MAIN APPLICATIONS IN EMERGENCY RADIOLOGY
Stroke and intracranial hemorrhage
In stroke patients, distinguish intracranial hemorrhage from contrast media staining early after recanalization treatment could be very complicated as they both appear as a hyperdensity area within the affected parenchyma. This distinction is of great importance when the decision to continue or initiate antiplatelet or anticoagulation therapy is being considered. DECT allows quantifying blood and iodine in VCN and iodine maps to differentiate the hyperdensities lesions on conventional CT [3].
In non-traumatic intracranial hemorrhage, an underlying lesion may be masked by the bleeding. VCN and iodine maps help to detect enhancing structures responsible for acute hemorrhage [4].
Many other neuroradiologic applications of DECT have been reported, which can be used as a complement to these previous two. These include bone subtraction to improve vessel visualization, carotid plaque characterization, and beam-hardening artifact reduction (especially in the posterior cranial fossa), among others.
Acute pulmonary embolism
DECT allows studying simultaneously arterial filling defects (thrombus) and parenchymal perfusion defects:
- Low-energy VME images provide higher sensitivity to detect small peripheral endoluminal clots as they increased vascular enhancement. In conventional studies, emboli in subsegmental arteries may go unnoticed. With DECT studies its detection increases, being important for its need for treatment to prevent chronic thromboembolic disease and the development of pulmonary hypertension.
- Also, a dual-energy lung parenchyma map, as almost an equivalent of lung perfusion, is used to detect iodine-defected triangular lesions that are not apparent on conventional CT [5]. It allows studying the impact of the thrombus on lung perfusion as well as quantifying its severity.
Bowel ischemia
Segmental hypoenhancement or non-enhancement of the bowel wall is one of the most reliable signs for detecting nonviable ischemic segments, but these are often very difficult to identify. Dual-energy studies improve the detection of subtle diminished bowel enhancement that is easily misdiagnosed on conventional CT. VMI and Iodine overlay maps can assess decreased or absent perfusion improving sensitivity and specificity of diagnosing bowel ischemia.
Also, in later stages of mesenteric ischemia, bowel hypoperfusion can be associated with submucosal hemorrhage. VNC images can identify increased attenuation of the wall due to intramural hemorrhage that could mask decreased iodine uptake [6].
Acute pancreatitis
VME and Iodine overlay images can increase the attenuation difference between normal and hypoenhanced parenchyma improving the detection of pancreatic ischemia and necrosis [7].
Also, VMI is helpful in identification noncalcified (cholesterol) gallstones in the biliary system [8]. Pancreatic and peripancreatic collections can also be evaluated with DECT to assess the presence of hematoma and preserved normal parenchyma.
Urolithiasis
DECT provides the possibility to determine the chemical composition of urinary calculi [9]. It helps to characterized and differentiate uric-acid stones, which are treatable with urine alkalization, from non-uric-acid stones (mainly calcium oxalate), that may be treated with more invasive procedures.
Active bleeding
VNC images enable to differentiate bleeding from any other preexisting hyperattenuating materials and eliminates the need for a true unenhanced acquisition. Low energy VME and iodine maps can accurately detect very subtle iodine extravasation improving the active bleeding diagnosis [10].
OTHER APPLICATIONS
Inflammatory processes
Iodine overlay maps improve detection of hyperemia as a marker of activity in many abdominal acute conditions like Crohn's disease [11]. Also, iodine maps help to identify complications that may be very subtle in conventional studies as mural hypoperfusion in gangrenous appendicitis or cholecystitis [12-13].
Trauma
Low VME images can help to characterize small organ lacerations [14]. The detection of bone marrow edema detects subtle fractures but with important surgical relevance and differentiates acute from chronic fractures (especially in vertebral compression fractures).
Vascular
Bone-subtraction images remove calcified plaques in arteries and Low energy VME images improve vessel opacification. Also, VNC maps quickly identify hematoma or bleeding with no need for a true unenhanced acquisition. DECT has also proven useful in complications of abdominal aneurysms, like infection or endoleaks within endovascular repairs [15].
ADVANTAGES AND DISADVANTAGES
Advantages:
- Increased diagnostic sensitivity; detection of anomalies in the absence of morphological or densitometric alterations.
- Reduction of radiation dose through VCN images by skipping the true non contrast acquisition.
- Low VME images increase the contrast resolution within the vessels, allowing the use of fewer doses of iv contrast.
- High VME images reduce the metallic artifact with the presence of prosthetic material and the artifact due to beam hardening.
Disadvantages:
- Inferior image quality to that of a single energy.
- Increase in the number of images and the weight of the studies for computer systems.
- High cost of equipment.
- Greater interpretive complexity for the radiologist.
- Reduced spectral separation of elements (iodine, calcium, uric acid).
- Presence of artifacts, especially in patients with high BMI.