Pulmonary embolism on suboptimal CTPA (spectral low monoE)

Case contributed by Craig Hacking
Diagnosis certain


Shortness of breath on exertion. Swollen leg. On OCP, morbidly obese.

Patient Data

Age: 40 years
Gender: Female

The scan is of suboptimal diagnostic quality and is limited by the patient's body habitus.

Occlusive filling defects are identified on the low monoE recons in multiple segmental right lower lobe pulmonary arteries. No signs of right ventricular strain. RV/LV ratio is 0.8 (normal is <1.0). No dilation of the main pulmonary artery. The heart and mediastinal structures are normal.

Reduced lung volumes with mild dependent atelectasis. No pleural effusion or pneumothorax.

The partially imaged spleen appears enlarged, measuring 166 mm in AP length. No mass in the lower neck. Bones and soft tissues are normal.


Segmental pulmonary emboli within the right lower lobe. No evidence of right heart strain.

Case Discussion

Case example of positive CTPA with a dual-layer spectral CT:

  • the low monoenergetic (monoE, 45 keV) recons are used to provide an iodine boost to the pulmonary arteries, good if there is suboptimal contrast opacification as in this case.
  • the Z effective (Zeff) recons provides a map of perfusion which details the presence of contrast in the lung, good to identify perfusion defects that may be due to subtle PEs.

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