Prevalence Of Carotid Artery Calcification Research Articles

Prevalence of carotid artery calcification detected by different dental imaging techniques and their relationship with cardiovascular risk factors, age and gender

BackgroundAtherosclerosis and its secondary diseases display a major threat to patient’s health. Sequelae, like carotid artery calcification (CAC), usually develop over decades and remain asymptomatic for a long time, making preventive measures to reduce mortality and morbidity extremely important. Through panoramic radiography (PR) and cone beam computed tomography (CBCT), dentists may have helpful tools in aiding the holistic care of patients. In this context, the correlation of atherosclerotic risk factors and CAC development have not yet been sufficiently investigated. Thus, the aim of this observational radiological study was to evaluate the diagnostic value of PR compared with CBCT for the detection of CAC in patients older than 60 years. The radiological findings were correlated with gender, age, and cardiac risk factors.MethodsPRs and CBCTs of N = 607 patients were used for the qualitative analysis and compared. Basic patient information such as age, gender, body mass index (BMI), smoking history as well as patient’s detailed medical history, including heart disease and cardiovascular risk factors such as hypercholesterolemia, arterial hypertension and diabetes mellitus type II were documented and their relation to CAC provided by radiological data was estimated in the form of odds ratios (OR), which were calculated using logistic regression models. Proportions of CAC in different risk groups were compared using Fisher’s exact test, the significance level was set to α ≤ 0.05. The interrater reliability of two physicians was estimated using Cohen’s kappa.ResultsWith an accuracy of 90.6%, a sensitivity of 67.5% and a specificity of 99.5% compared to CBCT, PR was a reliable method for the diagnosis of CAC. The overall detection rate for CAC was 27.8% across all age groups. Age (OR: 1.351; p = 0.021), the male sex (OR: 1.645; p = 0.006), arterial hypertension (OR: 2.217; p = < 0.001), heart disease (OR: 1.675; p = 0.006), hypercholesterolemia (OR: 1.904; p = 0.003) and chronic obstructive pulmonary disease (OR: 2.016; p = 0.036) were statistically significant risk factors. When correlated, neither history of stroke nor nicotine abuse showed any statistical significance.ConclusionsDue to the capabilities of PR in the diagnosis of CAC, dentists can play a vital role in the early diagnosis of vascular disease. Awareness should therefore be raised among dentists regarding the detection of CAC in patients over 60 years of age, with a particular focus on those with arterial hypertension and hypercholesterolaemia.

Carotid Artery Calcification in Panoramic Radiography and Related Risk Factors

Background and Objectives: The carotid artery calcification (CAC) can be seen in panoramic radiographs that are usually used in dentistry. This study aims to determine the prevalence of CAC in Qom, Iran using panoramic radiographs, and find its related factors. Methods: This is a descriptive cross-sectional study. Panoramic radiographs of 417 patients aged ≥40 years referred to a specialized oral and maxillofacial radiology center in Qom city in 2021 were examined for the presence of CAC and a questionnaire was used to find the related risk factors. The collected data were analyzed in SPSS software, vertion 22 using Chi-square test and t-test. Results: Of 417 participants, 141 (33.8%) were male and 276 (66.2%) were female. The prevalence of CAC was 1.4%. There was a significant association between CAC and history of cardiovascular diseases (P=0.03), but the incidence of CAC had no association with the history of diabetes, smoking, hypertension, cerebrovascular accident, and myocardial infarction (P&gt;0.05). Conclusion: The incidence of CAC is associated with the history of cardiovascular diseases. Further prospective studies with larger sample sizes are recommended.

Prevalence of Carotid Artery Calcification on Digital Panoramic Radiographs in Hemodialysis Patients on Kidney Transplant Waiting List.

