Материал: part17

Angiography is a procedure that requires a dye to be injected into the patient for the purpose of enhancing the imaging of vascular​ structures in the eye. A standard step in this procedure is imaging the eye at specified intervals to detect the pooling of small amounts​ of dye and/or blood in the retina. For a doctor or technician to properly interpret angiography images it is important to know how much​ time had elapsed between the dye being injected in the patient (time 0) and the image frame being taken. It is known that such dyes​ can have an affect on OPT tomographic images as well (and it may be possible to use such dyes to enhance vascular structure in​ theOPTimages),thereforetimesynchronizationwillbeappliedtothecreationoftheOPTimagesaswellasanyassociatedOPimages​

The angiographic acquisition is instantiated as a multi-frame OPT Image. The variable time increments between frames of the image​ are captured in the Frame Time Vector of the OPT Multi-frame Module. For multiple sets of images, e.g., sets of retinal scan images,​ the Slice Location Vector will be used in addition to the Frame Time Vector. For 5 sets of 6 scans there will be 30 frames in the Multi-​ frame Image. The first 6 values in the Frame Time Vector will give the time from injection to the first set of scans, the second 6 will​ contain the time interval for the second set of 6 scans, and so on, for a total of 5 time intervals.​

Another example of an angiographic study with related sets of images is a sequence of SLO/OCT/"ICG filtered" image triples (or​ SLO/OCT image pairs) that are time-stamped relative to a user-defined event. This user-defined event usually corresponds to the​ inject time of ICG (indocyanine green) into the patients blood stream. The resultant images form an angiography study where the​ patient's blood flow can be observed with the "ICG filtered" images and can be correlated with the pathologies observed in the SLO​ and OCT images that are spatially related to the ICG image with a pixel-to-pixel correspondence on the X-Y plane.​

U.3.2.4 3D Reconstruction Exam​

The prognosis of some pathologies can be aided by a 3D visualization of the affected areas of the eye. For example, in certain cases​ the density of cystic formations or the amount of drusen present can be hard to ascertain from a series of unrelated two-dimensional​ longitudinal images of the eye. However, some OCT machines are capable of taking a sequence of spatially related two-dimensional​ imagesinasuitablyshortperiodoftime.Theseimagescaneitherbeorientedlongitudinally(perpendiculartotheretina)ortransversely​ (near-parallel to the retina). Once such a sequence has been captured, it then becomes possible for the examined volume of data to​ be reconstructed for an interactive 3D inspection by a user of the system (see Figure U.3-5). It is also possible for measurements,​ including volumes, to be calculated based on the 3D data.​

A reference image is often combined with the OCT data to provide a means of registering the 3D OCT data-set with a location on the​ surface of the retina (see Figure U.3-6 and Figure U.3-7).​

Figure U.3-5. Example 3D reconstruction​

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Figure U.3-6. Longitudinal OCT Image with Reference Image (inset)​

Figure U.3-7. Superimposition of Longitudinal Image on Reference Image​

U.3.2.5 Transverse Imaging​

While the majority of ophthalmic tomography imaging consists of sets of longitudinal images (also known as B scans or line scans),​ transverse images (also known as coronal or "en face" images) can also provide useful information in determining the full extent of​ the volume affected by pathology.​

Longitudinalimagesareorientedinamannerthatisperpendiculartothestructurebeingexamined,whiletransverseimagesareoriented​ in an "en face" or near parallel fashion through the structure being examined.​

Transverse images can be obtained from a directly as a single scan (as shown in Figure U.3-8 and Figure U.3-9) or they can also be​ reconstructed from 3D data (as shown in Figure U.3-10 and Figure U.3-11). A sequence of transverse images can also be combined​ to form 3D data.​

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Figure U.3-8. Transverse OCT Image​

Figure U.3-9. Correlation between a Transverse OCT Image and a Reference Image Obtained​ Simultaneously​

FigureU.3-8,FigureU.3-9,FigureU.3-10andFigureU.3-11areallimagesofthesamepathologyinthesameeye,butthetwodifferent​ orientations provide complementary information about the size and shape of the pathology being examined. For example, when ex-​ aminingmacularholes,determiningtheamountofsurroundingcysticformationisimportantaidinthefollowingtreatment.Determining​ theextentofsuchcysticformationismuchmoreeasilyascertainedusingtransverseimagesratherthanlongitudinalimages.Transverse​ imagesarealsoveryusefulinlocatingmicro-pathologiessuchascoveredmacularholes,whichmaybeoverlookedusingconventional​ longitudinal imaging.​

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Figure U.3-10. Correspondence between Reconstructed Transverse and Longitudinal OCT Images​

Figure U.3-11. Reconstructed Transverse and Side Longitudinal Images​

In Figure U.3-10, the blue green and pink lines show the correspondence of the three images. In Figure U.3-11, the Transverse image​ is highlighted in yellow.​

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