count the number of patients who have undergone the procedure of dx ultrasound-abdomen this year.
select count( distinct admissions.subject_id ) from admissions where admissions.hadm_id in ( select procedures_icd.hadm_id from procedures_icd where procedures_icd.icd9_code = ( select d_icd_procedures.icd9_code from d_icd_procedures where d_icd_procedures.short_title = 'dx ultrasound-abdomen' ) and datetime(procedures_icd.charttime,'start of year') = datetime(current_time,'start of year','-0 year') )