Screening patients with chest pain in the emergency department using electron beam tomography: a follow-up study

Relation between Coronary Artery Calcium Score and Cardiovascular Events in Hodgkin Lymphoma Survivors: A Cross-Sectional Matched Cohort Study

BACKGROUND

Thoracic radiotherapy is one of the corner stones of HL treatment, but it is associated with increased risk of cardiovascular events. As HL is often diagnosed at a young age, long-term follow-up including screening for coronary artery disease (CAD) is recommended.

OBJECTIVES

This study aims to evaluate the presence of coronary artery calcium score (CACS) in relation to cardiovascular events in HL patients treated with thoracic radiotherapy compared to a non-cancer control group.

METHODS

Consecutive HL patients who underwent evaluation for asymptomatic CAD with coronary computed tomography angiography > 10 years after thoracic irradiation were included. The study population consisted of 97 HL patients matched to 97 non-cancer patients on gender, age, cardiovascular risk factors, and statin use.

RESULTS

Mean age during CT scan in the HL population was 45.5 ± 9.9 and in the non-cancer population 45.5 ± 10.3 years. CACS was elevated (defined as >0) in 49 (50.5%) HL patients and 30 (30.9%) control patients. HL survivors had an odds ratio of 2.28 [95% CI: 1.22-4.28] for having a CACS > 0 compared to the matched population (p = 0.006). Prevalence of CACS > 90th percentile differed significantly: 17.1% in HL survivors vs. 4.6% in the matched population (p = 0.009). Non-obstructive coronary artery stenosis was more prevalent in the HL population than in the control population (45.7% vs. 28.4%, respectively, p = 0.01). During follow-up of 8.5 [5.3; 9.9] years, nine HL patients experienced an event including two patients with a CACS of zero. No events occurred in the control population.

CONCLUSION

In a matched study population, HL survivors have a higher prevalence of a CACS > 0 and an increased risk of cardiovascular events after thoracic irradiation compared to a matched non-cancer control group.

The Added Value of a High CT Coronary Artery Calcium Score in the Management of Patients Presenting with Acute Chest Pain vs. Stable Chest Pain

Background: Contrast computerized tomography (CT) scan is occasionally aborted due to a high coronary artery calcium score (CACS). For the same CACS in our clinical practice, we observed a higher occurrence of severe coronary artery disease (CAD) in patients with acute chest pain (ACP) compared to patients with stable chest pain (SCP). Since it is known that ACP differs in many ways from SCP, the aim of this study was to compare the predictive value of a high CACS for the diagnosis of severe CAD between ACP and SCP patients. Methods: This single center observational retrospective study included consecutive patients who underwent cardiac CT for chest pain and were found to have a CACS of >200 Agatston units. Patients were divided into two groups, ACP and SCP. Severe CAD was defined as ≥70% stenosis on coronary CT angiography or invasive coronary angiography. Baseline characteristics and final diagnosis of severe CAD were compared. Results: The cohort included 220 patients, 106 with ACP and 114 with SCP. ACP patients had higher severe CAD rates (60.4% vs. 36.8%; p < 0.001). On multivariate analysis including cardiac risk factors, CACS > 400 au (OR = 2.34 95% CI [1.32−4.15]; p = 0.004) and ACP (OR = 2.54 95% CI [1.45−4.45]; p = 0.001) were independent predictors of severe CAD. The addition of the clinical setting of ACP added significant incremental predictive value for severe stenosis. Conclusion: A high CACS is more associated with severe CAD in patients presenting with ACP than SCP. The findings suggest that the CACS could impact the management of patients during the scan.

Cardiac CT angiography in current practice: An American society for preventive cardiology clinical practice statement✰

In this clinical practice statement, we represent a summary of the current evidence and clinical applications of cardiac computed tomography (CT) in evaluation of coronary artery disease (CAD), from an expert panel organized by the American Society for Preventive Cardiology (ASPC), and appraises the current use and indications of cardiac CT in clinical practice. Cardiac CT is emerging as a front line non-invasive diagnostic test for CAD, with evidence supporting the clinical utility of cardiac CT in diagnosis and prevention. CCTA offers several advantages beyond other testing modalities, due to its ability to identify and characterize coronary stenosis severity and pathophysiological changes in coronary atherosclerosis and stenosis, aiding in early diagnosis, prognosis and management of CAD. This document further explores the emerging applications of CCTA based on functional assessment using CT derived fractional flow reserve, peri‑coronary inflammation and artificial intelligence (AI) that can provide personalized risk assessment and guide targeted treatment. We sought to provide an expert consensus based on the latest evidence and best available clinical practice guidelines regarding the role of CCTA as an essential tool in cardiovascular prevention - applicable to risk assessment and early diagnosis and management, noting potential areas for future investigation.

Coronary artery calcium score: pivotal role as a predictor for detecting coronary artery disease in symptomatic patients

Chest pain and dyspnea are common presentations for symptomatic individuals with suspected coronary artery disease (CAD) in the primary care office and cardiology clinics. However, it is imperative to properly diagnose who should undergo further evaluation for cardiac etiologies of chest pain, with either noninvasive or invasive imaging tests. The purpose of this review is to highlight the role of coronary artery calcium (CAC) score as a screening tool for symptomatic patients to detect CAD. The purpose of CAC scoring is to establish the presence and severity of coronary atherosclerosis that can play a vital role in symptomatic patients. The use of CAC testing in symptomatic patients has traditionally been limited due to fundamental concerns, including the occurrence of coronary calcification relatively late in the atherosclerotic process and high prevalence of CAC in the population. Further issue relates to its low specificity for obstructive CAD, as well as demonstration of significant ethnic variability in plaque composition and calcification patterns. CAC testing gained attention as an inexpensive, rapid, reproducible and a well-tolerated alternative to exclude CAD in symptomatic patients and defer further invasive imaging tests. This article will review the available literature in regard to the use of CAC in symptomatic populations.

Coronary artery calcium score and risk of cardiovascular events without established coronary artery disease: a systemic review and meta-analysis

BACKGROUND

Coronary artery calcium (CAC) is an indicator of atherosclerosis, and the CAC score is a useful noninvasive assessment of coronary artery disease.

OBJECTIVE

To compare the risk of cardiovascular outcomes in patients with CAC > 0 versus CAC = 0 in asymptomatic and symptomatic population in patients without an established diagnosis of coronary artery disease.

