MRI Brain "quick scan" coding and billing

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At our organization we occasionally do what our radiologists refer to as a "quick brain MRI" or "vent check". They are doing a shorter (3 minute) non contrast brain MRI on pediatric patients as an alternative to a head CT, to avoid the use of radiation, for a suspected VP shunt. This vent check is different from other MRs in that is only contains one type of sequence, which is designed to only provide information about the presence of simple fluid. The table time is only 3 minutes, so the radiologists wonder if it should be a lower charge. From a coding perspective, we don't feel it is actually a reduced service (based solely on time spent), and there isn't a specific CPT for this service. Does anyone else have this exam at their organization and are you charging the full brain MR 70551 or using a -52 reduced services modifier?