New Heidelberg Angiograph Offers Valuable
High-resolution dynamic images provide additional information for the management of CNV.
BY KEITH CROES AND ELLEN KUREK
The Heidelberg Retina Angiograph (HRA) confocal laser scanning system (Heidelberg Engineering, Vista, Calif), has delivered crisp, minutely detailed, high-speed, real-time digital angiographic images since its entry onto the market in 2002. Last year, Heidelberg introduced its latest model, the HRA2, which has a smaller, more powerful camera than the original HRA and is easier to manipulate. We discussed the HRA and the new HRA2 system with three retina specialists and one of Heidelberg's experts.
Steve A. Thomas, CRA, imaging product specialist for Heidelberg Engineering, explains that like its predecessor the HRA, the HRA2's main advantages over conventional imaging are its image quality, dynamic capabilities, and efficiency.
Compared to both the original HRA and fundus cameras, the HRA2 takes higher-resolution images, which means better definition and greater detail. With fluorescein, the HRA2 enables physicians to see details just 5 μm in size three times smaller than the 15 μm details visible with a fundus camera image and all in an image that is just 1536 x 1536 pixels with a 30° field of view. Fundus cameras with much larger image sizes cannot match this resolution, and the HRA2's images require less storage space. In addition, users can expand the HRA2's field of view to 120° with the system's automatic mosaic image construction feature and increase it to 150° by combining this feature with the accessory Staurenghi Wide Field lens.
EXCELLENT IMAGE QUALITY
The HRA2's confocal scanning laser system and pixel-illumination pattern suppress scattered light. "With a fundus camera, light is scattered inside the eye, and the camera cannot resolve the information," Steve Thomas says. "Because the HRA2 suppresses scattered light, it can resolve to 5 μm per pixel, compared to the fundus camera's 15 μm to 18 μm per pixel." Indocyanine green (ICG) angiograms performed with the HRA2 provide greater chorioretinal detail than ordinary fundus camera ICG angiograms, because of both reduced light scatter and the HRA2 laser's particular sensitivity to the ICG dye, according to Thomas. This means that the HRA2's ICG images lack the fuzzy, diffuse quality of ICG images from fundus cameras.
The HRA2 also takes images in up to 64 consecutive focal planes to a depth of 8 mm, which produces a 3-D image series that can aid physicians in evaluating choroidal melanoma. In terms of field of view, the HRA2 is narrower than the conventional fundus camera. Fundus cameras are generally capable of 45° or 50°, 30° or 35°, and 20°, whereas the HRA2's fields of view are 30°, 20°, and 15°. Users can create 60° photomontages using an automated feature or make 120° photomontages manually. One disadvantage of the HRA systems is their lack of color imaging, which facilitates angiogram interpretation. The physicians interviewed say they overcome this issue easily by using the color fundus cameras if needed.
DYNAMIC ANGIOGRAPHY AND COMPARISON
The HRA systems offer still-frames and full-motion ICG angiography a significant advantage over the fundus camera's static-only ICG angiography, notes HRA user Greg Rosenthal, MD, of Vision Associates in Toledo, Ohio. "The ICG still frame is worthless," he says. "The resolution is not good, and we're only collecting a frame every 3 seconds if we're lucky. For most choroidal circulation, the action is there and gone in 6 seconds. What's the chance of finding something? Very small." The value of the HRA systems, according to Dr. Rosenthal, is that they offer "infrared imaging, extremely high resolution, and, most importantly, video." Robert Murphy, MD, of the Retina Group in Fairfax, Va, and an HRA2 user, agrees. "With static pictures, all we got was a little fuzzy spot," he explains. "Now we take videos of the eye's circulation, much as a cardiologist would look at blood circulation in a cardiac angiogram. We get real-time video of the vessels filling, which gives us an enormous amount of detailed information."
For Dr. Rosenthal, his HRA system's detailed images initially created a challenge: separating normal from abnormal blood vessels. "To accomplish this, we go to the end of the video to see the veins, and then drag the bar back to the start of the video. We can mentally subtract the veins quickly, and the arterial pathology comes into view nicely," he says.
The HRA2 also enables users to perform fluorescein and ICG imaging simultaneously and view the images on the monitor side by side. This saves time, and it is intended to aid diagnosis by helping physicians correlate the choroidal pathology on the ICG angiogram with the fluorescein angiogram's retinal landmarks.
ADDITIONAL IMAGING MODES
In addition to its fluorescein and ICG imaging capabilities, the HRA2 also offers several noninvasive imaging modes, including blue-reflectance and infrared-reflectance imaging. Blue-reflectance imaging may be valuable for viewing details of the ocular nerve fiber layer, but it requires a clear media without cataracts, which would absorb the blue light.
Noninvasive imaging with barely visible infrared reflectance light is suitable for viewing the fundus of an extremely light-sensitive patient such as a child, as well as for viewing through a cataract, visualizing a choroidal nevus, or evaluating the retinal pigment epithelium (RPE). With the HRA2, users can view these images simultaneously with fluorescein or ICG angiography.
Shann Lin, MD, of Progressive Vision Institute in Pottsville, Pa, also notes that the HRA2 only does stereo imaging in infrared-reflectance mode, which he considers to be a limitation. "I still want a digital fundus picture," he says.
