LSFG quantifies speckle blur as the blur rate and uses it as the blood flow evaluation quantity.
The blood flow evaluation quantity has evolved as shown in the table below throughout the history of LSFG development.
The key point is the image sensor used to observe the speckles.
Previously, a custom-made area sensor with high temporal resolution was used, but it became difficult to obtain, and currently a general-purpose CCD camera is used.
| Blood Flow Evaluation Quantity |
Image Sensor | Overview |
| BR value (Blur Rate value) = NB value (Normalized Blur) |
Custom-made Pixels: 100×100 Scan cycle: 1/500 [sec] |
The reciprocal of the standard deviation of light intensity detected by the image sensor was used as the blood flow evaluation quantity. The BR value has a physical meaning as the S/N ratio (Signal to Noise ratio), which is the reciprocal of the speckle intensity contrast. |
| SBR value (Square Blur Rate value) |
Custom-made Pixels: 100×100 Scan cycle: 1/500 [sec] |
While the BR value had been used as the blood flow evaluation quantity, it was found that the linearity of the BR value deteriorated as blood cell movement velocity increased. Subsequent research revealed that the square of the BR value is proportional to blood cell movement velocity, so the SBR value, which is the square of the BR value, was adopted as the blood flow evaluation quantity. |
| MBR value (Mean Blur Rate value) |
General-purpose CCD Pixels: 750×360 Scan cycle: 1/30 [sec] |
Since the custom-made area sensor became difficult to obtain, research was conducted to derive the blood flow evaluation quantity using a general-purpose CCD camera, resulting in the creation of the MBR value. Because sufficient temporal resolution could not be obtained with a general-purpose CCD camera, a method was devised to compensate for the insufficient temporal resolution with broader spatial resolution. The MBR value is a blood flow evaluation quantity calculated from values obtained from both temporal and spatial variations. |
References
- Naoki Konishi, Yoshinori Tokimoto, Kazuhiro Kohra and Hitoshi Fujii
New Laser Speckle Flowgraphy System Using CCD Camera
Optical Review, 9, No.4, 163-169, 2002 doi:10.1007/s10043-002-0163-4 [Link] - Tetsuya Sugiyama
Basic Technology and Clinical Applications of the Updated Model of Laser Speckle Flowgraphy to Ocular Diseases
Photonics, 1, no.3, 220-234, 2014. doi:10.3390/photonics1030220 [Link]
Relationship Among the Blood Flow Evaluation Quantities
The relationships among the blood flow evaluation quantities are summarized as follows:
SBR = BR2
MBR = 2 × SBR = 2 × BR2
The BR value and SBR value differ in their linearity with respect to velocity. In high-velocity regions such as vessels, both the displayed values and their rates of change differ.
The SBR value and MBR value have a simple relationship of MBR = 2 × SBR.