Cardiac tumor

Benefits or pitfalls of dual-energy CT

61-year-old female, BMI 28.5 kg/m,2 HR 72-82 bpm presented with episodic chest pain with night sweats for 4 months, fever for 2 weeks. No cardiac structural change or vascular modification detected on echocardiography.

Besides providing information about coronary artery anatomy, CCTA spectral imaging can also be used to determine the different tissue components of the space-occupying lesions and to determine pericardial metastasis.

Key images

Findings

Axial images, volume rendered (VR) images

On conventional CT images accurate analysis of the mediastinal space-occupying lesion was not obvious. The measured CT value was 60.1 HU at the periphery (S1) and 30.5 HU in the central part of the lesion (S3). On monoenergetic 50 keV images, the peripheral areas appeared more dense with a CT value 117 HU, while the CT value of the central portion appeared less dense with a density of only 13.2 HU. Iodine density images demonstrated iodine uptake of the peripheral areas of the lesion (0.8 mg/ml), while the central area of the lesion showed no blood supply (0 mg/ml). Z effective images also showed a difference between effective atomic numbers of the periphery compared to the central area (7.9 and 7.1 respectively). However, no difference in iodine content or effective atomic numbers was found between peripheral areas of the space occupying lesion and the thickened pericardium (S2, see Table 1).

In spectral analysis, the spectral attenuation curves, Z effective map, histogram, monoenergetic 50 keV CT value, and scatter plot of S1 and S2 were basically similar, suggesting that they were homologous. The central area of the lesion (S3) was completely different from S1 and S2, suggesting they were non-homologous.

Discussion

In spectral analysis, the distribution patterns of spectral curves, histograms, and scatter plots of various tissue components are different, and this can help to determine the tissue homology.

Conventional CCTA image showed the details of different branches of coronary arteries. The position of RCA, right atrium and right ventricle were changed due to the space occupying lesion. The lumen of the RCA was also narrowed (red arrow). VR image showed the occupying lesion in the mediastinum (blue color). Images 4a-d showed the axial views of the heart. The heterogeneous low attenuation lesion was adjacent to the ascending aorta and the pulmonary artery trunk. Irregularly thickened pericardium was also noted.

Monoenergetic 50 keV

Iodine density image

Z effective image

Monoenergetic 50 keV, Iodine density, Z effective images showed that the periphery of the lesion was solid and enhancing; however, no enhancement was found in the central area. Quantitative measurements of the solid peripheral components of the lesion, thickened pericardium, and the central area of the lesion were shown as follows:

Spectral attenuation curves: S1 and S2 are two similar curves, indicating that S1 and S2 are homologous.

S3 is different from S1 and S2, which means that they are non-homologous.

Histogram Z effective: Histogram of S1 and S2 are similar, which means that they are homologous. S3 is non-homologous with S1 and S2.

Z effective/monoenergetic 50 keV scatter plot showed that the distribution of S1 and S2 are similar, which means they are homologous. However, the distribution of S3 is different from S1 and S2, which means they are non-homologous.