1*THE HEART WILL ALWAYS PRODUCE A PERFUSION/VENTILATION 'DEFECT'. THIS MAY BE VERY PRONOUNCED WHEN THERE IS SIGNIFICANT CARDIOMEGALY*

2*IN PATIENTS WITH PULMONARY VENOUS HYPERTENSION THE INJECTION OF MICROSPHERES SHOULD BE GIVEN WITH THE PATIENT SITTING UPRIGHT TO ACHIEVE DISTRIBUTION TO THE BASES*

3*IT IS VITAL IMPORTANT TO EVALUATE THE CURRENT CHEST X-RAY FOR PROPER INTERPRETATION OF THE LUNG SCAN*

4*EMBOLI ARE COMMONLY SEGMENTAL BECAUSE THEY BLOCK THE VASCULAR SUPPLY TO A SEGMENT*
*PARENCHYMAL DISEASE IS NOT PRIMARILY VASCULAR, AND THEREFORE IS NON-SEGMENTAL*
*SUBSEGMENTAL DEFECTS MAY BE CAUSED BY EITHER EMBOLI OR PARENCHYMAL LUNG DISEASE*

5*OVER 90% OF ALL LUNG SCANS ARE UNDERTAKEN AS PART OF THE INITIAL EVALUATION OR FOLLOW-UP OF PATIENTS SUSPECTED OR KNOWN TO HAVE PULMONARY EMBOLISM*
*A NORMAL PERFUSION LUNG STUDY EXCLUDES PTE*
*THE PATTERN OF BILATERAL SEGMENTAL PERFUSION DEFECTS WHICH ARE NORMALLY VENTILATED IS DIAGNOSTIC OF PTE*
*AN ABNORMAL PERFUSION SCAN SHOWING MULTIPLE DEFECTS WHICH CHANGES OVER SEVEN DAYS RAISES THE PROBABILITY OF PTE BEING PRESENT*
*THE ACCURATE DIAGNOSIS OF PTE IS IMPORTANT, SINCE ANTI-COAGULATION IS ASSOCIATED WITH A SIGNIFICANT RISK OF MAJOR COMPLICATIONS. HOWEVER, THERAPEUTIC ANTICOAGULATION IN THE PRESENCE OF PTE REDUCES THE MORTALITY FOURFOLD*
*A PULMONARY ANGIOGRAM DISPLAYS THE ANATOMY OF THE PULMONARY VASCULAR BED, WHILE A LUNG SCAN DISPLAYS THE DISTRIBUTION OF VENTILATION AND PULMONARY BLOOD FLOW*

6*THE DISADVANTAGES OF 133XE ARE THAT A SINGLE VIEW ONLY CAN BE OBTAINED AND THE NEED TO PERFORM THE STUDY PRIOR TO THE PERFUSION SCAN; THEREFORE THE OPTIMAL VIEW CANNOT BE SELECTED TO DEMONSTRATE VENTILATION IN A PARTICULAR AREA OF INTEREST*

7*SUBTRACTION OF PERFUSION FROM A SUBSEQUENT VENTILATION IMAGE MAY ASSIST IN DIFFICULT CASES WHEN BOTH RADIOPHARMACEUTICAL ARE 99m Tc-LABELLED*

8*THE PRESENCE OF PARENCHYMAL LUNG DISEASE IS NOT A CONTRAINDICATION TO PERFORMING A PERFUSION LUNG SCAN, BUT IT MUST BE ASSESSED WITH THE VENTILATION SCAN WITH EXTREME CARE*

9*CAREFUL ANALYSIS OF PERFUSION/VENTILATION LUNG SCANS MAY ALLOW THE DIAGNOSIS OF PULMONARY EMBOLIC DISEASE, EVEN IN THE PRESENCE OF PLEURAL EFFUSION*

10*IF AN EMBOLUS IS GOING TO CLEAR, IT WILL DO SO BY THREE MONTHS. WHAT IS LEFT AFTER THREE MONTHS WILL PERSIST INDEFINITELY*

11*A PERSISTENT PERFUSION DEFECT WITH NORMAL VENTILATION CAN OCCUR WITHOUT INFARCTION BECAUSE THE NUTRITIONAL REQUIREMENTS ARE MET BY AN ADEQUATE BRONCHIAL BLOOD SUPPLY*

12*IN SPITE OF THE CLASSICAL FEATURES OF PULMONARY EMBOLISM, THE DATE OF A PULMONARY EMBOLUS CANNOT BE ASCERTAINED WITH CERTAINTY*