METHODS

A systematic search of electronic databases was conducted until January 2018 for any cohort study reporting cardiovascular events in patients with CAC > 0 compared with absence of CAC.

RESULTS

Forty-five studies were included with 192 080 asymptomatic 32 477 symptomatic patients. At mean follow-up of 11 years, CAC > 0 was associated with an increased risk of major adverse cardiovascular and cerebrovascular events (MACE) compared to a CAC = 0 in asymptomatic arm [pooled risk ratio (RR) 4.05, 95% confidence interval (CI) 2.91-5.63, P < 0.00001, I2 = 80%] and symptomatic arm (pooled RR 6.06, 95% CI 4.23-8.68, P < 0.00001, I2 = 69%). CAC > 0 was also associated with increased risk of all-cause mortality in symptomatic population (pooled RR 7.94, 95% CI 2.61-24.17, P < 0.00001, I2 = 85%) and in asymptomatic population CAC > 0 was associated with higher all-cause mortality (pooled RR 3.23, 95% CI 2.12-4.93, P < 0.00001, I2 = 94%). In symptomatic population, revascularization in CAC > 0 was higher (pooled RR 15, 95% CI 6.66-33.80, P < 0.00001, I2 = 72) compared with CAC = 0. Additionally, CAC > 0 was associated with more revascularization in asymptomatic population (pooled RR 5.34, 95% CI 2.06-13.85, P = 0.0006, I2 = 93). In subgroup analysis of asymptomatic population by gender, CAC > 0 was associated with higher MACE (RR 6.39, 95% CI 3.39-12.84, P < 0.00001).

CONCLUSION

Absence of CAC is associated with low risk of cardiovascular events compared with any CAC > 0 in both asymptomatic and symptomatic population without coronary artery disease.

Triglyceride Glucose-Waist Circumference Better Predicts Coronary Calcium Progression Compared with Other Indices of Insulin Resistance: A Longitudinal Observational Study

The triglyceride glucose (TyG) index, a product of triglyceride and fasting glucose, is a reliable marker for insulin resistance. We aimed to investigate the association between the TyG-related markers and coronary artery calcification (CAC) progression. We enrolled 1145 asymptomatic participants who underwent repeated CAC score measurements during routine health examinations. Homeostasis model assessment of insulin resistance (HOMA-IR), TyG index, TyG-BMI (body mass index), and TyG-WC (waist circumference) were calculated. Progression of CAC was defined as (1) incident CAC in a CAC-free population, or an (2) increase of ≥2.5 units between the baseline and final square root of the CAC scores in participants with detectable CAC. According to the quartiles of parameters, we stratified the subjects into four groups. The prevalence of progression increased with the TyG-WC quartile (15.0%, 24.1%, 31.0%, and 32.2% for each of the groups; p < 0.001). The multivariate-adjusted odds ratio (95% confidence interval) for CAC score progression was 1.66 (1.01–2.77) when the highest and lowest TyG-WC index quartiles were compared. Furthermore, the predictability of TyG-WC for CAC progression was better than the other indices in terms of the area under the curve. The TyG-WC index predicted CAC progression better than other indices and could be a potential marker of future coronary atherosclerosis.

Cumulative Burden of Financial Hardship From Medical Bills Across the Spectrum of Diabetes Mellitus and Atherosclerotic Cardiovascular Disease Among Non-Elderly Adults in the United States

Background Atherosclerotic cardiovascular disease (ASCVD) has a strong association with diabetes mellitus (DM), accounting for approximately two thirds of deaths in this patient population. Many individuals with ASCVD and DM are vulnerable to financial hardship associated with treatment-related expenses. Therefore, we examined the burden of financial hardship from medical bills across the spectrum of ASCVD status with and without DM. Methods and Results Using data from the National Health Interview Survey from 2013 to 2017, we used logistic regression analysis to examine the association of ASCVD and DM status with financial hardship and an inability to pay medical bills from a representative sample of non-elderly adults in the United States. Our study population consisted of 121 672 individuals. Approximately 3.1% of the weighted population had ASCVD, 5.6% had DM, and 1.3% had both ASCVD and DM. Nearly 50% of individuals with ASCVD and DM reported financial hardship from medical bills (23% being unable to pay medical bills at all), whereas ≈28% of those with neither ASCVD nor DM reported financial hardship from medical bills (8% being unable to pay medical bills at all). Individuals with concurrent ASCVD and DM had the highest relative odds of expressing an inability to pay at all when compared with those with neither condition (odds ratio, 2.69; 95% CI, 2.21-3.28). Conclusions Individuals with concurrent ASCVD and DM are at a disproportionately high risk of being unable to pay their medical bills. The findings provide strong evidence for developing more effective public health policies that protect vulnerable populations from financial hardship.

Postsystolic shortening on echocardiography as a gateway to cardiac computed tomography in patients with suspected stable angina pectoris

Postsystolic shortening (PSS) by speckle-tracking echocardiography (STE) is a marker of myocardial ischemia and may improve diagnostic strategy. We sought to evaluate if PSS is associated with the coronary artery calcium score (CACS) and stenosis by computed tomography angiography (CTA) in patients with suspected stable angina pectoris (SAP). We retrospectively studied 437 SAP patients (age 58 ± 11 years, 41% male) who underwent STE, evaluation of CACS and assessment of significant stenosis (≥ 50%) by CTA. The postsystolic index (PSI) was defined as follows: 100x([peak negative strain cardiac cycle - peak negative strain systole])/peak negative strain cardiac cycle. A wall had PSS if any segment within the wall had a PSI ≥ 20%. We defined categories for walls with PSS: 0, 1, 2 and ≥ 3, and CACS: 0, 1-100, 101-400 and > 400. Each additional wall with PSS was associated with a 43% relative increase in CACS (95%CI +9% to +87%, P = 0.010), while each 1% absolute increase in the PSI was associated with a 9% relative increase in CACS (95%CI +1% to +18%, P = 0.031). Walls with PSS (OR 1.81 per 1 wall increase, 95%CI 1.27-2.59, P = 0.001) and the PSI (OR 1.12 per 1% increase, 95%CI 1.04-1.21, P = 0.004) were associated with the occurrence of CACS > 400. Additionally, walls with PSS (OR 1.53 per 1 wall increase, 95%CI 1.21-1.93, P < 0.001) was a predictor of significant stenosis by CTA. PSS is associated with CACS and significant stenosis by CTA in patients with SAP and may aid in the selection of patients referred for cardiac computed tomography.