The detection of carotid artery calcification at an early stage is important to reduce the effects of cardiovascular disease in patients undergoing hemodialysis. This study sought to evaluate the prevalence of carotid artery calcification from panoramic radiographs of patients who were undergoing hemodialysis and to assess the relationship between such calcification and certain medical and periodontal parameters. We evaluated 120 panoramic radiographs from patients who were undergoing hemodialysis for the presence of carotid artery calcification. Full-mouth periodontal clinical and medical parameters were recorded, and patients were diagnosed on the basis of the new periodontal disease classification. Patient medical records from the same period (the same week) during which the panoramic radiographs were taken were also assessed. Among the 120 participating patients, pano - ramic radiographs from 27 patients (22.5%) showed a uni- or bilaterally radiopaque mass. Of the periodontal clinical parameters investigated for associations between patients with and without carotid artery calcification, there was only a significant difference shown for probing pocket depth (P = .017). No significant differences were found between the groups with and without carotid artery calcification with regard to any other medical or periodontal parameter. In our study group, suspected carotid artery calcifications were detected on panoramic radiographs in about one-fourth of total patients receiving hemodialysis. Because of the significant relationship found between probing pocket depth and carotid artery calcification, the presence of periodontal disease may be associated with calcifications in these patients. Dentists should maintain awareness in detecting these lesions when evaluating panoramic radiographs of patients undergoing hemodialysis.

Carotid artery calcification in panoramic radiographs associates with oral infections and mortality.

To study the prevalence of carotid artery calcification (CAC) in relation to apical and marginal periodontitis, subgingival dysbiotic bacterial species and serum and saliva immune responses against them. In addition, the aim was to analyse the association of CAC with angiographically verified coronary artery disease (CAD) and mortality. In the present random Parogene cohort, the patients had an indication for coronary angiography. Apical and marginal periodontitis were diagnosed during clinical and radiographic oral examinations, and CAC on panoramic radiographs (n=492). Presence and severity of CAD were registered from angiography. Subgingival dysbiotic bacterial species were quantitated using checkerboard DNA-DNA-hybridization, and serum and saliva antibody levels were determined by immunoassays. The cohort was followed-up for 10years or until death (median 9.9, range 0.21-10.4) via linkage to the national death register. The statistical models were adjusted for age, gender, smoking, hypertension, diabetes and dyslipidemia. A total of 102 (20.7%) patients had detectable CAC, which was moderate in 81 (16.4%) and severe in 21 (4.3%). CAC was associated (OR, 95% CI) with severe apical periodontitis (2.25, 1.15-4.41), root canal fillings (1.15, 1.04-1.26), alveolar bone loss (2.66, 1.21-5.84), severe periodontal inflammation (2.23, 1.11-4.47), high level of gram-negative subgingival species (2.73, 1.34-5.50), saliva IgG against dysbiotic species (1.05, 1.01-1.10/unit) and severe (2.58, 1.36-4.90) and chronic (2.13, 1.15-3.93) CAD. A total of 105 (20.7%) patients died during the follow-up and 53 (10.4%) deaths were because of cardiovascular diseases (CVD). Severe CAC predicted worse survival with HRs (95% CI) of 3.08 (1.58-6.06) for all-cause and 3.43 (1.42-8.25) for CVD death. CAC on panoramic tomography was associated with (i) apical and marginal periodontitis and dysbiotic bacterial species giving rise to an immunological response, and with (ii) severe, chronic CAD and increased mortality. The results further emphasize the role of oral infections in CAD and the importance of referring a patient with CAC for a cardiovascular evaluation.

Prevalence of carotid artery calcification detected by digital panoramic radiographs in a sample of yemeni dental patients.

Background: Carotid artery calcification (CAC) is one of risk factors of cardiovascular disorders (CVDs). Digital panoramic radiographs can detect it. Aim of the study: This study aimed to determine the prevalence of CAC detected by digital panoramic radiographs in a sample of Yemeni dental patients. Materials and Methods: An observational and analytical cross-sectional study was used to investigate a convenience sample of 443 patients. These patients were interviewed face-to-face for their socio-demographic information and their medical background regarding CVDs and associated risk factors. The researchers for detection of CAC assessed the digital panoramic radiographs. Results: High income and middle-aged patients were risk factors of CVDs significantly associated with increased incidence of CAC (42 patients (9.5%) and 32 patients (7.2%), respectively). Patients with a previous medical consultation, previous medications and family history of CVDs revealed a significant higher prevalence of CAC (p=0.001). Conclusion: There was an increased prevalence of CAC detected on digital panoramic radiographs, as a risk factor of CVDs. CAC was more common in females than males.

