97598 has a work RVU of only .24 so billing 18-19 units of this really isn't "over-coding" as long as your documentation supports that measurement. The claim should show it billed as x18 or x19 units and not listed on 18 or 19 individual lines. There is a global of 0 days for 97597 and so billing this service once per day, along with the 97598 add-on code is needed, is allowable.
Torilinne
SCC, CPC, CGIC