Individually tailored contrast enhancement in CT pulmonary angiography

Abstract

Objective: The purpose was to evaluate individually shaped contrast media (CM) delivery in CT pulmonary angiography (CTPA) for suspected pulmonary embolism (PE).

Methods: 100 consecutive emergency patients with clinical suspicion of PE were evaluated. High-pitch CTPA was performed on a second-generation dual-source CT using the following parameters: 100 kV, 200-250 mAsref, rotation time 0.28 s, 128 × 0.6 mm col. and image reconstruction 1.0/0.8 mm (B30f). Group 1 (n = 50) then received a fixed CM bolus (300 = mgI ml(-1), volume = 90 ml and flow rate = 6 ml s(-1)); Group 2 (n = 50) received a body weight-adapted CM bolus determined by dedicated contrast injection software. For analysis, groups were further subdivided into low-weight (40-75 kg) and high-weight (76-117 kg) groups. Technical image quality was graded using a four-point Likert scale (1 = non-diagnostic; 2 = diagnostic; 3 = good and 4 = excellent image quality) at the level of the pulmonary trunk and pulmonary arteries. Objective image quality analysis was performed by measuring contrast enhancement in Hounsfield units (HU) at the same levels. Attenuation levels > 180 HU were considered diagnostic.

Results: All examinations were graded as diagnostic at each level. The individual minimum pulmonary attenuation was 184 and 270 HU for Group 1 and 2, respectively. Mean attenuation was as follows: Group 1: 475 ± 105 HU (40-75 kg) and 402 ± 115 HU (76-117 kg), p < 0.03. Group 2: 424 ± 76 HU (40-75 kg) and 418 ± 100 HU (76-117 kg), p = 0.8. For Group 2, CM volumes were: 55 ± 5 ml (40-75 kg) and 66 ± 5 ml (76-117 kg), leading to 16-51% CM reduction.

Conclusion: Even under emergency conditions, individualized CM protocols can provide diagnostic and robust image quality in CTPA for PE with a substantial reduction of CM volume for lower weight patients, compared with a fixed CM protocol.

Advances in knowledge: CM volume can substantially be reduced by using individualized CM protocols in CT angiography for PE without compromising the diagnostic image quality.

Figures

Figure 1.

Images show the regions of interest for attenuation measurement at the level of the pulmonary trunk (top left), right pulmonary artery (right top), left pulmonary artery (left bottom) and paraspinal muscle (right bottom).

Figure 2.

Scatter dot shows all patients by weight in kilograms with their corresponding received contrast media (CM) volume. All Group 1 patients received 90 ml CM. All patients in Group 2 received less CM (range: 44–76 ml), and for low-weight patients, the CM dose reduction was most pronounced.

Figure 3.

This bar graph shows the mean iodine per kilogram load for the low-weight and high-weight patients in Group 1 (left) and Group 2 (right). The iodine per kilogram is reduced for Group 2 both in low- and high-weight categories.

Figure 4.

Error bars show the mean attenuation and 95% confidence intervals for both injection protocols and weight groups. The intervals define the values that are most plausible for the mean of a greater population. A decreased mean attenuation was seen for the higher weight group within the standard protocol (left) and similar mean attenuation was seen for both weight groups within the individualized protocol (right). HU, Hounsfield units.

Figure 5.

Images show contrast enhancement at the level of the pulmonary trunk (W–C levels: 600–125). Left images show two patients from Group 1 including low weight (top) and high weight (bottom) with attenuation values of 532 and 362 HU, respectively. Right images show two patients from Group 2 including low weight (top) and high weight (bottom) with attenuation values of 555 and 520 HU, respectively. Both bottom images also show right lobar pulmonary embolism.