections for sharp turns. (C) Electricity-free pneumatic distal scanning mechanism for distortion-free imaging.

Fig. 2.. PneumaOCT design.

(A) Schematic of pneumaOCT consisting of a steerable catheter accommodating an OCT imaging probe inside. (B) Schematic of the steerable catheter. (C) Schematic of the OCT imaging probe. The zoom-in view shows the distal design. (D) Schematic illustrating the bending of the pneumatic actuator. (E) PneumaOCT system overview. The pressure regulator controls the distal bending of the steerable catheter. The circumferential scanning speed of the imaging probe is adjusted by using the throttle valve to regulate the airflow rate. (F) Proximal and distal airflow paths of pneumaOCT illustrate exhaust air during OCT imaging.

Fig. 3.. PneumaOCT characterization.

(A) displays the bending modes of (i) 10- and (ii) 20-mm actuators at 0.20-MPa air pressure, respectively, along with (iii) 30-mm actuator at 0.16-MPa. (B) displays the force measurement of three catheters at 0.16-MPa air pressure, respectively. (C) shows unbending and tortuous modes of pneumaOCT, and the laser detector–based measurement of scanning speed. In the tortuous mode, the pneumaOCT is bent three times continuously, with each bend at an angle of approximately 70° and radius of curvature of about 40 mm (see fig. S2). (D to F) Air pressure versus the normalized radius of curvature, bending angle, and distal force of the steerable catheter in different actuator lengths. The insets display the measurement schematic. Lines and shaded ribbons represent means and 5× SDs of five trials, respectively. (G and H) Airflow rate versus mean circumferential scanning speed of the pneumaOCT and relative SD of the speed, respectively, measured in 1 min at 0.20-MPa air pressure. (I) Airflow rate versus relative speed variation between unbending and tortuous modes. The relative speed variation is calculated using ∣v₁ − v₂ ∣ × 100 % /v₁, where v₁ and v₂ are the mean scanning speeds of unbending and tortuous modes, respectively.

Fig. 4.. In vivo pneumaOCT imaging in narrow lumens.

(A) Schematic of experimental setting to perform pneumaOCT imaging in mouse esophagus and colon. (B) PneumaOCT images of the mouse esophagus and colon at a scanning speed of 51 RPS using the airflow rate of 0.4 liter/min, respectively. (C and D) 3× enlarged views of boxed areas in (B) esophagus and colon, respectively. (E and F) Hematoxylin and eosin (H&E) histology correlated to images in (C) and (D), respectively. EP, stratified squamous epithelium; LP, lamina propria; MM, muscularis mucosae; SM, submucosa; CM1, circular muscle; LM, longitudinal muscle; CM2, colonic mucosa; MI, muscularis interna. (G) PneumaOCT images of mouse esophagus and colon at scanning speeds of 106, 175, and 248 RPS using airflow rates of 0.6, 0.8, and 1.0 liter/min, respectively. All scale bars are 500 μm. (H) Comparison of structural similarity index between OCT images acquired at scanning speeds of 74 to 248 RPS and those acquired at 51 RPS.

Fig. 5.. The pneumaOCT deployment and imaging in human bronchial phantom.

(A) Schematic of experimental operation. (B) Deployment trajectories, i.e., paths 1 to 6. The distal diameters of the bronchioles in paths 1 to 6 are 3.3, 3.8, 2.9, 3.9, 3.7, and 3.5 mm, respectively. (C) Snapshots illustrating the key operations taken to deploy pneumaOCT through path 1. The scale bar is 10 mm.

Fig. 6.. Side-by-side comparison of pneumaOCT and conventional proximal-scanning OCT imaging.

Representative pneumaOCT image (A) and proximal-scanning OCT image (B) after path 1 in human bronchial phantom. Representative OCT images after other paths are shown in figs. S8 and S9. The scale bars are 500 μm. (C) 2× enlarged views of boxed areas in (B). The distortions are indicated by the orange boxes. (D) Illustration of wrapped versus unwrapped OCT image. (E) Representative correlation factor curves calculated using the unwrapped pneumaOCT and proximal-scanning OCT images (A and B) to identify the distortion regions. The pair of dotted lines represents the threshold of ±0.1 in the correlation factor relative to the mean value. Other representative correlation factor curves calculated using OCT images acquired through paths 2 to 6 are shown in fig. S10. (F) The mean distortion ratios and relative SDs of OCT images are calculated for each dataset consisting of 50 randomly selected images acquired through paths 1 to 6 in human bronchial phantom at the scanning speed of 51 RPS.

Fig. 7.. PneumaOCT imaging of ex vivo porcine lung.

(A) Porcine lung with four imaged peripheral lung lobes: LS (left superior), LI (left inferior), RS (right superior), and RI (right inferior). (B) PneumaOCT equipped with a miniature camera. (C) Representative photo captured by the miniature camera in a bronchus. (D) Representative pneumaOCT images obtained in various peripheral lung lobes. The scale bars are 500 μm. (E) Representative correlation factor curves calculated using the unwrapped pneumaOCT images of LS and RI lobes in (D) to identify the distortion regions. The pair of dotted lines represents the threshold of ±0.1 in the correlation factor relative to the mean value. Other representative correlation factor curves calculated using pneumaOCT images acquired through LI and RS lobes are shown in fig. S11. (F) The mean distortion ratios and relative SDs of pneumaOCT images are calculated for each dataset consisting of 50 randomly selected images acquired through four different lobes at a scanning speed of 51 RPS.