LSFG NAVI


LSFG NAVI - laser speckle flowgraphy technology

Abstract

The LSFG NAVI is a non-invasive ophthalmic imaging device manufactured by Softcare Co., Ltd. (Japan) that uses laser speckle flowgraphy technology to quantitatively assess ocular blood flow in real-time.

Technical Specifications

Hardware Components

  • Camera: Digital charge-coupled device camera (750 × 360 pixels)

  • Laser Source: Diode laser at a wavelength of 830 nm

  • Fundus Camera: Built-in fundus camera system for imaging

  • Acquisition Speed: A total of 118 images are acquired at a rate of 30 frames per second over a 4-second measurement period

Measurement Parameters

  • Temporal Resolution: Real-time blood flow measurement capabilities

  • Measurement Duration: 4-second standard measurement period

  • Frame Rate: 30 frames per second acquisition

  • Wavelength: 830 nm infrared laser for tissue penetration

Technology Principles

Laser Speckle Phenomenon

Laser speckle flowgraphy (LSFG) is a noninvasive, real-time technique that uses laser scattering to determine blood flow in the ONH, retina, and choroid. The system analyzes speckle patterns created when coherent laser light interacts with moving red blood cells.

Blood Flow Parameters

The LSFG NAVI calculates several key parameters:

  1. Mean Blur Rate (MBR): A new parameter defined as twice the square blur rate (SBR), providing quantitative blood flow measurement

  2. Specific Regional Parameters:

    • MA (Mean All): Mean MBRs throughout the ONH

    • MV (Mean Vessel): Mean MBRs of the ONH vessels

    • MT (Mean Tissue): Mean MBRs of the ONH tissue

Advanced Analysis Features

Pulse Wave Analysis

The system provides sophisticated pulse wave parameters:

  • Skew: Quantifies the asymmetry of the waveform distribution, varying with the bias of the waveform shape

  • BOT (Blow Out Time): An indicator that represents the time of the wave maintaining more than half of the mean of maximum and minimum MBR during a beat

  • Rising Rate: Analysis of blood flow acceleration patterns

  • Falling Rate: The equivalent ratio after the peak

  • FAI (Flow Acceleration Index): Calculated from the maximum change among all frames (1/30 s) in a rising curve

  • ATI (Acceleration Time Index): Derived from a ratio of the time before reaching the peak to a whole heartbeat

  • RI (Resistivity Index): Calculated by dividing the difference of the maximum and minimum MBR by the maximum MBR

Retinal Vessel Analysis

All of the retinal vessels around the ONH can be distinguished semi-automatically with the specific software. The total retinal flow indexes of arteries and veins can be calculated separately.

Clinical Applications

Primary Applications

  1. Glaucoma Assessment: Significant correlations between optic nerve head microcirculation and visual field defects and nerve fiber layer loss in glaucoma patients

  2. Optic Nerve Head Analysis: Comprehensive blood flow assessment of the optic disc

  3. Choroidal Circulation: Real-time choroidal blood flow measurement

  4. Retinal Vascular Diseases: Assessment of various retinal vascular conditions

Specific Disease Applications

The LSFG NAVI has been used in research and clinical assessment of:

  • Normal tension glaucoma

  • Central retinal vein occlusion

  • Diabetic retinopathy

  • Vogt-Koyanagi-Harada disease

  • Acute central serous chorioretinopathy

Regulatory Status

Softcare Co., Ltd. received 510(k) clearance from the U.S. Food and Drug Administration (FDA) for LSFG-NAVI, indicating its approval for clinical use in the United States.

System Variants

Softcare offers multiple LSFG models:

  • LSFG-NAVI: Standard clinical model

  • LSFG-LITE: Simplified version

  • LSFG-Micro: Specialized microscopic applications

  • LSFG-MRC: Research-oriented configuration

  • LSFG-NAVI-OPE: Developed recently for ocular blood flow measurement in subjects in a supine position

Advantages

Clinical Benefits

  1. Non-Invasive: Contact-free measurement without dilation requirements

  2. Real-Time Results: Immediate blood flow visualization

  3. Quantitative Analysis: Precise numerical blood flow parameters

  4. Reproducibility: The reproducibility was reported to be favorable in not only normal subjects but also glaucoma patients

Research Applications

  • Basic research applications including posture change effects on ocular blood flow

  • Age correlation studies with fundus pathology including age-related arterial sclerosis

  • Drug effect monitoring in glaucoma treatment

Limitations

  • Depth Sectioning: Unlike OCT-A, LSFG has no depth sectioning ability

  • Two-Dimensional Analysis: Primarily surface blood flow analysis

  • Learning Curve: Requires training for optimal parameter interpretation

The LSFG NAVI represents a clinically validated, FDA-cleared technology that provides quantitative, real-time assessment of ocular blood flow, making it valuable for both clinical diagnosis and research applications in ophthalmology.