Prognostic Value of Coronary Artery Calcium in the PROMISE Study (Prospective Multicenter Imaging Study for Evaluation of Chest Pain)

BACKGROUND

Coronary artery calcium (CAC) is an established predictor of future major adverse atherosclerotic cardiovascular events in asymptomatic individuals. However, limited data exist as to how CAC compares with functional testing (FT) in estimating prognosis in symptomatic patients.

METHODS

In the PROMISE trial (Prospective Multicenter Imaging Study for Evaluation of Chest Pain), patients with stable chest pain (or dyspnea) and intermediate pretest probability for obstructive coronary artery disease were randomized to FT (exercise electrocardiography, nuclear stress, or stress echocardiography) or anatomic testing. We evaluated those who underwent CAC testing as part of the anatomic evaluation (n=4209) and compared that with results of FT (n=4602). We stratified CAC and FT results as normal or mildly, moderately, or severely abnormal (for CAC: 0, 1-99 Agatston score [AS], 100-400 AS, and >400 AS, respectively; for FT: normal, mild=late positive treadmill, moderate=early positive treadmill or single-vessel ischemia, and severe=large ischemic region abnormality). The primary end point was all-cause death, myocardial infarction, or unstable angina hospitalization over a median follow-up of 26.1 months. Cox regression models were used to calculate hazard ratios (HRs) and C statistics to determine predictive and discriminatory values.

RESULTS

Overall, the distribution of normal or mildly, moderately, or severely abnormal test results was significantly different between FT and CAC (FT: normal, n=3588 [78.0%]; mild, n=432 [9.4%]; moderate, n=217 [4.7%]; severe, n=365 [7.9%]; CAC: normal, n=1457 [34.6%]; mild, n=1340 [31.8%]; moderate, n=772 [18.3%]; severe, n=640 [15.2%]; P<0.0001). Moderate and severe abnormalities in both arms robustly predicted events (moderate: CAC: HR, 3.14; 95% confidence interval, 1.81-5.44; and FT: HR, 2.65; 95% confidence interval, 1.46-4.83; severe: CAC: HR, 3.56; 95% confidence interval, 1.99-6.36; and FT: HR, 3.88; 95% confidence interval, 2.58-5.85). In the CAC arm, the majority of events (n=112 of 133, 84%) occurred in patients with any positive CAC test (score >0), whereas fewer than half of events occurred in patients with mildly, moderately, or severely abnormal FT (n=57 of 132, 43%; P<0.001). In contrast, any abnormality on FT was significantly more specific for predicting events (78.6% for FT versus 35.2% for CAC; P<0.001). Overall discriminatory ability in predicting the primary end point of mortality, nonfatal myocardial infarction, and unstable angina hospitalization was similar and fair for both CAC and FT (C statistic, 0.67 versus 0.64). Coronary computed tomographic angiography provided significantly better prognostic information compared with FT and CAC testing (C index, 0.72).

CONCLUSIONS

Among stable outpatients presenting with suspected coronary artery disease, most patients experiencing clinical events have measurable CAC at baseline, and fewer than half have any abnormalities on FT. However, an abnormal FT was more specific for cardiovascular events, leading to overall similarly modest discriminatory abilities of both tests.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT01174550.

Zero Calcium Score as a Filter for Further Testing in Patients Admitted to the Coronary Care Unit with Chest Pain

BACKGROUND:

The accuracy of zero coronary calcium score as a filter in patients with chest pain has been demonstrated at the emergency room and outpatient clinics, populations with low prevalence of coronary artery disease (CAD).

OBJECTIVE:

To test the gatekeeping role of zero calcium score in patients with chest pain admitted to the coronary care unit (CCU), where the pretest probability of CAD is higher than that of other populations.

METHODS:

Patients underwent computed tomography for calcium scoring, and obstructive CAD was defined by a minimum 70% stenosis on invasive angiography.

RESULTS:

In 146 patients studied, the prevalence of CAD was 41%. A zero calcium score was present in 35% of the patients. The sensitivity and specificity of zero calcium score yielded a negative likelihood ratio of 0.16. After logistic regression adjustment for pretest probability, zero calcium score was independently associated with lower odds of CAD (OR = 0.12, 95%CI = 0.04-0.36), increasing the area under the ROC curve of the clinical model from 0.76 to 0.82 (p = 0.006). Zero calcium score provided a net reclassification improvement of 0.20 (p = 0.0018) over the clinical model when using a pretest probability threshold of 10% for discharging without further testing. In patients with pretest probability < 50%, zero calcium score had a negative predictive value of 95% (95%CI = 83%-99%), with a number needed to test of 2.1 for obtaining one additional discharge.

CONCLUSION:

Zero calcium score substantially reduces the pretest probability of obstructive CAD in patients admitted to the CCU with acute chest pain. (Arq Bras Cardiol. 2017; [online].ahead print, PP.0-0).

FUNDAMENTO:

A acurácia do escore de cálcio coronário zero como um filtro nos pacientes com dor torácica aguda tem sido demonstrada na sala de emergência e nos ambulatórios, populações com baixa prevalência de doença arterial coronariana (DAC).

OBJETIVOS:

Testar o papel do escore de cálcio zero como filtro nos pacientes com dor torácica admitidos numa unidade coronariana intensiva (UCI), na qual a probabilidade pré-teste de DAC é maior do que em outras populações.

MÉTODOS:

Pacientes foram submetidos a tomografia computadorizada para quantificar o escore de cálcio, DAC obstrutiva foi definida por uma estenose mínima de 70% na cineangiocoronariografia invasiva. Um escore clínico para estimar a probabilidade pré-teste de DAC obstrutiva foi criado em amostra de 370 pacientes, usado para definir subgrupos na definição de valores preditivos negativos do escore zero.

