Principle of Operation of the DxU 850m Iris Ultrasound System
The DxU 850m Iris is a high-frequency ultrasound biomicroscopy system that operates at frequencies between 35-80 MHz, providing high-resolution cross-sectional imaging of anterior eye segment structures while overcoming visual barriers caused by corneal opacities.
Core Operating Principles
The DxU 850m Iris functions based on the following key principles:
Ultrasound Technology Fundamentals
- Utilizes high-frequency sound waves (35-80 MHz range) to generate real-time cross-sectional images of the anterior segment 1
- Employs pulse-inversion imaging technology, which overcomes limitations of traditional harmonic imaging by:
- Transmitting a pulse of sound into the eye
- Following with a second inverted pulse in the same direction
- Summing the echoes to cancel linear tissue responses while enhancing nonlinear components 2
- This technique allows for continuous real-time imaging with high spatial resolution and sensitivity 2
Imaging Capabilities
- Provides superior visualization of anterior segment structures even through opaque corneas 2
- Can image virtually all anterior segment anatomy including cornea, iridocorneal angle, anterior chamber, iris, ciliary body, and lens 2
- Particularly valuable for detecting:
- Ruptured or dislocated Descemet's membrane
- Retrocorneal membranes
- Iridocorneal and lenticulocorneal adhesions
- Small anterior segment foreign bodies 2
Technical Advantages
Penetration Through Opacities
- Primary advantage over light-based imaging devices is the ability to penetrate through corneal opacities, anterior segment, or vitreous opacities 2
- This makes it invaluable for evaluating patients with corneal edema or opacification where optical imaging methods are limited 2
Resolution and Frequency Balance
- The 35-80 MHz frequency range provides significantly improved resolution compared to conventional 10 MHz ultrasound 2
- Higher frequencies (>30 MHz) provide superior spatial resolution but limited penetration, making them ideal for anterior segment structures 1
- The system balances resolution and penetration depth for optimal anterior segment imaging 1
Clinical Applications
Corneal Pathology Assessment
- Particularly useful in identifying root causes of corneal edema or opacity 2
- Can detect:
Surgical Planning
- Aids in surgical planning for corneal procedures by providing detailed structural information 2
- Especially helpful in congenital and traumatic cases 2
- Can guide endothelial keratoplasty management in the immediate postoperative period 2
Foreign Body Detection
- Can locate small anterior segment foreign bodies that are difficult to detect by slit-lamp examination or anterior segment OCT 2
Practical Operation
Imaging Technique
- Examination begins with conventional B-mode imaging to identify target structures 2
- The transducer is then held motionless while switching to contrast-specific imaging mode 2
- A dual-screen format shows both B-mode and contrast-enhanced images for improved anatomical guidance 2
- Proper probe positioning at a 90° angle is essential for consistent measurements 1
Comparison to Other Imaging Modalities
Advantages Over Optical Imaging
- Unlike anterior segment OCT, which is limited by corneal opacities, the DxU 850m Iris can image through opaque tissues 2
- Provides real-time cross-sectional images rather than static ones 2
Complementary Role
- Often used in conjunction with other imaging modalities like anterior segment OCT
- While OCT provides higher resolution for transparent tissues, ultrasound biomicroscopy excels when optical clarity is compromised 2
Common Pitfalls and Considerations
- Using too high a frequency can result in inadequate penetration depth 1
- Improper probe positioning can affect measurement accuracy 1
- Requires technical expertise for optimal image acquisition and interpretation 2
The DxU 850m Iris represents an essential diagnostic tool for ophthalmologists, particularly when dealing with corneal pathologies that limit conventional optical imaging techniques.