Radiation Dose to Patients From Cardiac Diagnostic Imaging

Coronary computed tomography angiography for early triage of patients with acute chest pain: the ROMICAT (Rule Out Myocardial Infarction using Computer Assisted Tomography) trial

OBJECTIVES

This study was designed to determine the usefulness of coronary computed tomography angiography (CTA) in patients with acute chest pain.

BACKGROUND

Triage of chest pain patients in the emergency department remains challenging.

METHODS

We used an observational cohort study in chest pain patients with normal initial troponin and nonischemic electrocardiogram. A 64-slice coronary CTA was performed before admission to detect coronary plaque and stenosis (>50% luminal narrowing). Results were not disclosed. End points were acute coronary syndrome (ACS) during index hospitalization and major adverse cardiac events during 6-month follow-up.

RESULTS

Among 368 patients (mean age 53 +/- 12 years, 61% men), 31 had ACS (8%). By coronary CTA, 50% of these patients were free of coronary artery disease (CAD), 31% had nonobstructive disease, and 19% had inconclusive or positive computed tomography for significant stenosis. Sensitivity and negative predictive value for ACS were 100% (n = 183 of 368; 95% confidence interval [CI]: 98% to 100%) and 100% (95% CI: 89% to 100%), respectively, with the absence of CAD and 77% (95% CI: 59% to 90%) and 98% (n = 300 of 368, 95% CI: 95% to 99%), respectively, with significant stenosis by coronary CTA. Specificity of presence of plaque and stenosis for ACS were 54% (95% CI: 49% to 60%) and 87% (95% CI: 83% to 90%), respectively. Only 1 ACS occurred in the absence of calcified plaque. Both the extent of coronary plaque and presence of stenosis predicted ACS independently and incrementally to Thrombolysis In Myocardial Infarction risk score (area under curve: 0.88, 0.82, vs. 0.63, respectively; all p < 0.0001).

CONCLUSIONS

Fifty percent of patients with acute chest pain and low to intermediate likelihood of ACS were free of CAD by computed tomography and had no ACS. Given the large number of such patients, early coronary CTA may significantly improve patient management in the emergency department.

Triple rule-out CT in patients with suspicion of acute pulmonary embolism: findings and accuracy

RATIONALE AND OBJECTIVES

The aim of this study was to prospectively investigate the diagnostic value of triple rule-out computed tomography (CT) in patients suspected of having acute pulmonary embolism (PE).

MATERIALS AND METHODS

A total of 125 patients with suspicion of PE, of whom 14 patients had the additional clinical suspicion of acute aortic syndrome, underwent electrocardiogram-gated triple rule-out dual-source CT. The contrast media application protocol was adjusted to obtain a homogenous attenuation of the pulmonary arteries, thoracic aorta, and coronary arteries. The diagnostic performance of triple rule-out CT was assessed by using adjudicated discharge diagnoses as reference standards.

RESULTS

A total of 161 adjudicated cardiovascular discharge diagnoses were made in the 125 patients (including all true-positive and true-negative findings): acute PE was found in 26 (21%) and was excluded by CT in 99 (79%), coronary artery disease was found in 3 (3%) and was excluded by catheter angiography in 9 (6%), left ventricular systolic dysfunction was found in 2 (2%) and was excluded by echocardiography in 8 (6%), and acute aortic syndrome was found in 5 (4%) and was excluded by CT in 9 (7%) patients. Nonvascular chest disease was found in 34 (27%) and included pneumonia (n = 17), neoplasms (n = 5), fractures/osteolysis (n = 3), pericarditis (n = 2), and post-pneumonectomy syndrome (n = 1). Triple rule-out CT was normal in 53 (42%) patients. Overall sensitivity, specificity, and positive and negative predictive value of triple rule-out CT for cardiovascular disease were 100% (95% confidence interval [CI] 90-100%), 98% (95%CI 94-100%), 95% (95%CI 82-99%), and 100% (95%CI 97-100%, respectively).

