Spiral CT quantification of aorto-renal calcification and its use in the detection of atheromatous renal artery stenosis: A study in 42 patients

Does the Location of Fat Accumulation Affect the Degree of Aortic and Renal Arterial Calcification?

The vascular risk associated with obesity is particularly associated with visceral adiposity, but recent studies suggest that ectopic fat might contribute to the increased risk of atherosclerotic cardiovascular disease. Our study aimed to explore the connection between arterial calcification of the aorta and renal arteries with visceral and ectopic fat deposits, including liver, pancreatic, and renal sinus fat. Retrospective analysis of thoracoabdominal multi-slice computed tomography (MSCT) scans of 302 patients included measurements of calcification volumes of thoracic and abdominal aorta, and of both renal arteries. On the same scans, the visceral fat volume, liver-to-spleen ratio, pancreatic-to-spleen ratio, and both renal sinus fat areas were retrieved. Logistic regression showed the left kidney sinus fat area to be the most strongly associated with calcifications in the aorta and both renal arteries (coef. from 0.578 to 0.913, p < 0.05). The visceral fat positively predicted aortic calcification (coef. = 0.462, p = 0.008), and on the contrary, the pancreatic fat accumulation even showed protective effects on thoracic and abdominal aorta calcification (coef. = -0.611 and -0.761, p < 0.001, respectively). The results suggest that ectopic fat locations differently impact the calcification of arteries, which should be further explored.

Renal artery calcification and mortality among clinically asymptomatic adults

OBJECTIVES

The goal of this study was to assess the associations between renal artery calcification (RAC) and mortality in a healthy outpatient cohort with no known cardiovascular disease (CVD).

BACKGROUND

Studies in individuals with known diabetes and kidney disease have suggested that RAC confers additional mortality risk independent of coronary artery calcification, but this hypothesis has not been explored in healthier populations.

METHODS

RAC was assessed by using computed tomography scan in healthy outpatients with no known CVD. Cox proportional hazards models were used to examine the association of RAC with mortality.

RESULTS

The mean age of participants was 57 years; 42.6% were women. RAC was present in 622 (14%) of 4,450 participants. Over a median follow-up of 8.2 years, there were 178 deaths. After adjustment for age, sex, diabetes, smoking, cholesterol, and family history of CVD, the presence of RAC conferred a >60% increased hazard for all-cause mortality (hazard ratio [HR]: 1.63 [95% confidence interval (CI): 1.17 to 2.29]). Adjustment for calcification in other vascular beds attenuated this association (HR: 1.40 [95% CI: 0.99 to 1.97]). Adjustment for hypertension, a potential mediator of the association, did not substantially change the results (HR: 1.44 [95% CI: 1.02 to 2.03]). Adding RAC to a model including Framingham risk and coronary artery calcification improved the predictive ability of the model, from 0.73 to 0.77 (p = 0.0002); the net reclassification index was 14.4% for the addition of RAC. Results for cardiovascular mortality were not significant and were limited by the small number of cardiovascular deaths.

CONCLUSIONS

RAC was associated with an increased risk of subsequent all-cause mortality in healthy outpatient individuals, independent of traditional cardiac risk factors. The risk was modestly attenuated by adjustment for vascular calcification in other vascular beds, suggesting partial confounding by systemic calcified atherosclerosis. The effect did not seem to be mediated by hypertension.

Segmentation of the outer vessel wall of the common carotid artery in CTA

A novel method is presented for carotid artery vessel wall segmentation in computed tomography angiography (CTA) data. First the carotid lumen is semi-automatically segmented using a level set approach initialized with three seed points. Subsequently, calcium regions located within the vessel wall are automatically detected and classified using multiple features in a GentleBoost framework. Calcium regions segmentation is used to improve localization of the outer vessel wall because it is an easier task than direct outer vessel wall segmentation. In a third step, pixels outside the lumen area are classified as vessel wall or background, using the same GentleBoost framework with a different set of image features. Finally, a 2-D ellipse shape deformable model is fitted to a cost image derived from both the calcium and vessel wall classifications. The method has been validated on a dataset of 60 CTA images. The experimental results show that the accuracy of the method is comparable to the interobserver variability.

