CT pulmonary angiography in patients with acute or chronic renal insufficiency: Evaluation of a low dose contrast material protocol

Abstract

Adverse effects of intravenous contrast media (CM) in patients with renal risk factors and acute kidney injury are still controversially discussed. The aim of this study was to investigate whether dual-energy (DE) pulmonary CT angiography (CTPA) in combination with a noise optimized virtual monoenergetic imaging algorithm allows for a reduction of CM. This IRB-approved study comprised 150 patients with suspected pulmonary embolism (78 male; mean age 65 ± 17years). 50 patients with acute/chronic renal failure were examined on a 3^rd generation dual-source CT with an optimized DE CTPA protocol and a low CM injection protocol (5.4 g iodine). 100 further patients were either examined with a standard CTPA protocol or a standard DE CTPA (32 g iodine). For the DE CTPA virtual monoenergetic spectral datasets (40-100 keV) were reconstructed. Main pulmonary arteries at 50 keV and peripheral pulmonary arteries at 40 keV datasets provided the highest contrast-to-noise-ratio (CNR) for both the standard DE CTPA and the optimized protocol, with significantly higher CNR values for the standard DE CTPA protocol (p < 0.05). No pulmonary embolism was missed on the optimized CM protocol. DE CTPA utilizing image reconstruction at 40/50 keV allowed for a reduction of 84% in iodine load while maintaining CNR, which is especially important in patients with acute/chronic renal failure.

Figure 1

Simplified image reconstruction work flow of the monoenergetic reconstruction algorithm. A frequency-split technique is used which decomposes both the low keV images (in which iodine pixels have a high contrast to the surrounding tissue, typically at 40 keV) and images at higher keV (in which surrounding tissue has low image noise, typically at approximately 70 keV) into two sets of sub-images. In a next step, the lower spatial frequency stack at low keV is combined with the high spatial frequency stack at optimal keV from a noise perspective to combine the benefits of both images stacks.

Figure 2

73-year-old woman with a peripheral pulmonary embolism (white arrows). Axial slices of main pulmonary arteries of a low contrast media dual-energy CTPA: (A) mixed 0.8-weighted virtual polyenergetic spectral (VPS) image, and virtual monoenergetic spectral (VMS) images at a level of 40 keV (B), 50 keV (C), 60 keV (D), 70 keV (E), 80 keV (F), 90 keV (G) and 100 keV (H).

Figure 3

Box- and Whisker-Plots with values for attenuation (A,B) and contrast-to-noise-ratio (CNR; C,D) in the main pulmonary arteries (PA, A,C) and the peripheral PA (B,D) of a standard CTPA protocol, virtual polyenergetic spectral datasets (VPS) and virtual monochromatic spectral (VMS) datasets of a low contrast media dual-energy CTPA at nine-teen different energy levels.

Figure 4

62-year-old woman with suspected pulmonary embolism. Axial slices of peripheral pulmonary arteries of a low contrast media dual-energy CTPA: (A) mixed 0.8-weighted virtual polyenergetic spectral (VPS) image, and virtual monoenergetic spectral (VMS) images at a level of 40 keV (B), 50 keV (C), 60 keV (D), 70 keV (E), 80 keV (F), 90 keV (G) and 100 keV (H). The VMS image at 50 keV displays superior subjective image quality when compared to VPS image.