RESULTADOS:

Em 146 pacientes estudados, a prevalência de DAC foi 41% e o escore de cálcio zero foi demonstrado em 35% deles. A sensibilidade e a especificidade para escore de cálcio zero resultaram numa razão de verossimilhança negativa de 0,16. Após ajuste com um escore clínico com a regressão logística para a probabilidade pré-teste, o escore de cálcio zero foi preditor independente associado a baixa probabilidade de DAC (OR = 0,12, IC95% = 0,04-0,36), aumentando a área abaixo da curva ROC do modelo clínico de 0,76 para 0,82 (p = 0,006). Considerando a probabilidade de DAC < 10% como ponto de corte para alta precoce, o escore de cálcio aumentou a proporção de pacientes para alta precoce de 8,2% para 25% (NRI = 0,20; p = 0,0018). O escore de cálcio zero apresentou valor preditivo negativo de 90%. Em pacientes com probabilidade pré-teste < 50%, o valor preditivo negativo foi 95% (IC95% = 83%-99%).

CONCLUSÃO:

O escore de cálcio zero reduz substancialmente a probabilidade pré-teste de DAC obstrutiva em pacientes internados em UCI com dor torácica aguda. (Arq Bras Cardiol. 2017; [online].ahead print, PP.0-0).

Impact of Coronary Calcification on Clinical Management in Patients With Acute Chest Pain

BACKGROUND

Coronary artery calcification (CAC) may impair diagnostic assessment of coronary computed tomography angiography (CTA). We determined whether CAC affects efficiency of coronary CTA in patients with suspected acute coronary syndrome (ACS).

METHODS AND RESULTS

This is a pooled analysis of ACRIN-PA (American College of Radiology Imaging Network-Pennsylvania) 4005 and the ROMICAT-II trial (Rule Out Myocardial Infarction/Ischemia Using Computer Assisted Tomography) comparing an initial coronary CTA strategy to standard of care in acute chest pain patients. In the CTA arms, we investigated appropriateness of downstream testing, cost, and diagnostic yield to identify patients with obstructive coronary artery disease on subsequent invasive coronary angiography across CAC score strata (Agatston score: 0, >0-10, >10-100, >100-400, >400). Out of 1234 patients (mean age 51±8.8 years), 80 (6.5%) had obstructive coronary artery disease (≥70% stenosis) and 68 (5.5%) had ACS. Prevalence of obstructive coronary artery disease (1%-64%), ACS (1%-44%), downstream testing (4%-72%), and total (2337-8484 US$) and diagnostic cost (2310-6678 US$) increased across CAC strata (P<0.001). As the increase in testing and cost were lower than the increase of ACS rate in patients with CAC>400, cost to diagnose one ACS was lowest in this group (19 283 US$ versus 464 399 US$) as compared with patients without CAC. The diagnostic yield of invasive coronary angiography was highest in patients with CAC>400 (87% versus 38%).

CONCLUSIONS

Downstream testing, total, and diagnostic cost increased with increasing CAC, but were found to be appropriate because obstructive coronary artery disease and ACS were more prevalent in patients with high CAC. In patients with acute chest pain undergoing coronary CTA, cost-efficient testing and excellent diagnostic yield can be achieved even with high CAC burden.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifiers: NCT01084239 and NCT00933400.

Impact of Advanced Modeled Iterative Reconstruction on Coronary Artery Calcium Quantification

RATIONALE AND OBJECTIVES

To evaluate the influence of advanced modeled iterative reconstruction (ADMIRE) on the coronary artery calcium (CAC) scores by computed tomography (CT).

MATERIALS AND METHODS

Sixty patients underwent CAC imaging with dual-source 192-slice CT. Agatston, volume and mass score were calculated from filtered back projection (FBP) and iterative reconstructions with different levels of ADMIRE. Friedman test and Wilcoxon rank sum test were used for multiple comparisons of CAC values and the difference ratio among different ADMIRE groups using FBP as reference.

RESULTS

The median Agatston score (range) using FBP was 115 (0.1-3047) and significantly decreased with incremental ADMIRE levels 1-5: 96 (0.1-2813), 91 (0-2764), 87 (0-2699), 80 (0-2590), 70 (0-2440); all P < 0.001. In comparison with FBP Agatston, volume and mass scores significantly decreased with increasing ADMIRE levels 1-5 (P < 0.001): from -12% to -39%, from -14% to -41%, and from -13% to -40%, respectively. In four patients with low calcium burden, the use of ADMIRE 2 or higher resulted in the disappearance of calcium that was detectable using FBP or ADMIRE 1. The decrease of CAC in high-level ADMIRE resulted in a reassignment to a lower Agatston risk group in 27%.

CONCLUSIONS

ADMIRE causes a substantial reduction of the CAC scores measured by cardiac CT, which leads to an underestimation of cardiovascular risk scores in some patients.

Defining severe familial hypercholesterolaemia and the implications for clinical management: a consensus statement from the International Atherosclerosis Society Severe Familial Hypercholesterolemia Panel

Familial hypercholesterolaemia is common in individuals who had a myocardial infarction at a young age. As many as one in 200 people could have heterozygous familial hypercholesterolaemia, and up to one in 300 000 individuals could be homozygous. The phenotypes of heterozygous and homozygous familial hypercholesterolaemia overlap considerably; the response to treatment is also heterogeneous. In this Review, we aim to define a phenotype for severe familial hypercholesterolaemia and identify people at highest risk for cardiovascular disease, based on the concentration of LDL cholesterol in blood and individuals' responsiveness to conventional lipid-lowering treatment. We assess the importance of molecular characterisation and define the role of other cardiovascular risk factors and advanced subclinical coronary atherosclerosis in risk stratification. Individuals with severe familial hypercholesterolaemia might benefit in particular from early and more aggressive cholesterol-lowering treatment (eg, with PCSK9 inhibitors). In addition to better tailored therapy, more precise characterisation of individuals with severe familial hypercholesterolaemia could improve resource use.

Association between serum gamma-glutamyltransferase and the progression of coronary artery calcification

BACKGROUND

Elevated serum gamma-glutamyltransferase (GGT) has been demonstrated to be associated with coronary artery calcification (CAC). CAC progression is an important marker of atherosclerosis and correlates with future cardiovascular risk. However, there is a lack of research that directly examines the association between serum GGT and CAC progression. The aim of this study was to elucidate the association between serum GGT activity and CAC progression.

METHODS

We enrolled 1246 asymptomatic participants who underwent repeated CAC score measurement during routine health examinations. To eliminate the dependence of the inter scan variability on the baseline CAC scores, square root-transformed CAC scores were used to analyze CAC progression. In addition, the annualized rate of change in CAC scores was computed.