Prevalence of Carotid Artery Calcification Detected on Panoramic Radiographs of Patients with a History of Hypertension or Myocardial Infarction

Background: Atherosclerosis is characterized by the deposition of lipids on the internal walls of blood vessels, damaging various tissues of the body by complete or partial occlusion of the vessels. Sometimes the calcified plaques in the carotid artery can be detected on panoramic radiographs, helping the practitioners decrease the risk of Cerebrovascular Accident (CAV). Objective: This study aimed to assess the frequency of Carotid Artery Calcification (CAC) detected in panoramic radiographs of patients with hypertension or myocardial infarction. Methods: A total of 400 panoramic radiographs of patients &gt;40 years of age were evaluated. The images belonged to patients with a history of hypertension or myocardial infarction and healthy individuals referred from the AL Zahra Cardiology Department to Isfahan School of Dentistry and a private oral and maxillofacial imaging center. All the images were evaluated for the presence of CAC. Data were analyzed with SPSS 19, using the Chi-squared test, Fisher's exact test, t-test and ANOVA (α=0.05). Results: The prevalence rate of CAC was 4%. According to the results, there was a significant relationship between CAC and hypertension (P=0.003), with no significant relationship between the prevalence of these lesions, stage of hypertension and myocardial infarction. Conclusion: According to the results, the prevalence of CAC on panoramic radiographs was significant; therefore, it seems that the detection of CAC on panoramic radiographs of patients must be considered by dentists.

Prevalence of Soft Tissue Calcifications in Panoramic Radiographs of Patients Referred to Guilan School of Dentistry Within 1 Year and its Relationship With Systemic Diseases

Background: Soft tissue calcifications are the deposition of calcium salts, mainly calcium phosphate, in soft tissue. They most often are detected as incidental findings during radiographic examinations. The goal is to identify them correctly to determine whether treatment is required. The aim of this study was to investigate the prevalence of soft tissue calcifications in panoramic radiographs and their relationship with age, gender and underlying diseases. Methods: In this descriptive cross-sectional study, panoramic radiographs of 654 patients were examined within one year. The prevalence of soft tissue calcification, their location and certain factors such as age, sex, underlying disease were examined. Results: The prevalence of elongated stylohyoid ligament calcification, laryngeal cartilage calcification, carotid artery calcification, lymph node calcification, and sialolith were 20.2%, 9.8%, 2.4%, 1.8%, 0.6%, and 0.1%, respectively. Stylohyoid ligament and vascular calcifications were significantly correlated with cardiovascular disease and hypertension. Gender and soft tissue calcification were not significantly associated. The prevalence of tonsillolith was significantly higher in men (P=0.0001). A significant correlation was found between soft tissue calcification and age groups, so that as age increased, the prevalence of carotid artery calcification, stylohyoid ligament calcification, and tonsillolith increased. Conclusions: The present study shows that soft tissue calcifications are not unusual findings in panoramic radiographs. They increase significantly with aging but have no significant association with gender. The prevalence of soft tissue calcification is higher in cardiovascular disease patients.

C-reactive protein levels and the association of carotid artery calcification with tooth loss.

The relationship between carotid artery calcification (CAC) and tooth loss was investigated and its association with inflammatory mediator levels was evaluated. Ninety-two participants were examined for health and periodontal status. Panoramic radiographs were obtained for CAC identification. C-reactive protein (CRP), intercellular cell adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) levels were measured. Fifteen participants (16.3%) had CAC, 12 (80.0%) of whom were female. Mean age of participants with CAC was 55.3±12.2years, while that of participants without CAC was 48.9±9.4years. Median number of tooth loss in participants with CAC was 11, whereas that of individuals without CAC was 3 (P=0.008). Age and presence of CAC were associated with the number of tooth loss, independent of health status (β=0.452, P=<0.001 and β=0.257, P=0.005). Based on CRP levels, 10 participants (71.4%) were at intermediate risk of coronary heart disease (range, 1.0-2.3μgml-1 ), while four participants (28.6%) were at low risk (<1.0μgml-1 ). CRP, ICAM-1, or VCAM-1 levels were not significantly related to the presence of CAC or tooth loss. Patients with higher tooth loss have a greater prevalence of CAC. Patients with CAC should be referred for medical consultation.

Ocena występowania zwapnień tętnicy szyjnej i wybranych danych z wywiadu medycznego na podstawie obrazowania pantomograficznego

Ocena występowania zwapnień tętnicy szyjnej i wybranych danych z wywiadu medycznego na podstawie obrazowania pantomograficznego

Prevalence of carotid artery calcification in postmenopausal women and its correlation with atherogenic risk factors.