Incidental renal artery calcifications: a study of 350 consecutive abdominal computed tomography scans

BACKGROUND

Calcifications in arteries are thought to represent atherosclerosis.

METHODS

Consecutive abdominal tomographic scans performed during a 4-month period were evaluated and assessed for renal artery calcifications (RAC). Scans that showed calcifications were evaluated for renal artery narrowing and for various characteristics of the atherosclerotic plaque.

RESULTS

Of 350 consecutive examinees, 43% were men, 40% had hypertension and 38% had hypercholesterolaemia. The age was 61 +/- 13 years. Aortic calcifications were found in 54% and RAC in 102 (29%), of whom 53 had bilateral calcifications. Subjects with RAC were older, 72 +/- 6 versus 55 +/- 12 years. Adjusted odds ratios of RAC were 2.2 (95% CI 1.1-4.6) for male gender, 2.4 (1.2-4.8) for hypertension and 2.9 (1.4-5.8) for hypercholesterolaemia, whereas family history of hypertension was protective with 0.5 (0.3-0.9). All patients with calcified renal arteries had aortic calcifications, versus 35% of those without RAC. A significant correlation was found between the severity of calcifications and the degree of renal artery narrowing (r = 0.7), and also between the presence of bilateral calcifications and a high-grade narrowing.

CONCLUSIONS

RAC strongly relates to atherosclerosis. Calcifications and artery narrowing may have a role in the pathogenesis of hypertension. Bilateral calcifications suggest atherosclerotic renal artery stenosis.

Automatic detection of calcifications in the aorta from CT scans of the abdomen. 3D computer-aided diagnosis

RATIONALE AND OBJECTIVES

Automated detection and quantification of arterial calcifications can facilitate epidemiologic research and, eventually, the use of full-body calcium scoring in clinical practice. An automatic computerized method to detect calcifications in CT scans is presented.

MATERIALS AND METHODS

Forty abdominal CT scans have been randomly selected from clinical practice. They all contained contrast material and belonged to one of four categories: containing "no," "small," "moderate," or "large" amounts of arterial calcification. There were ten scans in each category. The experiments were restricted to the vertical range from the point where the superior mesenteric artery branches off of the descending aorta until the first bifurcation of the iliac arteries. The automatic method starts by extracting all connected objects above 220 Hounsfield units (HU) from the scan. These objects include all calcifications, as well as bony structures and contrast material. To distinguish calcifications from non-calcifications, a number of features are calculated for each object. These features are based on the object's size, location, shape characteristics, and surrounding structures. Subsequently a classification of each object is performed in two stages. First the probability that an object represents a calcification is computed assuming a multivariate Gaussian distribution for the calcifications. Objects with low probability are discarded. The remaining objects are then classified into calcifications and non-calcifications using a 5-nearest-neighbor classifier and sequential forward feature selection. Based on the total volume of calcifications determined by the system, the scan is assigned to one of the four categories mentioned above.

RESULTS

The 40 scans contained a total of 249 calcifications as determined by a human observer. The method detected 209 calcifications (sensitivity 83.9%) at the expense of on average 1.0 false-positive object per scan. The correct category label was assigned to 30 scans and only 2 scans were off by more than one category. Most incorrect classifications can be attributed to the presence of contrast material in the scans.

CONCLUSION

It is possible to identify the majority of arterial calcifications in abdominal CT scans in a completely automatic fashion with few false positive objects, even if the scans contain contrast material.

Osteoprotegerin plasma concentrations correlate with severity of peripheral artery disease

OBJECTIVE

Osteoprotegerin (OPG), a member of the tumor necrosis factor receptor family, is involved in the process of bone turnover and also in the pathogenesis of osteoporosis and premature calcification of the vascular system. In the present study on patients with peripheral artery disease (PAD), we correlated plasma OPG concentrations with severity of disease and the presence of cardiovascular risk factors.

