SprayVIEW -- A High-Speed Digital Imaging and Analysis System

Author(s):
Socratis Kalogrianitis - Image Therm Engineering Inc.
Dino Farina - Image Therm Engineering Inc.

Industry:
Consumer Goods

Products:
Vision, LabVIEW

The Challenge:
Building an imaging system to capture, process, and analyze the time-evolving fluid dynamics of high-speed nasal sprays.

The Solution:
Developing the SprayVIEW Nasal Spray Characterization System using National Instruments LabVIEW with IMAQ vision software, a high-speed digital camera, and a Lasiris diode laser.

Introduction
The fluid dynamic characterization of the aerosol spray emitted by nasal inhalers is crucial in determining the overall performance of the inhaler. Thorough characterization of the spray’s plume geometry is the best indicator of the overall performance of most nasal inhalers. The most representative performance quantities in the characterization of an inhaler design include measurements of the spray’s divergence angle as it exits the inhaler, the spray’s cross-sectional ellipticity and uniformity, and the time-evolution of the developing spray.
The current nasal spray testing standard at many pharmaceutical companies involves firing the spray pump at a solid, thin-layer chromatography (TLC) plate. Users expose the particle-covered TLC plate to ultraviolet radiation, which causes the plate’s coating to fluoresce and highlight the outline of the spray pattern. Marking instruments and mechanical calipers are used to draw and measure an outline of the deposited patterns on the plate.

Experience has revealed many problems with this technique, including:

• Radical changes to the fluid dynamics of the spray caused by the presence of the TLC plate
• Flow complications induced by the large amount of spray particle bouncing off the plate
• User error causing inaccurate measurements of the spray pattern
• Lack of support for plume geometry measurements

Hardware Implementation and System Setup
We conducted a thorough search of existing technology to use or adapt to this system. We finally implemented a hybrid design consisting of off-the-shelf and custom-made components and software. The basic components of the system include:

• SprayVIEW system software built using National Instruments LabVIEW and IMAQ Vision software
• High-speed digital camera system
• Lasiris Magnum 4000, 4 W, laser diode sheet generator operating at 810 nm
• InnovaSystems pneumatically controlled mechanical actuator with digital trigger

We chose LabVIEW and IMAQ Vision to build the SprayVIEW system software because they provided the best mix of image processing functionality and user interface development tools needed to implement the f inal custom application. In addition, the SCSI Toolkit for LabVIEW from Icon Technologies provided seamless integration for downloading the digital images from the high-speed camera into the SprayVIEW system.

Plume Geometry Test Setup
The user fills the spray pump with test fluid and places it in the mouth of the actuator, which is precalibrated for compression force and duration as per company testing guidelines. The camera captures 500 fps at a resolution of 512x240 pixels. The input trigger is armed and set to wait for the actuator to f ire. The user turns the laser on and focuses its light sheet to a thickness of approximately 1 mm.

In the configuration above, the user has positioned the laser to illuminate a plane of particles parallel to the flow direction along the centerline of the spray. The camera’s position is perpendicular to the laser sheet plane. The user temporarily places the calibration target in the plane of the laser sheet and adjusts the camera lens until the target comes into focus. Because the camera views the scene normally, no perspective correction is necessary - the target image is solely for calibrating the physical coordinate system of the plume geometry images. The user then removes the target image, fires the actuator trigger, and the acquired images are downloaded from the camera into the SprayVIEW system.

Image Processing and Analysis
We specif ically designed our SprayVIEW software to combine powerful image processing and analysis functionality with an intuitive and easy-to-use interface for detailed study of spray images. With the software’s VCR-like controls and variety of color palettes, the user can visualize the details and development of the time-evolution of the spray images.

With the time-average or summation tool, it is possible to combine a user-selectable range of spray images to simulate the trajectory of the individual particles in the spray. For example, the user can represent the 200+ valid images from a typical test as one image and measure spray uniformity, ellipticity, and divergence angle. The summary image is also the closest representation of the TLC-plate technique, and this pseudo-backward compatibility forms a key requirement for FDA approval of the system.

Users analyze and process spray pattern images using the pattern tools. With these tools, the user can specify the major and minor axes of an elliptical pattern template on the summation image. The axis speci ication is accomplished using interactive cursors dynamically linked to line profiles of particle intensity along the axes in absolute and percentage units. The user can adjust the cursors until the most representative elliptical pattern is specified, based on the intensity profiles and computed measurements of the ellipticity ratio. Once the user has specified this elliptical template, he or she can use the VCR controls to play back the images in the time-evolution of the spray while simultaneously displaying an overlay of the elliptical template. With this feature, the user can visualize the time-evolution of the particle distribution and dynamically compare it to the time-averaged pattern of the particles in an intuitive manner.

Similarly, the user can analyze and process plume geometry images using the geometry tools, specifying the vertex and included angle of a set of two intersecting, orthogonal lines on the summation image. The user can accomplish the line specif ication using interactive cursors dynamically linked to line prof iles of particle intensity along the lines in absolute and percentage units. The user can adjust the cursors until the most representative line pattern template is specif ied based on the intensity profiles and computed measurements of the divergence angle. Once again, the user can simultaneously overlay this line pattern template on the time-evolving images and play it back using the VCR controls for comparison purposes.

Results and Summary
Muro Pharmaceutical and Image Therm Engineering successfully combined their joint knowledge and experience with nasal spray drug development, fluid mechanics, high-speed imaging, and image processing software to develop the novel SprayVIEW Spray Characterization System. With the SprayVIEW system, spray-based drug developers can characterize the time-evolution, cross-sectional ellipticity, and divergence angle of spray patterns quickly and effectively. The system’s non-intrusive, optical-based design provides significantly improved measurement performance over the currently accepted TLC-plate-based testing technique. With the highly modular hardware and software implementation of the system, users can easily customize their systems to meet the needs of a variety of spray-testing applications both in R&D and production environments.

For more information, contact:

Dino J. Farina

President

Image Therm Engineering, Inc.

159 Summer Street

Waltham, MA 02452

Tel: (781) 893-7793

E-mail: dfarina@imagetherm.com

Web: www.imagetherm.com

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