Our routine head dual-energy CT (DECT) protocol includes a set of mixed 120-kV images that mirror typical single-energy CT (SECT) images and a second set of 190-keV (virtual high-energy monochromatic) images that are adopted due to their greater sensitivity in detecting traumatic intracranial hemorrhages.1 We arrived at this topic after observing higher hemorrhagic contusion volumes on follow-up 120-kV images compared with 190-keV images. This discrepancy was seen in patients after admission contrast-enhanced whole-body CT imaging, which is widely used for the work-up of patients with blunt polytrauma. We demonstrated that the discrepancy in measured volumes is caused by iodinated contrast leak, likely through the dysfunctional and fragmented microvasculature in the penumbra of the contusions.
The concept of progressive microvascular failure associated with contusions has been demonstrated, where the energy deposited in the penumbra (nonhemorrhagic parenchyma around the contusion) activates mechanosensitive molecular processes, upregulating sulfonylurea receptor 1, which has been implicated in delayed microvascular dysfunction and fragmentation.2 The high attenuation of the leaked iodine in the penumbra resembles that of hematoma on 120-kV images, resulting in volume overestimation. The attenuation contribution of iodine is negligible at the higher end of the monochromatic energy spectrum. Hence, 190-keV or virtual noncontrast images demonstrate the actual hematoma size.
We described the enhancing penumbra as “pseudohematoma.” With the mean ratio of pseudohematoma to true hematoma of 0.29 or 29%, we found that hemorrhagic progression of contusions would be overestimated in approximately 30% of patients. Because various studies have demonstrated iodine leak in primary intracerebral hemorrhages, the possibility of volume overestimation should also be considered in follow-up SECT studies performed after CT angiography of the brain.
Using the same DECT principle, we realized the feasibility of quantifying the amount of iodine leak in contusions and also the volume of pseudohematoma, which otherwise are not possible with SECT. We recently finished conducting follow-up studies and found a strong predictive capability of iodine quantity in contusions when determining in-hospital mortality, Rancho Los Amigos Scale scores, and disability rating scores at hospital discharge. The predictive ability can be explained, not only by the ability to account for the volume of the epicenter and penumbra (pseudohematoma), but also for the magnitude of capillary dysfunction and fragmentation.