RESULTS

Serum GGT activities were significantly higher in "progressors" than "nonprogressors". The prevalence of progression increased with the GGT tertile (11.9%, 20.1% and 27.9% in the 1st, 2nd, and 3rd GGT tertiles, respectively; p < 0.001). In the multivariate logistic regression analysis, the odds ratio (95% confidence interval) for CAC score progression was 1.85 (1.14-3.00) in the highest GGT tertile group. By multivariate linear regression analysis, baseline serum GGT activity demonstrated a positive association with the annualized change in CAC score (β = 0.002; p = 0.006) after adjusting for cardiovascular risk factors.

CONCLUSION

Elevated serum GGT levels are independently associated with CAC progression. Serum GGT levels may be a potential biomarker of future coronary atherosclerosis and prognosis.

Low high-sensitivity troponin I and zero coronary artery calcium score identifies coronary CT angiography candidates in whom further testing could be avoided

RATIONALE AND OBJECTIVES

Pilot study to determine whether among subjects receiving coronary computed tomography angiography (CTA), the combination of high-sensitivity troponin I (hsTnI) and coronary artery calcium score (CACS) identifies a low-risk population in whom CTA might be avoided.

MATERIALS AND METHODS

A cross-sectional study of 314 symptomatic patients receiving CTA as part of their acute coronary syndrome evaluation was conducted. hsTnI was measured with Abbott Laboratories' hsTnI assay. CACSs were calculated via the Agatston method. Patients were followed for at least 30 days after discharge for the occurrence of major adverse cardiac events (MACEs; all-cause mortality, acute coronary syndrome, and revascularization).

RESULTS

Of 314 subjects studied, 213 (67.8%) had no coronary artery stenosis, and 67 (21.3%), 28 (8.9%), and 6 (1.9%) had maximal coronary artery stenosis of 1%-49%, 50%-69%, and 70% or greater, respectively. All MACEs occurred during index hospitalization and include one myocardial infarction and four revascularizations. Sixty-two percent (189/307) of subjects had zero CACS, and 24% (76/314) of subjects had undetected hsTnI. No subjects with undetectable hsTnI or zero CACS had an MACE. A strategy of avoiding further testing in subjects with undetectable initial hsTnI, performing CACS on subjects with detectable initial hsTnI but nonincreased hsTnI (less than 99th percentile), and obtaining CTA in subjects with Agatston greater than 0 will have a negative predictive value of 100.0% (95% confidence interval, 98.2%-100.0%). This strategy will avoid CTA in 63% (198/314) of subjects.

CONCLUSIONS

In this pilot study, the addition of CACS to hsTnI improves the identification of low-risk subjects in whom CTA might be avoided.

Use of coronary artery calcium scanning beyond coronary computed tomographic angiography in the emergency department evaluation for acute chest pain: the ROMICAT II trial

BACKGROUND

Whether a coronary artery calcium (CAC) scan provides added value to coronary computed tomographic angiography (CCTA) in emergency department patients with acute chest pain remains unsettled. We sought to determine the value of CAC scan in patients with acute chest pain undergoing CCTA.

METHODS AND RESULTS

In the multicenter Rule Out Myocardial Infarction using Computer-Assisted Tomography (ROMICAT) II trial, we enrolled low-intermediate risk emergency department patients with symptoms suggesting acute coronary syndrome (ACS). In this prespecified subanalysis of 473 patients (54±8 years, 53% men) who underwent both CAC scanning and CCTA, the ACS rate was 8%. Overall, 53% of patients had CAC=0 of whom 2 (0.8%) developed ACS, whereas 7% had CAC>400 with 49% whom developed ACS. C-statistic of CAC>0 was 0.76, whereas that using the optimal cut point of CAC≥22 was 0.81. Continuous CAC score had lower discriminatory capacity than CCTA (c-statistic, 0.86 versus 0.92; P=0.03). Compared with CCTA alone, there was no benefit combining CAC score with CCTA (c-statistic, 0.93; P=0.88) or with selective CCTA strategies after initial CAC>0 or optimal cut point CAC≥22 (P≥0.09). Mean radiation dose from CAC acquisition was 1.4±0.7 mSv. Higher CAC scores resulted in more nondiagnostic CCTA studies although the majority remained interpretable.

CONCLUSIONS

In emergency department patients with acute chest pain, CAC score does not provide incremental value beyond CCTA for ACS diagnosis. CAC=0 does not exclude ACS, nor a high CAC score preclude interpretation of CCTA in most patients. Thus, CAC results should not influence the decision to proceed with CCTA, and the decision to perform a CAC scan should be balanced with the additional radiation exposure required.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT01084239.

Accuracy of multidetector computed tomography for detection of coronary artery stenosis in acute coronary syndrome compared with stable coronary disease: a CORE64 multicenter trial substudy

BACKGROUND

Multi-detector computed tomography angiography (MDCTA) is a promising method for risk assessment of patients with acute chest pain. However, its diagnostic performance in higher-risk patients has not been investigated in a large international multicenter trial. Therefore, in the present study we sought to estimate the diagnostic accuracy of MDCTA to detect significant coronary stenosis in patients with acute coronary syndrome (ACS).

METHODS

Patients included in the CORE64 study were categorized as suspected-ACS or non-ACS based on clinical data. A 64-row coronary MDCTA was performed before invasive coronary angiography (ICA) and both exams were evaluated by blinded, independent core laboratories.

RESULTS

From 371 patients included, 94 were categorized as suspected ACS and 277 as non-ACS. Patient-based analysis showed an area under the receiver-operating-characteristic curve (AUC) for detecting ≥ 50% coronary stenosis of 0.95 (95% CI: 0.88-0.98) in ACS and 0.92 (95% CI: 0.88-0.95) in non-ACS group (P=0.29). The sensitivity, specificity, positive and negative predictive values of MDCTA were 0.90(0.80-0.96), 0.88(0.70-0.98), 0.95(0.87-0.99) and 0.77(0.58-0.90) in suspected ACS patients and 0.87(0.81-0.92), 0.86(0.79-0.92), 0.91(0.85-0.95) and 0.82(0.74-0.89) in non-ACS patients (P NS for all comparisons). The mean calcium scores (CS) were 282 ± 449 in suspected ACS and 435 ± 668 in non-ACS group. The accuracy of CS to detect significant coronary stenosis was only moderate and the absence or minimal coronary artery calcification could not exclude the presence of significant coronary stenosis, particularly in ACS patients.