PATIENTS AND METHODS

Sixty-seven consecutive inpatients (26 females; mean age 70 years (S.D.: 12), undergoing percutaneous transluminal angioplasty (PTA) because of advanced symptomatic PAD of the lower extremities were studied. Severity grade of disease (clinical stage after "Fontaine", functional measurements in terms of the ankle brachial index (ABI) and "Bollinger score" of angiographies), biochemical parameters and a detailed cardiovascular risk profile were documented. Fasting plasma concentrations of OPG were measured by a commercial sandwich enzyme immunoassay.

MAIN RESULTS

The mean plasma concentrations of OPG were 5.3 pmol/l (S.D.: 3.3). Plasma OPG concentrations in subjects with PAD, clinical stages III-IV (n=15) were 7.9 pmol/l (S.D.: 5.3) and were significantly higher than in patients without ischemic ulcerations (n=52; 4.6 pmol/l; S.D.: 2.0; p<0.01). The mean value of Bollinger score was 29.1 (S.D.: 19.8). OPG was positively correlated with Bollinger score of disease (r=0.31; p<0.02), age (r=0.58; p<0.01) and creatinine-values (r=0.32; p<0.01) and negatively correlated with ABI (r=-0.39; p<0.03).

CONCLUSION

In patients with PAD, plasma OPG concentrations were significantly higher in subjects with ischemic ulcerations than in those without and were positively correlated with higher severity grade of disease, age and creatinine-values. Further studies are required to analyze the role of OPG as a diagnostic marker for severity of atherosclerotic disease and to assess a possible therapeutic potential as "vasculoprotegerin".

Micro-CT of Carotid Arteries: A Tool for Experimental Studies

Micro-computed tomography (micro-CT) is a high-resolution, non-destructive tool for two- and three-dimensional imaging and quantification. The ability of this technique to assess atherosclerosis of the carotid artery was evaluated in three human cadaver samples based on the original axial acquisitions, multiplanar reconstructions and volume rendering techniques. Quantitative analysis included the calculation of: (1) the original lumen perimeter, original lumen area, plaque area, residual lumen area, calcified area and gross sectional area reduction of the vascular lumen from two-dimensional slices; (2) the total tissue volume, soft tissue volume and calcified tissue volume from the three-dimensional data set. This preliminary study demonstrates the potential of micro-CT as a supplementary method for the two- and three-dimensional ex vivo evaluation of carotid atherosclerosis.

RANK ligand and osteoprotegerin: paracrine regulators of bone metabolism and vascular function

In 1997, investigators isolated a secreted glycoprotein that blocked osteoclast differentiation from precursor cells, prevented osteoporosis (decreased bone mass) when administered to ovariectomized rats, and resulted in osteopetrosis (increased bone mass) when overexpressed in transgenic mice. Since then, the isolation and characterization of the protein named osteoprotegerin (OPG) has stimulated much work in the fields of endocrinology, rheumatology, and immunology. OPG functions as a soluble decoy receptor for receptor activator of nuclear factor-kappaB ligand (RANKL, or OPG ligand) and shares homologies with other members of the tumor necrosis factor receptor superfamily. OPG acts by competing with the receptor activator of nuclear factor-kappaB, which is expressed on osteoclasts and dendritic cells for specifically binding to RANKL. RANKL is crucially involved in osteoclast functions and bone remodeling as well as immune cell cross-talks, dendritic cell survival, and lymph node organogenesis. More recently, emerging evidence from in vitro studies and mouse genetics attributed OPG an important role in vascular biology. In fact, OPG could represent the long sought-after molecular link between arterial calcification and bone resorption, which underlies the clinical coincidence of vascular disease and osteoporosis, which are most prevalent in postmenopausal women and elderly people.