Aim:The aim of the present study was to determine the prevalence of carotid artery calcification (CAC) in postmenopausal females on panoramic radiographs and to study the correlation of CAC with possible risk factors such as hypertension, osteoporosis, and hypercholesterolemia, among others.Materials and Methods:Totally, 1214 panoramic radiographs of postmenopausal females attending the Department of Oral Medicine and Radiology were examined for the presence of CAC. The subjects were also assessed for the presence of various risk factors and the possible correlation to CAC. Statistical analysis was done using Chi-square test, and P < 0.05 was considered to be statistically significant.Results:Two hundred and seventy-eight postmenopausal females presented with CAC and a prevalence of 22.9%. These patients presented with a medical history that was laden with risk factors, of which hypertension (71.2%) was the most common risk factor. Hypertension, hypercholesterolemia, osteoporosis, and obesity were significantly (P < 0.05) related to the presence of CAC while age, diabetes, and smoking were not significantly (P > 0.05) related to CAC.Conclusion:The incidental finding of CAC on panoramic radiographs during the routine dental examination can provide life-saving information for the identification of postmenopausal females who are at a higher risk for stroke. Oral clinicians should, therefore, record a proper medical history of such patients to identify the atherogenic risk factors and refer such patients to the physician for careful evaluation and conformation of the disease.

Prevalence of carotid artery calcification in patients with chronic renal disease identified by panoramic radiography.

This study aimed to evaluate the prevalence of carotid artery calcification (CAC) in the panoramic radiographs of patients with chronic renal disease and to ascertain the medical parameters. A total of 100 panoramic radiographs were observed. The division of patients according to renal disease was as follows: 37 in early-stage renal disease (ESG), 32 in predialysis (PDG), and 31 in hemodialysis (HDG). There were 21 images with opacities suggestive of CAC (6 from ESG, 7 from PDG, and 8 from HDG). The medical parameters were as follows: Triglyceride levels were significantly higher (P < .0001) in patients with CAC compared with those without CAC; potassium levels were higher in the group with CAC compared with the group without CAC (P < .0001); and the calcium levels were lower in the group with CAC compared with the group without CAC (P < .0001). The patients with renal injury and changes in triglyceride and potassium levels had a higher prevalence of CAC on panoramic radiography.

Fibroblast growth factor 23 is associated with carotid artery calcification in chronic kidney disease patients not undergoing dialysis: a cross-sectional study

BackgroundFibroblast growth factor 23 (FGF23) is an important hormone in the regulation of phosphate metabolism. It is unclear whether FGF23 is associated with carotid artery calcification (CAAC) in predialysis patients. The present study aimed to clarify the relationship between FGF23 and CAAC in patients with chronic kidney disease (CKD) who were not on dialysis.MethodsOne-hundred ninety-five predialysis CKD patients were enrolled in this cross-sectional study. CAAC was assessed using multidetector computed tomography, and the prevalence of CAAC was examined. Intact FGF23 was measured in each patient. The risk factors for CAAC were evaluated using a logistic regression model.ResultsWe found CAAC in 66% of the patients. The prevalence of CAAC significantly increased across CKD stages: it was 37% in CKD stages 1–2, 58% in stage 3; 75% in stage 4, and 77% in stage 5 (p < 0.01). In multivariate analysis, smoking, diabetes mellitus and log FGF23 were each identified as risk factors for CAAC. The study population was divided in quartiles of FGF23 levels. Compared with the lowest FGF23 quartile, each subsequent quartile had a progressively higher odds ratio (OR) for CAAC, adjusted for confounders (ORs [95% confidence interval] of 2.34 [0.78 to 7.31], 5.28 [1.56 to 19.5], and 13.6 [2.92 to 74.6] for the second, third, and fourth quartiles, respectively.ConclusionsThe prevalence of CAAC is increased with the decline in the kidney function. FGF23 is independently related to CAAC in patients with CKD who are not on dialysis.