CONCLUSIONS

Triple rule-out CT is feasible in patients with suspicion of PE, reveals a wide range of vascular and non-vascular chest disease, and offers an excellent overall diagnostic performance.

Technical advances in cardiovascular imaging

Cardiovascular imaging technology is continuously evolving and provides an increasing array of tests to evaluate cardiovascular morphology and function. A basic understanding of imaging technology is helpful to select the best modality to answer a specific clinical question. This article provides a brief overview of recent technical developments in computed tomography (CT), magnetic resonance (MR), and echocardiography, which have increased our diagnostic understanding and may modulate treatment planning of patients with cardiovascular diseases: electrocardiographically (ECG)-gated CT, 4D-flow magnetic resonance imaging (MRI), and three-dimensional (3D) echocardiography.

Determinants of vessel contrast in BMI-adapted low dose CT coronary angiography with prospective ECG-triggering

We evaluated the determinants of vessel contrast in prospectively ECG-triggered CT coronary angiography (CTCA). Seventy patients underwent low-dose CTCA using body mass index (BMI)-adapted tube parameters and a fixed contrast material bolus. Contrast to noise ratio (CNR) was calculated from contrast (between coronaries and perivascular tissue) and image noise (standard deviation of aortic attenuation). Cardiac output (CO) was calculated from gated (99m)Tc-tetrofosmin-SPECT. Mean radiation dose was 2.13 +/- 0.69 mSv. Image noise was not affected by BMI (r = 0.1, P = 0.36), while CNR was inversely related to body surface area (BSA) (r = -0.5, P < 0.001) and CO (r = -0.45, P < 0.001). After successfully overcoming the impact of BMI on image noise by adapting tube parameters, CNR mainly depends on coronary vessel contrast. The latter reflects the dilution of the contrast material by blood volume and CO, which are both correlated to BSA. Therefore, BSA adapted contrast administration may help to compensate for this effect.

Sixty-four-slice multidetector computed tomography: an accurate imaging modality for the evaluation of coronary arteries in dilated cardiomyopathy of unknown etiology

BACKGROUND

The goal of this study was to assess the safety, feasibility, and diagnostic accuracy of 64-slice multidetector computed tomography (MDCT) for the evaluation of coronary arteries in dilated cardiomyopathy (DCM) of unknown etiology. Sixteen-slice MDCT is useful in patients affected by DCM. However, technical limitations, such as cardiac arrhythmias, an inability of patients to sustain a long breath-hold, and the need of a high dose of contrast agent may limit its accuracy and widespread use.

METHODS AND RESULTS

Invasive coronary angiography (ICA) and MDCT coronary angiography were performed on 132 consecutive patients (82 men; age 63+/-11 years) affected by DCM (ejection fraction, 34+/-10%) of unknown etiology. In 2 patients (1.5%), MDCT was not feasible because of atrial fibrillation. Of the remaining 130 patients, 88 exhibited normal and 42 exhibited diseased coronary arteries in both MDCT and ICA. All patients with coronary artery disease except for 1 were correctly classified by MDCT as 1-vessel (11 cases), 2-vessel (13 cases), and 3-vessel (18 cases) disease. In the segment-based analyses, the overall feasibility for MDCT was 98.5% (1902 of 1930 segments). Segment-based and patient-based analyses for the detection of luminal stenosis of >50% and >70% were performed. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of MDCT for the detection of >50% stenosis were 98.1%, 99.9%, 98.7%, 99.8%, and 99.7%, respectively. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of MDCT for the detection of >70% stenosis were 99.5%, 98.6%, 94.1%, 99.9%, and 99.4%, respectively.

CONCLUSIONS

Excellent feasibility and diagnostic accuracy, combined with low invasiveness, make 64-slice MDCT an ideal imaging modality for the anatomic evaluation of coronary circulation in patients with DCM of unknown etiology.