CONCLUSIONS

The diagnostic accuracy of MDCTA to detect significant coronary stenosis is high and comparable for both ACS and non-ACS patients.

Inverse association between bone microarchitecture assessed by HR-pQCT and coronary artery calcification in patients with end-stage renal disease

It is a matter of debate whether vascular calcification and bone loss are simultaneously occurring but largely independent processes or whether poor bone health predisposes to vascular calcification, especially in patients with kidney disease. Here we investigated the association between the changes of microarchitecture in weight bearing bone and the extent of coronary artery calcification in patients with chronic renal failure. The bone microarchitecture of the tibia using high-resolution peripheral quantitative computed tomography (HR-pQCT), bone mineral density using dual X-ray absorptiometry (DXA) of the lumbar spine, femoral neck and distal radius as well as coronary artery calcification using multi-slice CT and reported as Agatston score were measured in 66 patients with end-stage renal disease on chronic hemodialysis. Markers of bone turnover, vitamin D status and intact parathyroid hormone (iPTH) were assessed. CAC score was found to be <100 in 39% and ≥100 in 61% of patients. The median [95% CI] total CAC score was 282 [315-2587]. By univariate analysis, significant correlations between CAC and age (R=0.52, p<0.001), weight (R=0.3, p<0.01) and serum cross laps (CTX, R=-0.39, p<0.01) were found, and parameters of bone microarchitecture were numerically but not significantly lower in patients with CAC scores ≥100. In multivariate analysis stratifying for gender and correcting for age, tibial density (Dtot) and bone volume/total volume (BV/TV) were significantly lower in patients with CAC scores ≥100 (p<0.05 for both). Low trabecular bone volume and decreased cortical bone density are associated with coronary artery calcification in dialysis patients.

Distribution of coronary calcifications in patients with suspected coronary heart disease

BACKGROUND

Coronary calcifications are a marker of coronary atherosclerosis. The role of coronary calcium scoring (CS) as part of the initial evaluation of patients with suspected coronary heart disease (CHD) is controversially discussed. The primary goal of this study was to characterize the coronary calcium distribution in this particular patient population. In a second step, we aimed to establish a possible clinical implication using CS for the diagnosis of CHD.

METHODS

Calcium scoring procedure was performed by either using a multidetector or a dual-source computed tomographic scanner. All patients underwent invasive coronary angiography (ICA) as the current criterion standard for CHD detection. A total of 4,137 (2,780 men, mean age 60.5 ± 12.4 years) consecutive patients were included.

RESULTS

Mean CS was 288 ± 446 (range 0-5,252). Overall coronary artery calcifications significantly increased with patients' age. In 2,048 patients (mean CS 101 ± 239, range 0-5252), significant CHD (≥50% stenosis) was excluded by ICA (1,939 patients without calcifications). In remaining 2,089 patients (51%, mean CS 607 ± 821, range 0-5,252), significant CHD was documented leading to intervention in 732 patients. A threshold of zero calcifications (existence of calcified tissue) had the best overall sensitivity and negative predictive value with 99%. Overall specificity with 34% and overall positive predictive value with 24% were rather low.

CONCLUSION

Coronary calcium scoring is able to exclude significant CHD in patients with suspected CHD with a high negative predictive value and, therefore, possibly reduce the number of invasive diagnostic examinations. Because of the low specificity and positive predictive value, CS cannot be used to indicate ICA.

Coronary artery calcium score: a review

Context

Coronary artery disease (CAD) is the foremost cause of death in many countries and hence, its early diagnosis is usually concerned as a major healthcare priority. Coronary artery calcium scoring (CACS) using either electron beam computed tomography (EBCT) or multislice computed tomography (MSCT) has been applied for more than 20 years to provide an early CAD diagnosis in clinical routine practice. Moreover, its association with other body organs has been a matter of vast research.

Evidence Acquisition

In this review article, techniques of CACS using EBCT and MSCT scanners as well as clinical and research indications of CACS are searched from PubMed, ISI Web of Science, Google Scholar and Scopus databases in a time period between late 1970s through July 2013 and following appropriate selection, dealt with. Moreover, the previous and ongoing research subjects and their results are discussed.

Results

The CACS is vastly applied in early detection of CAD and in many other research fields.

Conclusions

CACS has remarkably changed the screening techniques to detect CAD earlier than before and is generally accepted as a standard of reference for determination of risk of further cardiac events.

Individuals with coronary artery disease at a young age and features of the metabolic syndrome have an increased prothrombotic potential

The relation between coagulation and atherosclerosis has been extensively described, pointing towards a hypercoagulable state in patients with atherosclerosis, especially in young individuals. However, not all studies were conclusive. It is known that the metabolic syndrome (MetS), a risk factor for coronary artery disease (CAD), is related to a higher incidence of thrombo-embolic events. We hypothesised that individuals with CAD at a young age and MetS have an increased prothrombotic potential. It was the study objective to analyse the endogenous thrombin potential (ETP) and related thrombin generation parameters in patients with CAD before the age of 51 in men and 56 in women with and without MetS features and their healthy first-degree relatives. In this case-control study we included 118 CAD patients and 50 first-degree relatives (controls). Parameters of thrombin generation were obtained with calibrated automated thrombinography. An adjusted general linear model (GLM) showed a positive association between the peak thrombin levels and the presence of CAD at a young age. Based on the NCEP criteria we divided our patient group in CAD patients with and without MetS, and compared them to the controls without MetS. We showed that CAD patients with MetS have increased ETP levels, both in comparison with healthy first-degree relatives and with CAD patients without MetS. There were no differences in ETP between patients without MetS and healthy controls. In conclusion, this study shows that individuals with CAD at a young age and MetS features have an increased prothrombotic potential, compared to CAD patients without MetS.

Role of imaging for acute chest pain syndromes

Acute chest pain suggestive of ischemic cardiac origin, with a normal or nondiagnostic electrocardiogram and negative initial cardiac markers for myocardial necrosis represent a significant diagnostic dilemma for clinicians. Multiple imaging modalities play a pivotal role in early diagnosis and safe discharge of these patients. In this review, we compare the current imaging modalities available for these patients including their diagnostic accuracy, feasibility, and cost effectiveness. Acute rest myocardial perfusion imaging significantly improves the clinical outcome in these patients and reduces the overall cost when incorporated into the decision making pathway. The choice of imaging modality recommended should be based on local institutional expertise and the overall clinical presentation. The imaging modality with high diagnostic accuracy and negative predictive value will provide for precise risk stratification which is important to clinical decision making, including patients who require admission to the hospital and those who can be safely discharged.