13*RESOLUTION OF PERFUSION DEFECTS AFTER PULMONARY EMBOLI IS VERY VARIABLE. DEFECTS MAY RESOLVE COMPLETELY, PARTIALLY, OR REMAIN UNCHANGED*
*A PERFUSION/VENTILATION SCAN SHOULD BE PERFORMED PRIOR TO DISCONTINUING ANTICOAGULANT THERAPY TO ASSESS RESIDUAL DEFECTS*

14*PREVIOUS TUBERCULOSIS MAY LEAD TO DISPROPORTIONATELY LARGE PERFUSION DEFECTS ON THE LUNG SCAN WHEN COMPARED WITH RADIOLOGICAL FINDINGS*

15*IT IS ESSENTIAL TO ASSESS WHETHER A PATIENT HAVING A LUNG SCAN HAS ACUTE BRONCHOSPASM AT THE TIME THAT THE STUDY IS PERFORMED*
*IT IS ESSENTIAL TO OBTAIN A VENTILATION STUDY WHENEVER PERFUSION DEFECTS ARE FOUND*

16*VASCULITIS CAUSED BY POLYARTERITIS NODOSA, SYSTEMIC LUPUS ERYTHEMATOSUS OR OTHER COLLAGEN DISORDERS IS PHYSIOLOGICALLY INDISTINGUISHABLE FROM PULMONARY EMBOLI AND WILL CAUSE UNMATCHED PERFUSION/VENTILATION DEFECTS*

17*METASTASES ARE AN UNCOMMON CAUSE OF PULMONARY ARTERIAL LESIONS*
*THE TYPICAL FINDINGS ON LUNG SCANS FOLLOWING RADIATION ARE GREATER DIMINUTION OF PERFUSION THAN OF VENTILATION IN THE IRRADIATED AREA. FURTHERMORE, RADIATION FIELDS WILL RARELY CORRESPOND TO BRONCHOPULMONARY SEGMENTS*

18*SUBSEGMENTAL PERFUSION DEFECTS WITH NORMAL VENTILATION MAY BE SEEN WITH BOTH TUMOUR AND FAT EMBOLI*

19*THE PRESENCE OF OBSTRUCTIVE AIRWAYS DISEASE SHOULD NOT CAUSE DIAGNOSTIC PROBLEMS ON A PERFUSION LUNG SCAN, WHEN A VENTILATION STUDY IS ALSO OBTAINED*
*WHEN THERE IS EXTENSIVE PARENCHYMAL LUNG DISEASE WITH MAJOR PERFUSION DEFECTS, THE PRESENCE OF COEXISTENT PULMONARY EMBOLIC DISEASE CANNOT BE ABSOLUTELY EXCLUDED*

20*THE DELAYED WASHOUT ON A XENON STUDY CAN PROVIDE USEFUL ADDITIONAL INFORMATION IN THE DIAGNOSIS OF CHRONIC OBSTRUCTIVE AIRWAYS DISEASE*

21*PATIENTS WITH CHRONIC LUNG DISEASE MAY DEMONSTRATE TEMPORARY VENTILATION DEFECTS AS A RESULT OF MUCOUS PLUGGING OF THE BRONCHI*

22*MISMATCHED DEFECTS, WHERE THE VENTILATION IS AFFECTED BUT THE PERFUSION CHANGES ARE INSIGNIFICANT OR LESS MARKED, MAY OCCASIONALLY BE SEEN IN ACUTE PNEUMONIA. HOWEVER, USUALLY THE PERFUSION IS SIMILARLY AFFECTED*

23*MISMATCH USUALLY MEANS BETTER VENTILATION THAN PERFUSION. HOWEVER, IT MAY BE REVERSE, AS IN THE CASE OF PNEUMONIA, WHEN THE ALVEOLAR DISTURBANCE IS MORE AFFECTED THAN THE BLOOD FLOW*

24*A MASS LESION IN THE LUNG PARTICULARLY AT THE HILUM, WILL CAUSE A MASSIVE PERFUSION DEFECT, AND USUALLY A MATCHING VENTILATION ABNORMALITY. OCCASIONALLY, IT MAY INVOLVE THE PULMONARY ARTERY ONLY AND SPARE THE BRONCHUS, IN WHICH CASE THERE MAY BE MISMATCH DEFECT*

25*INCREASED LUNG PERMEABILITY IS NON-SPECIFIC AND MAY BE SEEN IN MAY CONDITIONS. THE COMMONEST SITUATION TO CAUSE INCREASED PERMEABILITY IS CIGARETTE SMOKING. USUALLY THE CHANGE OF PERMEABILITY IS NOT SIGNIFICANT CLINICALLY; HOWEVER, IF IT IS VERY RAPID, IT MAY BE IMPOSSIBLE TO ACHIEVE A SATISFACTORY VENTILATION STUDY WITH AEROSOLS*