Set analysis help needed

[us_enterprise_s]

Hi,

I am working on a set analysis expression and have been struggling with the last piece.

I appreciate all help.

=aggr

(

     only

     (

          {$

               <PatientName=P({$<ScanType={'XR'}>}PatientName)>

                    *

               <PatientName=P({$<ScanType={'CT'}>}PatientName)>

          }

     PatientName

     ),

PatientName

)

Existing expression correctly identifies all patients who had both 'XR' and 'CT'. I need to further modify it, so that it only looks for patients who had a XR, within 40 days prior to the CT.

I have a field, ScanStart, that tells me when the scan took place.

[us_enterprise_s]

nothing?