WHAT IS OCT ANGIOGRAPHY
OCT Angiography (OCT-A) is a technology that can visualise retinal blood vessels by the reconstruction of the retinal tomograms. It can provide detailed visualisation of even very small blood vessels, without dilating the pupil or requiring an injection with fluorescein.
HOW DOES OCT-A WORK?
For OCT-A , 2 to 10 sequential scans ( 20 to 30 msec apart) at identical position are made . By distinguishing the differences between several successive scans, it is possible to visualise only the motion. This is done by a special algorithm that detects blood vessel signals based on Amplitude Decorrelation.
WHAT CAN OCT ANGIOGRAPHY VISUALISE?
With OCT-Angiography retinal layers can be observed from the superficial capillaries to the choriocapillaris. The layers can be freely selected, depending on pathology and the area to be observed.
BENEFITS OF OCT ANGIOGRAPHY
Examinations can be performed without any pupil dilation and are completely non-Invasive – so without the need for an injection with fluorescein dye – eliminating any risk of an allergic reaction. And OCT-A examinations just take seconds , where a classic FAG examination can take from 20 minutes up to one hour! In the near future, the Angio Expert software will have additional possibilities to analyse vessel density and measure the avascular zone; which will be extremely helpful to monitor progression.
Currently OCT Angiography can perhaps not completely replace the classic fluorescein angiography, but it is a very valuable additional diagnostic tool that is growing in importance.
ANGIO EXPERT (OPTIONAL)
The OCT-HS100 can be upgraded with the optional Canon Angio Expert software ( even existing systems can be upgraded very easily) . The extensive AX software will allow practitioners to visualise the microvasculature in the retina and choroid in a very patient friendly and non-invasive way. Blood vessel examination – angiography – can now be done without the injection of a contrast medium or the need for pupils to be dilated. This makes examinations far less intrusive for patients.
Angio Expert uses real-time auto retinal tracking to provide high quality images and is very fast : standard scans are done in less than 3 seconds and it can provide wide field scans – up to 12 mm wide.
The software is available in 2 versions: Angio Expert HD and Angio Expert Lite.
With OCT-Angiography the retinal layers can be observed from superficial capillaries to the choriocapillaris . Angio Expert has freely selectable layers , depending on pathology and area to be observed the optimum information can be obtained . Default layers that are standard available in the software can be modified very easily by adjusting the offset values – or simply create your ow definition. Up to 8 default layers can be preset.
REAL-TIME AUTO RETINAL TRACKING
Involuntary eye movements during examinations are unfortunately unavoidable. Canon’s retinal tracking uses the built-in SLO to track the retina in real-time to maintain the exact scanning position automatically. With the additional rotational tracking it greatly reduces motion artifacts and increases the image quality greatly.
Additionally, when the eye movement during capture is too much and cannot completely be compensated by the retinal tracking, re-scanning is done automatically for the areas that were partially incomplete and the final image will be corrected.
PROJECTION ARTIFACT REMOVAL
Projection artifacts are a result of shadows caused by the inner retinal vessels . The light that traverses these blood vessels will be reflected back by deeper layers (e.g. pigment retinal epithelium), and the final image will show a similar vascular pattern as the overlying vessels. These projection artifacts from the overlying retinal circulation then appear on CNV and Outer Retina and interfer strongly with the correct diagnosis. In Angio Expert a sophisticated algoritm will remove these artifacts. PA removal is crucial to judge whether vessels are really caused by neo-vascularisation or are simply projection artifacts.
FLOW FUSION TECHNOLOGY
By combining the data of mulitiple OCTA acquisitions , the image quality with high contrast and clear flow visualization is greatly improved and it can even help to eliminate motion artifacts. There 2 ways to utilise this technology ; use the real-time tracking control and new repeat acquisition mode of the OCT-HS100 to capture up to 9 consecutive scans at identical positions for a fantastic image quality, or do the acquisitions in multiple sessions ( but on same day), for a very patient friendly examination.
With this optional software module , up to 17.5 mm ultrawide wide OCTA mosaic images are possible with just 4 or 5 acquisitions .This function of course also allows for difficult patients to be scanned in mulitiple sessions, utilizing quicker but smaller scans that can be recombined into the required scan size.
Standard Scan sizes ranges from 3x 3 to 8 x 8 mm; the optional HD software additonally offers sizes up to 10 x 10 mm, as well vertical wide ( 3 x 9 ), horizontal wide 9 x 3 and 12 x 4 mm.
HIGH PIXEL DENSITY SCANS (HD ONLY)
Standard scans have a size of 232 x 232 pixels, the high pixel density scans have an extremely large format of up to 696 x 696 pixels, providing an unsurpassed image quality.
medium : 464 x 464 pixels
large : 696 x 696 pixels
wide (V): 696 x 232 pixels
wide (H): 232 x 696 pixels
EXTREME WIDE FIELD (HD ONLY)
With a single acquistion, very wide images from 3 x 3 ~ 10 x 10 and even of up to 12 x 4 mm can be obtained.