Unlike the original HRA, the HRA2 also provides autofluorescence imaging to help physicians confirm diagnoses of macular holes, pseudo-vittelliform lesions, RPE atrophy, central serous chorioretinopathy, and Best's disease. This modality may also aid the study of Stargardt's dystrophy when users employ the normal fluorescein angiography setting without injecting fluorescein. Patients without cataracts get the best imaging.
Dr. Murphy explains, "Basically, autofluorescence highlights areas of devitalized retinal tissue that seem to correlate very well with atrophy that's going to develop within the next several years. It's a useful predictor."
Real-time angiography helps physicians locate feeder vessels and choroidal neovascularization (CNV) associated with macular degeneration, and the HRA2 offers improved diagnosis and treatment of the disease. "The level of detail in the HRA2's images shows circulation in the large and small vessels that feed CNV complexes. And since the imaging is dynamic, we see these vessels fill up and then drain, which can happen quite quickly," Thomas explains. The HRA2 uses a rapid frame rate to capture that circulation. In comparison, a fundus camera requires physicians to compare still images captured as far as 1 or 2 seconds apart.
"It doesn't capture enough images, and the resolution doesn't show the small details," Thomas notes. He says that the HRA2 is most frequently used to perform high-speed ICG to identify the choroidal involvement with CNV before photodynamic therapy. They can see the success or failure of the PDT treatment based on the initial angiography a difficult claim for conventional imaging techniques.
"For the first time, we can treat the lesion by sealing off the blood supply with a tiny laser spot. That's what feeder vessel treatment is," says Dr. Murphy. "In the past, we had to cauterize the entire lesion a huge area destroying the retina in the process. This is a quantum leap forward."
Although the HRA2 is particularly useful for locating and treating feeder vessels, it also helps physicians differentiate retinal angiomatous proliferation from CNV, which promotes early diagnosis and treatment. It can even help distinguish recurrence from persistence after laser therapy.
"It's not just for feeder vessels," Dr. Rosenthal says. "It completely changes the user's understanding of the choroidal vasculature. It's a huge improvement over fluorescein alone. And for tumors and any subretinal pathology, it gives us more information."
In addition to offering patients better clinical outcomes, the low light levels used in HRA systems make examinations much more comfortable. The retinal light exposure required for the HRA2 is only about 1% of that needed with a photographic system, and without a bright flash and lag time between consecutive images, the system minimizes patient eye movement.
EASE OF USE
Dr. Murphy recalls that it took a relatively short time to teach his photographers to use the HRA model. "I've taught 3 photographers, and they all took good images on the first day," he says.
The HRA systems have touch-screen displays, enabling the photographer to switch quickly from 1 mode to the next. Thomas also says that several enhancements make the HRA2 model even easier to use than the HRA. "The overall ergonomics and ease of use have been much improved for the HRA2," he notes. "And it's designed to support software and firmware upgrades and Heidelberg add-ons to grow along with the user's needs."
For Dr. Lin, teaching photographers to use the HRA2 has been a satisfactory experience. He explains, "the photographer needs to adapt to the different way the camera moves, but my photographer was able to complete the imaging with the HRA2 in about 15 minutes after using it for about 2 months."
Some users of the HRA model have noted difficulty in reproducing the clinical results that have been reported in the literature regarding detection and treatment of feeder vessels in patients with CNV. Several factors have contributed to this difficulty, according to the physicians interviewed.
Dr. Lin points out that problems may begin with improper dye injection techniques, which prevent them from seeing the feeder vessels. He explains, "many people just push it like fluorescein, so they can't find the feeder vessel. We've got to make sure the ICG is concentrated in a very small dose, and then we push it in bolus and flush it with saline."
Treatment experience may be a factor as well, according to Dr. Lin. "We have to change the way we think," he says. "Today, we know that CNV has a natural healing process the RPE may start to envelop the CNV, but the CNV grows too fast for the RPE to keep up. We want to modify the flow in the choroidal vasculature, reducing it enough to tilt the balance and stabilize."
In addition, "people often treat the wrong feeder vessel," asserts Dr. Lin. "We have to choose which vessels to treat carefully, because there are often multiple feeder vessels. If we shut one down, there are still other ways for the fluid to get into the retinal circulation."
Dr. Murphy suggests that the problem may be even simpler. "Surgeons who have difficulty with the HRA are not experienced with the technology," he explains. "Ophthalmologists who invest time in learn to use the system are very enthusiastic about it."
Finally, the $105,000 cost of the HRA2 makes obtaining an attractive monetary return on the investment difficult. "It's an excellent investment for the practice," Dr. Murphy says of the HRA2, "but the primary value to the practice is the added ability to treat and reduce visual loss, not financial gain."
Dr. Lin agrees. "It's expensive. Retinal specialists have to think about that. Of course I lose money, but I bought this one because I want the best," he explains. Both physicians agree that existing reimbursement codes apply to imaging and procedures performed with the HRA2.
Many retinal specialists who already own the HRA model are reluctant to upgrade to the HRA2 because of its cost. As Dr. Rosenthal observes, "a lot people are so happy with the HRA that they don't see any reason to invest in the HRA2." With the discontinuation of the original HRA and the upgradeability of the new HRA2, it is likely that many retinal specialists will make the transition sometime in the future.