The limited utility of routine cardiac stress testing in emergency department chest pain patients younger than 40 years

STUDY OBJECTIVE

This is a study designed to evaluate the utility of routine provocative cardiac testing in low-risk young adult (younger than 40 years) patients evaluated for an acute coronary syndrome in an emergency department (ED) setting.

METHODS

This was a retrospective observational study of patients aged 23 to 40 years who were evaluated for acute coronary syndrome in an ED-based chest pain unit from March 2004 to September 2007. All patients had serial cardiac biomarker testing to rule out myocardial infarction and then underwent provocative cardiac testing to identify the presence of myocardial ischemia. Patients were excluded from the study if they had known coronary artery disease, had ECG findings diagnostic of myocardial infarction or ischemia, or self-admitted, or tested positive for cocaine use.

RESULTS

Of the 220 patients who met inclusion criteria, 6 patients (2.7%; 95% confidence interval 1% to 5.8%) had positive stress test results. Among these 6 patients, 4 underwent subsequent coronary angiography that demonstrated no obstructive coronary disease, suggesting the initial provocative study was falsely positive. For the remaining 2 patients, no diagnostic angiography was performed. Discounting the patients who had negative angiography results, only 2 of 220 study patients (0.9%; 95% confidence interval 0.1% to 3.2%) had a provocative test result that was positive for myocardial ischemia.

CONCLUSION

In our study, a combination of age younger than 40 years, nondiagnostic ECG result, and 2 sets of negative cardiac biomarker results at least 6 hours apart identified a patient group with a very low rate of true-positive provocative testing. Routine stress testing added little to the diagnostic evaluation of this patient group and was falsely positive in all patients who consented to diagnostic coronary angiography (4 of 6 cases).

Radiation exposure in cardiac multislice spiral computed tomography (MSCT)

Computed tomographic (CT) imaging involves exposure to ionizing radiation, with a consequent potential risk to the patient. Here we review the technical factors that affect the radiation dose in cardiac CT diagnostic procedures, the parameters that are used to measure and compare radiation doses, the magnitude of radiation exposure, and how to efficiently reduce it.

Randomized trial of computerized quantitative pretest probability in low-risk chest pain patients: effect on safety and resource use

STUDY OBJECTIVE

We hypothesize that the presentation of a quantitative pretest probability of acute coronary syndrome would safely reduce unnecessary resource use in low-risk emergency department (ED) chest pain patients.

METHODS

Randomized controlled trial of adult patients with chest pain paired with their clinicians. Patients had neither obvious evidence of acute coronary syndrome nor obvious other reason for admission. Clinicans provided their unstructured point estimate for pretest probability before randomization. Clinicans and patients in the intervention group received a printout of pretest probability of acute coronary syndrome result displayed numerically and graphically. Controls received no printout. Patients were followed for 45 days for predefined criteria of acute coronary syndrome and efficacy endpoints. Endpoints were compared between groups, with 95% confidence intervals (CIs) for differences.

RESULTS

Four hundred were enrolled, and 31 were excluded for cocaine use or elopement from care. The mean pretest probability estimates of acute coronary syndrome were 4 (SD 5%) from clinicians and 4 (SD 6%) from the computer. Safety and efficacy endpoints for controls (n=185) versus intervention patients (n=184) were as follows: (1) delayed or missed diagnosis of acute coronary syndrome: 1 of 185 versus 0 of 184 (95% CI for difference -2.8% to 15.0%); (2) hospital admission with no significant cardiovascular diagnosis, 11% versus 5% (-0.2% to 11%); (3) thoracic imaging imparting greater than 5 mSv radiation with a negative result, 20% versus 9% (95% CI for difference = 3.8% to 18.0%); (4) median length of stay, 11.4 hours versus 9.2 hours (95% CI for difference = -2.9 to 7.6 hours); (5) reported feeling "very satisfied" with clinician explanation of problem on follow-up survey, 38% versus 49% (95% CI for difference = 0.9% to 21.0%); (6) readmitted within 7 days, 11% versus 4% (95% CI for difference = 2.5% to 13.2%).

