title: Multidetector computed tomography pulmonary angiography: does arm position affect pulmonary artery enhancement?
abstract: OBJECTIVE
  To evaluate whether arm position affects pulmonary artery enhancement in computed tomographic pulmonary angiography (CTPA).
  
  
  METHODS
  Study protocol had local ethics committee approval. Eighty-six patients who received 16 detector row CTPA for suspected pulmonary embolism were scanned with their contrast-injected arm resting at their side and compared with 94 patients who were scanned with both arms resting above their head. Two radiologists assessed pulmonary artery enhancement with a region-of-interest measurement of the main pulmonary artery density, scored the degree of beam-hardening artifact arising from the superior vena cava (SVC) and from the dependent arm that crossed the pulmonary arteries (1 = no artifact, 5 = artery obscured), and measured the degree of central venous compression of the injected veins at the thoracic inlet. A 2-tailed t test was performed to compare pulmonary artery density and central venous compression.
  
  
  RESULTS
  There was no difference in pulmonary artery enhancement between the 2 arm positions. Mean density of contrast in the main pulmonary artery was 329 Hounsfield units (HU) (95% confidence interval (CI), 310-350) in the arm-down group, compared with 325 HU (95% CI, 306-346) in the arm-up group (P = 0.65). Greater compression of the central veins occurred in the arm-up group (48.5%; 95% CI, 42.3%-54.8%) than in the arm-down group (22.3%; 95% CI, 16.8%-27.8%) (P < 0.05). There was also more beam hardening arising from contrast in the SVC in the arm-up group (P < 0.0001).
  
  
  CONCLUSIONS
  Arm position does not affect pulmonary arterial enhancement during CTPA. There was greater central venous compression and more beam-hardening artifact arising from the SVC when the arm was held above the head.
authors.affiliation: Department of Radiology, Waitemata District Health Board, Auckland, New Zealand. marting@u.washington.edu
authors.forename: Martin L D
authors.initials: ML
authors.lastname: Gunn
authors.forename: Adam
authors.initials: A
authors.lastname: Worthington
authors.forename: Damien
authors.initials: D
authors.lastname: Hoon
authors.forename: John Mark
authors.initials: JM
authors.lastname: Barnett
authors.forename: C Craig
authors.initials: CC
authors.lastname: Blackmore
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000792:Angiography / Q000379:methods; D001132:Arm; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008875:Middle Aged; D011187:Posture; D011446:Prospective Studies; D011651:Pulmonary Artery / Q000000981:diagnostic imaging*; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed / Q000379:methods*