[Dual-energy computed tomography: what is it useful for?]

Ultralow-dose CT of the petrous bone using iterative reconstruction technique, tin filter and high resolution detectors allows an adequate assessment of the petrous bone structures

OBJECTIVES

To assess image quality and radiation dose in computed tomography (CT) studies of the petrous bone done with a scanner using a tin filter, high-resolution detectors, and iterative reconstruction, and to compare versus in studies done with another scanner without a tin filter using filtered back projection reconstruction.

MATERIAL AND METHODS

Thirty two patients (group 1) were acquired with an ultra-low dose CT (32-MDCT, 130kV, tin filter and iterative reconstruction). Images and radiation doses were compared to 36 patients (group 2) acquired in a 16-MDCT (120kV and filtered back-projection). Muscle density, bone density, and background noise were measured. Signal-to-noise ratio (SNR) was calculated. To assess image quality, two independent radiologists subjectively evaluated the visualization of the different structures of the middle and inner ear (0=not visualized, 3=perfectly identified and delimited). Interobserver agreement was calculated. Effective dose at different anatomical levels with the dose-length product was recorded.

RESULTS

In the quantitative analysis, there were no significant differences in image noise between the two groups. In the qualitative analysis, a similar or slightly lower subjective score was obtained in the delimitation of different structures of the ossicular chain and cochlea in the 32-MDCT, compared to 16-MDCT, with statistically significant differences. Mean effective dose (±standard deviation) was 0.16±0.04mSv for the 32-MDCT and 1.25±0.30mSv for the 16-MDCT.

CONCLUSIONS

The use of scanners with tin filters, high-resolution detectors, and iterative reconstruction allows to obtain images with adequate quality for the evaluation of the petrous bone structures with ultralow doses of radiation (0.16±0.04mSv).

Ultralow-dose CT of the petrous bone using iterative reconstruction technique, tin filter and high resolution detectors allows an adequate assessment of the petrous bone structures

OBJECTIVES

To assess image quality and radiation dose in computed tomography (CT) studies of the petrous bone done with a scanner using a tin filter, high-resolution detectors, and iterative reconstruction, and to compare versus in studies done with another scanner without a tin filter using filtered back projection reconstruction.

MATERIAL AND METHODS

Thirty two patients (group 1) were acquired with an ultra-low dose CT (32-MDCT, 130 kV, tin filter and iterative reconstruction). Images and radiation doses were compared to 36 patients (group 2) acquired in a 16-MDCT (120 kV and filtered back-projection). Muscle density, bone density, and background noise were measured. Signal-to-noise ratio (SNR) was calculated. To assess image quality, two independent radiologists subjectively evaluated the visualization of the different structures of the middle and inner ear (0 = not visualized, 3 = perfectly identified and delimited). Interobserver agreement was calculated. Effective dose at different anatomical levels with the dose-length product was recorded.

RESULTS

In the quantitative analysis, there were no significant differences in image noise between the two groups. In the qualitative analysis, a similar or slightly lower subjective score was obtained in the delimitation of different structures of the ossicular chain and cochlea in the 32-MDCT, compared to 16-MDCT, with statistically significant differences. Mean effective dose (± standard deviation) was 0.16 ± 0.04 mSv for the 32-MDCT and 1.25 ± 0.30 mSv for the 16-MDCT.

CONCLUSIONS

The use of scanners with tin filters, high-resolution detectors, and iterative reconstruction allows to obtain images with adequate quality for the evaluation of the petrous bone structures with ultralow doses of radiation (0.16±0.04 mSv).

Dual energy CT in the management of antiplatelet therapy in patients with acute ischemic stroke for carotid obstruction

BACKGROUND AND PURPOSE

Acute tandem occlusions often require carotid stenting. Combination of mechanical and pharmacologic therapies in addition to antiplatelet drugs administered to prevent acute stent thrombosis might increase the risk of intracerebral hemorrhage. We present a protocol of antiplatelet regimen based on early post-procedural dual-energy CT (DE-CT).

MATERIAL AND METHODS

Fifty consecutive stroke patients with tandem occlusions treated with acute carotid stenting after intracranial thrombectomy and TICI 2b/3 were reviewed. All patients received intravenous lysine acetylsalicylate during the procedure. Dual (aspirin+clopidogrel with or without clopidogrel load, groups A and B, respectively) or mono (aspirin) antiplatelet regimen (group C) was administered 12-24 h later according to brain DE-CT findings. Carotid ultrasonography was performed at 24 h and before discharge. We evaluated the rate of subsequent symptomatic intracranial hemorrhage (SICH) and acute stent thrombosis in each group.

RESULTS

Between June 2014 and December 2016, 50 patients were included (mean age 66 years, 76% men, baseline NIHSS 16, median time from symptom onset to recanalization 266 min). According to DE-CT, 24 patients were assigned to group A, 19 to group B and 7 to group C (4 of them had SICH at that time). One patient suffered a subsequent SICH (belonging to group B). There was only one stent thrombosis without clinical repercussions in group B.

CONCLUSIONS

DE-CT may contribute to select antiplatelet regimen after acute carotid stenting in tandem occlusions.

Dual-energy computed tomography for the detection of focal liver lesions

OBJECTIVE

To qualitatively and quantitatively explore the spectral study of focal liver lesions, comparing it with the usual polychromatic assessment with single-energy computed tomography.

MATERIAL AND METHODS

We prospectively studied 50 patients with at least one focal liver lesion who were referred for abdominal multidetector computed tomography with intravenous contrast material. The portal phase was acquired with dual energy sources. The density of the lesions and of the surrounding liver parenchyma was measured both in the baseline polychromatic acquisition and in the posterior monochromatic reconstructions at 40 keV, 70 keV, and 140 keV. Spectral curves were traced and the dual-energy indices and contrast-to-noise ratio were calculated. Lastly, the quality of the images and the detectability of the lesions were assessed qualitatively.

RESULTS

Densitometric differences between the different types of lesions (avascular and vascularized) and the liver were greater at low energy levels (left side of the spectral curve) than in the polychromatic evaluation. In the subjective assessment, the 40keV energy level had the greatest lesion detectability.

CONCLUSIONS

Monochromatic spectral study with dual-energy computed tomography provides better lesion detectability at 40keV compared to that provided by the ordinary polychromatic evaluation.

Imaging techniques used in the diagnostic workup of acute venous thromboembolic disease

Early diagnosis is one of the most important factors affecting the prognosis of pulmonary embolism (PE); however, the clinical presentation of PE is often very unspecific and it can simulate other diseases. For these reasons, imaging tests, especially computed tomography angiography (CTA) of the pulmonary arteries, have become the keystone in the diagnostic workup of PE. The wide availability and high diagnostic performance of pulmonary CTA has led to an increase in the number of examinations done and a consequent increase in the population's exposure to radiation and iodinated contrast material. Thus, other techniques such as scintigraphy and venous ultrasonography of the lower limbs, although less accurate, continue to be used in certain circumstances, and optimized protocols have been developed for CTA to reduce the dose of radiation (by decreasing the kilovoltage) and the dose of contrast agents. We describe the technical characteristics and interpretation of the findings for each imaging technique used to diagnose PE and discuss their advantages and limitations; this knowledge will help the best technique to be chosen for each case. Finally, we comment on some data about the increased use of CTA, its clinical repercussions, its "overuse", and doubts about its cost-effectiveness.