Well, you're correct in noting that using ultrasound to determine what a given liver lesion is the least accurate imaging mode. But it still does provide a good amount of information that, when combined with your other data, can give your doctor a pretty good idea about what's up.
One very important thing to keep in mind is that liver lesions, found in people without advanced liver disease (end-stage fibrosis/cirrhosis), are almost always benign. Primary liver cancers, in healthy liver patients, are extremely rare. And if a malignant tumor is found within a healthy liver, it is usually a metastasis lesion. This is why your radiologist included the note "In the absence of malignancy" in your report. And, since your primary doctor knows your current/past history, he concluded your lesions are very likely benign (I assume you don't have another form of cancer, hopefully!).
As you also noted, hemangiomas are benign, so there isn't anything to be concerned about. The standard practice is to simply monitor them for a short period of time. But you could talk to your doctor and have them use a CT or MRI for your next imaging scan, likely in 6 months to a year. If it was me, I'd like to have the different imaging modality, just for the extra data it can provide, especially since they'll be wanting to do a followup imaging procedure anyway. It will be a little more money though.
If a benign lesion were to get to bigger and it started to cause some compressive effects on the surrounding liver tissue, this will show up in your blood work. Your liver enzymes (alt,ast) would likely show a small elevation, especially your alkaline phosphatase (alp). But this would be very unlikely, hemangiomas aren't generally naughty.
I appreciate you comment. That actually really does put me at ease. I have never been diagnosed with any other form of cancer. I had a call into the doctor to ask about this, and they basically said the same thing you just did. I am much much more at ease now. I was just worried about the "In absence of malignancy" line because I didn't really understand what it meant. Now knowing what it means is much easier on my mind. Especially since I don't really have any other liver symptoms.
I did previously have an US and in that they had mentioned my liver was enlarged, but went to the GI and he said since I was a big person (6'4" 220lbs) that mine is probably just bigger to begin with. He was not concerned. I do not have access to results of that US to know if they noticed the lesions then or not.
I also had blood work done one evening when I went to the ER for what turned out to be anxiety. Which was just in June and the liver stuff was all within the correct range. Although the AST (SGOT) appears to be considerably higher than it was in my previous 4 blood tests (which the last one prior to this one was 2011). It was 28 compared to being 10, 10, 13, 13. Not sure if that is significant for anything or not.
I am much less concerned now though about the possibility of it being malignant. I am following up with the doctor through the phone though just to verify that any other tests aren't necessary. Also I know drinking is bad for your liver no matter what, but will it cause any complications if I have a few drinks from time to time with these? I am planning on asking the doctor as well, but you seem pretty well versed on the liver so thought I would ask here too.
You can have a few drinks without worry. Your liver is very healthy and your hemangiomas will not be adversely affected by the alcohol. Obviously moderation is always the key in maintaining a healthy liver. Have fun!