CONCLUSION

Presentation of a quantitative estimate of the pretest probability of acute coronary syndrome to clinicians and low-risk ED chest pain patients was associated with reduced resource use, without evidence of increased rate of premature discharge of patients with acute coronary syndrome.

Low-dose CT coronary angiography using prospective ECG-triggering: impact of mean heart rate and heart rate variability on image quality

RATIONALE AND OBJECTIVES

The aim of this study was to evaluate the effect of mean heart rate (HR) and HR variability on image quality in low-dose computed tomographic coronary angiography (CTCA) using prospective electrocardiographic (ECG) triggering.

MATERIALS AND METHODS

One hundred thirty-six consecutive patients were scheduled for low-dose CTCA using prospective ECG triggering. The image quality of all coronary segments was rated on a 5-point scale by two independent readers (scores of 1-3 were considered diagnostic, and scores of 4 and 5 were considered nondiagnostic). Intravenous beta blockers were administered targeting HR < 65 beats/min before scanning, but not if HR increased during scanning.

RESULTS

After the exclusion of seven patients because of arrhythmia (n = 4) or mean HRs > 65 beats/min despite using beta blockers (n = 3), 129 patients underwent computed tomographic scanning. The estimated mean effective radiation dose was 2.2 +/- 0.7 mSv (range, 1.1-3.5). The mean HR during scanning was 58.4 +/- 6.6 beats/min (range, 44.2-80.1), with a variability of 1.6 +/- 1.0 beats/min (range, 0.2-5.3). Mean HR (r = 0.49, P < .001) but not mean HR variability (r = 0.14) was related to image quality. Nondiagnostic image quality on CTCA was found in 5% of the coronary segments in 21 of 129 patients. However, on receiver-operating characteristic analysis, a cutoff HR of 62 beats/min was determined, below which nondiagnostic segments were significantly less frequent (2% vs 14%, P < .001).

CONCLUSION

Prospective triggering allows low-dose CTCA but requires a low HR. Because a low HR offers a prolonged diastole, widening the optimal phase for scanning, HR variability seems to have a negligible impact on image quality.

Patient radiation doses in interventional cardiology procedures

Interventional cardiology procedures result in substantial patient radiation doses due to prolonged fluoroscopy time and radiographic exposure. The procedures that are most frequently performed are coronary angiography, percutaneous coronary interventions, diagnostic electrophysiology studies and radiofrequency catheter ablation. Patient radiation dose in these procedures can be assessed either by measurements on a series of patients in real clinical practice or measurements using patient-equivalent phantoms. In this article we review the derived doses at non-pediatric patients from 72 relevant studies published during the last 22 years in international scientific literature. Published results indicate that patient radiation doses vary widely among the different interventional cardiology procedures but also among equivalent studies. Discrepancies of the derived results are patient-, procedure-, physician-, and fluoroscopic equipmentrelated. Nevertheless, interventional cardiology procedures can subject patients to considerable radiation doses. Efforts to minimize patient exposure should always be undertaken.

Reassessment of radiation risks from electrophysiology procedures compared to coronary angiography

BACKGROUND

Electrophysiology (EP) procedures have been reported to carry a significantly greater radiation risk than that of coronary angiography (CA). This is largely due to numerous reports linking severe deterministic radiation effects to long procedure and fluoroscopy times (FTs). This study documents low radiation doses achieved by strategies involving operator training and education as well as equipment and technique optimisation to reduce radiation risks.

METHODS

Records relating to 732 diagnostic EP and 1744 therapeutic EP procedures performed between January 2002 and December 2007 were analysed. Data from 1458 diagnostic only CA procedures performed in 2006 was used for comparison. For each procedure type, FT, number of digital frames acquired and estimated effective dose (E) were compared.