Calcium-phosphorus product concentration is a risk factor of coronary artery disease in metabolic syndrome

BACKGROUND

High serum phosphorus and the calcium-phosphorus product concentration has been associated with increased mortality and cardiovascular events in patients with chronic kidney disease.

OBJECTIVE

This study was designed to determine the relationship between calcium-phosphorus product concentration and the presence of coronary artery calcification in subjects with metabolic syndrome (MetS).

METHODS

We reviewed the medical records of 2056 general subjects with a mean age of 55.1 ± 9.9 years and a glomerular filtration rate of 88.9 ± 16.2 mL/min/1.73 m(2). The enrolled subjects consisted of 384 (18.7%) subjects with MetS and 1672 (81.3%) subjects without MetS. The severity of coronary artery calcification was assessed by the coronary artery calcification score (CACS) using multi-detector computed tomography (MDCT).

RESULTS

The CACS correlated with calcium-phosphorus product concentration in subjects with MetS (r = 0.184, P < 0.01). The odds ratio of calcium-phosphorus product concentration having CACS >50 was 1.053 in subjects with MetS (P < 0.05). After adjustment for age, sex, diabetes, and dyslipidemia, calcium-phosphorus product concentrations had a positive correlation with CACS in subjects with MetS. In single regression analysis, calcium-phosphorus product concentration as independent variable was the significant predictor of CACS in subjects with MetS. Using a multivariate analysis, calcium-phosphorus product concentration remained a significant factor associated with CACS in subjects with MetS.

CONCLUSIONS

Calcium-phosphorus product concentration was weakly associated with CACS and an independent factor predicting for CACS by MDCT in subjects with MetS. These results suggest that calcium-phosphorus product concentration might be considered as a risk factor of coronary artery disease in subjects with MetS.

Significance of coronary calcification for prediction of coronary artery disease and cardiac events based on 64-slice coronary computed tomography angiography

This work aims to validate the clinical significance of coronary artery calcium score (CACS) in predicting coronary artery disease (CAD) and cardiac events in 100 symptomatic patients (aged 37-87 years, mean 62.5, 81 males) that were followed up for a mean of 5 years. Our results showed that patients with CAD and cardiac events had significantly higher CACS than those without CAD and cardiac events, respectively. The corresponding data were 1450.42 ± 3471.24 versus 130 ± 188.29 (P < 0.001) for CAD, and 1558.67 ± 513.29 versus 400.46 ± 104.47 (P = 0.031) for cardiac events. Of 72 patients with CAD, cardiac events were found in 56 (77.7%) patients. The prevalence of cardiac events in our cohort was 13.3% for calcium score 0, 50% for score 11-100, 56% for score 101-400, 68.7% for score 401-1,000, and 75.0% for score >1000. Increased CACS (>100) was also associated with an increased frequency of multi-vessel disease. Nonetheless, 3 (20%) out of 15 patients with zero CACS had single-vessel disease. Significant correlation (P < 0.001) was observed between CACS and CAD on a vessel-based analysis for coronary arteries. It is concluded that CACS is significantly correlated with CAD and cardiac events.

Coronary Artery Calcium Testing in Symptomatic Patients: An Issue of Diagnostic Efficiency

The detection and quantification of coronary artery calcification (CAC) significantly improves cardiovascular risk prediction in asymptomatic patients. Many have advocated for expanded CAC testing in symptomatic patients based on data demonstrating that the absence of quantifiable CAC in patients with possible angina makes obstructive coronary artery disease (CAD) and subsequent adverse events highly unlikely. However, the widespread use of CAC testing in symptomatic patients may be limited by the high background prevalence of CAC and its low specificity for obstructive CAD, necessitating additional testing ('test layering') in a large percentage of eligible patients. Further, adequately powered prospective studies validating the comparative effectiveness of a 'CAC first' approach with regards to cost, safety, accuracy and clinical outcomes are lacking. Due to marked reductions in patient radiation exposure and higher comparative accuracy and prognostic value make coronary computed tomographic angiography the preferred CT-based test for appropriately selected symptomatic patients.

What is the role of calcium scoring in the age of coronary computed tomographic angiography?

Non-contrast-enhanced CT for coronary artery calcification (CAC) as a marker of coronary atherosclerosis has been studied extensively in the primary prevention setting. With rapidly evolving multidetector CT technology, contrast-enhanced coronary CT angiography (CCTA) has emerged as the non-invasive method of choice for detailed imaging of the coronary tree. In this review, we systematically evaluate the role of CAC testing in the age of CCTA in both asymptomatic and symptomatic patients, across varying levels of risk. Although the role of CAC testing is well established in asymptomatic subjects, its use in evaluating those with stable symptoms that represent possible obstructive coronary artery disease is controversial. Nevertheless, available data suggest that in low-to-intermediate risk symptomatic patients, CAC scanning may serve as an appropriate gatekeeper to further testing with either CCTA (if no or only mild CAC present) versus functional imaging or invasive coronary angiography (when moderate or severe CAC present). Given the strong short-term prognostic value of CAC = 0, studies are needed to further evaluate the role of CAC scanning in low-risk patients with acute chest pain presenting to the emergency room.

Role of nonenhanced multidetector CT coronary artery calcium testing in asymptomatic and symptomatic individuals

Arteriosclerotic cardiovascular disease is the leading cause of death in the United States, with coronary artery disease (CAD) accounting for half of all cardiovascular disease deaths. Current risk assessment approaches for coronary heart disease, such as the Framingham risk score, substantially misclassify intermediate- to long-term risk for the occurrence of CAD in asymptomatic individuals. A screening modality such as a simple non-contrast-enhanced, or noncontrast, computed tomographic (CT) detection of coronary artery calcium (CAC) improves the ability to accurately predict risk in vulnerable groups and adds information above and beyond global risk assessment as shown by the recent Multi-Ethnic Study of Atherosclerosis. In addition, absence of CAC is associated with a very low risk of future CAD and as a result can be used to identify a group among which further testing and pharmacotherapies can be avoided. The Expert Consensus Document by the American College of Cardiology Foundation and the American Heart Association now recommends screening individuals at intermediate risk but did not find enough evidence to recommend CAC testing and further stratification of those in the low- or high-risk categories for CAD. In addition, emerging guidelines have suggested that absence of CAC can act as a "gatekeeper" for further testing among low- and intermediate-risk patients presenting with chest pain. This review of the current literature outlines the role of CAC testing in both asymptomatic and symptomatic individuals.

