Spectral CT of carotid atherosclerotic plaque: comparison with histology.

OBJECTIVE: To distinguish components of vulnerable atherosclerotic plaque by imaging their energy response using spectral CT and comparing images with histology. METHODS: After spectroscopic calibration using phantoms of plaque surrogates, excised human carotid atherosclerotic plaques were imaged using MARS CT using a photon-processing detector with a silicon sensor layer and microfocus X-ray tube (50 kVp, 0.5 mA) at 38-µm voxel size. The plaques were imaged, sectioned and re-imaged using four threshold energies: 10, 16, 22 and 28 keV; then sequentially stained with modified Von Kossa, Perl's Prussian blue and Oil-Red O, and photographed. Relative Hounsfield units across the energies were entered into a linear algebraic material decomposition model to identify the unknown plaque components. RESULTS: Lipid, calcium, iron and water-like components of plaque have distinguishable energy responses to X-ray, visible on spectral CT images. CT images of the plaque surface correlated very well with histological photographs. Calcium deposits (>1,000 µm) in plaque are larger than iron deposits (<100 µm), but could not be distinguished from each other within the same voxel using the energy range available. CONCLUSIONS: Spectral CT displays energy information in image form at high spatial resolution, enhancing the intrinsic contrast of lipid, calcium and iron within atheroma. KEY POINTS: Spectral computed tomography offers new insights into tissue characterisation. Components of vulnerable atherosclerotic plaque are spectrally distinct with intrinsic contrast. Spectral CT of excised atherosclerotic plaques can display iron, calcium and lipid. Calcium deposits are larger than iron deposits in atheroma. Spectral CT may help in the non-invasive detection of vulnerable plaques.

Age-specific incidence of neoplasms in untreated NZR/Gd rats: an inbred strain with cardiovascular tumours and liver glycogen storage disease.

NZR/Gd is a new inbred strain of albino rats subject to epithelial mesotheliomas of the heart and also to hepatic glycogen storage disease. The age-specific incidences of neoplasms in 650 untreated NZR rats are tabulated by sex and histopathologic type. In males the most common neoplasms were artio-caval mesotheliomas (12 per cent.) and lung adenomas (10 per cent.), while in females most were pituitary adenomas (23 per cent.), lung adenomas (10 per cent.) or tumours of breast (7 per cent.), heart (4 per cent.) or liver or uterine cervix (3 per cent.). Uncommon tumours (less than 2 per cent.) were pancreas islet cell adenomas, lymphoma, hemangioma, fibroma or tumours of kidney, ovary or bile ducts. The detailed histopathology of the artio-caval tumours reported earlier was confirmed, but it now appears there is a male preponderance (4 : 1), and larger tumours showed their malignancy by invasion of adjacent structures and occasionally by distant metastasis. In males the primary site was evenly divided between right atrium and inferior vena cava. Metastasis of tumours of all types was uncommon, but multiple primary tumours were frequently found, especially in the endocrine system of female rats. Almost one-third of the tumours were associated with at least one other neoplasm arising in a different tissue. Overall tumour statistics in NZR/Gd rats were quite similar to other inbred strains for which quantitative reports are available, and the virtual absence of other diseases and long life-span (up to 1250 days) indicated no serious effect of the hepatic glycogen storage disease on survival. The NZR rats seem to be unique in producing atrio-caval mesotheliomas, and they have a much higher incidence of alveolar lung adenomas (10 per cent.) tham other reported strains.