Superior vena cava imaging

Discussion

Dialysis tube placement after surgery, CT re-examination before extubation to exclude thrombus.

Spectral virtual low monoenergetic images increased confidence of evaluation of superior vena cava.

Axial images, multiplanar reformations (MPR)

Enhancement of the superior vena cava in conventional images is not suited for diagnosis. It is impossible to assess the presence of thrombus. Spectral virtual monoenergetic images at 40 keV improved attenuation of iodine and depiction of the superior vena cava. Spectral low keV virtual monoenergetic images, iodine density images, and effective atomic number images are useful for the detection of small thrombus attached to the superior vena cava cannula.

Imaging of the superior vena cava requires the injection of a larger dose of contrast agent in order to achieve satisfactory enhancement. In addition, the conventional helical scan is susceptible to heart and blood vessel pulsation artifacts. The application of prospective ECG-gating scan helps in reducing the radiation dose and avoiding pulsation artifacts. In addition, the spectral virtual low monoenergetic imaging can reduce the amount of contrast agent and improve the detection of small hidden lesions.

Conventional image: Attenuation of the superior vena cava lumen is 74.8 HU, and superior vena cava enhancement is insufficient to rule out the presence of thrombus.

Spectral virtual monoenergetic 40 keV image: The CT value of the superior vena cava lumen increased to 164.9 HU, and the superior vena cava is now evaluable. The arrow indicates potential filling defect, suggesting small thrombus.

Injection protocol: Contrast concentration: 370 mgI/mL, Contrast volume 30 mL, flow rate 3 mL/s. The total amount of saline is 40 mL, and the flow rate is 4 mL/s

Scanning protocol: ECG-gating, step-and-shoot, delayed acquisition 60s after contrast injection

Conventional image: The CT value of the superior vena cava lumen was measured to be 74.8 HU.

Spectral virtual monoenergetic 40 keV image: The CT value of the superior vena cava lumen was increased to 164.9 HU. The superior vena cava is now sufficiently enhanced for evaluation. The red circle showed a lowdensity filling defect indicating a suspected small thrombus formation.

Iodine density image: The superior vena cava lumen is filled with iodinecontaining blood, and the red arrow indicates a small area free of iodine. The measured iodine density is 0 mg/mL, suggesting the presence of a small thrombus formation. The blue arrow indicates the superior vena cava cannula (dialysis tube). The yellow arrow shows a little local iodine retention.

Z effective image: The normal superior vena cava lumen exhibited an effective atomic number of 8.5 (light blue color). The red arrow indicates the location of the thrombus on the dialysis cannula with an effective atomic value of 7.3 (orange color).

History

Benefits or pitfalls of dual-energy CT

Key images

Findings