Prevalence of carotid artery calcification on panoramic radiographs in patients with renal stones

To determine the prevalence of carotid artery calcification (CAC) detected in routine dental radiography (PRs) in patients with kidney stones (KSs) and to investigate the relationship between CAC-atherosclerosis and KSs. Materials and methods: A total of 108 patients with renal stones were included in the present study. A history of renal colic, with confirmed hematuria and voiding of the calculus, radiographic evidence of KSs, or previous surgical and endoscopic removal of KSs, was used to define the nephrolithiasis. KS patients were evaluated by PR in terms of the presence of CAC. Subjects with either unilateral or bilateral CAC on these radiographs were identified. Results: Of the 108 patients included in the data analysis, 18 (16.6%) were detected as having CAC upon PR; of these, there were 8 males (11.5% of all males) and 10 females (25.6% of all females) (P > 0.05). There was no significant difference between the patients with CAC and the patients without CAC in any aspect of biochemical parameters, and also in the history of predisposing factors (P > 0.05). The CAC prevalence (16.6%) was significantly higher in patients with KSs when compared to the normal population (5.06%) in our previous study (P > 0.05). Conclusion: Our study shows that CAC is significantly higher in patients with KSs when compared to the normal population. This study may draw the attention of clinicians to the fact that patients with KSs should be evaluated further for atherosclerosis and treated for vascular risk factors.

The Prevalence of Carotid Artery Calcification on the Panoramic Radiographs of End-stage Renal Disease Patients with Peritoneal Dialysis: Do Incidental Findings Provide Life-saving Information?

This study investigated the presence of carotid artery calcifications (CACs) on panoramic radiographs (PRs) in end-stage renal disease (ESRD) patients treated with peritoneal dialysis (PD), and analysed the relationship between CAC prevalence and PD duration. A random sample of 110 PRs were collected from ESRD patients (15 with questionable CACs were subsequently excluded). CACs were found in 26 (27.4%) patients; 10 males (23.3% of all males) and 16 females (30.8% of all females). The overall mean PD period was 4.0 +/- 3.2 years. There was a significant difference in PD period between patients with and without CACs (5.3 +/- 3.1 years versus 3.5 +/- 3.1 years, respectively). To our knowledge, this study has the highest CAC prevalence, is the first to be carried out in ESRD patients being treated with PD and has the largest sample of ESRD patients (n = 95). We believe dentists should carefully evaluate patients' PRs for evidence of CACs, enabling these incidental findings to provide life-saving information.

The Prevalence of Carotid Artery Calcification on the Panoramic Radiographs in Cappadocia Region Population

The aim of this study is to determine retrospectively the presence of carotid artery calcifications (CACs) detected on panoramic radiographs (PRs) in a group of Turkish population. Further, the relationships between CACs and gender, life style, and medical history were evaluated. During the years 2004 to 2006, a random sample of 1282 PRs was collected from patients older than 40 years who were being treated by the School of Dentistry, Erciyes University. Of these 1282 PRs, 750 PRs were included in this study. Medical data was collected from the archival records of the dental school. About 38 (5.06%) CACs were found on the PRs of 12 (4.5%) males and 26 (5.4%) females. The CAC prevalence was not significantly different between the males and females (P=0.583). These calcifications were unilateral in 26 (68.4%) and bilateral in 12 (31.6%) subjects. Of those in the positive group, there were 12 subjects (31.58%) with hyperlipidemia, 12 subjects (31.58%) with hypertension, 7 subjects (18.4%) with diabetes mellitus, 6 subjects (15.8%) with cardiovascular disease, and 6 subjects (15.8%) with smoking history. This study has the highest CACs prevalence in comparison to the other studies. Therefore, dentists caring for subjects with dental problems should carefully evaluate their PRs for the evidence of CACs, and refer them for medical evaluation as indicated. So, incidental findings could provide life-saving information.