RESULTS

Although the FT for CA procedures is significantly less than for therapeutic EP procedures (FT for diagnostic EP being similar), EP procedures generally are associated with lower E, the exception being procedures for atrial fibrillation (AF).

CONCLUSION

Through the application of a comprehensive exposure minimisation strategy, the radiation risk to patients undergoing diagnostic and, therapeutic EP procedures (except AF ablation procedures) is significantly less than that faced by patients undergoing CA. E, however, is heavily dependent on procedure type and as such care must be taken in undertaking generalised comparisons for audit and benchmarking purposes.

Prospectively gated axial CT coronary angiography: preliminary experiences with a novel low-dose technique

To assess image quality and radiation exposure with prospectively gated axial CT coronary angiography (PGA) compared to retrospectively gated helical techniques (RGH). Forty patients with suspected coronary artery disease (CAD) and a stable heart rate below 65 bpm underwent CT coronary angiography (CTCA) using a 64-channel CT system. The patient cohort consisted of 20 consecutive patients examined using a PGA technique and 20 patients examined using a standard RGH technique. Both groups were matched demographically according to age, gender, body mass index, and heart rate. For both groups, two independent observers assessed image quality for all coronary segments on an ordinal scale from 1 (nonassessable) to 5 (excellent quality). Image quality and radiation exposure were compared between patient groups. There were no significant differences in vessel-based image quality between the two groups (P > 0.05). Mean (+/- SD) effective radiation exposure in the PGA group was 3.7 +/- 0.8 mSv compared to 18.9 +/- 3.8 mSv in the RGH group without ECG-based tube current modulation (P < 0.001). Preliminary experience shows PGA technique to be a promising approach for CTCA resulting in a substantial reduction in radiation exposure with image quality comparable to that of standard RGH technique.

Accuracy of low-dose computed tomography coronary angiography using prospective electrocardiogram-triggering: first clinical experience

AIMS

To evaluate the accuracy of low-dose computed tomography coronary angiography (CTCA) using prospective ECG-triggering for the assessment of coronary artery disease (CAD).

METHODS AND RESULTS

A total of 30 patients (19 males, 11 females, mean age 58.8 +/- 9.9 years) underwent low-dose CTCA and invasive coronary angiography (CA) [median 2 days (0, 41)]. Before CT scanning, intravenous beta-blocker was administered in 18 of 30 patients as heart rate (HR) was >65 b.p.m., achieving a mean HR of 55.7 +/- 7.9 b.p.m. CAD was defined as coronary artery narrowing > or =50%, using CA as standard of reference. The estimated mean effective radiation dose was 2.1 +/- 0.7 mSv (range: 1.0-3.3), yielding 96.0% (383/399) of evaluable segments. On an intention-to-diagnose-base, all non-evaluative segments were included in the analysis. Vessels with a non-evaluative segment and no further finding were censored as false positive. Patient-based analysis revealed sensitivity, specificity, positive predictive value, and negative predictive value of 100, 83.3, 90.0, and 100%, respectively. The respective values per vessel were 100, 88.9, 85.7, and 100%, respectively.

CONCLUSION

Prospective ECG-triggering allows low-dose CTCA and provides high diagnostic accuracy in the assessment of CAD in patients with stable sinus rhythm and a low heart rate.

Low radiation dose imaging of myocardial perfusion and coronary angiography with a hybrid PET/CT scanner

Objectives:

To test the image quality and feasibility of a sequential low radiation dose protocol for hybrid cardiac PET/CT angiography (CTA).

Background:

Multidetector computed tomography (MDCT) is a non-invasive method for coronary angiography. The negative predictive value of MDCT is high but perfusion imaging has a role in detecting functional significance of coronary lesions. This has encouraged combining these techniques. However, radiation dose is of concern. We report our first experiences with a low dose sequential CTA mode applicable to hybrid imaging.

