Hi, where are you generating your thumbnails from (what software)? Are the original images on your HDD pretty good quality? How are you re-sizing them before uploading them exactly?
Images this small will definitely look better if they're not sasved as .jpg compressed files. Consider using .png 24 files for such small thumbs and although the image size will increase, the quality will be so much better.
However, if the full size images on your product pages are the best quality version of these images then you will not be able to improve the 45px; thumnails any as the original quality just isn't good enough to produce a thumb this small. If this is the case then consider increasing the dimensions of your thumbnails to at least 100px; wide.
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