Utility of coronary artery calcium scoring in the evaluation of patients with chest pain

Although coronary artery calcium (CAC) scoring has an established role in risk-stratifying asymptomatic patients at intermediate risk of coronary heart disease (CHD), its utility in the evaluation of patients with chest pain is uncertain. We conducted a literature review of articles investigating the utility of: (1) CAC scoring in elective patients with indeterminate chest pain symptoms, (2) CAC as a "gatekeeper" in the triage of patients presenting to the emergency department (ED) with chest pain, and (3) the cost-effectiveness of the use of CAC scoring in the ED. We also evaluated the predictive accuracy of the absence of CAC in a pooled analysis of applicable studies. Only studies evaluating patients classified as low or intermediate risk were included. Low to intermediate risk was established by Framingham risk scores, Thrombolysis in Myocardial Infarction scores, Diamond-Forrester classification, or by the absence of typical angina symptoms, ischemic electrocardiogram, positive cardiac biomarkers, or a prior history of CHD. In our pooled analysis, the presence of any CAC resulted in a high sensitivity (range 70%-100%) for predicting the presence of obstructive coronary disease among symptomatic patients subsequently referred for coronary angiography. More importantly, a CAC score of 0 in low- and intermediate-risk ED populations with chest pain had a high negative predictive value (99.4%) for CHD events over an average follow-up of 21 months. CAC scoring also seems cost-effective in this population. Although further research is needed, carefully selected ED patients with a normal electrocardiogram, normal cardiac biomarkers, and CAC = 0 may be considered for early discharge without further testing.

Non-invasive imaging in coronary artery disease including anatomical and functional evaluation of ischaemia and viability assessment

Coronary artery disease has an important impact on the morbidity and mortality statistics and health economics worldwide. Diagnosis of coronary artery disease is important in risk stratification and guides further management. Invasive coronary angiography is the traditional method of imaging the coronary arteries and remains the gold standard. It detects luminal stenosis but provides little information about the vessel wall or plaques. Besides, not all anatomical lesions are functionally significant. This has lent itself to a wide variety of imaging techniques to identify and assess a flow-limiting stenosis. The approach to diagnosis of coronary artery disease is broadly based on anatomical and functional imaging. Coronary CT and MRI of coronary arteries provide an anatomical assessment of coronary stenosis. Coronary calcium score and coronary CT assess subclinical atherosclerosis by assessing the atherosclerotic plaque burden. The haemodynamic significance of a coronary artery stenosis can be assessed by stress radioisotope studies, stress echocardiography and stress MRI. The more recent literature also focuses on plaque assessment and identification of plaques that are likely to give rise to an acute coronary syndrome. There is an explosion of literature on the merits and limitations of the different imaging modalities. This review article will provide an overview of all the imaging modalities in the diagnosis of coronary artery disease.

Impact of epicardial fat volume on coronary artery disease in symptomatic patients with a zero calcium score

BACKGROUND

This study sought to evaluate the prevalence of coronary artery disease (CAD) and the impact of epicardial fat volume (EFV) on CAD in symptomatic patients with a zero calcium score (CS) using multislice computed tomography (MSCT).

METHODS

In this study, 1308 consecutive symptomatic patients who underwent 64-slice MSCT with a zero CS were evaluated. EFV was quantified with CS data sets. Presence of an obstructive plaque (diameter stenosis >50%) and a CT-derived vulnerable plaque, which was defined as a plaque with remodeling index >1.10 and mean CT density value <3 0HU, was assessed with a CT coronary angiography.

RESULTS

Obstructive plaques were detected in 86 patients (7%) and CT-derived vulnerable plaques in 63 (5%). EFV was larger in patients with obstructive plaques than no plaque (124.3 ± 43.2 cm(3) vs. 95.1 ± 40.3 cm(3); p<0.01). Patients with CT-derived vulnerable plaques had a greater amount of EFV than no plaque (133.0 ± 40.2 cm(3) vs. 95.1 ± 40.3 cm(3); p<0.01). Multivariate analysis revealed EFV as a predictor of the presence of an obstructive and a CT-derived vulnerable plaque (per 10 cm(3); Odds ratio (OR) 1.10; 95% confidence interval (CI), 1.04-1.16; p<0.01 and OR 1.19; 95% CI, 1.12-1.27; p<0.01). The combination of EFV and Framingham risk score (FRS) resulted in an area under the receiver-operating characteristic curve for prediction of obstructive and CT-derived vulnerable plaque of 0.75 and 0.75, which was significantly higher than 0.68 and 0.64 for FRS alone (p=0.02 and p<0.01).

CONCLUSIONS

A zero CS doesn't exclude CAD and EFV can be a useful marker of CAD in symptomatic zero CS patients.

Coronary CT and the coronary calcium score, the future of ED risk stratification?

Accurate and efficient evaluation of acute chest pain remains clinically challenging because traditional diagnostic modalities have many limitations. Recent improvement in non-invasive imaging technologies could potentially improve both diagnostic efficiency and clinical outcomes of patients with acute chest pain while reducing unnecessary hospitalizations. However, there is still controversy regarding much of the evidence for these technologies. This article reviews the role of coronary artery calcium score and the coronary computed tomography in the assessment of individual coronary risk and their usefulness in the emergency department in facilitating appropriate disposition decisions. The evidence base and clinical applications for both techniques are also described, together with cost- effectiveness and radiation exposure considerations.

[Radiologists in the emergency department: when and how to use multislice CT]

Chest pain is a challenging clinical problem in the emergency department. Despite advances in clinical diagnosis, many patients with atypical chest pain are needlessly hospitalized and others are mistakenly discharged. Faced with the specific clinical situation in which a patient has chest pain, an initially normal or inconclusive electrocardiogram, and normal cardiac biomarkers, multislice CT has proven useful for ruling out the conditions that involve the greatest morbidity and mortality and for establishing the cause of pain. This article reviews the current usefulness of multislice CT in the diagnostic workup of patients presenting at the emergency department with chest pain. We review the technique, define the most appropriate population, describe the acquisition protocols, and discuss the advantages and disadvantages of each study protocol.