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Contrast Opacification Using a Reduced Volume of Iodinated Contrast Material and Low Peak Kilovoltage in Pulmonary CT Angiography: Objective and Subjective Evaluation

¹ Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, 15 Francis St., Boston, MA 02115.
² Applied Imaging Science Laboratory, Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
³ Department of Biostatistics, Harvard School of Public Health, Boston, MA.

OBJECTIVE. The purpose of our study was to evaluate whether a reduced volume of iodinated contrast material for pulmonary CT angiography (CTA) using a low peak kilovoltage (kVp) technique yields equivalent opacification in all vessels.

MATERIALS AND METHODS. Four hundred fifty-two consecutive pulmonary CTA patients (265 women and 187 men; age range, 18–91 years; mean age, 56.2 years) were retrospectively evaluated. Patients were grouped into those receiving 125 mL (n = 229) and 75 mL (n = 223) of 370 mg I/mL iodinated contrast material. Low kVp was used in all patients. Hounsfield units were measured at lobar, posterobasal segment, posterobasal ramus, and medial basal subsegmental ramus in the left lower lobe. Three thoracic radiologists blinded to contrast dose independently and randomly evaluated the quality of enhancement using a 3-point scale at the same levels. The two-sample Student's t test was used to compare contrast opacification between groups; Spearman's correlation and the C-statistic were used to assess objective and subjective measurements. Interreader agreement was measured using Kendall's coefficient.

RESULTS. Mean contrast opacification differences between 125 mL versus 75 mL were not statistically significant (p > 0.21) at the lobar, segmental, and posterior basal rami, although the mean trended (p = 0.07) toward higher opacification of the medial basal ramus among 75 mL patients. Across all four pulmonary artery segments, there was good concordance between subjective and objective measurements, significantly higher than the null value of 0.50 (p > 0.05). For subsegmental arteries, concordance between objective and subjective measures was greater for the 75 mL group (p < 0.05). There was good interreader concordance, with a concordance coefficient of 0.70 (95% CI, 0.66–0.74).

CONCLUSION. Both objective and subjective measures of contrast opacification support a reduction from 125 to 75 mL of contrast medium required for pulmonary CTA.

Keywords: pulmonary CT angiography • pulmonary embolism

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