Long-Term Cigarette Smoking Increases the Prevalence of Carotid Artery Calcification Seen on Panoramic Dental Radiographs in Male Patients

Panoramic dental radiographs are commonly used in general dentistry and oral and maxillofacial surgery to examine upper and lower teeth, maxilla, mandible and the surroundings simultaneously. Carotid artery calcification, a specific indicator of atherosclerotic change of the carotid arteries, can be seen on the radiographs. Many studies have suggested that cigarette smoking is a risk factor of atherosclerotic change as well as cerebral infarction. We hypothesized that smoking could increase the prevalence of carotid artery calcification, and compared the radiographs of smokers and non-smokers aged 50 years and over: 146 male smokers, 165 male non-smokers, 42 female smokers and 422 female non-smokers. This is the first study to focus on carotid artery calcification seen on panoramic dental radiographs to show the connection between smoking and atherosclerotic change. In male patients, carotid artery calcification was seen in 18 (14.1%) of the smokers, and in 8 (4.8%) of the non-smokers, which clearly shows that male patients aged 50 years old or over are more likely to develop carotid artery calcification if they smoke. However, there is no significant difference between female smokers and female non-smokers in the same age group. Dentists are in a good position to find carotid artery calcification on radiographs. When this is found on a radiograph, the patient should be advised to stop smoking and be referred to a physician for further tests. Clinicians should be aware that this radiographic finding indicates the presence of atherosclerotic change of the carotid arteries.

Carotid artery calcification detected on panoramic radiographs in a group of Thai population

To determine the prevalence of carotid artery calcification (CAC) detected on panoramic radiographs in a Thai population. The panoramic radiographs of the patients 50 and older (N = 1,370) visiting Mahidol University from January 1998 through September 2004 were retrospectively reviewed for CAC. The medical records of the positive subjects were then reviewed. Thirty-four (2.5%) of the 1,370 patients, 16 men and 18 women, with a mean age of 69 and a range of 50 to 87 years, had 1 or more CACs. These calcifications were unilateral in 25 (73.5%) and bilateral in 9 (26.5%) subjects. Of those positive subjects, 18 reported hypertension, 10 reported diabetes mellitus, and 5 reported hyperlipidemia. Although it is uncommon to find CAC in the Thai population, dentists should be aware of this calcification on the routine panoramic radiographs and promptly refer for cerebrovascular and cardiovascular evaluation.

The prevalence of carotid artery calcification on the panoramic radiographs of patients with renal disease

The prevalence of carotid artery calcification on the panoramic radiographs of patients with renal disease

Continuous Ambulatory Peritoneal Dialysis Patients Show High Prevalence of Carotid Artery Calcification which is Associated with a Higher Left Ventricular Mass Index

This study examined intima-media thickness and arterial plaque occurrence in the carotid and brachial arteries in continuous ambulatory peritoneal dialysis (CAPD) patients. The study compared 25 CAPD patients with 25 normotensive age- and sex-matched controls. Intima-media thickness and presence of plaque in carotid and brachial artery were measured three times using high-resolution B-mode echocardiography. Left ventricular mass was calculated using the Penn Convection equation. Blood samples were obtained to assess levels of phosphorus, total calcium, serum albumin, C-reactive protein, and lipid profiles. Compared to the control group, CAPD patients had greater mean carotid and brachial intima-media thickness, and a higher proportion of subjects with calcified plaques. The left ventricular mass index was higher in CAPD patients with carotid artery calcified plaques compared to CAPD patients without carotid artery calcified plaques. CAPD patients with such plaque were significantly associated with diabetes mellitus, higher C-reactive protein levels and a lower 2-yr survival rate. The present study showed an high prevalence of carotid calcification in CAPD patients and those with such calcification had a greater incidence of diabetes mellitus, higher C-reactive protein levels and left ventricular mass index, and a lower survival rate.

The prevalence of carotid artery calcification on the panoramic radiographs of patients with renal disease

To determine the prevalence of carotid calcification on dental panoramic radiographs in end-stage renal disease (ESRD) patients on haemodialysis and renal transplant recipients. Panoramic radiographs of 69 adult patients with renal disease (34 with haemodialysis and 35 with renal transplantations) (age range 17-74 years; mean age 39.45 years) and 50 controls (age-match, free of systemic disease) were examined on panoramic radiographs for any unusual radiopacity adjacent to or just below the intervertebral space between C3 and C4. Patients with such calcifications were referred to ultrasound examination. Using Chi-squared tests, calcification prevalence rates were statistically compared. The statistical difference between renal disease patients and control group was significant (chi2 = 17.91, P < 0.001). On comparison of haemodialysis patients and renal transplant recipients with controls, statistical difference (P=0.007) was found to be significant. Carotid artery calcification was higher in haemodialysis patients and renal transplant recipients. These patients with such calcifications should be referred for further evaluation and treatment of carotid arteries, coronary arteries and vascular risk factors.