Methods:

In the first phase, 10 consecutive cardiac MDCT angiographies were performed with spiral acquisition and compared in terms of image quality and dose with the following 10 patients performed with a new sequential mode. In the second phase, feasibility and radiation dose of a combined ¹⁵O-water rest-stress PET perfusion/sequential CTA protocol were assessed in another group of 61 consecutive patients.

Results:

Mean effective radiation dose was 60% lower in the sequential group than in the spiral group (19·3 versus 7·6 mSv, P<0·001). In the second phase, the new sequential hybrid protocol proved possible in 87% of the patients given the preconditions determined by the manufacturer. Mean effective dose of the CT acquisition was 7·6 mSv and total dose from the PET/CTA hybrid study 9·5 mSv.

Conclusion:

Low dose PET/CT allows cardiac hybrid studies with <10 mSv. The protocol can be applied to almost nine out of 10 patients with CT image quality comparable to spiral acquisition.

Noninvasive assessment of coronary anatomy and myocardial perfusion: going toward an integrated imaging approach

Many noninvasive imaging techniques are available for the evaluation of patients with known or suspected chronic coronary artery disease. Among these, computed tomography-based techniques allow the quantification of coronary atherosclerotic calcium and noninvasive imaging of coronary arteries, whereas nuclear cardiology is the most widely used noninvasive approach for the assessment of myocardial perfusion. The available single-photon emission computed tomography flow agents are characterized by a cardiac uptake proportional to myocardial blood flow. In addition, different positron emission tomography tracers may be used for the quantitative measurement of myocardial blood flow and coronary flow reserve. Extensive research is currently being performed in the development of noninvasive coronary angiography and myocardial perfusion imaging using cardiac magnetic resonance. Finally, new multimodality imaging systems have been recently developed, bringing together anatomical and functional information. This review sought to provide a description of the relative merits of noninvasive imaging techniques in the assessment of coronary anatomy and myocardial perfusion in patients with known or suspected coronary artery disease.

Optimal electrocardiographic pulsing windows and heart rate: effect on image quality and radiation exposure at dual-source coronary CT angiography

PURPOSE

To determine the optimal width and timing of the electrocardiographic (ECG) pulsing window within the cardiac cycle in relation to heart rate (HR), image quality, and radiation exposure in patients who are suspected of having coronary artery disease.

MATERIALS AND METHODS

The institutional review board approved the study, and all patients gave informed consent. Dual-source computed tomography (CT) was performed in 301 patients (mean HR, 70.1 beats per minute +/- 13.3 [standard deviation]; range, 43-112 beats per minute) by using a wide ECG pulsing window (25%-70% of the R-R interval). Data sets were reconstructed in 5% steps from 20%-75% of R-R interval. Image quality was assessed by two observers on a per-segment level and was classified as good or impaired. High-quality data sets were those in which each segment was of good quality. The width and timing of the image reconstruction window was calculated. On the basis of these findings, an optimal HR-dependent ECG pulsing protocol was designed, and the potential dose-saving effect on effective dose (in millisieverts) was calculated.

RESULTS

At low HR (< or = 65 beats per minute), high-quality data sets were obtained during end diastole (ED); at high HR (> or = 80 beats per minute), they were obtained during end systole (ES); and at intermediate HR (66-79 beats per minute), they were obtained during both ES and ED. Optimal ECG pulsing windows for low, intermediate, and high HR were at 60%-76%, 30%-77%, and 31%-47% of the R-R interval, respectively, and with these levels, the effective dose was decreased at low HR from 18.7 to 6.8 mSv, at intermediate HR from 14.7 to 13.4 mSv, and at high HR from 11.3 to 4.2 mSv.

CONCLUSION

With optimal ECG pulsing, radiation exposure to patients, particularly those with low or high HR, can be reduced with preservation of image quality.