Purpose: The aim of this phantom study was to evaluate the feasibility
of 80 kVp protocols for pulmonary CT-angiography using 300 and
400 mgI/mL contrast media in various patient sizes.
Materials and methods: The segmental pulmonary arteries were
simulated by plastic tubes filled with 1:30 diluted solutions of 300
and 400 mgI/mL contrast media in a chest phantom mimicking thick,
intermediate and thin patients. Volume scanning was done with a CT
scanner at 80, 100, 120 and 140 kVp. Contrast-to-noise ratios (CNR)
for both contrast media were evaluated and compared with the volume
CT dose index (CTDIvol). Figure of merit (FOM), calculated as
CNR2/CTDIvol, was used to quantify image quality improvement per
exposure risk to the patient.
Results: Exposure was reduced by 44% in the thin phantom with the
use of 80 instead of 140 kVp without deterioration of CNR. FOM
correlated with kVp in the thin phantom (r= -.897- -.999; p <.05) but
not in the intermediate and thick phantoms (p = 0.09- 0.71). Compared
to the 300 mgI/mL concentration, the same CNR for 400 mgI/mL
contrast medium was achieved at a lower CTDIvol by 18 to 40%.
Conclusion: Low kVp protocols for pulmonary embolism are potentially
advantageous especially in thin and, to a lesser extent, in intermediate
patients. The use of 80 kVp in obese patients may be problematic
due to the limitation of the tube current available, reduced
CNR and high skin dose. The high CNR of the 400 mgI/mL contrast
medium together with lower tube energy and/or current can be utilized
for exposure reduction.