Left internal carotid artery is difficult to evalution in doppler study. what will be impact on health and what is cure for this.

Well, ....: Depending on why you even had the doppler done will answer the question. That simply means anatomically, they may not have seen the carotid well on the study. If you and your Doctor have concerns about the patency of the Artery, then a dye study could be ordered to confirm this since the doppler was inadequate.

Cannot answer: Can't say in your case, but typically "difficult to evaluate" = "unable to visualize" or "incompletely seen" or "obscured." Report may state why,example: "due to motion artifact" which means the image is blurry because the patient moved during the test. It does not necessarily mean something is wrong, it just means that the part mentioned was not seen well enough to give an accurate description.

There is no: health impact or cure. It sounds like you have a large neck and/or your carotid artery does not take a straight course, making it technically difficult to evaluate on ultrasound. This does not imply your carotid is abnormal, it is simply a limitation of the ultrasound test. Next imaging test to check the carotids, not subject to these limitations, would be MRA or CTA.

Not necessarily: Anything. From your description, it sounds more like a technical issue rather than a concerning anatomic issue with your carotid artery. Before, I'd worry about anything make sure there something to actually worry about like a stenosis(narrowing) or clot.